Negative electrode, kit for manufacturing negative electrode mixture layer, and method for manufacturing negative electrode

Abstract

A negative electrode according to an embodiment of the present invention may comprise: a negative electrode current collector; and a negative electrode mixture layer which is formed on at least one surface of the negative electrode current collector, and which contains a silicon-based substance and a binder, the negative electrode mixture layer may include a first layer in contact with the negative electrode current collector on the negative electrode current collector and a second layer in contact with the first layer on the first layer, and a weight ratio of the binder included in an upper half portion of the first layer in a thickness direction and the second layer, respectively, may be 5: 1 or more.

Description

Technical Field

[0001] The present invention relates to a negative electrode, a kit for manufacturing a negative electrode mixture layer, and a method for manufacturing the negative electrode. Background Art

[0002] With the development of electronics, communications and aerospace industries, the demand for lithium secondary batteries as energy sources is increasing dramatically. In particular, as the importance of global environmental protection policies is emphasized, the electric vehicle market is growing rapidly, and research and development of lithium secondary batteries are being actively carried out both at home and abroad.

[0003] A lithium secondary battery includes a positive electrode (cathode), a negative electrode (anode), and a separator between the positive and negative electrodes. The positive and negative electrodes respectively contain active materials that can insert and extract lithium ions.

[0004] Natural graphite, artificial graphite, or the like is generally used for the negative electrode of lithium secondary batteries. However, due to the low energy density of graphite, research is underway to improve the energy density by developing new negative electrode materials. Summary of the Invention

[0005] (1) Technical issues to be resolved

[0006] The present invention provides a negative electrode capable of improving the energy density and capacity retention rate of a secondary battery, a kit for manufacturing a negative electrode mixture layer, and a method for manufacturing the negative electrode.

[0007] (2) Technical solution

[0008] The negative electrode according to the present invention may include: a negative electrode collector; and a negative electrode mixture layer, the negative electrode mixture layer being formed on at least one side of the negative electrode collector, and the negative electrode mixture layer containing a silicon-based substance and a binder, wherein the negative electrode mixture layer may include a first layer in contact with the negative electrode collector on the negative electrode collector and a second layer in contact with the first layer on the first layer, and the weight ratio of the binder respectively contained in the upper half in the thickness direction of the first layer and the second layer may be 5:1 or more.

[0009] The kit for manufacturing a negative electrode mixture layer according to the present invention may include: a first composition including a silicon-based substance and a binder; and a second composition including a silicon-based substance and excluding the binder.

[0010] The manufacturing method of the negative electrode according to the present invention may include the following steps: applying a first composition containing a silicon-based substance and a binder on a negative electrode current collector to form a first layer; and applying a second composition containing a silicon-based substance and not containing the binder on the first layer to form a second layer.

[0011] (3) Beneficial effects

[0012] According to the present technology, the energy density of a secondary battery and the capacity retention rate during rapid charging can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a diagram for explaining the structure of a negative electrode according to an embodiment of the present invention.

[0014] Figure 2 is an image showing the distribution of the binder in the negative electrode according to one embodiment of the present invention.

[0015] Figure 3 Graphs showing differences in lifespan characteristics between secondary batteries including negative electrodes according to one example of the present invention and a comparative example.

[0016] Figure 4 Graphs showing differences in power characteristics between secondary batteries including negative electrodes according to one embodiment of the present invention and one comparative example. Best Practice

[0017] The description of the structure or function of the implementation scheme disclosed in this specification or this application is merely illustrative for the purpose of illustrating the implementation scheme according to the technical idea of the present invention. The implementation scheme according to the technical idea of the present invention can be implemented in various ways in addition to the implementation scheme disclosed in this specification or this application, and it is not to be interpreted that the technical idea of the present invention is limited to the implementation scheme described in this specification or this application.

[0018] Hereinafter, a negative electrode according to the present invention and a secondary battery including the negative electrode will be described.

[0019] <Negative electrode>

[0020] The negative electrode according to the present invention may include: a negative electrode collector; and a negative electrode mixture layer, the negative electrode mixture layer being formed on at least one side of the negative electrode collector, and the negative electrode mixture layer containing a silicon-based substance and a binder, wherein the negative electrode mixture layer may include a first layer in contact with the negative electrode collector on the negative electrode collector and a second layer in contact with the first layer on the first layer, and the weight ratio of the binder respectively contained in the upper half in the thickness direction of the first layer and the second layer may be 5:1 or more.

[0021] The negative electrode 1000 according to the present invention may include a negative electrode current collector 100 and a negative electrode mixture layer 200 formed on at least one side of the negative electrode current collector 100. Figure 1 The structures of the negative electrode 1000 and the negative electrode mixture layer 200 included in the negative electrode 1000 according to the embodiment of the present invention are understood.

[0022] The negative electrode current collector 100 is not particularly limited as long as it is a conductive material that does not cause chemical changes in the secondary battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc. can be used. In addition, fine concavo-convex patterns can be formed on the surface to enhance the binding force of the negative electrode active material. The negative electrode current collector 100 can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0023] The negative electrode mixture layer 200 is formed on at least one side of the negative electrode collector 100 and may include a silicon-based material and a binder.

[0024] In the embodiment, the silicon-based material can be used as the negative electrode active material. The silicon-based material shows a higher capacity than the carbon-based material, so the same per unit volume can achieve a high energy density. The silicon-based material can include a material selected from SiO x (0≤x<2), one or more of Si / C composite and Si alloy. x corresponds to SiO x The ratio of the number of O and Si contained in (0≤x<2). SiO x (0≤x<2) average particle size (D 50 ) can be 4 μm to -9 μm or 5 μm to 7 μm. When the above range is met, the life of the secondary battery can be prevented from being reduced due to the volume expansion of the silicon-based material, and the side reaction on the surface of the silicon-based material can be suppressed. SiO x The specific surface area (0≤x<2) can be 4m 2 / g to 9m 2 / g or 5m 2 / g to 8m 2 / g. When the above range is met, the conductive network with the conductive material can be improved. The Si / C composite can be formed by combining carbon with SiO x (0≤x<2) The particles are heat treated (firing) in a bonded state to coat the SiO x (0≤x<2) The form of the particle surface or carbon is dispersed in the SiO x(0≤x<2) The form inside the particle. The Si alloy (Si-alloy) can be a form of Si alloyed with one or more metals selected from Zn, Al, Mn, Ti, Fe and Sn. The content of the silicon-based material can be 1% to 20% by weight relative to the total solid weight of the negative electrode mixture layer, specifically 1% to 10% by weight. When the above range is met, the energy density of the secondary battery can be increased while improving the energy capacity retention rate.

[0025] The binder preferably uses a binder having excellent adhesion to the negative electrode current collector, for example, one or more selected from polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyimide, polyamide-imide, polyvinyl alcohol, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, acrylated styrene-butadiene rubber and epoxy resin can be used. Specifically, the binder can use styrene-butadiene rubber. The content of the binder can be 0.05% to 5.0% by weight, 0.1% to 5.0% by weight, 0.1% to 4.0% by weight or 0.1% to 3.0% by weight relative to the total solid weight of the negative electrode mixture layer. When the above range is met, the resistance characteristics of the secondary battery can be improved while maintaining the adhesion at the interface between the negative electrode current collector and the negative electrode mixture layer.

[0026] Typically, the binder is present unevenly in the form of small particles between the negative electrode active materials. If the binder content on the surface of the negative electrode active material increases, it blocks the gaps between the negative electrode active materials, thereby reducing the insertion of lithium ions transferred from the positive electrode into the negative electrode. This increases the resistance of the secondary battery, causing lithium salts to precipitate on the negative electrode surface and reducing the capacity retention rate of the secondary battery.

[0027] As described above, since the content distribution of the binder in the negative electrode active material has a significant influence on the performance of the secondary battery, the purpose of the present invention is to improve the capacity retention rate of the secondary battery while minimizing the deformation of the negative electrode by optimizing the content distribution of the binder in the negative electrode mixture layer containing the negative electrode active material.

[0028] The negative electrode mixture layer 200 may include a first layer 210 in contact with the negative electrode current collector 100 on the negative electrode current collector 100 and a second layer 220 in contact with the first layer 210 on the first layer 210. The first layer 210 may be divided into an upper half 211 and a lower half 212 in the thickness direction. The thickness (t1 / 2) of the upper half 211 and the lower half 212 may be the same. In addition, in the embodiment, the thickness (t1) of the first layer 210 and the second layer 220 may be the same as each other. For example, based on the thickness direction of the negative electrode mixture layer 200, if the length from the surface of the negative electrode current collector 100 to the surface of the negative electrode mixture layer 200 is 100, the thickness from the surface of the negative electrode current collector 100 to the surface of the first layer 210 may be 50, and the thickness of the upper half 211 of the first layer may be 25.

[0029] The weight ratio of the adhesive respectively contained in the upper half 211 of the first layer and the second layer 220 may be 5:1 or more, specifically 6:1 or more, and more specifically 7:1 or more.

[0030] The weight ratio of the binder in the upper half 211 of the first layer to the binder in the second layer 220 can be indirectly measured by dyeing the binder with a metal oxide and then measuring the content of the dyed metal using energy dispersive X-ray spectroscopy. Examples of the metal oxide include osmium tetroxide (OsO4) and ruthenium tetroxide (RuO4).

[0031] For example, the negative electrode mixture layer 200 is cut in the thickness direction, and then the binder contained in the negative electrode mixture layer 200 is dyed with osmium tetroxide (OsO4), and the osmium (Os) atomic ratio of the cross section in the thickness direction of the dyed negative electrode mixture layer 200 is measured using energy dispersive X-ray spectroscopy. Since the measured osmium (Os) atomic ratio of the cross section of the negative electrode mixture layer 200 is correlated with the content of the binder, the weight ratio of the binder in the upper half 211 of the first layer to the binder in the second layer 220 can be calculated based on this.

[0032] When the weight ratio of the binder in the upper half 211 of the first layer to the binder in the second layer 220 is less than 5:1, the phenomenon of lithium ions being inserted into the negative electrode is reduced, resulting in an increase in the resistance of the secondary battery and the precipitation of lithium salts on the negative electrode surface.

[0033] In one embodiment, the weight ratio of the binder in the upper half 211 of the first layer to the binder in the second layer 220 may be 20:1 or less, specifically 15:1, and more specifically 12:1 or less. When the weight ratio of the binder is 20:1 or less, the brittleness of the negative electrode is reduced, and cracking in the negative electrode can be prevented.

[0034] In one embodiment, a binder may be included in the composition for forming the first layer 210, and no binder may be included in the composition for forming the second layer 220. However, even if the first layer 210 and the second layer 220 are formed by this embodiment, part of the binder included in the composition for forming the first layer 210 may migrate to the second layer 220, and thus the second layer 220 may include a relatively small amount of binder.

[0035] Furthermore, the silicon-based material contained in the negative electrode mixture layer 200 contains silicon (Si) atoms, which can exhibit a color distinguishable from that of osmium (Os) when measured using energy-dispersive X-ray spectroscopy. Based on this, the measured ratio of the binder-to-silicon weight ratio in the upper half 211 of the first layer to the binder-to-silicon weight ratio in the second layer 220, and more specifically, the ratio of the osmium-to-silicon weight ratio in the upper half 211 of the first layer to the osmium-to-silicon weight ratio in the second layer 220, can be 6 or greater. Specifically, the ratio of the osmium-to-silicon weight ratio in the upper half 211 of the first layer to the osmium-to-silicon weight ratio in the second layer 220 can be 8 or greater, and more specifically, 10 or greater.

[0036] In addition, the weight ratio of the binder to silicon in the upper half 211 of the first layer to the weight ratio of the binder to silicon in the second layer 220 may be 30 or less, specifically 20 or less, and more specifically 16 or less. When the weight ratio of the binder to silicon in the upper half 211 of the first layer to the weight ratio of the binder to silicon in the second layer 220 is 30 or less, the brittleness of the negative electrode is reduced, and cracking of the negative electrode can be prevented.

[0037] In an embodiment, the negative electrode mixture layer 200 may further include a carbon-based substance. The carbon-based substance may include one or more selected from artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P, and graphene. In one embodiment, the first layer 210 and the second layer 220 included in the negative electrode mixture layer 200 may include a silicon-based substance and a carbon-based substance, respectively.

[0038] In an embodiment, the negative electrode mixture layer 200 may further include a conductive material to improve conductivity. The conductive material may be one or more selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal fiber, carbon fluoride, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives.

[0039] In an embodiment, the negative electrode mixture layer 200 may further include a thickener to ensure advantages in the preparation process. The thickener can improve the problem of cracks on the negative electrode surface by enhancing the cohesive force of the binder. The thickener may include one or more selected from carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, methyl ethyl hydroxyethyl cellulose, and cellulose gum.

[0040] In an embodiment, the negative electrode mixture layer 200 may further include carbon nanotubes. Carbon nanotubes form a conductive network between silicon-based materials, thereby minimizing the problem of isolated conductive paths caused by volume expansion of the silicon-based materials due to long-term use of the secondary battery. The carbon nanotubes may include single-walled carbon nanotubes and multi-walled carbon nanotubes. Single-walled carbon nanotubes, due to their high flexibility, can more effectively form a conductive network between silicon-based materials, thereby improving the energy capacity retention rate of the secondary battery.

[0041] The average diameter of the single-walled carbon nanotubes may be 0.1 nm to 8.0 nm, 1.5 nm to 5.0 nm, or 1.5 nm to 3.0 nm. When the above range is met, the average diameter is the average value of 100 single-walled carbon nanotubes in the negative electrode active material layer calculated by SEM. The average length of the single-walled carbon nanotubes may be 3 μm to 20 μm, 4 μm to 20 μm, or 5 μm to 20 μm. When the above range is met, even if the volume of the silicon-based material changes excessively, the conductive network connecting the silicon-based materials can be maintained, thereby further improving the energy capacity retention rate of the secondary battery. The average length is the average value of 100 single-walled carbon nanotubes in the negative electrode active material layer calculated by SEM.

[0042] Multi-walled carbon nanotubes refer to carbon nanotubes that have multiple single-walled carbon nanotubes. Compared to single-walled carbon nanotubes, multi-walled carbon nanotubes are more economical, and multi-walled carbon nanotubes can be arranged on the surface of the silicon-based material together with the single-walled carbon nanotubes, thereby helping to form a conductive network with adjacent silicon-based materials. The average diameter of the multi-walled carbon nanotubes can be 5nm to 200nm, 5nm to 100nm, or 5nm to 50nm. When the above range is met, they can be easily dispersed in the negative electrode active material composition and can effectively form a conductive network between the silicon-based materials. The average diameter is the average value of the diameters of 100 multi-walled carbon nanotubes in 200 layers of the negative electrode mixture layer calculated by SEM measurement. The average length of the multi-walled carbon nanotubes can be 0.1μm to 100μm, 0.1μm to 50μm, or 0.1μm to 3μm. When the above range is met, even with a small amount of multi-walled carbon nanotubes, the formation of a conductive network in the negative electrode active material composition can be maximized. The average length is an average value calculated after measuring the lengths of 100 multi-walled carbon nanotubes in the negative electrode mixture layer 200 by SEM.

[0043] The loading amount of the negative electrode mixture layer 200 can be 4 mg / cm 2 Up to 20 mg / cm 2 , 6mg / cm 2 Up to 18 mg / cm 2 or 8 mg / cm 2 Up to 16 mg / cm 2 . When the above range is met, the capacity of the secondary battery can be increased while suppressing the unevenness of the binder or conductive material. The load amount may refer to the sum of the solid weights of the negative electrode mixture layer after drying on the negative electrode current collector 100 or the sum of the solid weights after the calendering process. For example, at least 5 points with a specified interval are punched into a circle in the length direction of the negative electrode to obtain a sample, and then the sum of the weights of the negative electrode mixture layer 200 in the sample is measured, which can be calculated as the load amount of the negative electrode mixture layer 200.

[0044] <Kit for producing negative electrode mixture layer>

[0045] The kit for manufacturing a negative electrode mixture layer according to the present invention may include: a first composition including a silicon-based substance and a binder; and a second composition including a silicon-based substance and excluding the binder.

[0046] The kit for manufacturing a negative electrode mixture layer according to the present invention may include a first composition and a second composition.

[0047] The first composition may include a silicon-based material and a binder. The silicon-based material may serve as the negative electrode active material as described above. In addition, the first composition may further include a carbon-based material as the negative electrode active material.

[0048] In addition, the binder can improve the binding force between the negative electrode current collector and the negative electrode active material, thereby improving the capacity retention rate of the secondary battery, and for example, may include styrene-butadiene rubber.

[0049] Furthermore, in an embodiment, the first composition may further comprise the aforementioned conductive material to improve conductivity. Furthermore, in an embodiment, the first composition may further comprise the aforementioned thickener to ensure advantages in preparation process.

[0050] In an embodiment, the first composition may be in the form of a solvent containing the silicon-based substance and the binder, etc. The solvent may be, for example, water, but is not limited thereto.

[0051] The second composition includes a silicon-based substance and may not include a binder.

[0052] The silicon-based material contained in the second composition can serve as the negative electrode active material as described above. In addition, the second composition can further contain a carbon-based material as the negative electrode active material.

[0053] Furthermore, the second composition does not include a binder, thereby making it possible to prevent an increase in resistance of the secondary battery and precipitation of a lithium salt on the surface of the negative electrode.

[0054] In addition, the second composition may further include the above conductive material to improve conductivity. In addition, in an embodiment, the second composition may further include the above thickener to ensure advantages in preparation process.

[0055] In an embodiment, the second composition may be in the form of a solvent containing the silicon-based substance and the like, and the solvent may be, for example, water, but is not limited thereto.

[0056] <Method for Manufacturing Negative Electrode>

[0057] The manufacturing method of the negative electrode according to the present invention may include the following steps: applying a first composition containing a silicon-based substance and a binder on a negative electrode current collector to form a first layer; and applying a second composition containing a silicon-based substance and not containing the binder on the first layer to form a second layer.

[0058] First, the method for manufacturing a negative electrode according to the present invention may include the step of forming a first layer. The first layer may be formed by coating a first composition on the negative electrode current collector. The first composition may include a silicon-based material and a binder. The first composition is the same as the first composition described in the above-mentioned kit for manufacturing a negative electrode mixture layer, and therefore will not be repeated below.

[0059] Next, the method for manufacturing a negative electrode according to the present invention may include the step of forming a second layer. The second layer may be formed by coating a second composition on the negative electrode current collector. The second composition may include a silicon-based material and no binder. The second composition is the same as the second composition described in the above-mentioned kit for manufacturing a negative electrode mixture layer, and therefore will not be repeated below.

[0060] The first and second layers can be formed by known methods. In one embodiment, the first and second layers can be formed by applying the first composition to the negative electrode current collector without drying, then applying the second composition, and then drying. Alternatively, the first and second layers can be formed by applying the first composition to the negative electrode current collector, drying it, and then applying the second composition, and then drying it.

[0061] The first layer and the second layer can be formed in a wet-on-wet manner using, for example, a slot-die coater, a roll-coater, a knife coater, an extrusion coater, or a gravure coater.

[0062] <Secondary Battery>

[0063] The secondary battery according to the present invention includes the above-mentioned negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode.

[0064] The secondary battery includes a negative electrode. For the negative electrode, the same negative electrode current collector, first layer, second layer, etc. as those described above for the negative electrode can be used.

[0065] In a secondary battery, in addition to the negative electrode according to the present invention, it also includes a positive electrode and a separator. The positive electrode may include a positive electrode current collector and an active material layer disposed on the positive electrode current collector. The active material layer may include an active material. For example, the positive electrode active material layer may include a positive electrode active material, and the positive electrode active material may be a substance that can intercalate and deintercalate lithium ions.

[0066] The positive electrode active material may be a lithium metal oxide. For example, the positive electrode active material may be one of lithium manganese-based oxide, lithium nickel-based oxide, lithium cobalt-based oxide, lithium nickel manganese-based oxide, lithium nickel cobalt aluminum-based oxide, lithium iron phosphate-based compound, lithium manganese phosphate-based compound, lithium cobalt phosphate-based compound, and lithium vanadium phosphate-based compound, and is not necessarily limited to the specific examples.

[0067] The separator can be between the negative electrode and the positive electrode. The separator is provided to prevent a short circuit between the negative electrode and the positive electrode and to generate the flow of ions. The separator can include a porous polymer film or a porous non-woven fabric. Wherein, the porous polymer film can be composed of a single layer or multiple layers of polyolefin-based polymers such as ethylene polymer, propylene polymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer. The porous non-woven fabric can include high-melting-point glass fiber, polyethylene terephthalate fiber. However, it is not limited thereto. According to an embodiment, the separator can be a high-heat-resistant separator (ceramic coated separator, CCS) comprising ceramic.

[0068] The negative electrode, the positive electrode and the separator can be made into an electrode assembly by winding, lamination, folding or zigzag stacking. In addition, the electrode assembly is provided together with the electrolyte, so that a secondary battery according to the present invention can be made. The secondary battery can be any of a cylindrical, prismatic, pouch and coin shape using a can, but is not limited thereto.

[0069] The electrolyte may be a non-aqueous electrolyte. The electrolyte may include a lithium salt and an organic solvent. The organic solvent may include at least one of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate (MPC), dipropyl carbonate (DPC), vinylene carbonate (VC), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, propylene sulfide, or tetrahydrofuran. DETAILED DESCRIPTION

[0070] Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. However, the following Examples and Comparative Examples are merely illustrative for describing the present invention in more detail, and the present invention is not limited to the following Examples and Comparative Examples.

[0071] Example

[0072] Example 1

[0073] <Preparation of First Composition>

[0074] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a thickness of 10 μm (0.1 μm), silicon oxide (SiO), multi-walled carbon nanotubes, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a ratio of 92.8:3:0.4:1.2:2.6 (based on weight) to prepare a first negative electrode active material composition.

[0075] <Preparation of Second Composition>

[0076] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a thickness of 10 μm (0.1 μm), silicon oxide (SiO), multi-walled carbon nanotubes, and carboxymethyl cellulose were mixed at a ratio of 95.4:3:0.4:1.2 (based on weight) to prepare a second negative electrode active material composition.

[0077] <Manufacturing of negative electrode>

[0078] The first composition was coated on a copper film, and then the second negative electrode active material composition was coated on the first composition. The mixture was then dried under vacuum at 130°C for one hour to produce a negative electrode having a first layer made from the first composition and a second layer made from the second composition. The loading ratio of the first and second layers was 5:5.

[0079] <Manufacturing of positive electrode>

[0080] As the active material, Li[Ni 0.88 Co- 0.10 Mn 0.02 ]O2, carbon black, and polyvinylidene fluoride (PVdF) were mixed in a ratio of 96:3:1 (by weight) to prepare a slurry. The slurry was evenly coated on aluminum foil and vacuum-dried to produce a positive electrode.

[0081] <Manufacturing of Secondary Batteries>

[0082] The negative and positive electrodes are notched to the specified size and stacked. A polyethylene (PE) separator is placed between the negative and positive electrodes to form a battery cell. The tabs of the negative and positive electrodes are then welded. The welded negative electrode / separator / positive electrode assembly is placed in a soft pack and sealed on all three sides, excluding the electrolyte injection area.

[0083] The electrolyte was injected through the electrolyte injection part, and the remaining surface was sealed, and then immersed for more than 12 hours. The electrolyte was an electrolyte solution prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC / DEC.

[0084] Afterwards, pre-charging was performed at a current corresponding to 0.25C for 36 minutes. Degassing was performed after 1 hour, and aging was performed for at least 24 hours. Formation charge and discharge were then performed (charge conditions were CC-CV 0.2C 4.2V 0.05C cut-off, and discharge conditions were CC 0.2C 2.5V cut-off). Afterwards, standard charge and discharge were performed to produce a secondary battery (charge conditions were CC-CV 0.33C 4.2V 0.05C cut-off, and discharge conditions were CC 0.33C 2.5V cut-off).

[0085] Example 2

[0086] <Preparation of First Composition>

[0087] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a thickness of 10 μm (0.1 μm), silicon oxide (SiO), multi-walled carbon nanotubes, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a ratio of 92.8:3:0.4:1.2:2.6 (based on weight) to prepare a first negative electrode active material composition.

[0088] <Preparation of Second Composition>

[0089] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a thickness of 10 μm (0.1 μm), silicon oxide (SiO), multi-walled carbon nanotubes, and carboxymethyl cellulose were mixed at a ratio of 95.4:3:0.4:1.2 (based on weight) to prepare a second negative electrode active material composition.

[0090] <Manufacturing of negative electrode>

[0091] The first composition was coated on a copper film, and then the second negative electrode active material composition was coated on the first composition. The mixture was then dried under vacuum at 130°C for one hour to produce a negative electrode having a first layer made from the first composition and a second layer made from the second composition. The loading ratio of the first and second layers was 4:6.

[0092] <Manufacturing of positive electrode>

[0093] As the active material, Li[Ni 0.88 Co- 0.10 Mn 0.02 ]O2, carbon black, and polyvinylidene fluoride (PVdF) were mixed at a ratio of 96:3:1 (by weight) to prepare a slurry. The slurry was evenly coated on aluminum foil and vacuum-dried to manufacture a positive electrode.

[0094] <Manufacturing of Secondary Batteries>

[0095] The negative and positive electrodes are cut to the specified size and stacked together. A polyethylene (PE) separator is placed between the two electrodes to form a battery cell. The tabs of the negative and positive electrodes are then welded together. The welded negative electrode / separator / positive electrode assembly is placed in a soft pack and sealed on all three sides, excluding the electrolyte injection area.

[0096] The electrolyte was injected through the electrolyte injection part, and the remaining surface was sealed, and then immersed for more than 12 hours. The electrolyte was an electrolyte solution prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC / DEC.

[0097] Afterwards, pre-charging was performed for 36 minutes at a current corresponding to 0.25C. After one hour, degassing was performed and aging was performed for at least 24 hours. Formation charge and discharge were then performed (charge conditions were CC-CV 0.2C 4.2V 0.05C cut-off, and discharge conditions were CC 0.2C 2.5V cut-off). Standard charge and discharge were then performed to produce a secondary battery (charge conditions were CC-CV 0.33C 4.2V 0.05C cut-off, and discharge conditions were CC 0.33C 2.5V cut-off).

[0098] Comparative Example 1

[0099] <Preparation of First Negative Electrode Active Material Composition>

[0100] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a thickness of 10 μm (0.1 μm), silicon oxide (SiO), multi-walled carbon nanotubes, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a ratio of 93:3:0.4:1.2:2.4 (based on weight) to prepare a first negative electrode active material composition.

[0101] <Preparation of Second Negative Electrode Active Material Composition>

[0102] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50A negative electrode active material having a thickness of 10 μm (0.1 μm), silicon oxide (SiO), multi-walled carbon nanotubes, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a ratio of 95.2:3:0.4:1.2:0.2 (based on weight) to prepare a second negative electrode active material composition.

[0103] <Manufacturing of negative electrode>

[0104] A negative electrode was manufactured by the same process as in Example 1, except that the first composition and the second composition were used.

[0105] <Manufacturing of Secondary Batteries>

[0106] A secondary battery was manufactured by the same process as that of manufacturing the positive electrode and the secondary battery of Example 1, except that the above-described negative electrode was used.

[0107] Comparative Example 2

[0108] <Preparation of First Composition>

[0109] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a thickness of 10 μm (0.1 μm), silicon oxide (SiO), multi-walled carbon nanotubes, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a ratio of 93.4:3:0.4:1.2:2.0 (based on weight) to prepare a first negative electrode active material composition.

[0110] <Preparation of Second Composition>

[0111] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a thickness of 10 μm (0.1 μm), silicon oxide (SiO), multi-walled carbon nanotubes, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a ratio of 94.8:3:0.4:1.2:0.6 (based on weight) to prepare a second negative electrode active material composition.

[0112] <Manufacturing of negative electrode>

[0113] A negative electrode was manufactured by the same process as in Example 1, except that the first composition and the second composition were used.

[0114] <Manufacturing of Secondary Batteries>

[0115] A secondary battery was manufactured by the same process as that of manufacturing the positive electrode and the secondary battery of Example 1, except that the above-described negative electrode was used.

[0116] Comparative Example 3

[0117] <Preparation of First Composition>

[0118] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a thickness of 10 μm (0.1 μm), multi-walled carbon nanotubes, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a ratio of 95.8:0.4:1.2:2.6 (based on weight) to prepare a first negative electrode active material composition.

[0119] <Preparation of Second Composition>

[0120] Mix artificial graphite (D 50 :13μm) and natural graphite (D 50 A negative electrode active material having a diameter of 10 μm (0.1 μm), multi-walled carbon nanotubes, and carboxymethyl cellulose were mixed at a ratio of 98.4:0.4:1.2 (based on weight) to prepare a second negative electrode active material composition.

[0121] <Manufacturing of negative electrode>

[0122] A negative electrode was manufactured by the same process as in Example 1, except that the first composition and the second composition were used.

[0123] <Manufacturing of Secondary Batteries>

[0124] A secondary battery was manufactured by the same process as that of manufacturing the positive electrode and the secondary battery of Example 1, except that the above-described negative electrode was used.

[0125] Experimental example

[0126] Experimental Example 1 - Measurement of Binder Content Distribution in Negative Electrode

[0127] In order to detect the binder in the negative electrode, the negative electrodes manufactured in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were stained with osmium tetroxide (OsO4). Afterwards, the cross section of the negative electrode mixture layer was cut and subjected to SEM-EDAX analysis. According to the SEM-EDAX analysis results, the osmium (Os) element distribution of the cross section of the negative electrode mixture layer represents the distribution of styrene-butadiene rubber as a binder. The cross section in the thickness direction of the negative electrode mixture layer stained with osmium tetroxide (OsO4) was divided into two layers, the area relatively close to the negative electrode current collector was divided into the first layer, and the area relatively far from the negative electrode current collector was divided into the second layer. In addition, the cross section in the thickness direction of the first layer was divided into two layers again, the area relatively close to the negative electrode current collector was divided into the lower half of the first layer, and the area relatively far from the negative electrode current collector was divided into the upper half of the first layer.

[0128] At this time, the content ratio of the osmium (Os) element present in the upper half of the first layer to the osmium (Os) element present in the second layer was measured, and the results are shown below. Figure 2 and Table 1.

[0129] Furthermore, during SEM-EDAX analysis, utilizing the properties of silicon, which exhibits a different color from osmium, the weight ratio of the osmium (Os) element to the silicon (Si) element in the upper half of the first layer was measured to compare the weight ratio of the osmium (Os) element to the silicon (Si) element in the second layer. The results are shown in Table 1 below.

[0130] Experimental Example 2-Measurement of Capacity Retention

[0131] The negative electrodes manufactured in Example 1, Example 2 and Comparative Example 1 and Comparative Example 2 were repeatedly charged (CC / CV 2.0C4.2V 0.1C cut-off) and discharged (CC 0.33C 2.5V cut-off) while measuring the discharge capacity. The percentage of the value of the 150th discharge capacity divided by the 1st discharge capacity was calculated as the capacity retention rate. The results are shown in Tables 1 and 2 below. Figure 3 middle.

[0132] [Table 1]

[0133]

[0134] According to Table 1, it can be confirmed that Example 1 and Example 2, in which the weight ratio of styrene-butadiene rubber as a binder in the upper half of the first layer and in the second layer satisfies 5:1 or more, have a more excellent capacity retention rate of the secondary battery than Comparative Example 1 and Comparative Example 2. Specifically, the type of active material, the type of binder and the load amount of the negative electrode mixture layer used in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are the same, but in Comparative Example 1 and Comparative Example 2, the weight ratio of styrene-butadiene rubber in the upper half of the first layer to the styrene-butadiene rubber in the second layer is less than 5:1, so there is a difference from Example 1 and Example 2. That is, in Comparative Example 1 and Comparative Example 2, since the second composition contains a binder, the content of styrene-butadiene rubber contained in the second layer is relatively high, and the resistance in the negative electrode mixture layer increases, so it can be confirmed that the capacity retention rate of the secondary battery is reduced. On the other hand, in the case of Example 1 and Example 2, since the second composition does not contain a binder, the content of styrene-butadiene rubber contained in the second layer is relatively small, and the resistance in the negative electrode mixture layer is reduced, so it can be confirmed that it can have an excellent capacity retention rate. More specifically, referring to Figure 3It can be confirmed that the capacity retention rates of the secondary batteries including the negative electrodes of Example 1 and Example 2 after 150 charge and discharge cycles are 94.2% and 94.0%, respectively. On the other hand, the capacity retention rate of the secondary battery including the negative electrode of Comparative Example 1 after 150 charge and discharge cycles is only 92.3%, and the capacity retention rate of the secondary battery including the negative electrode of Comparative Example 2 after 150 charge and discharge cycles is only 88.8%.

[0135] Furthermore, it was confirmed that the DC resistance increase rate of the secondary batteries including the negative electrodes of Examples 1 and 2 was 20% or less after 150 charge and discharge cycles, whereas the DC resistance increase rate of the secondary batteries including the negative electrodes of Comparative Examples 1 and 2 exceeded 20%.

[0136] <Experimental Example 3>

[0137] The actual power at room temperature (1050W 4.3V cut-off) of the negative electrodes manufactured in Example 1 and Comparative Example 3 was measured, and the battery resistance was compared and shown in FIG. Figure 4 middle.

[0138] like Figure 4 As shown, when the same power is applied, Example 1 has a low overvoltage and a long power retention time, while Comparative Example 3 has a higher overvoltage and a power retention time of 58.7% of the level of the Example.

[0139] That is, when graphite alone is used in the second layer, as in Comparative Example 3, the pores of the negative electrode active material may be clogged during the electrode rolling process, thereby reducing power characteristics. On the other hand, when a silicon-based active material is mixed, as in Example 1, the electrode rolling characteristics are improved, thereby improving power characteristics. Furthermore, by using silicon, which has a high available capacity per unit volume, the energy density of the battery can be increased.

[0140] [Explanation of Reference Numerals]

[0141] 100: negative electrode current collector

[0142] 200: Negative electrode mixture layer

[0143] 210: First floor

[0144] 211: Upper half of the first floor

[0145] 212: Lower half of the second floor

[0146] 220: Second floor

[0147] 1000: negative electrode

Claims

1. A negative electrode comprising: negative electrode current collector; as well as a negative electrode mixture layer formed on at least one side of the negative electrode current collector and comprising a silicon-based substance and a binder, wherein the negative electrode mixture layer includes a first layer on the negative electrode current collector in contact with the negative electrode current collector and a second layer on the first layer in contact with the first layer, A weight ratio of the binder contained in the upper half in the thickness direction of the first layer and the second layer, respectively, is 5:1 or more.

2. The negative electrode according to claim 1, wherein The thickness of the upper half of the first layer is half of the total thickness of the first layer.

3. The negative electrode according to claim 1, wherein The adhesive comprises styrene-butadiene rubber.

4. The negative electrode according to claim 1, wherein The content of the binder is 0.05 wt % to 5.0 wt % relative to the total solid weight of the negative electrode mixture layer.

5. The negative electrode according to claim 1, wherein The silicon-based material comprises SiO x , one or more of Si / C composite and Si alloy, wherein 0≤x<2.

6. The negative electrode according to claim 1, wherein A ratio of a weight ratio of the binder to silicon in an upper half in a thickness direction of the first layer to a weight ratio of the binder to silicon in the second layer is 6 or more.

7. The negative electrode according to claim 1, wherein The content of the silicon-based material is 1 wt % to 20 wt % relative to the total solid weight of the negative electrode mixture layer.

8. The negative electrode according to claim 1, wherein The negative electrode mixture layer further includes a carbon-based substance.

9. The negative electrode according to claim 8, wherein The carbon-based substance is one or more selected from artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P and graphene.

10. The negative electrode according to claim 8, wherein The first layer and the second layer include the silicon-based substance and the carbon-based substance, respectively.

11. The negative electrode according to claim 5, wherein The negative electrode mixture layer further includes carbon nanotubes.

12. The negative electrode according to claim 11, wherein The carbon nanotubes include at least one selected from single-walled carbon nanotubes and multi-walled carbon nanotubes.

13. The negative electrode according to claim 1, wherein The loading amount of the negative electrode mixture layer is 4 mg / cm 2 Up to 20 mg / cm 2 .

14. A kit for manufacturing a negative electrode mixture layer, comprising: a first composition comprising a silicon-based substance and a binder; as well as A second composition comprising a silicon-based substance and excluding the binder.

15. The kit for producing a negative electrode mixture layer according to claim 14, wherein The first composition and the second composition each further comprise a carbon-based substance.

16. A method for manufacturing a negative electrode, comprising the following steps: coating a first composition comprising a silicon-based material and a binder on a negative electrode current collector to form a first layer; as well as A second composition including a silicon-based substance and not including the binder is coated on the first layer to form a second layer.

17. The method for manufacturing a negative electrode according to claim 16, wherein: The first composition and the second composition each further comprise a carbon-based substance.

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