Sodium ion battery negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of sodium-ion batteries, and discloses a sodium-ion battery negative electrode material and a preparation method thereof. The preparation method comprises the following steps: S1, mixing pretreated hard carbon, nano molybdenum disulfide, a sodium supplementing agent and polyacrylic acid, performing spray drying, and performing heat treatment to obtain a composite active material; s2, uniformly mixing diallylamine, sodium hydroxide and tetrahydrofuran under the protection of nitrogen, cooling and stirring, adding 3-chloropropyltrimethoxysilane, stirring for 2-4 hours, removing a solvent, and performing post-treatment to obtain modified silane; taking mercaptoimidazole, naphthalenethiol, triethylamine and ethanol, heating, stirring and activating, adding the modified silane, heating, stirring and reacting for 4-6 hours, and removing a solvent to obtain a modifier; s3, adding the composite active material into ethanol and water, adding a modifier, heating, stirring, filtering, washing and drying to obtain a modified composite active material; and mixing the modified composite active material with polyaniline to obtain the negative electrode material.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion batteries and discloses a sodium ion battery negative electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used due to their small size, high energy density, and recyclability. However, the shortage and uneven distribution of lithium resources have limited their further development. Sodium and lithium are in the same main group and have similar properties. Sodium is abundant in reserves and low in cost. As an electrode material, it also has an excellent energy storage mechanism and is considered to be the best candidate to replace lithium batteries.

[0003] The performance of the negative electrode material of the sodium ion battery directly determines the performance of the sodium ion battery. The ideal negative electrode material requires a higher output voltage, and at the same time requires good cycle performance and good stability. It cannot produce excessive volume expansion, otherwise it is easy to cause problems such as cracking and falling off, affecting the service life. In summary, it is of great significance to study a sodium ion battery negative electrode material with high output voltage, good cycle performance, good stability and long service life and its preparation method. Summary of the invention

[0004] The object of the present invention is to provide a sodium ion battery negative electrode material and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing a negative electrode material for a sodium ion battery, comprising the following steps: S1: mixing pretreated hard carbon, nano-molybdenum disulfide, a sodium supplement, and polyacrylic acid, spray drying at 150-160°C, and heat treating to obtain a composite active material; S2: adding the composite active material to a mixed solution of ethanol and water, adding a modifier, heating and stirring, filtering, washing, and drying to obtain a modified composite active material; mixing the modified composite active material with polyaniline to obtain a negative electrode material; The preparation of the modifier comprises the following steps: mixing diallylamine, sodium hydroxide and tetrahydrofuran under nitrogen protection, cooling to 5-10°C, stirring and adding 3-chloropropyltrimethoxysilane, stirring for 2-4 hours, removing the solvent, post-treating (adding deionized water for mixing and drying the organic phase) to obtain modified silane; taking mercaptoimidazole, naphthalenethiol, triethylamine and ethanol, heating to 40-50°C for stirring and activation, adding the modified silane, heating to 75-78°C for stirring and reaction for 4-6 hours, and removing the solvent to obtain the modifier.

[0006] More optimally, the composite active material comprises the following raw materials, by weight: 60-70 parts of pretreated hard carbon, 20-30 parts of nano molybdenum disulfide, 2-5 parts of sodium supplement, and 2-3 parts of polyacrylic acid; The modified composite active material comprises the following raw materials, calculated by weight: 1-2 parts of composite active material and 0.1-0.15 parts of modifier.

[0007] More optimally, in the negative electrode material, the mass ratio of the modified composite active material to polyaniline is (8~9):1.

[0008] More optimally, the modified silane includes the following raw materials, calculated by mass: 8-10 parts of diallylamine, 4-5 parts of sodium hydroxide, 120-150 parts of tetrahydrofuran, and 20-25 parts of 3-chloropropyltrimethoxysilane; the modifier includes the following raw materials, calculated by mass: 8-10 parts of mercaptoimidazole, 15-18 parts of naphthalenethiol, 10-15 parts of triethylamine, 80-100 parts of ethanol, and 25-30 parts of modified silane.

[0009] More optimally, the preparation method of the pretreated hard carbon is: adding the hard carbon to a nitric acid aqueous solution with a concentration of 8-12 mol / L, treating at 70-90°C for 12-15 hours, washing with water, and drying to obtain the pretreated hard carbon; the amount of hard carbon added is 20-30% of the mass of the nitric acid aqueous solution; the hard carbon is biomass hard carbon, with a particle size D50 of 8-15 μm and a specific surface area of ​​80-100 m / g.

[0010] More optimally, the sodium supplement includes Na 2 SO 4 , NaCl, NaNO 3 、Na 3 PO 4 、Na 2 HPO 4 One or more of .

[0011] More optimally, the heat treatment process is: 600~800℃ for 2~4h.

[0012] More optimally, the above-mentioned negative electrode material is coated on the surface of the negative electrode current collector copper foil to obtain a negative electrode active layer of 150-200 μm, vacuum dried at 110-120° C. for 4 hours, and the pole ears are welded to obtain the negative electrode sheet of the sodium ion battery.

[0013] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: when the hard carbon material is used alone as the negative electrode active material of the sodium ion battery, the tip discharge effect is prone to occur, and there is a disadvantage of low capacity. The present invention first pre-treats the hard carbon to obtain a porous structure, and then mixes it with nano molybdenum disulfide and a sodium supplement under the action of a polyacrylic acid binder, and obtains a composite active material after heat treatment; the hard carbon with a porous structure can be more tightly combined with the nano molybdenum disulfide and the sodium supplement, can provide a buffer space, and reduce problems such as volume expansion and cracks; the nano molybdenum disulfide has a layered structure and a large surface area, provides a fast channel for the embedding and extraction of sodium ions, and improves the specific capacity; the sodium supplement makes up for the irreversible consumption of the sodium element in the cycle of the sodium ion battery, and improves the first efficiency and capacity of the sodium ion battery; the amount of nano molybdenum disulfide added needs to be controlled, otherwise it will lead to problems such as reduced electrical performance and increased volume expansion rate.

[0014] Introducing N and S elements is a common method to improve the performance of negative electrode materials. However, directly introducing too much nano-molybdenum disulfide into the above-mentioned composite active material will cause performance degradation, so the composite active material is further modified; the preparation steps of the modifier are as follows: first, diallylamine and 3-chloropropyltrimethoxysilane are used to prepare a modified silane containing N elements and multiple double bonds, and then the double bonds and mercapto groups are reacted to graft mercaptoimidazole and naphthalenethiol; mercaptoimidazole can increase the adsorption force between the negative electrode material and the negative electrode current collector during application, and can also To improve the transmission of sodium ions on the negative electrode surface and improve electrical performance; the structure of naphthalene has strong rigidity, which can inhibit expansion, cracking and other phenomena, and improve the stability and service life of the battery; the modifier can effectively inhibit side reactions on the negative electrode surface, improve the cycle performance and high-temperature stability of the sodium ion battery, and its structure can produce multiple conjugations to form large delocalized π bonds, improve the conductivity of the negative electrode surface, and interact with the binder polyaniline to improve compatibility; but the amount of modifier added should not be too much, as too much addition will affect the conductivity of the negative electrode material. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] It should be noted that there is no special restriction on the purchase manufacturers of all raw materials involved in the present invention, and exemplary examples include: ethanol (CAS: 64-17-5); nano molybdenum disulfide (AM-MOS 2-096-1, 100nm); polyacrylic acid (Hubei Junrui JR1196); diallylamine (CAS: 124-02-7); 3-chloropropyltrimethoxysilane (CAS: 2530-87-2); mercaptoimidazole (2-mercaptoimidazole, CAS: 872-35-5); naphthalenethiol (2-naphthalenethiol, CAS: 91-60-1); polyaniline (Yuanye S27440); hard carbon (particle size D50 is 10μm, specific surface area is 80m / g); Unless otherwise specified, the following are parts by mass and mass ratios; Example 1: S1: Add hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treat at 70°C for 12 h, wash with water, and dry to obtain pretreated hard carbon; the amount of hard carbon added is 30% of the mass of the nitric acid aqueous solution; S2: 65 parts of pretreated hard carbon, 25 parts of nano-molybdenum disulfide, 4 parts of NaCl, and 3 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Mix 9 parts of diallylamine, 5 parts of sodium hydroxide and 120 parts of tetrahydrofuran under nitrogen protection, cool to 5°C, stir and add 22 parts of 3-chloropropyltrimethoxysilane, stir for 4 hours, remove the solvent, and post-treat to obtain modified silane; take 10 parts of mercaptoimidazole, 15 parts of naphthalenethiol, 15 parts of triethylamine and 100 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 28 parts of modified silane, heat to 78°C and stir to react for 5 hours, remove the solvent to obtain a modifier; S4: Take 1 part of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.1 parts of the modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0017] Example 2: S1: Add hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treat at 70°C for 12 h, wash with water, and dry to obtain pretreated hard carbon; the amount of hard carbon added is 30% of the mass of the nitric acid aqueous solution; S2: 60 parts of pretreated hard carbon, 20 parts of nano-molybdenum disulfide, 2 parts of NaCl, and 2 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Mix 8 parts of diallylamine, 4 parts of sodium hydroxide and 120 parts of tetrahydrofuran under nitrogen protection, cool to 5°C, stir and add 20 parts of 3-chloropropyltrimethoxysilane, stir for 4 hours, remove the solvent, and post-treat to obtain modified silane; take 8 parts of mercaptoimidazole, 15 parts of naphthalenethiol, 10 parts of triethylamine and 80 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 25 parts of modified silane, heat to 78°C and stir to react for 5 hours, remove the solvent to obtain a modifier; S4: Take 1 part of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.1 parts of the modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0018] Example 3: S1: adding hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treating at 70°C for 12 h, washing with water, and drying to obtain pretreated hard carbon; the amount of hard carbon added is 30% of the mass of the nitric acid aqueous solution; S2: 70 parts of pretreated hard carbon, 30 parts of nano-molybdenum disulfide, 5 parts of NaCl, and 3 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Mix 10 parts of diallylamine, 5 parts of sodium hydroxide and 150 parts of tetrahydrofuran under nitrogen protection, cool to 5°C, stir and add 25 parts of 3-chloropropyltrimethoxysilane, stir for 4 hours, remove the solvent, and post-treat to obtain modified silane; take 10 parts of mercaptoimidazole, 18 parts of naphthalenethiol, 15 parts of triethylamine and 100 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 30 parts of modified silane, heat to 78°C and stir to react for 5 hours, remove the solvent to obtain a modifier; S4: Take 2 parts of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.15 parts of a modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0019] Example 4: S1: Add hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treat at 70°C for 12 h, wash with water, and dry to obtain pretreated hard carbon; the amount of hard carbon added is 30% of the mass of the nitric acid aqueous solution; S2: 70 parts of pretreated hard carbon, 20 parts of nano-molybdenum disulfide, 5 parts of NaCl, and 2 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Mix 8 parts of diallylamine, 5 parts of sodium hydroxide and 150 parts of tetrahydrofuran under nitrogen protection, cool to 5°C, stir and add 25 parts of 3-chloropropyltrimethoxysilane, stir for 4 hours, remove the solvent, and post-treat to obtain modified silane; take 8 parts of mercaptoimidazole, 18 parts of naphthalenethiol, 15 parts of triethylamine and 100 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 30 parts of modified silane, heat to 78°C and stir to react for 5 hours, remove the solvent to obtain a modifier; S4: Take 1 part of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.12 parts of the modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0020] Example 5: S1: Add hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treat at 70°C for 12 h, wash with water, and dry to obtain pretreated hard carbon; the amount of hard carbon added is 28% of the mass of the nitric acid aqueous solution; S2: 70 parts of pretreated hard carbon, 20 parts of nano-molybdenum disulfide, 5 parts of NaCl, and 2 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Mix 8 parts of diallylamine, 5 parts of sodium hydroxide and 150 parts of tetrahydrofuran under nitrogen protection, cool to 5°C, stir and add 25 parts of 3-chloropropyltrimethoxysilane, stir for 4 hours, remove the solvent, and post-treat to obtain modified silane; take 8 parts of mercaptoimidazole, 18 parts of naphthalenethiol, 15 parts of triethylamine and 100 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 30 parts of modified silane, heat to 78°C and stir to react for 5 hours, remove the solvent to obtain a modifier; S4: Take 1 part of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.1 parts of the modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0021] Comparative Example 1 (the proportion of nano-molybdenum disulfide added is increased, and the other method steps are consistent with Example 1): S1: adding hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treating at 70° C. for 12 h, washing with water, and drying to obtain pretreated hard carbon; the amount of hard carbon added is 30% of the mass of the nitric acid aqueous solution; S2: 55 parts of pretreated hard carbon, 35 parts of nano-molybdenum disulfide, 4 parts of NaCl, and 3 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Mix 9 parts of diallylamine, 5 parts of sodium hydroxide and 120 parts of tetrahydrofuran under nitrogen protection, cool to 5°C, stir and add 22 parts of 3-chloropropyltrimethoxysilane, stir for 4 hours, remove the solvent, and post-treat to obtain modified silane; take 10 parts of mercaptoimidazole, 15 parts of naphthalenethiol, 15 parts of triethylamine and 100 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 28 parts of modified silane, heat to 78°C and stir to react for 5 hours, remove the solvent to obtain a modifier; S4: Take 1 part of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.1 parts of the modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0022] Comparative Example 2 (using vinyltrimethoxysilane instead of modified silane, and the remaining steps are consistent with Example 1): S1: adding hard carbon to a 10 mol / L nitric acid aqueous solution, treating at 70° C. for 12 h, washing with water, and drying to obtain pretreated hard carbon; the amount of hard carbon added is 30% of the mass of the nitric acid aqueous solution; S2: 65 parts of pretreated hard carbon, 25 parts of nano-molybdenum disulfide, 4 parts of NaCl, and 3 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Take 10 parts of mercaptoimidazole, 15 parts of naphthalenethiol, 15 parts of triethylamine, and 100 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 28 parts of vinyltrimethoxysilane, heat to 78°C and stir to react for 5 hours, remove the solvent, and obtain a modifier; S4: Take 1 part of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.1 parts of the modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0023] Comparative Example 3 (changing the amount of the modifier added in the modified composite active material, and the other method steps are consistent with Example 1): S1: adding hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treating at 70° C. for 12 h, washing with water, and drying to obtain pretreated hard carbon; the amount of hard carbon added is 30% of the mass of the nitric acid aqueous solution; S2: 65 parts of pretreated hard carbon, 25 parts of nano-molybdenum disulfide, 4 parts of NaCl, and 3 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Mix 9 parts of diallylamine, 5 parts of sodium hydroxide and 120 parts of tetrahydrofuran under nitrogen protection, cool to 5°C, stir and add 22 parts of 3-chloropropyltrimethoxysilane, stir for 4 hours, remove the solvent, and post-treat to obtain modified silane; take 10 parts of mercaptoimidazole, 15 parts of naphthalenethiol, 15 parts of triethylamine and 100 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 28 parts of modified silane, heat to 78°C and stir to react for 5 hours, remove the solvent to obtain a modifier; S4: Take 1 part of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.2 parts of the modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0024] Comparative Example 4 (the amount of mercaptoimidazole and naphthalenethiol added was changed, and the other method steps were consistent with Example 1): S1: adding hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treating at 70° C. for 12 h, washing with water, and drying to obtain pretreated hard carbon; the amount of hard carbon added was 30% of the mass of the nitric acid aqueous solution; S2: 65 parts of pretreated hard carbon, 25 parts of nano-molybdenum disulfide, 4 parts of NaCl, and 3 parts of polyacrylic acid were mixed at 70°C for 8 hours, spray-dried at 160°C, and kept at 700°C for 3 hours to obtain a composite active material; S3: Mix 9 parts of diallylamine, 5 parts of sodium hydroxide and 120 parts of tetrahydrofuran under nitrogen protection, cool to 5°C, stir and add 22 parts of 3-chloropropyltrimethoxysilane, stir for 4 hours, remove the solvent, and post-treat to obtain modified silane; take 15 parts of mercaptoimidazole, 5 parts of naphthalenethiol, 15 parts of triethylamine and 100 parts of ethanol, heat to 45°C and stir to activate for 20 minutes, add 28 parts of modified silane, heat to 78°C and stir to react for 5 hours, remove the solvent to obtain a modifier; S4: Take 1 part of the composite active material, add it to a mixed solution of 10 parts of ethanol and 2 parts of water, add 0.1 parts of the modifier, heat to 75°C and stir for 18 hours, filter, wash and dry to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0025] Comparative Example 5 (the preparation method is changed, and the remaining steps are consistent with those of Example 1): S1: adding hard carbon to a nitric acid aqueous solution with a concentration of 10 mol / L, treating at 70° C. for 12 h, washing with water, and drying to obtain pretreated hard carbon; the amount of hard carbon added is 30% of the mass of the nitric acid aqueous solution; S2: 65 parts of pretreated hard carbon, 25 parts of nano-molybdenum disulfide, and 4 parts of NaCl are mixed to obtain a composite active material; S3: Take 10 parts of mercaptoimidazole and 15 parts of naphthalenethiol, mix them, and obtain a modifier; S4: taking 1 part of the composite active material and 0.1 part of the modifier to obtain a modified composite active material; S5: Mixing the modified composite active material and polyaniline in a mass ratio of 8:1 to obtain a negative electrode material.

[0026] Performance test: The negative electrode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were coated on the surface of the negative electrode current collector copper foil to obtain a 180 μm negative electrode active layer, vacuum dried at 110 ° C for 4 h, and the tabs were welded to obtain the negative electrode sheet of the sodium ion battery; the negative electrode sheet and the positive electrode sheet, electrolyte, and separator were used to make a sodium ion battery, wherein the counter electrode was metallic sodium, the separator was a glass fiber membrane, and the electrolyte was 1M NaClO 4 / EC:DEC(1:1)+5wt%FEC, and conduct performance testing; (1) Conduct constant current charge and discharge tests on a LANDCT2001A tester with a charge and discharge current density of 300mA / g to test the initial charge specific capacity and the capacity retention rate after 50 cycles of charge and discharge; (2) Stand at 25°C for 30 minutes, charge to 4.0V at a constant current of 0.5C, and further charge to a current of 0.5C at a constant voltage of 4.0V, and then test the volume of the battery using the drainage method; Place the sodium ion battery at 60°C for 30 days, and then test the volume using the same method to measure the volume expansion rate; See Table 1 for details; Table 1:

[0027] Conclusion: In comparative example 1, the amount of nano-molybdenum disulfide is increased, and the first charge specific capacity and capacity retention rate decrease significantly due to excessive addition, and the volume expansion rate increases; in comparative example 2, vinyltrimethoxysilane is used instead of modified silane, and although the next reaction can be carried out, the performance is not as good as the embodiment due to structural changes; in comparative example 3, the amount of modifier added in the modified composite active material is increased, which affects the electrical properties and causes performance degradation; in comparative example 4, the addition ratio of mercaptoimidazole and naphthylthiol is changed, and the performance is affected, which shows that the control of the addition amount is of great significance; in comparative example 5, pretreated hard carbon, nano-molybdenum disulfide, and NaCl are directly mixed, and mercaptoimidazole and naphthylthiol are directly added without composite modification, and the performance decreases significantly; in summary, the sodium ion battery prepared by the negative electrode material prepared by the present invention has high energy, good cycle performance, good high-temperature storage performance, and low expansion rate.

[0028] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode material for a sodium ion battery, characterized in that: The following steps are involved: S1: pretreated hard carbon, nano-molybdenum disulfide, sodium supplement, and polyacrylic acid are mixed, spray-dried, and heat-treated to obtain a composite active material; S2: Mix diallylamine, sodium hydroxide and tetrahydrofuran under nitrogen protection, cool to 5-10°C, stir and add 3-chloropropyltrimethoxysilane, stir for 2-4 hours, remove the solvent, and post-treat to obtain modified silane; take mercaptoimidazole, naphthylthiol, triethylamine and ethanol, heat to 40-50°C and stir to activate, add modified silane, heat to 75-78°C and stir to react for 4-6 hours, remove the solvent to obtain a modifier; S3: adding the composite active material to a mixed solution of ethanol and water, adding a modifier, heating and stirring, filtering, washing, and drying to obtain a modified composite active material; mixing the modified composite active material with polyaniline to obtain a negative electrode material.

2. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: The composite active material comprises the following raw materials, calculated by weight: 60-70 parts of pretreated hard carbon, 20-30 parts of nano molybdenum disulfide, 2-5 parts of sodium supplement, and 2-3 parts of polyacrylic acid; The modified composite active material comprises the following raw materials, calculated by weight: 1-2 parts of composite active material and 0.1-0.15 parts of modifier.

3. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: In the negative electrode material, the mass ratio of the modified composite active material to polyaniline is (8~9):

1.

4. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: The modified silane includes the following raw materials, calculated by weight: 8 to 10 parts of diallylamine, 4 to 5 parts of sodium hydroxide, 120 to 150 parts of tetrahydrofuran, and 20 to 25 parts of 3-chloropropyltrimethoxysilane; the modifier includes the following raw materials, calculated by weight: 8 to 10 parts of mercaptoimidazole, 15 to 18 parts of naphthalenethiol, 10 to 15 parts of triethylamine, 80 to 100 parts of ethanol, and 25 to 30 parts of modified silane.

5. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: The preparation method of the pretreated hard carbon is as follows: adding the hard carbon to a nitric acid aqueous solution with a concentration of 8-12 mol / L, treating at 70-90° C. for 12-15 hours, washing with water, and drying to obtain the pretreated hard carbon; the amount of the hard carbon added is 20-30% of the mass of the nitric acid aqueous solution; the hard carbon is biomass hard carbon, the particle size D50 is 8-15 μm, and the specific surface area is 80-100 m / g.

6. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: The sodium supplement includes one or more of Na2SO4, NaCl, NaNO3, Na3PO4, and Na2HPO4.

7. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: The heat treatment process is: 600~800℃ insulation for 2~4h.

8. A negative electrode material prepared according to the method for preparing a negative electrode material for a sodium ion battery according to any one of claims 1 to 7.

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