Negative electrode sheet, electrochemical apparatus, and method for manufacturing a negative electrode sheet

Abstract

This invention relates to a negative electrode sheet, an electrochemical apparatus, and a method for manufacturing a negative electrode sheet, belonging to the field of secondary battery technology. The negative electrode sheet includes a current collector and a negative electrode active material layer. The negative electrode active material layer is located on at least one surface of the current collector and includes a first active material layer and a second active material layer, which are stacked and installed along the direction toward the current collector. The ratio S1 / S2 of the structural stability parameters of the first and second active material layers satisfies 0.01 to 10.0. The negative electrode sheet, electrochemical apparatus, and method for manufacturing a negative electrode sheet create a structure in which the hardness of the negative electrode active material layer decreases in a gradient along the direction toward the current collector by adjusting the structural stability parameters of the two-layer structure in the negative electrode active material layer, thereby effectively optimizing the pore distribution and structural stability of the negative electrode active material layer and further improving the rapid charging, circulation, and storage performance of lithium-ion batteries.

Description

[Technical Field]

[0001] The present invention relates to the field of secondary batteries, and more specifically to a negative electrode sheet, an electrochemical apparatus, and a method for manufacturing a negative electrode sheet. [Background technology]

[0002] In conventional lithium-ion battery systems, the charging capacity, circulation performance, processing performance, and safety performance of the lithium-ion battery are largely determined by the negative electrode. Currently, optimization strategies for negative electrode sheets typically focus on aspects such as press density, surface density, and active material ratio. However, as battery cell performance gradually approaches the bottleneck, it becomes necessary to specifically subdivide the influence of the electrode plate level on battery cell performance, thereby improving the performance expression of the battery cell more effectively at an essential level.

[0003] Currently, simply adjusting the press density, surface density, and active material ratio of the negative electrode material does not offer significant room to optimize the rapid charging and circulation performance of battery cells. It is necessary to rationally consider the physical and chemical characteristics of the negative electrode sheet and comprehensively adjust the material ratio, hardness distribution, and press density of the negative electrode active material layer to optimize the distribution and orientation of particles and pores in the negative electrode active material layer. This improves the dynamic balance of the negative electrode sheet and further optimizes the rapid charging and circulation performance of lithium-ion batteries.

[0004] Therefore, it is necessary to design a negative electrode sheet, an electrochemical apparatus, and a method for manufacturing the negative electrode sheet, thereby solving the above-mentioned problems. [Overview of the project]

[0005] In view of the shortcomings of the conventional technology described above, the present invention provides a negative electrode sheet, an electrochemical apparatus, and a method for manufacturing a negative electrode sheet. By comprehensively adjusting the material ratio, hardness distribution, and press density of the negative electrode active material layer in the negative electrode sheet, the invention improves upon the technical problem in the conventional technology, where it is difficult to comprehensively optimize the distribution and orientation of particles and pores in the negative electrode active material layer, and thus is unable to effectively balance the dynamic performance of the negative electrode sheet.

[0006] To achieve the above-mentioned objectives and other related objectives, the present invention provides a negative electrode sheet comprising a current collector and a negative electrode active material layer.

[0007] However, the negative electrode active material layer is located on at least one surface of the current collector, the negative electrode active material layer includes a first active material layer and a second active material layer, the first active material layer and the second active material layer are stacked and installed along the direction toward the current collector, and the ratio S1 / S2 of the structural stability parameters of the first active material layer and the second active material layer satisfies 0.01 to 10.0.

[0008] In one example of the present invention, the negative electrode material in the negative electrode active material layer includes a graphite material.

[0009] In one example of the present invention, the ratio S1 / S2 of the structural stability parameters of the first active material layer and the second active material layer satisfies the range of 0.1 to 5.0.

[0010] In one example of the present invention, the structural stability parameter S1 of the first active material layer is 3 to 16.

[0011] JPEG2026519677000002.jpg31170

[0012] JPEG2026519677000003.jpg15170

[0013] In one example of the present invention, the press density of the negative electrode active material layer is 1.65 to 1.75 g / cm³. 3 That is the case.

[0014] The present invention also provides a method for manufacturing a negative electrode sheet, the manufacturing method comprising: mixing a first negative electrode material with a binder, a conductive agent and a thickener to form a slurry to obtain a first active material layer slurry; mixing a second negative electrode material with a binder, a conductive agent and a thickener to form a slurry to obtain a second active material layer slurry; and sequentially applying the second active material layer slurry and the first active material layer slurry to at least one surface of a current collector, followed by drying, pressing, die-cutting and punching to obtain a negative electrode sheet, wherein the hardness of the first negative electrode material is higher than that of the second negative electrode material.

[0015] In one example of the present invention, the ratio S1 / S2 of the structural stability parameters of the first anode material and the second anode material satisfies the range of 0.01 to 10.0.

[0016] In one example of the present invention, the average particle size Dv50 of the first anode material is 11 to 17 μm, and the average particle size Dv50 of the second anode material is 16 to 19 μm.

[0017] The present invention also provides an electrochemical apparatus comprising a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet as described in any of the above examples.

[0018] The anode sheet, electrochemical apparatus, and method for manufacturing the anode sheet in the present invention adjust the structural stability parameters of the two-layer structure in the anode active material layer to form a structure in which the hardness gradient decreases in the direction in which the anode active material layer approaches the current collector. This effectively optimizes the pore distribution and structural stability of the anode active material layer, forming an anode sheet with low flexibility, high orientation, and abundant pores during pressing, and further improving the rapid charging, circulation, and storage performance of lithium-ion batteries. Therefore, the present invention effectively overcomes several practical problems in existing technologies and has high utility and significance. [Brief explanation of the drawing]

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings that need to be used in the description of the embodiments or the prior art will be briefly introduced below. The accompanying drawings in the following description are only a part of the embodiments of the present invention, and it is obvious that those skilled in the art can obtain other accompanying drawings based on these accompanying drawings without creative labor.

[0020] [Figure 1] It is a schematic structural diagram of a negative electrode sheet in an embodiment of the present invention. [Figure 2] It is a schematic flowchart of a method for manufacturing a negative electrode sheet in an embodiment of the present invention.

Modes for Carrying Out the Invention

[0021] Hereinafter, the implementation modes of the present invention will be described through specific specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present invention according to the content disclosed in this specification. The present invention can be further implemented or applied in other different specific implementation modes, and various modifications or changes can be made to the details of each item in this specification without departing from the spirit of the present invention based on different viewpoints and applications. It should be noted that in the case of no contradiction, the following embodiments and the features in the embodiments can be combined with each other. Also, it should be understood that the terms used in the embodiments of the present invention are for describing a specific specific implementation scheme and are not for limiting the protection scope of the present invention. The test methods not specifically specified in the following embodiments are usually carried out according to conventional conditions or according to the conditions recommended by each manufacturer.

[0022] In addition, the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are also only for the sake of clarifying the description and are not used to limit the scope in which the present invention can be implemented. The change or adjustment of their relative relationship is considered to be within the scope in which the present invention can be implemented when there is no substantial change in the technical content.

[0023] In this specification, the structural stability parameter S of the anode material is an index of the structural stability of secondary particles of the material (a single particle is defined as 100.0). For a specific definition, please refer to the test method for structural stability parameters described later.

[0024] The degree of curvature τ of the negative electrode sheet is defined as follows: it is the ratio of the actual length of the pores in the negative electrode active material layer of the negative electrode sheet to the shortest distance of the negative electrode active material layer in the direction perpendicular to the current collector.

[0025] The porosity ε of the negative electrode sheet is defined as follows: it is the ratio of the volume of pores in the porous negative electrode material to the apparent volume (or total volume) of the porous negative electrode material, and is generally expressed as a percentage.

[0026] Degree of orientation of negative electrode sheet V OI This represents the degree of depositional orientation of negative electrode material particles in the negative electrode sheet and is defined as the intensity ratio of the I004 / I110 peaks in the XRD diffraction of the negative electrode material in the negative electrode sheet.

[0027] The average particle size Dv50 of a material can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size Dv50 can be measured, for example, by laser diffraction. Laser diffraction can typically measure particle sizes from the submicron range to several millimeters, thereby providing highly reproducible and high-resolution results.

[0028] This invention provides a negative electrode sheet, which is used in the manufacture of an electrochemical apparatus. An electrochemical apparatus typically includes a positive electrode sheet, a negative electrode sheet, an electrolyte, a separator, and corresponding connecting auxiliary components and circuits. The positive electrode material and negative electrode material in the positive electrode sheet and negative electrode sheet can store and release energy by insertion and removal of lithium ions, the electrolyte is a carrier for lithium ion transport between the positive and negative electrodes, and the separator isolates the positive and negative electrodes and prevents short circuits by being permeable to lithium ions but non-conductive. The positive electrode sheet and negative electrode sheet typically play a decisive role in important performance factors of a lithium battery, such as the magnitude of its energy storage function, the energy density of its battery cells, its circulating performance, and its safety.

[0029] As shown in Figure 1, the negative electrode sheet provided by the present invention comprises a current collector 100 and a negative electrode active material layer 200, wherein the negative electrode active material layer 200 is located on at least one surface of the current collector 100. Specifically, the current collector 100 has two opposing surfaces in its thickness direction, and the negative electrode active material layer 200 is installed on any one or both of the two surfaces of the current collector 100. The current collector 100 can be made of a material having good conductivity and mechanical strength, and performs the functions of conductivity and current collection. In some embodiments, the current collector 100 can be made of copper foil.

[0030] As shown in Figure 1, the negative electrode active material layer 200 includes a first active material layer 210 and a second active material layer 220. In the negative electrode active material layer 200, the first active material layer 210 and the second active material layer 220 are stacked in a direction toward the current collector 100, the second active material layer 220 is placed on the surface of the current collector 100, and the first active material layer 210 is placed on the second active material layer 220.

[0031] In the negative electrode active material layer 200, the first active material layer 210 and the second active material layer 220 are stacked in a direction toward the current collector 100. Therefore, by adjusting the ratio of the structural stability parameter S of the first active material layer 210 and the second active material layer 220, the material hardness of the negative electrode active material layer 200 after pressing can be gradually decreased toward the direction toward the current collector 100. A material structure in the negative electrode active material layer 200 where the upper part is tight and the lower part is loose toward the direction toward the current collector 100 is advantageous because it forms a suitable particle and pore distribution during the pressing process, and further increases the structural stability and pore richness of the negative electrode sheet.

[0032] In some embodiments, the ratio S1 / S2 of the structural stability parameters of the first active material layer and the second active material layer material in the negative electrode active material layer satisfies 0.01 to 10.0, and a negative electrode active material layer with appropriate overall hardness and abundant porosity can be formed on the negative electrode sheet.

[0033] When the ratio S1 / S2 of the structural stability parameters of the first active material layer and the second active material layer material is between 0.01 and 10.0, the pore distribution of the negative electrode sheet is favorable, the structural stability is relatively high, the porosity ε of the negative electrode sheet is between 15% and 30%, and the degree of curvature τ of the negative electrode sheet is between 3 and 6. When the S1 / S2 ratio is excessively high, it is advantageous to improve the pore richness and hardness of the negative electrode sheet, but it significantly reduces the structural stability and press density of the negative electrode sheet. When the S1 / S2 ratio is excessively low, it leads to a decrease in the pore richness of the negative electrode sheet, reduces the porosity ε of the negative electrode sheet to below 15%, increases the pore curvature τ to above 6, further deteriorates the dynamic performance of the negative electrode sheet, and significantly reduces the charge-discharge performance of the secondary battery.

[0034] In some implementations, the ratio S1 / S2 of the structural stability parameters of the first active material layer and the second active material layer in the negative electrode active material layer satisfies the following conditions: 0.01 ≤ S1 / S2 ≤ 3, 0.1 ≤ S1 / S2 ≤ 3, 0.1 ≤ S1 / S2 ≤ 5, 1 ≤ S1 / S2 ≤ 7, 3 ≤ S1 / S2 ≤ 7, 3 ≤ S1 / S2 ≤ 8, 3 ≤ S1 / S2 ≤ 10, 5 ≤ S1 / S2 ≤ 7, or 5 ≤ S1 / S2 ≤ 10, etc.

[0035] In several preferred implementations, the ratio S1 / S2 of the structural stability parameters of the first active material layer and the second active material layer in the negative electrode active material layer satisfies 0.0.1 to 5.0. When the ratio S1 / S2 of the structural stability parameters of the first active material layer and the second active material layer in the negative electrode sheet is within an appropriate range, it is advantageous to improve the porosity, press density, and structural stability of the negative electrode sheet while reducing the degree of porosity curvature of the negative electrode sheet.

[0036] In some embodiments, on the basis that the negative electrode sheet satisfies the above conditions, the structural stability parameter S1 of the first active material layer is 3.0 to 16.0, for example, 3.0, 3.7, 5.0, 7.4, 8.0, 8.3, 10.0, 10.4, 13.4, 15.1, 15.6, or 16.0. The structural stability parameter S2 of the second active material layer can be any value that satisfies the range of the ratio of structural stability parameters (0.01 ≤ S1 / S2 ≤ 10.0), for example, the structural stability parameter S2 of the second active material layer can be any value that satisfies the range of the ratio of stability parameters between 1.0 and 100.0.

[0037] JPEG2026519677000004.jpg57170

[0038] JPEG2026519677000005.jpg48170

[0039] JPEG2026519677000006.jpg41170

[0040] Further investigation by the inventors has revealed that, in addition to satisfying the above-mentioned conditions, the negative electrode sheet of the present invention can further improve the performance of a secondary battery if it selectively satisfies one or more of the following design conditions.

[0041] In several preferred implementations, the press density P of the negative electrode sheet is 1.65 to 1.75 g / cm³. 3 For example, 1.65 g / cm³ 3 1.67 g / cm³ 3, 1.70 g / cm 3 , 1.73 g / cm 3 or 1.75 g / cm 3 is.

[0042] In some preferred embodiments, the porosity ε of the negative electrode sheet is 15% - 30%, for example, 15%, 17%, 20%, 22%, 25%, 27%, 29% or 30%.

[0043] In some preferred embodiments, the degree of bend τ of the negative electrode sheet is 3 - 5, for example, 3.0, 3.3, 3.37, 3.5, 3.6, 3.64, 3.8, 4.0, 4.2, 4.5, 4.7 or 5.0.

[0044] In some preferred embodiments, the degree of orientation V OI of the negative electrode sheet is 14 - 24, for example, 14, 16, 18, 21, 22, 23 or 24.

[0045] In some embodiments, the negative electrode material in the negative electrode active material layer includes a core and a coating layer. The core includes a graphite material, the coating layer covers the surface of the core, and the coating layer includes amorphous carbon.

[0046] In the above embodiments, the graphite material includes natural graphite, artificial graphite and graphitized carbon. Preferably, the graphite material can be artificial graphite.

[0047] In the above embodiments, the amorphous carbon coating layer can be formed by carbonization of an organic carbon source. For example, the organic carbon source can be selected from polymer materials, such as coal pitch, petroleum pitch, phenolic resin and other polymer materials.

[0048] Because amorphous carbon has a disordered structure and relatively high interlayer distances, coating the core material with amorphous carbon allows active ions to diffuse more quickly within the anode material particles, thereby improving the rapid charging capability of the anode material. At the same time, the amorphous carbon coating layer also provides protection to the core, significantly reducing graphite layer delamination of the core material caused by solvent co-insertion, and giving the anode material relatively high structural stability. Therefore, the anode material can exhibit relatively high capacity and cyclic lifetime.

[0049] Furthermore, it needs to be explained that the negative electrode active material layer also includes a binder and a conductive agent. However, the binder is selected from at least one of polyamide-imide, styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, sodium carboxymethylcellulose, and lithium carboxymethylcellulose. The conductive agent is selected from at least one of carbon black, SP, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0050] Referring to Figure 2, the present invention provides a method for manufacturing a negative electrode sheet, which includes the following steps.

[0051] S1, the first negative electrode material, binder, conductive agent, and thickener are mixed to form a slurry to obtain the first active material layer slurry.

[0052] S2, the second negative electrode material, binder, conductive agent, and thickener are mixed to form a slurry to obtain the second active material layer slurry.

[0053] S3. The second active material layer slurry and the first active material layer slurry are sequentially applied to at least one surface of the current collector to form a negative electrode active material layer on the current collector (in the negative electrode active material layer, the second active material layer is applied on the current collector, and the first active material layer is applied on the second active material layer). After application, drying, pressing, die-cutting, and punching are performed to obtain a negative electrode sheet.

[0054] In this negative electrode sheet manufacturing method, a first and second negative electrode material with suitable physical parameters are selected to produce a first active material layer slurry and a second active material layer slurry. The second and first active material layer slurry are then sequentially applied to a current collector to realize the design of the interlayer structure of the negative electrode active material layer. After drying and pressing, the negative electrode active material layer with this interlayer structure can arrange material particles of different particle sizes at suitable intervals, thereby forming a porous structure with abundant and highly oriented pores between the particles. Furthermore, the structural stability and suitability of the pore distribution of the negative electrode active material layer are further improved based on the dynamics of the selected negative electrode material.

[0055] In steps S1 and S2, the first and second anode materials used are both anode materials having a graphite core and an amorphous carbon coating. The graphite material is selected from one or more types of natural graphite, artificial graphite, and graphitized carbon, and the amorphous carbon can be formed by carbonizing an organic carbon source on the graphite material. For example, the organic carbon source can be selected from polymer materials such as coal pitch, petroleum pitch, and phenolic resin.

[0056] In steps S1 and S2, the binder is selected from at least one of polyimide, styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, sodium carboxymethylcellulose, and lithium carboxymethylcellulose, of which styrene-butadiene rubber is preferred. The conductive agent is selected from at least one of carbon black, SP, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene, of which carbon black is preferred. Sodium carboxymethylcellulose (CMC) is selected as the thickener.

[0057] In some embodiments, in steps S1 and S2, the ratio S1 / S2 of the structural stability parameters of the selected first anode material and second anode material satisfies 0.01 to 10.0. Under these structural parameters, the hardness of the first anode material is higher than that of the second anode material. By employing second and first anode materials within this range of structural stability parameter ratio, a two-layer structure of the anode active material layer can be formed on the current collector along the direction away from the current collector, and after press working, the internal hardness of the anode active material layer tends to decrease in a gradient along the direction towards the current collector, thereby improving the structural stability and suitability of the pore distribution of the anode sheet.

[0058] Furthermore, in several preferred implementations, the ratio S1 / S2 of the structural stability parameters of the selected first anode material and second anode material satisfies 0.1 to 5.0.

[0059] In some embodiments, a first active material layer slurry is produced in steps S1 and S2 by selecting a first anode material having an average particle size Dv50 of 11 to 17 μm, for example, a first anode material having an average particle size Dv50 of 11 μm, 11.2 μm, 12.2 μm, 13 μm, 13.3 μm, 13.7 μm, 14 μm, 14.5 μm, 15 μm, 15.6 μm, 16 μm, 16.2 μm, or 17 μm. A second active material layer slurry is produced by selecting a second anode material having an average particle size Dv50 of 16 to 19 μm, for example, a second anode material having an average particle size Dv50 of 16 μm, 16.7 μm, 17 μm, 17.5 μm, 18 μm, 18.3 μm, 18.7 μm, or 19 μm. Furthermore, the average particle size Dv50 of the selected second anode material is set higher than the average particle size Dv50 of the first anode material.

[0060] In this embodiment, during step S3, a two-layer negative electrode active material layer is formed by applying a second active material layer slurry and a first active material layer slurry onto the current collector. The negative electrode active material layer has a two-layer structure with similar average particle sizes Dv50, and the average particle size Dv50 of the outer first active material layer in the two-layer structure is low, while the average particle size Dv50 of the inner second active material layer is high.

[0061] The overall interlayer structure of the negative electrode active material layer has a low average particle size Dv50 in the outer layer and a high average particle size Dv50 in the inner layer. As a result, the gaps between the inner layer material particles and the gaps between the outer layer material particles are large, and during the pressing process of the negative electrode sheet, the material particles of the first active material are pressed and embedded between the material particles of the second active material layer. This causes the particles in the negative electrode active material layer to form a spaced arrangement with high space utilization efficiency, and a large number of spaced particles tend to improve both the orientation and porosity of the negative electrode active material layer. Furthermore, because the average particle size Dv50 of the two-layer structure of the negative electrode active material layer is relatively close, the pore structure formed between the particles after pressing has relatively high orientation and relatively low curvature.

[0062] JPEG2026519677000007.jpg40170

[0063] During process S3, a two-chamber coating die head is used. The first active material layer slurry is injected into the upper chamber of the two-chamber coating die head, and the second active material layer slurry is injected into the lower chamber of the two-chamber coating die head. Subsequently, the first and second active material layer slurries in the upper and lower chambers of the two-chamber coating die head are coated at a weight ratio of 1:1 with a coating weight of 105 g / m². 2 The material is uniformly applied to both surfaces of the current collector according to the parameters, thereby forming a negative electrode active material layer on the current collector surface in which a two-layer structure of a second active material layer and a first active material layer is stacked in the direction away from the current collector. After application, the negative electrode active material layer on the current collector can be dried, pressed, die-cut, and punched to obtain a negative electrode sheet.

[0064] The present invention further provides an electrochemical apparatus comprising a negative electrode sheet described in any of the above embodiments of the present invention or a negative electrode sheet manufactured by the manufacturing method described in any of the above embodiments, the electrochemical apparatus being, for example, a secondary lithium-ion battery, the battery comprising a positive electrode sheet, a negative electrode sheet, a separator placed between the positive electrode sheet and the negative electrode sheet, and an electrolyte. In this battery, the positive electrode sheet, the positive electrode material on the negative electrode sheet, and the negative electrode material can store and release energy by the insertion and removal of lithium ions, the electrolyte is a carrier for lithium ion transport between the positive and negative electrodes, and the separator isolates the positive and negative electrodes and prevents short circuits by being permeable to lithium ions but not conductive.

[0065] The positive electrode sheet, separator, and electrolyte can employ materials and manufacturing methods common in this field, as shown below for example.

[0066] The manufacturing process for secondary lithium-ion batteries is as follows:

[0067] Manufacturing of positive electrode sheets: Ternary positive electrode material (LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode slurry is obtained by mixing O2, conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1.5:1.5, adding the solvent N-methylpyrrolidone (NMP), and stirring thoroughly. The positive electrode slurry is applied to an aluminum foil positive electrode current collector, and a positive electrode sheet is produced by drying, cold rolling, slitting, and other processes. The conductive agent can be further selected from at least one conductive material such as acetylene black, carbon nanotubes, graphene, or VGCF. The binder can be further selected from at least one of PVDF, PTFE, etc.

[0068] Please refer to the above for the negative electrode sheet manufacturing process.

[0069] Separator manufacturing: A porous PE membrane with a thickness of 11 μm is selected as the separator. Of these, the separator thickness ranges from 9 μm to 18 μm, the air permeability is 180 s / 100 mL to 380 s / 100 mL, and the porosity is 30% to 50%.

[0070] Preparation of electrolyte: Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are uniformly mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Subsequently, a thoroughly dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0071] Battery assembly: The manufactured positive electrode sheet, separator, and negative electrode sheet are sequentially stacked so that the separator is positioned between the positive and negative electrode sheets to provide isolation. Then, the assembly is enclosed in an aluminum plastic film, dried, and the electrolyte prepared above is injected. After sealing, settling, molding, and other processes, a 1Ah soft pack battery (i.e., lithium-ion battery) is finally manufactured.

[0072] The technical plan of the present invention will be described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available or can be obtained by methods common in the art.

[0073] Example 1

[0074] JPEG2026519677000008.jpg31170

[0075] The method for manufacturing the negative electrode sheet includes the following:

[0076] S1, the first anode material, binder styrene-butadiene rubber, sodium carboxymethylcellulose, and conductive agent carbon black (purchased from Imerys Graphite & Carbon GmbH of Switzerland, model number Super P, abbreviated as SP) are mixed in a ratio of 94.7:2.5:1.8:1 by weight. 82 parts by weight of water are added to 100 parts by weight of the mixture and stirred to obtain the first active material layer slurry. However, the first anode material is selected to be an artificial graphite material with a structural stability parameter S1 of 3.7 and an average particle size Dv50 of 15.6 μm.

[0077] S2, the second anode material, binder styrene-butadiene rubber, sodium carboxymethylcellulose, and conductive agent carbon black (purchased from Imerys Graphite & Carbon GmbH of Switzerland, model number Super P, abbreviated as SP) are mixed in a ratio of 94.7:2.5:1.8:1 by weight. 82 parts by weight of water are added to 100 parts by weight of the mixture and stirred to obtain a slurry of the second active material layer. However, the second anode material is selected to be an artificial graphite material with a structural stability parameter S2 of 2.3 and an average particle size Dv50 of 16.7 μm.

[0078] Using a two-chamber coating die head (MANST, model BG01A-400-30B), the first active material layer slurry is injected into the upper chamber of the two-chamber coating die head, and the second active material layer slurry is injected into the lower chamber of the two-chamber coating die head. Then, the first and second active material layer slurries in the upper and lower chambers of the two-chamber coating die head are mixed in a weight ratio of 1:1, with a coating weight of 105 g / m². 2 The 8μm copper foil current collector is uniformly coated on both sides according to the specified parameters. The current collector is then dried and roll-pressed, and the pressing density of the negative electrode active material layer on the current collector is set to 1.65 g / m². 3 Finally, the negative electrode sheet is obtained through die-cutting and punching.

[0079] In this embodiment, a secondary lithium-ion battery is manufactured using the above-mentioned negative electrode sheet, and the manufacturing method for the secondary lithium-ion battery is as follows.

[0080] (1) Manufacturing of positive electrode sheets:

[0081] Ternary cathode material (LiNi 0.8 Co 0.1 Mn 0.1 Mix O2, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1.5:1.5, add solvent N-methylpyrrolidone (NMP), and stir thoroughly to obtain a positive electrode slurry. Stir under the action of a vacuum stirrer until a uniformly transparent consistency is obtained to obtain the positive electrode slurry. The positive electrode slurry is uniformly applied to a 16 μm aluminum foil current collector, and after drying the aluminum foil current collector at room temperature, transfer it to an oven and dry at 80°C to 120°C for 6 hours, after which a positive electrode sheet is obtained by cold pressing and slitting.

[0082] (2) Refer to this embodiment for the manufacturing process of the negative electrode sheet.

[0083] (3) Preparation of electrolyte:

[0084] In a glove box under an argon gas atmosphere with a water content of <10 ppm, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are uniformly mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Subsequently, a thoroughly dried lithium salt LiPF6 is dissolved in the resulting organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0085] (4) Manufacturing of separators:

[0086] A porous PE membrane with a thickness of 11 μm is selected as the separator.

[0087] (5) Battery assembly:

[0088] The positive electrode sheet, separator, and negative electrode sheet manufactured as described above are sequentially stacked so that the separator is positioned between the positive and negative electrode sheets to provide isolation. Then, the assembly is wrapped in aluminum plastic film, dried in a vacuum oven at 120°C, injected with 3.0 g / Ah electrolyte, pressed, and then subjected to processes such as standing, heat / colour / pressure, molding, fixing, and grading to finally produce a 1 Ah soft pack battery (i.e., lithium-ion battery).

[0089] The specific steps and conditions for electrolyte formation are as follows: After injecting the electrolyte, maintain a hot-pressure environment of 0.1 MPa, charge at 0.02C for 17 minutes at 45°C in a standing state, let stand for 5 minutes, then charge again at 0.02C to 0.3Ah, then remove the gas bag and vacuum seal, and let stand at room temperature for 48 hours to complete the electrolyte formation.

[0090] Example 2

[0091] The difference between this embodiment and Embodiment 1 is that, in manufacturing the negative electrode sheet, a first negative electrode material with a structural stability parameter S1 of 7.4 and an average particle size Dv50 of 13.7 μm is used in step S1.

[0092] JPEG2026519677000009.jpg22170

[0093] Example 3

[0094] The difference between this embodiment and Embodiment 1 is that, in manufacturing the negative electrode sheet, a first negative electrode material with a structural stability parameter S1 of 10.4 and an average particle size Dv50 of 12.2 μm is used in step S1.

[0095] JPEG2026519677000010.jpg22170

[0096] Example 4

[0097] The difference between this embodiment and Embodiment 1 is that, in manufacturing the negative electrode sheet, in steps S1 and S2, a first negative electrode material with a structural stability parameter S1 of 8.3 and an average particle size Dv50 of 13.3 μm is used, and a second negative electrode material with a structural stability parameter S2 of 1.2 and an average particle size Dv50 of 18.3 μm is used. In step S3, after coating the negative electrode active material layer onto the current collector, the press density of the negative electrode active material layer on the current collector is set to 1.75 g / m² by roll pressing. 3 The goal is to adjust it accordingly.

[0098] JPEG2026519677000011.jpg22170

[0099] Example 5

[0100] The difference between this embodiment and Embodiment 1 is that, in manufacturing the negative electrode sheet, in steps S1 and S2, a first negative electrode material with a structural stability parameter S1 of 8.0 and an average particle size Dv50 of 16.2 μm is used, and a second negative electrode material with a structural stability parameter S2 of 100 and an average particle size Dv50 of 18.0 μm is used. In step S3, after coating the negative electrode active material layer onto the current collector, the press density of the negative electrode active material layer on the current collector is set to 1.75 g / m² by roll pressing. 3 The goal is to adjust it accordingly.

[0101] JPEG2026519677000012.jpg22170

[0102] Example 6

[0103] The difference between this embodiment and Embodiment 1 is that, in manufacturing the negative electrode sheet, in steps S1 and S2, a first negative electrode material with a structural stability parameter S1 of 15.6 and an average particle size Dv50 of 11.2 μm is used, and a second negative electrode material with a structural stability parameter S2 of 1.2 and an average particle size Dv50 of 18.3 μm is used. In step S3, after coating the negative electrode active material layer onto the current collector, the press density of the negative electrode active material layer on the current collector is set to 1.75 g / m² by roll pressing. 3 The goal is to adjust it accordingly.

[0104] JPEG2026519677000013.jpg22170

[0105] Example 7

[0106] The difference between this embodiment and Embodiment 6 is that, in manufacturing the negative electrode sheet, a first negative electrode material with a structural stability parameter S1 of 13.4 and an average particle size Dv50 of 12.6 μm is used in step S1.

[0107] JPEG2026519677000014.jpg22170

[0108] Example 8

[0109] The difference between this embodiment and Embodiment 1 is that, in manufacturing the negative electrode sheet, in steps S1 and S2, a first negative electrode material with a structural stability parameter S1 of 9.7 and an average particle size Dv50 of 13.1 μm is used, and a second negative electrode material with a structural stability parameter S2 of 2.3 and an average particle size Dv50 of 16.7 μm is used. In step S3, after coating the negative electrode active material layer onto the current collector, the press density of the negative electrode active material layer on the current collector is set to 1.75 g / m² by roll pressing. 3 The goal is to adjust it accordingly.

[0110] JPEG2026519677000015.jpg22170

[0111] Example 9

[0112] The difference between this embodiment and Embodiment 1 is that, in manufacturing the negative electrode sheet, in steps S1 and S2, a first negative electrode material with a structural stability parameter S1 of 1.51 and an average particle size Dv50 of 13.7 μm is used, and a second negative electrode material with a structural stability parameter S2 of 1.2 and an average particle size Dv50 of 18.3 μm is used. In step S3, after coating the negative electrode active material layer onto the current collector, the press density of the negative electrode active material layer on the current collector is set to 1.75 g / m² by roll pressing. 3 The goal is to adjust it accordingly.

[0113] JPEG2026519677000016.jpg22170

[0114] Material parameter tests were performed on the negative electrode sheets manufactured in Examples 1 to 9, and rapid charging time tests, circulating capacity retention rate tests, and storage performance tests were performed on secondary lithium-ion batteries equipped with the negative electrode sheets manufactured in Examples 1 to 10.

[0115] (1) Structural stability parameter S test of the negative electrode material:

[0116] Referring to the National Standard GB / T24533-2019 of the People's Republic of China, the powder sample is pressed into a sheet, and before testing, it is held under a standard pressure of 2T for 20 seconds. After releasing the pressure for 10 minutes, the formal operation begins, and the powder pressure at 5T is measured as P0. Subsequently, the powder is tested at pressures of 2.5T, 3T, 3.5T, ..., 2+0.5nT, ..., and the pressed densities are recorded as P1, P2, P3, ..., Pn, ... respectively. When Pn / Pn-1 ≥ 1.05, this Pn is called the particle structure-degraded pressed density, and the structural stability parameter S = 2+0.5n / 5 is recorded.

[0117] (2) Porosity ε test of the negative electrode sheet:

[0118] Refer to the test method of the National Standard GB21650.1-2008 of the People's Republic of China and perform the test by selecting a small amount of negative electrode sheet.

[0119] (3) Test of the degree of flexibility τ of the negative electrode sheet:

[0120] The test will be conducted using the imaging method described in Ebner M, Wood V. Tool for Tortuosity Estimation in Lithium Ion Battery Porous Electrodes[J]. Journal of the Electrochemical Society, 2014, 162(2):A3064-A3070.

[0121] (4) Degree of orientation of the negative electrode sheet V OI test:

[0122] Referring to the National Standard GB / T23442-2009 of the People's Republic of China, a small amount of negative electrode sheet was selected and tested, and the intensity ratio of the I004 / I110 peaks in the XRD diffraction of the negative electrode sheet was used to determine the degree of orientation V. OI Let's assume that.

[0123] (5) Rapid charging time test:

[0124] The battery cell is directly charged to an 8% State of Charge (SOC) state with a current of 0.33C. Then, based on the measured three-electrode window test of the battery cell, the charging windows of 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% are designated as C1, C2, C3, C4, C5, C6, C7, and C8, respectively, and the battery is charged to 80% using a step charge. That is, C1 is used from 8% to 10%, C2 is used from 10% to 20%, and so on, and the charging time from 8% to 80% SOC is recorded as the evaluation criterion for rapid charging capability. However, the calculation formula is as follows.

[0125] T=(0.02 / C1+0.1 / C2+0.1 / C3+0.1 / C4+0.1 / C5+0.1 / C6+0.1 / C7+0.1 / C8)×60.

[0126] (6) Circulation volume retention rate test:

[0127] Under 25°C conditions, the battery cells are subjected to a charge-discharge cycle using a charge-discharge method of 0.21 A / g (calculated using the mass of the positive electrode material) and 2.8 to 4.25 V. The number of cycles when the initial capacity is reduced to 80% is recorded and used as the material circulation capability evaluation value.

[0128] (7) Storage performance test:

[0129] The capacity is measured at 25°C with a current of 0.33C and recorded as C0. The battery cells are then stored under high-temperature conditions of 60°C. After that, the battery cells are removed at 7-day intervals and their capacity is tested at room temperature, and recorded as C1, C2, ..., Cn. The number of days until Cn deteriorates to 80% of C0 is recorded as the storage capacity evaluation criterion.

[0130] For the manufacturing parameters of the negative electrode sheets in Examples 1 through 9, please refer to Tables 1 and 2, and for the performance test results of the negative electrode sheets in secondary lithium batteries, please refer to Table 3.

[0131] Table 1: Parameters of the negative electrode material selected to manufacture the negative electrode sheet in Examples 1 to 9 [Table 1]

[0132] Table 2: Material parameters of negative electrode sheets manufactured in Examples 1 to 9 [Table 2]

[0133] Table 3: Rapid charging performance, cyclic discharge performance, and storage performance of secondary lithium-ion batteries equipped with negative electrode sheets manufactured in Examples 1 to 9. [Table 3]

[0134] JPEG2026519677000020.jpg40170

[0135] JPEG2026519677000021.jpg56170

[0136] JPEG2026519677000022.jpg65170

[0137] Comparing the test results of Examples 1 to 5 and Examples 6 to 7, when the ratio S1 / S2 of the structural stability parameters of the first active material layer and the second active material layer material exceeds 10.0 in the negative electrode active material layer, the rapid charging performance, circulation performance, and storage performance of the secondary lithium-ion battery all further decrease. As shown in the test results, with increasing S1 / S2 in the negative electrode sheet, the rapid charging time to 80% SOC of the secondary lithium-ion battery increases further from a baseline of 15 minutes, the number of circulation cycles that maintain 80% capacity decreases further from a baseline of 1700 cycles, and the number of days that maintain 80% storage capacity also decreases further to less than 170 days.

[0138] JPEG2026519677000023.jpg56170

[0139] JPEG2026519677000024.jpg56170

[0140] JPEG2026519677000025.jpg56170

[0141] The embodiments described above are illustrative in illustrating the principles and effects of the present invention and do not limit the invention. Anyone familiar with the art can modify or change the embodiments described above without departing from the spirit and scope of the invention. Accordingly, all equivalent modifications or changes completed by a person ordinary in the art without departing from the spirit and technical idea disclosed herein should still be incorporated into the claims of the invention. [Explanation of Symbols]

[0142] 100: Current collector 200: Negative electrode active material layer 210: First active material layer 220: Second active material layer.

Claims

1. Current collector and, A negative electrode active material layer is located on at least one surface of the current collector and includes a first active material layer and a second active material layer, wherein the first and second active material layers are stacked and installed in a direction toward the current collector. Of these, the ratio S of the structural stability parameters of the first active material layer and the second active material layer １ / S ２ A negative electrode sheet characterized by satisfying the range of 0.01 to 10.

0.

2. The negative electrode sheet according to claim 1, characterized in that the negative electrode material in the negative electrode active material layer includes a graphite material.

3. The ratio S of the structural stability parameters of the first active material layer and the second active material layer. １ / S ２ The negative electrode sheet according to claim 1, characterized in that it satisfies 0.1 to 5.

0.

4. Structural stability parameter S of the first active material layer １ The negative electrode sheet according to claim 1, characterized in that the value is 3 to 16.

5.

6.

7. The press density of the negative electrode active material layer is 1.65 to 1.75 g / cm³. ３ The negative electrode sheet according to claim 1, characterized in that it is the same as the one described in claim 1.

8. A method for manufacturing a negative electrode sheet according to any one of claims 1 to 7, The first negative electrode material is mixed with a binder, a conductive agent, and a thickener to form a slurry, thereby obtaining a first active material layer slurry. The second negative electrode material is mixed with a binder, a conductive agent, and a thickener to form a slurry, thereby obtaining a second active material layer slurry. The method includes sequentially applying the second active material layer slurry and the first active material layer slurry to at least one surface of the current collector, followed by drying, pressing, die-cutting, and punching to obtain a negative electrode sheet, A method for manufacturing a negative electrode sheet, characterized in that the hardness of the first negative electrode material is higher than the hardness of the second negative electrode material.

9. The ratio S of the structural stability parameters of the first anode material and the second anode material. １ / S ２ The method for manufacturing a negative electrode sheet according to claim 8, characterized in that the value satisfies 0.01 to 10.

0.

10. The method for manufacturing a negative electrode sheet according to claim 8, characterized in that the average particle size Dv50 of the first negative electrode material is 11 to 17 μm, and the average particle size Dv50 of the second negative electrode material is 16 to 19 μm.

11. An electrochemical apparatus characterized by comprising a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet according to any one of claims 1 to 7.

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