Negative electrode sheet, method for manufacturing the same, and secondary battery
By generating a composite SEI film with nanopores and a network structure on the surface of silicon-based materials, the problems of volume expansion and SEI film instability in silicon-based anode materials are solved, thereby improving the cycle life and electrical performance of lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SVOLT ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2026-04-16
- Publication Date
- 2026-06-12
AI Technical Summary
Existing technologies cannot effectively suppress the volume expansion of silicon-based anode materials and improve the stability of the solid electrolyte interphase (SEI) film, leading to rapid capacity decay of lithium-ion batteries.
A coating layer formed by the reaction of flexible amine monomers and acyl chloride monomers is generated on the surface of silicon-based materials, forming a composite SEI film with nanopores and network structure, which enhances its strength and flexibility and adapts to the volume changes of silicon-based materials.
It significantly improves the cycle life and electrical performance of lithium-ion batteries, with a capacity retention rate exceeding 94.1% at 25°C, making it suitable for industrial production.
Smart Images
Figure CN122202192A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of secondary battery technology, specifically to a negative electrode sheet, its preparation method, and a secondary battery. Background Technology
[0002] Lithium-ion batteries have been widely used in electric vehicles and various electronic devices due to their outstanding advantages such as high energy density and long cycle life. However, the current mainstream anode active material is graphite, whose performance is approaching its theoretical specific capacity limit of 372 mAh / g. The single graphite anode system can no longer meet the industry's ever-increasing energy density requirements.
[0003] Compared to graphite, silicon-based materials have a higher theoretical specific capacity, with Li... 15 Taking Si4 as an example, its theoretical specific capacity at room temperature is as high as 3579 mAh / g, making it a highly attractive next-generation lithium-ion battery anode material, which is expected to achieve a major application breakthrough in improving the energy density of lithium-ion batteries.
[0004] However, silicon-based anode materials undergo drastic volume changes during lithium insertion / extraction, with a volume change rate exceeding 300%. Such drastic volume fluctuations not only lead to silicon particle pulverization but also trigger repeated rupture and regeneration of the solid electrolyte interphase (SEI) membrane, resulting in electrical contact failure of the active material and the consumption of a large amount of active lithium, ultimately causing rapid capacity decay of the battery.
[0005] CN114005958 A discloses a silicon-carbon composite negative electrode sheet and a battery including the negative electrode sheet. The negative electrode sheet includes a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer. The first negative electrode active material layer is disposed on the surface of the negative electrode current collector, and the second negative electrode active material layer is disposed on the surface of the first negative electrode active material layer. The first negative electrode active material layer comprises a silicon-based material and low-expansion graphite; the second negative electrode active material layer comprises fast-charging graphite. By coating the surface of the first negative electrode active material layer formed of silicon-based material and low-expansion graphite with a second negative electrode active material layer formed of fast-charging graphite, the structure of the silicon-based material can be stabilized, its expansion during charging and discharging can be suppressed, and the battery life can be improved.
[0006] However, the aforementioned patents cannot suppress or reduce the expansion of silicon-based materials themselves, nor do they improve the stability of their surface SEI film.
[0007] Therefore, developing a highly stable artificial SEI film and applying it directly to silicon-based materials is of paramount importance for promoting the development of silicon-based anode batteries. Summary of the Invention
[0008] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a negative electrode sheet, a method for preparing the same, and a secondary battery.
[0009] To achieve the above objectives, the present invention adopts the following technical solution:
[0010] In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector, the negative electrode active layer comprising a silicon-based material, the surface of the silicon-based material having a coating layer, the coating layer being a network structure formed by the reaction of a flexible amine monomer and an acyl chloride monomer, wherein the flexible amine monomer contains two or more amino groups; and the acyl chloride monomer contains two or more carbonyl chloride functional groups.
[0011] This invention utilizes an amine monomer containing two or more amino groups and an acyl chloride monomer containing two or more carbonyl chloride functional groups to react and generate an in-situ coating layer on the surface of a silicon-based material. This coating layer possesses nanoporous and network structures, enabling it to form an integrated structure with the SEI film generated during battery pre-charge formation. This significantly enhances the strength of the composite SEI film and mitigates the SEI film rupture caused by volume expansion, thereby significantly improving the electrical performance of the silicon-based anode battery. Simultaneously, the amine monomers, as flexible segments, can dissipate stress and strain through expansion and contraction, giving it high flexibility as well. In summary, this composite SEI film combines high strength and high flexibility, allowing it to adapt to the significant deformation of silicon-based materials during expansion and contraction without easily breaking, thus significantly improving the cycle life of the battery.
[0012] In this invention, the surface of silicon-based material refers to the exposed surface of silicon-based material, including both the surface of silicon-based material exposed on the outside of the negative electrode active layer and the surface of silicon-based material exposed on the void side inside the negative electrode active layer.
[0013] Preferably, the flexible amine monomer has the structure shown in Formula I or Formula II.
[0014]
[0015] Formula I;
[0016]
[0017] Formula II;
[0018] In this invention, m and n are each independently chosen from integers between 10 and 30, such as 10, 15, 20, 25, or 30. The values of m and n can be the same or different. If the value of m or n is too low, the amine monomer chain length is too short, resulting in insufficient flexibility. If the value of m or n is too high, the molecular weight of the amine monomer is too high, which is not conducive to uniform diffusion and distribution within the electrode.
[0019] Preferably, the acyl chloride monomer includes at least one of pyromellitic methyl methacrylate (PMMA), terephthaloyl chloride (TBMA), and isophthaloyl chloride (IMMA).
[0020] Preferably, the average thickness of the coating layer is 10nm to 100nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, or 100nm. If the average thickness of the coating layer is too small, the coating will be incomplete, and the effect of suppressing the expansion of silicon-based materials will be limited; if the average thickness of the coating layer is too large, it will hinder ion transport, thereby reducing electrical performance.
[0021] Preferably, the negative electrode active layer further includes a conductive agent and a binder, wherein the mass ratio of the silicon-based material, the conductive agent, and the binder is (80~90):(5~10):(5~10), wherein the silicon-based material is selected from the range of "80~90", for example, it can be 80, 82, 83, 85, 86, 88, or 90, etc.; the conductive agent is selected from the range of "5~10", for example, it can be 5, 6, 7, 8, 9, or 10, etc.; and the binder is selected from the range of "5~10", for example, it can be 5, 6, 7, 8, 9, or 10, etc.
[0022] Preferably, the silicon-based material includes at least one of silicon-oxygen materials, silicon-carbon materials, and pre-lithium silicon-oxygen materials. In this invention, pre-lithium silicon-oxygen refers to silicon-oxygen materials containing the element Li.
[0023] Preferably, the conductive agent includes at least one of Super P, Ketjen Black, acetylene black, graphene, and carbon nanotubes, but is not limited to the types listed above. Other conductive agents commonly used in the art are also applicable to this invention.
[0024] Preferably, the adhesive comprises polyacrylic acid.
[0025] In a second aspect, the present invention provides a method for preparing a negative electrode sheet as described in the first aspect, the method comprising the following steps:
[0026] A negative electrode slurry comprising silicon-based material, conductive agent and binder is provided. The negative electrode slurry is coated onto a negative electrode current collector and dried to obtain a coated electrode sheet. The coated electrode sheet includes a negative electrode current collector and a negative electrode active layer located on the surface of the negative electrode current collector.
[0027] The coated electrode is immersed in a first solution phase containing flexible amine monomers and kept for a period of time t1. After drying, it is immersed in a second solution phase containing acyl chloride monomers and kept for a period of time t2. The flexible amine monomers react with the acyl chloride monomers to form a network structure on the surface of the silicon-based material, thereby obtaining the negative electrode.
[0028] In the method of this invention, by immersing the coated electrode in a first solution phase containing flexible amine monomers and maintaining it for a period of time t1, the flexible amine monomers can be adsorbed onto the exposed surface of the silicon-based material. Subsequently, it is immersed in a second solution phase containing acyl chloride monomers and maintained for a period of time t2. Since the flexible amine monomers and acyl chloride monomers react readily, they will form a cross-linked coating layer with nanopores and a network structure in situ on the exposed surface of the silicon-based material. The method of this invention is simple, operates under mild conditions, and is suitable for industrial production.
[0029] Preferably, the mass fraction of the flexible amine monomer in the first solution phase is 2% to 6%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6%. If the amount added is too low, a high-strength cross-linked coating layer cannot be formed, and expansion cannot be effectively suppressed, resulting in poor battery performance; if the amount added is too high, the coating layer formed is too thick, hindering lithium-ion transport and affecting battery performance.
[0030] Preferably, the time period t2 is 10 min to 60 min, for example, it can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, etc.
[0031] Preferably, the drying temperature is 60℃~80℃, for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃.
[0032] Preferably, the mass fraction of the acyl chloride monomer in the second solution phase is 0.2% to 0.6%, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, or 0.6%. If the amount added is too low, a high-strength cross-linked coating layer cannot be formed, and expansion cannot be effectively suppressed, resulting in poor battery performance; if the amount added is too high, the coating layer formed is too thick, hindering lithium-ion transport and affecting battery performance.
[0033] Preferably, the time period t2 is 10 min to 60 min, for example, it can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, etc.
[0034] Thirdly, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode described in the first aspect or a negative electrode prepared by the method described in the second aspect.
[0035] This invention does not specifically limit the structure and composition of the positive electrode, separator, and electrolyte. Those skilled in the art can prepare them according to the methods disclosed in the prior art, or they can use commercially available products.
[0036] In one embodiment, the positive electrode sheet includes a positive current collector and a positive active layer disposed on the surface of the positive current collector, wherein the positive active layer includes a positive active material, a conductive agent, and a binder.
[0037] In one embodiment, the positive electrode active material includes, but is not limited to, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.
[0038] Compared with existing technologies, the present invention has the following beneficial effects:
[0039] (1) This invention utilizes an amine monomer containing two or more amino groups and an acyl chloride monomer containing two or more carbonyl chloride functional groups to react and generate a coating layer in situ on the surface of a silicon-based material. This coating layer has nanoporous and network structure characteristics, enabling it to form an integrated structure with the SEI film generated during battery pre-charge formation. This significantly improves the strength of the composite SEI film and mitigates the SEI film rupture problem caused by volume expansion, thereby significantly improving the electrical performance of the silicon-based anode battery. Simultaneously, the amine monomer, as a flexible chain segment, can dissipate stress and strain through stretching and contraction, giving it high flexibility as well. In summary, this composite SEI film combines high strength and high flexibility, allowing it to adapt to the significant deformation of silicon-based materials during expansion and contraction without easily breaking, thus significantly improving the battery's cycle performance. After 200 cycles at 25°C, the capacity retention rate is above 94.1%, preferably above 95.1%.
[0040] (2) The method of the present invention is simple, the conditions are mild, and it is suitable for industrial production. Attached Figure Description
[0041] Figure 1 The graphs show the cycle performance of lithium-ion secondary batteries prepared from the negative electrode sheets of Examples 1, 1, 2, and 3. Detailed Implementation
[0042] The technical solution of the present invention will be further illustrated below through specific embodiments.
[0043] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.
[0044] The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.
[0045] In the following embodiments, the CAS number of PEODA-20 is 9046-10-0, and its structural formula is as follows: (Where m is 20).
[0046] In the following embodiments, the CAS number of PEODA-10 is 9046-10-0, and its structural formula is as follows: (Where m is 10).
[0047] In the following embodiments, the CAS number of PEODA-30 is 9046-10-0, and its structural formula is as follows: (Where m is 30).
[0048] Example 1
[0049] This embodiment provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. The negative electrode active layer includes a silicon-carbon material, and the surface of the silicon-carbon material has a coating layer (average thickness of 50 nm). The coating layer is a network structure formed by the reaction of a flexible amine monomer and an acyl chloride monomer; the flexible amine monomer is PEODA-20; and the acyl chloride monomer is trimesoyl pyromellitic acid chloride. The negative electrode current collector is a copper foil; the negative electrode active layer includes silicon-carbon material, Super P, and polyacrylic acid, with a mass ratio of silicon-carbon material, Super P, and polyacrylic acid of 85:5:10.
[0050] This embodiment also provides a method for preparing the above-mentioned negative electrode sheet, the method comprising the following steps:
[0051] S1. Silicon carbon material, Super P, and polyacrylic acid are mixed in a mass ratio of 85:5:10. An appropriate amount of deionized water is added as a solvent, and the mixture is stirred and dispersed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated onto both sides of a copper foil and dried at 70°C to form a negative electrode active layer on the surface of the copper foil, thus obtaining an unmodified silicon-based negative electrode.
[0052] S2. Weigh out PEODA-20 monomer and dissolve it in water to obtain a first solution phase with a mass fraction of 4%. Immerse the unmodified silicon-based anode obtained in S1 into the first solution phase and keep it for 30 minutes. After taking it out, dry it at 70°C for later use.
[0053] S3. Weigh out the trimesoyl chloride monomer and dissolve it in n-hexane to obtain a second solution phase with a mass fraction of 0.4%. Immerse the silicon-based negative electrode treated in S2 into the second solution phase and keep it for 30 minutes. After taking it out, dry it at 70°C to obtain the negative electrode sheet.
[0054] Example 2
[0055] This embodiment provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. The negative electrode active layer includes a silicon-carbon material, and the surface of the silicon-carbon material has a coating layer (average thickness of 10 nm). The coating layer is a network structure formed by the reaction of a flexible amine monomer and an acyl chloride monomer; the flexible amine monomer is PEODA-20; and the acyl chloride monomer is trimesoyl pyromellitic acid chloride. The negative electrode current collector is a copper foil; the negative electrode active layer includes silicon-carbon material, Super P, and polyacrylic acid, with a mass ratio of silicon-carbon material, Super P, and polyacrylic acid of 85:5:10.
[0056] This embodiment also provides a method for preparing the above-mentioned negative electrode sheet, the method comprising the following steps:
[0057] S1. Silicon carbon material, Super P, and polyacrylic acid are mixed in a mass ratio of 85:5:10. An appropriate amount of deionized water is added as a solvent, and the mixture is stirred and dispersed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated onto both sides of a copper foil and dried at 70°C to form a negative electrode active layer on the surface of the copper foil, thus obtaining an unmodified silicon-based negative electrode.
[0058] S2. Weigh out PEODA-20 monomer and dissolve it in water to obtain a first solution phase with a mass fraction of 2%. Immerse the unmodified silicon-based anode obtained in S1 into the first solution phase and keep it for 45 minutes. After taking it out, dry it at 70°C for later use.
[0059] S3. Weigh out the trimesoyl chloride monomer and dissolve it in n-hexane to obtain a second solution phase with a mass fraction of 0.2%. Immerse the silicon-based negative electrode treated in S2 into the second solution phase and keep it for 20 minutes. After taking it out, dry it at 80°C to obtain the negative electrode sheet.
[0060] Example 3
[0061] This embodiment provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. The negative electrode active layer includes a silicon-carbon material, and the surface of the silicon-carbon material has a coating layer (average thickness of 100 nm). The coating layer is a network structure formed by the reaction of a flexible amine monomer and an acyl chloride monomer; the flexible amine monomer is PEODA-20; and the acyl chloride monomer is trimesoyl pyromellitic acid chloride. The negative electrode current collector is a copper foil; the negative electrode active layer includes silicon-carbon material, Super P, and polyacrylic acid, with a mass ratio of silicon-carbon material, Super P, and polyacrylic acid of 85:5:10.
[0062] This embodiment also provides a method for preparing the above-mentioned negative electrode sheet, the method comprising the following steps:
[0063] S1. Silicon carbon material, Super P, and polyacrylic acid are mixed in a mass ratio of 85:5:10. An appropriate amount of deionized water is added as a solvent, and the mixture is stirred and dispersed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated onto both sides of a copper foil and dried at 70°C to form a negative electrode active layer on the surface of the copper foil, thus obtaining an unmodified silicon-based negative electrode.
[0064] S2. Weigh out PEODA-20 monomer and dissolve it in water to obtain a first solution phase with a mass fraction of 6%. Immerse the unmodified silicon-based anode obtained in S1 into the first solution phase and keep it for 20 minutes. After taking it out, dry it at 60°C for later use.
[0065] S3. Weigh out the trimesoyl chloride monomer and dissolve it in n-hexane to obtain a second solution phase with a mass fraction of 0.6%. Immerse the silicon-based negative electrode treated in S2 into the second solution phase and keep it for 60 minutes. After taking it out, dry it at 70°C to obtain the negative electrode sheet.
[0066] Example 4
[0067] The difference between this embodiment and Embodiment 1 is that PEODA-20 monomer is replaced with PEODA-10 monomer.
[0068] Example 5
[0069] The difference between this embodiment and Embodiment 1 is that PEODA-20 monomer is replaced with PEODA-30 monomer.
[0070] Example 6
[0071] The difference between this embodiment and Embodiment 1 is that pyromellitic chloromethyl chloride is replaced with terephthaloyl chloride.
[0072] Example 7
[0073] The difference between this embodiment and Embodiment 1 is that the mass fraction of the first solution phase is 1%.
[0074] Example 8
[0075] The difference between this embodiment and Embodiment 1 is that the mass fraction of the first solution phase is 7%.
[0076] Example 9
[0077] The difference between this embodiment and Embodiment 1 is that the mass fraction of the second solution phase is 0.1%.
[0078] Example 10
[0079] The difference between this embodiment and Embodiment 1 is that the mass fraction of the second solution phase is 0.7%.
[0080] Comparative Example 1
[0081] The difference between this comparative example and Example 1 is that PEODA-60 is replaced with piperazine.
[0082] Comparative Example 2
[0083] The difference between this comparative example and Example 1 is that PEODA-60 is replaced with a single-ended amino polyether, which contains one amino group.
[0084] Comparative Example 3
[0085] The difference between this comparative example and Example 1 is that the carbon material does not have a coating layer on its surface.
[0086] Lithium-ion secondary batteries were prepared using the negative electrode sheets of Examples 1-10 and Comparative Examples 1-3. The specific methods included:
[0087] Preparation of positive electrode: The ternary positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96:2:2. An appropriate amount of N-methylpyrrolidone (NMP) is added as a solvent and stirred to disperse evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both sides of an aluminum foil and dried at 90°C to obtain a positive electrode sheet.
[0088] Electrolyte preparation: In a glove box, weigh an appropriate amount of lithium salt and fluoroethylene carbonate (FEC) and dissolve them in a solvent to obtain an electrolyte. The lithium salt in the electrolyte is 1 mol / L LiPF6, the solvent is a mixture of DMC and EMC, and the concentration of FEC in the electrolyte is 10 wt%.
[0089] Lithium-ion secondary batteries were prepared using the negative electrode sheets prepared in Examples 1-10 and Comparative Examples 1-3. The method included: forming a cell by winding or stacking a positive electrode sheet, a negative electrode sheet, and a PE separator; injecting an electrolyte; and then encapsulating the cell to obtain a lithium-ion secondary battery.
[0090] The lithium-ion secondary battery was tested for electrical performance using the Xinwei testing system, employing constant current-constant voltage charging (CC-CV charging) and constant current discharging (CC discharging) modes. Specifically, at 25°C, the battery was charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage of 4.2V until the current dropped to 0.05C, followed by discharging at 1C to 2.5V. The discharge capacity at this point was recorded as Q1. This cycle was repeated 200 times, and the discharge capacity at the 200th cycle was recorded as Q2. The cycle capacity retention rate was calculated using the formula: Q2 / Q1 × 100%.
[0091] The test results are shown in Table 1 and Figure 1 .
[0092]
[0093] As shown in Table 1, this invention utilizes amine monomers containing two or more amino groups and acyl chloride monomers containing two or more carbonyl chloride functional groups to react on the surface of silicon-based materials, thereby forming a cross-linked coating layer with nanoporous and network structures, which significantly improves the cycle life of the battery. In Comparative Example 3, without coating the silicon-based material, the battery's cycle capacity retention was only 81.6%.
[0094] A comparison of Examples 1 and 7-8 shows that there is a preferred range for the concentration of the first solution phase made of flexible amine monomers. If the concentration of the first solution phase is too low, a high-strength cross-linked coating layer cannot be formed, expansion cannot be effectively suppressed, and battery performance deteriorates. If the concentration of the first solution phase is too high, the coating layer formed will be too thick, hindering lithium-ion transport and affecting battery performance.
[0095] A comparison of Examples 1 and 9-10 shows that there is a preferred range for the concentration of the second solution phase prepared by the acyl chloride monomer. If the concentration of the second solution phase is too low, a high-strength cross-linked coating layer cannot be formed, expansion cannot be effectively suppressed, and battery performance deteriorates. If the concentration of the second solution phase is too high, the coating layer formed will be too thick, hindering lithium-ion transport and affecting battery performance.
[0096] The comparison between Example 1 and Comparative Example 1 shows that if the flexible amine monomer is replaced with piperazine, the cycle performance of the lithium-ion battery will be greatly reduced. This is because piperazine monomer is a rigid monomer, and the modified layer formed by it is too rigid and cannot dissipate the stress generated by the huge volume change of the silicon-based active material. The SEI film is prone to rupture and regeneration, resulting in poor cycle performance.
[0097] The comparison between Example 1 and Comparative Example 2 shows that if there is only one amino group in the acyl chloride monomer, it will be unable to form a cross-linking network with pyromellitic trimethylolpropionate chloride, resulting in a poorer effect in inhibiting volume expansion and poorer cycle performance.
[0098] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.
Claims
1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. The negative electrode active layer includes a silicon-based material, and the surface of the silicon-based material has a coating layer. The coating layer is a network structure formed by the reaction of flexible amine monomers and acyl chloride monomers. The flexible amine monomers contain more than two amino groups, and the acyl chloride monomers contain more than two carbonyl chloride functional groups.
2. The negative electrode sheet according to claim 1, characterized in that, The flexible amine monomer has the structure shown in Formula I or Formula II. Formula I; Formula II; Where m and n are each independently chosen from integers between 10 and 30.
3. The negative electrode sheet according to claim 1, characterized in that, The acyl chloride monomers include at least one of pyromellitic terephthaloyl chloride, terephthaloyl chloride, and isophthaloyl chloride.
4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The average thickness of the coating layer is 10 nm to 100 nm.
5. The negative electrode sheet according to any one of claims 1-3, characterized in that, The negative electrode active layer also includes a conductive agent and a binder, and the mass ratio of the silicon-based material, the conductive agent and the binder is (80~90):(5~10):(5~10).
6. The negative electrode sheet according to claim 5, characterized in that, The silicon-based material includes at least one of silicon-oxygen materials, silicon-carbon materials, and pre-lithium silicon-oxygen materials; Preferably, the conductive agent includes at least one of Super P, Ketjen Black, acetylene black, graphene, and carbon nanotubes; Preferably, the adhesive comprises polyacrylic acid.
7. A method for preparing a negative electrode sheet as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: A negative electrode slurry comprising silicon-based material, conductive agent and binder is provided. The negative electrode slurry is coated onto a negative electrode current collector and dried to obtain a coated electrode sheet. The coated electrode sheet includes a negative electrode current collector and a negative electrode active layer located on the surface of the negative electrode current collector. The coated electrode is immersed in a first solution phase containing flexible amine monomers and kept for a period of time t1. After drying, it is immersed in a second solution phase containing acyl chloride monomers and kept for a period of time t2. The flexible amine monomers react with the acyl chloride monomers to form a network structure on the surface of the silicon-based material, thereby obtaining the negative electrode.
8. The method for preparing the negative electrode sheet according to claim 7, characterized in that, The mass fraction of flexible amine monomers in the first solution phase is 2%~6%; Preferably, the time period t1 is 10 min to 60 min; Preferably, the drying temperature is 60℃~80℃.
9. The method for preparing the negative electrode sheet according to claim 7, characterized in that, The mass fraction of acyl chloride monomers in the second solution phase is 0.2%~0.6%; Preferably, the time period t2 is 10 min to 60 min.
10. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode sheet is the negative electrode sheet according to any one of claims 1-6, or the negative electrode sheet prepared by the method according to any one of claims 7-9.