A sodium battery composite negative electrode sheet, a preparation method thereof and an application thereof

Abstract

A sodium-ion battery composite negative electrode sheet, a preparation method thereof and an application thereof provided by the present invention belong to the technical field of sodium-ion batteries. The specific preparation method comprises the following steps: Step 1: Perform carbon coating treatment on an inorganic solid electrolyte to obtain a carbon-coated inorganic solid electrolyte composite material A; Step 2: Dissolve and disperse a polymer and an auxiliary agent in a solvent, and stir and disperse evenly to obtain a polymer solution; Step 3: Add the composite material A to the polymer solution for grafting reaction to obtain a composite material B with a hard-core hairy ball structure; Step 4: Dope the composite material B into a negative electrode material, and after homogenization, coat it on a current collector to obtain a sodium-ion battery composite negative electrode sheet. The electrode particles of the sodium-ion battery composite negative electrode sheet prepared by the present invention have good adhesion performance with the current collector, and the solid-state battery assembled with the sodium-ion battery composite negative electrode sheet has good cycle performance and excellent safety performance.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly relates to a sodium-ion battery composite negative electrode sheet, a preparation method thereof, and an application thereof. Background Art

[0002] At present, during the preparation process of electrode sheets, inorganic solid electrolytes are usually doped to improve the interfacial compatibility between the electrode sheet and the solid electrolyte membrane, reduce the interfacial impedance, and further improve the ionic conductivity of the electrode sheet and promote the interfacial ion transport. However, the electronic conductivity of inorganic solid electrolytes is poor, and adding them to electrode materials will reduce the electronic conductivity of the electrode sheet; moreover, the density of inorganic solid electrolytes is much larger than that of positive or negative electrode materials, and the solid electrolytes are prone to sedimentation during the pulping and dispersion process of positive and negative electrode slurries and are not easily uniformly dispersed; in addition, during the slurry coating and drying process, the binder will float due to capillary action and is unevenly distributed in the upper and lower layers of the electrode sheet, resulting in poor adhesion performance between the active material of the electrode sheet and the current collector. In severe cases, the electrode sheet will peel off from the current collector, affecting the electrochemical performance and safety performance of the battery cell. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to provide a sodium-ion battery composite negative electrode sheet that can reduce the interfacial impedance with the solid electrolyte membrane and a preparation method thereof, effectively promoting the interfacial sodium-ion transport. There is good adhesion performance between the electrode particles of the sodium-ion battery composite negative electrode sheet and the current collector, and a solid-state battery assembled with the sodium-ion battery composite negative electrode sheet, a solid electrolyte membrane, and a sodium-ion battery positive electrode has good cycle performance and excellent safety performance.

[0004] Technical Solution: To achieve the above object of the invention, the present invention provides a preparation method of a sodium-ion battery composite negative electrode sheet, specifically including the following steps:

[0005] Step 1: Perform carbon coating treatment on the inorganic solid electrolyte to obtain a carbon-coated inorganic solid electrolyte composite material A;

[0006] Step 2: Dissolve and disperse the polymer and the auxiliary agent in a solvent, and stir and disperse evenly to obtain a polymer solution;

[0007] Step 3: Add the composite material A to the polymer solution, and the high molecular polymer in the polymer solution undergoes a grafting reaction with the active sites on the carbon on the surface of the composite material A to obtain a composite material B with a hard-core hairy ball structure;

[0008] Step 4: Dope the composite material B into the negative electrode material, homogenize it, and coat it on the current collector to obtain a sodium-ion battery composite negative electrode sheet.

[0009] The present invention carbon-coats inorganic solid electrolyte particles, which can improve the ionic conductivity and electronic conductivity performance of the electrode; a polymer molecular chain is grafted on the surface of the carbon-coated inorganic solid electrolyte particles. Under this structure, the binder is not likely to float during the drying process due to the high density of the inorganic electrolyte particles, improving and enhancing the adhesion performance between the electrode and the current collector; relying on the volume effect and steric hindrance effect of the grafted polymer molecular chain, the inorganic electrolyte promotes the uniform dispersion of the electrolyte particles, which can effectively reduce the interfacial impedance with the solid electrolyte membrane and promote the interfacial sodium ion transport.

[0010] Among them, the composite material A formed after the carbon coating treatment of the inorganic solid electrolyte is selected from Na-β″-Al 2 O 3 / C composite material, Na 1+x Zr 2 P 3-x Si x O 12 / C composite material (0≤x≤3), Na 3 PS 4 / C composite material, Na 3 SbS 4 / C composite material, Na 11 Sn 2 PS 12 / C composite material, or any mixture of one or more of them.

[0011] Optionally, in step one, the inorganic solid electrolyte and the carbon source are mixed in a mass ratio of 0.1-10. Specifically, the carbon source is selected from any one or a mixture of sucrose, glucose, PVDF (polyvinylidene fluoride), PVP (polyvinylpyrrolidone), and citric acid. The solvent is selected from any one or a mixture of water, ethanol, NMP (N-methylpyrrolidone), and ethylene glycol dimethyl ether. The inorganic solid electrolyte and the carbon source are stirred for 1-24 hours in a ratio of 0.1-10, then dried at a temperature of 80-120°C for 6-24 hours, and then baked in a tube furnace at a temperature of 500-1000°C for 3-12 hours.

[0012] Optionally, by mass percentage, the polymer solution in step two includes: 1-50% polymer, 0-10% auxiliary agent, and 40-99% solvent.

[0013] Among them, the polymer is selected from any one or a mixture of PAA (polyacrylic acid), polyacrylate, PAN (polyacrylonitrile), PEO (polyethylene oxide), PVA (polyvinyl alcohol), SBR (styrene-butadiene rubber), CMC (carboxymethyl cellulose), sodium alginate. The auxiliary agent is selected from any one or a mixture of a dispersant, an antifoaming agent, and a wetting agent. The solvent is selected from any one or a mixture of deionized water, NMP (N-methylpyrrolidone), EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate), DEC (diethyl carbonate), EMC (ethyl methyl carbonate), FEC (fluoroethylene carbonate).

[0014] Optionally, the grafting reaction conditions in step three are as follows: Add composite material A to a high-speed mixer (a mixing device with greater frictional force), then slowly add the polymer solution, and stir at a temperature of 90 °C for 10 - 360 minutes. React the polymer molecules with the active sites on the carbon, so as to graft the polymer molecules onto the surface of the carbon-coated electrolyte material, and then dry the above product after ball milling or sand milling to obtain the modified inorganic solid electrolyte material with a hard-core fluff structure.

[0015] Optionally, the negative electrode material in step four includes a negative electrode active material, a conductive agent, a binder, and a solvent. By mass percentage, the specific ratio of each component in the negative electrode material to composite material B is as follows:

[0016]

[0017] Wherein, the total solid content is 100%.

[0018] Specifically, mix the negative electrode active material, the conductive agent, the binder, composite material B, and the solvent in proportion, and uniformly disperse to obtain a composite negative electrode slurry; then coat the composite negative electrode slurry on a current collector, and obtain a composite negative electrode sheet after drying, rolling, and die cutting. Among them, the negative electrode active material is selected from graphite, hard carbon, soft carbon, alloy-based negative electrode materials, and preferably hard carbon. The conductive agent is selected from any one or a mixture of conductive graphite, conductive carbon black, carbon fiber, carbon nanotube, graphene. The binder is selected from any one or a mixture of polyacrylic acid-based, acrylate-based, SBR, polyacrylonitrile, CMC. Preferably, the solvent is deionized water and the current collector is aluminum foil.

[0019] Optionally, the radius of composite material A in step 1 is 0.225 - 0.414 μm. Adding composite material A particles with a radius of 0.225 - 0.414 μm to the negative electrode slurry can effectively reduce the porosity of the electrode sheet, thereby reducing the use of the electrolyte, and thus improving the safety performance of the battery cell.

[0020] Optionally, in the sodium-ion composite negative electrode sheet prepared in step 4, the peeling strength between the electrode particles and the current collector > 10 N / m, and the bonding performance between the electrode particles and the current collector is excellent.

[0021] The present invention also provides a sodium-ion composite negative electrode sheet prepared by the preparation method of the sodium-ion composite negative electrode sheet described above.

[0022] The present invention also provides an application of the sodium-ion composite negative electrode sheet in a sodium-ion battery. Assembling the sodium-ion composite negative electrode sheet, the sodium-ion positive electrode sheet, and the sodium-ion solid electrolyte membrane into a solid battery has good low-temperature performance, cycling performance, and excellent safety performance. Among them, the proportion of the positive active material in the sodium-ion positive electrode sheet is 91-99%, which is any one of a layered oxide material, a polyanion compound material, a Prussian and its analog material, preferably a layered oxide material; the proportion of the binder is 0.5-4%, preferably PVDF; the proportion of the conductive agent is 0.5-5%, which is a complex of any one or more of conductive graphite, conductive carbon black, carbon fiber, carbon nanotube, and graphene; the proportion of the solvent is 40-100%, preferably NMP.

[0023] Beneficial effects: In the preparation method of the sodium-ion composite negative electrode sheet of the present invention, the inorganic solid electrolyte particles are first carbon-coated to increase the electronic conductivity of their surface; then the binder polymer molecular chains are grafted onto the surface of the carbon-coated inorganic electrolyte particles to form a modified inorganic solid electrolyte material with a hard-core hairy ball structure. This hard-core hairy ball structure can interact with the binder during the homogenization process, and the molecular chains of the binder will be intertwined with the molecular chains of the polymer. The binder relies on the high density of the inorganic solid electrolyte and is not easy to float during the drying process, improving the bonding performance between the electrode particles and the current collector; the inorganic solid electrolyte promotes the uniform dispersion of the electrolyte particles relying on the volume effect and steric hindrance effect of the grafted polymer molecular chains.

[0024] The sodium-ion composite negative electrode sheet prepared by the present invention can reduce the interfacial impedance with the solid electrolyte membrane, promote the interfacial sodium-ion transport, and improve the ionic conductivity and electronic conductivity performance of the electrode sheet. At the same time, there is good bonding performance between the composite electrode sheet electrode particles and the current collector, and the solid battery assembled with the composite negative electrode sheet, the solid electrolyte membrane, and the sodium-ion positive electrode has good cycling performance and excellent safety performance. Description of the Drawings

[0025] Figure 1 For the discharge performance of the sodium-ion batteries prepared in Example 1 and Comparative Example 1 at -20 °C;

[0026] Figure 2 For the cycling performance of the sodium-ion batteries prepared in Example 1 and Comparative Example 1 at room temperature of 0.5C. Detailed Embodiments

[0027] The present invention will be described in detail and completely through specific embodiments. Unless otherwise specified, all percentage units are in mass percentage.

[0028] Example 1:

[0029] Mix Na 3 Zr 2 PSi 2 O 12 inorganic solid electrolyte and sucrose at a ratio of 2.5 times and stir for 5 hours, then dry at a temperature of 100 °C for 12 hours, and then bake in a tube furnace at a temperature of 800 °C for 6 hours for carbon coating treatment to obtain Na 3 Zr 2 PSi 2 O 12 / C composite material. Mix polyacrylic acid and deionized water at a ratio of 20%:80%, fully dissolve, stir and disperse evenly to obtain a polyacrylic acid solution.

[0030] Add Na 3 Zr 2 PSi 2 O 12 / C into a blender, and then add the polyacrylic acid solution. The ratio of the polyacrylic acid solution to Na 3 Zr 2 PSi 2 O 12 / C is 70%:30%. Stir at a temperature of 90 °C for 240 minutes. The polyacrylic acid binder molecules react with the active sites on the surface carbon of Na 3 Zr 2 PSi 2 O 12 / C to obtain a Na 3 Zr 2 PSi 2 O 12 / C solid electrolyte composite material grafted with polyacrylic acid binder molecules on the surface.

[0031] Mix the Na 3 Zr 2 PSi 2 O 12 / C solid electrolyte composite material grafted with polyacrylic acid binder molecules on the surface, hard carbon negative electrode, conductive carbon black, aqueous binder SBR, CMC, and solvent deionized water according to a mass ratio of 5%:91%:2%:1%:1%:100%, and disperse evenly to obtain a negative electrode slurry; coat the negative electrode slurry on aluminum foil, and obtain a composite negative electrode sheet after drying, rolling, and die-cutting. The peel strength of the composite negative electrode sheet is tested to be 11.8 N / m.

[0032] The positive electrode sheet, composite negative electrode sheet, and solid electrolyte membrane are assembled into a battery, a small amount of electrolyte is injected, and a 5.5Ah solid-state sodium ion battery is obtained after activation. The internal resistance of the battery cell is 2.63mΩ, and the capacity retention rate after 145 cycles at room temperature and 0.5C is 98.3%. Figure 2 The low temperature -20℃ battery discharge capacity retention rate is 90.3%. Figure 1 It can pass the extreme acupuncture test (burning the acupuncture needle to red at high temperature on the basis of the national standard to increase the difficulty of the acupuncture test) without catching fire or exploding.

[0033] Embodiment 2:

[0034] Will Na 3 Zr 2 PSi 2 O 12 The inorganic solid electrolyte and glucose were stirred at a ratio of 2.5 for 5 hours, then dried at 100°C for 12 hours, and then baked in a tube furnace at 800°C for 6 hours for carbon coating to obtain Na 3 Zr 2 PSi 2 O 12 / C composite material. Polyacrylic acid and deionized water are mixed in a ratio of 20%:80%, fully dissolved, stirred and dispersed evenly to obtain a polyacrylic acid solution.

[0035] Will Na 3 Zr 2 PSi 2 O 12 / C is added to the mixer, and then the polyacrylic acid solution is added. The polyacrylic acid solution and Na 3 Zr 2 PSi 2 O 12 The ratio of / C is 60%:40%, and the mixture is stirred at 90℃ for 240 minutes. 3 Zr 2 PSi 2 O 12 / C surface carbon active sites on the grafting reaction to prepare the surface grafted polyacrylic acid binder molecules Na 3 Zr 2 PSi 2 O 12 / C solid electrolyte composite materials.

[0036] The surface of the Na 3 Zr 2 PSi 2 O 12The / C solid electrolyte composite material, hard carbon anode, conductive carbon black, aqueous binder SBR, CMC, and solvent deionized water are mixed in a ratio of 5%:89%:2%:3%:1%:100% and uniformly dispersed to obtain the anode slurry; the anode slurry is coated on aluminum foil and dried, rolled, and die-cut to obtain the composite anode sheet. The peel strength of the composite anode sheet is tested to be 12.1 N / m.

[0037] The positive electrode sheet, composite anode sheet, and solid electrolyte membrane are assembled into a battery, a little electrolyte is injected, and after formation activation, a 5.5 Ah solid sodium-ion battery is obtained. The internal resistance of the battery cell is 2.66 mΩ, and the capacity retention rate at room temperature with 0.5C cycling for 147 weeks is 98.3%. The capacity retention rate of the battery cell at low temperature of -20°C is 90%. It can pass the extreme needle-punch test (on the basis of the national standard, the needle-punch steel needle is heated to red-hot to increase the difficulty of the needle-punch experiment), without catching fire or exploding.

[0038] Example 3:

[0039] Mix sodium 3 zirconium 2 phosphosilicate 2 oxide 12 inorganic solid electrolyte and glucose in a ratio of 2.5 times and stir for 5 hours, then dry at a temperature of 100°C for 12 hours, and then bake in a tube furnace at a temperature of 800°C for 6 hours for carbon coating treatment to obtain sodium 3 zirconium 2 phosphosilicate 2 oxide 12 / C composite material. Mix SBR, dispersant CMC, and deionized water in a ratio of 25%:5%:70%, fully dissolve, and stir and disperse evenly to obtain the SBR solution.

[0040] Add sodium 3 zirconium 2 phosphosilicate 2 oxide 12 / C into a blender, then add the SBR solution. The ratio of the SBR solution to sodium 3 zirconium 2 phosphosilicate 2 oxide 12 / C is 70%:30%, stir at a temperature of 90°C for 300 minutes, and the SBR binder molecules react with the active sites on the surface carbon of sodium 3 zirconium 2 phosphosilicate 2 oxide 12 / C to carry out a grafting reaction to obtain sodium 3 zirconium 2 phosphosilicate 2 oxide 12 / C solid electrolyte composite material with surface-grafted SBR binder molecules.

[0041] The surface of the Na 3 Zr 2 PSi 2 O 12 / C solid electrolyte composite material, hard carbon negative electrode, conductive carbon black, water-based binder SBR, CMC, solvent deionized water are mixed in a ratio of 5%: 91%: 2%: 1%: 1%: 100%, and evenly dispersed to obtain negative electrode slurry; the negative electrode slurry is coated on aluminum foil, and a composite negative electrode sheet is obtained after drying, rolling, and die-cutting. The peel strength of the composite negative electrode sheet is tested to be 11.2N / m.

[0042] The positive electrode sheet, composite negative electrode sheet, and solid electrolyte membrane are assembled into a battery, a small amount of electrolyte is injected, and a 5.5Ah solid-state sodium ion battery is obtained after activation. The internal resistance of the battery cell is 2.64mΩ, and the capacity retention rate after 146 cycles at room temperature and 0.5C is 98.2%. The low-temperature -20℃ battery cell discharge capacity retention rate is 89.8%; it can pass the extreme puncture test (the puncture steel needle is burned to red at high temperature on the basis of the national standard to increase the difficulty of the puncture test) without fire or explosion.

[0043] Embodiment 4:

[0044] Will Na 3 Zr 2 PSi 2 O 12 The inorganic solid electrolyte and sucrose were stirred at a ratio of 2.5 for 5 hours, then dried at 100 ° C for 12 hours, and then baked in a tube furnace at 800 ° C for 6 hours for carbon coating to obtain Na 3 Zr 2 PSi 2 O 12 / C composite material. Polyacrylic acid and deionized water are mixed in a ratio of 20%:80%, fully dissolved, stirred and dispersed evenly to obtain a polyacrylic acid solution.

[0045] Will Na 3 Zr 2 PSi 2 O 12 / C is added to the mixer, and then the polyacrylic acid solution is added. The polyacrylic acid solution and Na 3 Zr 2 PSi 2 O 12 The ratio of / C is 70%:30%, and the mixture is stirred at 90℃ for 240 minutes. 3 Zr 2 PSi 2 O 12 / C surface carbon active sites on the grafting reaction to prepare the surface grafted polyacrylic acid binder molecules Na 3 Zr 2 PSi 2 O 12 / C solid electrolyte composite materials.

[0046] The surface of the Na 3 Zr 2 PSi 2 O 12 / C solid electrolyte composite material, hard carbon negative electrode, conductive carbon black, CMC, solvent deionized water are mixed in a ratio of 5%: 92%: 2%: 1%: 100%, and evenly dispersed to obtain negative electrode slurry; the negative electrode slurry is coated on aluminum foil, and a composite negative electrode sheet is obtained after drying, rolling, and die cutting. The peel strength of the composite negative electrode sheet is tested to be 10.9N / m.

[0047] The positive electrode sheet, composite negative electrode sheet, and solid electrolyte membrane are assembled into a battery, a small amount of electrolyte is injected, and a 5.5Ah solid-state sodium ion battery is obtained after activation. The internal resistance of the battery cell is 2.65mΩ, and the capacity retention rate is 98% after 146 cycles at room temperature and 0.5C. The discharge capacity retention rate of the low-temperature -20℃ battery cell is 89.9%; it can pass the extreme puncture test (the puncture steel needle is burned to red at high temperature on the basis of the national standard to increase the difficulty of the puncture test) without fire or explosion.

[0048] Comparative Example 1:

[0049] Mix the hard carbon negative electrode, conductive carbon black, water-based binder SBR, CMC, and solvent deionized water in a ratio of 94%: 2%: 3%: 1%: 100% and evenly disperse to obtain negative electrode slurry; apply the negative electrode slurry on aluminum foil, dry, roll and die-cut to obtain a common negative electrode sheet. The negative electrode sheet peel strength is tested to be 8.4N / m.

[0050] The positive electrode sheet, negative electrode sheet, and solid electrolyte membrane are assembled into a battery, a small amount of electrolyte is injected, and a 5.5Ah solid-state sodium ion battery is obtained after activation. The internal resistance of the battery cell is 2.81mΩ, and the capacity retention rate after 146 cycles at room temperature and 0.5C is 97.3%. Figure 2 The low temperature -20℃ battery discharge capacity retention rate is 88%, and the low temperature discharge curve is shown in Figure 1 ; It can pass the extreme puncture test (burning the puncture steel needle at high temperature until it turns red on the basis of the national standard to increase the difficulty of the puncture experiment) without catching fire or exploding.

[0051] Comparative Example 2:

[0052] Will Na 1+x Zr 2 P 3-x Si x O12 The / C solid electrolyte composite material, hard carbon anode, conductive carbon black, aqueous binder SBR, CMC, and solvent deionized water are mixed in a ratio of 5%:89%:2%:3%:1%:100% and uniformly dispersed to obtain the anode slurry; the anode slurry is coated on aluminum foil and dried, rolled, and die-cut to obtain the composite anode sheet. The peel strength of the composite anode sheet is tested to be 8.5 N / m.

[0053] The positive electrode sheet, composite anode sheet, and solid electrolyte membrane are assembled into a battery, a little electrolyte is injected, and after formation activation, a 5.5 Ah solid sodium-ion battery is obtained. The internal resistance of the battery cell is 2.65 mΩ, and the capacity retention rate at room temperature with 0.5C cycling for 145 weeks is 97.8%. The discharge capacity retention rate of the battery cell at low temperature of -20°C is 90%; it can pass the extreme needle-punch test (on the basis of the national standard, the needle-punch steel needle is heated to red-hot to increase the difficulty of the needle-punch experiment), without catching fire or exploding.

[0054] In the above Examples 1-4 and Comparative Examples 1-2 of the present invention, the preparation of the positive electrode sheet in the sodium-ion battery is specifically as follows: The layered oxide sodium battery positive electrode material, conductive carbon black, PVDF binder, and solvent NMP are mixed in a mass ratio of 94%:2.5%:3.5%:60% and uniformly dispersed to obtain the positive electrode slurry; the positive electrode slurry is coated on aluminum foil and dried, rolled, and die-cut to obtain the positive electrode sheet.

[0055] In the above Examples 1-4 and Comparative Examples 1-2 of the present invention, the preparation of the solid electrolyte membrane is specifically as follows: 95% inorganic solid electrolyte, 4% aqueous binder, and 1% additive are dissolved and dispersed in 150% deionized water and stirred evenly. The inorganic solid electrolyte is Na 3 Zr 2 PSi 2 O 12 ; the aqueous binder is polyacrylic acid; the additive is the dispersant CMC. The above electrolyte solution is coated on both sides of the PI porous flexible membrane and dried in an oven drying tunnel, and then wound up to obtain the solid electrolyte membrane. The porosity of the PI porous flexible membrane is 57%, the pore diameter is 1-15 microns, and the thickness is 16 microns. The obtained solid electrolyte membrane has a thickness of 26 microns, a longitudinal tensile strength of 398 kgf / cm 2 , and the sodium-ion conductivity > 6*10 -4 S / cm.

[0056] The above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a sodium battery composite negative electrode sheet, characterized in that, it specifically includes the following steps: Step 1: Perform carbon coating treatment on the inorganic solid electrolyte to obtain a carbon-coated inorganic solid electrolyte composite material A; Step 2: Dissolve and disperse the polymer and the auxiliary agent in a solvent, and stir and disperse evenly to obtain a polymer solution; Step 3: Add the composite material A to the polymer solution for grafting reaction to obtain a composite material B with a hard-core and hairy-ball structure; Step 4: Dope the composite material B into the negative electrode material, homogenize and coat it on the current collector to obtain a sodium battery composite negative electrode sheet; Among them, in Step 1, the mass ratio of the inorganic solid electrolyte to the carbon source is 0.1 - 10 times; By mass percentage, the polymer solution in Step 2 includes: 1 - 50% polymer, 0 - 10% auxiliary agent, 40 - 99% solvent; The polymer is selected from any one or a mixture of more than one of PAA, polyacrylate, PAN, PEO, PVA, SBR, CMC, sodium alginate; Among them, in Step 4, the negative electrode material includes a negative electrode active material, a conductive agent, a binder, and a solvent; By mass percentage, the specific ratio of each component in the negative electrode material to the composite material B is: Among them, the total solid content is 100%.

2. The preparation method of the sodium battery composite negative electrode sheet according to claim 1, characterized in that, the grafting reaction conditions in Step 3 are: add the composite material A to a blender, then add the polymer solution, and stir at a temperature of 90°C for 10 - 360 minutes.

3. The preparation method of the sodium battery composite negative electrode sheet according to claim 1, characterized in that, the radius of the composite material A in Step 1 is 0.225 - 0.414 μm.

4. The preparation method of the sodium battery composite negative electrode sheet according to claim 1, characterized in that, in the sodium battery composite negative electrode sheet prepared in Step 4, the peel strength between the electrode particles and the current collector > 10 N / m.

5. A sodium battery composite negative electrode sheet prepared by the preparation method of the sodium battery composite negative electrode sheet according to any one of claims 1 - 4.

6. The application of the sodium battery composite negative electrode sheet according to claim 5 in the preparation of a sodium ion battery.

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