Silicon-based negative electrode material and preparation method therefor, and lithium-ion battery

Abstract

A silicon-based negative electrode material and a preparation method therefor, and a lithium-ion battery. The silicon-based negative electrode material comprises a silicon material, a first shell layer coating the surface of the silicon material, and a second shell layer coating the surface of the first shell layer, wherein the first shell layer comprises an electrically conductive material, which has gaps; and the second shell layer comprises carbon. By means of forming a passion fruit-like structure having a silicon active material, a hollow electrically conductive network and a carbon shell, the problem of a short cycle life caused by the volume expansion of a silicon-based material is alleviated, and electron transfer inside a silicon-based composite material with a hollow carbon shell is effectively improved, thereby increasing the electrical conductivity and the number of cycles of a battery prepared from the silicon-based negative electrode material. By means of controlling the decomposition of a carbon source, the preparation method realizes multi-layer coating on a silicon-based material, and the process is simple and controllable, which is conducive to green, safe and large-scale production.

Description

Silicon-based negative electrode material, preparation method, and lithium-ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number 202311777795.2 filed with the Patent Office of China on December 21, 2023, entitled “A silicon-based negative electrode material, preparation method and lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present disclosure belongs to the technical field of battery materials, and particularly relates to a silicon-based negative electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0004] Silicon-based materials have the advantages of high specific capacity, abundant reserves, low price, and environmental friendliness. Its theoretical specific capacity is as high as 4200mAh·g -1 , the discharge platform is ~0.4V vs.Li / Li + , it will not generate lithium dendrites and can also ensure the operating voltage of the entire battery. Therefore, silicon-based materials are the next generation of high-energy density negative electrode materials with the greatest potential to replace the current graphite negative electrode.

[0005] However, during the cycling process of silicon-based materials, lithium insertion and delithiation will cause a huge volume expansion (300%), leading to material pulverization. During the cycling process, the solid electrolyte membrane (SEI membrane) collapses and reconstructs, the electrode structure collapses, and the electron transfer resistance between active materials and between active materials and current collectors increases. At the same time, the electrical conductivity of silicon-based materials is also low. These factors lead to severe capacity decay and poor cycle life of silicon-based negative electrode materials. Therefore, improving the initial efficiency and cycle life of silicon-based materials is the key to the commercial application of silicon-based materials. Summary of the Invention

[0006] The present disclosure provides a silicon-based negative electrode material, comprising a silicon material, a first shell layer coated on the surface of the silicon material, and a second shell layer coated on the surface of the first shell layer; the first shell layer comprises a conductive material having gaps; and the second shell layer comprises carbon.

[0007] In some embodiments, the mass ratio of the silicon material, the first shell layer, and the second shell layer is (60-80): (5-10): (10-20).

[0008] In some embodiments, the silicon material is selected from at least one of silicon, silicon-carbon alloy, or silicon-oxygen compound.

[0009] In some embodiments, the particle size of the silicon material is 0.02-5 μm.

[0010] In some embodiments, the thickness of the first shell layer is 0.2-5 μm.

[0011] In some embodiments, the thickness of the second shell layer is 0.5-2 μm.

[0012] In some embodiments, the porosity of the first shell layer is 60-90%.

[0013] In some embodiments, the conductive material includes one or more of Super P, acetylene black, or carbon nanotubes.

[0014] In another aspect, the present disclosure provides a method for preparing a silicon-based negative electrode material, comprising the following steps:

[0015] A silicon source, an organic solvent, a conductive agent, a dispersant, and a surfactant are mixed and reacted to solidify to obtain a dispersant / conductive agent-coated silicon material, which is denoted as Si@dispersant / CC.

[0016] The carbon source is mixed with the Si@dispersant / CC, and the mixture is reacted and solidified to obtain Si@dispersant / CC coated with the carbon source, which is recorded as Si@dispersant / CC@carbon source;

[0017] The Si@dispersant / CC@carbon source is heat-treated to remove the dispersant, which is recorded as Si@void / CC@carbon source;

[0018] The Si@void / CC@carbon source is sintered to obtain the silicon-based negative electrode material, which is recorded as Si@void / CC@C.

[0019] In some embodiments, the organic solvent comprises dimethyl sulfoxide or dimethylformamide.

[0020] In some embodiments, the conductive agent includes one or more of Super P, acetylene black AB, or carbon nanotubes.

[0021] In some embodiments, the dispersant includes one or more of polymethyl methacrylate and polyethyl methacrylate.

[0022] In some embodiments, the surfactant includes one or more of polyethylene glycol octylphenyl ether, alkylphenol polyoxyethylene ether, or fatty alcohol polyoxyethylene ether.

[0023] In some embodiments, the carbon source comprises one or more of polyvinyl alcohol, asphalt, monosaccharide, disaccharide, polysaccharide, saccharide derivatives, polyimide, polyacrylonitrile, polystyrene, polydivinylbenzene, polypyrrole, polythiophene, and polyaniline.

[0024] In some embodiments, the mass ratio of the silicon source: organic solvent: conductive agent: dispersant: surfactant is (5-10): (80-90): (0.5-2): (5-12): (0.01-0.1).

[0025] In some embodiments, the mass ratio of Si@dispersant / CC:carbon source is (1-5):(1-5).

[0026] In some embodiments, the heat treatment temperature is 200-250°C.

[0027] In some embodiments, the heating rate of the heat treatment is 1-5° C. / min.

[0028] In some embodiments, the heat treatment time is 4 to 12 hours.

[0029] In some embodiments, the sintering temperature is 800-1100°C.

[0030] In some embodiments, the heating rate of the sintering is 1-5° C. / min.

[0031] In some embodiments, the sintering time is 4 to 12 hours.

[0032] In some embodiments, the step of heat-treating the Si@dispersant / CC@carbon source to remove the dispersant comprises:

[0033] Treating Si@dispersant / CC@carbon source with a modifier to obtain Si@dispersant / CC@modified carbon source;

[0034] heat-treating the Si@dispersant / CC@modified carbon source to remove the dispersant;

[0035] Wherein, the modifier includes one or more of ammonium iodide, ammonium hydrogen phosphate or ammonium dihydrogen phosphate.

[0036] The present disclosure also provides a lithium-ion battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the silicon-based negative electrode material in any one of the above embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only represent the embodiments of the present disclosure by way of example, and the dimensional ratios in the drawings do not directly correspond to the actual ratios of the embodiments. At the same time, the following drawings only show certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope.

[0038] FIG1 is a SEM characterization diagram of the internal structure of the silicon-based negative electrode material provided in an embodiment of the present disclosure

[0039] FIG2 is a SEM characterization image of the surface structure of the silicon-based negative electrode material provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0040] The advantages of the embodiments in the application content will be explained in the embodiment section of the specification below, and some of them are obvious from the specification, or can be obtained through some embodiments of the embodiments of the present disclosure.

[0041] The technical solution of the present disclosure will be further described below with reference to the accompanying drawings and through some implementation methods.

[0042] In order to make the purpose, technical solutions and advantages of the present disclosure more clear, the present disclosure is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the embodiments described herein are only used to explain the present disclosure and are not intended to limit the present disclosure. In addition, the technical features involved in the various embodiments of the present disclosure described below can be combined with each other as long as they do not conflict with each other. Without departing from the principles of the embodiments of the present disclosure, several improvements and modifications can be made, and these improvements and modifications are also considered to be within the scope of protection of the embodiments of the present disclosure.

[0043] The first embodiment of the present disclosure provides a silicon-based negative electrode material, including a silicon material, a first shell layer coated on the surface of the silicon material, and a second shell layer coated on the surface of the first shell layer; the first shell layer includes a conductive material, and the conductive material has gaps.

[0044] The present disclosure provides a silicon-based negative electrode material, which aims to improve the electrical performance of the negative electrode silicon-based material to meet the urgent demand for high energy density and high operating reliability in application environments such as portable electronic devices and electric vehicles.

[0045] In some embodiments, the second shell layer includes carbon; the mass ratio of the silicon material, the first shell layer, and the second shell layer is (60-80): (5-10): (10-20).

[0046] In some embodiments, the silicon material is selected from at least one of silicon, silicon-carbon alloy, or silicon-oxygen compound.

[0047] By carbon-coating silicon materials, the conductivity of silicon-based materials can be effectively improved, and the volume expansion of silicon-based materials can be suppressed. By designing a conductive network layer with gaps to vacuum-coat silicon particles, on the one hand, it helps the electron transfer between silicon particles and improves the initial efficiency of silicon-based materials. On the other hand, it can provide expansion space for silicon lithium insertion and delithiation, so that the external SEI film will not be damaged by silicon expansion, effectively improving battery life.

[0048] In some embodiments, the silicon material has a particle size of 0.02 to 5 μm. The silicon material may be spherical or a mass of small spheres. It is understood that the particle size of the silicon material (unit: μm) may be any one of 0.02, 0.1, 1, 2, 3, 4, or 5, or a range between any two values.

[0049] In some embodiments, the thickness of the first shell layer is 0.2 to 5 μm. It is understandable that the thickness of the first shell layer (unit: μm) can be any value among 0.2, 0.5, 1, 2, 3, 4, 5 or a range between any two values.

[0050] In some embodiments, the thickness of the second shell layer is 0.5-2 μm. It is understandable that the thickness of the second shell layer (unit: μm) can be any one of 0.5, 1, 1.5, 2 or a range between any two values.

[0051] In some embodiments, the porosity of the first shell layer is 60% to 90%. It is understood that the porosity of the first shell layer can be any one of 60%, 65%, 70%, 75%, 80%, 85%, and 90%, or a range between any two of these values. When the porosity of the first shell layer satisfies the aforementioned range, the first shell layer formed of the conductive material can effectively mitigate the expansion of the silicon-based material while ensuring good electrical conductivity.

[0052] In some embodiments, the conductive material includes one or more of Super P, acetylene black, or carbon nanotubes, wherein the carbon nanotubes can be single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0053] In another aspect, the present disclosure provides a method for preparing a silicon-based negative electrode material, comprising the following steps:

[0054] A silicon source, an organic solvent, a conductive agent, a dispersant, and a surfactant are mixed and reacted to solidify to obtain a dispersant / conductive agent-coated silicon material, which is denoted as Si@dispersant / CC.

[0055] The carbon source is mixed with Si@dispersant / CC, and the mixture is reacted and solidified to obtain Si@dispersant / CC coated with the carbon source, which is recorded as Si@dispersant / CC@carbon source;

[0056] Si@dispersant / CC@carbon source was heat-treated to remove the dispersant, and was recorded as Si@void / CC@carbon source;

[0057] The Si@void / CC@carbon source is sintered to obtain a silicon-based negative electrode material, which is denoted as Si@void / CC@C.

[0058] Generally, chemical vapor deposition, sacrificial SiO2 template method, etc. are usually used to prepare silicon-based negative electrode materials. The preparation method is complex, the yield is low, the cost is high, and the nano-silicon material is easy to agglomerate, which is not conducive to large-scale production. The preparation method provided in the embodiment of the present disclosure realizes multi-layer coating of silicon-based materials by performing step-by-step sintering and regulating the decomposition of the carbon source, and the process is simpler.

[0059] The silicon source may be a silicon material obtained by crushing high-purity silicon, a silicon material obtained by purifying photovoltaic silicon waste, or a silicon pellet synthesized in liquid or gas phase.

[0060] In some embodiments, the organic solvent includes dimethyl sulfoxide or dimethylformamide.

[0061] In some embodiments, the conductive agent includes one or more of Super P, acetylene black, or carbon nanotubes, wherein the carbon nanotubes can be single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0062] In some embodiments, the dispersant includes one or more of polymethyl methacrylate and polyethyl methacrylate.

[0063] In some embodiments, the surfactant includes one or more of polyethylene glycol octylphenyl ether, alkylphenol polyoxyethylene ether, or fatty alcohol polyoxyethylene ether.

[0064] In some embodiments, the carbon source comprises one or more of polyvinyl alcohol, asphalt, monosaccharides, disaccharides, polysaccharides, sugar derivatives, polyimide, polyacrylonitrile, polystyrene, polydivinylbenzene, polypyrrole, polythiophene, and polyaniline.

[0065] In some embodiments, the mass ratio of silicon source: organic solvent: conductive agent: dispersant: surfactant is (5-10): (80-90): (0.5-2): (5-12): (0.01-0.1).

[0066] In some embodiments, the mass ratio of Si@dispersant / CC:carbon source is (1-5):(1-5).

[0067] In some embodiments, the heat treatment temperature is 200-250°C. It can be understood that the heat treatment temperature value (unit: °C) can be any value among 200, 210, 220, 230, 240, 250 or a range between any two values.

[0068] In some embodiments, the sintering temperature is 800-1100°C. It can be understood that the sintering temperature (unit: °C) can be any one of 800, 850, 900, 950, 1000, 1050, 1100 or a range between any two values.

[0069] The heat treatment process is carried out in an air atmosphere at 200-250°C, reaching the decomposition temperature of the dispersant, but below the decomposition temperature of the carbon source. This allows the dispersant to decompose while preventing the carbon source from decomposing at the same time. The second sintering step is carried out in an inert gas atmosphere at 800-1100°C, decomposing the carbon source into carbon. This step-by-step process using different temperatures ensures that only the first shell layer forms a void structure.

[0070] In some embodiments, the heating rate of the heat treatment is 1 to 5°C / min. It can be understood that the heating rate of the heat treatment (unit: °C / min) can be any one of 1, 2, 3, 4, 5 or a range between any two values.

[0071] In some embodiments, the heat treatment time is 4 to 12 hours. It can be understood that the heat treatment time (unit: h) can be any one of 4, 6, 8, 10, 12 or a range between any two values.

[0072] In some embodiments, the sintering heating rate is 1-5°C / min. It is understandable that the sintering heating rate (unit: °C / min) can be any one of 1, 2, 3, 4, 5 or a range between any two values.

[0073] In some embodiments, the sintering time is 4 to 12 hours. It is understandable that the sintering time (unit: h) can be any one of 4, 6, 8, 10, 12 or a range between any two values.

[0074] When the heat treatment of Si@dispersant / CC@carbon source and the process parameters of Si@void / CC@carbon source meet the above-mentioned value ranges, especially the temperature and time control of heat treatment and sintering meet the above-mentioned value ranges, the decomposition of the dispersant in the material can be effectively controlled, and while forming relatively uniform gaps between the conductive materials, hollow spheres of carbon-coated conductive material are obtained, and the size of the spheres is between 10 and 50 μm.

[0075] In some embodiments, the step of heat-treating Si@dispersant / CC@carbon source to remove the dispersant comprises:

[0076] Treating Si@dispersant / CC@carbon source with a modifier to obtain Si@dispersant / CC@modified carbon source;

[0077] The Si@dispersant / CC@modified carbon source was thermally treated to remove the dispersant;

[0078] The modifier includes one or more of ammonium iodide, ammonium hydrogen phosphate, and ammonium dihydrogen phosphate.

[0079] Specifically, the preparation method provided in this embodiment can be achieved by the following steps:

[0080] S1. A silicon source, an organic solvent, a dispersant, a conductive agent, and a surfactant are mixed in a certain proportion, subjected to ultrasonic stirring for reaction, and then slowly added to deionized water for solidification. The resulting solid is then filtered and dried to obtain a dispersant / conductive additive-coated silicon material, denoted as Si@dispersant / CC.

[0081] S2. Slowly add the carbon source to deionized water and continue stirring until the carbon source is completely dissolved, wherein the mass ratio of carbon source to water is 1:9 to 1:3. Then, the above-mentioned Si@dispersant / CC and carbon source are mixed in deionized water in a ratio of 2-10%:2-10%:80-96%. The mixed solution is stirred and reacted at 25-45°C, and then added to a low-temperature methanol solution for solidification. After the mixed solution is filtered and dried, a carbon source-coated Si@dispersant / conductive agent is obtained, which is recorded as Si@dispersant / CC@carbon source.

[0082] S3. Place the Si@dispersant / CC@carbon source in an ammonium iodide solution and stir. Then, filter the solution with suction to obtain the Si@dispersant / CC@modified carbon source. Remove any iodine residue from the surface of the Si@dispersant / CC@modified carbon source with acetone and dry the solution. Subsequently, transfer the sample to a muffle furnace and heat-treat it in air. The dispersant is consumed during the heat treatment, resulting in a Si@void / CC@carbon source with a hollow structure.

[0083] S4. Move the Si@void / CC@ carbon source into a tube furnace and sinter it under the protection of an inert gas such as argon or nitrogen to obtain a silicon-based negative electrode material, which is recorded as Si@void / CC@C.

[0084] An embodiment of the present disclosure further provides a lithium-ion battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the silicon-based negative electrode material of any one of the above embodiments.

[0085] The battery provided by the present disclosure is described below with reference to specific embodiments:

[0086] Example 1

[0087] This embodiment provides a silicon-based negative electrode material, which is prepared by the following steps:

[0088] S1. Silicon particles, dimethyl sulfoxide (DMSO), polymethyl methacrylate (PMMA), carbon nanotubes, and Triton-x (polyethylene glycol octylphenyl ether) were mixed in a mass ratio of 8:82:8:1.5:0.5, with a silicon particle diameter of 0.1 μm. Ultrasonic stirring was performed at 60°C for 12 hours. The mixture was then slowly added to deionized water using ultrasonic spray for solidification. The resulting solid was then filtered and dried to obtain dispersant / conductive additive-coated silicon particles, designated Si@PMMA / CC.

[0089] S2. Slowly add polyvinyl alcohol (PVA) to hot deionized water and continue stirring until the PVA is completely dissolved, where the mass ratio of PVA to water is 15:85. Then, the above-mentioned Si@PMMA / CC and PVA are mixed in deionized water in a ratio of 5%:5%:90%. The mixed solution is stirred at 45°C for 12 hours and solidified in a 4°C methanol solution using an ultrasonic spray pump. After the mixed solution is filtered and dried, PVA-coated Si@PMMA / CC is obtained, which is recorded as Si@PMMA / CC@PVA.

[0090] S3. Si@PMMA / CC@PVA was placed in an ammonium iodide solution with stirring and reacted at 60°C for 4 hours. The mixture was then filtered to obtain Si@PMMA / CC@PVA-S. Any iodine residue on the surface of the Si@PMMA / CC@PVA-S was washed with acetone and dried. The sample was then transferred to a muffle furnace and heated at a rate of 5°C / min to 240°C. The temperature was maintained for 6 hours and the sample was heat-treated in air. The PMMA was consumed during the heat treatment, resulting in Si@void / CC@PVA with a hollow structure.

[0091] S4. The Si@void / CC@PVA-S was transferred to a tube furnace and sintered under an inert gas atmosphere, such as argon or nitrogen, at a heating rate of 2°C / min to 1000°C. The temperature was maintained for 8 hours to obtain a silicon-based anode material, designated Si@void / CC@C. SEM analysis of the Si@void / CC@C is shown in Figures 1 and 2.

[0092] Example 2

[0093] S1. Silicon-carbon powder, DMSO, PMMA, carbon nanotubes, and Triton-x were mixed in a mass ratio of 10:82:6:1:0.5 to a diameter of 0.25 μm. Ultrasonic stirring was performed at 60°C for 12 hours. The mixture was then slowly added to deionized water using ultrasonic spray for solidification. The resulting solid was then filtered and dried to obtain dispersant / conductive additive-coated silicon particles, designated Si@PMMA / CC.

[0094] S2. Slowly add polyethylene glycol (PEG) to hot deionized water and continue stirring until the PEG is completely dissolved, where the mass ratio of PEG to water is 10:90. The Si@PMMA / CC and PEG are then mixed in deionized water at a ratio of 5%:5%:90%. The mixed solution is stirred at 45°C for 12 hours and then solidified in a 4°C methanol solution using an ultrasonic spray pump. The mixed solution is filtered and dried to obtain PEG-coated Si@PMMA / CC, referred to as Si@PMMA / CC@PEG.

[0095] S3. Si@PMMA / CC@PEG was placed in a solution of ammonium dihydrogen phosphate and stirred. The mixture was reacted at 60°C for 4 hours, followed by filtration to obtain Si@PMMA / CC@PEG-S. Iodine residue on the surface of the SiC@PMMA / CC@PEG-S was removed with acetone and then dried. Subsequently, the sample was transferred to a muffle furnace and heated at a rate of 5°C / min to 240°C. The temperature was maintained for 4 hours, and the sample was heat-treated in air. PMMA was consumed during the heat treatment, resulting in Si@void / CC@PEG-S with a hollow structure.

[0096] S4. Move Si@void / CC@PEG-S into a tubular furnace and sinter it under the protection of inert gas such as argon and nitrogen at a heating rate of 2°C / min to 1100°C. Keep the temperature for 6 hours to obtain a silicon-based negative electrode material, which is recorded as Si@void / CC@C.

[0097] Example 3

[0098] S1. Commercial silica (Lanxi Zhide New Materials Co., Ltd.), dimethylformamide, polyethyl methacrylate, conductive carbon black, and alkylphenol polyoxyethylene ether were mixed in a mass ratio of 6:80:10:2:0.5, resulting in a 0.08 μm diameter silica particle. Ultrasonic stirring was performed at 80°C for 12 hours, followed by slow dripping into deionized water using ultrasonic spray for solidification. The resulting solid was then filtered and dried to obtain dispersant / conductive additive-coated silica particles, designated Si@PL / CC.

[0099] S2. Slowly add polyvinyl alcohol (PVA) to hot deionized water and continue stirring until the PVA is completely dissolved, where the mass ratio of PVA to water is 15:85. Then, the above Si@PL / SP and PVA are mixed in deionized water at a ratio of 5%:5%:90%. The mixed solution is stirred at 45°C for 12 hours and solidified in a 4°C methanol solution using an ultrasonic spray pump. After filtering and drying the mixed solution, PVA-coated Si@PL / CC is obtained, which is recorded as Si@PL / CC@PVA.

[0100] S3. Si@PL / CC@PVA was placed in an ammonium iodide solution and stirred. The mixture was reacted at 60°C for 4 hours, followed by filtration to obtain Si@PL / CC@PVA-S. Any iodine residue on the surface of the Si@PL / CC@PVA-S was washed with acetone and then dried. Subsequently, the sample was transferred to a muffle furnace and heated at a rate of 4°C / min to 260°C. The temperature was maintained for 6 hours, and the sample was heat-treated in air. The PL was consumed during the heat treatment, resulting in Si@void / CC@PVA-S with a hollow structure.

[0101] S4. Move Si@void / CC@PVA-S to a tubular furnace and sinter it under the protection of an inert gas such as argon or nitrogen at a heating rate of 2°C / min to 1000°C. Keep the temperature for 8 hours to obtain a silicon-based negative electrode material, which is recorded as Si@void / CC@C.

[0102] Example 4

[0103] Based on Example 1, Si@void / CC@C was prepared by using 50 nm silicon spheres as silicon material and SWCNT as conductive additives according to the same operation.

[0104] Example 5

[0105] Based on Example 3, the silicon-oxygen material in Example 3 was used, CVD-coated with carbon, and then the same operation was performed to obtain Si@void / CC@C.

[0106] Comparative Example 1

[0107] In S1, no carbon nanotubes were added, and the remaining steps were the same as those in Example 1 to obtain a hollow carbon-coated silicon negative electrode Si@void@C.

[0108] Comparative Example 2

[0109] In S1, the mass ratio of silicon particles, DMSO, polymethyl methacrylate (PMMA), carbon nanotubes, and Triton-x was changed to 8:80:10:1.5:0.5, increasing the proportion of PMMA to increase the thickness of the hollow layer. The remaining steps were the same as in Example 1 to obtain the hollow carbon-coated silicon anode Si@void / CC@C-2.

[0110] Comparative Example 3

[0111] In step S2, Si@PMMA / CC and PVA were mixed in deionized water in a ratio of 3%:7%:90%. Increasing the mass ratio of PVA increased the thickness of the outer carbon shell. The remaining steps were identical to those in Example 1, yielding the hollow carbon-coated silicon anode Si@void / CC@C-3.

[0112] Comparative Example 4

[0113] In S1, the mass ratio of silicon particles, DMSO, polymethyl methacrylate (PMMA), carbon nanotubes, and Triton-x was changed to 8:82:8:2.5:0.5, increasing the proportion of CNTs and adding a conductive additive while maintaining the thickness of the hollow layer. The remaining steps were the same as in Example 1, resulting in a hollow carbon-coated silicon anode Si@void / CC@C-4.

[0114] The relevant process parameters of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1.

[0115] Table 1

[0116] The particle diameter and porosity of the silicon-based negative electrode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were tested, as shown in Table 2.

[0117] Table 2

[0118] Battery assembly and testing:

[0119] The negative electrode sheets were prepared using the silicon-based materials in Examples 1 to 5 and Comparative Examples 1 to 4, and button-type batteries were assembled and electrochemical performance tests and analyses were performed, as follows:

[0120] S1: Prepare the negative electrode sheet.

[0121] The above-mentioned composite negative electrode material was used as the negative electrode active material. The three substances were weighed according to the mass ratio of active material: conductive agent (Super-P) and sodium alginate (CMC) = 8:1:1, mixed in solvent NMP, and stirred evenly to obtain a negative electrode slurry; the negative electrode slurry was coated on copper foil and vacuum dried at 120°C for 12 hours to obtain a negative electrode sheet.

[0122] S2: Assembling the battery

[0123] Using metallic lithium sheets as the counter electrode, an electrolyte of 1M LiPF6 (EC:EMC:DMC=3:4:3 vol%) + 10% FEC and a glass fiber separator, CR2032 button cells were assembled in a glove box filled with Ar gas, where the contents of H2O and O2 were kept below 0.1 ppm.

[0124] S3: Electrochemical performance test analysis

[0125] Electrochemical performance testing was conducted at room temperature using a LAND CT2001A battery testing system. Each button cell was tested for charge and discharge capacity using a 0.1C / 0.1C charge-discharge cycle with a test voltage range of 0.001 to 2V. Cycling performance testing was also performed using a 1C / 1C cycle. The test results are listed in Table 3 below.

[0126] Table 3

[0127] As can be seen from Table 3, the silicon-based negative electrode material obtained using the method provided by the disclosed solution has good comprehensive performance in terms of cycle and conductivity. Compared with the examples, Comparative Example 1 has only a hollow structure and no conductive additives, resulting in a higher overall DCR of the material and significant degradation in the later stages of the cycle. Comparative Example 2, after thickening the hollow layer, slightly increased the specific capacity, slightly increased the cycle, and increased the resistance. Comparative Example 3, after increasing the thickness of the outer carbon shell, reduced the specific capacity and increased the resistance. Comparative Example 4, after adding a conductive additive, reduced the resistance, reduced the specific capacity, and degraded the cycle. Industrial Applicability

[0128] In summary, the present disclosure provides a silicon-based negative electrode material, a preparation method, and a lithium-ion battery. The silicon-based negative electrode material provided by the present disclosure forms a passion fruit-like structure of silicon active material-hollow conductive network-carbon shell. On the one hand, the voids in the conductive network layer alleviate the problem of short cycle life caused by the volume expansion of the silicon-based material. On the other hand, the conductive agent is mixed with the silicon-based material to effectively improve the electron transfer inside the hollow carbon shell silicon-based composite material, thereby improving the conductivity and cycle number of the battery prepared by the silicon-based negative electrode material. The preparation method realizes multi-layer coating of the silicon-based material by controlling the decomposition of the carbon source. The process is simple and controllable, which is conducive to green production, safe production, and large-scale production.

Claims

1. A silicon-based negative electrode material, characterized in that: It comprises a silicon material, a first shell layer coated on the surface of the silicon material and a second shell layer coated on the surface of the first shell layer; the first shell layer comprises a conductive material having gaps; and the second shell layer comprises carbon.

2. A silicon-based negative electrode material according to claim 1, characterized in that: The silicon material is selected from at least one of silicon element, silicon carbon, and silicon oxide compounds.

3. A silicon-based negative electrode material according to claim 1 or 2, characterized in that: The particle size of the silicon material is 0.02-5 μm.

4. A silicon-based negative electrode material according to any one of claims 1 to 3, characterized in that: The mass ratio of the silicon material, the first shell layer, and the second shell layer is (60-80):(5-10):(10-20).

5. A silicon-based negative electrode material according to any one of claims 1 to 4, characterized in that: The thickness of the first shell layer is 0.2 to 5 μm; and / or, The thickness of the second shell layer is 0.5-2 μm.

6. A silicon-based negative electrode material according to any one of claims 1 to 5, characterized in that: The porosity of the first shell layer is 60-90%.

7. A silicon-based negative electrode material according to any one of claims 1 to 6, characterized in that: The conductive material includes one or more of Super P, acetylene black or carbon nanotubes.

8. A method for preparing a silicon-based negative electrode material according to any one of claims 1 to 7, characterized in that: The steps include: A silicon source, an organic solvent, a conductive agent, a dispersant and a surfactant are mixed and reacted to solidify to obtain a dispersant / conductive agent coated silicon material, which is recorded as Si@dispersant / CC; The carbon source is mixed with the Si@dispersant / CC, and the mixture is reacted and solidified to obtain Si@dispersant / CC coated with the carbon source, which is referred to as Si@dispersant / CC@carbon source; The Si@dispersant / CC@carbon source is subjected to heat treatment to remove the dispersant, which is recorded as Si@void / CC@carbon source; The Si@void / CC@carbon source is sintered to obtain the silicon-based negative electrode material, which is recorded as Si@void / CC@C.

9. The method for preparing a silicon-based negative electrode material according to claim 8, characterized in that: The organic solvent comprises dimethyl sulfoxide or dimethylformamide; and / or, The conductive agent includes one or more of Super P, acetylene black or carbon nanotubes; and / or, The dispersant includes one or more of polymethyl methacrylate or polyethyl methacrylate; and / or, The surfactant includes one or more of polyethylene glycol octylphenyl ether, alkylphenol polyoxyethylene ether or fatty alcohol polyoxyethylene ether; and / or, The carbon source includes one or more of polyvinyl alcohol, asphalt, monosaccharide, disaccharide, polysaccharide, sugar derivatives, polyimide, polyacrylonitrile, polystyrene, polydivinylbenzene, polypyrrole, polythiophene and polyaniline.

10. The method for preparing a silicon-based negative electrode material according to claim 8 or 9, characterized in that: The mass ratio of the silicon source: organic solvent: conductive agent: dispersant: surfactant is (5-10): (80-90): (0.5-2): (5-12): (0.01-0.1).

11. A method for preparing a silicon-based negative electrode material according to any one of claims 8 to 10, characterized in that: The mass ratio of the Si@dispersant / CC:carbon source is (1-5):(1-5).

12. A method for preparing a silicon-based negative electrode material according to any one of claims 8 to 11, characterized in that: The heat treatment temperature is 200-250°C; and / or, The heating rate of the heat treatment is 1 to 5°C / min; and / or, The heat treatment time is 4 to 12 hours.

13. A method for preparing a silicon-based negative electrode material according to any one of claims 8 to 11, characterized in that: The sintering temperature is 800-1100° C.; and / or, The heating rate of the sintering is 1-5°C / min; and / or, The sintering time is 4 to 12 hours.

14. A method for preparing a silicon-based negative electrode material according to any one of claims 8 to 13, characterized in that: The step of heat treating the Si@dispersant / CC@carbon source to remove the dispersant comprises: Treating Si@dispersant / CC@carbon source with a modifier to obtain Si@dispersant / CC@modified carbon source; thermally treating the Si@dispersant / CC@modified carbon source to remove the dispersant; Wherein, the modifier includes one or more of ammonium iodide, ammonium hydrogen phosphate or ammonium dihydrogen phosphate.

15. A lithium ion battery, comprising a negative electrode plate, characterized in that: The negative electrode plate comprises the silicon-based negative electrode material as claimed in any one of claims 1 to 7 or comprises the silicon-based negative electrode material prepared by the preparation method as claimed in any one of claims 8 to 14.

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