Silicon-carbon negative electrode material, preparation method and application thereof

Abstract

The present application relates to a kind of silicon-carbon negative electrode material and its preparation method and application.The silicon-carbon negative electrode material includes silicon-carbon composite material and the composite coating layer coated on the surface of the silicon-carbon composite material, wherein the material of the composite coating layer includes hydrophilic first polymer and hydrophobic second polymer, the solubility parameter SP of the composite coating layer is 11J 1 / 2 ·cm ‑3 / 2 ‑50J 1 / 2 ·cm ‑3 / 2 The silicon-carbon negative electrode material described in the present application has a composite coating layer structure with a balance of hydrophilicity and hydrophobicity, which effectively reduces the gas production problem of electrode material during manufacturing and use without affecting the uniform dispersion of the slurry, improves the process safety factor and the good yield of pole piece, and improves the cycle stability and life of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to silicon-carbon anode materials, their preparation methods, and applications. Background Technology

[0002] Nanoscale silicon-carbon anode materials possess high specific capacity, but their high specific surface area leads to low initial efficiency and significant volume expansion. Therefore, surface modification and elemental doping techniques are commonly used to improve their performance, with pre-lithiation technology showing particularly significant improvements in initial efficiency and battery energy density. However, these improvements fail to address the gas generation issues during the manufacturing and use of silicon-carbon anode materials. For instance, severe gas generation in the silicon-carbon anode slurry during electrode manufacturing poses safety hazards during homogenization and can cause problems such as coating tailing, pinholes, pores, particles, scratches, and material shedding after electrode drying, ultimately affecting the yield of the anode sheet and the performance and lifespan of the battery. Summary of the Invention

[0003] Based on this, it is necessary to provide a silicon-carbon anode material, its preparation method, and its application to address the above-mentioned problems. The silicon-carbon anode material has a composite coating structure with balanced hydrophilicity and hydrophobicity, which effectively reduces the gas generation problem of the electrode material during manufacturing and use without affecting the uniform dispersion of the slurry, improves the process safety factor and electrode yield, and enhances the cycle stability and life of the battery.

[0004] A silicon-carbon anode material includes a silicon-carbon composite material and a composite coating layer covering the surface of the silicon-carbon composite material. The composite coating layer comprises a hydrophilic first polymer and a hydrophobic second polymer, and the solubility parameter SP of the composite coating layer is 11 J. 1 / 2 ·cm -3 / 2 -50J 1 / 2 ·cm -3 / 2 .

[0005] In one embodiment, the solubility parameter SP of the composite coating layer is φ1δ1 + φ2δ2, where φ1 and φ2 represent the mass fractions of the first polymer and the second polymer in the composite coating layer material, respectively, and δ1 and δ2 represent the solubility parameters of the first polymer and the second polymer, respectively.

[0006] In one embodiment, the absolute value of the difference in solubility parameters between the first polymer and the second polymer is 5 J. 1 / 2 ·cm -3 / 2 -40J 1 / 2 ·cm -3 / 2 .

[0007] In one embodiment, the solubility parameter of the first polymer is 20 J. 1 / 2 ·cm -3 / 2 -50J 1 / 2 ·cm -3 / 2 The first polymer includes at least one of cationic polymers, anionic polymers, zwitterionic polymers, or nonionic polymers.

[0008] In one embodiment, the solubility parameter of the second polymer is 10 J. 1 / 2 ·cm -3 / 2 -30J 1 / 2 ·cm -3 / 2 The second polymer includes at least one of polyolefin compounds, polyester compounds, polyamide compounds, polyether compounds, polyoxymethylene, epoxy resin, phenolic resin, polysulfone resin, or rubber.

[0009] In one embodiment, the composite coating layer satisfies at least one of the following conditions:

[0010] (1) In the composite coating layer, the mass fraction of the first polymer is greater than or equal to the mass fraction of the second polymer;

[0011] (2) The thickness of the composite coating layer is 1 nm-1 μm;

[0012] (3) The material of the composite coating layer also includes at least one of a conductive agent or a crosslinking agent.

[0013] In one embodiment, the median particle size of the silicon-carbon composite material is 1 μm-20 μm.

[0014] In one embodiment, a carbon coating layer with a thickness of 1 nm to 10 nm is further included between the silicon-carbon composite material and the composite coating layer.

[0015] A method for preparing a silicon-carbon anode material as described above includes: dispersing a silicon-carbon composite material, a first polymer, and a second polymer in a solvent to obtain a mixture, and drying the mixture to obtain the silicon-carbon anode material.

[0016] In one embodiment, the mixture satisfies at least one of the following conditions:

[0017] (1) The mass ratio of the silicon-carbon composite material to the first polymer and the second polymer is (70-100):(0.1-15):(0.1-15);

[0018] (2) In the mixture, the mass-to-volume ratio of the silicon-carbon composite material to the solvent is 0.01 g / mL to 0.30 g / mL;

[0019] (3) The solvent includes at least one of N-methylpyrrolidone, acetone, N,N-dimethylformamide, water, dimethyl sulfoxide, tetrahydrofuran, dichloromethane, methanol or ethanol;

[0020] (4) The mixture also includes at least one of a conductive agent or a crosslinking agent.

[0021] In one embodiment, the drying method includes at least one of spray drying, vacuum drying, freeze drying, or hot air drying.

[0022] In one embodiment, the drying method is to perform spray drying and vacuum drying sequentially, wherein the temperature of the spray drying is 100℃-300℃ and the temperature of the vacuum drying is 50℃-250℃.

[0023] A negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer comprises a silicon-carbon negative electrode material as described above.

[0024] A battery comprising a negative electrode as described above.

[0025] The silicon-carbon anode material of this invention comprises a composite coating layer consisting of a hydrophilic first polymer and a hydrophobic second polymer. This composite coating layer has a specific solubility parameter (SP), achieving a hydrophilic-hydrophobic balance during electrode preparation and use. On one hand, during slurry preparation, the composite coating layer isolates the silicon-carbon anode material from moisture without affecting the uniform dispersion of the slurry, reducing gas generation from the anode material and thus improving process safety and electrode yield. Furthermore, the composite coating layer can form a stable interface on the electrode surface, reducing electrolyte decomposition and consequently reducing gas generation caused by electrolyte decomposition. On the other hand, the composite coating layer reduces direct contact between the silicon-carbon composite material and the electrolyte during cycling, which helps buffer the volume expansion of silicon, thereby reducing electrode material cracking and peeling, and improving battery cycle stability and lifespan.

[0026] Therefore, the silicon-carbon anode material provided by this invention significantly reduces the amount of gas generated during the manufacturing and use of the electrode material without affecting the uniform dispersion of the slurry, and has stable water resistance and processing performance. Using it in batteries is beneficial to improving battery stability. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 Here is a SEM image of the silicon-carbon anode material prepared in Example 1;

[0029] Figure 2 The figures show a comparison of the dispersion effects of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 2 in water. In Example 1, a shows the dispersion effect of the silicon-carbon anode material prepared in Example 1 in water, and in Comparative Example 2, b shows the dispersion effect of the silicon-carbon anode material prepared in Comparative Example 2 in water. Detailed Implementation

[0030] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0032] This invention provides a silicon-carbon anode material, comprising a silicon-carbon composite material and a composite coating layer covering the surface of the silicon-carbon composite material, wherein the composite coating layer comprises a hydrophilic first polymer and a hydrophobic second polymer, and the solubility parameter SP of the composite coating layer is 11 J. 1 / 2 ·cm -3 / 2 -50J 1 / 2 ·cm -3 / 2 , including but not limited to 11J 1 / 2 ·cm -3 / 2 12J 1 / 2 ·cm -3 / 2 14.53J 1 / 2 ·cm -3 / 2 16J 1 / 2 ·cm -3 / 2 19.9J 1 / 2 ·cm -3 / 2 20J 1 / 2 ·cm -3 / 2 21.9J1 / 2 ·cm -3 / 2 23.3J 1 / 2 ·cm -3 / 2 25.6J 1 / 2 ·cm -3 / 2 26.4J 1 / 2 ·cm -3 / 2 30J 1 / 2 ·cm -3 / 2 35J 1 / 2 ·cm -3 / 2 40J 1 / 2 ·cm -3 / 2 45J 1 / 2 ·cm -3 / 2 50J 1 / 2 ·cm -3 / 2 The point value of any one of them or the range value between any two.

[0033] The silicon-carbon anode material of this invention has a composite coating layer composed of a hydrophilic first polymer and a hydrophobic second polymer. Since the surface of the silicon-carbon composite material has both hydrophobic carbon structure and hydrophilic silicon-based structure, the hydrophilic first polymer coats the silicon-based surface through physical or chemical adsorption, while the hydrophobic second polymer coats the carbon surface through hydrophobic interaction. The two polymers are combined through the physical entanglement of polymer chains and non-covalent bond interaction forces to form a dense composite coating layer, which gives the composite coating layer a specific solubility parameter (SP), and can achieve hydrophilic-hydrophobic balance during the preparation and use of the electrode.

[0034] On the one hand, during the homogenization process, the composite coating layer isolates the silicon-carbon anode material from moisture without affecting the uniform dispersion of the slurry, reducing gas generation from the anode material and thus improving the process safety factor and electrode yield. Moreover, the composite coating layer can also form a stable interface on the electrode surface, reducing electrolyte decomposition and thus reducing the gas generated by electrolyte decomposition. On the other hand, the composite coating layer can reduce the direct contact between the silicon-carbon composite material and the electrolyte during cycling, which is beneficial for buffering the volume expansion of silicon, thereby reducing the cracking and peeling of the electrode material and improving the cycle stability and service life of the battery.

[0035] It should be noted that there are multiple ways to calculate the solubility parameter of the composite coating layer. The present invention preferably uses SP = φ1δ1 + φ2δ2 for calculation, where φ1 and φ2 represent the mass fractions of the first polymer and the second polymer in the composite coating layer material, respectively, and δ1 and δ2 represent the solubility parameters of the first polymer and the second polymer, respectively.

[0036] In one embodiment, the absolute value of the difference in solubility parameters between the first polymer and the second polymer is 5J. 1 / 2·cm -3 / 2 -40J 1 / 2 ·cm -3 / 2 , including but not limited to 5J 1 / 2 ·cm -3 / 2 6J 1 / 2 ·cm -3 / 2 7J 1 / 2 ·cm -3 / 2 8J 1 / 2 ·cm -3 / 2 10J 1 / 2 ·cm -3 / 2 11J 1 / 2 ·cm -3 / 2 14J 1 / 2 ·cm -3 / 2 16J 1 / 2 ·cm -3 / 2 20J 1 / 2 ·cm -3 / 2 25J 1 / 2 ·cm -3 / 2 30J 1 / 2 ·cm -3 / 2 35J 1 / 2 ·cm -3 / 2 40J 1 / 2 ·cm -3 / 2 The point value of any one of them or the range value between any two is more conducive to controlling the distribution of hydrophilic and hydrophobic groups in the composite coating layer, making the network structure of the composite coating layer more uniform and dense, thereby further reducing the gas generation problem.

[0037] In one embodiment, the solubility parameter of the first polymer is 20 J. 1 / 2 ·cm -3 / 2 -50J 1 / 2 ·cm -3 / 2 including but not limited to 20J 1 / 2 ·cm -3 / 2 23J 1 / 2 ·cm -3 / 2 25.5J 1 / 2 ·cm -3 / 2 27J 1 / 2 ·cm -3 / 2 27.3J 1 / 2 ·cm -3 / 2 33J 1 / 2 ·cm -3 / 2 34.6J 1 / 2 ·cm -3 / 2 40J 1 / 2 ·cm -3 / 2 45J 1 / 2 ·cm -3 / 2 50J 1 / 2 ·cm-3 / 2 The value of any one of the points or the range between any two, wherein the first polymer includes at least one of cationic polymers, anionic polymers, zwitterionic polymers or nonionic polymers.

[0038] Among them, the cationic polymer is preferably at least one of nitrogen (N)-containing cationic polymers and phosphorus (P)-containing cationic polymers, such as polydimethyldiallylammonium chloride-acrylamide; the anionic polymer is preferably at least one of anionic polymers containing carboxylic acid groups, anionic polymers containing carboxyl salt groups, anionic polymers containing sulfonic acid groups, anionic polymers containing sulfonate groups, anionic polymers containing phosphate groups, anionic polymers containing phosphate salt groups, anionic polymers containing sulfate groups, and anionic polymers containing sulfate groups, such as polyacrylate-acrylate; among the zwitterionic polymers, the cationic polymer is preferably nitrogen (N)-containing cationic polymer. The polymer is preferably at least one of ions and phosphorus (P) cations, and the anion is preferably at least one of carboxylate, sulfonate, phosphate, and sulfate. The nonionic polymer is preferably at least one of polyethylene glycol (PEG), polypropylene glycol (PPG), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyvinylpyrrolidone (PVP), polyacrylamide (PAM), polyhydroxyethyl methacrylate (PHEMA), methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), carboxymethyl cellulose (CMC), hyaluronic acid (HA), agarose, and various synthetic peptides and proteins (such as collagen and gelatin).

[0039] In one embodiment, the solubility parameter of the second polymer is 10 J. 1 / 2 ·cm -3 / 2 -30J 1 / 2 ·cm -3 / 2 , including but not limited to 10J 1 / 2 ·cm -3 / 2 12.7J 1 / 2 ·cm -3 / 2 15J 1 / 2 ·cm -3 / 2 18.2J 1 / 2 ·cm -3 / 2 19.4J 1 / 2 ·cm -3 / 2 20J 1 / 2 ·cm -3 / 2 25J 1 / 2 ·cm -3 / 2 30J 1 / 2 ·cm -3 / 2The value of any one of the following or the range of values ​​between any two, wherein the second polymer includes at least one of polyolefin compounds, polyester compounds, polyamide compounds, polyether compounds, polyoxymethylene, epoxy resin, phenolic resin, polysulfone resin or rubber.

[0040] The polyolefin compounds are preferably at least one of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyvinyl fluoride (PVF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polybutadiene (PB), polyisoprene (PIP), and polychloroprene (PCP); the polyester compounds are preferably at least one of polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl acetate (PVAc), polycarbonate, polyester, and polyurethane; the polyether compounds are preferably at least one of polyvinyl alkyl ether, polyphenylene ether, and polybis(chloromethyl)butoxycyclohexane; and the rubber is preferably at least one of polysulfide rubber and silicone rubber.

[0041] It should be noted that the molecular weights of the first polymer and the second polymer are each independently selected from 1,000 to 1,000,000, and the monomers corresponding to any two or more of the above polymers can be copolymerized to form one or more forms of random copolymers, alternating copolymers, block copolymers, and graft copolymers. This invention does not limit these forms.

[0042] In the composite coating layer, the mass ratio of the first polymer to the second polymer is 100:1 to 1:100, including but not limited to any one of 100:1, 1:4, 1:1, 7:3, and 1:100 or any range between the two. Preferably, the mass fraction of the first polymer is greater than or equal to the mass fraction of the second polymer, which is beneficial for further controlling the distribution of hydrophilic and hydrophobic groups in the composite coating layer.

[0043] In one embodiment, the thickness of the composite coating layer is 1nm-1μm, preferably 1nm-100nm, and more preferably 1nm-20nm, which helps to reduce gas generation problems while maintaining excellent electrical performance.

[0044] In one embodiment, the composite coating layer may also contain materials such as small molecule or polymeric additives, including but not limited to at least one of conductive agents or crosslinking agents, which is beneficial to further optimize electrode performance and improve the overall performance of the battery.

[0045] The conductive agent includes, but is not limited to, at least one of graphene, acetylene black, carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, flake graphite, polyaniline, polypyrrole, polyacetylene, polythiophene, and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) conductive agent (PEDOT:PSS conductive agent).

[0046] Crosslinking agents include, but are not limited to, small molecule or high molecular weight crosslinking agents containing at least one functional group of hydroxyl, amino, carboxyl, aldehyde, epoxy, double bond, or halogen.

[0047] Specifically, the crosslinking agent is selected from any one or a combination of at least two of the following: 1,4-butanediol, ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, glycerol, trimethylolpropane, 3,3-dichloro-4,4-diaminodiphenylmethane, 3,5-dimethylthiotoluenediamine, 3,5-diethyltoluenediamine, 2,4-diamino-3,5-dimethylthiochlorobenzene, isophoronediamine, ethanolamine, diethanolamine, triethanolamine, N,N-bis(2-hydroxypropyl)aniline, 1,4-cyclohexanediol, hydrogenated bisphenol A, dimethylene phenyl glycol, hydroquinone bis-β-hydroxyethyl ether, resorcinol hydroxy ether, glyceryl allyl ether, glycidyl allyl ether, or dicumyl peroxide.

[0048] In one embodiment, the median particle size of the silicon-carbon composite material is 1 μm-20 μm, preferably 1 μm-10 μm.

[0049] It is understood that the silicon-carbon composite material is a conventional composite material of silicon and carbon, which can be prepared by chemical vapor deposition, sol-gel method, high temperature pyrolysis method, mechanical ball milling method, hydrothermal synthesis method and electrospinning method, etc., or existing commercial products can be used. This invention does not limit this, but preferably uses a composite material of porous carbon and silicon.

[0050] In one embodiment, a carbon coating layer is further included between the silicon-carbon composite material and the composite coating layer, the thickness of which is 1nm-10nm, preferably 3nm-7nm.

[0051] The present invention provides a method for preparing the silicon-carbon anode material as described above, comprising: dispersing a silicon-carbon composite material, a first polymer, and a second polymer in a solvent to obtain a mixture, and drying the mixture to obtain the silicon-carbon anode material.

[0052] In one embodiment, the mass ratio of the silicon-carbon composite material to the first polymer and the second polymer is (70-100):(0.1-15):(0.1-15), including but not limited to any one of 50:1:1, 60:0.5:0.5, 70:0.7:0.3, 75:1:1, 45:1.5:1.5, 30:0.5:0.5, and 50:0.5:2, or any range between any two.

[0053] In one embodiment, the mass-to-volume ratio of the silicon-carbon composite material to the solvent in the mixture is 0.01 g / mL to 0.30 g / mL, including but not limited to any one of 0.01 g / mL, 0.06 g / mL, 0.067 g / mL, 0.09 g / mL, 0.1 g / mL, 0.14 g / mL, 0.15 g / mL, and 0.30 g / mL, or a range between any two.

[0054] In one embodiment, the solvent includes at least one of N-methylpyrrolidone, acetone, N,N-dimethylformamide, water, dimethyl sulfoxide, tetrahydrofuran, dichloromethane, methanol, or ethanol.

[0055] In one embodiment, the mixture may also contain small molecule or polymeric additives, including but not limited to at least one of conductive agents or crosslinking agents, which is beneficial for further optimizing electrode performance and improving the overall performance of the battery.

[0056] When the mixture contains a conductive agent, the mass fraction of the conductive agent in the mixture is 0.1%-20%, preferably 0.1%-10%.

[0057] In one embodiment, the silicon-carbon composite material is further subjected to carbon coating treatment before mixing and preparation. The carbon coating treatment can be carried out using conventional processes, such as chemical vapor deposition (CVD), and the present invention does not limit it.

[0058] In one embodiment, the drying method includes at least one of spray drying, vacuum drying, freeze drying, or hot air drying, preferably a two-step drying process, and more preferably spray drying and vacuum drying are performed sequentially, which is beneficial to improving preparation efficiency and production safety.

[0059] Furthermore, the spray drying temperature is 100℃-300℃, preferably 100℃-200℃; the vacuum drying temperature is 50℃-250℃, preferably 100℃-200℃; and the vacuum drying time is 0.5h-8h, preferably 1h-3h.

[0060] The present invention also provides a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer comprises the silicon-carbon negative electrode material as described above. It is understood that the negative electrode active material layer may also include materials such as binders, and the present invention does not limit this.

[0061] The present invention also provides a battery. The battery includes the negative electrode as described above. It is understood that the battery also includes a positive electrode, a separator, and an electrolyte; however, the present invention does not limit the positive electrode, separator, and electrolyte.

[0062] The silicon-carbon anode material provided by this invention significantly reduces the amount of gas generated during the manufacturing and use of the electrode material without affecting the uniform dispersion of the slurry, and has stable water resistance and processing performance. Its use in batteries is beneficial to improving battery stability.

[0063] The following specific embodiments will further illustrate the silicon-carbon anode material, its preparation method, and its applications. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0064] It should be noted that the silicon-carbon composite material used in the examples and comparative examples was purchased from Zhejiang Lichen Technology New Material Co., Ltd., model CONE-LSCSSC-21800.

[0065] Example 1

[0066] 50g of silicon-carbon composite material (average particle size approximately 8.4μm) and 1g of nonionic hydrophilic polyvinyl alcohol (27.3J) were mixed. 1 / 2 ·cm -3 / 2 ), 1g of hydrophobic polyvinylidene fluoride (12.7J) 1 / 2 ·cm -3 / 2 1 g of carbon nanotubes and 1 g of carbon nanotubes were dispersed in 750 mL of N-methylpyrrolidone and ultrasonically dispersed for 20 min to obtain a mixture. The mixture was then spray-dried at 250 °C to obtain a crude product, and the crude product was then dried under vacuum at 130 °C for 3 hours to obtain a silicon-carbon anode material.

[0067] The silicon-carbon anode material prepared in Example 1 was characterized by SEM, as follows: Figure 1 As shown, carbon nanotubes and polymers are uniformly dispersed on the surface.

[0068] Example 2

[0069] 60g of silicon-carbon composite material (average particle size approximately 8.5μm) and 0.5g of cationic hydrophilic polydimethyldiallyl ammonium chloride-acrylamide (33J) were mixed. 1 / 2 ·cm -3 / 2 0.5g of hydrophobic polystyrene (18.2J) 1 / 2 ·cm -3 / 2 1 g of polypyrrole and 1 g of polypyrrole were dispersed in 1000 mL of acetone solution and ultrasonically dispersed for 10 min to obtain a mixture. The mixture was then spray-dried at 100 °C to obtain a crude product, and the crude product was then dried under vacuum at 150 °C for 3 hours to obtain a silicon-carbon anode material.

[0070] Example 3

[0071] 70g of silicon-carbon composite material (average particle size approximately 6.5μm) and 0.7g of anionic hydrophilic polyacrylate-acrylate (23J) were mixed. 1 / 2 ·cm -3 / 2 ), 0.3g of hydrophobic polyvinylidene fluoride (12.7J) 1 / 2 ·cm -3 / 2 1 g of PEDOT:PSS and 1 g of PEDOT:PSS were dispersed in 500 mL of N,N-dimethylformamide solution and stirred at high speed for 15 min to obtain a mixture. The mixture was then spray-dried at 180 °C to obtain a crude product, which was then dried under vacuum at 150 °C for 3 hours to obtain a silicon-carbon anode material.

[0072] Example 4

[0073] 75g of silicon-carbon composite material (average particle size approximately 7.8μm) and 1g of nonionic hydrophilic polyvinyl alcohol (27.3J) were mixed. 1 / 2 ·cm -3 / 2 ), 1g of hydrophobic polycarbonate (19.4J) 1 / 2 ·cm -3 / 2 1 g of carbon black and 1 g of carbon black were dispersed in a mixed solution of 500 mL of deionized water and DMF (volume ratio 1:1) and stirred at high speed for 15 min to obtain a mixture. The mixture was then spray-dried at 185 °C to obtain a crude product, and then dried under vacuum at 110 °C for 1.5 h to obtain a silicon-carbon anode material.

[0074] Example 5

[0075] 45g of silicon-carbon composite material (average particle size approximately 8.1μm) and 1.5g of polyhydroxyethyl methacrylate (25.5J) were mixed. 1 / 2 ·cm -3 / 2 ), 1.5g of polymethyl methacrylate (18.2J) 1 / 2 ·cm -3 / 21 g of multi-walled carbon nanotubes and 1 g of water were dispersed in a mixed solvent of 500 mL of water and acetone (volume ratio 1:1) and ultrasonically dispersed for 10 min to obtain a mixture. The mixture was then spray-dried at 150 °C to obtain a crude product, and the crude product was then dried under vacuum at 140 °C for 2 hours to obtain a silicon-carbon anode material.

[0076] Example 6

[0077] 30g of silicon-carbon composite material (average particle size approximately 8.2μm) and 0.5g of lithium-b-polyacrylic acid random polymer (34.6J) were mixed. 1 / 2 ·cm -3 / 2 0.5g of polystyrene (18.2J) 1 / 2 ·cm -3 / 2 0.5 g of PEDOT:PSS conductive polymer was dispersed in a mixed solvent of 300 mL of water and acetone (volume ratio 3:2) and ultrasonically dispersed for 15 min to obtain a mixture. The mixture was then spray-dried at 150 °C to obtain a crude product, which was then dried under vacuum at 90 °C for 1 hour to obtain a silicon-carbon anode material.

[0078] Example 7

[0079] The difference between Example 7 and Example 1 is that the mixture also includes 1g of ethylene glycol crosslinking agent.

[0080] Example 8

[0081] The difference between Example 8 and Example 1 is that 0.5g of nonionic hydrophilic polyvinyl alcohol (27.3J) was added. 1 / 2 ·cm -3 / 2 ) and 2g of hydrophobic polyvinylidene fluoride (12.7J) 1 / 2 ·cm -3 / 2 ).

[0082] Comparative Example 1

[0083] The difference between Comparative Example 1 and Example 1 is that nonionic hydrophilic polyvinyl alcohol was not added.

[0084] Comparative Example 2

[0085] The difference between Comparative Example 2 and Example 1 is that hydrophobic polyvinylidene fluoride was not added.

[0086] The silicon-carbon anode materials prepared in Examples 1-8 and Comparative Examples 1-2 were characterized and tested. The test results are shown in Table 1.

[0087] Table 1

[0088]

[0089] 5g of the silicon-carbon anode materials obtained in Example 1 and Comparative Example 2 were weighed out and placed in 80mL of water for stirring and dispersion. The dispersion effect was as follows: Figure 2 As shown, a is a dispersion diagram of the silicon-carbon anode material prepared in Example 1 in water, and b is a dispersion diagram of the silicon-carbon anode material prepared in Comparative Example 2 in water. Figure 2 It is evident that the silicon-carbon anode material prepared in Example 1 can be uniformly dispersed in water, while the silicon-carbon anode material prepared in Comparative Example 2 is completely stratified in water, which is not conducive to the subsequent battery processing of silicon-carbon anode materials and will affect battery performance.

[0090] The silicon-carbon composite material used in Example 1 was used as a blank control example. The silicon-carbon anode materials prepared in Examples 1-8 and Comparative Examples 1-2, as well as the blank control example, were subjected to gas generation tests and soft-pack battery tests.

[0091] The gas production test method is as follows: Take 5g of the test material and 50g of water and add them to a sealed bottle. Dissolve them completely by centrifugation and stirring. Then, place the bottle in a constant temperature room at 25℃ and test the gas production (H2) for 24 hours on the 1st, 3rd, 5th and 7th days. The test results are shown in Table 2.

[0092] Table 2

[0093]

[0094] As shown in Table 2, the uncoated polymer-coated silicon-carbon gas production rate was approximately 2.58 CC / kg / day. Comparative Example 1, a silicon-carbon material coated with a hydrophilic polymer, showed a SP value of 27.3 J after hydrophilic polymer coating modification, compared to the uncoated example. 1 / 2 ·cm -3 / 2 This resulted in a sharp increase in silicon-carbon gas production (4.41 CC / kg); Comparative Example 2 was a silicon-carbon material coated with a hydrophobic polymer (SP value 12.7 J). 1 / 2 ·cm -3 / 2 Compared to the blank control, the introduction of hydrophobic polymers effectively improved the gas production of silicon-carbon materials (1.16 CC / kg / day). Example 1 was a silicon-carbon material co-coated with hydrophilic / hydrophobic polymers. The introduction of hydrophobic polymers effectively alleviated the high gas production caused by the introduction of hydrophilic polymers. Examples 2-6 further verified this view.

[0095] The soft-pack testing method was as follows: the test material was doped with artificial graphite at a mass ratio of 2:8, and 0.2% CNT was added as the negative electrode; NCM811 ternary material was used as the positive electrode material, a mixed solvent of EC and DEC with a volume ratio of 1:1 was used as the electrolyte solvent, and Celgard 2400 membrane was used as the separator to prepare the soft-pack lithium-ion battery. Cyclic testing (capacity retention after 200 cycles) was then conducted under the following conditions: voltage range 2.5V-4.2V, charge / discharge 1C / 1C. The cycle test results are shown in Table 3.

[0096] Table 3

[0097]

[0098] As can be seen from Table 3, Comparative Example 1 is a silicon-carbon material coated with a hydrophilic polymer (SP value 27.3 J). 1 / 2 ·cm -3 / 2 Comparative Example 2 is a silicon-carbon material coated with a hydrophobic polymer (SP value 12.7 J). 1 / 2 ·cm -3 / 2 The capacity retention rates of Examples 1-8 after 200 cycles were 91.6% and 90.2%, respectively. Compared with Comparative Examples 1-2, the capacity retention rates after 200 cycles of Examples 1-8 were significantly improved. Furthermore, Example 7 shows that the strategy of using a crosslinking agent to crosslink the composite coating layer on the silicon-carbon surface can effectively improve the cycle stability of the silicon-carbon anode material. Comparative Example 2, due to only coating with a hydrophobic polymer, although the hydrophobic effect can reduce gas production, has poor dispersibility and is prone to delamination during electrode manufacturing, resulting in a reduced capacity retention rate and therefore poor overall performance.

[0099] In summary, the hydrophilic / hydrophobic polymer co-coating structure provided by this invention can effectively reduce gas generation in electrode materials during manufacturing and use, improve the processing performance of silicon carbon, reduce direct contact between silicon carbon materials and electrolyte, buffer the volume expansion of silicon, thereby reducing the cracking and peeling of electrode materials and improving the cycle stability and service life of the battery.

[0100] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0101] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material comprises a silicon-carbon composite material and a composite coating layer covering the surface of the silicon-carbon composite material. The composite coating layer comprises a hydrophilic first polymer and a hydrophobic second polymer. The hydrophilic first polymer coats the silicon-based surface, and the hydrophobic second polymer coats the carbon surface. The two polymers are bonded together through physical entanglement of polymer chains and non-covalent interactions to form the composite coating layer. The solubility parameter SP of the composite coating layer is 11 J. 1 / 2 ·cm -3 / 2 -50J 1 / 2 ·cm -3 / 2 .

2. The silicon-carbon anode material according to claim 1, characterized in that, The solubility parameter SP of the composite coating layer = 1δ1+ 2δ2, where, 1 and 2 represents the mass fraction of the first polymer and the second polymer in the composite coating material, respectively, and δ1 and δ2 represent the solubility parameters of the first polymer and the second polymer, respectively.

3. The silicon-carbon anode material according to claim 1, characterized in that, The absolute value of the difference in solubility parameters between the first polymer and the second polymer is 5 J. 1 / 2 ·cm -3 / 2 -40J 1 / 2 ·cm -3 / 2 .

4. The silicon-carbon anode material according to any one of claims 1-3, characterized in that, The solubility parameter of the first polymer is 20 J. 1 / 2 ·cm -3 / 2 -50J 1 / 2 ·cm -3 / 2 The first polymer includes at least one of cationic polymers, anionic polymers, zwitterionic polymers, or nonionic polymers.

5. The silicon-carbon anode material according to any one of claims 1-3, characterized in that, The solubility parameter of the second polymer is 10 J. 1 / 2 ·cm -3 / 2 -30J 1 / 2 ·cm -3 / 2 The second polymer includes at least one of polyolefin compounds, polyester compounds, polyamide compounds, polyether compounds, polyoxymethylene, epoxy resin, phenolic resin, polysulfone resin, or rubber.

6. The silicon-carbon anode material according to claim 1, characterized in that, The composite coating layer satisfies at least one of the following conditions: (1) In the composite coating layer, the mass fraction of the first polymer is greater than or equal to the mass fraction of the second polymer; (2) The thickness of the composite coating layer is 1 nm-1 μm; (3) The material of the composite coating layer also includes at least one of a conductive agent or a crosslinking agent.

7. The silicon-carbon anode material according to claim 1, characterized in that, The median particle size of the silicon-carbon composite material is 1μm-20μm.

8. The silicon-carbon anode material according to claim 1, characterized in that, Between the silicon-carbon composite material and the composite coating layer, there is also a carbon coating layer with a thickness of 1 nm-10 nm.

9. A method for preparing a silicon-carbon anode material as described in any one of claims 1-8, characterized in that, include: The silicon-carbon composite material, the first polymer, and the second polymer are dispersed in a solvent to obtain a mixture, which is then dried to obtain the silicon-carbon anode material.

10. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The mixture satisfies at least one of the following conditions: (1) The mass ratio of the silicon-carbon composite material to the first polymer and the second polymer is (70-100):(0.1-15):(0.1-15); (2) In the mixture, the mass-to-volume ratio of the silicon-carbon composite material to the solvent is 0.01 g / mL to 0.30 g / mL; (3) The solvent includes at least one of N-methylpyrrolidone, acetone, N,N-dimethylformamide, water, dimethyl sulfoxide, tetrahydrofuran, dichloromethane, methanol or ethanol; (4) The mixture also includes at least one of a conductive agent or a crosslinking agent.

11. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The drying method includes at least one of spray drying, vacuum drying, freeze drying, or hot air drying.

12. The method for preparing the silicon-carbon anode material according to claim 11, characterized in that, The drying method involves sequential spray drying and vacuum drying, wherein the spray drying temperature is 100℃-300℃ and the vacuum drying temperature is 50℃-250℃.

13. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material layer, wherein the negative active material layer comprises the silicon-carbon negative electrode material as described in any one of claims 1-8.

14. A battery, characterized in that, Including the negative electrode sheet as described in claim 13.

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