Negative electrode material, negative electrode slurry, negative electrode sheet and preparation method thereof, and lithium ion battery

Abstract

A negative electrode material, negative electrode slurry, negative electrode sheet, preparation method, and lithium-ion battery belong to the field of battery technology. The negative electrode material includes graphite secondary particles and silicon negative electrode particles. The particle size distribution of the graphite secondary particles is 10μm < D10 < 12μm, 15μm < D50 < 17μm, and 35μm < D90 < 37μm. The particle size distribution of the silicon negative electrode particles is 5μm < D10 < 6μm, 8μm < D50 < 10.5μm, and 15μm < D90 < 17μm. The negative electrode sheet is formed by coating the negative electrode slurry including the negative electrode material on a carbon-coated current collector. This improves the negative electrode sheet's resistance to expansion and deformation, as well as the bonding stability between the negative electrode coating and the carbon-coated current collector, thereby increasing the cycle life of the lithium-ion battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to negative electrode materials, negative electrode slurries, negative electrode sheets, preparation methods, and lithium-ion batteries. Background Art

[0002] Lithium-ion secondary batteries, with their advantages of high voltage, low self-discharge, lack of memory effect, light weight, and compact size, have attracted considerable attention and are widely used in various fields. Graphite anode materials, with their limited theoretical capacity, have been widely used, while silicon-based anode materials, with their significant high capacity, have become a research hotspot and are gradually moving from laboratory research to commercial application.

[0003] However, silicon-based composite materials experience significant expansion and contraction during long-term cycling, leading to particle breakage and further electrolyte consumption, resulting in low cycle retention. Furthermore, the significant volume expansion of the negative electrode can disrupt the conductive network within the electrode, causing separation between the coating and the current collector, increasing electrode resistance and reducing battery cycle life. Summary of the Invention

[0004] Based on the above-mentioned deficiencies, the present application provides a negative electrode material, a negative electrode slurry, a negative electrode sheet, a preparation method and a lithium-ion battery to partially or completely improve the problem of low cycle life of batteries in the related art.

[0005] This application is implemented as follows:

[0006] In a first aspect, an example of the present application provides a negative electrode material, comprising:

[0007] A mixture of graphite secondary particles and silicon negative electrode particles; the graphite secondary particles are formed by mixing graphite primary particles; the silicon negative electrode particles include at least one of silicon oxide particles and single crystal silicon particles; the particle size distribution of the graphite secondary particles is 10μm<D10<12μm, 15μm<D50<17μm, 35μm<D90<37μm; the particle size distribution of the silicon negative electrode particles is 5μm<D10<6μm, 8μm<D50<10.5μm, 15μm<D90<17μm.

[0008] In the above implementation process, a mixture of graphite secondary particles and silicon negative electrode particles is used as the negative electrode material. Compared with a pure graphite negative electrode, it has a higher specific capacity and can improve the energy density of a lithium-ion battery including a negative electrode prepared from the negative electrode material.

[0009] Furthermore, the negative electrode material is formed by mixing graphite secondary particles with a particle size distribution of 10μm < D10 < 12μm, 15μm < D50 < 17μm, and 35μm < D90 < 37μm with silicon anode particles with a particle size distribution of 5μm < D10 < 6μm, 8μm < D50 < 10.5μm, and 15μm < D90 < 17μm. The secondary graphite particles have high isotropy and less volume expansion. The larger secondary particle size ensures that larger gaps can be formed between the particles, which can accommodate the volume expansion of the smaller silicon anode particles. Furthermore, the silicon anode particles in this particle size range can appropriately reduce their own volume expansion and make them more easily dispersed in the gaps between the graphite secondary particles. This prevents the expansion of the silicon anode particles from affecting the overall expansion of the formed negative electrode sheet, thereby improving the cycle life of the corresponding battery including the negative electrode sheet.

[0010] In combination with the first aspect, in a first possible implementation manner of the first aspect of the present application, the mass percentage of the silicon negative electrode particles in the mixture does not exceed 20%.

[0011] In combination with the first aspect, in a second possible implementation manner of the first aspect of the present application, in the mixture, the mass ratio of the silicon negative electrode particles to the graphite secondary particles is 1:4-9.

[0012] In the above implementation process, adding silicon negative electrode materials such as silicon oxide or single crystal silicon in an appropriate mass proportion to the mixture forming the negative electrode material can greatly improve the specific capacity. At the same time, the secondary graphite particles in the mixture can also effectively accommodate the volume expansion of the silicon negative electrode material, thereby avoiding the destruction of the internal conductive network of the negative electrode sheet obtained from the negative electrode material, the increase of the electrode sheet resistance and the reduction of the battery cycle life.

[0013] By mixing silicon negative electrode particles of a specific particle size with graphite secondary particles in a mass ratio of 1:4-9 to form a mixture, the expansion rate of the prepared negative electrode sheet can be further reduced.

[0014] In a second aspect, an example of the present application provides a negative electrode slurry, comprising: the negative electrode material provided in the first aspect, a conductive agent, and a binder.

[0015] In the above implementation process, the negative electrode slurry formed by the negative electrode material, conductive agent and binder provided by the first aspect, since the negative electrode material includes graphite secondary particles and silicon negative electrode particles of a specific particle size, the graphite secondary particles can provide reserved space for the expansion of the silicon negative electrode particles, thereby reducing the expansion rate of the negative electrode sheet formed by the negative electrode slurry.

[0016] Adding a conductive agent to the negative electrode slurry can increase the conductivity of the negative electrode coating formed after coating, and adding a binder to the negative electrode slurry can effectively disperse the various particle components while also improving the adhesion of the negative electrode slurry, making the coating formed after coating more stable.

[0017] In combination with the second aspect, in a first possible implementation of the second aspect of the present application, the conductive agent is selected from at least one of conductive carbon black, acetylene black, superconducting carbon black, graphene, conductive graphite, carbon fiber or carbon nanotubes.

[0018] In combination with the second aspect, in a first possible implementation of the second aspect of the present application, the binder is selected from at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose or polyacrylic acid.

[0019] In the above implementation process, conductive carbon black, acetylene black, superconducting carbon black, graphene, conductive graphite, carbon fiber and carbon nanotubes have good conductivity, and materials such as carbon fiber and carbon nanotubes also have a high aspect ratio, which can form a long-range conductive connection skeleton before and after the silicon negative electrode material shrinks, thereby improving the stability of continuous conduction.

[0020] Binders such as styrene-butadiene rubber, sodium carboxymethyl cellulose or polyacrylic acid can more evenly disperse the negative electrode material and conductive agent in the negative electrode slurry, so that a more stable and uniform negative electrode coating can be formed when the negative electrode material adheres to the current collector.

[0021] In a third aspect, an example of the present application provides a method for preparing a negative electrode sheet, comprising:

[0022] The negative electrode slurry provided in the second aspect is coated on the current collector.

[0023] In the above implementation process, the negative electrode slurry provided in the second aspect is applied to the current collector, forming a coating containing a conductive material on the current collector. Because the conductive material contains graphite secondary particles and silicon negative electrode particles of a specific particle size, it can increase the specific capacity of the electrode sheet while reducing the expansibility of the prepared negative electrode sheet. Applying the negative electrode slurry to the current collector to prepare the negative electrode sheet is simple.

[0024] In combination with the third aspect, in a first possible implementation of the third aspect of the present application, the negative electrode slurry provided by the second aspect is coated on a carbon-coated current collector;

[0025] Optionally, the carbon-coated current collector is a carbon-coated copper foil.

[0026] In the aforementioned implementation process, the negative electrode slurry is applied to a carbon-coated current collector. The surface of the carbon-coated current collector, such as carbon-coated copper foil, has a soft carbon layer with good flexibility and conductivity. Upon contact with the silicon negative electrode particles, the carbon layer on the surface of the carbon-coated current collector deforms to better encapsulate the silicon negative electrode particles. This prevents poor contact with the copper foil current collector after the silicon negative electrode particles undergo significant volume expansion, reduces the chance of the coating detaching from the current collector, and thereby improves the cycle life of the corresponding battery.

[0027] In a fourth aspect, an example of the present application provides a negative electrode sheet prepared according to the method for preparing a negative electrode sheet provided in the third aspect.

[0028] In a fifth aspect, an example of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer; the negative electrode material in the negative electrode active material layer is the negative electrode material provided in the first aspect.

[0029] In the above-mentioned implementation process, the negative electrode sheet prepared by the preparation method provided by the third aspect or the negative electrode active material layer in the negative electrode sheet is formed by the negative electrode material provided by the first aspect. Since the conductive material contains graphite secondary particles and silicon negative electrode particles with a specific particle size distribution, it can increase the specific capacity of the electrode sheet while reducing the expansibility of the prepared negative electrode sheet.

[0030] In a sixth aspect, an example of the present application provides a lithium-ion battery, comprising:

[0031] The fourth aspect or the fifth aspect provides a negative electrode sheet, a positive electrode sheet, a separator and an electrolyte; the separator is located between the positive electrode sheet and the negative electrode sheet, and the electrolyte infiltrates the positive electrode sheet, the negative electrode sheet and the separator.

[0032] In the above implementation process, since the negative electrode sheet provided by the fourth aspect is prepared from a mixture of graphite secondary particles of a specific particle size and silicon negative electrode particles, the silicon negative electrode particles can increase the capacity of the electrode sheet, and the graphite secondary particles can provide reserved space for the expansion of the silicon negative electrode particles, which can increase the specific capacity of the negative electrode sheet while reducing the expansion rate of the negative electrode sheet, thereby improving the energy density and cycle life of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art.

[0034] Figure 1 Schematic diagram of the structure of the negative electrode material provided for the example of this application;

[0035] Figure 2 Schematic diagram of the structure of the negative electrode sheet provided for this application example.

[0036] Icon: 1-graphite secondary particles; 2-silicon anode particles; 3-copper foil; 4-carbon layer. DETAILED DESCRIPTION

[0037] The embodiments of the present application will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present application and should not be construed as limiting the scope of the present application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall prevail.

[0038] The following is a detailed description of the negative electrode material, negative electrode slurry, negative electrode sheet, preparation method, and lithium-ion battery provided in the examples of this application:

[0039] Lithium-ion secondary batteries, with their advantages of high voltage, low self-discharge, no memory effect, light weight, and compact size, have attracted considerable attention and are widely used in various fields. Graphite anode materials, with their limited theoretical capacity, have been widely used. Silicon-based anode materials (silicon oxide or silicon materials), however, have become a research hotspot due to their significant high capacity advantages and are gradually moving from laboratory research to commercial application.

[0040] However, silicon-based composite negative electrodes experience significant expansion and contraction during long-term cycling, leading to particle breakage and further electrolyte consumption, resulting in low cycle retention. Furthermore, the significant volume expansion of the negative electrode can disrupt the conductive network within the electrode, causing separation between the coating and the current collector, increasing electrode resistance and reducing battery cycle life.

[0041] Based on this, see Figure 1 The inventors provide a negative electrode material, which includes a mixture of graphite secondary particles 1 and silicon negative electrode particles 2. The graphite secondary particles 1 are formed by mixing graphite primary particles, and the silicon negative electrode particles 2 include at least one of silicon oxide particles and single crystal silicon particles.

[0042] The particle size distribution of the graphite secondary particles 1 is 10 μm < D10 < 12 μm, 15 μm < D50 < 17 μm, and 35 μm < D90 < 37 μm, and the particle size distribution of the silicon negative electrode particles 2 is 5 μm < D10 < 6 μm, 8 μm < D50 < 10.5 μm, and 15 μm < D90 < 17 μm.

[0043] The negative electrode material is formed by mixing graphite secondary particles 1 having a particle size distribution of 10μm < D10 < 12μm, 15μm < D50 < 17μm, and 35μm < D90 < 37μm, and silicon negative electrode particles 2 having a particle size distribution of 5μm < D10 < 6μm, 8μm < D50 < 10.5μm, and 15μm < D90 < 17μm. The graphite particles in the secondary particle shape have high isotropy and reduced volume expansion. The larger secondary particle size ensures that larger gaps can be formed between the particles, which can accommodate the volume expansion of the smaller silicon negative electrode particles 2. Furthermore, the silicon negative electrode particles 2 within the above particle size range can appropriately reduce their own volume expansion while being more easily dispersed in the gaps between the graphite secondary particles 1. This prevents the expansion of the silicon negative electrode particles 2 from affecting the overall expansion of the formed negative electrode sheet, thereby improving the cycle life of the corresponding battery including the negative electrode sheet.

[0044] See also Figure 1 The negative electrode material includes a mixture of graphite secondary particles 1 and silicon negative electrode particles 2.

[0045] The particle size distribution D10, D50 and D90 of the graphite secondary particles 1 refer to the particle sizes corresponding to when the cumulative particle size distribution percentages reach 10%, 50% and 90%, respectively.

[0046] Illustratively, the particle size distribution of the graphite secondary particles is D10=10 μm, D50=15 μm, and D90=35.

[0047] For example, the particle size distribution of the graphite secondary particles is D10=12 μm, D50=15 μm, and D90=35.

[0048] For example, the particle size distribution of the graphite secondary particles is D10=11 μm, D50=17 μm, and D90=35.

[0049] For example, the particle size distribution of the graphite secondary particles is D10=11 μm, D50=16 μm, and D90=37.

[0050] Furthermore, the present application does not limit the specific preparation form of the graphite secondary particles 1. In some possible embodiments, the graphite primary particles are granulated to obtain the graphite secondary particles 1 formed by mixing the graphite primary particles.

[0051] The particle size distributions D10, D50 and D90 of the silicon negative electrode particles 2 refer to the particle sizes corresponding to the cumulative particle size distribution percentages reaching 10%, 50% and 90%, respectively.

[0052] Exemplarily, the mixture includes silicon negative electrode particles 2 with D10=5.5 μm, D50=9.5 μm and D90=16 μm and graphite secondary particles 1 with a particle size distribution of D10=11 μm, D50=16 μm and D90=36 μm.

[0053] Furthermore, the present application does not limit the specific material of the silicon negative electrode particles 2. In some possible embodiments, the silicon negative electrode particles 2 are silicon oxide particles or silicon particles. Exemplarily, the silicon negative electrode particles 2 include both silicon monoxide particles and silicon particles. Exemplarily, the silicon negative electrode particles 2 are silicon monoxide particles; or the silicon negative electrode particles 2 are silicon material.

[0054] Furthermore, the present application does not limit the specific addition ratio of the silicon negative electrode particles 2 and the graphite secondary particles 1 in the mixture. Relevant personnel can make corresponding adjustments as needed on the premise of ensuring that the graphite secondary particles 1 of the added particle size can form a certain space to accommodate the volume expansion of the silicon negative electrode particles 2 of the added particle size.

[0055] In some possible implementations, the mass percentage of the silicon negative electrode particles 2 in the mixture does not exceed 20%.

[0056] Exemplarily, in the mixture, the mass ratio of the silicon negative electrode particles 2 to the graphite secondary particles 1 is 1:9.

[0057] Furthermore, the silicon negative electrode particles 2 (D10=5.5 μm, D50=9.5 μm, D90=16 μm) and the graphite secondary particles 1 (D10=11 μm, D50=16 μm, D90=36 μm) were uniformly mixed in a mass ratio of 1:9.

[0058] The present application also provides a method for preparing a negative electrode sheet, including:

[0059] The negative electrode slurry is coated on the current collector.

[0060] The negative electrode slurry includes the negative electrode material provided in the example of this application, a conductive agent and a binder.

[0061] The negative electrode material provided in the first aspect is combined with a conductive agent and a binder to form a negative electrode slurry, which can make the components in the negative electrode slurry more evenly dispersed, and improve the conductivity, specific capacity and resistance to volume expansion of the negative electrode sheet formed after the negative electrode slurry is coated on the current collector.

[0062] The present application does not limit the specific type of the conductive agent. In some possible embodiments, the conductive agent is selected from at least one of conductive carbon black, acetylene black, superconducting carbon black, graphene, conductive graphite, carbon fiber or carbon nanotubes.

[0063] Exemplarily, the conductive agent is selected from superconducting carbon black and carbon nanotubes.

[0064] Furthermore, the present application does not limit the specific type of the binder. In some possible embodiments, the binder is selected from at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, or polyacrylic acid.

[0065] Exemplarily, the negative electrode slurry includes silicon negative electrode particles 2 (D10=5.5μm, D50=9.5μm and D90=16μm), graphite secondary particles 1 (D10=11μm, D50=16μm and D90=36μm), conductive agents of superconducting carbon black and carbon nanotubes, and binders of sodium carboxymethyl cellulose and styrene-butadiene rubber.

[0066] Furthermore, the present application does not limit the specific addition ratio of the negative electrode material, the conductive agent and the binder in the negative electrode slurry. For example, the silicon negative electrode particles 2 (D10 = 5.5 μm, D50 = 9.5 μm and D90 = 16 μm) and the graphite secondary particles 1 (D10 = 11 μm, D50 = 16 μm and D90 = 36 μm) are uniformly mixed in a mass ratio of 1:9, and then uniformly mixed with superconducting carbon black, carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 94.5:1.2:0.3:1.5:2.5 to form a negative electrode slurry.

[0067] Furthermore, the present application does not limit the specific form of the current collector. In some possible implementations, the negative electrode slurry can be coated on a carbon-coated current collector.

[0068] For example, the negative electrode slurry may be coated on a carbon-coated copper foil to form a negative electrode sheet.

[0069] See also Figure 2 The negative electrode slurry provided in this example is coated on a carbon-coated copper foil. The surface of the copper foil 3 has a soft carbon layer 4, which has good flexibility and conductivity. After the silicon negative electrode particles 2 in the negative electrode material come into contact with the carbon layer 4, the carbon layer 4 can produce a certain deformation, which can better wrap the silicon negative electrode particles 2, thereby preventing the silicon negative electrode particles 2 from having poor contact with the copper foil 3 after a large volume expansion, thereby increasing the contact internal resistance.

[0070] After the negative electrode slurry is coated on the carbon-coated current collector, it is then dried, cold pressed and cut to obtain the negative electrode sheet.

[0071] The above-described method for preparing a negative electrode sheet provides a negative electrode sheet. The silicon negative electrode particles 2 in the negative electrode sheet increase the specific capacity of the negative electrode sheet, and the graphite secondary particles 1 of a specific particle size provide space for the silicon negative electrode particles 2 of a specific particle size to expand in volume, thereby improving the negative electrode sheet's resistance to volume expansion and deformation. Furthermore, the negative electrode slurry is coated on a carbon-coated copper foil to form the negative electrode sheet. The carbon layer 4 on the surface of the carbon-coated copper foil has good flexibility and is deformable, better encapsulating the silicon negative electrode particles 2. This prevents the silicon negative electrode particles 2 from falling off the current collector due to poor contact with the current collector after volume expansion, further improving the structural stability and electrical performance of the negative electrode sheet, and thereby increasing the cycle life of the lithium-ion battery containing the negative electrode sheet.

[0072] The example of the present application also provides a lithium-ion battery, including the negative electrode sheet, positive electrode sheet, separator and electrolyte provided in the example of the present application.

[0073] The lithium-ion battery includes the negative electrode sheet provided in this example. The negative electrode sheet contains a certain proportion of graphite secondary particles 1 and silicon negative electrode particles 2. It has good physical properties such as resistance to expansion and deformation and anti-shedding ability, as well as electrical properties such as large specific capacity, which makes the lithium-ion battery have a good cycle life.

[0074] In some possible implementations, the positive electrode sheet is formed by coating the positive electrode slurry on the positive electrode current collector.

[0075] Exemplarily, a positive electrode slurry containing a positive electrode active material is coated on an aluminum foil to form a positive electrode sheet.

[0076] Furthermore, the positive electrode slurry includes positive electrode active materials such as lithium nickel cobalt manganese, lithium cobalt oxide, lithium nickel oxide or lithium manganese oxide, conductive agents such as graphite, acetylene black or carbon fiber, and binders such as polyvinylidene fluoride, polytetrafluoroethylene or styrene butadiene rubber.

[0077] The present application does not limit the specific material of the diaphragm, and the diaphragm can be a conventional commercial lithium-ion battery separator.

[0078] Exemplarily, the separator is a polyethylene separator and a polypropylene separator.

[0079] The present application does not limit the specific configuration of the electrolyte, and relevant personnel can make corresponding choices according to needs. The electrolyte can be a conventional commercial lithium-ion battery electrolyte.

[0080] The electrolyte of lithium-ion batteries is mainly composed of three parts: solvent, lithium salt and additives; the solvent is usually a mixture of cyclic carbonate solvents (such as ethylene carbonate, propylene carbonate, etc.) and linear carbonate solvents (such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.); lithium salts generally use lithium hexafluorophosphate (LiPF6), lithium tetrafluorophosphate (LiPF4), etc. as conductive salts.

[0081] Furthermore, the examples of the present application also provide a method for preparing a lithium-ion battery, including: preparing a negative electrode sheet, preparing a positive electrode sheet and assembling a battery cell.

[0082] Among them, the battery cell assembly includes: placing the separator between the positive electrode sheet and the negative electrode sheet, and preparing the bare battery cell by winding; making a packaging bag with an aluminum-plastic film composite material, placing the bare battery cell in the packaging bag and packaging it to obtain a dry battery cell; the dry battery cell is subjected to baking to remove water, liquid injection, sealing, standing, formation, degassing packaging and capacity division processes to obtain a lithium-ion battery.

[0083] The negative electrode material, negative electrode slurry, negative electrode sheet, preparation method and lithium-ion battery of the present application are further described in detail below with reference to the embodiments.

[0084] Example 1

[0085] Example 1 provides a lithium ion battery, which is prepared by the following method:

[0086] (1) Preparation of negative electrode sheet

[0087] Silica particles (D10 = 5.5 μm, D50 = 9.5 μm, and D90 = 16 μm) and secondary graphite particles (D10 = 11 μm, D50 = 16 μm, and D90 = 36 μm) were uniformly mixed in a mass ratio of 1:9. The mixture was then mixed with superconducting carbon black, carbon nanotubes, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 94.5:1.2:0.3:1.5:2.5 to form a negative electrode slurry. The negative electrode slurry was evenly coated on both sides of a carbon-coated copper foil (8 μm thick), then dried, cold-pressed, and slit to produce negative electrode sheets. The initial thickness and peak compaction density of the negative electrode sheets were measured.

[0088] (2) Preparation of positive electrode sheet

[0089] The positive electrode active material lithium nickel cobalt manganese (LiNi 0.8 Co 0.1 Mn 0.1 O2) is mixed with superconducting carbon black, carbon nanotubes, and polytetrafluoroethylene in a mass ratio of 96.8:1.5:0.5:1.2 to form a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of aluminum foil (12μm thick), then dried, cold-pressed, and slit to produce positive electrode sheets.

[0090] (3) Battery cell assembly

[0091] The separator is placed between the negative electrode sheet obtained in step (1) and the positive electrode sheet obtained in step (2), and a bare cell is prepared by winding; a packaging bag is made of an aluminum-plastic film composite material, and the bare cell is placed in the packaging bag and packaged to obtain a dry cell; the dry cell is baked to remove water, injected with liquid, sealed, allowed to stand, formed, degassed, packaged, and volume-divided to obtain a lithium-ion battery.

[0092] Example 2

[0093] Example 2 provides a lithium ion battery, which differs from Example 1 in that:

[0094] In step (1), the negative electrode slurry is evenly coated on both sides of the copper foil 3 (the thickness of the copper foil 3 is 8 μm), and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0095] Comparative Example 1

[0096] Comparative Example 1 provides a lithium ion battery, which differs from Example 1 in that:

[0097] In step (1), the particle sizes of the silicon oxide particles are D10=7 μm, D50=12 μm and D90=18 μm.

[0098] Comparative Example 2

[0099] Comparative Example 2 provides a lithium ion battery, which differs from Example 1 in that:

[0100] In step (1), the particle sizes of the silicon oxide particles are D10=4 μm, D50=6 μm and D90=13 μm.

[0101] Comparative Example 3

[0102] Comparative Example 3 provides a lithium ion battery, which differs from Example 1 in that:

[0103] In step (1), the particle sizes of the graphite secondary particles are D10=6 μm, D50=12 μm and D90=21 μm.

[0104] Comparative Example 4

[0105] Comparative Example 4 provides a lithium ion battery, which differs from Example 1 in that:

[0106] In step (1), the particle sizes of the graphite secondary particles are D10=15 μm, D50=20 μm and D90=45 μm.

[0107] Experimental example

[0108] (1) The lithium-ion batteries provided in Examples 1 and 2, and Comparative Examples 1 to 4, were tested for first-cycle efficiency, negative electrode sheet full-charge expansion rate (the expansion rate was calculated based on the full-charge thickness of the negative electrode sheet after the lithium-ion battery was fully charged and the initial thickness of the negative electrode sheet), and cycle life.

[0109] (2) The negative electrode sheets of the lithium ion batteries provided in Examples 1 and 2, and Comparative Examples 1 to 4 after cycling were tested to determine the degree of separation between the negative electrode coating and the current collector in the negative electrode sheets.

[0110] The test results are shown in Table 1.

[0111] Table 1

[0112]

[0113] Analysis of results: Combining the data of Example 1 and Comparative Example 1, it can be seen that when the particle size of the silicon negative electrode particles is outside the particle size range of 5μm<D10<6μm, 8μm<D50<10.5μm and 15μm<D90<17μm (in Comparative Example 1, the particle size of the silicon oxide particles is D10=7μm, D50=12μm and D90=18μm), the full-charge expansion rate of the negative electrode sheet is large, and the cycle life of the obtained lithium-ion battery is low.

[0114] Combining the data of Example 1 and Comparative Example 3, it can be seen that when the particle size distribution of the graphite secondary particles is other than 10μm<D10<12μm, 15μm<D50<17μm, 35μm<D90<37μm (in Comparative Example 3, the particle size of the graphite secondary particles is D10=6μm, D50=12μm and D90=21μm), the full charge expansion rate of the negative electrode sheet is large, and the cycle life of the obtained lithium-ion battery is low.

[0115] In combination with Example 1 and Comparative Examples 3 and 4, when the particle size of the graphite secondary particles is greater than or less than the limits of this application of 10μm<D10<12μm, 15μm<D50<17μm, 35μm<D90<37μm, the electrode expansion rate is large and the cycle life is low.

[0116] Combining the data of Example 1 and Example 2, it can be seen that applying the negative electrode slurry provided in this application on a carbon-coated current collector such as carbon-coated copper foil can prevent the negative electrode coating from falling off the current collector, which can further increase the cycle life of the lithium-ion battery.

[0117] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A negative electrode material, characterized in that include: A mixture of graphite secondary particles and silicon negative electrode particles; the graphite secondary particles are formed by mixing graphite primary particles; the silicon negative electrode particles include at least one of silicon oxide particles and single crystal silicon particles; the particle size distribution of the graphite secondary particles is 10μm<D10<12μm, 15μm<D50<17μm, 35μm<D90<37μm; the particle size distribution of the silicon negative electrode particles is 5μm<D10<6μm, 8μm<D50<10.5μm, 15μm<D90<17μm; in the mixture, the mass ratio of the silicon negative electrode particles to the graphite secondary particles is 1:4-9.

2. A negative electrode slurry, characterized in that: include: The negative electrode material, conductive agent and binder according to claim 1.

3. The negative electrode slurry according to claim 2, characterized in that The conductive agent is selected from at least one of conductive carbon black, acetylene black, superconducting carbon black, graphene, conductive graphite, carbon fiber or carbon nanotubes; The binder is selected from at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose or polyacrylic acid.

4. A method for preparing a negative electrode sheet, characterized in that: include: The negative electrode slurry according to claim 2 or 3 is coated on a current collector.

5. The method for preparing a negative electrode sheet according to claim 4, wherein: The current collector is a carbon-coated current collector.

6. The method for preparing a negative electrode sheet according to claim 5, wherein: The carbon-coated current collector is a carbon-coated copper foil.

7. A negative electrode sheet, characterized in that: The negative electrode sheet is prepared according to the method for preparing the negative electrode sheet according to any one of claims 4 to 6.

8. A negative electrode sheet, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer comprises the negative electrode material according to claim 1 .

9. A lithium-ion battery, characterized in that: include: The negative electrode sheet, positive electrode sheet, separator and electrolyte according to claim 7 or 8, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the electrolyte infiltrates the positive electrode sheet, the negative electrode sheet and the separator.

Images