Title of the invention: Anode active material for secondary battery, electrode including the same, and method for manufacturing the same
Technical field
[One]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0000664 filed on January 3, 2019, and all contents disclosed in the documents of the Korean patent application are included as part of this specification.
[2]
The present invention relates to a negative active material for a secondary battery, a negative electrode including the same, and a method of manufacturing the same. In more detail, the present invention relates to an anode active material having improved cycle swelling and high rate charging characteristics, an anode, and a method of manufacturing the same.
Background
[3]
As the price of energy sources rises due to the depletion of fossil fuels and interest in environmental pollution increases, the demand for eco-friendly alternative energy sources is becoming an indispensable factor for future life. In particular, technology development for mobile devices As the demand and demand increase, the demand for secondary batteries as an energy source is rapidly increasing.
[4]
Typically, in terms of the shape of the battery, there is a high demand for prismatic secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with a thin thickness. There is high demand for lithium secondary batteries such as lithium ion polymer batteries.
[5]
In general, secondary batteries constitute a positive electrode and a negative electrode by coating an electrode mixture containing an electrode active material on the surface of a current collector, and an electrode assembly is formed with a separator interposed therebetween, and then a cylindrical or rectangular metal can or aluminum laminate sheet. It is mounted inside the pouch-shaped case of the electrode assembly, and is manufactured by mainly injecting or impregnating a liquid electrolyte into the electrode assembly or using a solid electrolyte.
[6]
In addition, secondary batteries are classified according to the structure of the electrode assembly of the anode/separator/cathode structure. Typically, long sheet-shaped anodes and cathodes are wound up with a separator interposed between them. Roll (wound type) electrode assembly, stacked (stacked) electrode assembly in which a plurality of anodes and cathodes cut in units of a predetermined size are sequentially stacked with a separator interposed, A stack/folding electrode assembly having a structure in which bi-cells or full cells stacked in a state are wound with a separator sheet may be mentioned.
[7]
Meanwhile, the electrode generates an electric current through the exchange of ions, and the positive electrode and the negative electrode constituting the electrode have a structure in which an electrode active material is coated on an electrode current collector made of metal.
[8]
Among them, in the case of the negative electrode, conventionally, lithium metal was used as the negative electrode in the secondary battery, but the battery short-circuit due to the formation of dendrites and the risk of explosion due thereto are known, while maintaining structural and electrical properties, and reversible Phosphorus lithium ions are being replaced by carbon-based compounds capable of intercalation and desorption.
[9]
The carbon-based compound has a very low discharge potential of about -3V with respect to the standard hydrogen electrode potential, and exhibits excellent electrode life characteristics due to very reversible charging and discharging behavior due to the uniaxial orientation of the graphene layer. . In addition, when charging Li ions, since the electrode potential is 0V Li/Li+, which can exhibit a potential similar to that of pure lithium metal, there is an advantage that higher energy can be obtained when configuring a battery with an oxide-based positive electrode.
[10]
The carbon-based compound includes crystalline carbon and amorphous carbon. As for crystalline carbon, graphite carbon such as natural graphite and artificial graphite is representative, and amorphous carbon is heat treated with non-graphitizable carbons (hard carbons) obtained by carbonizing a polymer resin and pitch. And the resulting graphitizable carbons (soft carbons).
[11]
In particular, as a carbon-based material, natural graphite having a high capacity or excellent artificial graphite such as high-temperature characteristics is used, but it exhibits a lower capacity than artificial graphite artificial graphite and natural graphite, and is produced by secondary particle formation and coating treatment. And poor processability such as a decrease in electrode adhesion, and poor electrode rolling characteristics.
[12]
Korean Patent Publication No. 2014-0132791 discloses a negative electrode material using spheroidized natural graphite. However, in the case of an anode active material using natural graphite, the mechanical strength of the electrode is weakened, and the cycle swelling and rapid charging performance during charging and discharging are poor. In this case, the electrode may swell during charging and discharging, resulting in a problem such as a reduction in cycle life.
[13]
Therefore, it is necessary to develop a technology for solving the above problems.
Detailed description of the invention
Technical challenge
[14]
The present invention was invented to solve the above problems, and in a negative electrode active material using natural graphite, natural graphite obtained by granulating and secondary granulating flaky natural graphite, and spheroidizing natural graphite with increased sphericity and tap density. An object of the present invention is to provide a negative electrode active material with improved cycle characteristics, swelling characteristics, and rapid charging performance to the level of artificial graphite even when natural graphite is used by using a mixture of graphite, a negative electrode including the same, and a manufacturing method thereof.
Means of solving the task
[15]
The negative active material for a secondary battery according to the present invention,
[16]
It is a mixture of flaky natural graphite and spheroidized natural graphite,
[17]
The average particle diameter (D 50 ) of the flaky natural graphite may be 10 to 15 μm, and the average particle diameter (D 50 ) of the spheroidized natural graphite may be 14 μm or less.
[18]
In addition, in the negative active material for a secondary battery according to the present invention, the scaled natural graphite may be granulated and secondary particles.
[19]
In addition, in the negative active material for a secondary battery according to the present invention, the negative active material may contain 40 to 60% by weight of the scale-like natural graphite, and 40 to 60% by weight of the spheroidized natural graphite, based on the total weight of the negative active material. It may contain 45 to 55% by weight of flaky natural graphite and 45 to 55% by weight of the spheroidized natural graphite.
[20]
In addition, in the negative active material for a secondary battery according to the present invention, the average particle diameter of the scaled natural graphite may be 12 to 13 μm, and the average particle diameter of the spheroidized natural graphite may be 9 to 11 μm.
[21]
In addition, in the negative active material for a secondary battery according to the present invention, the average particle diameter of the scaled natural graphite may be equal to or greater than the average particle diameter of the spheroidized natural graphite.
[22]
In addition, in the negative active material for a secondary battery according to the present invention, the sphericity of the scaled natural graphite may be 0.4 to 0.6.
[23]
In addition, in the negative active material for a secondary battery according to the present invention, the spheroidization degree of spheroidized natural graphite may be 0.7 to 0.95.
[24]
In addition, in the negative active material for a secondary battery according to the present invention, the tap density of the flaky natural graphite may be 0.9 to 1.2 g/cc.
[25]
In addition, in the negative active material for a secondary battery according to the present invention, the tap density of the spheroidized natural graphite may be 1.0 to 1.4 g/cc.
[26]
In addition, in the negative active material for a secondary battery according to the present invention, in the scaled natural graphite, the orientation index of the electrode may be 10 to 15 at a porosity of 28% after rolling.
[27]
In addition, in the negative active material for a secondary battery according to the present invention, in the spheroidized natural graphite, the orientation index of the electrode may be 5 to 14 at a porosity of 28% after rolling.
[28]
In addition, the present invention provides a negative electrode for a secondary battery, wherein the negative electrode for a secondary battery includes a current collector and a negative electrode mixture layer coated on the current collector,
[29]
The negative electrode mixture layer includes a conductive material, a binder, and the negative electrode active material.
[30]
In addition, the present invention provides a secondary battery,
[31]
The secondary battery may include a negative electrode, a positive electrode, a separator and an electrolyte interposed between the negative electrode and the positive electrode, and the negative electrode may be a negative electrode including the negative active material.
[32]
In addition, the present invention provides a method of manufacturing a negative electrode for a secondary battery. The method of manufacturing a negative electrode for a secondary battery includes preparing a negative electrode mixture and applying the negative electrode mixture on a current collector and then drying it,
[33]
The negative active material included in the negative electrode mixture includes a mixture of flaky natural graphite and spheroidized natural graphite,
[34]
The negative active material is as described above.
Effects of the Invention
[35]
In the negative electrode active material using natural graphite, by using a mixture of natural graphite obtained by granulating and secondary granulating flaky natural graphite and spheroidizing natural graphite with increased sphericity and tap density, the level of artificial graphite is even when natural graphite is used. As a result, it is possible to improve cycle characteristics, swelling characteristics, and rapid charging performance.
Brief description of the drawing
[36]
1 is a schematic diagram showing the structure of a negative electrode for a secondary battery including a negative active material according to the present invention.
Best mode for carrying out the invention
[37]
Terms used in the present specification and claims are not limited to their usual or dictionary meanings and should not be interpreted, and that the inventor can appropriately define the concept of terms in order to describe his own invention in the best way. Based on the principle, it should be interpreted as a meaning and concept consistent with the technical idea of ​​the invention. Therefore, the configuration shown in the embodiments described in the present specification is only one of the most preferred embodiments of the present invention and does not represent all of the technical spirit of the present invention, and various equivalents that can replace them at the time of the present application And it should be understood that there may be variations.
[38]
In the entire specification of the present application, when a part is said to be ``connected'' with another part, this includes not only ``directly connected'' but also ``electrically connected'' with another element interposed therebetween. .
[39]
Throughout this specification, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other It is to be understood that it does not preclude the presence or addition of features, numbers, steps, actions, components, parts, or combinations thereof. Further, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where the other part is "directly above", but also the case where there is another part in the middle. Conversely, when a part such as a layer, a film, a region, or a plate is said to be "under" another part, this includes not only the case where the other part is "directly below", but also the case where there is another part in the middle. In addition, in the present application, the term "above" may include a case where it is disposed not only on the top but also on the bottom.
[40]
The terms "about", "substantially" and the like used throughout this specification are used as a meaning at or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and are accurate to aid the understanding of the present application. Or absolute figures are used to prevent unfair use of the stated disclosure by unconscionable infringers.
[41]
In the entire specification of the present application, the term "combination(s) thereof" included in the expression of the Makushi format refers to one or more mixtures or combinations selected from the group consisting of the constituent elements described in the expression of the Makushi format, It means to include at least one selected from the group consisting of the above components.
[42]
Hereinafter, the present invention will be described in detail.
[43]
The negative active material for a secondary battery according to the present invention contains a graphite material as a main component.
[44]
Specifically, the negative active material is composed of natural graphite, and more specifically, the natural graphite is a mixture of scaled natural graphite and spheroidized natural graphite.
[45]
As described above, however, as the charging/discharging cycle of natural graphite is repeated, a swelling phenomenon may occur due to an electrolyte solution decomposition reaction occurring at the edge of the natural graphite, and charging/discharging efficiency and capacity may be deteriorated. In addition, natural graphite has many internal voids, and there is a problem in that the internal voids are clogged during electrode rolling and receive a lot of mechanical stress.
[46]
Therefore, as described later, by using a mixture of natural graphite obtained by granulating and secondary granulating flaky natural graphite and spheroidizing natural graphite with increased sphericity and tap density, the cycle characteristics are comparable to that of artificial graphite even when natural graphite is used. , Swelling characteristics and rapid charging performance can be improved
[47]
More specifically, spheroidized graphite has a relatively narrow particle size distribution and less fine powder distribution than that of flaky graphite. As the fine powder content decreases, the phase stability of the negative electrode mixture can be maintained, and ultimately, adhesion to the electrode current collector. This improved effect can be obtained.
[48]
In particular, when a negative electrode active material containing spheroidized natural graphite is used as a negative electrode of a battery, there are various advantages as described above, but microcavities are formed between the spheroidized natural graphite. As the expansion is repeated, a conductive path between the particles and the particles becomes distant, so that the cycle characteristics of the battery may be deteriorated. The disadvantages due to such microcavities can be compensated for by using a conductive material, but there is a limit to making a passage for electrons between negative active materials only with a dot or line type conductive material.
[49]
Therefore, as the natural graphite is mixed in a certain ratio, the natural graphite is distributed among the spheroidized natural graphite particles, preventing the spheroidized natural graphite particles from being separated from each other, thereby forming a conductive path between the particles. It is possible to remarkably improve the cycle characteristics and life of the battery.
[50]
[51]
First, the scale-like natural graphite contained in the negative active material of the present invention will be described.
[52]
Flaky natural graphite is a crystal having a thickness in the C-axis direction, which is a direction perpendicular to the AB plane, in which a number of hexagonal mesh planes (AB planes) are stacked in a planar shape by forming a network structure with regular carbon atoms.
[53]
Since the bonding force (van der Waals force) between the stacked AB surfaces is much smaller than that of the AB surfaces in the in-plane direction (covalent bonding), peeling between the AB surfaces is likely to occur. Therefore, since the thickness of the lamination is thin with respect to the enlargement of the AB plane, the overall shape of the scale is shown.
[54]
In the negative active material for a secondary battery according to the present invention, the scaled natural graphite may have an average particle diameter (D 50 ) of 10 to 15 μm, preferably 12 to 15 μm, and most preferably 12 to 13 It may be μm. In the present invention, the particle diameter of the scaled natural graphite means a particle diameter measured based on a long diameter, and the average particle diameter (D 50 ) means a particle diameter in which the accumulation of the smallest particles in the order of particle diameter becomes 50%. By using scaled natural graphite whose average particle diameter is within the above range, the distance through which lithium ions must be diffused after insertion is relatively small, so the diffusion resistance of lithium ions is small, the insertion and removal of lithium ions is free, and rapid charging at energy density You can get the advantage of improving your ability.
[55]
If the average particle diameter of the flaky natural graphite is less than 10 μm, the initial efficiency of the secondary battery may decrease due to an increase in the specific surface area, thereby reducing the battery performance, requiring a large amount of binder, and preventing problems such as filter clogging in the process. Can cause. On the contrary, when the average particle diameter of the flaky natural graphite exceeds 15 μm, the electrode adhesion may decrease and the cycle characteristics of the battery may deteriorate, and it may be difficult to uniformly mix the spheroidized natural graphite and the flaky natural graphite. In addition, since the filling density of the active material is lowered, the capacity may decrease, which is not preferable.
[56]
The average particle diameter can be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of about several mm from a submicron region, and high reproducibility and high resolution results can be obtained. More specifically, in the particle size measurement of the spheroidized natural graphite, after dispersing the spherical natural graphite in an ethanol/water solution, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000), and ultrasonic waves at about 28 kHz. After irradiating with an output of 60 W, it can calculate based on the particle size distribution in a measuring device.
[57]
In addition, the scaled natural graphite may be granulated and secondary particles. The secondary particle refers to a large particle that can be physically classified by collecting and combining primary particles, and the high density, and the primary particle refers to an original particle when a different type of particle is formed from a certain particle. In addition, granulation refers to a process in which primary particles are spontaneously or artificially agglomerated or agglomerated to form an aggregate consisting of a plurality of primary particles, thereby forming secondary particles. Can be.
[58]
The method of granulating or secondary granulating the flaky natural graphite is not particularly limited and may be performed by a method conventional in the art. For example, a binder, a catalyst, etc. may be mixed with primary particles of scaled natural graphite and heat treated to prepare graphite secondary particles in which the heterogeneous primary particles are aggregated, bonded or granulated. Specifically, the scaled natural graphite particles may be added to a vacuum reactor under a nitrogen or argon atmosphere and heat treated at 1000 to 2800°C to prepare secondary particles. By heat treatment in the above temperature range, the catalyst may be removed to form pores in the finally produced graphite secondary particles, and graphite secondary particles having very few defects and high crystallinity can be obtained. In other words, when heat treatment is performed at a temperature of less than 1000°C, there is a risk that the graphitization does not occur normally and capacity expression may not be achieved. It may be desirable to perform in the range of.
[59]
Alternatively, secondary particles of flaky graphite can be obtained by subjecting the primary particles to pressure. In addition, anisotropic pressure treatment is also possible during the pressure treatment, but isotropic pressure treatment that can obtain a high tap density is more preferable.
[60]
The isotropic pressure treatment method is not particularly limited as long as it is a method capable of isotropically pressurizing, and for example, a gas such as hydrostatic pressure isotropic press using water as a pressurizing medium by placing the scaly graphite particles as raw materials in a container such as a rubber type. Pressurization treatment such as isotropic pressing using air pressure using as a pressurizing medium may be mentioned.
[61]
By using the scaled natural graphite granulated as described above, it is possible to obtain a negative electrode active material having good rollability and high density compared to using the primary particles of the scaled natural graphite.
[62]
In addition, in the negative active material according to the present invention, the sphericity of the scaled natural graphite may be 0.4 to 0.6, more preferably 0.4 to 0.5. Here, the degree of sphericity may mean a short diameter compared to a long diameter of the particles. The degree of sphericity can be measured through a particle shape analyzer. Specifically, after deriving the cumulative distribution of the sphericity degree of the scale-like natural graphite particles through a particle shape analyzer, the sphericity degree corresponding to 50% of the distribution ratio from the particles having a large sphericity degree is determined by the scale-like natural graphite particles. It can be judged as sphericity.
[63]
If the degree of sphericity is less than 0.4, the surface of the scaled natural graphite particles is too uneven, resulting in a problem of low electrode adhesion.If the degree of sphericity exceeds 0.6, the scaled natural graphite shrinks and expands of the spheroidized natural graphite particles. When the conductive paths between the particles and the particles become distant during the repetition, it is difficult to prevent the spheroidized natural graphite particles from being isolated, and thus the cycle characteristics of the battery may be deteriorated.
[64]
Meanwhile, the tap density of the flaky natural graphite may be 0.9 to 1.2 g/cc, more preferably 0.9 to 1.0 g/cc. The tap density of the active material is the apparent density of the powder obtained by vibrating the container under certain conditions when filling the powder. In the present invention, the tap density was measured by performing tapping 2000 times using TAP-2S manufactured by LOGAN, which is a tap density measuring device.
[65]
The higher the tap density, the higher the packing density of the electrode. Specifically, in order to manufacture an electrode, an active material is mixed with a binder or a conductive agent, coated on a current collector in a thin film state, and pressure is applied to make the electrode hard. In this case, if the filling is not done well, the electrode cannot be made thin and occupy a large volume, so that a high capacity cannot be realized under a given volume condition of the battery.
[66]
When the tap density of the flaky natural graphite is less than 0.9 g/cc, the contact area between the particles is insufficient, so that the adhesion properties may be deteriorated, and the energy density per unit volume may decrease. On the other hand, if the tap density of flaky natural graphite exceeds 1.2 g/cc, the tortuosity of the electrode and the wet-ability of the electrolyte decrease, resulting in a decrease in the output characteristics during charging and discharging, and the initial efficiency. There is a problem that it may cause a decrease in the value and deterioration of high-temperature properties, which is not preferable.
[67]
In addition, in the negative electrode active material according to the present invention, the orientation index of the electrode may be 10 to 15, more preferably 11 to 14 at a porosity of 28% after rolling of the flaky natural graphite.
[68]
The orientation index indicates the degree to which crystal structures inside the cathode are arranged in a certain direction, it is possible to evaluate in which direction the crystals are oriented in the electrode, and can be measured by X-ray diffraction (XRD). More specifically, the orientation index is the area ratio obtained by integrating the peak intensities of the (110) and (004) planes after measuring the (110) plane and the (004) plane of the negative active material included in the negative electrode by XRD ((004) )/(110)), and more specifically, XRD measurement conditions are as follows.
[69]
-Target: Cu (Kα ray) graphite monochromator
[70]
-Slit: diverging slit = 1 degree, receiving slit = 0.1mm, scattering slit = 1 degree
[71]
-Measurement area and step angle/measurement time:
[72]
(110) plane: 76.5 degrees <2θ <78.5 degrees, 0.01 degrees / 3 seconds
[73]
(004) plane: 53.5 degrees <2θ <56.0 degrees, 0.01 degrees / 3 seconds,
[74]
In the above, 2θ represents the diffraction angle.
[75]
The XRD measurement is an example, and other measurement methods may also be used.
[76]
The orientation index of the negative electrode may depend on the compressive force applied when applying and rolling the negative electrode active material to the negative electrode current collector, and when the orientation index is within the above range, a high energy density per unit volume can be obtained, and it is stable even during rolling. It is possible to not only exhibit high electrode density, but also exhibit excellent electrode adhesion, thereby improving cycle characteristics and swelling phenomenon. When the orientation index is less than 10, the crystallinity of the active material decreases, and thus the object of the present invention to improve the swelling and cycle characteristics cannot be achieved. Since it is not easy, diffusion resistance increases and lithium precipitation occurs during high-rate charging and discharging, resulting in deterioration of life characteristics. In addition, the orientation index is measured at a porosity of 28% after rolling because the highest energy density can be obtained at a porosity of 28% when an electrode is manufactured by rolling after coating an electrode active material.
[77]
[78]
Next, the spheroidized natural graphite used in the negative active material according to the present invention will be described.
[79]
The spheroidized natural graphite can be obtained by applying an external mechanical force to the general natural graphite and subjecting it to a granulated spheroidization treatment. For example, spheroidized natural graphite is spheroidized for 10 to 30 minutes at a rotor speed of 30 m/s to 100 m/s in a spheroidizing device after treating the scaled natural graphite with an acid or a base. It can be produced by making, but is not limited thereto.
[80]
The average particle diameter (D 50 ) of the spheroidized natural graphite may be 14 μm or less, preferably 11 μm or less, and more preferably 9 to 11 μm. When the average particle diameter of graphite exceeds 14 µm, the particle diameter increases and the filling density decreases. As charging and discharging are repeated, the binding properties between the particles and the particle and the current collector deteriorate, resulting in a significant decrease in cycle characteristics and swelling characteristics. Can be.
[81]
In addition, the average particle diameter of the scaled natural graphite in the negative active material may be equal to or larger than the average particle diameter of spheroidized natural graphite. When the average particle diameter of spheroidized natural graphite is larger than the average particle diameter of the scaled natural graphite, the spheroidized natural graphite cannot be uniformly filled between the scaled natural graphite, and electrode adhesion and tap density may decrease.
[82]
More specifically, the sphering average particle diameter (D Natural graphite 50 ) has an average particle diameter (D in the scaly natural graphite 50 can be 0.5 to 1 times, preferably 0.8 to 1 times the of). When the ratio between the average particle diameter of artificial graphite and the average particle diameter of spheroidized natural graphite is within the above range, the filling density of the active material in the electrode is improved, and the specific surface area of ​​the active material is reduced, thereby preventing side reactions with the electrolyte.
[83]
The spheronization degree of the spheroidized natural graphite may be 0.7 to 0.95, more preferably 0.8 to 0.9. When the spheronization degree is within the above range, the shape of the spheroidized natural graphite becomes close to the sphere, so that the expanded image of lithium ions in the electrolyte increases, and the tap density can be further increased as the shape of the spheroidized natural graphite becomes uniform .
[84]
When the degree of sphericity is less than 0.7, the surface of the spheroidized natural graphite particles is too uneven, resulting in a problem of low electrode adhesion, and when the degree of sphericity exceeds 0.95, a large amount of natural graphite is required to derive a high degree of sphericity. Accordingly, the production yield of spheroidized natural graphite may be lowered, which is inefficient.
[85]
In addition, the tap density of the spheroidized natural graphite may be 1.0 to 1.4 g/cc, and preferably 1.2 to 1.3 g/cc.
[86]
The tap density of the spheroidized natural graphite is affected by the particle size of the spheroidized natural graphite, and the tap density may decrease as the particle diameter of spheroidized natural graphite increases, and the tap density may increase as the particle diameter decreases. In general, in order to improve the adhesion between the active material and the electrode current collector, the greater the contact area between the particles, the greater the adhesion area, and thus the adhesion is improved.
[87]
When the tap density of the spheroidized natural graphite is less than 1.0 g/cc, the contact area between particles is insufficient, so that adhesion properties may decrease, and energy density per unit volume may decrease. On the other hand, when the tap density of spheroidized natural graphite exceeds 1.4 g/cc, the tortuosity of the electrode and the wet-ability of the electrolyte decrease, resulting in a decrease in the output characteristics during charging and discharging. There is a problem that it may cause a decrease in efficiency and deterioration of high-temperature characteristics, which is not preferable.
[88]
In addition, as described above, the average particle diameter of the flaky natural graphite may be the same as or larger than that of the spheroidized natural graphite, and the tap density is affected by the particle diameter. Or less than that.
[89]
Next, the spheroidized natural graphite may have an orientation index of 5 to 14, preferably 8 to 11, at a porosity of 28% after rolling. When the orientation index is within the above range, it is possible to exhibit stable and high electrode density even during rolling, as well as excellent electrode adhesion, thereby improving cycle characteristics and swelling.
[90]
If the orientation index is less than 5, the crystallinity of the active material decreases, and thus the object of the present invention to improve the swelling and cycle characteristics cannot be achieved. Since it is not easy, diffusion resistance increases and lithium precipitation occurs during high-rate charging and discharging, resulting in deterioration of life characteristics.
[91]
In addition, the negative active material according to the present invention may contain 40 to 60% by weight of the scaled natural graphite based on the total weight of the negative active material, and preferably 45 to 55% by weight. Likewise, the negative active material may contain 40 to 60% by weight of the spheroidized natural graphite based on the total weight of the negative active material, and preferably may contain 45 to 55% by weight. More preferably, the weight ratio of the spheroidized natural graphite and the scaled natural graphite particles may be 1:1. Within the above range, the scale-like natural graphite particles and the spheroidized natural graphite particles are uniformly mixed, and the performance of the electrode may be improved.
[92]
When the content of the scaled natural graphite in the negative electrode active material is less than 40% and the content of spheroidized natural graphite exceeds 60%, the content of spheroidized natural graphite is excessively increased, so that the spheroidized natural graphite particles are repeated when charging and discharging the battery. As the contraction and expansion of the particles are repeated, the conductive path between the particles and the particles becomes distant, so that the cycle characteristics of the battery may be easily deteriorated. Conversely, when the content of the flaky natural graphite exceeds 60% and the content of spheroidized natural graphite is less than 40%, the content of the flaky natural graphite, which has a relatively non-uniform shape, is excessively increased and the filling density of the active material decreases. As a result, rate characteristics and output characteristics may be deteriorated.
[93]
In addition, when one of the flaky natural graphite and the spheroidized natural graphite is used too much, the voids in the negative electrode active material layer exist excessively due to the morphology of each particle, so that filling between the flaky natural graphite and the natural graphite cannot be performed smoothly. . As a result, adhesion between particles in the negative active material and adhesion between the negative active material and the current collector may be poor. When the amounts of artificial graphite and spheroidized natural graphite are adjusted within the above range, the voids in the negative electrode active material layer are reduced, and since the artificial graphite and spheroidized natural graphite are present in a state in which they are smoothly engaged with each other, electrode adhesion can be improved.
[94]
[95]
The present invention also provides a negative electrode for a secondary battery comprising the negative active material.
[96]
1 is a schematic diagram showing the structure of a negative electrode for a secondary battery including a negative active material according to the present invention.
[97]
Referring to FIG. 1, the negative electrode 10 may be prepared by applying a negative electrode mixture including a negative electrode active material on the current collector 11 and drying it. The negative electrode mixture includes a binder, a conductive material, and A filler or the like may be optionally further included. In this case, a mixture of the above-described scaled natural graphite 12 and spheroidized natural graphite 13 may be used as the negative active material.
[98]
In the case of a negative electrode current collector sheet, it is generally made to have a thickness of 3 to 500 µm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel For example, carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, and the like may be used. In addition, like the positive electrode current collector, it is possible to strengthen the bonding force of the negative electrode active material by forming fine irregularities on the surface thereof, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.
[99]
The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.
[100]
The binder is a component that aids in bonding of an active material and a conductive material and bonding to a current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Examples of such a binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, poly Propylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluorine rubber, and various copolymers.
[101]
The filler is selectively used as a component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes to the battery, and examples thereof include olefinic polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber are used.
[102]
Other ingredients, such as viscosity modifiers, adhesion promoters, and the like, may be further included optionally or as a combination of two or more. The viscosity modifier is a component that adjusts the viscosity of the electrode mixture so as to facilitate the mixing process of the electrode mixture and the application process on the current collector thereof, and may be added up to 30% by weight based on the total weight of the negative electrode mixture. Examples of such viscosity modifiers include carboxy methylcellulose, polyvinylidene fluoride, and the like, but are not limited thereto. In some cases, the solvent described above may simultaneously serve as a viscosity modifier.
[103]
The adhesion promoter is an auxiliary component added to improve the adhesion of the active material to the current collector, and may be added in an amount of 10% by weight or less relative to the binder, for example, oxalic acid, adipic acid, Formic acid (formic acid), acrylic acid (acrylic acid) derivatives, itaconic acid (itaconic acid) derivatives, etc. are mentioned.
[104]
The present invention also provides a secondary battery manufactured by the present method. Specifically, the secondary battery includes two or more electrodes for secondary batteries manufactured according to the present invention, and the electrode assembly is embedded in a battery case, wherein the secondary battery is wound with a separator interposed between the electrodes for secondary batteries. And a non-aqueous electrolyte containing a lithium salt is impregnated with the electrode assembly. The secondary battery electrode may be a positive electrode and/or a negative electrode. In this case, the negative electrode may be used as described above, and the negative electrode may be assembled into an electrode assembly and then sealed in a battery case together with an electrolyte to be manufactured into a lithium secondary battery through an activation process. The secondary battery may be a cylindrical battery, a prismatic battery, a pouch-type battery or a coin-type battery, and there is no particular limitation on the shape and structure of the battery.
[105]
The electrode assembly is not particularly limited as long as it has a structure consisting of an anode and a cathode, and a separator interposed therebetween, and for example, a folding type structure, a stack type structure, or a stack/folding type (SNF) structure, or a lamination/stack It may be a type (LNS) structure structure.
[106]
The electrode assembly of the folding-type structure includes at least one anode, at least one cathode, and at least one separator interposed between the anode and the cathode, and the anode, the separator, and the cathode do not cross each other at one end and the other end. It may be a structure that does not.
[107]
In addition, the electrode assembly of the stacked structure includes at least one anode, at least one cathode, and at least one separator interposed between the anode and the cathode, and the anode, the separator, and the cathode cross each other at one end and the other end. It can be a structure to do.
[108]
The electrode assembly of the stack/folding structure includes at least one anode, at least one cathode, and at least one separator interposed between the anode and the cathode, and the separator includes a first separator and a second separator, One end and the other end of each of the anode, the first separator, and the cathode do not cross each other, and the second separator may have a structure surrounding a side surface of an electrode on which an electrode tab is not formed.
[109]
The electrode assembly having a lamination/stack type structure may include one or more improved electrodes in which a separator is laminated on one or both surfaces. The improved electrode may be implemented in a structure in which, for example, a separator is bonded to one side of an anode or a cathode. In addition, the separator may be implemented in a structure in which both sides of an anode or both sides of a cathode are bonded. In addition, it may be implemented in a structure in which an anode, a separator, and a cathode are bonded to each other while a separator is interposed between the anode and the cathode.
[110]
In the secondary battery according to the present invention, the positive electrode may be prepared by applying an electrode mixture containing a positive electrode active material on a current collector and then drying. The positive electrode mixture may optionally contain a binder, a conductive material, a filler, etc. It can be included more.
[111]
In the present invention, the positive electrode current collector is generally made to have a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Surface treatment of carbon, nickel, titanium, silver, etc. may be used on the surface of The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.
[112]
In the present invention, the positive electrode active material is a material capable of causing an electrochemical reaction, as a lithium transition metal oxide, containing two or more transition metals, and, for example, lithium cobalt oxide (LiCoO 2) substituted with one or more transition metals. ), layered compounds such as lithium nickel oxide (LiNiO 2 ); Lithium manganese oxide substituted with one or more transition metals; Formula LiNi 1-y M y O 2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, and including one or more of the above elements, 0.01≤y≤0.7) Lithium nickel-based oxide represented by; Li 1+z Ni 1/3 Co 1/3 Mn 1/3 O 2 , Li 1+z Ni 0.4 Mn 0.4 Co 0.2 O 2Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (here, -0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤ 0.8, 0≤d≤0.2, 0≤e≤0.2, b+c+d<1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl) Lithium nickel cobalt manganese composite oxide; Formula Li 1 + x M 1-y M ' y PO 4-z X z , and (wherein, M = a transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S, or N, and -0.5≦x≦+0.5, 0≦y≦0.5, 0≦z≦0.1, and the like), but are not limited thereto.
[113]
In the positive electrode, additive materials such as a binder, a conductive material, and a filler are as described above.
[114]
The separator is interposed between the anode and the cathode, and an insulating thin ultrathin having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 300 μm. Examples of such separation membranes include olefin-based polymers such as polypropylene having chemical resistance and hydrophobicity; Sheets or non-woven fabrics made of glass fiber or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.
[115]
The lithium salt-containing non-aqueous electrolyte is composed of an electrolyte and a lithium salt, and as the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like is used.
[116]
As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid tryster, trimethoxy methane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo An aprotic organic solvent such as an acid derivative, a tetrahydrofuran derivative, an ether, a methyl pyropionate, or an ethyl propionate may be used.
[117]
As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymerization agent or the like containing an ionic dissociating group may be used.
[118]
As the inorganic solid electrolyte, for example, Li 3 N, LiI, Li 5 NI 2 , Li 3 N-LiI-LiOH, LiSiO 4 , LiSiO 4 -LiI-LiOH, Li 2 SiS 3 , Li 4 SiO 4 , Nitrides , halides, and sulfates of Li such as Li 4 SiO 4 -LiI-LiOH and Li 3 PO 4 -Li 2 S-SiS 2 may be used.
[119]
The lithium salt is a material that is soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , CH 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.
[120]
In addition, for the purpose of improving charge/discharge properties, flame retardancy, etc., the electrolyte solution includes, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, and nitro. Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene sultone), and the like may be further included.
[121]
In one preferred example, lithium salts such as LiPF 6 , LiClO 4 , LiBF 4 , and LiN(SO 2 CF 3 ) 2 are used in the cyclic carbonate of EC or PC as a highly dielectric solvent and DEC, DMC or EMC as a low viscosity solvent. The lithium salt-containing non-aqueous electrolyte may be prepared by adding it to a mixed solvent of linear carbonate.
[122]
[123]
In addition, the present invention provides a method of manufacturing a negative electrode including the negative electrode active material.
[124]
The method of manufacturing the negative electrode includes preparing a negative electrode mixture, and drying after applying the negative electrode mixture on a current collector.
[125]
In addition, the negative electrode active material included in the negative electrode mixture includes a mixture of flaky natural graphite and spheroidized natural graphite,
[126]
Specifically, the negative active material may be the same as described above.
[127]
More specifically, in the method of manufacturing the negative electrode, the preparing of the negative electrode mixture may include spheronizing natural graphite; Preparing scaled natural graphite; And mixing the spheroidized natural graphite and the scaled natural graphite.
[128]
Spheronizing the natural graphite; Is a step of applying a mechanical external force to the general scale-like natural graphite to perform spheronization treatment.After treating the scale-like natural graphite with an acid or a base as described above, 30 m/s to 100 m/s in a spheroidizing device It can be obtained by spheronizing for 10 to 30 minutes at a rotor speed of.
[129]
In addition, spheronizing the natural graphite; And preparing scale-like natural graphite. Classifying so that the particle size distribution of the prepared spheroidized natural graphite and scaled natural graphite particles is uniform; It may further include.
[130]
Through the classifying step, the average particle diameter (D 50 ) of the spheroidized natural graphite and the scaled natural graphite may be adjusted to the above-described value.
[131]
The classification process may be performed by any method, but it is appropriate to perform the classification process by air flow classification. When performing the air flow classification process, the conditions of the air flow classification process can be appropriately adjusted according to the type of active material and the like.
[132]
When the spheroidized natural graphite and the flaky natural graphite are prepared, the spheroidized natural graphite and the flaky natural graphite are mixed, and the mixing method is not particularly limited. It can be uniformly mixed at high speed using a Nauter mixer or a ribbon mixer.
[133]
The spheroidized natural graphite and the flaky natural graphite are mixed, a binder and a conductive material are added, and a solvent such as water is added thereto to prepare a negative electrode mixture slurry. It may contain more.
[134]
[135]
Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited by the following examples. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.
[136]
[137]
[Example 1]
[138]
Preparation of cathode
[139]
A negative electrode was manufactured using a negative electrode active material containing 50% by weight of scaled natural graphite and 50% by weight of spheroidized natural graphite. Specifically, scale-like natural graphite having a small particle diameter granulated and secondary particles of the negative active material and natural graphite having a small particle diameter having a high sphericity degree and a high tap density were used.
[140]
The flaky natural graphite has an average particle diameter (D 50 ) of 12 μm, a degree of sphericity of 0.5, a tap density of 1.0 g/cc, and an orientation index of 11 at a porosity of 28% after electrode rolling, and the spheroidized natural graphite Silver had an average particle diameter (D 50 ) of 10 μm, a degree of sphericity of 0.9, a tap density of 1.3 g/cc, and an orientation index of 8 at a porosity of 28% after electrode rolling.
[141]
The natural graphite was used as a negative electrode active material, SuperC65 as a conductive material, styrene butadiene high part (SBR) as a binder, and carboxymethylcellulose (CMC) as a thickener were mixed in a weight ratio of 96.6:1:1.3:1.1, respectively, and water was added. A slurry was prepared.
[142]
The slurry prepared as described above was coated on a copper foil, and vacuum-dried at about 130° C. for 10 hours to prepare a negative electrode having an area of 1.4875 cm 2 . At this time, the loading amount of the negative electrode was prepared to be 3.61mAh/cm 2 .
[143]
[144]
Manufacturing of battery cells
[145]
By applying the negative electrode active material on copper foil, 1.7671 cm 2 load amount to the area of the 3.61mAh / cm 2 working electrode (cathode) LiCoO as a cathode active material in the manufacture, and the aluminum foil so that the second positive electrode material mixture containing (LCO) Was applied to prepare a 1.4875 cm 2 counter electrode (anode). An electrode assembly was manufactured by interposing a polyethylene separator between the working electrode and the counter electrode. And 1M LiPF 6 was added to a solvent in which 0.5% by weight of a nonaqueous electrolyte additive VC was added in a volume ratio of 1:4 to prepare a nonaqueous electrolyte, and then injected into the electrode assembly. I did. The electrode assembly was put into a case to prepare a coin-type full-cell secondary battery.
[146]
In addition, the negative electrode active material is 1.4875 cm was applied to the copper foil 2 area to the loading amount of the 3.61mAh / cm 2 1.7671cm to prepare a working electrode (cathode), so that, as a counter electrode (anode) 2, a lithium metal having an area of Was used. An electrode assembly was manufactured by interposing a polyethylene separator between the working electrode and the counter electrode. And 1M LiPF 6 was added to a solvent in which 0.5% by weight of a nonaqueous electrolyte additive VC was added in a volume ratio of 1:4 to prepare a nonaqueous electrolyte, and then injected into the electrode assembly. I did. The electrode assembly was put into a case to prepare a coin-type half-cell secondary battery.
[147]
[148]
[Example 2]
[149]
Preparation of cathode
[150]
A negative electrode was manufactured using a negative electrode active material containing 50% by weight of scaled natural graphite and 50% by weight of spheroidized natural graphite. Specifically, scale-like natural graphite having a small particle diameter granulated and secondary particles of the negative active material and natural graphite having a small particle diameter having a high sphericity degree and a high tap density were used.
[151]
The flaky natural graphite had an average particle diameter (D 50 ) of 13 μm, a degree of sphericity of 0.4, a tap density of 0.9 g/cc, and an orientation index of 14 at a porosity of 28% after electrode rolling, and the spheroidized natural graphite Silver had an average particle diameter (D 50 ) of 11 µm , a sphericity of 0.8, a tap density of 1.2 g/cc, and an orientation index of 11 at a porosity of 28% after electrode rolling.
[152]
The natural graphite was used as a negative electrode active material, SuperC65 as a conductive material, styrene butadiene high part (SBR) as a binder, and carboxymethylcellulose (CMC) as a thickener were mixed in a weight ratio of 96.6:1:1.3:1.1, respectively, and water was added. A slurry was prepared.
[153]
The slurry prepared as described above was coated on a copper foil, and vacuum-dried at about 130° C. for 10 hours to prepare a negative electrode having an area of 1.4875 cm 2 . At this time, the loading amount of the negative electrode was prepared to be 3.61mAh/cm 2 .
[154]
[155]
Manufacturing of battery cells
[156]
A battery (coin-type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material of Example 2.
[157]
[158]
[Example 3]
[159]
A negative electrode and a battery (coin type) in the same manner as in Example 1, except that the negative electrode active material contained 60% by weight of the scaled natural graphite of Example 1 and 40% by weight of the spheroidized natural graphite of Example 1. Of full-cell and half-cell batteries) were prepared.
[160]
[161]
[Example 4]
[162]
A negative electrode and a battery (coin type) in the same manner as in Example 1, except that the negative active material contained 40% by weight of the scaled natural graphite of Example 1 and 60% by weight of the spheroidized natural graphite of Example 1. Of full-cell and half-cell batteries) were prepared.
[163]
[164]
[Example 5]
[165]
A negative electrode and a battery (coin-type full-cell and half-cell batteries) were prepared in the same manner as in Example 1, except that the average particle diameter of scaled natural graphite in the negative active material was 14 μm.
[166]
[167]
[Example 6]
[168]
A negative electrode and a battery (coin-type full-cell and half-cell batteries) were prepared in the same manner as in Example 1, except that the average particle diameter of scaled natural graphite in the negative active material was 15 μm.
[169]
[170]
[Example 7]
[171]
In the negative active material, a negative electrode and a battery (coin-type full-cell and half-cell batteries) were prepared in the same manner as in Example 1, except that the spheroidization degree of spheroidized natural graphite was 0.7 and the tap density was 1.10 g/cc.
[172]
[173]
[Comparative Example 1]
[174]
A negative electrode and a battery (coin type) in the same manner as in Example 1, except that the negative electrode active material contained 75% by weight of the scaled natural graphite of Example 1 and 25% by weight of the spheroidized natural graphite of Example 1. Of full-cell and half-cell batteries) were prepared.
[175]
[176]
[Comparative Example 2]
[177]
A negative electrode and a battery (coin type) in the same manner as in Example 1, except that the negative electrode active material contained 65% by weight of the scaled natural graphite of Example 1 and 35% by weight of the spheroidized natural graphite of Example 1. Of full-cell and half-cell batteries) were prepared.
[178]
[179]
[Comparative Example 3]
[180]
A negative electrode and a battery (coin type) in the same manner as in Example 1, except that the negative electrode active material contained 35% by weight of the scaled natural graphite of Example 1 and 65% by weight of the spheroidized natural graphite of Example 1. Of full-cell and half-cell batteries) were prepared.
[181]
[182]
[Comparative Example 4]
[183]
A negative electrode and a battery (coin-type Of full-cell and half-cell batteries) were prepared.
[184]
[185]
[Comparative Example 5]
[186]
[187]
A negative electrode was manufactured using a negative electrode active material containing 50% by weight of scaled natural graphite and 50% by weight of spheroidized natural graphite. Specifically, scale-like natural graphite having a large particle diameter granulated and secondary particleized in the negative active material and natural graphite having a small particle diameter having a high sphericity degree and a high tap density were used.
[188]
The flaky natural graphite has an average particle diameter (D 50 ) of 16 μm, a degree of sphericity of 0.3, a tap density of 0.9 g/cc, and an orientation index of 18 at a porosity of 28% after electrode rolling, and the spheroidized natural graphite Silver had an average particle diameter (D 50 ) of 10 μm, a degree of sphericity of 0.9, a tap density of 1.3 g/cc, and an orientation index of 8 at a porosity of 28% after electrode rolling.
[189]
A battery was manufactured in the same manner as in Example 1, except that a negative electrode and a coin-type full cell and a half cell including the negative electrode were prepared using the negative active material.
[190]
[191]
[Comparative Example 6]
[192]
A negative electrode was manufactured using a negative electrode active material containing 50% by weight of scaled natural graphite and 50% by weight of spheroidized natural graphite. Specifically, scale-like natural graphite having a small particle diameter granulated and secondary particles of the negative electrode active material and natural graphite having a large particle size having a high sphericity degree and a high tap density were used.
[193]
The flaky natural graphite has an average particle diameter (D 50 ) of 12 μm, a degree of sphericity of 0.5, a tap density of 1.0 g/cc, and an orientation index of 11 at a porosity of 28% after electrode rolling, and the spheroidized natural graphite Silver had an average particle diameter (D 50 ) of 17 µm , a sphericity of 0.8, a tap density of 1.2 g/cc, and an orientation index of 18 at a porosity of 28% after electrode rolling.
[194]
A battery was manufactured in the same manner as in Example 1, except that a negative electrode and a coin-type full cell and a half cell including the negative electrode were prepared using the negative active material.
[195]
[196]
[Comparative Example 7]
[197]
A negative electrode was manufactured using a negative electrode active material containing 50% by weight of scaled natural graphite and 50% by weight of spheroidized natural graphite. Specifically, scale-like natural graphite having a small particle size granulated and secondary particle sized in the negative active material and natural graphite having a large particle size having a low sphericity degree and a low tap density were used.
[198]
The flaky natural graphite has an average particle diameter (D 50 ) of 12 μm, a degree of sphericity of 0.5, a tap density of 1.0 g/cc, and an orientation index of 11 at a porosity of 28% after electrode rolling, and the spheroidized natural graphite Silver had an average particle diameter (D 50 ) of 17 μm , a sphericity of 0.3, a tap density of 0.8 g/cc, and an orientation index of 28 at a porosity of 28% after electrode rolling.
[199]
A battery was manufactured in the same manner as in Example 1, except that a negative electrode and a coin-type full cell and a half cell including the negative electrode were prepared using the negative active material.
[200]
[201]
[Comparative Example 8]
[202]
A negative electrode was prepared using a negative electrode active material containing 50% by weight of spheroidized natural graphite and 50% by weight of other spheroidized natural graphite. Specifically, spheronized natural graphite having a low sphericity and tap density and a large particle diameter and spheroidized natural graphite having a low sphericity and tap density and a large particle diameter were used for the negative active material.
[203]
The spheroidized natural graphite had an average particle diameter (D 50 ) of 21 μm, a sphericity of 0.5, a tap density of 0.8 g/cc, and an orientation index of 35 at a porosity of 28% after electrode rolling, and the other spheroidization Natural graphite had an average particle diameter (D 50 ) of 17 μm, a degree of sphericity of 0.3, a tap density of 0.8 g/cc, and an orientation index of 28 at a porosity of 28% after electrode rolling.
[204]
A battery was manufactured in the same manner as in Example 1, except that a negative electrode and a coin-type full cell and a half cell including the negative electrode were prepared using the negative active material. Table 1 below shows the content ratios of the flaky natural graphite and spheroidized natural graphite used in each of the Examples and Comparative Examples, and Table 2 shows the physical properties of each natural graphite.
[205]
[Table 1]
division Flaky natural graphite (% by weight) Spheroidized natural graphite (% by weight)
Example 1 50 50
Example 2 50 50
Example 3 60 40
Example 4 40 60
Example 5 50 50
Example 6 50 50
Example 7 50 50
Comparative Example 1 75 25
Comparative Example 2 65 35
Comparative Example 3 35 65
Comparative Example 4 25 75
Comparative Example 5 50 50
Comparative Example 6 50 50
Comparative Example 7 50 50
Comparative Example 8 50 50
[206]
(Comparative Example 8 is not a mixture of flaky natural graphite and spheroidized natural graphite, but a mixture of two types of spheroidized natural graphite having different physical properties)
[207]
[Table 2]
division Physical properties of flaky natural graphite Properties of spheroidized natural graphite
D 50 (㎛) Sphericity Tap density (g/cc) OI D 50 (㎛) Sphericity Tap density (g/cc) OI
Example 1 12 0.5 One 11 10 0.9 1.3 8
Example 2 13 0.4 0.9 14 11 0.8 1.2 11
Example 3 12 0.5 One 11 10 0.9 1.3 8
Example 4 12 0.5 One 11 10 0.9 1.3 8
Example 5 14 0.5 One 11 10 0.9 1.3 8
Example 6 15 0.5 One 11 10 0.9 1.3 8
Example 7 12 0.5 One 11 10 0.7 1.1 8
Comparative Example 1 12 0.5 One 11 10 0.9 1.3 8
Comparative Example 2 12 0.5 One 11 10 0.9 1.3 8
Comparative Example 3 12 0.5 One 11 10 0.9 1.3 8
Comparative Example 4 12 0.5 One 11 10 0.9 1.3 8
Comparative Example 5 16 0.3 0.9 18 10 0.9 1.3 8
Comparative Example 6 12 0.5 One 11 17 0.8 1.2 18
Comparative Example 7 12 0.5 One 11 17 0.3 0.8 28
Comparative Example 8 21 0.5 0.8 35 17 0.3 0.8 28
[208]
(Comparative Example 8 is not a mixture of flaky natural graphite and spheroidized natural graphite, but a mixture of two types of spheroidized natural graphite having different physical properties)
[209]
[Experimental Example 1]
[210]
In-situ SAC Swelling Test
[211]
Using the above manufactured coin-type full cell, the charging range is set so that the SOC is from 0 to 95%, the first cycle is 0.1C, the second cycle is 0.2C, and the third cycle is charged at 0.5C from the 30th cycle. Meanwhile, the change in the thickness of the cathode electrode during charging and discharging was expressed as a swelling ratio (%). The results are shown in Table 3 below.
[212]
[213]
[Experimental Example 2]
[214]
Li-Plating Test
[215]
Using the coin-type half cell prepared above, the half cell was charged and discharged at 1C for 3 cycles, and then charged at 3C for 15 minutes, and the profile was first differentiated. At this time, the inflection point indicated by dQ/dV was checked to quantify the lithium plating SOC (Li-Plating SOC, %), which is the SOC at the time when lithium precipitation occurs on the surface of the anode. The results are shown in Table 3 below.
[216]
[217]
[Experimental Example 3]
[218]
Peel Strength Test
[219]
The cathode electrode was rolled with a porosity of 28% to perform a Peel Strength Test. At this time, the electrode was oriented at a right angle of 90 degrees using a slide glass and the current collector was peeled off to measure the electrode adhesion (peeling strength), and the results are shown in Table 3 below.
[220]
[221]
[Table 3]
division Swelling Ratio (%) Li-Plating SOC (%) Electrode adhesion (gf)
Example 1 21.3 46 37
Example 2 22.2 44 35
Example 3 21.7 43 34
Example 4 22.1 45 36
Example 5 23.5 43 35
Example 6 23.2 42 32
Example 7 23.8 44 35
Comparative Example 1 28.5 35 26
Comparative Example 2 28.1 36 24
Comparative Example 3 29.5 34 27
Comparative Example 4 29.7 32 24
Comparative Example 5 29.5 30 26
Comparative Example 6 29.8 33 23
Comparative Example 7 32.6 27 21
Comparative Example 8 34.7 22 24
[222]
[223]
As can be seen in Table 1, in Examples 1 and 2 using the negative electrode active material according to the present invention, secondary granulated scale-like natural graphite and spheroidized natural graphite having a high degree of sphericity and tap density were used. Examples 1 and 2 are in Comparative Example 5 using flaky natural graphite having a large particle diameter, Comparative Example 6 using spheroidized natural graphite having a large particle diameter, and Comparative Example 7 using natural graphite having a low sphericity degree and tap density. In comparison, it can be seen that the swelling characteristics and cycle characteristics are improved. Likewise, it can be seen that Examples 1 and 2 have improved swelling characteristics and cycle characteristics compared to Comparative Example 8 using spheronized natural graphite having poor sphericity and tap density.
[224]
In addition, with respect to the content ratio of flaky natural graphite and spheroidized natural graphite, Examples 1 to 4 in which the content ratio of flaky natural graphite and spheroidized natural graphite is within the above range were swelling compared to Comparative Examples 1 to 4 It can be seen that the characteristics and cycle characteristics are improved.
[225]
Finally, it can be seen that the swelling characteristics and cycle characteristics of Examples 1 and 5 to 7 in which the particle diameter of the spheroidized natural graphite is within the range of the present invention were improved compared to Comparative Example 6.
[226]
[227]
The above description is merely illustrative of the technical spirit of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the protection scope of the present invention should be interpreted by the following claims, and all technologies within the scope equivalent thereto. The idea should be construed as being included in the scope of the present invention.
[228]
[Explanation of code]
[229]
10: cathode
[230]
11: whole house
[231]
12: scale-like natural graphite
[232]
13: spheroidized natural graphite
Claims
[Claim 1]
As a negative active material for a secondary battery, the negative active material is a mixture of flaky natural graphite and spheroidized natural graphite, the average particle diameter (D 50 ) of the flaky natural graphite is 10 to 15 μm, and the average particle diameter of spheroidized natural graphite ( D 50 ) is a negative active material for a secondary battery, characterized in that less than 14㎛.
[Claim 2]
The negative active material of claim 1, wherein the scaled natural graphite is granulated and secondary particles.
[Claim 3]
The negative active material according to claim 1, wherein the negative active material contains 40 to 60% by weight of the scaled natural graphite and 40 to 60% by weight of the spheroidized natural graphite based on the total weight of the negative active material.
[Claim 4]
The negative active material of claim 3, wherein the negative active material contains 45 to 55% by weight of the scaled natural graphite and 45 to 55% by weight of the spheroidized natural graphite based on the total weight of the negative active material.
[Claim 5]
The negative active material according to claim 1, wherein the scaled natural graphite has an average particle diameter of 12 to 15 μm, and the spheroidized natural graphite has an average particle diameter of 9 to 11 μm.
[Claim 6]
The negative active material according to claim 1, wherein the average particle diameter of the flaky natural graphite is equal to or larger than the average particle diameter of the spheroidized natural graphite.
[Claim 7]
The negative active material of claim 1, wherein the scale of natural graphite is in the range of 0.4 to 0.6.
[Claim 8]
The negative active material of claim 1, wherein the spheronization degree of the spheroidized natural graphite is 0.70 to 0.95.
[Claim 9]
The negative active material of claim 1, wherein the tap density of the flaky natural graphite is 0.9 to 1.2 g/cc.
[Claim 10]
The negative active material of claim 1, wherein the spheroidized natural graphite has a tap density of 1.0 to 1.4 g/cc.
[Claim 11]
The negative active material for a secondary battery according to claim 1, wherein in the flaky natural graphite, an orientation index of the electrode is 10 to 15 at a porosity of 28% after rolling.
[Claim 12]
The negative active material of claim 1, wherein in the spheroidized natural graphite, an orientation index of the electrode is 5 to 14 at a porosity of 28% after rolling.
[Claim 13]
A negative electrode for a secondary battery comprising a current collector and a negative electrode mixture layer coated on the current collector, wherein the negative electrode mixture layer comprises a conductive material, a binder, and the negative active material of any one of claims 1 to 12. .
[Claim 14]
A secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode is the negative electrode of claim 13.