Method of manufacturing a negative electrode, negative electrode obtained thereby and secondary battery comprising said negative electrode

Abstract

Disclosed are a method of manufacturing a negative electrode, a negative electrode manufactured by the method, and a secondary battery including the negative electrode, the method including the steps of: preparing a negative electrode slurry including a low-expansion natural graphite, a binder polymer, a conductive material, and a dispersion medium; forming a preliminary negative electrode having a preliminary negative electrode active material layer by applying the negative electrode slurry on at least one surface of a negative electrode current collector and drying; and pressing the preliminary negative electrode to manufacture a negative electrode having a final negative electrode active material layer, wherein a difference between a specific surface area of the preliminary negative electrode active material layer before pressing and a specific surface area of the final negative electrode active material layer after pressing is 0.5 m 2 / g to 1.0 m 2 / g; and a difference between a particle size D90 and a particle size D10 of the low-expansion natural graphite is 10 µm or less, wherein D90 and D10 respectively indicate particle sizes at points corresponding to 90% and 10% in a particle number cumulative distribution of particle sizes in a laser diffraction particle size analyzer-based particle size analyzer; and a total pore volume of the low-expansion natural graphite is 10 cm 3 / g to 20 cm 3 / g.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing a negative electrode, the resulting negative electrode, and a secondary battery comprising said negative electrode. In particular, this disclosure relates to a method for manufacturing a negative electrode having improved capacity and cycle characteristics, the resulting negative electrode, and a secondary battery comprising said negative electrode.

[0002] This application claims priority to Korean Patent Application No. 10-2019-0148063, filed in Korea on November 18, 2019, the disclosure of which is incorporated herein by reference. Background Technology

[0003] Recently, energy storage technology has received increasing attention. As its applications have expanded to power mobile phones, portable cameras, and laptops, and even electric vehicles, research and development efforts on electrochemical devices have become increasingly concrete. In this context, electrochemical devices have garnered the most attention. Within this field, the development of rechargeable secondary batteries has become a focal point. Recently, in developing such batteries, active research has been conducted on designing novel electrodes and cells to improve capacity density and specific energy.

[0004] Among commercially available secondary batteries, lithium secondary batteries, developed in the early 1990s, have attracted attention due to their higher operating voltage, significantly higher energy density, longer cycle life, and lower self-discharge rate compared to conventional batteries such as Ni-MH, Ni-Cd, and lead-sulfate batteries that use aqueous electrolytes.

[0005] In particular, with the rapid development of the market for electric vehicles, robots and energy storage systems, there is a need for secondary batteries with high energy density, stability, compact size, low weight and long service life.

[0006] Currently, graphite is widely used as the negative electrode active material in secondary batteries. In particular, when natural graphite is used instead of synthetic graphite, the cost of the raw materials for the negative electrode can be reduced to less than half. However, due to its large specific surface area and porosity within the active material, conventional natural graphite exhibits problems related to cycling and swelling characteristics in secondary batteries using it as the negative electrode. Summary of the Invention

[0007] Technical issues

[0008] This disclosure aims to address the problems in the related technologies, and therefore relates to a method for manufacturing a negative electrode that can improve the capacity, cycle characteristics and fast charging characteristics of a secondary battery.

[0009] This disclosure also relates to providing a negative electrode obtained by the method described.

[0010] In addition, this disclosure relates to providing a secondary battery including the negative electrode.

[0011] Technical solution

[0012] In one aspect of this disclosure, a method for manufacturing a negative electrode according to any of the following embodiments is provided.

[0013] According to a first embodiment, a method for manufacturing a negative electrode is provided, comprising the following steps:

[0014] Prepare a negative electrode slurry containing low-expansion natural graphite, binder polymer, conductive material and dispersion medium;

[0015] The negative electrode slurry is applied to at least one surface of the negative electrode current collector and then dried to form a pre-negative electrode having a pre-negative electrode active material layer; and

[0016] The prepared negative electrode is pressed to obtain a negative electrode with a final negative electrode active material layer.

[0017] The difference between the specific surface area of ​​the preparatory negative electrode active material layer before pressing and the specific surface area of ​​the final negative electrode active material layer after pressing is 0.5–1.0 μm. 2 / g,

[0018] The particle size D of the low-expansion natural graphite 90 With D 10 The difference between them is less than 10 μm, where D 90 and D 10 These respectively refer to the particle size at the 90% and 10% points in the cumulative particle number distribution of particle size in a laser diffraction particle size analyzer, and

[0019] The low-expansion natural graphite has a density of 10-20 cm. 3 / g total pore volume.

[0020] According to the second embodiment, a method for manufacturing a negative electrode as defined in the first embodiment is provided, wherein the difference between the specific surface area of ​​the pre-prepared negative electrode active material layer before pressing and the specific surface area of ​​the final negative electrode active material layer after pressing is 0.6 to 0.9 μm. 2 / g.

[0021] According to a third embodiment, a method for manufacturing a negative electrode as defined in the first or second embodiment is provided, wherein the particle size D of the low-expansion natural graphite is... 90 With D 10 The difference between them is 5–10 μm.

[0022] According to a fourth embodiment, a method for manufacturing a negative electrode is provided as defined in any one of the first to third embodiments, wherein the low-expansion natural graphite has a density of 12–18 cm⁻¹. 3 / g total pore volume.

[0023] According to the fifth embodiment, a method for manufacturing a negative electrode as defined in any one of the first to fourth embodiments is provided, wherein the difference in orientation degree (I004 / I110) between the pre-concentrated negative electrode active material layer before pressing and the final negative electrode active material layer after pressing is 4 to 8.

[0024] According to the sixth embodiment, a method for manufacturing a negative electrode as defined in any one of the first to fifth embodiments is provided, wherein the difference in orientation degree (I004 / I110) between the pre-concentrated negative electrode active material layer before pressing and the final negative electrode active material layer after pressing is 5 to 7.

[0025] According to the seventh embodiment, a negative electrode is provided, which is obtained by a method as defined in any one of the first to sixth embodiments.

[0026] According to the eighth embodiment, a secondary battery is provided, comprising a negative electrode, a positive electrode as defined in the seventh embodiment, and a separator inserted between the negative electrode and the positive electrode.

[0027] According to the ninth embodiment, a secondary battery as defined in the eighth embodiment is provided, wherein the positive electrode comprises lithium cobalt oxide.

[0028] According to the tenth embodiment, a secondary battery as defined in the eighth or ninth embodiment is provided, wherein the secondary battery is a pouch-type secondary battery.

[0029] Beneficial effects

[0030] According to one embodiment of this disclosure, a method for manufacturing a negative electrode can be provided, wherein low-expansion natural graphite with controlled particle size is used as the negative electrode active material, and the pressing conditions are controlled so that the structure of the initially coated negative electrode active material layer, i.e., specific surface area, orientation, and porosity, is maintained even after pressing. In this way, swelling problems of the negative electrode are prevented, ensuring the lithium-ion transport path so that the secondary battery can be charged quickly, and improving the output and cycle characteristics of the secondary battery. Detailed Implementation

[0031] Preferred embodiments of the present disclosure will be described in detail below. Before the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted based on the meaning and concepts corresponding to the technical aspects of the present disclosure, on the basis of allowing the inventors to appropriately define the terminology for the best interpretation.

[0032] In one aspect of this disclosure, a method for manufacturing a negative electrode is provided, comprising the following steps:

[0033] Prepare a negative electrode slurry containing low-expansion natural graphite, binder polymer, conductive material and dispersion medium;

[0034] The negative electrode slurry is applied to at least one surface of the negative electrode current collector and then dried to form a pre-negative electrode having a pre-negative electrode active material layer; and

[0035] The prepared negative electrode is pressed to obtain a negative electrode with a final negative electrode active material layer.

[0036] The difference between the specific surface area of ​​the preparatory negative electrode active material layer before pressing and the specific surface area of ​​the final negative electrode active material layer after pressing is 0.5–1.0 μm. 2 / g,

[0037] The particle size D of the low-expansion natural graphite 90 With D 10 The difference between them is less than 10 μm, where D 90 and D 10 These respectively refer to the particle size at the 90% and 10% points in the cumulative particle number distribution of particle size in a laser diffraction particle size analyzer, and

[0038] The low-expansion natural graphite has a density of 10-20 cm. 3 / g total pore volume.

[0039] Each step will be explained in more detail below.

[0040] First, prepare a negative electrode slurry containing low-expansion natural graphite, binder polymer, conductive material, and dispersion medium.

[0041] The negative electrode slurry can be obtained by dispersing the negative electrode active material, the conductive material, and the binder polymer in the dispersion medium. If desired, the negative electrode slurry may also contain fillers.

[0042] The low-expansion natural graphite refers to a natural graphite active material obtained by reducing pores in the active material caused by physical damage during processing to reduce side reactions with the electrolyte and exhibiting low volume swelling characteristics during charging / discharging.

[0043] The low-expansion natural graphite exhibits a particle size D 90 With D 10 The difference between them is less than 10 μm. According to one embodiment of this disclosure, the difference can be 1–10 μm, 1–8 μm, 5–10 μm, 6–9 μm, 8–10 μm, 5–8 μm, or 7–8 μm.

[0044] Here, D 90 D 10 These respectively refer to the particle size at the 90% and 10% points in the cumulative particle number distribution of particle size in a laser diffraction particle size analyzer. Specifically, D... 90 and D 10 The particle size distribution can be obtained by dispersing the powder to be tested, i.e., low-expansion natural graphite, in a dispersion medium, introducing the resulting dispersion into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500) to measure the differences in the particle size-based diffraction pattern as the particles pass through the laser beam, and then calculating the particle size distribution.

[0045] The particle size characteristics of the low-expansion natural graphite, i.e., D... 90 With D 10 The difference between them serves as a reference for determining whether the low-expansion natural graphite has a wide or narrow particle size distribution. With D 90 With D 10 The difference between them decreases, the low-expansion natural graphite has a narrow particle size distribution and contains particles with uniform particle size.

[0046] When the particle size D of the low-expansion natural graphite 90 With D 10 When the difference between the two is greater than 10μm, the increase in micro powder and large powder leads to the problem of battery performance degradation.

[0047] The low-expansion natural graphite can have a diameter of 10-20 cm. 3 / g total pore volume. According to one embodiment of this disclosure, the total pore volume can be 10-15 cm³. 3 / g, 15~20cm 3 / g, 12~18cm 3 / g, 12~15cm 3 / g, 15~18cm 3 / g, 14~16cm 3 / g, 14~15cm 3 / g or 15-16cm 3 / g.

[0048] The total pore volume of the low-expansion natural graphite refers to the sum of the pore volumes of all pores present throughout the low-expansion natural graphite. The total pore volume of the low-expansion natural graphite can be determined using the BJH plotting program while nitrogen is adsorbed onto the low-expansion natural graphite powder using a BET BEL adsorption system.

[0049] According to one embodiment of this disclosure, in addition to the low-expansion natural graphite, the negative electrode active material may also include other carbonaceous materials, silicon-based materials (such as silicon oxides of SiOx (0 < x < 2)), Si, etc., as negative electrode active materials.

[0050] The carbonaceous material may include at least one selected from the group consisting of crystalline natural graphite, amorphous hard carbon, low-crystallinity soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon.

[0051] According to one embodiment of this disclosure, in addition to containing the low-expansion natural graphite, the negative electrode active material may also include a negative electrode active material selected from: metal composite oxides such as Li x Fe2O3 (0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, or Ge; Me': Al, B, P, Si, elements of Group 1, 2, or 3 of the periodic table, or halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium alloys; silicon alloys; tin alloys; metal oxides, such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, etc.; conductive polymers, such as polyacetylene; Li-Co-Ni materials; titanium oxides; and lithium titanium oxides; etc. In particular, the negative electrode active material may also contain carbonaceous materials and / or Si.

[0052] Based on the total weight of the mixture containing the negative electrode active material, the conductive material is typically added in an amount of 1% to 50% by weight. This conductive material is not particularly limited, as long as it is conductive and does not cause any chemical changes in the corresponding battery. Specific examples of the conductive material include: graphite, such as natural or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxides; conductive materials, such as polyphenylene derivatives; etc.

[0053] On the other hand, elastic graphite materials can be used as conductive materials, and can optionally be used in combination with the aforementioned materials.

[0054] The adhesive polymer is a component that facilitates the adhesion of the active material to the conductive material and to the current collector, and is typically added in an amount of 1% to 50% by weight based on the total weight of the mixture containing the negative electrode active material. Specific examples of the adhesive polymer include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0055] The dispersion medium may contain water, alcohols such as ethanol, acetone, etc.

[0056] The filler is a component that inhibits the swelling of the negative electrode and is optionally used. Such a filler is not particularly limited, as long as it is a fibrous material and does not cause any chemical changes in the corresponding battery. Specific examples of the filler include: olefin polymers, such as polyethylene or polypropylene; and fibrous materials, such as glass fiber or carbon fiber.

[0057] According to one embodiment of this disclosure, based on 100 parts by weight of the low-expansion natural graphite, the negative electrode slurry may contain 1 to 3 parts by weight, 1 to 2.5 parts by weight, 2 to 2.5 parts by weight, 1 to 2 parts by weight, or 1.2 to 1.5 parts by weight of the binder polymer, 0.2 to 1.5 parts by weight, 0.2 to 1.2 parts by weight, 0.2 to 1 part by weight, or 0.4 to 0.8 parts by weight of the conductive material, and 0.5 to 1.5 parts by weight, or 0.8 to 1.2 parts by weight of the dispersion medium.

[0058] Next, the negative electrode slurry is applied to at least one surface of the negative electrode current collector and then dried to form a pre-negative electrode containing a pre-negative electrode active material layer.

[0059] The negative electrode current collector is not particularly limited, as long as it is conductive and does not cause any chemical changes in the corresponding battery. Specific examples of negative electrode current collectors include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, etc. Furthermore, similar to the positive electrode current collector, to enhance adhesion to the negative electrode active material, fine surface irregularities can be formed on the surface of the negative electrode current collector. The negative electrode current collector can be used in various shapes, including films, sheets, foils, meshes, porous bodies, foams, non-woven meshes, etc.

[0060] Typically, the negative electrode current collector has a thickness of 3 to 500 μm.

[0061] The negative electrode slurry is applied to at least one surface of the negative electrode current collector and dried, wherein the application and drying methods are not particularly limited, as long as they are conventionally used in the art.

[0062] According to one embodiment of this disclosure, the negative electrode slurry can be applied by a coating method using a slot die. Alternatively, Mayer rod coating, gravure coating, dip coating, spray coating, etc., can be used.

[0063] Furthermore, the drying process can be carried out, for example, by heating or hot air jetting at temperatures that, as the solvent evaporates, maximize the removal of water contained in the negative electrode and increase the adhesive strength of the adhesive polymer. Specifically, the drying process can be carried out at a temperature equal to or higher than the boiling point of the solvent and equal to or lower than the melting point of the adhesive polymer. More specifically, the drying process can be carried out at 50–150°C, 70–150°C, 100–150°C, 70–120°C, or 100–120°C for 1–50 hours.

[0064] Then, the prepared negative electrode is pressed to obtain a negative electrode containing a final negative electrode active material layer. According to one embodiment of this disclosure, the prepared negative electrode is pressed using a pressing device such as a roller press under linear pressure applied to achieve a target thickness and target porosity, and then vacuum dried to obtain a negative electrode containing a final negative electrode active material layer formed on a current collector. According to one embodiment of this disclosure, the target thickness may be 50–100 μm, 50–80 μm, 80–100 μm, or 75–85 μm, and the target porosity may be 20%–30%, 25%–30%, or 20%–25%. Furthermore, the vacuum drying may be performed at 100–150°C, 100–130°C, or 130–150°C for 1–15 hours, 1–8 hours, or 8–15 hours.

[0065] The difference between the specific surface area of ​​the preparatory negative electrode active material layer before pressing and the specific surface area of ​​the final negative electrode active material layer after pressing is 0.5–1.0 μm. 2 / g. According to one embodiment of this disclosure, the difference in specific surface area can be 0.5 to 0.8 m². 2 / g, 0.8~1.0m 2 / g, 0.6~0.9m 2 / g, 0.6~0.8m 2 / g, 0.8~0.9m 2 / g or 0.7~0.8m2 / g.

[0066] The specific surface area can be determined by using a BET BEL adsorption system to adsorb nitrogen gas onto the active material.

[0067] Furthermore, the difference between the orientation degree of the pre-prepared negative electrode active material layer before pressing and the orientation degree of the final negative electrode active material layer after pressing is 4 to 8. According to one embodiment of this disclosure, the difference in orientation degree can be 4 to 6, 6 to 8, 5 to 7, 5 to 6, 6 to 7, or 5.5 to 6.5.

[0068] The orientation degree (I004 / I110) of the negative electrode active material layer refers to the peak intensity ratio (I004 / I110) of the (004) plane to the (110) plane, as determined by electrode-state X-ray diffraction, and this peak intensity ratio can be obtained by X-ray diffraction. The electrode-state X-ray diffraction refers to X-ray diffraction performed after the composite particles have been formed into an electrode (negative electrode) state. The X-ray diffraction can be performed using a Bruker D4 Endeavor X-ray diffractometer with Cu-Kα rays, and the measured values ​​can be corrected using the Topas3 fitting program.

[0069] According to another aspect of this disclosure, a negative electrode obtained by the above-described method for manufacturing a negative electrode is provided.

[0070] In another aspect of this disclosure, a secondary battery is provided, which is obtained by forming an electrode assembly using a negative electrode obtained by the above method, a positive electrode containing a positive electrode active material, and a separator, and by introducing the electrode assembly and an electrolyte into a battery case.

[0071] Specific examples of the positive electrode active material may include, but are not limited to: layered compounds, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or those compounds replaced by one or more transition metals; lithium manganese oxide, such as those with the chemical formula Li... 1+x Mn 2-x Lithium manganese oxides represented by O4 (where x is 0–0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides, such as LiV3O8, LiFe3O4, V2O5, or Cu2V2O7; and those represented by the chemical formula LiNi. 1-y M y Lithium nickel oxide represented by O2 (where M is Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y is 0.01–0.3); LiMn 2- y M yTernary lithium manganese composite oxides represented by O2 (where M is Co, Ni, Fe, Cr, Zn, or Ta, and y is 0.01–0.1) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn); LiMn2O4, where Li is partially replaced by alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3; ternary lithium transition metal composite oxides, such as Li(Ni a Co b Mn c )O2 (0<a<1, 0<b<1, 0<c<1, a+b+c=1); etc.

[0072] According to one embodiment of this disclosure, the positive electrode active material may comprise lithium cobalt oxide, including LiCoO2, etc. When such lithium cobalt oxide is used as the positive electrode active material, the leaching of other metals such as nickel and manganese from the surface of the negative electrode can be suppressed.

[0073] The positive electrode active material can be dispersed in a solvent together with a binder polymer, a conductive material, and other additives to form a positive electrode mixture slurry. The positive electrode mixture slurry can then be coated onto at least one surface of a positive electrode current collector, followed by drying and pressing to form a positive electrode.

[0074] Non-limiting examples of the positive current collector include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of the negative current collector include foils made of copper, gold, nickel, copper alloys, or combinations thereof.

[0075] The binder polymer, conductive material, and other additives used in the positive electrode may be the same as or different from those used in the negative electrode. Refer above to the description of the binder polymer and conductive material in relation to the negative electrode.

[0076] The diaphragm is inserted between the positive and negative electrodes and uses an insulating film with high ion permeability and mechanical strength as the diaphragm. The diaphragm typically has a pore size of 0.01–10 μm and a thickness of 5–300 μm. The diaphragm may comprise a porous polymer substrate alone, such as a porous polymer membrane substrate or a porous polymer nonwoven mesh substrate, or may comprise a porous coating containing inorganic particles and a binder polymer disposed on at least one surface of the porous polymer substrate. The porous polymer membrane substrate may be a porous polymer membrane made of polyolefins such as polyethylene or polypropylene. In addition to polyolefins, the porous polymer membrane substrate may be made of polymers comprising, alone or in combination, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyethylene naphthalate, etc.

[0077] Non-limiting examples of the adhesive polymers include, but are not limited to: polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl co-vinyl acetate, polyethylene oxide, polyarylates, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, etc.

[0078] According to one embodiment of this disclosure, the adhesive polymer can be classified into dispersant adhesive polymers that also act as dispersants and non-dispersant adhesive polymers. The dispersant adhesive polymer is a polymer having at least one dispersant functional group in its main chain or side chain, and the dispersant functional group includes OH groups, CN groups, etc. Specific examples of the dispersant adhesive polymer include cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, etc. Specific examples of the non-dispersant adhesive polymer include the adhesive polymers listed above, excluding the examples of the dispersant adhesive polymers.

[0079] For example, the weight ratio of the inorganic particles to the total weight of the binder polymer and the crosslinking polymer can be 50:50 to 99:1, particularly 70:30 to 95:5. When the weight ratio of the inorganic particles to the total weight of the binder polymer and the crosslinking polymer meets the range defined above, the problem of reduced pore size and porosity of the resulting coating due to increased content of the binder polymer and the crosslinking polymer can be prevented. The problem of deteriorated peel resistance of the resulting coating due to decreased content of the binder polymer and the crosslinking polymer can also be solved.

[0080] Non-limiting examples of the inorganic particles include inorganic particles having a dielectric constant of 5 or more, particularly 10 or more, inorganic particles having lithium-ion transport properties, or mixtures thereof.

[0081] Non-limiting examples of the inorganic particles having a dielectric constant of 5 or higher may include BaTiO3, Pb(Zr,Ti)O3(PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT), Pb(Mg) 1 / 3 Nb 2 / 3O3PbTiO3 (PMN-PT), Hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, AlO(OH), Al2O3 . H2O or mixtures thereof.

[0082] As used herein, the term "inorganic particles with lithium-ion transport capability" refers to inorganic particles that contain lithium but do not store lithium, yet transport lithium ions. Non-limiting examples of such inorganic particles with lithium-ion transport capability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li... x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y Glass (1 < x < 4, 0 < y < 13) such as 14Li₂O-9Al₂O₃-38TiO₂-39P₂O₅, lanthanum lithium titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0<x<4, 0<y<1, 0<z<1, 0<w<5) as Li 3.25 Ge 0.25 P 0.75 S4, Lithium nitride (Li x N y (0 < x < 4, 0 < y < 2) such as Li3N, SiS2 glass (Li x Si y S z (0 < x < 3, 0 < y < 2, 0 < z < 4) such as Li3PO4-Li2S-SiS2 and P2S5 series glasses (Li x P y S z (0 < x < 3, 0 < y < 3, 0 < z < 7) such as LiI-Li2S-P2S5 or mixtures thereof.

[0083] While there is no particular limitation on the thickness of the porous coating, it can be 1–10 μm or 1.5–6 μm. Furthermore, the porosity of the porous membrane is not particularly limited, but it can be 35%–65%.

[0084] The electrolyte comprises conventional electrolyte components, such as organic solvents and electrolyte salts. The electrolyte salts that can be used are those with A... + B - Salts of structure, in which A + Includes alkali metal cations, such as Li + Na + K + or a combination thereof, and B - Includes anions, such as PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - Or combinations thereof. Lithium salts are particularly preferred. For example, LiClO4, LiCF3SO3, LiPF6, LiAsF6, LiN(CF3SO2)2 or mixtures thereof can be used.

[0085] The organic solvent used for the electrolyte may comprise solvents generally known to those skilled in the art, such as cyclic carbonate solvents with or without halogen substituents; linear carbonate solvents; ester solvents, nitrile solvents, phosphate / ester solvents, or mixtures thereof. Specific examples of solvents that may be used include: propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, pentyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, or mixtures thereof.

[0086] The electrolyte injection can be performed at appropriate steps during the battery manufacturing process, depending on the manufacturing method of the final product and the desired characteristics of the final product. In other words, the electrolyte injection can be performed before battery assembly or as a final step in battery assembly.

[0087] There are no particular limitations on the appearance or casing of the lithium secondary battery according to one embodiment of this disclosure. For example, the lithium secondary battery may be cylindrical, prismatic, pouch-shaped, or coin-shaped, similar to a can. According to one embodiment of this disclosure, the secondary battery may be a pouch-type battery.

[0088] Additionally, a lithium secondary battery according to one embodiment of this disclosure may include any conventional lithium secondary battery, such as a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0089] The embodiments will be described more fully below to facilitate a clear understanding of this disclosure. However, the embodiments described below may be embodied in many different forms and should not be construed as limiting themselves to the exemplary implementations set forth herein. Rather, these exemplary implementations are provided so that this disclosure will be thorough and comprehensive, and will fully convey the scope of this disclosure to those skilled in the art.

[0090] Example 1

[0091] <Manufacturing the Negative Electrode>

[0092] Low-expansion natural graphite, Super C65 as a conductive material, styrene-butadiene rubber (SBR) as a binder polymer, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96:1:2:1, and water was added to prepare a negative electrode slurry. Here, the particle size (D) of the low-expansion natural graphite is... 90 -D 10 The total pore volume is shown in Table 1 below.

[0093] The negative electrode slurry was prepared at 3.6 mAh / cm³. 2 The load is applied to one surface of a copper foil (current collector) and vacuum dried at 70°C for 1 hour to obtain a pre-anode containing a pre-anode active material layer.

[0094] Then, under linear pressure applied to achieve a target thickness of 80 μm and a target porosity of 25%, the prepared negative electrode is pressed using a roller press and vacuum dried at 130°C for 8 hours to obtain a negative electrode containing the final negative electrode active material layer formed on the current collector.

[0095] The specific surface area and orientation degree of the pre-formed negative electrode active material layer and the final negative electrode active material layer were measured. The differences in specific surface area and orientation degree before and after pressing are shown in Table 1 below. The method used to determine each difference will be explained below.

[0096] <The Manufacturing of the Positive Electrode>

[0097] First, lithium cobalt oxide (LiCoO2) as the positive electrode active material, carbon black as the conductive material, and polyvinylidene fluoride (PVDF) as the binder polymer were added to N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 96:2:2 to prepare a positive electrode slurry. The slurry was coated onto one surface of an aluminum current collector with a thickness of 15 μm and dried and pressed under the same conditions as the negative electrode to obtain the positive electrode. Here, the loading on the positive electrode active material layer was 20 mg / cm³ based on dry weight. 2 .

[0098] <Manufacturing of pouch-type secondary batteries>

[0099] To prepare a non-aqueous electrolyte, LiPF6 was added at a concentration of 1 M to a solvent containing ethylene carbonate and ethyl methyl carbonate mixed in a 3:7 volume ratio.

[0100] A polyolefin separator is inserted between the positive and negative electrodes obtained as described above, the resulting structure is introduced into a pouch-shaped shell, and the electrolyte is injected therein to obtain a pouch-shaped secondary battery.

[0101] <Manufacturing of Coin-Type Half-Cells>

[0102] Using the negative electrode obtained as described above and Li metal as the counter electrode, and inserting a polyolefin diaphragm between the negative electrode and the Li metal, an electrode assembly is obtained.

[0103] Then, LiPF6 was added at a concentration of 1M to a solvent containing ethylene carbonate and ethyl methyl carbonate mixed in a 3:7 volume ratio for a non-aqueous electrolyte to prepare the non-aqueous electrolyte. The non-aqueous electrolyte was then injected into the electrode assembly to obtain a coin-shaped half-cell.

[0104] Comparative Example 1

[0105] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10 Low-expansion natural graphite with high total pore volume.

[0106] Comparative Example 2

[0107] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10 Low-expansion natural graphite with high total pore volume.

[0108] Comparative Example 3

[0109] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10 Low-expansion natural graphite with high total pore volume.

[0110] Comparative Example 4

[0111] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10 Low-expansion natural graphite with high total pore volume.

[0112] Comparative Example 5

[0113] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10 Low-expansion natural graphite with high total pore volume.

[0114] Comparative Example 6

[0115] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10 Low-expansion natural graphite with high total pore volume.

[0116] Comparative Example 7

[0117] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10 Low-expansion natural graphite with high total pore volume.

[0118] Comparative Example 8

[0119] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10 Low-expansion natural graphite with high total pore volume.

[0120] Comparative Example 9

[0121] The negative electrode and the secondary battery containing it were obtained in the same manner as in Example 1, except that low-expansion natural graphite with a particle size (D) satisfying the conditions shown in Table 1 below were used. 90 -D 10Low-expansion natural graphite with high total pore volume.

[0122] Particle size D of low-expansion graphite 90 and D 10 The determination >

[0123] The powder to be measured is dispersed in a dispersion medium and introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500) to determine the differences in the particle size-based diffraction pattern as the particles pass through the laser beam, and then the particle size distribution is calculated. D is then determined by calculating the particle size at the 10% and 90% points of the cumulative particle number distribution based on particle size in the laser diffraction particle size analyzer. 10 and D 90 .

[0124] Determination of the total pore volume of low-expansion graphite

[0125] First, the specific surface area of ​​low-expansion graphite is determined, and the results are fitted using the BJH plotting program to calculate the total pore volume, which is the sum of micropores, mesopores, and macropores.

[0126] Here, the specific surface area of ​​low-expansion graphite was determined by the BET method, specifically by using the BELSORP-mini II available from BEL Japan Co., Ltd., based on the amount of nitrogen adsorbed at liquid nitrogen temperature (77K).

[0127] Determination of the specific surface area of ​​the pre-pressed negative electrode active material layer and the final negative electrode active material layer after pressing.

[0128] The "specific surface area" is determined by the BET method, specifically by using the amount of nitrogen adsorbed at liquid nitrogen temperature (77K) using the BELSORP-miniII, which is available from BEL Japan.

[0129] Determination of the orientation degree of the pre-pressed negative electrode active material layer and the final orientation degree of the pressed negative electrode active material layer.

[0130] The orientation degree of the negative electrode (I004 / I110) is the peak intensity ratio (I004 / I110) of the (004) plane to the (110) plane, determined by electrode-state X-ray diffraction, and this peak intensity ratio can be obtained by X-ray diffraction. The electrode-state X-ray diffraction refers to X-ray diffraction performed after the composite particles have been formed into an electrode (negative electrode) state. The X-ray diffraction is performed using a Bruker D4 Endeavor X-ray diffractometer with Cu-Kα rays, and the measurements are corrected using the Topas3 fitting program.

[0131] <Discharge Capacity Test>

[0132] The charging capacity and discharging capacity of each pouch-type secondary battery according to Example 1 and Comparative Examples 1 to 9 were determined during the charging and discharging processes of charging at a rate of 0.5C with a charging cutoff voltage of 4.4V and discharging at a rate of 0.5C with a discharging cutoff voltage of 3.3V. The results are shown in Table 1 below.

[0133] <Room Temperature Cycling Performance Test>

[0134] Each pouch-type secondary battery according to Example 1 and Comparative Examples 1-9 was subjected to 500 charge-discharge cycles at 25°C, consisting of a charge cutoff voltage of 4.4V at a rate of 0.5C and a discharge cutoff voltage of 3.3V at a rate of 0.5C. The room temperature cycling performance (%) was calculated as the ratio of the discharge capacity of the first cycle to the discharge capacity of the last cycle. The results are shown in Table 1 below.

[0135] <Hybrid Pulse Power Characterization (HPPC) Output Performance Resistance Increase Rate>

[0136] According to Example 1 and Comparative Examples 1 to 9, each pouch-type secondary battery was charged / discharged 3 times at 0.1C to check the battery capacity, and then charged / discharged at 2.5C and State of Charge (SOC) 50 to determine the HPPC resistance by using pulse voltage.

[0137] [Table 1]

[0138]

[0139] Referring to Table 1, in the case of the secondary battery of Example 1 containing a negative electrode obtained by the method according to this disclosure, the difference in specific surface area between the preparative negative electrode active material layer before pressing and the final negative electrode active material layer after pressing is 0.5 to 1.0 m². 2 / g, particle size D of low-expansion natural graphite 90 With D 10 The difference between them is less than 10 μm, and the total pore volume of low-expansion natural graphite is 10–20 cm³. 3 / g. Compared with Comparative Examples 1 to 9, which did not meet the above conditions, the secondary battery according to Example 1 showed excellent characteristics in terms of discharge capacity, room temperature cycling performance, and resistance increase rate.

[0140] The present disclosure has been described in detail. However, it should be understood that the detailed description and specific examples are given by way of illustration only while pointing out preferred embodiments of the present disclosure, as various variations and modifications within the scope of the present disclosure will become apparent to those skilled in the art from this detailed description.

Claims

1. A method for manufacturing a negative electrode, the method comprising the following steps: Prepare a negative electrode slurry containing low-expansion natural graphite, binder polymer, conductive material and dispersion medium; The negative electrode slurry is applied to at least one surface of the negative electrode current collector and then dried to form a pre-negative electrode with a pre-negative electrode active material layer; as well as The prepared negative electrode is pressed to obtain a negative electrode with a final negative electrode active material layer. The difference between the specific surface area of ​​the preparatory negative electrode active material layer before pressing and the specific surface area of ​​the final negative electrode active material layer after pressing is 0.5–1.0 μm. 2 / g, The particle size D of the low-expansion natural graphite 90 With D 10 The difference between them is less than 10 μm, where D 90 and D 10 These respectively refer to the particle size at the 90% and 10% points in the cumulative particle number distribution of particle size in a laser diffraction particle size analyzer, and The low-expansion natural graphite has a density of 10-20 cm. 3 / g total pore volume, The specific surface area was determined by the BET method using BELSORP-miniII from the amount of nitrogen adsorbed at a liquid nitrogen temperature of 77 K, and The total pore volume of the low-expansion natural graphite was determined by the BJH plotting program while nitrogen was adsorbed onto the low-expansion natural graphite powder using the BET BEL adsorption system.

2. The method for manufacturing a negative electrode according to claim 1, wherein the difference between the specific surface area of ​​the pre-prepared negative electrode active material layer before pressing and the specific surface area of ​​the final negative electrode active material layer after pressing is 0.6–0.9 μm. 2 / g.

3. The method for manufacturing a negative electrode according to claim 1, wherein the particle size D of the low-expansion natural graphite is... 90 With D 10 The difference between them is 5–10 μm.

4. The method for manufacturing a negative electrode according to claim 1, wherein the low-expansion natural graphite has a density of 12-18 cm⁻¹. 3 / g total pore volume.

5. The method for manufacturing a negative electrode according to claim 1, wherein the difference in orientation degree I004 / I110 between the pre-pressed negative electrode active material layer and the final negative electrode active material layer after pressing is 4 to 8.

6. The method for manufacturing a negative electrode according to claim 5, wherein the difference in orientation degree I004 / I110 between the pre-pressed negative electrode active material layer and the final negative electrode active material layer after pressing is 5 to 7.

7. A negative electrode, obtained by the method according to any one of claims 1 to 6, wherein the negative electrode is used in a secondary battery.

8. A secondary battery comprising a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode as described in claim 7.

9. The secondary battery according to claim 8, wherein the positive electrode comprises lithium cobalt oxide.

10. The secondary battery according to claim 8, wherein the secondary battery is a pouch-type secondary battery.

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