Negative active material, method for preparing the same, and use thereof

Abstract

This invention relates to negative electrode active materials, their preparation methods, and applications. The negative electrode active material comprises a silicon-based material and a polymer coating layer covering its surface. The polymer coating layer comprises a water-soluble polymer and a surfactant, and the water contact angle of the polymer coating layer is 65°–85°. The surfactant has the chemical formula A1–R–A2, where A1 and A2 are each independently selected from polar groups containing at least one element selected from N, O, P, and S, and R is selected from substituted or unsubstituted C8–C6 groups. 50 Aliphatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Aliphatic hydrocarbon segments containing heteroatoms, substituted or unsubstituted C8-C 50 Alicyclic hydrocarbon segments, substituted or unsubstituted C8-C 50 Alicyclic hydrocarbon segments containing heteroatoms, substituted or unsubstituted C8-C 50 Aromatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Aromatic hydrocarbon segments containing heteroatoms. This negative electrode active material has a bilayer protective structure of an inner hydrophobic layer and an outer hydrophilic layer, exhibiting excellent dispersibility and low gas production.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode active material, its preparation method, and its application. Background Technology

[0002] With the increasing demand for high-energy-density batteries, silicon-based materials, which have a relatively high theoretical specific capacity (approximately 4200 mAh / g), have become a popular research direction for battery anode materials. However, silicon-based materials suffer from severe volume expansion (up to 300%) during charge and discharge, causing the silicon-based materials to pulverize and peel off from the current collector. This results in a loss of electrical contact between active materials and between the active material and the current collector, while simultaneously forming a new solid electrolyte layer (SEI). Ultimately, this leads to a deterioration in electrochemical performance, limiting the practical application of batteries.

[0003] While surface modification, elemental doping, and pre-lithiation of silicon-based anode materials can help suppress volume expansion and improve performance, these methods also increase the instability of the silicon-based anode materials. This leads to a surge in gas generation during electrode manufacturing, particularly in materials with gas-generating defects. This not only poses safety risks during the homogenization process but can also cause defects such as pinholes, pores, particles, scratches, and material shedding during electrode coating and drying, thus reducing the overall performance of the electrode sheet. In particular, coating the surface of silicon-based anode materials with hydrophilic polymers, while helping to improve the dispersion of silicon-carbon during homogenization, exacerbates the side reaction of silicon with water, resulting in gas generation, leading to battery capacity loss and reduced lifespan. Summary of the Invention

[0004] Therefore, it is necessary to provide a negative electrode active material, its preparation method, and its application to address the above problems. The negative electrode active material has a unique double-layer protective structure with an inner hydrophobic layer and an outer hydrophilic layer. It not only has excellent dispersibility but also effectively suppresses gas production and volume expansion, which is beneficial to improving the stability and safety of the battery.

[0005] A negative electrode active material includes a silicon-based material and a polymer coating layer coated on the surface of the silicon-based material. The polymer coating layer includes a water-soluble polymer and a surfactant, and the water contact angle of the polymer coating layer is 65°-85°.

[0006] The surfactant has the chemical formula A1-R-A2, wherein A1 and A2 are each independently selected from polar groups containing at least one element selected from N, O, P, and S, and R is selected from substituted or unsubstituted C8-C groups. 50 Aliphatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Heteroatom-containing aliphatic hydrocarbon segments, substituted or unsubstituted C8-C 50Alicyclic hydrocarbon segments, substituted or unsubstituted C8-C 50 Alicyclic hydrocarbon segments containing heteroatoms, substituted or unsubstituted C8-C 50 Aromatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Aromatic hydrocarbon segments containing heteroatoms, with substituents selected from C1-C2. 20 Branched or straight-chain hydrocarbon groups, C1-C 20 Branched or straight-chain alkoxy groups, C3-C 20 Branched or straight-chain cycloalkyl groups, C6-C 30 Aromatic group, C5-C 30 At least one of the heteroaryl groups.

[0007] In one embodiment, A1 and A2 are each independently selected from at least one of the following groups: carboxylic acid group, carboxyl salt group, sulfonic acid group, sulfonate group, sulfate group, sulfate group, phosphate group, phosphate group, amino group, amide group, urea group, thiourea group, hydroxyl group, mercapto group, ammonium salt group, quaternary ammonium salt group, phosphonium salt group, quaternary phosphonium salt group, imidazole salt group, pyridine salt group, ammonium oxide group, polyether group, alkyl glycoside group or polysaccharide group.

[0008] In one embodiment, A1 and A2 are each independently selected from at least one of quaternary ammonium salt groups, carboxylic acid groups, amino groups, amide groups, alkyl glycoside groups, thiourea groups, and hydroxyl groups.

[0009] In one embodiment, when the heteroatom is selected from silicon atoms, the number of carbon atoms or silicon atoms in R is independently selected from 8 to 1000;

[0010] And / or, the molecular weight of R is 100-10000.

[0011] In one embodiment, the surfactant is selected from...

[0012] At least one of them.

[0013] In one embodiment, the water-soluble polymer is selected from at least one of polysaccharide polymers, polyether polymers, polyamide polymers, polysulfone polymers, polysulfide polymers, polyacrylic acid polymers, polyacrylate polymers, polyacrylamide polymers, polyacrylonitrile polymers, polyvinyl acetate polymers, polyvinyl alcohol polymers, polyvinyl alkyl ether polymers, polyepoxide polymers, polyethyleneimine polymers, and polyionic liquid polymers.

[0014] In one embodiment, the mass of the polymer coating layer is 0.2%-80% of the mass of the silicon-based material;

[0015] And / or, the mass ratio of the water-soluble polymer to the surfactant is 0.1:50-30:0.1;

[0016] And / or, the polymer coating layer further includes at least one of lithium salt additives, conductive agents, and crosslinking agents.

[0017] In one embodiment, the silicon-based material is selected from at least one of silicon microparticles, silicon nanoparticles, silicon-carbon materials, silicon-oxygen materials, and silicon alloy materials.

[0018] A method for preparing a negative electrode active material as described above includes: dispersing a silicon-based material, a water-soluble polymer, and a surfactant in a solvent to obtain a first mixture, and drying the first mixture to obtain the negative electrode active material;

[0019] Alternatively, a silicon-based material and a water-soluble polymer are dispersed in a solvent to obtain a second mixture. The second mixture is dried to obtain a composite. The composite is then dispersed with a surfactant in a solvent to obtain a third mixture. The third mixture is dried to obtain the negative electrode active material.

[0020] In one embodiment, the mass ratio of the silicon-based material to the water-soluble polymer and the surfactant is 100:(0.1-30):(0.1-50);

[0021] And / or, the dispersion speed is 100rpm-5000rpm;

[0022] And / or, the drying temperature is 25℃-200℃;

[0023] And / or, the first mixture further includes at least one of lithium salt additives, conductive agents, and crosslinking agents;

[0024] And / or, the second mixture further includes at least one of lithium salt additives, conductive agents, and crosslinking agents.

[0025] 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 the negative electrode active material as described above.

[0026] A battery comprising a negative electrode as described above.

[0027] In the negative electrode active material of the present invention, a water-soluble polymer, in conjunction with a surfactant with a special structure, coats the surface of a silicon-based material to form a polymer coating layer. In this polymer coating layer, both the R hydrophobic chain of the surfactant and the water-soluble polymer can act on the surface of the silicon-based material, and there is a hydrophobic interaction between the R hydrophobic chain of the surfactant and the hydrophobic groups in the water-soluble polymer, thereby forming a hydrophobic protective layer coating the surface of the silicon-based material. At the same time, the hydrophilic bi-headed structure in the surfactant is mainly distributed in a U-shape on the surface of the hydrophobic protective layer, forming a hydrophilic outer layer, thus forming a double-layer protective structure with an inner hydrophobic layer and an outer hydrophilic layer with a special water contact angle. This not only reduces the side reaction between silicon and water and effectively suppresses gas production by utilizing the inner hydrophobic effect, but also improves the dispersion effect of the negative electrode active material in aqueous slurry through the outer hydrophilic effect.

[0028] Furthermore, when silicon-based materials undergo volume expansion, surfactants with special structures can release stress through stretching, thereby effectively suppressing the volume expansion of the negative electrode active material and improving the stability and safety of the battery. Detailed Implementation

[0029] 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.

[0030] 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 specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0031] In traditional techniques, considering that the carbon structure on the surface of silicon-based materials is a hydrophobic layer, which is not conducive to the dispersion of silicon-based materials in water, it is usually preferable to coat the surface of silicon-based materials with hydrophilic polymers to improve their dispersibility during the homogenization process. However, the hydrophilic polymers on the surface can also cause more severe side reactions between silicon-based materials and water, thereby exacerbating the gas generation problem during the homogenization process.

[0032] Based on this, the present invention provides a negative electrode active material, comprising a silicon-based material and a polymer coating layer coated on the surface of the silicon-based material, wherein the polymer coating layer comprises a water-soluble polymer and a surfactant, and the water contact angle of the polymer coating layer is 65°-85°.

[0033] The surfactant has the chemical formula A1-R-A2, wherein A1 and A2 are each independently selected from polar groups containing at least one element selected from N, O, P, and S, and R is selected from substituted or unsubstituted C8-C groups. 50 Aliphatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Heteroatom-containing aliphatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Alicyclic hydrocarbon segments, substituted or unsubstituted C8-C 50 Alicyclic hydrocarbon segments containing heteroatoms, substituted or unsubstituted C8-C 50 Aromatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Aromatic hydrocarbon segments containing heteroatoms, with substituents selected from C1-C2. 20 Branched or straight-chain hydrocarbon groups, C1-C 20 Branched or straight-chain alkoxy groups, C3-C 20 Branched or straight-chain cycloalkyl groups, C6-C 30 Aromatic group, C5-C 30 At least one of the heteroaryl groups.

[0034] In the negative electrode active material of this invention, a water-soluble polymer, in conjunction with a surfactant with a special structure, coats the surface of a silicon-based material to form a polymer coating layer. In this polymer coating layer, both the R hydrophobic chain of the surfactant and the water-soluble polymer can act on the surface of the silicon-based material, and there is a hydrophobic interaction between the R hydrophobic chain of the surfactant and the hydrophobic groups in the water-soluble polymer, thereby forming a hydrophobic protective layer coating the surface of the silicon-based material. At the same time, the hydrophilic bi-headed structure in the surfactant is mainly distributed in a U-shape on the surface of the hydrophobic protective layer, forming a hydrophilic outer layer, thus forming a double-layer protective structure with an inner hydrophobic layer and an outer hydrophilic layer with a special water contact angle. This not only reduces the side reaction between silicon and water and effectively suppresses gas production by utilizing the inner hydrophobic effect, but also improves the dispersion effect of the negative electrode active material in aqueous slurry through the outer hydrophilic effect and the non-covalent bond interaction between the hydrophilic bi-headed structure in the surfactant and the hydrophilic groups in the water-soluble polymer.

[0035] In addition, on the one hand, when silicon-based materials undergo volume expansion, surfactants with special structures can release stress by being stretched, thereby effectively suppressing the volume expansion of the negative electrode active material; on the other hand, surfactants also have a similar effect to crosslinking agents, crosslinking with water-soluble polymers through non-covalent bonds to coat the surface of silicon-based materials, thereby improving the mechanical properties of the coating layer.

[0036] Therefore, using the negative electrode active material described in this invention in batteries is beneficial to improving battery stability and safety, and extending battery life.

[0037] It should be noted that surfactants can form a composite coating layer outside the water-soluble polymer, or they can be blended with the water-soluble polymer to form a cross-linked coating layer. This invention does not limit the positional relationship between the surfactant and the water-soluble polymer.

[0038] In one embodiment, the surfactant includes, but is not limited to, at least one of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.

[0039] Specifically, A1 and A2 are each independently selected from at least one of the following groups: carboxylic acid group, carboxyl salt group, sulfonic acid group, sulfonate group, sulfate group, sulfate group, phosphate group, phosphate group, amino group, amide group, urea group, thiourea group, hydroxyl group, mercapto group, ammonium salt group, quaternary ammonium salt group, phosphonium salt group, quaternary phosphonium salt group, imidazole salt group, pyridine salt group, ammonium oxide group, polyether group, alkyl glycoside group or polysaccharide group, preferably at least one of the following groups: quaternary ammonium salt group, carboxylic acid group, amino group, amide group, alkyl glycoside group, thiourea group, hydroxyl group.

[0040] The heteroatoms in R include, but are not limited to, at least one of oxygen, sulfur, nitrogen, silicon, and phosphorus atoms. When the heteroatoms are selected from silicon atoms, R can be understood as an organosilane segment. Preferably, the number of carbon atoms or silicon atoms in R is independently selected from 8 to 1000, and more preferably from 8 to 40.

[0041] In one embodiment, the molecular weight of R is 100-10000, preferably 100-700.

[0042] In one embodiment, R is preferably unsubstituted C8-C. 50 Aliphatic hydrocarbon chain segments.

[0043] In one embodiment, the surfactant is preferably...

[0044] At least one of them.

[0045] In one embodiment, the water-soluble polymer is selected from at least one of polysaccharide polymers, polyether polymers, polyamide polymers, polysulfone polymers, polysulfide polymers, polyacrylic acid polymers, polyacrylate polymers, polyacrylamide polymers, polyacrylonitrile polymers, polyvinyl acetate polymers, polyvinyl alcohol polymers, polyvinyl alkyl ether polymers, polyepoxide polymers, polyethyleneimine polymers, and polyionic liquid polymers.

[0046] Preferably, the water-soluble polymer is selected from at least one of polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyacrylamide (PAM), polyacrylic acid (PAA) and its salts, polyethyleneimine (PEI), sodium polyvinyl sulfate (PVS), sodium carboxymethyl cellulose (CMC-Na), polyimide salts, polyquaternary ammonium salts, polyquaternary phosphonium salts, gelatin, sodium alginate, sodium xylan polysulfate, chitosan, and povidone (PVP).

[0047] It is understood that the above-mentioned water-soluble polymers also include their corresponding physically or chemically modified polymers. The monomers corresponding to any two or more polymers can copolymerize to form one or more forms of random copolymers, alternating copolymers, block copolymers, and graft copolymers. This invention does not limit this.

[0048] In one embodiment, the molecular weight of the water-soluble polymer is 1,000-1,000,000.

[0049] In one embodiment, the mass of the polymer coating layer is 0.2%-80% of the mass of the silicon-based material, preferably 2%-20%.

[0050] In one embodiment, the mass ratio of the water-soluble polymer to the surfactant is 0.1:50-30:0.1, preferably 0.1:1-10:1.

[0051] In one embodiment, the polymer coating layer further includes at least one of lithium salt additives, conductive agents, and crosslinking agents.

[0052] Specifically, 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)-polystyrene sulfonic acid (PEDOT:PSS).

[0053] Lithium salt additives include, but are not limited to, at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0054] In one embodiment, the silicon-based material is selected from at least one of silicon microparticles, silicon nanoparticles, silicon-carbon materials, silicon-oxygen materials, and silicon alloy materials.

[0055] It should be noted that this invention does not limit silicon-based materials. Silicon-based materials 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., and can also be combined with other materials to form composite silicon-based materials through physical or chemical methods.

[0056] The present invention also provides a method for preparing the negative electrode active material as described above, comprising: dispersing a silicon-based material, a water-soluble polymer, and a surfactant in a solvent to obtain a first mixture, and drying the first mixture to obtain the negative electrode active material; or, dispersing a silicon-based material and a water-soluble polymer in a solvent to obtain a second mixture, drying the second mixture to obtain a composite, and then dispersing the composite and a surfactant in a solvent to obtain a third mixture, and drying the third mixture to obtain the negative electrode active material.

[0057] In the preparation method described in this invention, the hydrophilic groups in the water-soluble polymer bind to silicon atoms on the surface of the silicon-based material through hydrogen bonding, and the hydrophobic groups bind to carbon atoms on the surface of the silicon-based material through hydrophobic interactions. Simultaneously, the surfactant forms a U-shaped structure in the solvent, wherein the middle part of the U-shaped structure is a hydrophobic segment that can bind to carbon atoms on the surface of the silicon-based material through hydrophobic interactions, and the two ends of the U-shaped structure are polar hydrophilic ends that can increase the dispersibility of the silicon-based material in water through hydrophilic interactions. Furthermore, there are hydrophobic interactions between the hydrophobic segments of the surfactant and the hydrophobic groups of the water-soluble polymer, giving the surfactant an effect similar to a crosslinking agent, which is beneficial for improving the mechanical properties of the coating layer.

[0058] In one embodiment, the mass ratio of the silicon-based material to the water-soluble polymer and the surfactant is 100:(0.1-30):(0.1-50), preferably 100:(1-10):(1-10).

[0059] In one embodiment, the dispersion speed is 100rpm-5000rpm, including but not limited to any one of 100rpm, 500rpm, 1000rpm, 1500rpm, 2000rpm, 2500rpm, 3000rpm, 3500rpm, 4000rpm, 4500rpm, and 5000rpm, or a range between any two.

[0060] In one embodiment, the drying temperature is 25°C-200°C, including but not limited to any one of 25°C, 50°C, 60°C, 100°C, 120°C, 150°C, 180°C, and 200°C, or a range between any two.

[0061] In one embodiment, the drying method is selected from at least one of hot air drying, spray drying, or vacuum drying.

[0062] It should be noted that the solvent includes, but is not limited to, water, preferably water; the dispersion speed, drying temperature and drying method for preparing the first mixture, the second mixture and the third mixture can be the same or different, and the present invention does not limit them.

[0063] In one embodiment, the first mixture and / or the second mixture further include at least one of lithium salt additives, conductive agents, and crosslinking agents.

[0064] Specifically, 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)-polystyrene sulfonic acid (PEDOT:PSS).

[0065] Lithium salt additives include, but are not limited to, at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0066] 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 negative electrode active 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.

[0067] 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.

[0068] The following specific embodiments will further illustrate the negative electrode active material, its preparation method, and its application. 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.

[0069] It should be noted that the silicon-based material used in the examples and comparative examples was purchased from Zhejiang Lichen New Material Technology Co., Ltd., model C ONE-SC 1800, with a particle size of approximately 3μm-7μm and a specific surface area of ​​approximately 3m². 2 / g, with a carbon content of approximately 51.23% and a resistivity of approximately 4.63Ω·cm.

[0070] The surfactants used in the examples and comparative examples include: surfactant a (CAS: 1420-40-2), with the chemical formula […]. Surfactant b (CAS: 821-38-5), chemical formula is Surfactant C (CAS: 946602-82-0), chemical formula is Surfactant d (CAS: 710311-41-4), chemical formula is Surfactant e (CAS: 19101-02-1), chemical formula is

[0071] Example 1

[0072] 50g of silicon-based material, 1g of polyvinyl alcohol, 1g of surfactant a and 0.5g of graphene were added to 500mL of water and mechanically stirred at 1000rpm for 30 minutes at room temperature to obtain a mixture. The mixture was spray-dried at 200℃ and then dried under vacuum at 130℃ for 3 hours to obtain the negative electrode active material.

[0073] Example 2

[0074] 50g of silicon-based material, 1g of polyacrylamide, 1g of surfactant b, 0.5g of LiTFSI and 0.5g of acetylene black were added to 500mL of water and mechanically stirred at 200rpm for 60 minutes at room temperature to obtain a mixture. The mixture was then spray-dried at 150℃, and the dried product was subsequently dried under vacuum at 130℃ for 3 hours to obtain the negative electrode active material.

[0075] Example 3

[0076] 50g of silicon-based material, 1g of modified hydroxymethyl cellulose, 0.5g of surfactant c, 0.5g of LiFSI and 0.5g of carbon black were added to 500mL of water and mechanically stirred at 1000rpm for 30 minutes at room temperature to obtain a mixture. The mixture was then spray-dried at 140℃, and the dried product was subsequently dried under vacuum at 150℃ for 3 hours to obtain the negative electrode active material.

[0077] Example 4

[0078] 50g of silicon-based material, 1g of polyacrylamide, 0.2g of surfactant d and 0.5g of single-walled carbon nanotubes were added to 500mL of water and mechanically stirred at 1500rpm for 30 minutes at room temperature to obtain a mixture. The mixture was spray-dried at 150℃, and then the dried product was dried under vacuum at 130℃ for 3 hours to obtain the negative electrode active material.

[0079] Example 5

[0080] 50g of silicon-based material, 1g of polyacrylic acid, 0.4g of surfactant e and 0.5g of single-walled carbon nanotubes were added to 500mL of water and mechanically stirred at 1300rpm for 30 minutes at room temperature to obtain a mixture. The mixture was spray-dried at 120℃, and then the dried product was dried under vacuum at 130℃ for 3 hours to obtain the negative electrode active material.

[0081] Comparative Example 1

[0082] The difference between Comparative Example 1 and Example 1 is that surfactant a was not added.

[0083] Comparative Example 2

[0084] The difference between Comparative Example 2 and Example 1 is that polyvinyl alcohol was not added.

[0085] According to the ratio of water-soluble polymer and surfactant provided in Examples 1-5, the corresponding mixtures were prepared and dropped onto silicon wafers for spin coating to form films. Water was used as the test solvent, and the water contact angle was measured by a contact angle meter. The water contact angles of polyvinyl alcohol used in Comparative Example 1 and surfactant a used in Comparative Example 2 were tested in the same way. The results are shown in Table 1.

[0086] Table 1

[0087]

[0088]

[0089] As shown in Table 1, Comparative Example 1 shows the water contact angle of the polyvinyl alcohol-coated silicon-based material. Compared with Comparative Example 1, the water contact angle of Example 1 increased from 60° to 78° with the addition of surfactant a. This proves that the addition of surfactant effectively improves the overall hydrophilic and hydrophobic properties of the system and helps maintain dispersibility.

[0090] The negative electrode active materials prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to gas generation tests and pouch cell tests.

[0091] (1) Gas production test method includes: take 5g of negative electrode active material and 50g of water into a sealed bottle, and make it fully dissolved by centrifugal stirring. Then, place it in a constant temperature room at 25℃ and test the amount of gas (H2) produced in the bottle on the 1st, 3rd, 5th and 7th days respectively. The test results are shown in Table 2.

[0092] (2) The testing method for the soft-pack battery includes: doping the negative electrode active material with artificial graphite at a mass ratio of 2:8 and adding 0.5% carbon nanotubes (CNTs) as the negative electrode; using NCM811 ternary material as the positive electrode material; using a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 as the electrolyte solvent; and using a Celgard 2400 membrane as the separator to prepare a 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.

[0093] Table 2

[0094]

[0095] According to the data in Table 2, Comparative Example 1 is a silicon-based material coated with polyvinyl alcohol, with an average daily gas production of about 4.23 cc / kg / day; Example 1 is a silicon-based material co-coated with polyvinyl alcohol and surfactant, with an average daily gas production of about 1.55 cc / kg / day. Obviously, the silicon-based materials co-coated with water-soluble polymer and surfactant provided in Examples 1-5 can effectively reduce the gas production of silicon-based materials.

[0096] Table 3

[0097]

[0098] As shown in Table 3, the silicon-based materials co-coated with water-soluble polymers and surfactants provided in Examples 1-5 effectively improved the battery's initial efficiency (approximately 1%) and cycle stability. Furthermore, referring to Tables 1-3, it can be seen that Comparative Example 2, due to the absence of hydrophilic polyvinyl alcohol, also reduced gas production to some extent. However, the lack of polyvinyl alcohol also resulted in poor dispersibility, leading to agglomeration or sedimentation of the negative electrode material after 200 cycles, thus reducing cycle stability. In contrast, the silicon-based materials co-coated with water-soluble polymers and surfactants provided by this invention not only exhibit excellent dispersibility but also effectively suppress gas production and volume expansion, significantly improving battery stability and safety.

[0099] 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.

[0100] 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 negative electrode active material, characterized in that, The negative electrode active material includes a silicon-based material and a polymer coating layer covering the surface of the silicon-based material. The polymer coating layer includes a water-soluble polymer and a surfactant. The water contact angle of the polymer coating layer is 65°-85°. The R hydrophobic chain of the surfactant and the water-soluble polymer both act on the surface of the silicon-based material, and there is a hydrophobic interaction between the R hydrophobic chain of the surfactant and the hydrophobic groups in the water-soluble polymer, thereby forming a hydrophobic protective layer covering the surface of the silicon-based material. At the same time, the hydrophilic bi-headed structure in the surfactant is distributed in a U-shape on the surface of the hydrophobic protective layer, forming a hydrophilic outer layer, thus forming a double-layer protective structure with an inner hydrophobic layer and an outer hydrophilic layer with a special water contact angle. The surfactant has the chemical formula A1-R-A2, wherein A1 and A2 are each independently selected from at least one of quaternary ammonium salt groups, carboxylic acid groups, amino groups, amide groups, alkyl glycoside groups, thiourea groups, and hydroxyl groups, and R is selected from substituted or unsubstituted C8-C groups. 50 Aliphatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Heteroatom-containing aliphatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Alicyclic hydrocarbon segments, substituted or unsubstituted C8-C 50 Alicyclic hydrocarbon segments containing heteroatoms, substituted or unsubstituted C8-C 50 Aromatic hydrocarbon segments, substituted or unsubstituted C8-C 50 Aromatic hydrocarbon segments containing heteroatoms, with substituents selected from C1-C2. 20 Branched or straight-chain hydrocarbon groups, C1-C 20 Branched or straight-chain alkoxy groups, C3-C 20 Branched or straight-chain cycloalkyl groups, C6-C 30 Aromatic group, C5-C 30 At least one of the heteroaryl groups.

2. The negative electrode active material according to claim 1, characterized in that, When the heteroatom is selected from silicon atoms, the number of carbon atoms or silicon atoms in R is independently selected from 8 to 1000; And / or, the molecular weight of R is 100-10000.

3. The negative electrode active material according to claim 1, characterized in that, The surfactant is selected from , , , , At least one of them.

4. The negative electrode active material according to claim 1, characterized in that, The water-soluble polymer is selected from at least one of the following: polysaccharide polymers, polyether polymers, polyamide polymers, polysulfone polymers, polysulfide polymers, polyacrylic acid polymers, polyacrylate polymers, polyacrylamide polymers, polyacrylonitrile polymers, polyvinyl acetate polymers, polyvinyl alcohol polymers, polyvinyl alkyl ether polymers, polyepoxide polymers, polyethyleneimine polymers, and polyionic liquid polymers.

5. The negative electrode active material according to claim 1, characterized in that, The mass of the polymer coating layer is 0.2%-80% of the mass of the silicon-based material; And / or, the mass ratio of the water-soluble polymer to the surfactant is 0.1:50-30:0.1; And / or, the polymer coating layer further includes at least one of lithium salt additives, conductive agents, and crosslinking agents.

6. The negative electrode active material according to claim 1, characterized in that, The silicon-based material is selected from at least one of silicon microparticles, silicon nanoparticles, silicon-carbon materials, silicon-oxygen materials, and silicon alloy materials.

7. A method for preparing a negative electrode active material according to any one of claims 1-6, characterized in that, include: A silicon-based material, a water-soluble polymer, and a surfactant are dispersed in a solvent to obtain a first mixture, which is then dried to obtain the negative electrode active material. Alternatively, a silicon-based material and a water-soluble polymer are dispersed in a solvent to obtain a second mixture. The second mixture is dried to obtain a composite. The composite is then dispersed with a surfactant in a solvent to obtain a third mixture. The third mixture is dried to obtain the negative electrode active material.

8. The method for preparing the negative electrode active material according to claim 7, characterized in that, The mass ratio of the silicon-based material to the water-soluble polymer and the surfactant is 100:(0.1-30):(0.1-50); And / or, the dispersion speed is 100rpm-5000rpm; And / or, the drying temperature is 25°C-200°C; And / or, the first mixture further includes at least one of lithium salt additives, conductive agents, and crosslinking agents; And / or, the second mixture further includes at least one of lithium salt additives, conductive agents, and crosslinking agents.

9. 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 negative active material as described in any one of claims 1-6.

10. A battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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