Sodium ion battery negative electrode material and preparation method thereof

Abstract

The invention relates to the field of sodium-ion batteries, and particularly discloses a sodium-ion battery negative electrode material and a preparation method thereof. The preparation method of the sodium ion battery negative electrode material comprises the following steps: S1, preparing an active material: performing aluminum denudation treatment on titanium aluminum carbide to obtain two-dimensional titanium carbide, then blending the two-dimensional titanium carbide with PS microspheres, then sequentially blending with 2-methylimidazole, Co (NO3) 2.6 H2O and Ni (NO3) 2.6 H2O, stirring, filtering to obtain a precipitate, and vulcanizing and annealing the precipitate to obtain the active material; s2, preparing a modified PVA-CS adhesive; and S3, blending to obtain the sodium ion battery negative electrode material. The sodium ion battery negative electrode material has extremely high stability, excellent current bearing capacity and rich lithium ion transmission paths, can well relieve the volume expansion phenomenon and maintain the stability of SEI in the cycle process, and has excellent electrochemical performance and structural stability.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery negative electrode material and a preparation method thereof. Background Art

[0002] The field of electrochemical energy storage is currently booming. Lithium-ion batteries, with their high energy density and long cycle life, have become the mainstream product in this field. They have been widely used in many fields, such as electric vehicles and portable electronic devices, and have greatly promoted the development of these industries. They have brought many conveniences to people's lives and work, improved energy efficiency, promoted green travel, and promoted the miniaturization and high performance of electronic devices. However, the limited resources of lithium and the frequent price fluctuations have significantly restricted the large-scale application of lithium-ion batteries. Against this backdrop, sodium-ion batteries have gradually become a research hotspot due to their abundant sodium resources and low cost. They are regarded as a potential alternative to lithium-ion batteries and have important significance for alleviating lithium resource pressure and reducing energy storage costs. Currently, the development of sodium-ion batteries focuses mainly on the research of cathode materials and electrolytes, while the selection of anode materials plays a key role in their overall performance.

[0003] In existing technologies, to meet the performance requirements of sodium-ion batteries, various types of common sodium-ion battery anode materials are used. These include hard carbon, soft carbon, and alloy materials. Hard carbon materials, due to their structural characteristics, enable sodium ion insertion and extraction to a certain extent; soft carbon materials offer good conductivity and processing properties; and alloy materials store sodium ions by forming alloys with sodium. Past research and applications of these materials have each addressed the performance challenges of sodium-ion battery anodes and have found use in various applications. These materials have laid the foundation for research on sodium-ion battery anode materials and have provided researchers with a deeper understanding of their performance.

[0004] However, existing sodium-ion battery anode materials have significant drawbacks. Hard carbon, soft carbon, and alloy materials either have low specific capacities, failing to meet the high energy storage requirements of sodium-ion batteries; or they experience significant volume expansion during battery cycling, leading to structural damage and, consequently, poor cycling stability. This severely limits improvements in the overall performance of sodium-ion batteries, necessitating the development of new, high-performance anode materials to address these challenges. Summary of the Invention

[0005] In order to solve the above technical problems, the present application provides a sodium ion battery negative electrode material and a preparation method thereof.

[0006] In the first aspect, the present application provides a method for preparing a sodium ion battery negative electrode material, comprising the following steps: S1, preparing an active material: performing aluminum stripping treatment on titanium aluminum carbide to obtain two-dimensional titanium carbide, then blending the two-dimensional titanium carbide with PS microspheres, and then blending with 2-methylimidazole and Co(NO3)2·6H2O and Ni(NO3)2·6H2O in sequence, stirring, filtering to obtain a precipitate, sulfurizing the precipitate, annealing to obtain an active material; S2, preparing a modified PVA-CS adhesive; S3, blending: blending the active material, superconducting carbon black and modified PVA-CS adhesive in a weight ratio of (7-7.5):1:(1.5-2), stirring evenly to obtain a sodium ion battery negative electrode material.

[0007] By adopting the above technical solution, the present application first performs aluminum stripping treatment on titanium aluminum carbide to form two-dimensional titanium carbide with a morphology similar to graphene and good electrical conductivity, and then blends it with PS microspheres and uniformly wraps it on the surface of the PS microspheres. The PS microspheres can provide rigid support for it, and then blends the mixed material with 2-methylimidazole and Co(NO3)2·6H2O. Cobalt ions and 2-methylimidazole can coordinate to form a metal organic framework with a large specific surface area, and grow in situ on the surface of the PS microspheres to form a unique pore structure. It is then blended with Ni(NO3)2·6H2O, nickel ions are added to the system, the reaction is stirred, and the precipitate is filtered to obtain a sulfide, which is then sulfurized to introduce sulfur elements, and then annealing is performed at the same time. At the annealing temperature, the PS microspheres are carbonized, the organic phase in the system is volatilized, and the material eventually forms a hollow structure. During the sulfurization and annealing process, the Co in the metal organic framework is 2+ , doped Ni 2+ With S 2-Combined to form bimetallic sulfide, the Ni-Co-S bond cooperates with the carbon network, giving the active material extremely high conductivity. At the same time, the hollow structure of the active material effectively improves the material stability, inhibits the structural collapse of the active material during the charge and discharge cycle, and enhances the negative electrode material's ability to withstand current cycles. The binder in this application is a modified PVA-CS binder, which has excellent mechanical properties, adhesion properties and ionic conductivity, and has good affinity with the electrolyte. The negative electrode material prepared by blending it with active materials and superconducting carbon black has excellent electrochemical performance in actual use. Experimental data show that after 4000 cycles at a current density of 10A / g, the average single capacity decay rate is not higher than 0.0325‰, and it has a reversible specific capacity of more than 800mAh / g at a current density of 0.2A / g, and the first coulombic efficiency (ICE) is not less than 87.8%. It proves that the sodium ion battery negative electrode material of this application has extremely high stability, excellent current carrying capacity, rich lithium ion transmission paths, can effectively alleviate the volume expansion phenomenon, maintain the stability of the solid electrolyte interface film (SEI) during the cycle, and has excellent electrochemical properties and structural stability.

[0008] Preferably, the aluminum stripping treatment in step S1 is specifically as follows: immersing the titanium aluminum carbide in a hydrofluoric acid solution, stirring at a temperature of 30-40°C for 20-30 hours, centrifuging and washing with water until the pH of the wastewater is 4.8-5.2, adding ethanol in an ice water bath, centrifuging, adding water and shaking, continuing to centrifuge until stratification, taking the upper liquid phase, freezing, drying, and grinding to obtain two-dimensional titanium carbide.

[0009] By adopting the above technical solution, titanium aluminum carbide is immersed in a hydrofluoric acid solution, stirred at a specific temperature for a specific time, and aluminum can be stripped from the titanium aluminum carbide through water washing, centrifugation and other treatments to obtain two-dimensional titanium carbide with a morphology similar to graphene. This two-dimensional titanium carbide has good electrical conductivity. Subsequently, ethanol is added to an ice-water bath to extract the two-dimensional titanium carbide, providing a high-quality active material basis for the subsequent preparation of high-performance sodium-ion battery negative electrode materials, which helps to improve the electrochemical performance and structural stability of the negative electrode material, enhance conductivity, inhibit structural collapse during charge and discharge cycles, and alleviate volume expansion.

[0010] Preferably, in step S1, the usage ratio of Co(NO3)2·6H2O and Ni(NO3)2·6H2O is 10:(4-5).

[0011] By adopting the above technical solution and using Co(NO3)2·6H2O and Ni(NO3)2·6H2O in a specific proportion, cobalt ions and nickel ions can be better involved in the reaction, which is conducive to the formation of bimetallic sulfides with a more suitable cobalt-nickel ratio during the sulfidation and annealing process, further improving the conductivity and structural stability of the active material, thereby enhancing the electrochemical performance and current carrying capacity of the negative electrode material.

[0012] Preferably, the specific operations of sulfurization and annealing in step S1 are: adding thioacetamide, heating under the protection of inert gas, annealing, and cooling to obtain the active material.

[0013] Preferably, the amount of thioacetamide added is 500-550 wt % of the amount used for precipitation.

[0014] By adopting the above technical solution, the present invention adds an appropriate amount of thioacetamide to the active material preparation for sulfurization and annealing treatment, which can ensure that there is an appropriate amount of sulfur element in the system to participate in the reaction, so that the Co in the metal organic framework 2 + , doped Ni 2+ With S 2- Combined to form bimetallic sulfide, Ni-Co-S bonds cooperate with the carbon network to further enhance the conductivity of the active material. At the same time, it helps to form and stabilize the hollow structure of the active material, better inhibit the structural collapse of the active material during the charge and discharge cycle, and enhance the negative electrode material's ability to withstand current cycling.

[0015] Preferably, the heating rate is 2-2.5°C / min.

[0016] By adopting the above technical solution, the present application performs annealing at a rate of 2-2.5°C / min, which can accurately control the formation process of the active material and further optimize the microstructure of the active material, thereby improving the overall performance stability of the negative electrode material and ensuring that the negative electrode material can maintain good electrochemical performance at different current densities. If the heating rate is too fast, the sulfurization is insufficient, and it will cause rapid pyrolysis of the surface of the PS microspheres, violent escape of internal volatiles, and the formation of a closed-pore structure; if the heating rate is too slow, the carbon skeleton formed by the PS microspheres will shrink excessively, and adhesion will occur between the microspheres. Therefore, a moderate heating rate can ensure the formation of a hollow structure and further enhance the negative electrode material's ability to withstand current cycling.

[0017] Preferably, step S2 is specifically: blending methyldiethanolamine and 1,3-propane sultone in a weight ratio of (0.98-1): (1-1.04), stirring the reaction until no precipitation is generated, distilling, and drying to obtain a modifier, and blending the modifier, CS and PVA in a weight ratio of (5-10): 20:20 to obtain a modified PVA-CS adhesive.

[0018] By adopting the above technical solution, the present application uses methyldiethanolamine and 1,3-propanesultone to blend to obtain a modifier, and uses it to modify CS and PVA, thereby promoting the adhesive to form an amorphous state, improving the dispersion uniformity of the active material and superconducting carbon black and the bonding strength of the adhesive itself. Compared with the unmodified adhesive and the ordinary adhesive, the modified adhesive has a denser hydrogen bond network and higher conductivity. Its hydrogen bond network can protect the hollow structure of the active material in a stable state to a certain extent. Under external force stimulation, hydrogen bond breakage occurs preferentially at the point where the curvature of the hollow structure is maximum. Therefore, the modified PVA-CS adhesive of the present application has the advantages of inhibiting volume expansion, improving electrode peel strength, and optimizing electrochemical performance in three directions. Experimental data show that its average peel strength can reach above 1.36N / cm.

[0019] Preferably, the modifier, CS and PVA are blended in a weight ratio of 7:20:20.

[0020] By adopting the above technical solution, the weight ratio of the modifier, CS and PVA is strictly controlled in this application, and the adhesion of the adhesive is further improved. At this time, the average peel strength can be increased by more than 0.08N / cm.

[0021] In a second aspect, the present application provides a sodium ion battery negative electrode material prepared by the above preparation method.

[0022] By adopting the above technical solution, the sodium ion battery negative electrode material of the present application is coated on the surface of a metal sheet (copper foil is used as an example in this application), and a sodium ion battery negative electrode can be formed after drying overnight. After 4000 cycles at a current density of 10 A / g, the average single capacity decay rate is not higher than 0.0325‰, and the reversible specific capacity is more than 800 mAh / g at a current density of 0.2 A / g. The first coulombic efficiency (ICE) is not less than 87.8%, which proves that the sodium ion battery negative electrode material of the present application has excellent electrochemical properties and structural stability.

[0023] In summary, this application has the following beneficial technical effects: 1. The preparation method of the present application first subjects titanium aluminum carbide to aluminum stripping treatment to form two-dimensional titanium carbide, which, after being blended with PS microspheres, can obtain rigid support. Subsequently, the hollow structure active material formed by blending with related substances, sulfurization, and annealing has extremely high conductivity, effectively improving material stability, inhibiting structural collapse during charge and discharge cycles, and enhancing the negative electrode material's ability to withstand current cycling. At the same time, the modified PVA-CS binder of the present application has excellent mechanical properties, adhesion properties, and ionic conductivity, and has good affinity with the electrolyte. The resulting negative electrode material has excellent electrochemical performance. 2. The sodium ion battery negative electrode material of the present application has rich lithium ion transmission paths, can effectively alleviate the volume expansion phenomenon, maintain the stability of the solid electrolyte interface membrane during the cycle, has high stability and high reversible specific capacity, high first coulombic efficiency, and overall has excellent electrochemical performance and structural stability, and has high practical use value. DETAILED DESCRIPTION

[0024] Material Source Unless otherwise specified, the raw materials used in this application are all commercially available products, specifically: Titanium aluminum carbide was purchased from Shijiazhuang Dongming New Materials Technology Co., Ltd.; PS microspheres were purchased from Beijing Biotech Biotechnology Co., Ltd. with a particle size of 2 μm; CS powder was purchased from Shandong Xinxiong Biotechnology Co., Ltd. with a particle size of 5 μm; PVA powder was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Superconducting carbon black was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; Si-Gr powder, Si:Gr=8:2 (w / w); PVDF adhesive was purchased from Merck Chemicals, specification: Arkema 900; PVA adhesive was purchased from Shanghai Chenqi Chemical Technology Co., Ltd., specification 2688; Lithium styrenesulfonyl (trifluoromethanesulfonyl) imide, CAS No. 2605224-20-0.

[0025] The present application is further described in detail below with reference to examples and comparative examples.

[0026] Example 1.1 A method for preparing a negative electrode material for a sodium ion battery comprises the following steps: S1. Preparation of active material: 50 g of lithium fluoride and 2 L of 9 mol / L hydrochloric acid solution were mixed and stirred for 30 minutes to obtain a hydrofluoric acid solution. 50 g of titanium aluminum carbide was immersed in the entire hydrofluoric acid solution and stirred at 30°C for 30 hours. The resulting reaction solution was centrifuged at 11,000 rpm for 20 minutes. Deionized water was then added to the precipitate in the centrifuge tube, and ultrasonication was performed for 10 minutes. The centrifugation was continued at 11,000 rpm for 20 minutes. This process was repeated several times until the pH value of the wastewater after centrifugation reached 4.8-5. 2. Then, ethanol was added to the centrifuge tube, ultrasonicated in an ice water bath for 1 hour, centrifuged at 11000 r / min for 20 minutes, 20 mL of deionized water was added to the centrifugal precipitate, shaken, and centrifuged at 3500 r / min for 3 minutes after ultrasonication. The upper liquid phase was taken, freeze-dried, and ground to obtain two-dimensional titanium carbide. Subsequently, all the two-dimensional titanium carbide and PS microspheres were dispersed in water at a weight ratio of 1:5, stirred at 3500 r / min for 2 hours, and after stopping stirring, the precipitate was washed with deionized water several times and vacuum-dried at 60 °C. The mixture was dried overnight to obtain intermediate 1, which was dispersed in ethanol and ultrasonically treated for 10 minutes. 2-Methylimidazole (1400 wt% of the amount of intermediate 1) was added and stirred for 30 minutes to obtain liquid A. Co(NO3)2·6H2O (1300 wt% of the amount of intermediate 1) was dispersed in ethanol, 10 wt% of a surfactant (CTAB) was added and ultrasonically dispersed for 10 minutes to obtain liquid B, which was slowly poured into liquid A and stirred for 30 minutes. The precipitate was collected by centrifugation and dried in vacuo at 60°C overnight to obtain liquid B. Intermediate 2 was then co-dispersed with Ni(NO3)2·6H2O in ethanol, with the ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O being controlled to be 6:10. The mixture was stirred for 1.5 h, and the precipitate was collected by centrifugation and dried in vacuum overnight at 60°C to obtain a precipitate. The precipitate was placed downstream of a tube furnace, and thioacetamide in an amount equivalent to 600 wt% of the precipitate was placed upstream of the tube furnace. The mixture was heated to 500°C at a rate of 1.5°C / min under inert gas protection, annealed for 2 h, and then cooled to room temperature to obtain an active material. S2. Preparation of modified PVA-CS adhesive: 9.8 g of methyldiethanolamine and 10.4 g of 1,3-propane sultone were dispersed in 35 mL of DMF, stirred in an oil bath at 60° C. for 6 h until no precipitate was generated, unreacted monomers and DMF were removed by distillation under reduced pressure, and vacuum dried at 60° C. for 24 h to obtain a modifier; 20 g of CS powder and 4 mL of glacial acetic acid were dispersed in 980 mL of deionized water and stirred for 6 h to obtain liquid C; 20 g of PVA powder was dispersed in 380 mL of deionized water, stirred for 30 min, and stirred in an oil bath at 90° C. for 6 h to obtain liquid D; all of liquid C and liquid D were blended, 5 g of the modifier was added, and stirred for 1 h to obtain a modified PVA-CS adhesive; S3. Blending: 7.5 g of the active material obtained in step S1, 1 g of superconducting carbon black, and 1.5 g of the modified PVA-CS binder obtained in step S2 were blended and stirred evenly to obtain a negative electrode material for a sodium ion battery.

[0027] Example 1.2 A method for preparing a negative electrode material for a sodium ion battery comprises the following steps: S1. Preparation of active material: 50 g of lithium fluoride and 2 L of 9 mol / L hydrochloric acid solution were mixed and stirred for 30 minutes to obtain a hydrofluoric acid solution. 50 g of titanium aluminum carbide was immersed in the entire hydrofluoric acid solution and stirred at 40°C for 20 hours. The resulting reaction solution was centrifuged at 11,000 rpm for 20 minutes. Deionized water was then added to the precipitate in the centrifuge tube, and ultrasonication was performed for 10 minutes. The centrifugation was continued at 11,000 rpm for 20 minutes. This process was repeated several times until the pH value of the wastewater after centrifugation reached 4.8-5. 2. Then, ethanol was added to the centrifuge tube, ultrasonicated in an ice water bath for 1 hour, centrifuged at 11000 r / min for 20 minutes, 20 mL of deionized water was added to the centrifugal precipitate, shaken, and centrifuged at 3500 r / min for 3 minutes after ultrasonication. The upper liquid phase was taken, freeze-dried, and ground to obtain two-dimensional titanium carbide. Subsequently, all the two-dimensional titanium carbide and PS microspheres were dispersed in water at a weight ratio of 1:5, stirred at 3500 r / min for 2 hours, and after stopping stirring, the precipitate was washed with deionized water several times and vacuum-dried at 60 °C. The mixture was dried overnight to obtain intermediate 1, which was dispersed in ethanol and ultrasonically treated for 10 minutes. 2-Methylimidazole (1400 wt% of the amount of intermediate 1) was added and stirred for 30 minutes to obtain liquid A. Co(NO3)2·6H2O (1300 wt% of the amount of intermediate 1) was dispersed in ethanol, 10 wt% of a surfactant (CTAB) was added and ultrasonically dispersed for 10 minutes to obtain liquid B, which was slowly poured into liquid A and stirred for 30 minutes. The precipitate was collected by centrifugation and dried in vacuo at 60°C overnight to obtain liquid B. Intermediate 2 was then co-dispersed with Ni(NO3)2·6H2O in ethanol, with the ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O being controlled to be 6:10. The mixture was stirred for 1.5 h, and the precipitate was collected by centrifugation and dried in vacuum overnight at 60°C to obtain a precipitate. The precipitate was placed downstream of a tube furnace, and thioacetamide in an amount equivalent to 600 wt% of the precipitate was placed upstream of the tube furnace. The mixture was heated to 500°C at a rate of 1.5°C / min under inert gas protection, annealed for 2 h, and then cooled to room temperature to obtain an active material. S2. Preparation of modified PVA-CS adhesive: 10 g of methyldiethanolamine and 10 g of 1,3-propane sultone were dispersed in 35 mL of DMF, stirred in an oil bath at 60° C. for 6 h until no precipitate was generated, unreacted monomers and DMF were removed by distillation under reduced pressure, and vacuum dried at 60° C. for 24 h to obtain a modifier; 20 g of CS powder and 4 mL of glacial acetic acid were dispersed in 980 mL of deionized water and stirred for 6 h to obtain liquid C; 20 g of PVA powder was dispersed in 380 mL of deionized water, stirred for 30 min, and stirred in an oil bath at 90° C. for 6 h to obtain liquid D; all of liquid C and liquid D were blended, 10 g of the modifier was added, and stirred for 1 h to obtain a modified PVA-CS adhesive; S3. Blending: 7 g of the active material obtained in step S1, 1 g of superconducting carbon black, and 2 g of the modified PVA-CS binder obtained in step S2 were blended and stirred evenly to obtain a negative electrode material for a sodium ion battery.

[0028] Example 2.1 A method for preparing a negative electrode material for a sodium ion battery, which differs from Example 1.1 in that, in step S1, the ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O is controlled to be 5:10, and the rest is the same as Example 1.1.

[0029] Example 2.2 A method for preparing a negative electrode material for a sodium ion battery, which differs from Example 1.1 in that, in step S1, the ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O is controlled to be 4:10, and the rest is the same as Example 1.1.

[0030] Example 2.3 A method for preparing a negative electrode material for a sodium ion battery, which differs from Example 1.1 in that, in step S1, the ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O is controlled to be 3:10, and the rest is the same as Example 1.1.

[0031] Example 3.1 A method for preparing a negative electrode material for a sodium ion battery, which differs from Example 1.1 in that, in step S1, the amount of thioacetamide added is 550 wt % of the amount used for precipitation, and the rest is the same as Example 1.1.

[0032] Example 3.2 A method for preparing a negative electrode material for a sodium ion battery is different from that of Example 1.1 in that, in step S1, the amount of thioacetamide added is 500 wt % of the amount used for precipitation, and the rest is the same as that of Example 1.1.

[0033] Example 3.3 A method for preparing a negative electrode material for a sodium ion battery, which differs from Example 1.1 in that, in step S1, the amount of thioacetamide added is 450 wt % of the amount used for precipitation, and the rest is the same as Example 1.1.

[0034] Example 4.1 A method for preparing a negative electrode material for a sodium ion battery, which differs from Example 1.1 in that, in the sulfurization in step S1, the temperature is raised to 500° C. at a rate of 2° C. / min under inert gas protection, and the rest is the same as Example 1.1.

[0035] Example 4.2 A method for preparing a negative electrode material for a sodium ion battery, which differs from Example 1.1 in that, in the sulfurization in step S1, the temperature is raised to 500° C. at a rate of 2.5° C. / min under inert gas protection, and the rest is the same as Example 1.1.

[0036] Example 4.3 A method for preparing a negative electrode material for a sodium ion battery, which differs from Example 1.1 in that, in the sulfurization in step S1, the temperature is raised to 500° C. at a rate of 3° C. / min under inert gas protection, and the rest is the same as Example 1.1.

[0037] Example 5.1 A method for preparing a negative electrode material for a sodium ion battery is different from that of Example 1.1 in that, in step S2, 6 g of a modifier is added, and the rest is the same as that of Example 1.1.

[0038] Example 5.2 A method for preparing a negative electrode material for a sodium ion battery is different from that of Example 1.1 in that, in step S2, 7 g of a modifier is added, and the rest is the same as that of Example 1.1.

[0039] Example 5.3 A method for preparing a negative electrode material for a sodium ion battery is different from that of Example 1.1 in that 8 g of a modifier is added in step S2, and the rest is the same as that of Example 1.1.

[0040] Example 5.4 A method for preparing a negative electrode material for a sodium ion battery is different from that of Example 1.1 in that, in step S2, 9 g of a modifier is added, and the rest is the same as that of Example 1.1.

[0041] Comparative Example 1 The difference from Example 1.1 is that step S1 is removed, and the active material is replaced with Si-Gr powder in step S3. The rest is the same as Example 1.1.

[0042] Comparative Example 2.1 The difference from Example 1.1 is that step S2 is removed, and in step S3, the modified PVA-CS adhesive is replaced with PVDF adhesive. The rest is the same as Example 1.1.

[0043] Comparative Example 2.2 The difference from Example 1.1 is that step S2 is removed, and in step S3, the modified PVA-CS adhesive is replaced with PVA adhesive. The rest is the same as Example 1.1.

[0044] Comparative Example 2.3 The difference from Example 1.1 is that step S2 is removed, and the modified PVA-CS adhesive is replaced with a modified composite PVDF adhesive in step S3, which is prepared by the following method: 20 g of PVDF-HFP is dissolved in 300 mL of NMP, 12 g of benzophenone is added to the solution under nitrogen protection, and the reaction liquid is nitrogen bubbled for 15 min to remove oxygen in the solution. After the system is sealed, it is irradiated with a high-pressure mercury lamp (365 nm) for 45 min, and then 5 g of lithium styrenesulfonyl (trifluoromethanesulfonyl) imide monomer is added. The reaction is carried out under nitrogen protection and a temperature of 90 ° C for 10 h. After the reaction is completed, the mixed solution is poured into 2 L of anhydrous ethanol for precipitation, centrifuged and the solid component is collected to obtain a crude product, and the crude product is dissolved in NMP, then precipitated with anhydrous ethanol again and centrifuged. The above steps are repeated three times. Finally, the collected product is extracted with methanol for 36 h and dried in vacuo at 60 ° C overnight to obtain a modified composite PVDF adhesive.

[0045] Comparative Example 3 S1. Preparation of modified composite PVDF adhesive: 20 g PVDF-HFP was dissolved in 300 mL NMP, 12 g benzophenone was added to the solution under nitrogen protection, the reaction liquid was nitrogen bubbled for 15 min to remove oxygen in the solution, the system was sealed and irradiated with a high-pressure mercury lamp (365 nm) for 45 min, then 5 g styrenesulfonyl (trifluoromethanesulfonyl) imide lithium monomer was added, and the mixture was reacted under nitrogen protection at a temperature of 90 ° C for 10 h. After the reaction, the mixed solution was poured into 2 L of anhydrous ethanol for precipitation, centrifuged and the solid component was collected to obtain a crude product, which was then dissolved in NMP, and then precipitated with anhydrous ethanol again and centrifuged. The above steps were repeated three times. Finally, the collected product was extracted with methanol for 36 h and dried in vacuo at 60 ° C overnight to obtain a modified composite PVDF adhesive; S2. Blending: 7 g of Si-Gr powder, 1 g of superconducting carbon black, and 2 g of the modified composite PVDF binder obtained in step S1 are blended and stirred evenly to obtain a negative electrode material for a sodium ion battery.

[0046] Performance testing 1. The sodium ion battery negative electrode material obtained in the embodiment and comparative example was evenly coated on a copper foil and dried in a vacuum oven at 110°C overnight. The electrode was then cut into a pole piece with a diameter of 12 mm for use. The loading amount was 1.3 mg / cm. Glass fiber was used as a separator and a 1 mol / L dimethyl ether solution of sodium hexafluorophosphate was used as an electrolyte. The battery was assembled in an argon-filled glove box. The positive electrode was a sodium sheet with a diameter of 16 mm and the negative electrode was a copper foil with a diameter of 12 mm coated with an active material. A half-cell was assembled and the battery was tested in a potential window of 0.01-3.00 V at current densities of 0.2 A / g and 10 A / g, respectively. The average single capacity decay rate (‰) of the battery at 10 A / g for 4000 cycles, the reversible specific capacity (mAh / g) at 0.2 A / g, and the ICE (%) were recorded in Table 1. 2. The sodium ion battery negative electrode material obtained in the examples and comparative examples was evenly coated on a copper foil and dried in a vacuum oven at 110°C overnight. The electrode was then cut into a 3 cm × 8 cm square sheet sample. One side of the sheet was then attached to a single-sided tape with a size of 2.5 cm × 7.5 cm, and the other side was attached to a pre-fixed transparent glass with a double-sided tape. The single-sided tape was peeled off using a universal testing machine at a tensile rate of 10 mm / s, and the 180° peel strength (N / cm) of the sample was calculated.

[0047] Table 1 Performance test table Data Analysis: As can be seen from Table 1, the average single capacity decay rate of Examples 1.1-1.2 after 4000 cycles is 0.0325-0.0326‰, the reversible specific capacity is 800-803mAh / g, the ICE is 87.83-97.90%, and the peel strength is 1.36-1.37N / cm, which proves that the sodium ion battery negative electrode material of the present application has extremely high stability, excellent current carrying capacity, rich lithium ion transmission paths, can better alleviate the volume expansion phenomenon, maintain the stability of SEI during the cycle, and has excellent electrochemical properties and structural stability.

[0048] The difference between Examples 2.1-2.3 and Example 1.1 is that the usage ratio of Ni(NO3)2·6H2O and Co(NO3)2·6H2O is changed. The results show that the average single capacity decay rate of Examples 2.1-2.2 is significantly reduced, and the reversible specific capacity and ICE are improved. This proves that the use of Co(NO3)2·6H2O and Ni(NO3)2·6H2O in a specific proportion in this application can enable cobalt ions and nickel ions to better participate in the reaction, which is conducive to the formation of bimetallic sulfides with a more suitable cobalt-nickel ratio during the sulfidation and annealing process, further improving the conductivity and structural stability of the active material, thereby enhancing the electrochemical properties and current carrying capacity of the negative electrode material.

[0049] The difference between Examples 3.1-3.3 and Example 1.1 is that the amount of thioacetamide added is changed. The results show that the average single capacity decay rate of Examples 3.1-3.2 is significantly reduced, and the reversible specific capacity and ICE are improved. This proves that the addition of an appropriate amount of thioacetamide in the preparation of the active material for sulfurization and annealing can ensure that the system has an appropriate amount of sulfur element participating in the reaction, so that the Co in the metal organic framework 2+ , doped Ni 2+ With S 2- Combined to form bimetallic sulfide, Ni-Co-S bonds cooperate with the carbon network to further enhance the conductivity of the active material. At the same time, it helps to form and stabilize the hollow structure of the active material, better inhibit the structural collapse of the active material during the charge and discharge cycle, and enhance the negative electrode material's ability to withstand current cycling.

[0050] The difference between Examples 4.1-4.3 and Example 1.1 is that the heating rate during vulcanization is adjusted. The results show that the average single capacity decay rate of Examples 4.1-4.2 is significantly reduced, and the reversible specific capacity and ICE are improved. This proves that the present application can ensure the formation of a hollow structure by controlling the heating rate to be moderate, thereby further enhancing the negative electrode material's ability to withstand current cycling. If the heating rate is too fast, the vulcanization is insufficient, and the surface of the PS microspheres will be rapidly pyrolyzed, and the internal volatiles will escape violently, forming a closed-pore structure. If the heating rate is too slow, the carbon skeleton formed by the PS microspheres will shrink excessively, and adhesion will occur between the microspheres.

[0051] The difference between Examples 5.1-5.4 and Example 1.1 is that the amount of modifier added is changed. The results show that the average single capacity decay rate of 5.2 is significantly reduced, the reversible specific capacity and ICE are improved, and the peel strength is greatly increased. This proves that the present application further optimizes the properties of the adhesive by strictly controlling the weight ratio of the modifier, CS and PVA, and improves the three aspects of inhibiting volume expansion, improving electrode peel strength and optimizing electrochemical performance.

[0052] The difference between Comparative Example 1 and Example 1.1 is that the active material is replaced with Si-Gr powder. The results show that the average single capacity decay rate is greatly improved, the reversible specific capacity and ICE are significantly reduced, and the peel strength is reduced, which proves that the active material of the present application has extremely high conductivity. The hollow structure effectively improves the material stability, inhibits the structural collapse of the active material during the charge and discharge cycle, and enhances the negative electrode material's ability to withstand current cycling.

[0053] Comparative Examples 2.1-2.3 differ from Example 1.1 in that the modified PVA-CS adhesive is replaced with other adhesives. The results show that the average single capacity decay rate is greatly improved, the reversible specific capacity and ICE are significantly reduced, and the peel strength is significantly reduced. This demonstrates that the modified PVA-CS adhesive in this application has excellent mechanical properties, adhesion properties, and ionic conductivity, and has good affinity with the electrolyte, a denser hydrogen bond network, and higher conductivity. Its hydrogen bond network can, to a certain extent, protect the hollow structure of the active material in a stable state.

[0054] Comparative Example 3 differs from Example 1.1 in that the active material is replaced with Si-Gr powder and the modified PVA-CS binder is replaced with a modified composite PVDF binder. The results show that the average single capacity decay rate is improved, the reversible specific capacity and ICE are slightly reduced, and the peel strength is also reduced. However, the degree of performance degradation is not as good as that of Comparative Example 1 and Comparative Examples 2.1-2.3. This proves that the active material and the modified PVA-CS binder of the present application have a good synergistic effect, and the negative electrode material obtained by blending has excellent electrochemical performance in actual use.

[0055] The embodiments of this specific implementation method are all preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a negative electrode material for a sodium ion battery, characterized in that: The following steps are involved: S1. Preparation of active material: performing aluminum stripping treatment on titanium aluminum carbide to obtain two-dimensional titanium carbide, then blending the two-dimensional titanium carbide with PS microspheres, and then sequentially blending with 2-methylimidazole, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O, stirring, filtering to obtain a precipitate, and sulfurizing and annealing the precipitate to obtain an active material; S2, preparing a modified PVA-CS adhesive; S3. Blending: Blend the active material, superconducting carbon black and modified PVA-CS binder in a weight ratio of (7-7.5):1:(1.5-2), and stir evenly to obtain a sodium ion battery negative electrode material.

2. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: The aluminum stripping treatment in step S1 is specifically as follows: immersing the titanium aluminum carbide in a hydrofluoric acid solution, stirring at a temperature of 30-40°C for 20-30 hours, centrifuging and washing with water until the pH of the wastewater is 4.8-5.2, adding ethanol in an ice-water bath, centrifuging, adding water and shaking, continuing to centrifuge until stratification, taking the upper liquid phase, freezing, drying, and grinding to obtain two-dimensional titanium carbide.

3. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: In the step S1, the usage ratio of Co(NO3)2·6H2O and Ni(NO3)2·6H2O is 10:(4-5).

4. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: The specific operations of sulfurization and annealing in step S1 are: adding thioacetamide, heating under the protection of inert gas, annealing, and cooling to obtain the active material.

5. The method for preparing a negative electrode material for a sodium ion battery according to claim 4, wherein: The amount of thioacetamide added is 500-550 wt % of the amount used for precipitation.

6. The method for preparing a negative electrode material for a sodium ion battery according to claim 4, wherein: The heating rate is 2-2.5°C / min.

7. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: The step S2 specifically comprises: blending methyldiethanolamine and 1,3-propane sultone in a weight ratio of (0.98-1): (1-1.04), stirring the mixture until no precipitation is generated, distilling the mixture, and drying the mixture to obtain a modifier; and blending the modifier, CS, and PVA in a weight ratio of (5-10):20:20 to obtain a modified PVA-CS adhesive.

8. The method for preparing a negative electrode material for a sodium ion battery according to claim 7, wherein: The modifier, CS and PVA were blended in a weight ratio of 7:20:

20.

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

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