A nano-silicon negative electrode material and its preparation method

Abstract

The present invention provides a nano-silicon anode material and its preparation method. The method comprises: subjecting a diamine containing a benzimidazole group to a dianhydride for a polycondensation reaction, followed by a substitution reaction with a halogenated hydrocarbon to produce a polyamic acid salt; and mixing the polyamic acid salt with nano-silicon powder, followed by heating for an imidization reaction to produce the nano-silicon anode material. The nano-silicon anode material and its preparation method, by coating the nano-silicon powder with a polymer, prevents cracking and even pulverization of the silicon-based active material, thereby improving the cycle stability and capacity storage of the silicon anode material for lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a nano-silicon negative electrode material and a preparation method thereof. Background Art

[0002] In recent years, the rapid development of portable electronic devices, power tools and electric vehicle technology has put forward higher requirements on the performance of lithium-ion batteries, thus stimulating the research of a new generation of lithium-ion batteries with high specific capacity and long cycle life.

[0003] Compared to currently commercially available carbon-based anode materials, silicon anode materials have higher specific capacity and energy density, and are therefore considered promising anode materials for next-generation lithium-ion batteries. However, in actual use, silicon anode materials undergo dramatic volume changes during lithium insertion and extraction, leading to material pulverization, coating peeling from the current collector surface, and repeated rupture and formation of the solid electrolyte interface film. This results in low cycling stability and a short battery life. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a nano-silicon negative electrode material and a preparation method thereof. By coating the surface of nano-silicon powder with a polymer, the silicon-based active material can be prevented from cracking or even pulverizing, thereby improving the cycle stability and storage capacity of the silicon negative electrode material for lithium-ion batteries.

[0005] The present invention provides a method for preparing a nano-silicon negative electrode material, comprising the following steps:

[0006] S1, subjecting a diamine containing a benzimidazole group to a dianhydride for polycondensation reaction, and then subjecting the diamine to a substitution reaction with a halogenated hydrocarbon to obtain a polyamic acid salt;

[0007] S2. After mixing the polyamic acid salt and nano-silicon powder, heat them to carry out imidization reaction, thereby obtaining the nano-silicon negative electrode material.

[0008] Preferably, the diamine containing a benzimidazole group is represented by the following structural formula:

[0009]

[0010] Preferably, step S1 further comprises a polycondensation reaction of other diamines with dianhydride, wherein the other diamines are represented by the following structural formula:

[0011]

[0012] Preferably, the amount of the other diamine is 20-80% of the molar amount of the diamine containing benzimidazole groups.

[0013] Preferably, the dianhydride is represented by the following structural formula:

[0014]

[0015] Preferably, the halogenated hydrocarbon includes a halogenated alkane or a halogenated aromatic hydrocarbon, and the halogenated alkane or the halogenated aromatic hydrocarbon is represented by the following structural formula:

[0016]

[0017] Preferably, the particle size of the nano silicon powder is 50-200 nm;

[0018] Preferably, the amount of the polyamic acid salt is 1-5% of the mass of the nano-silicon powder.

[0019] Preferably, in step S2, the mixing temperature is 70-90° C. and the mixing time is 1-3 h.

[0020] Preferably, in step S3, the temperature of the imidization reaction is 100-300° C., and the time is 1-3 hours.

[0021] The present invention also provides a nano-silicon negative electrode material, which is prepared by the above preparation method.

[0022] Preferably, the nano-silicon negative electrode material comprises nano-silicon powder and a polymer layer wrapped on the surface of the nano-silicon powder.

[0023] In the present invention, the nano-silicon negative electrode material is prepared by subjecting a diamine containing a benzimidazole group to a polycondensation reaction with a dianhydride. The resulting polyamic acid molecular chain, due to the structure containing imidazole groups, can undergo a substitution reaction with a halogenated hydrocarbon to obtain a polyamic acid salt having a quaternary ammonium salt structure. The polyamic acid salt can form a very strong intermolecular affinity with the nano-silicon powder particles. After an imidization reaction, the surface of the silicon particles can be effectively coated with a polyimide containing an imidazole structure. The polyimide coating has strong toughness. When coated on the surface of the silicon particles, it will better buffer the volume change of the silicon particles during the lithium insertion and extraction process, avoid cracking of the active material, and thus prevent the irreversible consumption of lithium ions. DETAILED DESCRIPTION

[0024] Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration only and are not to be construed as limiting the scope of the present invention.

[0025] Example 1

[0026] A nano-silicon negative electrode material, the preparation method of which comprises:

[0027] S1. Under a nitrogen atmosphere, 10 mmol of 2-(3-aminophenyl)-5-aminobenzimidazole was dissolved in 40 mL of N,N-dimethylacetamide as a diamine raw material, and 10 mmol of 4,4'-(hexafluoroisopropylene) diphthalic anhydride was added as a dianhydride raw material after stirring and dissolving completely. The mixture was stirred until completely dissolved, and the reaction was stirred at room temperature for 3 h to obtain a polyamic acid solution; 10 mmol of o-dichlorobenzyl was added to the polyamic acid solution as a halogenated hydrocarbon raw material, and stirred for 2 h to obtain a polyamic acid salt solution with a quaternary ammonium salt structure;

[0028] S2. The polyamic acid salt solution obtained in step S1 is diluted with N,N-dimethylacetamide to a solution with a solid content of 2wt%, 1g of nano-silicon powder (average particle size of 60nm) is added to 1g of the solution, and the mixture is stirred and mixed at 80°C for 2h, vacuum dried, and ground into powder to obtain a solid powder; the solid powder is placed in a tube furnace, heated to 100°C, dried for 1h, then heated to 300°C, dried for 0.5h, cooled to room temperature and taken out to obtain the nano-silicon negative electrode material.

[0029] The above-mentioned nano-silicon negative electrode material is used as the negative electrode active material of the lithium-ion battery, and its electrochemical performance is tested. The specific process is as follows:

[0030] 1 g of the above-mentioned nano-silicon negative electrode material, 0.01 g of the conductive agent Super-P, and 0.02 g of the binder SBR were added to deionized water and stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil current collector, dried, and roll-pressed to obtain a negative electrode sheet; a lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) was used as an electrolyte solution. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0031] The above lithium-ion battery was subjected to constant current charge and discharge tests at room temperature. Specifically, the button battery was charged and discharged at a constant current of 0.5C within a voltage range of (3-0.01)V. The test results are shown in Table 1 below.

[0032] Example 2

[0033] A nano-silicon negative electrode material, the preparation method of which comprises:

[0034] S1. Under a nitrogen atmosphere, 10 mmol of 2-(4-aminophenyl)-5-aminobenzimidazole was dissolved in 40 mL of N,N-dimethylacetamide as a diamine raw material, and 10 mmol of 4,4'-oxydiphthalic anhydride was added as a dianhydride raw material after stirring and dissolving completely. The mixture was stirred until completely dissolved, and the reaction was stirred at room temperature for 3 h to obtain a polyamic acid solution; 10 mmol of o-dibromobenzyl was added to the polyamic acid solution as a halogenated hydrocarbon raw material, and stirred for 2 h to obtain a polyamic acid salt solution with a quaternary ammonium salt structure;

[0035] S2. The polyamic acid salt solution obtained in step S1 is diluted with N,N-dimethylacetamide to a solution with a solid content of 2wt%, 1g of nano-silicon powder (average particle size of 60nm) is added to 1g of the solution, and the mixture is stirred and mixed at 80°C for 2h, vacuum dried, and ground into powder to obtain a solid powder; the solid powder is placed in a tube furnace, heated to 100°C, dried for 1h, then heated to 300°C, dried for 0.5h, cooled to room temperature and taken out to obtain the nano-silicon negative electrode material.

[0036] The above-mentioned nano-silicon negative electrode material is used as the negative electrode active material of the lithium-ion battery, and its electrochemical performance is tested. The specific process is as follows:

[0037] 1 g of the above-mentioned nano-silicon negative electrode material, 0.01 g of the conductive agent Super-P, and 0.02 g of the binder SBR were added to deionized water and stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil current collector, dried, and roll-pressed to obtain a negative electrode sheet; a lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) was used as an electrolyte solution. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0038] The above lithium-ion battery was subjected to constant current charge and discharge tests at room temperature. Specifically, the button battery was charged and discharged at a constant current of 0.5C within a voltage range of (3-0.01)V. The test results are shown in Table 1 below.

[0039] Example 3

[0040] A nano-silicon negative electrode material, the preparation method of which comprises:

[0041] S1. Under a nitrogen atmosphere, 10 mmol of 2-(3-aminophenyl)-5-aminobenzimidazole was dissolved in 40 mL of N,N-dimethylacetamide as a diamine raw material, and after stirring and dissolving completely, 10 mmol of 1,2,3,4-cyclobutanetetracarboxylic dianhydride was added as a dianhydride raw material, and stirring was continued until all dissolved. The reaction was stirred at room temperature for 3 h to obtain a polyamic acid solution; 10 mmol of 1,4-dichlorobenzyl was added to the polyamic acid solution as a halogenated hydrocarbon raw material, and stirred for 2 h to obtain a polyamic acid salt solution with a quaternary ammonium salt structure;

[0042] S2. The polyamic acid salt solution obtained in step S1 is diluted with N,N-dimethylacetamide to a solution with a solid content of 2wt%, 1g of nano-silicon powder (average particle size of 60nm) is added to 1g of the solution, and the mixture is stirred and mixed at 80°C for 2h, vacuum dried, and ground into powder to obtain a solid powder; the solid powder is placed in a tube furnace, heated to 100°C, dried for 1h, then heated to 300°C, dried for 0.5h, cooled to room temperature and taken out to obtain the nano-silicon negative electrode material.

[0043] The above-mentioned nano-silicon negative electrode material is used as the negative electrode active material of the lithium-ion battery, and its electrochemical performance is tested. The specific process is as follows:

[0044] 1 g of the above-mentioned nano-silicon negative electrode material, 0.01 g of the conductive agent Super-P, and 0.02 g of the binder SBR were added to deionized water and stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil current collector, dried, and roll-pressed to obtain a negative electrode sheet; a lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) was used as an electrolyte solution. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0045] The above lithium-ion battery was subjected to constant current charge and discharge tests at room temperature. Specifically, the button battery was charged and discharged at a constant current of 0.5C within a voltage range of (3-0.01)V. The test results are shown in Table 1 below.

[0046] Example 4

[0047] A nano-silicon negative electrode material, the preparation method of which comprises:

[0048] S1, under nitrogen atmosphere, by 4mmol 4,4 '-diaminodiphenyl ether and 6mmol 2-(4-aminophenyl)-5-aminobenzimidazole as diamine raw material dissolution in 40mL of N, N-dimethylacetamide, stirring and dissolving completely after adding 10mmol4,4 '-(hexafluoroisopropylene) diphthalic anhydride as dianhydride raw material, then continue to stir to all dissolves, stirring reaction 3h under room temperature, obtain polyamic acid solution; In this polyamic acid solution, add 6mmol n-butyl bromide as halohydrocarbon raw material, and stir 2h, obtain the polyamic acid salt solution with quaternary ammonium salt structure;

[0049] S2. The polyamic acid salt solution obtained in step S1 is diluted with N,N-dimethylacetamide to a solution with a solid content of 2wt%, 1g of nano-silicon powder (average particle size of 60nm) is added to 1g of the solution, and the mixture is stirred and mixed at 80°C for 2h, vacuum dried, and ground into powder to obtain a solid powder; the solid powder is placed in a tube furnace, heated to 100°C, dried for 1h, then heated to 300°C, dried for 0.5h, cooled to room temperature and taken out to obtain the nano-silicon negative electrode material.

[0050] The above-mentioned nano-silicon negative electrode material is used as the negative electrode active material of the lithium-ion battery, and its electrochemical performance is tested. The specific process is as follows:

[0051] 1 g of the above-mentioned nano-silicon negative electrode material, 0.01 g of the conductive agent Super-P, and 0.02 g of the binder SBR were added to deionized water and stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil current collector, dried, and roll-pressed to obtain a negative electrode sheet; a lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) was used as an electrolyte solution. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0052] The above lithium-ion battery was subjected to constant current charge and discharge tests at room temperature. Specifically, the button battery was charged and discharged at a constant current of 0.5C within a voltage range of (3-0.01)V. The test results are shown in Table 1 below.

[0053] Example 5

[0054] A nano-silicon negative electrode material, the preparation method of which comprises:

[0055] S1, under nitrogen atmosphere, 4mmol 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 6mmol 2-(3-aminophenyl)-5-aminobenzimidazole were dissolved in 40mL of N,N-dimethylacetamide as diamine raw materials, and 10mmol 4,4'-(hexafluoroisopropylene) diphthalic anhydride was added as dianhydride raw material after stirring and dissolving completely, and then stirring was continued until all dissolved, and the reaction was stirred at room temperature for 3h to obtain a polyamic acid solution; 6mmol o-dichlorobenzyl was added to the polyamic acid solution as a halogenated hydrocarbon raw material, and stirred for 2h to obtain a polyamic acid salt solution with a quaternary ammonium salt structure;

[0056] S2. The polyamic acid salt solution obtained in step S1 is diluted with N,N-dimethylacetamide to a solution with a solid content of 2wt%, 1g of nano-silicon powder (average particle size of 60nm) is added to 1g of the solution, and the mixture is stirred and mixed at 80°C for 2h, vacuum dried, and ground into powder to obtain a solid powder; the solid powder is placed in a tube furnace, heated to 100°C, dried for 1h, then heated to 300°C, dried for 0.5h, cooled to room temperature and taken out to obtain the nano-silicon negative electrode material.

[0057] The above-mentioned nano-silicon negative electrode material is used as the negative electrode active material of the lithium-ion battery, and its electrochemical performance is tested. The specific process is as follows:

[0058] 1 g of the above-mentioned nano-silicon negative electrode material, 0.01 g of the conductive agent Super-P, and 0.02 g of the binder SBR were added to deionized water and stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil current collector, dried, and roll-pressed to obtain a negative electrode sheet; a lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) was used as an electrolyte solution. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0059] The above lithium-ion battery was subjected to constant current charge and discharge tests at room temperature. Specifically, the button battery was charged and discharged at a constant current of 0.5C within a voltage range of (3-0.01)V. The test results are shown in Table 1 below.

[0060] Example 6

[0061] A nano-silicon negative electrode material, the preparation method of which comprises:

[0062] S1, under nitrogen atmosphere, 4mmol 4,4'-diaminodiphenyl ether and 6mmol 2-(3-aminophenyl)-5-aminobenzimidazole were dissolved in 40mL of N,N-dimethylacetamide as diamine raw materials, and 10mmol 3,3',4,4'-biphenyltetracarboxylic dianhydride was added as dianhydride raw material after stirring and dissolving completely, and then stirring was continued until all dissolved, and the reaction was stirred at room temperature for 3h to obtain a polyamic acid solution; 6mmol o-dichlorobenzyl was added to the polyamic acid solution as a halogenated hydrocarbon raw material, and stirred for 2h to obtain a polyamic acid salt solution with a quaternary ammonium salt structure;

[0063] S2. The polyamic acid salt solution obtained in step S1 is diluted with N,N-dimethylacetamide to a solution with a solid content of 2wt%, 1g of nano-silicon powder (average particle size of 60nm) is added to 1g of the solution, and the mixture is stirred and mixed at 80°C for 2h, vacuum dried, and ground into powder to obtain a solid powder; the solid powder is placed in a tube furnace, heated to 100°C, dried for 1h, then heated to 300°C, dried for 0.5h, cooled to room temperature and taken out to obtain the nano-silicon negative electrode material.

[0064] The above-mentioned nano-silicon negative electrode material is used as the negative electrode active material of the lithium-ion battery, and its electrochemical performance is tested. The specific process is as follows:

[0065] 1 g of the above-mentioned nano-silicon negative electrode material, 0.01 g of the conductive agent Super-P, and 0.02 g of the binder SBR were added to deionized water and stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil current collector, dried, and roll-pressed to obtain a negative electrode sheet; a lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) was used as an electrolyte solution. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0066] The above lithium-ion battery was subjected to constant current charge and discharge tests at room temperature. Specifically, the button battery was charged and discharged at a constant current of 0.5C within a voltage range of (3-0.01)V. The test results are shown in Table 1 below.

[0067] Comparative Example 1

[0068] A nano-silicon negative electrode material, the preparation method of which comprises:

[0069] S1. Under a nitrogen atmosphere, 10 mmol of 2-(3-aminophenyl)-5-aminobenzimidazole as a diamine raw material was dissolved in 40 mL of N,N-dimethylacetamide. After stirring and dissolving completely, 10 mmol of 4,4'-(hexafluoroisopropylene) diphthalic anhydride was added as a dianhydride raw material, and stirring was continued until all dissolved. The reaction was stirred at room temperature for 3 h to obtain a polyamic acid solution;

[0070] S2. The polyamic acid solution obtained in step S1 is diluted with N,N-dimethylacetamide to a solution with a solid content of 2wt%, 1g of nano-silicon powder (average particle size of 60nm) is added to 1g of the solution, and the mixture is stirred and mixed at 80°C for 2h, vacuum dried, and ground into powder to obtain a solid powder; the solid powder is placed in a tube furnace, heated to 100°C, dried for 1h, then heated to 300°C, dried for 0.5h, cooled to room temperature and taken out to obtain the nano-silicon negative electrode material.

[0071] The above-mentioned nano-silicon negative electrode material is used as the negative electrode active material of the lithium-ion battery, and its electrochemical performance is tested. The specific process is as follows:

[0072] 1 g of the above-mentioned nano-silicon negative electrode material, 0.01 g of the conductive agent Super-P, and 0.02 g of the binder SBR were added to deionized water and stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil current collector, dried, and roll-pressed to obtain a negative electrode sheet; a lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) was used as an electrolyte solution. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0073] The above lithium-ion battery was subjected to constant current charge and discharge tests at room temperature. Specifically, the button battery was charged and discharged at a constant current of 0.5C within a voltage range of (3-0.01)V. The test results are shown in Table 1 below.

[0074] Comparative Example 2

[0075] A nano-silicon negative electrode material, the preparation method of which comprises:

[0076] S1. Under a nitrogen atmosphere, 10 mmol of 4,4'-diaminodiphenyl ether was dissolved as a diamine raw material in 40 mL of N,N-dimethylacetamide. After stirring and dissolving completely, 10 mmol of 4,4'-(hexafluoroisopropylene) diphthalic anhydride was added as a dianhydride raw material, and stirring was continued until all dissolved. The reaction was stirred at room temperature for 3 h to obtain a polyamic acid solution; 10 mmol of o-dichlorobenzyl was added to the polyamic acid solution as a halogenated hydrocarbon raw material, and stirred for 2 h to obtain a polyamic acid-o-dichlorobenzyl mixed solution;

[0077] S2. The polyamic acid-o-benzyl chloride mixed solution obtained in step S1 is diluted with N,N-dimethylacetamide to a solution with a solid content of 2 wt%, 1 g of nano-silicon powder (average particle size of 60 nm) is added to 1 g of the solution, and the mixture is stirred and mixed at 80 ° C for 2 h, vacuum dried, and ground into powder to obtain a solid powder; the solid powder is placed in a tube furnace, heated to 100 ° C, dried for 1 h, then heated to 300 ° C, dried for 0.5 h, cooled to room temperature and taken out to obtain the nano-silicon negative electrode material.

[0078] The above-mentioned nano-silicon negative electrode material is used as the negative electrode active material of the lithium-ion battery, and its electrochemical performance is tested. The specific process is as follows:

[0079] 1 g of the above-mentioned nano-silicon negative electrode material, 0.01 g of the conductive agent Super-P, and 0.02 g of the binder SBR were added to deionized water and stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil current collector, dried, and roll-pressed to obtain a negative electrode sheet; a lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) was used as an electrolyte solution. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0080] The above lithium-ion battery was subjected to constant current charge and discharge tests at room temperature. Specifically, the button battery was charged and discharged at a constant current of 0.5C within a voltage range of (3-0.01)V. The test results are shown in Table 1 below.

[0081] Table 1

[0082]

[0083] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a nano-silicon negative electrode material, characterized in that: The steps include: S1, subjecting a diamine containing a benzimidazole group to a dianhydride for polycondensation reaction, and then subjecting the diamine to a substitution reaction with a halogenated hydrocarbon to obtain a polyamic acid salt; S2, mixing the polyamic acid salt and nano-silicon powder, and then heating to perform imidization reaction to obtain the nano-silicon negative electrode material; The diamine containing a benzimidazole group is shown in the following structural formula: The dianhydride is shown in the following structural formula: The halogenated hydrocarbons include halogenated alkanes or halogenated aromatic hydrocarbons, and the halogenated alkanes or halogenated aromatic hydrocarbons are represented by the following structural formula:

2. The method for preparing the nano-silicon negative electrode material according to claim 1, characterized in that: In step S1, other diamines are further subjected to polycondensation reaction with dianhydride, wherein the other diamines are represented by the following structural formula:

3. The method for preparing the nano-silicon negative electrode material according to claim 2, characterized in that: The amount of the other diamine used is 20-80% of the molar amount of the diamine containing the benzimidazole group.

4. The method for preparing the nano-silicon negative electrode material according to any one of claims 1 to 3, characterized in that: The particle size of the nano silicon powder is 50-200 nm.

5. The method for preparing the nano-silicon negative electrode material according to claim 4, characterized in that: The amount of the polyamic acid salt used is 1-5% of the mass of the nano-silicon powder.

6. The method for preparing the nano-silicon negative electrode material according to any one of claims 1 to 3, characterized in that: In step S2, the mixing temperature is 70-90° C. and the mixing time is 1-3 hours.

7. The method for preparing the nano-silicon negative electrode material according to any one of claims 1 to 3, characterized in that: In step S2, the temperature of the imidization reaction is 100-300° C., and the time is 1-3 hours.

8. A nano-silicon negative electrode material, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 7.

9. The nano-silicon negative electrode material according to claim 8, characterized in that: The nano-silicon negative electrode material comprises nano-silicon powder and a polymer layer wrapped on the surface of the nano-silicon powder.

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