Title of the invention: negative electrode and secondary battery including same
technical field
[One]
Cross Citation with Related Applications
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0120025 filed on September 27, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
[3]
[4]
technical field
[5]
The present invention includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a carbon-based negative electrode active material, and the carbon-based negative electrode active material includes a plurality of scale-like artificial graphite primary particles. a core comprising; natural graphite disposed on the core; and an amorphous carbon-based material; wherein the natural graphite is contained in an amount of 10% to 30% by weight in the carbon-based negative active material, and the sphericity of the carbon-based negative active material is 0.78 to 0.83. It is a battery-related invention.
background
[6]
Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing.
[7]
Currently, a secondary battery is a representative example of an electrochemical device using such electrochemical energy, and its use area is gradually expanding. Recently, as technology development and demand for portable devices such as portable computers, portable telephones, and cameras increase, the demand for secondary batteries as an energy source is rapidly increasing. In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode may include an anode active material for inserting and deintercalating lithium ions from the positive electrode. A carbonaceous material such as graphite may be used as the negative electrode active material.
[8]
Artificial graphite may be used as the carbonaceous material, and the artificial graphite may also be used in the form of secondary particles. When the artificial graphite is used as an anode active material, there is an advantage in that rate characteristics of the secondary battery can be improved.
[9]
However, since the artificial graphite in the form of secondary particles generally has an irregular shape, the contact area between the binder in the negative electrode and the artificial graphite is reduced, so that the negative electrode adhesion (adhesion between the negative electrode active materials and/or the negative electrode active material and the current collector) adhesion) is low. There is also a method of forming a functional group including oxygen on the surface of the carbonaceous material, but this leads to a decrease in the capacity of the carbonaceous material.
[10]
Accordingly, the present invention proposes a new anode having improved anode adhesion.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[11]
One problem to be solved by the present invention is to provide an anode capable of improving anode adhesion and battery life characteristics, and a secondary battery including the same.
means of solving the problem
[12]
According to an embodiment of the present invention, a negative electrode active material layer is included, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a carbon-based negative electrode active material, and the carbon-based negative electrode active material includes a plurality of scales. A core comprising artificial graphite primary particles; natural graphite disposed on the core; and an amorphous carbon-based material; wherein the natural graphite is included in an amount of 10% to 30% by weight in the carbon-based negative active material, and the carbon-based negative active material has a sphericity of 0.78 to 0.83.
[13]
According to another embodiment of the present invention, a secondary battery including the negative electrode is provided.
Effects of the Invention
[14]
According to the present invention, since the carbon-based negative active material included in the negative electrode contains a core including artificial graphite at an appropriate level, the lifespan of the battery and the rapid charging effect can be improved. In addition, as natural graphite is included at an appropriate level on the surface of the carbon-based negative active material, the shape of the carbon-based negative active material becomes uniform and the surface of the carbon-based negative active material becomes smooth, so that the negative electrode binder and the carbon-based negative active material are in contact area can be increased. Accordingly, negative electrode adhesion may be improved, and lifespan characteristics of the battery may be improved.
Modes for carrying out the invention
[15]
Hereinafter, the present invention will be described in more detail to help the understanding of the present invention.
[16]
The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention.
[17]
The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise.
[18]
In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the presence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that the existence or addition of numbers, steps, elements, or combinations thereof, is not precluded in advance.
[19]
In the present specification, D 50 may be defined as a particle diameter corresponding to 50% of the cumulative volume in each particle size distribution curve (a graph curve of the particle size distribution). The D 50 may be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of several mm from a submicron region, and can obtain results of high reproducibility and high resolution.
[20]
In the present specification, sphericity and aspect ratio may be measured with a particle size analyzer (Morphologi4, Malvern).
[21]
[22]

[23]
[24]
The negative electrode according to an embodiment of the present invention includes a negative electrode active material layer,
[25]
The anode active material layer includes an anode active material,
[26]
The negative active material includes a carbon-based negative active material,
[27]
The carbon-based anode active material may include a core including a plurality of flaky primary particles of artificial graphite; natural graphite disposed on the core; and an amorphous carbon-based material;
[28]
The natural graphite is included in the carbon-based negative active material in an amount of 10% to 30% by weight,
[29]
The carbon-based negative active material may have a sphericity of 0.78 to 0.83.
[30]
[31]
The negative electrode may include a negative electrode active material layer, specifically, a current collector and the negative electrode active material layer.
[32]
The current collector may have conductivity without causing a chemical change in the battery, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a surface of aluminum or stainless steel treated with carbon, nickel, titanium, silver, or the like may be used. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.
[33]
The negative active material layer may be disposed on the current collector. The negative active material layer may be disposed on at least one surface of the current collector, and specifically, may be disposed on one or both surfaces of the current collector. Alternatively, the anode active material layer itself may exist as an anode without a current collector.
[34]
[35]
The anode active material layer may include an anode active material. The negative active material may include a carbon-based negative active material.
[36]
[37]
The carbon-based negative active material may include a core, natural graphite, and an amorphous carbon-based material.
[38]
[39]
The core may include a plurality of flaky artificial graphite primary particles. Specifically, the core may be in the form of secondary particles in which a plurality of flaky artificial graphite primary particles are combined. The secondary particles may be in the form of an assembly formed by artificially combining a plurality of flaky artificial graphite primary particles.
[40]
The average particle diameter (D 50 ) of the artificial graphite primary particles may be 3 μm to 15 μm, specifically 7 μm to 12 μm, and more specifically 10 μm to 12 μm. When the above range is satisfied, graphitization is easy and the specific surface area is at an appropriate level, so the capacity is excellent, and since the orientation is at an appropriate level, the fast charging performance of the battery is excellent.
[41]
The aspect ratio of the artificial graphite primary particles may be 0.5 to 1, specifically, may be 0.6 to 0.7. When the above range is satisfied, the shape of the carbon-based negative active material may be well maintained, and thus battery characteristics may be improved.
[42]
The core may further include an amorphous carbon-based material. The amorphous carbon-based material may serve to bind the artificial graphite primary particles in the core.
[43]
The average particle diameter (D 50 ) of the core may be 10 μm to 25 μm, specifically, 11 μm to 22 μm. When the above range is satisfied, dispersion of the negative active material in the negative electrode slurry is easy, and the output characteristics of the battery may be improved.
[44]
[45]
The natural graphite may be disposed on the core. The natural graphite may smooth the surface of the carbon-based anode active material, thereby increasing the anode adhesion.
[46]
The natural graphite may have a curved shape while surrounding the surface of the core. Accordingly, the surface of the carbon-based negative active material may be smooth, and the shape of the carbon-based negative active material may be more uniform.
[47]
The natural graphite may be included in the carbon-based negative active material in an amount of 10 wt% to 30 wt%, specifically 20 wt% to 30 wt%, and more specifically 25 wt% to 30 wt%. When the content is less than 10% by weight, it is difficult to expect improvement in the lifespan characteristics of the battery because the degree of improvement in negative electrode adhesion is insufficient. On the other hand, when the content is more than 30% by weight, the specific surface area of ​​the carbon-based negative active material is excessively increased to increase the electrolyte side reaction, and the degree of volume expansion of the carbon-based negative active material is increased. Accordingly, high-temperature storage performance and lifespan characteristics of the battery may be deteriorated.
[48]
[49]
The weight ratio of the core to the natural graphite may be 64.29:35.71 to 89.47:10.53, specifically 64.29:35.71 to 88.10:11.90, and more specifically 64.29:35.71 to 78:22. When the above range is satisfied, the negative electrode adhesion is good, the electrolyte side reaction can be suppressed, the degree of volume expansion of the carbon-based negative active material is suppressed, and the high temperature storage performance and lifespan characteristics of the battery can be improved.
[50]
[51]
The amorphous carbon-based material may serve to bond the core and the natural graphite. The amorphous carbon-based material may be disposed between the core and the natural graphite, the surface of the core, the natural graphite surface, and the like, and further may be disposed within the core as described above.
[52]
The amorphous carbon-based material may be included in an amount of 5 wt% to 16 wt% in the carbon-based material, and specifically may be included in an amount of 9 wt% to 14 wt%. When the above range is satisfied, the form of secondary particles having an appropriate particle size may be implemented, and thus initial efficiency may be improved.
[53]
[54]
The carbon-based negative active material may have a sphericity of 0.78 to 0.83, specifically 0.783 to 0.827, and more specifically, 0.795 to 0.825. When the sphericity is less than 0.78, the shape between the carbon-based negative active materials is not too uniform, and since the surface of the carbon-based negative active material has an excessively curved shape, the contact area between the negative electrode binder and the carbon-based negative active material is is lowered Accordingly, the negative electrode adhesion is lowered, and the lifespan characteristics of the battery are lowered. On the other hand, when the sphericity is greater than 0.83, the electrolyte side reaction increases and the volume expansion of the carbon-based negative active material greatly increases, so that the high-temperature storage performance and lifespan characteristics of the battery are deteriorated.
[55]
In the present invention, by adjusting the sphericity of the carbon-based negative active material to 0.78 to 0.83, the shapes of the carbon-based negative active materials may be similar to each other, and the surface of the carbon-based negative active material may be smoother, so that the negative electrode binder and the A contact area of ​​the carbon-based negative active material may increase. Accordingly, negative electrode adhesion may be improved, and lifespan characteristics of the battery may be improved.
[56]
The carbon-based negative active material may have an average particle diameter (D 50 ) of 11 μm to 26 μm, specifically 12 μm to 23 μm. When the above range is satisfied, the carbon-based negative active material may be well dispersed in the negative electrode slurry, and thus the output characteristics of the battery may be improved.
[57]
[58]
Although not limited thereto, the carbon-based negative active material may be prepared by the following method.
[59]
Specifically, the method for manufacturing the carbon-based negative electrode active material includes: a) mixing a core to which a plurality of needle cokes are bonded to each other, flaky natural graphite, and a carbonaceous precursor, and heat-treating them to form composite particles; b) spheronizing the composite particles; and c) graphitizing the spheroidized composite particles.
[60]
Through the heat treatment, the plurality of needle cokes become flaky primary particles of artificial graphite, and the carbonaceous precursor, such as pitch, becomes an amorphous carbon-based material.
[61]
The spheronization may be performed with a conventional spheronization equipment.
[62]
The graphitizing step may be performed in an Acheson high-temperature electric furnace.
[63]
[64]
The anode active material layer may further include an anode binder. The negative electrode binder maintains the shape of the negative electrode by connecting the negative active materials, and serves to increase adhesion to the negative electrode.
[65]
The negative electrode binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride), polyacrylonitrile (polyacrylonitrile), polymethyl methacrylate (polymethylmethacrylate), Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), It may include at least one selected from the group consisting of sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and a material in which hydrogen is substituted with Li, Na or Ca, etc. , may also include various copolymers thereof.
[66]
The negative electrode binder may be included in the anode active material layer in an amount of 1.2 wt% to 5 wt%, specifically, it may be included in an amount of 1.5 wt% to 4 wt%. When the above range is satisfied, coating of the negative electrode slurry is easy, and thus the negative electrode adhesion is excellent. In particular, the range of 1.2 wt% to 5 wt% corresponds to a level lower than the general negative electrode binder content. This is because the negative electrode of the present invention uses the above-described carbon-based negative electrode active material, and thus sufficient adhesion to the negative electrode can be derived even if a low amount of the negative electrode binder is used.
[67]
[68]
The negative active material layer may further include a conductive material.
[69]
The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black, such as acetylene black, Ketjen black, channel black, Farness black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.
[70]
[71]

[72]
[73]
The secondary battery according to another embodiment of the present invention may include a negative electrode, and the negative electrode is the same as the negative electrode of the above-described embodiment.
[74]
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 described above. Since the cathode has been described above, a detailed description thereof will be omitted.
[75]
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.
[76]
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, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.
[77]
The positive active material may be a commonly used positive active material. Specifically, the positive active material may include a layered compound such as lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), or a compound substituted with one or more transition metals; lithium iron oxides such as LiFe 3 O 4 ; Lithium manganese oxides such as Formula Li 1+c1 Mn 2-c1 O 4 (0≤c1≤0.33), LiMnO 3 , LiMn 2 O 3 , and LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); LiV 3 O 8 , V 2 O 5 , Cu 2 V vanadium oxides such as 2 O 7 ; 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 (where 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 (herein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn.) lithium manganese composite oxide; LiMn 2 O 4 in which part of Li in the formula is substituted with alkaline earth metal ions, and the like, but are not limited thereto. The positive electrode may be Li-metal.
[78]
The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.
[79]
In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite and 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 a conductive polymer such as a polyphenylene derivative, and the like, and one or a mixture of two or more thereof may be used.
[80]
[81]
In addition, the positive electrode binder serves to improve adhesion between the positive electrode active material particles and the adhesive force 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, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used.
[82]
As a separator, it separates the anode and the anode and provides a passage for lithium ions to move. It can be used without any particular limitation as long as it is normally used as a separator in a secondary battery. it is preferable Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.
[83]
The electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte, which can be used in manufacturing a lithium secondary battery.
[84]
Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.
[85]
As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, 1,2-dime ethoxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyropion An aprotic organic solvent such as methyl acid or ethyl propionate may be used.
[86]
In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are highly viscous organic solvents and have a high dielectric constant and thus well dissociate lithium salts. If the same low-viscosity, low-dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, which can be more preferably used.
[87]
A lithium salt may be used as the metal salt, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte. For example, as an anion of the lithium salt, 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 3 )SO 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 ) 2At least one selected from the group consisting of N − may be used.
[88]
In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, 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 jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included.
[89]
[90]
According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate-rate characteristics and cycle characteristics, a medium-to-large device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems can be used as a power source for
[91]
[92]
Hereinafter, preferred embodiments are presented to aid the understanding of the present invention, but the embodiments are merely illustrative of the present disclosure, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present disclosure, It goes without saying that such variations and modifications fall within the scope of the appended claims.
[93]
[94]
Examples and Comparative Examples
[95]
[96]
Example 1: Preparation of negative electrode
[97]
A core comprising a plurality of artificial graphite primary particles; natural graphite disposed on the core; and an amorphous carbon-based material for bonding the plurality of artificial graphite primary particles and the natural graphite to each other.
[98]
The negative electrode active material, binder (CMC and SBR), and carbon black as a conductive material were mixed with purified water as a solvent in a weight ratio of 95.6:3.4:1.0 and stirred to form a negative electrode slurry. After the negative electrode slurry was applied to a copper foil (current collector), the negative electrode current collector coated with the negative electrode slurry was rolled to a porosity of 28%, and vacuum dried at 130 ° C. for 10 hours to prepare a negative electrode (1.4875 cm 2 ) did The loading amount of the prepared negative electrode was 3.61mAh/cm 2 .
[99]
[100]
Examples 2 to 4 and Comparative Examples 1 and 2: Preparation of negative electrodes
[101]
Anodes of Examples and Comparative Examples were prepared by changing the anode active material as shown in Table 1 below.
[102]
[103]
[Table 1]
Average particle diameter of artificial graphite primary particles (D 50 ) (㎛) Aspect Ratio of Artificial Graphite Primary Particles Average particle diameter of core (D 50 ) (㎛) Weight ratio of core and natural graphite Sphericity of carbon-based negative active material Content of natural graphite in carbon-based negative active material (wt%)
Example 1 8 0.62 17 89.01:10.99 0.78 10
Example 2 9 0.63 18 82.95:17.05 0.79 15
Example 3 9 0.63 18 77.27:22.73 0.80 20
Example 4 10 0.65 20 65.12:34.88 0.82 30
Comparative Example 1 8 0.62 17 94.74:5.26 0.76 5
Comparative Example 2 10 0.65 21 51.22:48.78 0.85 40
[104]
The average particle diameter (D 50 ), the aspect ratio, and the sphericity were measured with a particle size analyzer (Morphologi4, Malvern).
[105]
Experimental Example 1: Evaluation of Anode Adhesion
[106]
The negative electrode adhesion to the negative electrode of Examples and Comparative Examples was evaluated.
[107]
The negative electrode was punched to a size of 20 mm × 150 mm and fixed to the center of a 25 mm × 75 mm slide glass using a tape, and then the peel strength was measured at 90 degrees while peeling off the current collector using UTM. The evaluation was determined as an average value by measuring the peel strength of 5 or more.
[108]
[109]
Experimental Example 2: Evaluation of battery life characteristics
[110]
A battery was manufactured in the following manner, and lifespan characteristics were evaluated.
[111]
Li[Ni 0.6 Mn 0.2 Co 0.2 ]O 2 was used as a cathode active material . The positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a solvent N-methyl-2 pyrrolidone in a weight ratio of 94:4:2 to prepare a positive electrode slurry.
[112]
The prepared positive electrode slurry was applied and dried on an aluminum metal thin film, which is a positive electrode current collector, having a thickness of 15 μm. At this time, the temperature of the circulated air was 110 ℃. Then, it was rolled and dried in a vacuum oven at 130° C. for 2 hours to prepare a positive electrode including a positive electrode active material layer.
[113]
The negative electrode and the prepared positive electrode and the porous polypropylene separator were assembled using a stacking method, and an electrolyte solution was injected into the assembled battery to prepare a lithium secondary battery.
[114]
After activating the cell by charging up to SOC 30% with 0.2C current, charge in CC/CV mode (4.2V, 0.05C cut-off) and discharge in CC mode (0.2C current, 3.0V cut-off) 3 round was conducted. Thereafter, the capacity retention rate of 300 cycles was compared through the 45°C 1C/1C lifetime evaluation.
[115]
[116]
[Table 2]
Cathode Adhesion (gf/10mm) Capacity retention rate (%)
Example 1 17 85.5
Example 2 20 87.1
Example 3 23 88.7
Example 4 30 90.0
Comparative Example 1 10 78.7
Comparative Example 2 35 79.9
Claims
[Claim 1]
a core comprising a negative active material layer, wherein the negative active material layer includes a negative electrode active material, the negative active material includes a carbon-based negative active material, and the carbon-based negative active material includes a plurality of flaky artificial graphite primary particles ; natural graphite disposed on the core; and an amorphous carbon-based material; wherein the natural graphite is included in an amount of 10% to 30% by weight in the carbon-based negative active material, and the sphericity of the carbon-based negative active material is 0.78 to 0.83.
[Claim 2]
The negative electrode according to claim 1, wherein the artificial graphite primary particles have an average particle diameter (D 50 ) of 3 μm to 15 μm.
[Claim 3]
The negative electrode according to claim 1, wherein the artificial graphite primary particles have an average particle diameter (D 50 ) of 10 μm to 12 μm.
[Claim 4]
The negative electrode according to claim 1, wherein the artificial graphite primary particle has an aspect ratio of 0.5 to 1.
[Claim 5]
The negative electrode according to claim 1, wherein the core has an average particle diameter (D 50 ) of 10 μm to 25 μm.
[Claim 6]
The negative electrode according to claim 1, wherein the weight ratio of the core to the natural graphite is 64.29:35.71 to 89.47:10.53.
[Claim 7]
The negative electrode according to claim 1, wherein the carbon-based negative active material has an average particle diameter (D 50 ) of 11 μm to 26 μm.
[Claim 8]
The negative electrode according to claim 1, further comprising a negative electrode binder.
[Claim 9]
The negative electrode according to claim 8, wherein the negative electrode binder is contained in an amount of 1.2 wt% to 5 wt% in the anode active material layer.
[Claim 10]
A secondary battery comprising the negative electrode of claim 1.