Silicon-carbon negative electrode material with polymer coating on surface, preparation method and application thereof

Abstract

The present invention relates to a silicon-carbon negative electrode material with a surface-coated polymer, comprising a silicon-carbon material and a coating layer coated on the surface of the silicon-carbon material, wherein the material of the coating layer comprises an amphiphilic comb-type polymer and a cross-linking agent, and the amphiphilic comb-type polymer comprises a hydrophilic side chain and a hydrophobic side chain. The present invention also relates to a preparation method of the silicon-carbon negative electrode material and its application. The present invention forms a coating layer by hydrophilic side chains, hydrophobic side chains and a cross-linking agent, which can effectively reduce the gas production of the silicon-carbon material, increase the dispersibility of the silicon-carbon material in water, and effectively reduce the volume expansion of the silicon-carbon negative electrode material. Therefore, the use of the silicon-carbon negative electrode material in an electrochemical energy storage device can effectively improve the electrochemical performance and safety of the electrochemical energy storage device.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage devices, and in particular to a silicon-carbon negative electrode material with a surface coated with a polymer, a preparation method and applications thereof. Background Art

[0002] Silicon-based materials are increasingly being used in batteries due to their high theoretical specific capacity, which can significantly increase the energy density of batteries. However, in actual applications, silicon-based negative electrode materials also face some challenges. For example, silicon-based materials have the problem of large volume expansion. The process of lithium insertion / delithiation will cause the volume of the negative electrode material to change dramatically, seriously affecting the cycle capacity and life of the battery. In addition, silicon-based materials will react with the electrolyte and water in the homogenization process to produce gas. The specific reaction formula is: Si + 4H2O = H4SiO4 + 2H2↑, which may cause safety issues and affect the performance and life of the battery. Summary of the Invention

[0003] Based on this, it is necessary to provide a silicon-carbon negative electrode material with a surface-coated polymer, a preparation method and its application to address the above problems; the silicon-carbon negative electrode material has low gas production and small volume expansion, and its application in electrochemical energy storage devices can effectively improve its electrochemical performance and safety.

[0004] A silicon-carbon negative electrode material comprises a silicon-carbon material and a coating layer coated on the surface of the silicon-carbon material, wherein the material of the coating layer comprises an amphiphilic comb-type polymer and a cross-linking agent, and the amphiphilic comb-type polymer comprises a hydrophilic side chain and a hydrophobic side chain.

[0005] In one embodiment, the amphiphilic comb polymer further satisfies at least one of the following conditions:

[0006] (1) The molecular weight of the amphiphilic comb polymer is 50,000-2,000,000;

[0007] (2) the molecular weight of the hydrophobic side chain of the amphiphilic comb polymer is 500-18000;

[0008] (3) The degree of polymerization of the hydrophobic side chains of the amphiphilic comb polymer is 5-120;

[0009] (4) The molecular weight of the hydrophilic side chain of the amphiphilic comb polymer is 4000-250000;

[0010] (5) The degree of polymerization of the hydrophilic side chains of the amphiphilic comb-type polymer is 100-1000.

[0011] In one embodiment, the carbon chain length of the hydrophilic side chain of the amphiphilic comb polymer is greater than the carbon chain length of the hydrophobic side chain.

[0012] In one embodiment, the mass fraction of the coating layer in the silicon-carbon negative electrode material is 0.5%-10%.

[0013] In one embodiment, the material of the coating layer further includes a conductive agent.

[0014] A method for preparing the silicon-carbon negative electrode material as described above comprises the following steps:

[0015] An amphiphilic comb-type polymer is provided, and the amphiphilic comb-type polymer, a silicon-carbon material and a cross-linking agent are mixed in water to obtain a slurry, which is then dried to obtain a silicon-carbon negative electrode material.

[0016] In one embodiment, the method for preparing the amphiphilic comb polymer comprises the following steps:

[0017] Will React with hydrophobic substances to prepare hydrophobic comb polymers. reacting with a hydrophilic substance to prepare a hydrophilic comb polymer, and then subjecting the hydrophobic comb polymer and the hydrophilic comb polymer to RAFT polymerization to obtain the amphiphilic comb polymer;

[0018] Wherein, R and R2 are independently selected from -H or -(CH2) a -CH3, a≥0; R1 is selected from -(CH2) b -X, wherein X is selected from hydroxyl, carboxyl, amino, thiol, urea, thiourea, amide or sulfonic acid, b≥0; R3 is selected from -(CH2) c -Y-(CH2) d -, wherein Y is selected from carbon, nitrogen, oxygen, sulfur, phosphorus, carbonyl, urea or amide, and c and d are natural numbers; R4 is selected from hydroxyl, sulfhydryl, carboxyl, amino, urea, thiourea, amide or sulfonic acid.

[0019] In one embodiment, the solubility parameter of the hydrophobic substance is 5J 1 / 2 cm -3 / 2 -30J 1 / 2 cm -3 / 2 , the solubility parameter of the hydrophilic substance is 15J 1 / 2 cm -3 / 2 -40J 1 / 2 cm -3 / 2 , and the solubility parameter of the hydrophilic substance is greater than the solubility parameter of the hydrophobic substance.

[0020] In one embodiment, in the step of mixing the amphiphilic comb polymer, the silicon-carbon material and the cross-linking agent in water to obtain a slurry, a conductive agent is also added.

[0021] A negative electrode sheet comprising the above-mentioned silicon-carbon negative electrode material.

[0022] An electrochemical energy storage device comprising the negative electrode sheet described above.

[0023] A polymer with an amphiphilic comb-shaped morphology is used in the preparation of a negative electrode material capable of inhibiting gas generation.

[0024] The amphiphilic comb-type polymer of the present invention has a hydrophilic side chain and a hydrophobic side chain. Since the surface of the silicon-carbon material mainly exhibits lipophilicity, the hydrophobic side chains of the amphiphilic comb-type polymer are mainly coated on the surface of the silicon-carbon material to form a hydrophobic coating layer. The hydrophilic side chains are cross-linked due to the hydrophilic effect and the cross-linking agent, surrounding the surface of the silicon-carbon material to form a dense hydrophilic coating layer. Furthermore, during the homogenization process, the hydrophilic coating layer can effectively increase the dispersibility of the silicon-carbon material in water, which is conducive to the preparation of a negative electrode sheet with excellent performance. At the same time, the hydrophobic coating layer can effectively reduce the contact between the silicon-carbon material and water, and reduce the amount of hydrogen produced by the reaction between silicon and water. In addition, the coating layer formed can effectively reduce the volume expansion of the silicon-carbon negative electrode material, reduce the risk of peeling of the negative electrode sheet, and improve the stability of the electrochemical energy storage device.

[0025] Therefore, using the silicon-carbon negative electrode material in an electrochemical energy storage device can effectively improve the electrochemical performance and safety of the electrochemical energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the silicon-carbon negative electrode material of the present invention; wherein 1 is a silicon-carbon material, 2 is a coating layer, 21 is an amphiphilic comb-type polymer, 211 is a hydrophobic side chain, 212 is a hydrophilic side chain, and 22 is a cross-linking agent;

[0027] Figure 2 This is the SEM image of the silicon-carbon negative electrode material of Example 1. DETAILED DESCRIPTION

[0028] To facilitate understanding of the present invention, the present invention 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. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments or embodiments and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, including any two related listed items, any more related listed items, or the combination of all related listed items.

[0030] like Figure 1 As shown, the silicon-carbon negative electrode material provided by the present invention includes a silicon-carbon material 1 and a coating layer 2 coated on the surface of the silicon-carbon material 1, wherein the material of the coating layer 2 includes an amphiphilic comb polymer 21 and a cross-linking agent 22. It should be noted that, Figure 1 It is only a schematic diagram to facilitate the explanation of the specific structure of the polymer layer and does not have a clear reference meaning. For example, the number of various lines in the figure does not represent the actual usage.

[0031] The amphiphilic comb-type polymer 21 of the present invention has hydrophilic side chains 212 and hydrophobic side chains 211. Since the surface of the silicon-carbon material 1 is mainly lipophilic, the hydrophobic side chains 211 of the amphiphilic comb-type polymer 21 are mainly coated on the surface of the silicon-carbon material 1 to form a hydrophobic coating layer. The hydrophilic side chains 212 surround the surface of the silicon-carbon material 1 due to hydrophilic effects, intermolecular forces and cross-linking by cross-linking agents, forming a dense hydrophilic coating layer.

[0032] Furthermore, during the homogenization process, the hydrophilic coating layer can effectively increase the dispersibility of the silicon-carbon material 1 in water, which is beneficial to the preparation of a negative electrode sheet with excellent performance; at the same time, the hydrophilic coating layer is also beneficial to the full penetration of the electrolyte into the negative electrode material, thereby improving the charge and discharge performance of the electrochemical energy storage device, and the hydrophobic coating layer can effectively reduce the contact between the silicon-carbon material 1 and the electrolyte and water during the homogenization process, thereby reducing the gas production.

[0033] In addition, the formed coating layer 2 can effectively reduce the volume expansion of the silicon-carbon negative electrode material, reduce the risk of peeling of the negative electrode sheet, and improve the stability of the electrochemical energy storage device.

[0034] Preferably, the molecular weight of the amphiphilic comb polymer 21 is 50,000-2,000,000, so that the appropriate molecular weight is conducive to forming the coating layer 2, improving the coating effect on the silicon-carbon material 1, and thus helping to reduce the degree of contact between the silicon-carbon material 1 and water, and at the same time improving the dispersibility of the silicon-carbon material 1 in water.

[0035] Preferably, the hydrophilic side chains 212 of the amphiphilic comb polymer 21 have a molecular weight of 4,000-250,000 and a degree of polymerization of 100-1,000, more preferably 300-800. Thus, a suitable chain length is beneficial for improving the dispersibility of the silicon-carbon material 1 in water and reducing the hydrophilic channels formed on the surface of the silicon-carbon material 1 by the shorter hydrophilic side chains, thereby improving dispersibility while reducing the degree of contact between the silicon-carbon material 1 and water.

[0036] Preferably, the molecular weight of the hydrophobic side chain 211 of the amphiphilic comb polymer 21 is 500-18000, and the degree of polymerization is 5-120, and the degree of polymerization is more preferably 10-50. Further preferably, the degree of polymerization and molecular weight of the hydrophobic side chain 211 are both lower than the degree of polymerization and molecular weight of the hydrophilic side chain 212, thereby facilitating the formation of a suitable coating layer 2, further reducing the degree of contact between the silicon-carbon material 1 and water, and increasing the dispersibility of the silicon-carbon material 1 in water.

[0037] Furthermore, preferably, the carbon chain length of the hydrophilic side chain 212 of the amphiphilic comb polymer 21 is greater than the carbon chain length of the hydrophobic side chain 211 .

[0038] Preferably, the mass fraction of the coating layer 2 in the silicon-carbon negative electrode material is 0.5%-10%, including but not limited to 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., so that the appropriate quality is conducive to improving the coating effect of the coating layer 2 on the silicon-carbon material 1, and can form a suitable polymer network structure, which is conducive to improving the gas production and volume expansion problems of the silicon-carbon negative electrode material.

[0039] The crosslinking agent 22 of the present invention can be a conventional crosslinking agent, whose molecular structure contains at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, aldehyde, sulfonic, boric, and halogen atoms. More preferably, the crosslinking agent is a hydrophilic crosslinking agent, such as at least one selected from the group consisting of boric acid, ethylenediamine, ethylene glycol, and 1,6-hexanediol. This facilitates crosslinking with the hydrophilic side chains 212, forming a denser hydrophilic coating layer and thereby enhancing the coating effect of the overall coating layer 2.

[0040] Preferably, the mass fraction of the cross-linking agent 22 in the silicon-carbon negative electrode material is 0.05%-5%, more preferably 0.1%-3%.

[0041] In order to further improve the conductivity of the silicon-carbon negative electrode material of the present invention, the coating layer 2 of the silicon-carbon negative electrode material also includes a conductive agent, which is dispersed in the polymer network structure formed by the amphiphilic comb polymer 21 and the cross-linking agent 22.

[0042] Preferably, the conductive agent is selected from common conductive agents used in negative electrode materials, and the present invention does not impose specific limitations thereon. Examples include graphene, carbon black, acetylene black, single-walled carbon nanotubes, or multi-walled carbon nanotubes. The mass fraction of the conductive agent in the silicon-carbon negative electrode material is preferably 0.05% to 3%, and more preferably 0.1% to 1%.

[0043] The present invention also provides a method for preparing the silicon-carbon negative electrode material, comprising the following steps:

[0044] An amphiphilic comb-type polymer is provided, and the amphiphilic comb-type polymer, a silicon-carbon material and a cross-linking agent are mixed in water to obtain a slurry, which is then dried to obtain a silicon-carbon negative electrode material.

[0045] Preferably, the solid content of the slurry obtained by mixing is 5%-50%, including but not limited to 5%, 10%, 20%, 30%, 40%, 50%, etc.

[0046] Preferably, the drying method is oven drying, spray drying or vacuum drying, and the drying temperature is 120°C-200°C, including but not limited to 120°C, 150°C, 180°C, 200°C, etc.

[0047] The amphiphilic comb polymer of the present invention can be prepared by referring to existing preparation methods. The present invention is prepared by the following steps:

[0048] Will React with hydrophobic substances to prepare hydrophobic comb polymers. The hydrophilic comb polymer is prepared by reacting with a hydrophilic substance, and then the hydrophobic comb polymer and the hydrophilic comb polymer are subjected to RAFT polymerization to obtain the amphiphilic comb polymer.

[0049] Wherein, R and R2 are independently preferably -H or -(CH2) a -CH3, wherein a≥0, more preferably 0 or 1. R1 is preferably -(CH2) b -X, wherein X is selected from hydroxyl, carboxyl, amino, thiol, urea, thiourea, amide or sulfonic acid, b≥0, more preferably an integer from 1 to 10. R3 is preferably -(CH2) c -Y-(CH2) d -, wherein Y is selected from carbon, nitrogen, oxygen, sulfur, phosphorus, carbonyl, urea or amide, c and d are natural numbers, more preferably integers from 1 to 15; R4 is selected from hydroxyl, thiol, carboxyl, amino, urea, thiourea, amide or sulfonic acid.

[0050] The mass ratio of the hydrophilic comb polymer to the hydrophobic comb polymer of the present invention is preferably 100:1-1:100, and more preferably 90:10-60:40, so that when the amphiphilic comb polymer obtained forms a coating layer, the coating layer has suitable hydrophilicity / hydrophobicity, which is beneficial to further regulate the coating effect, reduce the degree of contact between the silicon-carbon material and water, and at the same time improve the dispersibility of the silicon-carbon material in water.

[0051] Preferably, the hydrophobic substance is capable of undergoing a ring-opening polymerization reaction with the R1 group to form a hydrophobic side chain. The hydrophobic substance is an ester compound, preferably a cyclic ester compound, and can be a hydrophobic monomer or a hydrophobic polymer. Preferably, the hydrophobic substance is at least one of cyclopentanolactone, caprolactone, lactide, ethylene carbonate, or propylene carbonate.

[0052] Preferably, the hydrophilic substance can react with the R4 group to form a hydrophilic side chain. The hydrophilic substance can be a hydrophilic monomer or a hydrophilic polymer. Preferably, the hydrophilic substance is at least one of polyethylene glycol, a structured polysaccharide, hyaluronic acid, polyvinyl alcohol, polyacrylamide, or povidone.

[0053] Preferably, the solubility parameter of the hydrophobic substance is 5J 1 / 2 cm -3 / 2 -30J 1 / 2 cm -3 / 2 , the solubility parameter of the hydrophilic substance is 15J 1 / 2 cm -3 / 2 -40J 1 / 2 cm -3 / 2 , and the solubility parameter of the hydrophilic substance is greater than the solubility parameter of the hydrophobic substance, so that the amphiphilic comb-type polymer has a more suitable hydrophilic / hydrophobic property. Furthermore, during the homogenization process, the coordination of the hydrophobic side chains and the hydrophilic side chains is not only more conducive to reducing the contact between the silicon-carbon material and water and reducing the gas production, but also more conducive to improving the dispersibility of the silicon-carbon material in water and improving the performance of the negative electrode sheet.

[0054] Preferably, in the step of mixing the amphiphilic comb polymer, the silicon-carbon material and the cross-linking agent in water to obtain a slurry, a conductive agent is also added, thereby improving the conductivity of the prepared silicon-carbon negative electrode material.

[0055] The present invention also provides a negative electrode sheet, which includes the silicon-carbon negative electrode material. The silicon-carbon negative electrode material of the present invention has low gas production and small volume expansion, so the negative electrode sheet using the silicon-carbon negative electrode material has excellent performance.

[0056] The present invention also provides an electrochemical energy storage device, which includes the negative electrode sheet. Thus, the electrochemical energy storage device using the negative electrode sheet has excellent electrochemical performance and safety.

[0057] Optionally, the electrochemical energy storage device is preferably a lithium-ion battery, a sodium-ion battery, a supercapacitor, a fuel cell or a solar cell.

[0058] The present invention also provides a use of a polymer having an amphiphilic comb-shaped morphology structure in preparing a negative electrode material having a gas generation inhibiting effect.

[0059] Hereinafter, the surface-coated polymer silicon-carbon negative electrode material, preparation method and application thereof will be further described through the following specific examples.

[0060] Example 1

[0061] A hydrophobic comb polymer was prepared by the ring-opening reaction of acrylic acid and cyclopentanolactone at 120°C using stannous octoate as a catalyst. The molar ratio of acrylic acid to cyclopentanolactone was 1:1, and the amount of stannous octoate was 0.1 mol% of the total amount of acrylic acid and cyclopentanolactone. A hydrophilic comb polymer was prepared by grafting 3-(methacryloyloxy)propionic acid (CAS: 13318-10-0) onto polyethylene glycol using ammonium persulfate as an initiator at 60°C under a nitrogen atmosphere. The molar ratio of 3-(methacryloyloxy)propionic acid to polyethylene glycol was 10:1, and the amount of ammonium persulfate was 0.1 mol% of the 3-(methacryloyloxy)propionic acid. Then, using 2,2'-[thiocarbonyl(thio)]bis[2-methylpropionic acid] as a chain transfer agent, a hydrophobic comb polymer and a hydrophilic comb polymer in a mass ratio of 35:65 were RAFT polymerized under ultraviolet light to obtain an amphiphilic comb polymer poly(acrylic acid-g-valerolactone)-co-poly(3-(methacryloyloxy)propionic acid-g-ethylene glycol), wherein the amount of 2,2'-[thiocarbonyl(thio)]bis[2-methylpropionic acid] was 1 mol% of the total amount of the hydrophobic comb polymer and the hydrophilic comb polymer. The hydrophobic side chain polyvalerolactone had a molecular weight of 9,300 and a degree of polymerization of 80, the hydrophilic side chain polyethylene glycol had a molecular weight of 20,000 and a degree of polymerization of 450, and the molecular weight of poly(acrylic acid-g-valerolactone)-co-poly(3-(methacryloyloxy)propionic acid-g-ethylene glycol) was 470,000.

[0062] 200g of particles with a diameter of 2μm-15μm and a specific surface area of 10m 2 / g of silicon-carbon material, 3g of poly(acrylic acid-g-valerolactone)-co-poly(2-acrylic acid, 2-methyl-2-(carboxyloxy)ethyl ester-g-ethylene glycol), 1g of boric acid crosslinking agent and 0.8g of carbon black conductive agent were dispersed in 1000mL of water and stirred at 2000rpm / min for 1.5h to obtain a mixed slurry, and then the mixed slurry was spray-dried at 150℃ and vacuum-dried at 120℃ for 12h to obtain a silicon-carbon negative electrode material.

[0063] The SEM image of the silicon-carbon negative electrode material of this embodiment is as follows Figure 2 shown.

[0064] Example 2

[0065] Methacrylic acid, caprolactone, acrylamide, and starch were provided, and an amphiphilic comb-type polymer, poly(methacrylic acid-g-caprolactone)-co-poly(acrylamide-g-starch), was prepared according to the polymerization method of Example 1. The hydrophobic side chain polycaprolactone had a molecular weight of 6,400 and a degree of polymerization of 56, the hydrophilic side chain starch had a molecular weight of 75,000 and a degree of polymerization of 416, and the molecular weight of poly(methacrylic acid-g-caprolactone)-co-poly(acrylamide-g-starch) was 800,000.

[0066] According to the same preparation method as Example 1, poly(methacrylic acid-g-caprolactone)-co-poly(acrylamide-g-starch) was mixed with a silicon-carbon material and dried to prepare a silicon-carbon negative electrode material, wherein the cross-linking agent was ethylenediamine and the conductive agent was acetylene black.

[0067] Example 3

[0068] Methacrylic acid, lactide, 2-mercaptoethyl ester-2-acrylate, and carboxymethyl cellulose were provided, and an amphiphilic comb polymer (methacrylic acid-g-lactide)-co-poly(2-mercaptoethyl ester-2-acrylate-g-carboxymethyl cellulose) was prepared according to the polymerization method of Example 1. The hydrophobic side chain polylactide had a molecular weight of 4,600 and a degree of polymerization of 46; the hydrophilic side chain carboxymethyl cellulose had a molecular weight of 50,000 and a degree of polymerization of 270; and the molecular weight of poly(methacrylic acid-g-lactide)-co-poly(2-mercaptoethyl ester-2-acrylate-g-carboxymethyl cellulose) was 650,000.

[0069] According to the same preparation method as Example 1, (methacrylic acid-g-lactide)-co-poly(2-mercaptoethyl ester-2-acrylate-g-carboxymethyl cellulose) was mixed with a silicon-carbon material and dried to prepare a silicon-carbon negative electrode material, wherein the cross-linking agent was ethylene glycol and the conductive agent was carbon black.

[0070] Example 4

[0071] N-(aminocarbonyl)methacrylamide, ethylene carbonate, ((carbamoylamino)-2-methyl-2-propionic acid methyl ester) and polyvinyl alcohol were provided, and an amphiphilic comb-type polymer poly(N-(aminocarbonyl)methacrylamide-g-ethylene carbonate)-co-poly(((carbamoylamino)-2-methyl-2-propionic acid methyl ester)-g-vinyl alcohol) was prepared according to the polymerization method of Example 1. The hydrophobic side chain polyvinyl carbonate had a molecular weight of 3200 and a degree of polymerization of 37; the hydrophilic side chain polyvinyl alcohol had a molecular weight of 35,000 and a degree of polymerization of 794; and the molecular weight of poly(N-(aminocarbonyl)methacrylamide-g-ethylene carbonate)-co-poly(((carbamoylamino)-2-methyl-2-propionic acid methyl ester)-g-vinyl alcohol) was 500,000.

[0072] According to the same preparation method as Example 1, poly(N-(aminocarbonyl)methacrylamide-g-ethylene carbonate)-co-poly(((carbamylamino)-2-methyl-2-propionic acid methyl ester)-g-vinyl alcohol) was mixed with a silicon-carbon material and dried to prepare a silicon-carbon negative electrode material, wherein the cross-linking agent was boric acid and the conductive agent was a single-arm carbon nanotube.

[0073] Example 5

[0074] 4-Oxohex-5-ene-1-sulfonic acid, propylene carbonate, 3-aminopropyl-2-acrylate, and hyaluronic acid were provided, and an amphiphilic comb-type polymer, poly(4-oxohex-5-ene-1-sulfonic acid-g-propylene carbonate)-co-poly(3-aminopropyl-2-acrylate-g-hyaluronic acid), was prepared according to the polymerization method of Example 1. The molecular weight of the hydrophobic side chain polypropylene carbonate was 3000, the degree of polymerization was 29, the molecular weight of the hydrophilic side chain hyaluronic acid was 190,000, the degree of polymerization was 474, and the molecular weight of poly(4-oxohex-5-ene-1-sulfonic acid-g-propylene carbonate)-co-poly(3-aminopropyl-2-acrylate-g-hyaluronic acid) was 2,000,000.

[0075] According to the same preparation method as Example 1, poly(4-oxohex-5-ene-1-sulfonic acid-g-propylene carbonate)-co-poly(3-aminopropyl-2-acrylate-g-hyaluronic acid) was mixed with a silicon-carbon material to prepare a silicon-carbon negative electrode material, wherein the cross-linking agent was 1,6-hexanediol and the conductive agent was carbon black.

[0076] Example 6

[0077] 2-Methacrylic acid, caprolactone, acrylamide, and polyethylene glycol were provided, and an amphiphilic comb-type polymer, poly(2-methacrylic acid-g-caprolactone)-co-poly(acrylamide-g-ethylene glycol), was prepared according to the polymerization method of Example 1. The hydrophobic side chain polycaprolactone had a molecular weight of 15,000 and a degree of polymerization of 132; the hydrophilic side chain polyethylene glycol had a molecular weight of 2,000 and a degree of polymerization of 30; and the molecular weight of poly(2-methacrylic acid-g-caprolactone)-co-poly(acrylamide-g-ethylene glycol) was 180,000.

[0078] According to the same preparation method as in Example 1, poly(2-methacrylic acid-g-caprolactone)-co-poly(acrylamide-g-ethylene glycol) was mixed with the silicon-carbon material and dried to prepare a silicon-carbon negative electrode material.

[0079] Example 7

[0080] 2-Methacrylic acid, propylene carbonate, acrylamide, and polyethylene glycol were provided, and an amphiphilic comb-type polymer, poly(2-methacrylic acid-g-propylene carbonate)-co-poly(acrylamide-g-ethylene glycol), was prepared according to the polymerization method of Example 1. The hydrophobic side chain polypropylene carbonate had a molecular weight of 3000 and a degree of polymerization of 29, the hydrophilic side chain polyethylene glycol had a molecular weight of 2000 and a degree of polymerization of 30, and the molecular weight of poly(2-methacrylic acid-g-propylene carbonate)-co-poly(acrylamide-g-ethylene glycol) was 770,000.

[0081] According to the same preparation method as Example 1, poly(2-methacrylic acid-g-propylene carbonate)-co-poly(acrylamide-g-ethylene glycol) was mixed with the silicon-carbon material to prepare a silicon-carbon negative electrode material.

[0082] Comparative Example 1

[0083] The difference between Comparative Example 1 and Example 1 is that the silicon-carbon material is directly mixed with water to obtain a mixed slurry to prepare the silicon-carbon negative electrode material.

[0084] Comparative Example 2

[0085] Comparative Example 2 differs from Example 1 in that poly(acrylic acid-g-valerolactone)-co-poly(2-acrylic acid, 2-methyl-2-(carboxyoxy)ethyl ester-g-ethylene glycol) is replaced with a hydrophilic polymer, polyvinyl alcohol. The polyvinyl alcohol has a molecular weight of 89,000, a degree of polymerization of 2,100, and a solubility parameter of 16.05.

[0086] Comparative Example 3

[0087] Comparative Example 3 differs from Example 1 in that poly(acrylic acid-g-valerolactone)-co-poly(2-acrylic acid, 2-methyl-2-(carboxyoxy)ethyl ester-g-ethylene glycol) is replaced with the hydrophobic polymer polymethyl methacrylate, and no crosslinking agent is added. The polymethyl methacrylate has a molecular weight of 15,000, a degree of polymerization of 150, and a solubility parameter of 8.7.

[0088] The silicon-carbon negative electrode materials prepared in the above examples and comparative examples were subjected to gas production tests and soft-pack battery tests. The test methods are as follows:

[0089] Gas production test:

[0090] 5g of silicon-carbon anode material and 50mL of water were added to a sealed bottle and thoroughly dissolved by centrifugal stirring. The bottle was then placed in a constant temperature chamber at 25°C. The gas production (H2) in the bottle was measured after 24h, 72h, 120h, and 168h. The test results are shown in Table 1.

[0091] Soft pack battery test:

[0092] A soft-pack lithium-ion battery was fabricated using a silicon-carbon anode material doped with 80% artificial graphite as the negative electrode, the ternary material NCM111 as the positive electrode material, LiPF6 as the lithium salt, a 1:1 volume ratio mixture of EC and DEC as the electrolyte, and Celgard 2400 membrane as the separator. Cycling tests (capacity retention over 200 cycles) were conducted under the following conditions: voltage range: 2.5V-4.2V, charge / discharge rate: 1C / 1C. The cycling test results are shown in Table 2.

[0093] Table 1

[0094]

[0095] Table 2

[0096] 200-cycle capacity retention rate (%) Example 1 95.6 Example 2 97.2 Example 3 95.4 Example 4 97.9 Example 5 96.1 Example 6 93.5 Example 7 94.4 Comparative Example 1 90.8 Comparative Example 2 92.1 Comparative Example 3 91.8

[0097] As shown in Examples 1-7 and Comparative Examples 1-3 in Table 1, the silicon-carbon anode material of the present invention can effectively reduce gas production. Furthermore, as shown in Examples 1-5 and 6-7, when the molecular weight and degree of polymerization of the hydrophilic side chains of the amphiphilic comb polymer are both greater than those of the hydrophobic side chains, the resulting coating layer exhibits a greater coating effect, further reducing gas production.

[0098] In addition, as can be seen from Example 1 and Comparative Example 1 in Table 1, when there is no coating layer on the surface of the silicon-carbon material, the gas production is relatively large. As can be seen from Example 1 and Comparative Examples 2-3, when the surface of the silicon-carbon material is a hydrophilic coating layer or a hydrophobic coating layer, the gas production of the silicon-carbon negative electrode material cannot be effectively reduced.

[0099] It can be seen from Examples 1-7 and Comparative Examples 1-3 in Table 2 that the silicon-carbon negative electrode material of the present invention has a large capacity retention rate after 200 electrochemical cycles, indicating that the application of the silicon-carbon negative electrode material of the present invention in the electrochemical energy storage device can effectively improve its volume expansion problem.

[0100] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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 above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A silicon-carbon negative electrode material, characterized in that: The invention comprises a silicon-carbon material and a coating layer coated on the surface of the silicon-carbon material, wherein the material of the coating layer comprises an amphiphilic comb-type polymer and a cross-linking agent, wherein the amphiphilic comb-type polymer comprises a hydrophilic side chain and a hydrophobic side chain, wherein the hydrophobic side chains of the amphiphilic comb-type polymer are coated on the surface of the silicon-carbon material to form a hydrophobic coating layer, and the hydrophilic side chains are surrounded on the surface of the silicon-carbon material due to the hydrophilic effect and cross-linking of the cross-linking agent to form a dense hydrophilic coating layer.

2. The silicon-carbon negative electrode material according to claim 1, characterized in that The amphiphilic comb polymer further satisfies at least one of the following conditions: (1) The molecular weight of the amphiphilic comb polymer is 50,000-2,000,000; (2) the molecular weight of the hydrophobic side chain of the amphiphilic comb polymer is 500-18000; (3) The degree of polymerization of the hydrophobic side chains of the amphiphilic comb polymer is 5-120; (4) The molecular weight of the hydrophilic side chain of the amphiphilic comb polymer is 4000-250000; (5) The degree of polymerization of the hydrophilic side chains of the amphiphilic comb-type polymer is 100-1000.

3. The silicon-carbon negative electrode material according to claim 1 or 2, characterized in that: The carbon chain length of the hydrophilic side chain of the amphiphilic comb polymer is greater than the carbon chain length of the hydrophobic side chain.

4. The silicon-carbon negative electrode material according to claim 1, characterized in that The mass fraction of the coating layer in the silicon-carbon negative electrode material is 0.5%-10%.

5. The silicon-carbon negative electrode material according to claim 1, characterized in that The material of the coating layer also includes a conductive agent.

6. A method for preparing the silicon-carbon negative electrode material according to any one of claims 1 to 5, characterized in that: The following steps are involved: An amphiphilic comb-type polymer is provided, and the amphiphilic comb-type polymer, a silicon-carbon material and a cross-linking agent are mixed in water to obtain a slurry, which is then dried to obtain a silicon-carbon negative electrode material.

7. The method for preparing the silicon-carbon negative electrode material according to claim 6, characterized in that: The preparation method of the amphiphilic comb polymer comprises the following steps: Will React with hydrophobic substances to prepare hydrophobic comb polymers. reacting with a hydrophilic substance to prepare a hydrophilic comb polymer, and then subjecting the hydrophobic comb polymer and the hydrophilic comb polymer to RAFT polymerization to obtain the amphiphilic comb polymer; Wherein, R and R2 are independently selected from -H or -(CH2) a -CH3, a≥0; R1 is selected from -(CH2) b -X, wherein X is selected from hydroxyl, carboxyl, amino, thiol, urea, thiourea, amide or sulfonic acid, b≥0; R3 is selected from -(CH2) c -Y-(CH2) d -, wherein Y is selected from carbon, nitrogen, oxygen, sulfur, phosphorus, carbonyl, urea or amide, and c and d are natural numbers; R4 is selected from hydroxyl, sulfhydryl, carboxyl, amino, urea, thiourea, amide or sulfonic acid.

8. The method for preparing the silicon-carbon negative electrode material according to claim 7, characterized in that: The solubility parameter of the hydrophobic substance is 5J 1 / 2 cm -3 / 2 -30J 1 / 2 cm -3 / 2 , the solubility parameter of the hydrophilic substance is 15J 1 / 2 cm -3 / 2 -40J 1 / 2 cm -3 / 2 , and the solubility parameter of the hydrophilic substance is greater than the solubility parameter of the hydrophobic substance.

9. The method for preparing the silicon-carbon negative electrode material according to claim 6, wherein: In the step of mixing the amphiphilic comb polymer, the silicon-carbon material and the cross-linking agent in water to obtain a slurry, a conductive agent is also added.

10. A negative electrode sheet comprising the silicon-carbon negative electrode material according to any one of claims 1 to 5.

11. An electrochemical energy storage device comprising the negative electrode sheet according to claim 10.

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