Title of the Invention: Silicon-carbon composite negative electrode active material, negative electrode comprising the silicon-carbon composite negative electrode active material, and secondary battery including the negative electrode
technology field
[One]
Mutual Citation with Related Applications
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0048937 filed on April 22, 2020, and all contents disclosed in the literature of the Korean patent application are incorporated as part of this specification.
[3]
[4]
technology field
[5]
The present invention is a core comprising SiO X (0≤X<2); a carbon layer covering at least a portion of the surface of the core; a carbon nanotube structure located on the carbon layer; and polyvinylidene fluoride covering at least a portion of the carbon nanotube structure, wherein the carbon nanotube structure is formed by arranging and bonding 2 to 5,000 single-walled carbon nanotube units side by side with each other, wherein the A portion of the carbon nanotube structure relates to a silicon-carbon composite negative electrode active material bonded to the carbon layer, and a negative electrode and a secondary battery including the silicon-carbon composite negative electrode active material.
background art
[6]
Recently, as technology development and demand for mobile devices increase, the demand for batteries as an energy source is rapidly increasing, and accordingly, various studies on batteries that can meet various needs are being conducted. In particular, research on lithium secondary batteries having high energy density and excellent lifespan and cycle characteristics as a power source for such devices is being actively conducted.
[7]
A lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating/deintercalating lithium ions, a negative electrode including a negative electrode active material capable of intercalating/deintercalating lithium ions, and an electrode having a microporous separator interposed between the positive electrode and the negative electrode. It means a battery in which a non-aqueous electrolyte containing lithium ions is included in the assembly.
[8]
On the other hand, since the conductivity of the negative electrode cannot be secured only with the negative electrode active material, there is a problem in that the resistance of the battery is excessively high, so the negative electrode usually additionally includes a conductive material. Conventionally, point-shaped conductive materials such as carbon black have been mainly used, and linear conductive materials such as carbon nanotubes and carbon nanofibers have also been used to improve battery capacity by further improving conductivity.
[9]
Single-walled carbon nanotubes are one of the linear conductive materials, and improve conductivity in the negative electrode active material layer due to their elongated shape. Accordingly, conventionally, after preparing an anode slurry through a dispersion in which the single-walled carbon nanotubes are completely dispersed, an anode active material layer is prepared through the anode slurry.
[10]
However, when charging and discharging of the battery are repeated, as the negative active material repeatedly expands and contracts in volume, the single-walled carbon nanotubes are cut, making it difficult to maintain the conductive network in the negative active material layer. . In particular, when a silicon-based active material is used as an anode active material to improve battery capacity, the volume of the silicon-based active material expands excessively due to charging and discharging of the battery, causing the single-walled carbon nanotubes to break. Accordingly, the conductive network is blocked or reduced, which deteriorates the lifespan characteristics of the battery. In addition, since the single-walled carbon nanotubes exist while surrounding the surface of the silicon-based active material, they cannot smoothly perform a role of conductively connecting adjacent negative electrode active materials to each other.
[11]
Therefore, a new method capable of improving the lifespan of a battery when using a silicon-based active material is required.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[12]
One problem to be solved by the present invention is to provide a silicon-carbon composite negative electrode active material capable of improving lifespan characteristics of a battery.
[13]
Another problem to be solved by the present invention is to provide an anode including the silicon-carbon composite anode active material.
[14]
Another problem to be solved by the present invention is to provide a secondary battery including the negative electrode.
means of solving the problem
[15]
According to one embodiment of the present invention, a core containing SiO X (0≤X<2); a carbon layer covering at least a portion of the surface of the core; a carbon nanotube structure located on the carbon layer; and polyvinylidene fluoride covering at least a portion of the carbon nanotube structure, wherein the carbon nanotube structure is formed by arranging and bonding 2 to 5,000 single-walled carbon nanotube units side by side with each other, wherein the A silicon-carbon composite negative active material is provided in which a portion of the carbon nanotube structure is bonded to the carbon layer.
[16]
According to another embodiment of the present invention, an anode including the silicon-carbon composite anode active material is provided.
[17]
According to another embodiment of the present invention, a secondary battery including the negative electrode is provided.
Effects of the Invention
[18]
The silicon-carbon composite anode active material according to the present invention includes rope-shaped carbon nanotube structures (long fiber form) in which several single-walled carbon nanotube units are arranged side by side and bonded to each other, and the carbon nanotubes Since the structures have a thick and long shape, the conductive network in the anode is not broken and can be maintained more firmly even when the volume of the silicon-carbon composite anode active material expands during battery operation. In addition, a part of the carbon nanotube structure is connected to one silicon-carbon composite negative electrode active material and the other part is connected to another adjacent silicon-carbon composite negative electrode active material, so that the silicon-carbon composite negative electrode active materials can be conductively and effectively connected. A long conductive network can thus be formed within the cathode. Furthermore, based on the fact that the silicon-carbon composite negative electrode active material includes a carbon layer and that a part of the carbon nanotube structure can be firmly bonded to the carbon layer by crystallized polyvinylidene fluoride, carbon-based When the anode active material is used in combination with the silicon-carbon composite anode active material, it is possible to prevent the carbon nanotube structure from adsorbing to and existing only in the carbon-based anode active material, thereby forming a more efficient and uniform conductive network in the anode. It can be. As a result, the life of the battery can be improved by the above effects.
Brief description of the drawing
[19]
1 and 2 are SEM pictures of the cathode of Example 1 of the present invention, respectively.
[20]
3 is a SEM picture of the negative electrode of Example 3 of the present invention.
[21]
4 is a SEM picture of the negative electrode of Comparative Example 1 of the present invention.
[22]
5 is a SEM picture of the negative electrode of Comparative Example 3 of the present invention.
[23]
6 is a SEM picture of the negative electrode of Comparative Example 5 of the present invention.
[24]
7 is a SEM picture of the negative electrode of Comparative Example 7 of the present invention.
Mode for Carrying Out the Invention
[25]
Terms or words used in this specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention. It should be interpreted as a meaning and concept consistent with the technical idea of ​​the present invention based on the principle that there is.
[26]
Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.
[27]
In this specification, terms such as "comprise", "comprise" or "have" are intended to indicate that there is an embodied feature, number, step, component, or combination thereof, but one or more other features or It should be understood that the presence or addition of numbers, steps, elements, or combinations thereof is not precluded.
[28]
In this specification, "%" means % by weight unless expressly indicated otherwise.
[29]
In this specification, "specific surface area" is measured by the BET method, and can be specifically calculated from the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan.
[30]
In the present specification, the average particle diameter (D 50 ) may be defined as a particle diameter corresponding to 50% of the cumulative volume in the particle diameter distribution curve of the particles. The average particle diameter (D 50 ) may be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle diameters of several millimeters in the submicron region, and can obtain results with high reproducibility and high resolution.
[31]
Hereinafter, the present invention will be specifically described.
[32]
[33]
Silicon-carbon composite anode active material
[34]
[35]
A silicon-carbon composite anode active material according to the present invention includes a core containing SiO X (0≤X<2); a carbon layer covering at least a portion of the surface of the core; a carbon nanotube structure located on the carbon layer; and polyvinylidene fluoride covering at least a portion of the carbon nanotube structure, wherein the carbon nanotube structure is formed by arranging and bonding 2 to 5,000 single-walled carbon nanotube units side by side with each other, wherein the A part of the carbon nanotube structure may be combined with the carbon layer.
[36]
[37]
The core may include SiO X (0≤X<2). The SiO X (0≤X<2) may be specifically SiO. Since the core contains SiO X (0≤X<2), the capacity of the battery can be improved.
[38]
The average particle diameter (D 50 ) of the core may be 0.1 μm to 20 μm, specifically 1 μm to 10 μm. When the above range is satisfied, a side reaction between the core and the electrolyte may be suppressed and a lithium silicate formation reaction may be suppressed, so that the initial efficiency of the battery may be improved and the initial capacity of the battery may be improved.
[39]
[40]
The carbon layer may be located on the core. The carbon layer may be disposed on the surface of the core to cover at least a portion of the surface of the core.
[41]
The carbon layer may include at least one of crystalline carbon and amorphous carbon. Specifically, the carbon layer may include amorphous carbon. The amorphous carbon can properly maintain the strength of the carbon layer and suppress expansion of the core.
[42]
The amorphous carbon may be at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials. Specifically, the amorphous carbon may be formed by mixing and stirring at least one selected from the group consisting of tar, pitch, and other organic materials in a solvent such as tetrahydrofuran (THF), and carbonizing the hydrocarbon in an inert atmosphere. It can be formed by using it as a source for chemical vapor deposition.
[43]
The other organic carbide may be an organic carbide selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose carbide, and combinations thereof.
[44]
The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethylene, acetylene, propane, butane, butene, pentane, isobutane or hexane. Aromatic hydrocarbons of the substituted or unsubstituted aromatic hydrocarbons include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumaron, pyridine, Anthracene, phenanthrene, etc. are mentioned.
[45]
The carbon layer may be included in an amount of 0.1 part by weight to 20 parts by weight, specifically 0.1 part by weight to 10 parts by weight, and more specifically 0.1 part by weight, in the silicon-carbon composite negative electrode active material, based on 100 parts by weight of the core. It may be included in parts by weight to 5 parts by weight. When the above range is satisfied, excessive volume expansion of the silicon-carbon composite anode active material may be suppressed, and the conductivity of the anode active material layer may be improved, thereby improving capacity and lifespan of the battery.
[46]
The carbon layer may cover the entire surface of the core, or may cover only a part of the surface of the core. Particularly, when the carbon layer covers only a part of the surface of the core and a carbon layer having a rough morphology is formed on the surface of the core, diffusion of lithium ions may be improved. In addition, in this case, even in repeated charging and discharging of the battery, the destruction of the carbon layer due to the change in the volume of the core can be minimized, so the capacity and lifespan of the battery can be improved.
[47]
[48]
The carbon nanotube structure may include a plurality of single-walled carbon nanotube units. Specifically, the carbon nanotube structure may be a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded side by side with each other, and more specifically, the carbon nanotube structure includes 2 to 4,500 single-walled carbon nanotubes. It may be a carbon nanotube structure in which nanotube units are bonded to each other. More specifically, in consideration of the dispersibility of the carbon nanotube structure and the durability of the electrode, the carbon nanotube structure is most preferably a carbon nanotube structure in which 2 to 500 single-walled carbon nanotube units are bonded to each other. .
[49]
In the carbon nanotube structure, the single-walled carbon nanotube units are arranged side by side and combined (a cylindrical structure in the form of a bundle having flexibility in which the long axes of the units are coupled in parallel to each other) to form the carbon nanotube structure. can Within the electrode, the carbon nanotube structures may be connected to each other to form a network structure.
[50]
Conventional negative electrodes containing carbon nanotubes are generally bundled or entangled type carbon nanotubes (single-walled carbon nanotube units or multi-walled carbon nanotube units are attached or entangled with each other) ) is dispersed in a dispersion medium to prepare a conductive material dispersion, and then prepared using the conductive material dispersion. At this time, the carbon nanotubes are completely dispersed in the conventional conductive material dispersion, and exist as a conductive material dispersion in which single-stranded carbon nanotube units are dispersed. In the conventional conductive material dispersion, the carbon nanotube units are easily cut due to an excessive dispersion process, resulting in a shorter length than the initial length. In addition, the carbon nanotube units can be easily cut even during the rolling process of the cathode. During operation of the battery, an excessive volume change of the silicon-carbon composite anode active material further causes a problem in that the carbon nanotube units (particularly, the single-walled carbon nanotube units) are cut. Accordingly, there is a problem in that the conductivity of the negative electrode is lowered and the life characteristics of the battery are lowered. Moreover, in the case of multi-walled carbon nanotube units, structural defects are high due to the mechanism of node growth (nodes are not smooth and linear, but exist due to defects generated during the growth process). Therefore, during the dispersion process, the multi-walled carbon nanotube units are more easily cut, and the multi-walled carbon nanotube units cut short are likely to aggregate with each other due to π-π stacking by the carbon of the unit. Accordingly, it is difficult for the carbon nanotube units to be uniformly dispersed.
[51]
In contrast, in the case of the carbon nanotube structure included in the silicon-carbon composite negative electrode active material of the present invention, 2 to 5,000 single-walled carbon nanotube units maintaining high crystallinity without relatively structural defects are bonded side by side with each other. Since it has a rope shape, the conductivity of the negative electrode can be maintained because the length can be maintained smoothly without being cut even when the silicon-carbon composite particles are excessively changed in volume. In addition, due to the high conductivity of the single-walled carbon nanotube unit having high crystallinity, the conductivity of the negative electrode is increased, and the input characteristics, output characteristics, and life characteristics of the battery can be greatly improved. In addition, since the carbon nanotube structures in the negative electrode may be connected to each other to have a network structure, excessive volume change of the silicon-carbon composite negative electrode active material may be suppressed to prevent cracks from occurring, and at the same time, a strong conductive network may be secured. can In addition, even if a crack occurs in the silicon-carbon composite anode active material, the carbon nanotube structure crosses the crack and connects the silicon-carbon composite anode active material, so that the conductive network can be maintained. Furthermore, since the carbon nanotube structure is not easily broken and can maintain a long shape, the conductive network can be strengthened throughout the negative electrode active material layer. In addition, detachment of the silicon-carbon composite anode active material may be suppressed, and electrode adhesion may be greatly improved.
[52]
In the carbon nanotube structure, the average diameter of the single-walled carbon nanotube unit may be 0.5 nm to 10 nm, and specifically, 1 nm to 9 nm. When the average diameter is satisfied, there is an effect of maximizing conductivity in the negative electrode even with a very small amount of conductive material. The average diameter corresponds to an average value of the upper 100 single-walled carbon nanotubes and the lower 100 single-walled carbon nanotubes having large diameters when the manufactured negative electrode is observed through TEM.
[53]
The single-walled carbon nanotube unit may be included in the carbon nanotube structure in an amount of 95% to 100% by weight, specifically 100% by weight. In other words, the carbon nanotube structure does not include double-walled carbon nanotube units and multi-walled carbon nanotube units, and thus the silicon-carbon composite negative electrode active material also does not include double-walled carbon nanotube units and multi-walled carbon nanotube units. Accordingly, the conductive network of the silicon-carbon composite anode active material can be formed with high durability, and the conductivity of the anode active material layer can be effectively improved even with a small amount of the conductive material when a separate conductive material is applied and used.
[54]
In the carbon nanotube structure, the average length of the single-walled carbon nanotube units may be 1 μm to 100 μm, specifically 5 μm to 50 μm. When the average length is satisfied, a long conductive path for conductive connection between the silicon-carbon composite negative electrode active materials can be formed and a unique network structure can be formed, so that conductivity in the negative electrode can be maintained even with a very small amount of conductive material. There is an effect that can be maximized. The average length corresponds to an average value of the top 100 single-walled carbon nanotubes and the bottom 100 single-walled carbon nanotubes having a large length when the manufactured negative electrode is observed through TEM.
[55]
The specific surface area of ​​the single-walled carbon nanotube unit may be 500 m 2 /g to 1,000 m 2 /g, and specifically, 600 m 2 /g to 800 m 2 /g. When the above range is satisfied, since a conductive path in the negative electrode can be smoothly secured due to a large specific surface area, there is an effect of maximizing the conductivity in the negative electrode even with a very small amount of conductive material. The specific surface area of ​​the single-walled carbon nanotube unit can be specifically calculated from the amount of nitrogen gas adsorption under liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan.
[56]
The average diameter of the carbon nanotube structure may be 2 nm to 200 nm, specifically 5 nm to 150 nm, and more specifically 50 nm to 120 nm. When the above range is satisfied, it is effective in forming a conductive network and is advantageous in connecting between silicon-carbon composite anode active materials, so that excellent electrical conductivity can be realized. The average length corresponds to an average value of the diameters of the top 100 carbon nanotube structures and the bottom 100 carbon nanotube structures having large diameters when the manufactured negative electrode is observed through an SEM.
[57]
The average length of the carbon nanotube structure may be 1 μm to 100 μm, specifically 5 μm to 50 μm. When the above range is satisfied, it is effective in forming a conductive network and is advantageous in connecting active materials, so that excellent electrical conductivity can be realized. The average length corresponds to an average value of the lengths of the top 100 carbon nanotube structures and the bottom 100 carbon nanotube structures, when the manufactured negative electrode is observed through an SEM.
[58]
The carbon nanotube structure may be located on the carbon layer. Specifically, a portion of the carbon nanotube structure may be combined with the carbon layer. The bonding may be achieved by the crystallized polyvinylidene fluoride. Specifically, the polyvinylidene fluoride covers at least a portion of the carbon nanotube structure, and the carbon nanotube structure coated with the polyvinylidene fluoride is in contact with the carbon layer, so that the polyvinylidene fluoride The carbon nanotube structure and the carbon layer may be coupled to each other with the interposed therebetween.
[59]
A portion of the carbon nanotube structure may be combined with the carbon layer. If there is no carbon layer on the surface of the core, the carbon nanotube structure is not bonded to the core, so that the carbon nanotube structure wraps around the core and exists in the cathode in a state in which it is not bonded to the core. In such a case, it is difficult to electrically connect adjacent silicon-carbon composite anode active materials to the carbon nanotube structure, and even if the carbon nanotube structure is connected, the length of the conductive network is inevitably shortened.
[60]
On the other hand, in the present invention, a portion of the carbon nanotube structure is firmly bonded to the carbon layer, and other portions except for a portion of the carbon nanotube structure bonded to the carbon layer protrude from the silicon-carbon composite negative electrode active material. can exist Since the silicon-carbon composite anode active material includes a carbon layer, a part of the long rope-shaped carbon nanotube structure is strongly bonded to the carbon layer by a π-π action, and the other part of the carbon nanotube structure The portion is strongly bonded to the carbon layer of another adjacent silicon-carbon composite anode active material by a π-π action. Accordingly, other parts of the carbon nanotube structure other than a part bonded to the carbon layer may protrude from the silicon-carbon composite anode active material. Accordingly, since the carbon nanotube structure does not exist surrounding the silicon-carbon composite anode active material and strongly forms a long conductive network, the capacity and lifespan of the battery can be greatly improved despite repeated charging and discharging of the battery. .
[61]
The carbon nanotube structure may be included in an amount of 1 to 100, specifically 1 to 50, and more specifically, 1 to 20, in the silicon-carbon composite negative electrode active material. The meaning of being included here means that the carbon nanotube structure is bonded to the carbon layer by the polyvinylidene fluoride, rather than simply being in contact with it. This is measured by observing more than 500 silicon-carbon composite negative electrode active materials in the negative electrode with SEM, measuring the number of carbon nanotube structures bonded to the silicon-carbon composite negative electrode active material for each silicon-carbon composite negative electrode active material, and averaging them. can
[62]
The carbon nanotube structure may be included in 0.05 parts by weight to 5.0 parts by weight, specifically 0.05 parts by weight to 3.0 parts by weight, more specifically 0.05 parts by weight to 1.0 parts by weight, based on 100 parts by weight of the core on which the carbon layer is formed. may be included as a part. When the above range is satisfied, the conductive network in the negative electrode active material layer may have high durability even with a small amount of the carbon nanotube structure. In the case of preparing a conductive material dispersion for incorporating the carbon nanotube structure into the silicon-carbon composite negative electrode active material, when the bundled carbon nanotubes are completely dispersed (as a general dispersion method, as much as possible, single carbon nanotube units are dispersed so that they are separated from each other) In the case where the carbon nanotube structure does not occur or occurs unintentionally, it occurs in a very small amount (0.0025 parts by weight or less). That is, the above content range can never be achieved by general methods.
[63]
In the case of the prior art in which the negative electrode includes multi-walled carbon nanotube units as a conductive material, in order to compensate for the low conductivity of the multi-walled carbon nanotube unit, a high content of the multi-walled carbon nanotube unit has to be used. In addition, even when the negative electrode is manufactured through a conductive material dispersion in which the single-walled carbon nanotube units are completely dispersed, the single-walled carbon nanotube units can be used in a low content due to the problem of cutting the single-walled carbon nanotube units. couldn't
[64]
On the other hand, the carbon nanotube structure included in the silicon-carbon composite anode active material of the present invention has a form in which 2 to 5,000 single-walled carbon nanotube units are bonded side by side. Accordingly, the carbon nanotube structure can smoothly maintain its length without being cut even when the volume of the silicon-carbon composite anode active material is excessively changed. Therefore, the conductivity of the negative electrode can be maintained, and the conductivity of the negative electrode can be smoothly secured due to the high conductivity of the single-walled carbon nanotube unit. Accordingly, even when the content of the carbon nanotube structure in the silicon-carbon composite negative electrode active material is low, the battery may have excellent capacity and lifespan characteristics.
[65]
On the other hand, in some cases, the single-walled carbon nanotube units may be surface-treated through oxidation treatment or nitration treatment to improve affinity with the dispersant.
[66]
[67]
The polyvinylidene fluoride serves to bind a part of the carbon nanotube structure to the carbon layer.
[68]
The polyvinylidene fluoride may cover at least a portion of the carbon nanotube structure. The carbon layer and the carbon nanotube structure may be firmly bonded with the polyvinylidene fluoride interposed therebetween. Specifically, the polyvinylidene fluoride may be combined with the carbon layer and the carbon nanotube structure.
[69]
The polyvinylidene fluoride may exist in a crystallized state in the silicon-carbon composite anode active material. For example, unlike the present invention, if the core on the surface of the carbon layer, the carbon nanotube structure, and polyvinylidene fluoride are simply mixed, the carbon nanotube structure is not bonded to the carbon layer, and the carbon nanotube structure It is highly probable that they are aggregated with each other or exist only on the surface of some carbon layers. In addition, polyvinylidene fluoride exists concentrated only in the aggregated carbon nanotube structures or exists in the form of a kind of film on the surface of the carbon layer.
[70]
In contrast, in the manufacturing process of the silicon-carbon composite anode active material, in the present invention, after preparing a dispersion containing polyvinylidene fluoride and a carbon nanotube structure, which can serve as a dispersant and binder, the carbon layer is added to the dispersion. Since the cores located on the surface are mixed and dispersed, and then the polyvinylidene fluoride is crystallized, the carbon nanotube structure can be firmly bonded to the carbon layer by the crystallized polyvinylidene fluoride. . Accordingly, even in repeated charging and discharging processes of the battery, the conductive network formed by the carbon nanotube structure may have sufficient durability to be sufficiently maintained. Accordingly, the capacity and lifespan of the battery may be improved.
[71]
Here, the crystallization of polyvinylidene fluoride is further explained. Polyvinylidene fluoride corresponds to a thermoplastic resin and has both an amorphous (amorphous) region and a crystalline (Crystalline) region. As the number of crystalline regions increases, polyvinylidene fluoride may not be easily broken or deformed even when external stress occurs. When an appropriate level of heat is applied to polyvinylidene fluoride, sufficient crystallization proceeds around the crystal nuclei in polyvinylidene fluoride, and when it is cooled slowly, the number of crystal nuclei having chemical resistance increases and the degree of crystallinity can be increased. . Accordingly, the crystalline region is increased, and the polyvinylidene fluoride is changed to the extent that it can withstand external stress, so that the carbon nanotube structure and the carbon layer can be firmly bonded by the polyvinylidene fluoride. .
[72]
In addition, in general, in the case of a silicon-based active material, unlike a cathode active material that is vulnerable to moisture, an anode slurry can be prepared by an environmentally friendly and inexpensive aqueous dispersion process. In the aqueous dispersion process, when non-crystallized polyvinylidene fluoride is added to water as a solvent, the non-crystallized polyvinylidene fluoride is immediately gelled in the anode slurry, making it difficult to manufacture the anode itself. This is because when non-crystallized polyvinylidene fluoride reacts with polar water, the chain-type -(CH 2 -CF 2 ) n - structure reacts with the same nearby structure, and HF is easily desorbed to form polyvinylidene fluoride. This is because the chains of are cross-linked with each other and a gelation reaction occurs. That is, when non-crystallized general polyvinylidene fluoride is included in the anode active material, it is difficult to apply an aqueous dispersion process for preparing an anode slurry through water, and it is difficult to apply a water-based binder such as SBR or CMC to non-crystallized polyvinylidene fluoride. It is obvious that it is also difficult to use with fluoride.
[73]
[74]
However, since the polyvinylidene fluoride included in the silicon-carbon composite negative electrode active material of the present invention may be crystallized polyvinylidene fluoride, the gelation problem does not occur even in an aqueous dispersion process. In other words, the present invention is different from other technologies in that the silicon-carbon composite anode active material requiring aqueous dispersion may include polyvinylidene fluoride. Whether or not the polyvinylidene fluoride is crystallized can be easily confirmed by whether a gelation phenomenon occurs during preparation of the negative electrode slurry.
[75]
The weight average molecular weight of the polyvinylidene fluoride may be 10,000 g/mol to 1,000,000 g/mol, specifically 100,000 g/mol to 900,000 g/mol. When the above range is satisfied, the formation of the carbon nanotube structure is easy, and the dispersibility of the carbon nanotube structure in the conductive material dispersion may be improved.
[76]
The polyvinylidene fluoride may be included in an amount of 0.1 part by weight to 30 parts by weight, specifically 0.1 part by weight to 20 parts by weight, and more specifically, 0.1 part by weight to 10 parts by weight, based on 100 parts by weight of the core on which the carbon layer is formed. It may be included in parts by weight. When the above range is satisfied, the carbon nanotube structure is uniformly dispersed on the core on which the carbon layer is formed, and the carbon nanotube structure can be firmly fixed on the carbon layer. Accordingly, the carbon nanotube structure is not easily separated even during the manufacturing process of the negative electrode slurry, and a conductive network is effectively formed, so that the capacity and lifespan of the battery can be greatly improved.
[77]
The polyvinylidene fluoride may include modified polyvinylidene fluoride modified with a functional group, specifically a hydrophilic functional group, to improve affinity with the carbon nanotube structure. Specifically, the polyvinylidene fluoride may include modified polyvinylidene fluoride including at least one of an acid functional group and an ester functional group. The functional groups of the modified polyvinylidene fluoride may interact with single-walled carbon nanotube units in the carbon nanotube structure to form the carbon nanotube structure to have an appropriate diameter. In addition, the functional group allows the carbon nanotube structure to be uniformly dispersed throughout on the core on which the carbon layer is formed, and enhances the adhesive strength between the core on which the carbon layer is formed and the carbon nanotube structure.
[78]
The functional group may be included in the modified polyvinylidene fluoride in an amount of 0.1% to 5% by weight, specifically 0.3% to 3% by weight. When the above range is satisfied, the carbon nanotube structure may be formed to have an appropriate diameter. In addition, the functional group allows the carbon nanotube structure to be uniformly dispersed throughout on the core on which the carbon layer is formed, and enhances the adhesive strength between the core on which the carbon layer is formed and the carbon nanotube structure.
[79]
The modified polyvinylidene fluoride may be included in 1 wt% to 100 wt% based on the total weight of the polyvinylidene fluoride, specifically 1 wt% to 50 wt%, and more specifically 1 wt% % to 20% by weight. When the above range is satisfied, the carbon nanotube structure may be uniformly and firmly adhered to the core on which the carbon layer is formed.
[80]
[81]
The specific surface area of ​​the silicon-carbon composite anode active material may be 0.5 m 2 /g to 50 m 2 /g, specifically 0.5 m 2 /g to 30 m 2 /g, and more specifically 3 m 2 /g to 30 m 2 /g. 2 /g. When the above range is satisfied, battery performance may be maintained even when the contents of the conductive material and the binder are reduced, internal reactions of the battery may be reduced, and battery capacity and lifespan may be improved. Furthermore, when the specific surface area of ​​the silicon-carbon composite anode active material is 3 m 2 /g to 30 m 2 /g, the carbon layer covers a portion of the surface of the core, not the entire surface, and the silicon-carbon composite anode active material It means that the surface of is rough in the form of concavo-convex. Accordingly, destruction of the carbon layer may be reduced even during repeated charging and discharging processes of the battery, and close bonding between the carbon layer and the carbon nanotube structure may be maintained, and thus, the silicon-carbon composite negative electrode active material and the negative electrode active material The conductive network in the layer can be strengthened, and the capacity and life of the battery can be improved.
[82]
[83]
[84]
Manufacturing method of silicon-carbon composite anode active material
[85]
A method for manufacturing a silicon-carbon composite negative electrode active material according to another embodiment of the present invention,
[86]
(a) forming a carbon layer on a core containing SiO X (0≤X<2);
[87]
(b) preparing a dispersion of carbon nanotube structures including carbon nanotube structures and polyvinylidene fluoride;
[88]
(c) mixing the carbon nanotube structure dispersion and the core on which the carbon layer is formed; and
[89]
(d) bonding the carbon nanotube structure to the carbon layer; may include.
[90]
[91]
Here, the core, the carbon layer, and the carbon nanotube structure are the same as those described in the above-described embodiment of the silicon-carbon composite negative electrode active material. Also, the order of (a) and (b) may be changed.
[92]
[93]
In step (a), the carbon layer includes placing crystalline carbon or amorphous carbon on the core. The amorphous carbon may be a carbon-based material formed by using at least one carbide selected from the group consisting of tar, pitch, and other organic materials, or a hydrocarbon as a source of chemical vapor deposition. The carbon-based material is as described in relation to the above-described embodiment.
[94]
[95]
In step (b), the carbon nanotube structure dispersion is prepared by introducing a mixture of bundled carbon nanotubes and polyvinylidene fluoride into a dispersion medium (b-1); and (b-2) forming a carbon nanotube structure by ultrasonically crushing the mixture. The bundled carbon nanotubes exist in a bundle form by combining the above-mentioned single-walled carbon nanotube units, and include usually 2 or more, substantially 500 or more, for example, 5,000 or more single-walled carbon nanotube units.
[96]
[97]
In step (b-1), the bundled single-walled carbon nanotubes may be included in the mixture in an amount of 0.1% to 1.0% by weight, specifically 0.2% to 0.5% by weight. When the above range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, and a carbon nanotube structure at an appropriate level may be formed, and dispersion stability may be improved.
[98]
The polyvinylidene fluoride may be included in the mixture in an amount of 0.1% to 20% by weight, specifically 1% to 10% by weight. When the above range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, and a carbon nanotube structure at an appropriate level may be formed, and dispersion stability may be improved.
[99]
The polyvinylidene fluoride is the same as the polyvinylidene fluoride of the above-described embodiment, but has not yet been crystallized in step (b).
[100]
The weight ratio of the bundled carbon nanotubes to the polyvinylidene fluoride in the mixture may be 1:0.1 to 1:10, specifically 1:1 to 1:10. When the above range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, and a carbon nanotube structure at an appropriate level may be formed, and dispersion stability may be improved.
[101]
Examples of the dispersion medium include amide-based polar organic solvents such as dimethylformamide (DMF), diethyl formamide, dimethyl acetamide (DMAc), and N-methylpyrrolidone (NMP); Methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl alcohols such as -2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol; Ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol glycol ethers such as monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methylpropyl ketone, or cyclopentanone; and esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone, and any one or a mixture of two or more of these may be used, but is not limited thereto. More specifically, the dispersion medium may be N-methyl pyrrolidone (NMP).
[102]
The solid content in the mixture may be 0.1% to 20% by weight, specifically 1% to 10% by weight. When the above range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, and a carbon nanotube structure at an appropriate level may be formed, and dispersion stability may be improved.
[103]
[104]
In step (b-2), the step of dispersing the bundled carbon nanotubes in the mixture is sonification, homogenizer, bead mill, ball mill, basket mill, attrition mill, universal stirrer , It can be performed using a mixing device such as a clear mixer, spike mill or TK mixer. Among them, ultrasonic disintegration may be preferable. In the ultrasonic disruption method, when high-intensity ultrasonic waves are emitted into a solution, numerous bubbles in a vacuum state are created by extreme vibration, and these bubbles momentarily coalesce or grow, but immediately follow the vibration. It is violently crushed in a chain by When the bubbles are continuously crushed, strong shock waves are generated by the turbulent flow or vortex of the solution, and the bundled carbon nanotubes can be debundled through the energy of the shock waves. The ultrasonic disruption method enables fine dispersion at the nano level without cutting the single-walled carbon nanotubes in the length direction of the bundled carbon nanotubes. For this reason, the ultrasonic disintegration method is preferred.
[105]
The sonication method may be as follows. Ultrasound may be applied to the mixture to disperse the solids in the mixture.
[106]
At this time, the conditions under which the ultrasonic disintegration method is performed are as follows.
[107]
The ultrasonic disruption may be performed with an output of 800W to 1,500W, and specifically, it may be performed with an output of 800W to 1,200W. The ultrasonic disintegration may be performed for 0.5 to 5 hours, specifically, for 1 to 3 hours. When the above range is satisfied, the bundled carbon nanotubes may be separated to an appropriate level to form the carbon nanotube structure. Since the execution time means the total time during which ultrasonic disruption is applied, for example, if several times of ultrasonic disruption are performed, it means the total time over the several times.
[108]
The above conditions are for the bundled carbon nanotubes to be dispersed at an appropriate level to form a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded side by side in the prepared conductive material dispersion. This can be achieved only when the composition of the mixture, ultrasonic disruption conditions, and the like are strictly controlled. That is, in the formed carbon nanotube structure dispersion liquid, there are no or almost no single-walled carbon nanotube units that exist independently in the form of single strands, and most of them may exist in the above-described carbon nanotube structure.
[109]
[110]
In the step (c), the carbon nanotube structure dispersion and the core on which the carbon layer is formed may be mixed.
[111]
[112]
After that, in step (d), the carbon nanotube structures in the carbon nanotube structure dispersion may be bonded to the carbon layer. After uniformly mixing the core on which the carbon layer is formed and the dispersion of the carbon nanotube structure by stirring, the dispersion medium may be removed, and heat may be applied to crystallize the polyvinylidene fluoride. At this time, the heat applied may be, for example, 100 °C to 300 °C, specifically 100 °C to 200 °C. Accordingly, the carbon nanotube structure is firmly bonded to the carbon layer by the crystallized polyvinylidene fluoride, gelation of the polyvinylidene fluoride can be prevented during the aqueous dispersion process, and finally silicon-carbon composite A negative electrode active material is completed.
[113]
[114]
cathode
[115]
[116]
An anode according to another embodiment of the present invention may include the silicon-carbon composite anode active material of the above-described embodiment. Specifically, the anode may include an anode active material layer, and the anode active material layer may include the silicon-carbon composite anode active material of the above-described embodiment.
[117]
[118]
The negative electrode may be a self-supporting negative electrode, in which case the negative electrode active material layer itself corresponds to the negative electrode. Alternatively, the anode may include an anode current collector supporting the anode active material layer.
[119]
[120]
The anode current collector may be any material having conductivity without causing chemical change in the battery, and is not particularly limited. For example, as the anode current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. . Specifically, transition metals that adsorb carbon well, such as copper and nickel, can be used as the negative electrode current collector.
[121]
[122]
The negative electrode active material layer may be disposed on one side or both sides of the negative electrode current collector. Of course, in the case of the self-supporting negative electrode, the negative electrode active material layer may be a negative electrode itself without a negative electrode current collector.
[123]
The negative active material layer may include a silicon-carbon composite negative active material, and the silicon-carbon composite negative active material may be the silicon-carbon composite negative active material of the above-described embodiment.
[124]
[125]
The negative active material layer may further include a carbon-based active material.
[126]
Conventionally, technologies using a combination of a silicon-based active material and a carbon-based active material are frequently used. However, when using carbon nanotubes as a conductive material along with the above technologies, most of the carbon nanotubes are located on the surface of the carbon-based active material by a π-π reaction between carbon atoms of the same type, and the silicon-based active material forms a conductive network of the negative electrode. It does not affect the improvement, and there is a problem that the conductivity between the silicon-based active material is lowered, and the battery capacity and lifespan are lowered.
[127]
In the present invention, the carbon nanotube structure may be firmly bonded to the carbon layer by polyvinylidene fluoride in the silicon-carbon composite negative electrode active material, and gelation may not occur during the aqueous dispersion process. Therefore, it is possible to suppress the phenomenon of aggregation of the carbon nanotube structure only on the surface of the carbon-based active material, and since the carbon nanotube structure can behave only on the silicon-carbon composite negative electrode active material, the efficiency of application of the conductive material can be greatly increased. and it is possible to form a tight and solid conductive network. Accordingly, the conductive network may be maintained even during repeated charging and discharging processes of the battery, and the capacity and lifespan of the battery may be improved.
[128]
The carbon-based active material may be at least one selected from the group consisting of artificial graphite, natural graphite, and graphitized mesocarbon microbeads. Specifically, the carbon-based active material is preferably artificial graphite in that it can effectively control the volume expansion of the negative electrode while maintaining a conductive network together with the above-described silicon-carbon composite negative electrode active material, but is not limited thereto.
[129]
In the negative electrode, the silicon-carbon composite negative electrode active material and the carbon-based active material may be included in a weight ratio of 0.5:99.5 to 30:70, specifically, 1:99 to 20:80. When the above range is satisfied, excessive volume expansion of the silicon-carbon composite anode active material may be suppressed, and battery capacity may be improved.
[130]
[131]
In the negative active material layer, the carbon nanotube structure may be included in an amount of 0.01% to 0.5% by weight, specifically 0.01% to 0.3% by weight, and more specifically, 0.01% to 0.1% by weight. can When the above range is satisfied, the conductive network in the negative electrode may be effectively formed with high durability while minimizing the content of the carbon nanotube structure.
[132]
[133]
The negative active material layer may further include a binder. The binder is used to secure adhesion between silicon-carbon composite negative electrode active materials or between the silicon-carbon composite negative electrode active material and a current collector, and general binders used in the art may be used, and the type is not particularly limited. not. As the binder, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, starch, hydroxypropyl cellulose, regeneration Cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR ), fluororubber, or various copolymers thereof, and among these, one type alone or a mixture of two or more types may be used. In particular, when using an aqueous dispersion process, the binder is preferably an aqueous binder such as SBR or CMC.
[134]
The binder may be included in an amount of 10% by weight or less, preferably 0.1% to 5% by weight, based on the total weight of the negative electrode active material layer. When the content of the binder satisfies the above range, excellent negative electrode adhesion may be implemented while minimizing an increase in negative electrode resistance.
[135]
[136]
The negative electrode active material layer may further include a conductive material. The conductive material may be at least one selected from the group consisting of fullerene, carbon black, carbon nanotube, graphene, plate-like graphite, and the like.
[137]
[138]
secondary battery
[139]
Next, a secondary battery according to another embodiment of the present invention will be described.
[140]
A secondary battery according to another embodiment of the present invention may include the anode of the above-described embodiment.
[141]
Specifically, the secondary battery may include the negative electrode, the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode of the above-described embodiment. Since the cathode has been described above, a detailed description thereof will be omitted.
[142]
The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.
[143]
In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , those surface-treated with nickel, titanium, silver, etc. may be used. In addition, the cathode current collector may have a thickness of typically 3 μm to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.
[144]
The cathode active material may be a commonly used cathode active material. Specifically, the cathode active material may include layered compounds such as lithium cobalt oxide (LiCoO 2 ) and lithium nickel oxide (LiNiO 2 ), or compounds substituted with one or more transition metals; lithium iron oxides such as LiFe 3 O 4 ; lithium manganese oxides such as Li 1+c1 Mn 2-c1 O 4 (0≤c1≤0.33), LiMnO 3 , LiMn 2 O 3 , LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); LiV 3 O 8 , V 2 O 5 , Cu 2 V 2 O 7 and the like; vanadium oxide; Represented by the formula LiNi 1-c2 M c2 O 2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3) Ni site-type lithium nickel oxide; Formula LiMn 2-c3 M c3 O 2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li 2 Mn 3 MO 8 (here, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn). Lithium manganese composite oxide represented by; Examples include LiMn 2 O 4 in which Li in the formula is partially substituted with an alkaline earth metal ion, but is not limited thereto. The anode may be Li-metal.
[145]
The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.
[146]
At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery, any material that does not cause chemical change and has electronic conductivity can be used without particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or in a mixture of two or more.
[147]
[148]
In addition, the positive electrode binder serves to improve adhesion between particles of the positive electrode active material and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC) ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like may be used alone or in a mixture of two or more of them.
[149]
The separator separates the negative electrode and the positive electrode and provides a passage for lithium ion movement. If it is normally used as a separator in a secondary battery, it can be used without particular limitation. it is desirable Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.
[150]
Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.
[151]
Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.
[152]
As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dimethine Toxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxorane, formamide, dimethylformamide, dioxorane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid Triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, propionic acid An aprotic organic solvent such as ethyl may be used.
[153]
In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can be preferably used because they dissociate lithium salts well. When the same low-viscosity, low-dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be made and can be used more preferably.
[154]
The metal salt may be a lithium salt, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte solution. For example, the anion of the lithium salt is F - , Cl - , I - , NO 3 - , N (CN ) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 ( CF 3 ) 2 CO - , (CF 3SO 2 ) 2 CH - , (SF 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - and (CF 3 CF 2 SO 2 ) 2N - At least one selected from the group consisting of may be used.
[155]
In addition to the components of the electrolyte, the electrolyte may include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trialkylene carbonate for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included.
[156]
[157]
According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include the secondary battery having high capacity, high rate and cycle characteristics, a medium or large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system can be used as a power source for
[158]
[159]
Hereinafter, the present invention will be described in more detail through specific examples.
[160]
[161]
Preparation Example 1: Preparation of Carbon Nanotube Structure Dispersion
[162]
0.4 parts by weight of bundled carbon nanotubes (specific surface area: 650 m 2 /g) composed of single-walled carbon nanotube units having an average diameter of 1.5 nm and an average length of 5 μm and polyvinylidene fluoride (weight average molecular weight: 685,000 g) / mol. Standard Homo-polymer) 2.0 parts by weight was mixed with 97.6 parts by weight of N-methylpyrrolidone (NMP, N-methylpyrrolidone) as a dispersion medium to prepare a mixture so that the solid content was 2.4% by weight.
[163]
The mixture was stirred by an ultrasonic crushing method to disperse the bundled carbon nanotubes in a dispersion medium to prepare a carbon nanotube structure dispersion. At this time, ultrasonic disruption was performed for 1.5 hours at a power of 1,000 W. The carbon nanotube structure dispersion included a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units were bonded side by side. In the carbon nanotube structure dispersion, the carbon nanotube structure was 0.4% by weight and the modified polyvinylidene fluoride was 2.0% by weight.
[164]
[165]
Preparation Example 2: Preparation of multi-walled carbon nanotube monomer dispersion
[166]
4.0 parts by weight of bundled carbon nanotubes (specific surface area: 185 m 2 /g) composed of multi-walled carbon nanotube units having an average diameter of 10 nm and an average length of 1 μm, and carboxymethyl cellulose (weight average molecular weight: 100,000 g/mol, Degree of substitution: 1.0) 0.8 parts by weight was mixed with 95.2 parts by weight of water as a dispersion medium to prepare a mixture so that the solid content was 4.8% by weight.
[167]
The mixture was stirred by ultrasonic disruption to disperse the bundled carbon nanotubes in a dispersion medium to prepare a multi-walled carbon nanotube unit dispersion. At this time, ultrasonic disruption was performed for 1.5 hours at a power of 1,000 W. In the multi-walled carbon nanotube unit dispersion, the multi-walled carbon nanotube unit was 4.0% by weight and the carboxymethylcellulose was 0.8% by weight.
[168]
[169]
Preparation Example 3: Preparation of multi-walled carbon nanotube monomer dispersion
[170]
4.0 parts by weight of bundled carbon nanotubes (specific surface area: 185 m 2 /g) composed of multi-walled carbon nanotube units having an average diameter of 10 nm and an average length of 1 μm and polyvinylidene fluoride (weight average molecular weight: 685,000 g/g) mol, standard homo-polymer) 2.0 parts by weight was mixed with 94.0 parts by weight of NMP as a dispersion medium to prepare a mixture so that the solid content was 6.0% by weight.
[171]
The mixture was stirred by ultrasonic disruption to disperse the bundled carbon nanotubes in a dispersion medium to prepare a multi-walled carbon nanotube unit dispersion. At this time, ultrasonic disruption was performed for 1.5 hours at a power of 1,000 W. In the multi-walled carbon nanotube unit dispersion, the multi-walled carbon nanotube unit was 4.0% by weight and the polyvinylidene fluoride was 2.0% by weight.
[172]
[173]
Preparation Example 4: Preparation of Carbon Black Dispersion
[174]
0.4 parts by weight of carbon black (Imerys, Super C65) having an average particle diameter of 35 nm and 0.6 parts by weight of carboxymethyl cellulose (weight average molecular weight: 100,000 g/mol, degree of substitution: 1.0) were mixed with 99.0 parts by weight of water as a dispersion medium, and solid content A liquid mixture was prepared so that it would be 1.0% by weight. After introducing the mixed solution into the homogenizer, a pressure of 500 Bar was applied to the mixed solution, and the mixed solution was sequentially passed through a primary nozzle having a diameter of 300 mm and a secondary nozzle having a diameter of 800 μm. In the conductive material dispersion, the carbon black was 0.4% by weight and the carboxymethyl cellulose was 0.6% by weight.
[175]
[176]
Preparation Example 5: Preparation of single-walled carbon nanotube monomer dispersion
[177]
0.2 parts by weight of bundled carbon nanotubes (specific surface area: 650 m 2 /g) composed of single-walled carbon nanotube units having an average diameter of 1.5 nm and an average length of 5 μm or more and polyvinylidene fluoride (weight average molecular weight: 220,000 g) / mol, standard homo-polymer) 4.0 parts by weight was mixed with 95.8 parts by weight of NMP, a dispersion medium, to prepare a mixture so that the solid content was 4.2% by weight.
[178]
The mixture was stirred by ultrasonic disruption to disperse the bundled carbon nanotubes in a dispersion medium to prepare a dispersion of single-walled carbon nanotube units. At this time, ultrasonic disruption was performed for 5 hours at a power of 2,000 W.
[179]
In the single-wall carbon nanotube unit dispersion, the bundled carbon nanotubes were 0.2% by weight and the polyvinylidene fluoride was 4.0% by weight. The carbon nanotube structure shown in Preparation Example 1 was not detected.
[180]
[181]
Examples and Comparative Examples
[182]
[183]
Example 1: Preparation of silicon-carbon composite negative electrode active material and negative electrode
[184]
(1) Preparation of silicon-carbon composite negative electrode active material
[185]
For SiO (core) having an average particle diameter (D 50 ) of 6.6 μm , CVD (chemical vapor deposition) is performed at 1,000 ° C using an Ar / CH 4 mixed gas to form a carbon layer (amorphous carbon layer) on the SiO ) was formed. The carbon layer was 5 parts by weight based on 100 parts by weight of the core, and the carbon layer covered a part of the surface of the SiO (see FIG. 1).
[186]
On the other hand, the weight ratio of the core on which the carbon layer is formed, the carbon nanotube structure, and the polyvinylidene fluoride is 96.00: 0.67: 3.33 (0.69 part by weight of the carbon nanotube structure compared to 100 parts by weight of the core on which the carbon layer is formed) A mixed solution was formed by mixing the dispersion solution of Preparation Example 1 and the core on which the carbon layer was formed so as to be possible. The polyvinylidene fluoride was 3.47 parts by weight based on 100 parts by weight of the core on which the carbon layer was formed.
[187]
Thereafter, after stirring the mixed solution, distillation under reduced pressure using a rotary evaporator at 150 ° C was performed to remove the dispersion medium (NMP), heat treatment was performed in a vacuum oven at 150 ° C for 48 hours, and the oven was turned off (OFF). ) by natural cooling for 24 hours to prepare a silicon-carbon composite anode active material.
[188]
(2) Manufacture of cathode
[189]
The silicon-carbon composite negative electrode active material, artificial graphite (D 50 : 21 μm) and plate-like graphite (D 50 : 5.4 μm), which are carbon-based active materials, were used as negative electrode active materials. An anode slurry was prepared by mixing the anode active material and binders SBR and CMC (weight average molecular weight: 100,000 g/mol, substitution degree: 1.0) in water as a solvent. The weight ratio of the negative electrode active material and the binder was 96.8:3.2, the weight ratio of the silicon-carbon composite negative electrode active material, artificial graphite, and planar graphite was 15:80:5, and the weight ratio of SBR and CMC in the binder was 2.0:1.2. was The carbon nanotube structure was included in the negative electrode active material layer at 0.1% by weight.
[190]
Each of the anode slurries was applied to a copper (Cu) metal thin film having a thickness of 20 μm, which is an anode current collector, at a loading of 160 mg/25 cm 2 and dried. At this time, the temperature of the circulated air was 70°C. Subsequently, the negative electrode current collector to which the slurry was applied and dried was rolled and dried in a vacuum oven at 130° C. for 8 hours to prepare a negative electrode including a negative electrode active material layer.
[191]
[192]
Example 2: Preparation of silicon-carbon composite negative electrode active material and negative electrode
[193]
When manufacturing a silicon-carbon composite anode active material, the weight ratio of the core with a carbon layer, the carbon nanotube structure, and the polyvinylidene fluoride was 99.59:0.07:0.34 (100 parts by weight of the core with a carbon layer compared to the carbon 0.069 parts by weight of the nanotube structure and 0.345 parts by weight of the polyvinylidene fluoride) The same method as in Example 1, except that a mixed solution was formed by mixing the dispersion solution of Preparation Example 1 and the core on which the carbon layer was formed. A silicon-carbon composite negative electrode active material and negative electrode were prepared. The carbon nanotube structure was included in 0.01% by weight in the negative electrode active material layer.
[194]
[195]
Example 3: Preparation of silicon-carbon composite negative electrode active material and negative electrode
[196]
When preparing a silicon-carbon composite anode active material, SiO (core) having an average particle diameter (D 50 ) of 6.6 μm and pitch are melted/stirred in a THF solvent and carbonized for 2 hours in an inert atmosphere at 800° C. to form a carbon layer (amorphous carbon layer) was formed. The carbon layer was 5 parts by weight based on 100 parts by weight of the core, and the carbon layer covered a part of the surface of the SiO (see FIG. 2). Thereafter, a silicon-carbon composite anode active material and an anode were prepared in the same manner as in Example 1. The carbon nanotube structure was included in 0.1% by weight in the negative electrode active material layer.
[197]
[198]
Example 4: Preparation of silicon-carbon composite negative electrode active material and negative electrode
[199]
When manufacturing a silicon-carbon composite anode active material, the weight ratio of the core with a carbon layer, the carbon nanotube structure, and the polyvinylidene fluoride was 99.59:0.07:0.34 (100 parts by weight of the core with a carbon layer compared to the carbon 0.069 parts by weight of the nanotube structure and 0.345 parts by weight of the polyvinylidene fluoride) The same method as in Example 3, except that a mixed solution was formed by mixing the dispersion solution of Preparation Example 1 and the core on which the carbon layer was formed. A silicon-carbon composite negative electrode active material and negative electrode were prepared. The carbon nanotube structure was included in 0.01% by weight in the negative electrode active material layer.
[200]
[201]
Comparative Example 1: Preparation of negative electrode active material and negative electrode
[202]
A negative electrode active material and a negative electrode were prepared in the same manner as in Example 1, except that a core on which a carbon layer was not formed was used when forming the mixed solution in Example 1.
[203]
All parts of the carbon nanotube structure in the anode active material were present while wrapping around the surface of the SiO without being fixed to the surface of the anode active material (see FIG. 3 ). The carbon nanotube structure was included in the negative electrode active material layer at 0.1% by weight.
[204]
[205]
Comparative Example 2: Preparation of negative electrode active material and negative electrode
[206]
A silicon-carbon composite anode active material and a negative electrode were prepared in the same manner as in Example 2, except that a core having no carbon layer was used when forming the mixed solution in Example 2. In the anode active material, all parts of the carbon nanotube structure were present while wrapping around the surface of the SiO without being fixed to the surface of the anode active material. The carbon nanotube structure was included in the negative electrode active material layer at 0.01% by weight.
[207]
[208]
Comparative Example 3: Preparation of negative electrode active material and negative electrode
[209]
(1) Preparation of negative electrode active material
[210]
For SiO (core) having an average particle diameter (D 50 ) of 6.6 μm , CVD (chemical vapor deposition) is performed at 1,000 ° C using an Ar / CH 4 mixed gas to form a carbon layer (amorphous carbon layer) on the SiO ) to prepare a silicon-based negative electrode active material. The carbon layer was 5 parts by weight based on 100 parts by weight of the core, and the carbon layer covered a part of the SiO surface.
[211]
(2) Manufacture of cathode
[212]
Artificial graphite (D 50 : 21 μm) and plate-like graphite (D 50 : 5.4 μm), which are the silicon-based negative electrode active material and the carbon-based active material, were used as negative electrode active materials. An anode slurry was prepared by mixing the anode active material, binders SBR and CMC (weight average molecular weight: 100,000 g/mol, substitution degree: 1.0), and the carbon nanotube structure dispersion of Preparation Example 1 in water.
[213]
The weight ratio of the negative electrode active material, the carbon nanotube structure, and the binder was 96.7:0.1:3.2. The weight ratio of the silicon-based active material, artificial graphite, and planar graphite in the negative active material was 15:80:5, and the weight ratio of SBR and CMC in the binder was 2.0:1.2.
[214]
Each of the anode slurries was applied to a copper (Cu) metal thin film having a thickness of 20 μm, which is an anode current collector, at a loading of 160 mg/25 cm 2 and dried. At this time, the temperature of the circulated air was 70°C. Subsequently, the negative electrode current collector to which the slurry was applied and dried was rolled and dried in a vacuum oven at 130° C. for 8 hours to prepare a negative electrode including a negative electrode active material layer. The carbon nanotube structure was included in 0.1% by weight of the negative electrode active material layer.
[215]
[216]
Comparative Example 4: Preparation of negative electrode active material and negative electrode
[217]
An anode active material and an anode were prepared in the same manner as in Comparative Example 3, except that the weight ratio of the anode active material, the carbon nanotube structure, and the binder was 95.8:1.0:3.2. The carbon nanotube structure was included in 0.01% by weight in the negative electrode active material layer.
[218]
[219]
Comparative Example 5: Preparation of negative electrode
[220]
(1) Preparation of silicon-based negative electrode active material
[221]
For SiO (core) having an average particle diameter (D 50 ) of 6.6 μm , CVD (chemical vapor deposition) is performed at 1,000 ° C using an Ar / CH 4 mixed gas to form a carbon layer (amorphous carbon layer) on the SiO ) was formed. The carbon layer was 5 parts by weight based on 100 parts by weight of the core, and the carbon layer covered a part of the SiO surface.
[222]
(2) Manufacture of cathode
[223]
Artificial graphite (D 50 : 21 μm) and plate-like graphite (D 50 : 5.4 μm), which are the silicon-based negative electrode active material and the carbon-based active material, were used as negative electrode active materials. An anode slurry was prepared by mixing the anode active material, binders SBR and CMC (weight average molecular weight: 100,000 g/mol, substitution degree: 1.0), and the multi-walled carbon nanotube dispersion of Preparation Example 2 in water as a solvent. The weight ratio of the anode active material, the multi-walled carbon nanotube unit, and the binder was 95.8:1.0:3.2, and the weight ratio of the silicon-based anode active material, artificial graphite, and planar graphite was 15:80:5, and among the binders, SBR and The weight ratio of CMC was 2.0:1.2.
[224]
Each of the anode slurries was applied to a copper (Cu) metal thin film having a thickness of 20 μm, which is an anode current collector, at a loading of 160 mg/25 cm 2 and dried. At this time, the temperature of the circulated air was 70°C. Subsequently, the negative electrode current collector to which the slurry was applied and dried was rolled and dried in a vacuum oven at 130° C. for 8 hours to prepare a negative electrode including a negative electrode active material layer. The multi-walled carbon nanotube units were included in an amount of 1.0% by weight in the negative electrode active material layer.
[225]
[226]
Comparative Example 6: Preparation of negative electrode
[227]
An anode was prepared in the same manner as in Comparative Example 5, except that the carbon black dispersion of Preparation Example 4 was used instead of the multi-walled carbon nanotube dispersion of Preparation Example 2. The carbon black was included in an amount of 1.0% by weight in the negative electrode active material layer.
[228]
[229]
Comparative Example 7: Preparation of negative electrode active material and negative electrode
[230]
An anode active material and an anode were prepared in the same manner as in Example 1, except that the multi-walled carbon nanotube unit dispersion of Preparation Example 3 was used instead of the carbon nanotube structure dispersion of Preparation Example 1.
[231]
The weight ratio of the core on which the carbon layer was formed, the multi-walled carbon nanotube unit, and the polyvinylidene fluoride was 90.50:6.33:3.17 (100 parts by weight of the core on which the carbon layer was formed, the multi-walled carbon nanotube unit was 7.0 parts by weight, the polyvinylidene fluoride was 3.5 parts by weight). The multi-walled carbon nanotube units were included in an amount of 1.0% by weight in the negative electrode active material layer.
[232]
[233]
Comparative Example 8: Preparation of negative electrode active material and negative electrode
[234]
An anode active material and an anode were prepared in the same manner as in Example 1, except that the single-walled carbon nanotube unit dispersion of Preparation Example 5 was used instead of the carbon nanotube structure dispersion of Preparation Example 1.
[235]
The weight ratio of the core on which the carbon layer was formed, the single-walled carbon nanotube units, and the polyvinylidene fluoride was 92.88:0.65:6.47 (100 parts by weight of the core on which the carbon layer was formed, the single-walled carbon nanotube unit was 0.70 parts by weight, the polyvinylidene fluoride was 6.97 parts by weight). The single-walled carbon nanotube units were included in an amount of 0.1% by weight in the negative electrode active material layer.
[236]
[237]
[Table 1]
Average length (μm) Average diameter (nm)
Examples 1 to 4 and Comparative Examples 1 to 4 Carbon nanotube structure 26.5 100
Multi-walled carbon nanotube units of Comparative Examples 5 and 7 1.3 10
Carbon Black of Comparative Example 6 0.8 Particle size: 35
Single-walled carbon nanotube unit of Comparative Example 8 0.9 1.5
[238]
The carbon nanotube structure has a rope shape in which single-walled carbon nanotube units having a diameter of about 1.5 nm are coupled side by side with each other. The average length and average diameter correspond to average values ​​of the top 100 objects and the bottom 100 objects having the largest average diameter or length when the manufactured negative electrode is observed through TEM.
[239]
[240]
[Table 2]
Whether the carbon nanotube structure is bonded to the surface of the negative electrode active material Content of carbon nanotube structure in negative electrode active material layer (parts by weight) Specific surface area of ​​negative electrode active material (m 2 /g)
Example 1 O 0.1 5.2
Example 2 O 0.01 5.1
Example 3 O 0.1 2.3
Example 4 O 0.01 2.2
Comparative Example 1 O 0.1 1.7
Comparative Example 2 O 0.01 1.7
Comparative Example 3 X (simple blend) 0.1 4.6
Comparative Example 4 X (simple blend) 0.01 4.6
Comparative Example 5 X (multi-walled carbon nanotube monomer) 1.0 (content of multi-walled carbon nanotube monomers) 4.6
Comparative Example 6 X (carbon black) 1.0 (content of carbon black) 4.6
Comparative Example 7 O (multi-walled carbon nanotube monomer) 1.0 (multi-walled carbon nanotube monomer) 7.1
Comparative Example 8 O (single-walled carbon nanotube monomer) 0.1 (single-wall carbon nanotube monomer) 5.3
[241]
In Table 2, the anode active materials of Examples 1 to 4 mean silicon-carbon composite anode active materials.
[242]
[243]
Experimental Example
[244]
Experimental Example 1: Observation of cathode
[245]
The negative electrode active material layers of the negative electrodes of Examples 1 and 3 and Comparative Examples 1, 3, 5, and 7 were observed through a scanning electron microscope. 1 and 2 are SEM pictures of the cathode of Example 1 of the present invention. 3 is a SEM picture of the negative electrode of Example 3 of the present invention. 4 is a SEM picture of the negative electrode of Comparative Example 1 of the present invention. 5 is a SEM picture of the negative electrode of Comparative Example 3 of the present invention. 6 is a SEM picture of the negative electrode of Comparative Example 5 of the present invention. 7 is a SEM picture of the negative electrode of Comparative Example 7 of the present invention.
[246]
1, 2, and 3, a carbon nanotube structure in which 2 to 5000 single-walled carbon nanotube units are bonded side by side is observed, and the carbon nanotube structure is bonded to the surface of the amorphous carbon layer it can be seen that there is In addition, it can be seen that only a portion of the carbon nanotube structure is bonded to the amorphous carbon layer, and the remaining portion is in contact with an adjacent anode active material.
[247]
In addition, in the silicon-carbon composite negative electrode active materials of the embodiments, the polyvinylidene fluoride was covering at least a portion of the carbon nanotube structure, and a portion of the carbon nanotube structure was attached to the carbon layer to form the polyvinylidene fluoride. It was bound by crystallization of fluoride. In addition, as a result of confirming by SEM, it was found that the carbon nanotube structure protrudes linearly from the carbon layer. More specifically, an average of 2.5 carbon nanotube structures was included in the silicon-carbon composite anode active material. This corresponds to an average value obtained after examining 500 silicon-carbon composite anode active materials in the anode with SEM and checking the number of carbon nanotube structures present on the surface thereof. In addition, a part of the carbon nanotube structure was bonded to the carbon layer, and the other part of the carbon nanotube structure was not directly bonded to the carbon layer but protruded and existed in a shape like a beard.
[248]
Furthermore, comparing FIG. 2 and FIG. 5, in Comparative Examples 3 and 4, unlike Example 1, the carbon nanotube structures are not firmly bonded to the amorphous carbon layer, so most of the carbon nanotube structures are confirmed on the carbon-based active material. It became. It can be seen from FIG. 6 that most of the multi-walled carbon nanotube units exist only on the carbon-based active material. In FIG. 7 , only short-length multi-walled carbon nanotube units were present on the amorphous carbon layer, and no carbon nanotube structures were identified.
[249]
[250]
Experimental Example 2: High-temperature capacity retention rate (high-temperature life characteristics) evaluation
[251]
Using the negative electrodes of Examples and Comparative Examples, batteries were prepared as follows.
[252]
Li[Ni 0.6 Mn 0.2 Co 0.2 ]O 2 was used as a cathode active material . A positive electrode slurry was prepared by mixing the positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 94:4:2 with solvent N-methyl-2 pyrrolidone.
[253]
The prepared positive electrode slurry was applied to an aluminum metal thin film as a positive electrode current collector having a thickness of 15 μm and dried. At this time, the temperature of the circulated air was 110°C. Subsequently, it was rolled and dried in a vacuum oven at 130° C. for 2 hours to form a positive electrode active material layer.
[254]
Each of the negative electrodes of Examples 1 to 3 and Comparative Examples 1 to 4, the prepared positive electrode and the porous polyethylene separator were assembled using a stacking method, and the assembled battery was charged with an electrolyte solution (ethylene carbonate (EC) / ethyl methyl carbonate). (EMC) = 1/2 (volume ratio), a lithium secondary battery was prepared by injecting lithium hexafluorophosphate (LiPF 6 1 mol).
[255]
Each lithium secondary battery was charged and discharged under the following conditions.
[256]
Charging conditions: 0.5C constant current charge to 4.25V, then charge at 4.2V until 0.1C current rate flows
[257]
Discharge condition: Discharge at 0.5C current rate to 2.8V
[258]
When the charging and discharging were performed as one cycle, 100 cycles were performed at 45°C. Thereafter, the discharge capacity (capacity retention rate) after 100 cycles was evaluated based on 100% of the discharge capacity after one cycle, and the results are shown in Table 3.
[259]
[260]
[Table 3]
Example 1 Comparative Example 7 Comparative Example 8
High temperature capacity retention rate (%) 98.9 85.2 96.1
[261]
[Table 4]
Example 1 Comparative Example 3
High temperature capacity retention rate (%) 98.9 93.4
Example 2 Comparative Example 4
High temperature capacity retention rate (%) 89.1 88.1
[262]
[Table 5]
Example 1 Comparative Example 1
High temperature capacity retention rate (%) 98.9 95.3
Example 2 Comparative Example 2
High temperature capacity retention rate (%) 89.1 85.7
[263]
[Table 6]
Example 1 Comparative Example 5 Comparative Example 6
High temperature capacity retention rate (%) 98.9 84.3 79.2
[264]
[Table 7]
Example 1 Example 3
High temperature capacity retention rate (%) 98.9 97.2
Example 2 Example 4
High temperature capacity retention rate (%) 89.1 88.5
[265]
Referring to the above tables, as a comparison between experiments using carbon-based materials (carbon nanotube structures, single-walled carbon nanotube units) of the same content relative to 100 parts by weight of the silicon-carbon composite negative electrode active material, Example 1 and Comparative Example 8 can be compared In this case, it can be seen that the high temperature capacity retention rate of Example 1 is much higher. This is because the carbon nanotube structure is firmly bonded to the amorphous carbon layer, and even when the silicon-carbon composite negative electrode active material of the present invention is used in combination with the carbon-based active material, the carbon nanotube structure is bonded to the silicon-carbon composite negative electrode active material of the present invention. because you can keep In addition, since the carbon nanotube structure has a long length and may protrude from the silicon-carbon composite negative electrode active material (it does not cover only the silicon-carbon composite negative electrode active material to which the carbon nanotube structure is bonded), the adjacent silicon-carbon composite negative active material This is because a conductive network can be formed with a carbon composite anode active material and a carbon-based active material, and a relatively distant silicon-carbon composite anode active material and a carbon-based active material. On the other hand, in Comparative Example 8, only single-walled carbon nanotube units exist one by one instead of the carbon nanotube structure, and their lengths are very short, so it is difficult to form the conductive network as described above.
[266]
On the other hand, comparing Example 1 and Comparative Example 7, in Comparative Example 7, a relatively large amount of multi-walled carbon nanotube units was used to secure the conductivity of the negative electrode, but the short length of the multi-walled carbon nanotubes and the multi-walled carbon It can be seen that the lifespan characteristics are not good because the nanotubes mainly exist only on the surface of the carbon-based active material.
[267]
In addition, comparing Example 1 and Comparative Example 3, or comparing Example 2 and Comparative Example 4, the carbon layer and the carbon nanotube structure were not firmly bonded to each other by polyvinylidene fluoride, and a simple mixed form It can be seen that Comparative Example 3 having a simple mixed form compared to Example 1, Comparative Example 4 having a simple mixed form, has poorer life characteristics than Example 2.
[268]
Furthermore, when comparing Example 1 and Comparative Example 1, Example 2 and Comparative Example 2 including carbon nanotube structures having the same content, Comparative Example 1 without a carbon layer is better than Example 1 without a carbon layer. It can be seen that Example 2 has poorer life characteristics than Example 2. This is because there is no carbon layer as a medium through which the carbon nanotube structure can be bonded to the core, and thus the carbon nanotube structure is inevitably present only in the carbon-based active material, resulting in poor uniformity and durability of the conductive network.
[269]
In addition, in Example 1, Comparative Example 5, and Comparative Example 6, carbon black or multi-walled carbon nanotube units were used instead of carbon nanotube structures, and even the carbon black or multi-walled carbon nanotube units were used in the carbon layer. It can be seen that the capacity retention rates of Comparative Examples 5 and 6 in which the negative electrode active material was not prepared in a combined form were very low.
[270]
On the other hand, comparing Example 1 and Example 3 including carbon nanotube structures having the same content, and comparing Example 2 and Example 4, only a part of the core surface was coated (the ratio of the silicon-carbon composite negative electrode active material). It can be seen that Examples 1 and 2, which have a relatively large surface area, have excellent lifespan characteristics compared to Examples 3 and 4.
claims
[Claim 1]
A core containing SiO X (0≤X<2); a carbon layer covering at least a portion of the surface of the core; a carbon nanotube structure located on the carbon layer; and polyvinylidene fluoride covering at least a portion of the carbon nanotube structure, wherein the carbon nanotube structure is formed by arranging and bonding 2 to 5,000 single-walled carbon nanotube units side by side with each other, wherein the A portion of the carbon nanotube structure is a silicon-carbon composite negative electrode active material bonded to the carbon layer.
[Claim 2]
The silicon-carbon composite anode active material according to claim 1, wherein the carbon nanotube structure has an average diameter of 2 nm to 200 nm.
[Claim 3]
The silicon-carbon composite anode active material according to claim 1, wherein the carbon nanotube structure is a carbon nanotube structure formed by arranging and bonding 2 to 500 single-walled carbon nanotube units side by side with each other.
[Claim 4]
The silicon-carbon composite anode active material of claim 1, wherein the carbon nanotube structure has an average length of 1 μm to 100 μm.
[Claim 5]
The silicon-carbon composite anode active material of claim 1, wherein the single-walled carbon nanotube units are included in an amount of 95% to 100% by weight in the carbon nanotube structure.
[Claim 6]
The silicon-carbon composite anode active material of claim 1, wherein the carbon nanotube structure is included in an amount of 1 to 100 in the anode active material.
[Claim 7]
The silicon-carbon composite anode active material according to claim 1, wherein the carbon nanotube structure is included in an amount of 0.05 to 5.0 parts by weight based on 100 parts by weight of the core on which the carbon layer is formed.
[Claim 8]
The silicon-carbon composite anode active material of claim 1, wherein the carbon layer includes at least one of crystalline carbon and amorphous carbon.
[Claim 9]
The silicon-carbon composite anode active material of claim 1, wherein the carbon layer is included in an amount of 0.1 part by weight to 20 parts by weight based on 100 parts by weight of the core.
[Claim 10]
The silicon-carbon composite anode active material of claim 1, wherein the polyvinylidene fluoride exists in a crystallized state in the anode active material.
[Claim 11]
The silicon-carbon composite negative electrode active material of claim 1, wherein the polyvinylidene fluoride is included in an amount of 0.1 part by weight to 30 parts by weight based on 100 parts by weight of the core on which the carbon layer is formed.
[Claim 12]
The silicon-carbon composite anode active material according to claim 1, having a specific surface area of ​​0.5 m 2 /g to 50 m 2 /g.
[Claim 13]
An anode comprising the silicon-carbon composite anode active material of claim 1.
[Claim 14]
The negative electrode according to claim 13, further comprising a carbon-based active material.
[Claim 15]
A secondary battery comprising the anode of claim 13.