Negative plate of negative-electrode-free sodium ion battery, preparation method of negative plate and negative-electrode-free sodium ion battery

Abstract

The invention provides a negative plate of a negative-electrode-free sodium ion battery, a preparation method of the negative plate and the negative-electrode-free sodium ion battery, and relates to the technical field of batteries. The invention provides a negative plate of a negative-electrode-free sodium ion battery. The negative plate comprises a negative current collector and a modified solid electrolyte plate, the modified solid electrolyte sheet is attached to the surface of the negative electrode current collector; the modified solid electrolyte sheet is a solid electrolyte sheet of which two surfaces are coated with a conductive layer and a liquid retaining layer respectively; and the conductive layer of the modified solid electrolyte sheet is attached to the negative current collector. When the negative plate is used in the negative-electrode-free sodium ion battery, the use of a diaphragm can be reduced, the electrolyte injection amount can be reduced, the capacity exertion of a positive electrode can be ensured, side reactions and gas production can be reduced, the risk of short circuit can be avoided, the battery cost can be reduced, and the cycle life of the battery can be prolonged.

Description

Technical Field

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

[0002] The negative electrode-free sodium battery is a battery that uses layered oxides (such as nickel-iron-manganese oxide and copper-iron-manganese oxide) materials, Prussian blue analogs (such as iron-based Prussian white, etc.), polyanions (such as sodium iron sulfate, sodium iron phosphate, etc.) as the positive electrode, and aluminum foil current collector as the negative electrode. It mainly uses ethers as solvents and adds Na + Metal salts (such as sodium fluoride salts, sodium borate salts and sodium perchlorate salts, etc.) electrolytes and various additives (such as film-forming, flame retardant and overcharge protection, etc.) form an electrolyte. However, the sodium metal is completely exposed to the electrolyte, which will cause significant gas production and side reactions, seriously hindering the application of sodium ion batteries. Therefore, reducing the electrolyte in the battery and reducing the sodium dendrites exposed to the electrolyte have become the key points of this system.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The first object of the present invention is to provide a negative electrode sheet for a negative electrode-free sodium ion battery to solve the above technical problems.

[0005] The second object of the present invention is to provide a method for preparing the negative electrode sheet of the above-mentioned negative electrode-free sodium ion battery.

[0006] The third object of the present invention is to provide a negative electrode-free sodium ion battery.

[0007] In order to achieve the above objectives, the following technical solutions are adopted:

[0008] In a first aspect, the present invention provides a negative electrode sheet of a negative electrode-free sodium ion battery, comprising a negative electrode current collector and a modified solid electrolyte sheet; the modified solid electrolyte sheet is bonded to the surface of the negative electrode current collector;

[0009] The modified solid electrolyte sheet is a solid electrolyte sheet with a conductive layer and a liquid retaining layer coated on both sides respectively; the conductive layer of the modified solid electrolyte sheet is bonded to the negative electrode current collector;

[0010] The solid electrolyte sheet includes a sodium solid electrolyte and polytetrafluoroethylene, and the mass ratio of the sodium solid electrolyte is (9-19):1.

[0011] As a further technical solution, the sodium solid electrolyte includes at least one of sodium lanthanum zirconium oxide, sodium aluminum titanium phosphide or sodium aluminum oxide.

[0012] As a further technical solution, the preparation method of the solid electrolyte sheet is as follows:

[0013] The sodium solid electrolyte and polytetrafluoroethylene powder are mixed and then smelted in an open mill to prepare a solid electrolyte sheet.

[0014] As a further technical solution, before the smelting, the sodium solid electrolyte includes, by mass percentage, 15% to 25% of a sodium solid electrolyte with a particle size of 0.5 to 1.5 microns, 25% to 35% of a sodium solid electrolyte with a particle size of 2.5 to 3.5 microns, and the remainder is a sodium solid electrolyte with a particle size of 3.5 to 4.5 microns.

[0015] As a further technical solution, the conductive layer includes a conductive agent;

[0016] The conductive agent includes at least one of a carbon material or metal particles;

[0017] The carbon material includes conductive carbon black, acetylene black or graphite;

[0018] The metal particles include metal particles or alloy particles of gold, silver, copper, iron, aluminum or tin.

[0019] As a further technical solution, the liquid retaining layer includes a liquid retaining material, a semi-solid electrolyte and a binder;

[0020] The mass ratio of the liquid retaining material, the semi-solid electrolyte and the binder is (6-2):(2-6):1.

[0021] As a further technical solution, the liquid retaining material includes at least one of montmorillonite or hydrotalcite;

[0022] The semi-solid electrolyte includes at least one of PMMA (polymethyl methacrylate), PEO (polyethylene oxide), PEG (polyethylene glycol) or PAA (polyacrylic acid);

[0023] The binder includes SBR (styrene butadiene rubber).

[0024] In a second aspect, the present invention provides a method for preparing the negative electrode sheet of the above-mentioned negative electrode-free sodium ion battery, comprising the following steps:

[0025] The conductive layer slurry is coated on one side of the solid electrolyte sheet, and the liquid retaining layer slurry is coated on the other side of the solid electrolyte sheet. After drying, a modified solid electrolyte sheet is obtained, and then the modified solid electrolyte sheet is compounded with the negative electrode current collector to prepare a negative electrode sheet.

[0026] In a third aspect, the present invention provides a negative electrode-free sodium ion battery, wherein the negative electrode sheet of the negative electrode-free sodium ion battery is the negative electrode sheet of the negative electrode-free sodium ion battery;

[0027] There is no separator between the negative electrode and the positive electrode.

[0028] As a further technical solution, the negative electrode-free sodium ion battery is a laminated battery or a cylindrical battery.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The negative electrode sheet of the negative electrode-free sodium ion battery provided by the present invention is used in the negative electrode-free sodium ion battery. Since the modified solid electrolyte sheet uses a solid battery and a semi-solid electrolyte, the use of the diaphragm can be reduced and the amount of electrolyte injection can be reduced; the modified solid electrolyte sheet has a liquid retention layer, which has good electrolyte affinity and liquid retention capabilities, so that the electrolyte will be retained on the positive electrode side, ensuring the capacity of the positive electrode; the modified solid electrolyte sheet is arranged on the surface of the negative electrode current collector, so that there is no electrolyte on the negative electrode fluid side, avoiding contact between metallic sodium and the electrolyte, thereby reducing the reduction of the electrolyte by metallic sodium, reducing side reactions and gas production; and the conductive layer of the modified solid electrolyte sheet is in contact with the surface of the negative electrode current collector, and has excellent conductivity, so that the sodium metal is completely deposited on the surface of the negative electrode current collector, avoiding the risk of short circuit, and the deposited sodium metal is not in contact with the electrolyte (sodium ions are transmitted to the surface of the negative electrode current collector through the solid electrolyte), resulting in the effects of reducing battery cost and improving battery cycle life. DETAILED DESCRIPTION

[0031] The embodiments of the present invention will be described in detail below in conjunction with the embodiments and examples, but it will be appreciated by those skilled in the art that the following embodiments and examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified, proceed according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0032] The inventors have found that excess electrolyte is more likely to cause side reactions in a negative electrode-free sodium ion battery system. The diaphragm retains a lot of excess electrolyte, including the edges and pores of the diaphragm. Therefore, the modification of the aluminum current collector and the elimination of the diaphragm are very important for the development of the system. Based on this, the following scheme is proposed.

[0033] In a first aspect, the present invention provides a negative electrode sheet of a negative electrode-free sodium ion battery, comprising a negative electrode current collector and a modified solid electrolyte sheet; the modified solid electrolyte sheet is bonded to the surface of the negative electrode current collector;

[0034] The modified solid electrolyte sheet is a solid electrolyte sheet with a conductive layer and a liquid retaining layer coated on both sides respectively; the conductive layer of the modified solid electrolyte sheet is bonded to the negative electrode current collector;

[0035] The solid electrolyte sheet includes a sodium solid electrolyte and polytetrafluoroethylene, and the mass ratio of the sodium solid electrolyte can be, for example, but not limited to, 9:1, 15:1 or 19:1. The inventors have found that polytetrafluoroethylene can be used as a binder to form a large number of adhesive fibers through open milling. Therefore, a solid electrolyte sheet with a very large compaction density can be constructed.

[0036] The negative electrode sheet of the negative electrode-free sodium ion battery provided by the present invention is used in the negative electrode-free sodium ion battery. Since the modified solid electrolyte sheet uses a solid battery and a semi-solid electrolyte, the use of the diaphragm can be reduced and the amount of electrolyte injection can be reduced; the modified solid electrolyte sheet has a liquid retention layer, which has good electrolyte affinity and liquid retention capabilities, so that the electrolyte will be retained on the positive electrode side, ensuring the capacity of the positive electrode; the modified solid electrolyte sheet is arranged on the surface of the negative electrode current collector, so that there is no electrolyte on the negative electrode fluid side, avoiding contact between metallic sodium and the electrolyte, thereby reducing the reduction of the electrolyte by metallic sodium, reducing side reactions and gas production; and the conductive layer of the modified solid electrolyte sheet is in contact with the surface of the negative electrode current collector, and has excellent conductivity, so that the sodium metal is completely deposited on the surface of the negative electrode current collector, avoiding the risk of short circuit, and the deposited sodium metal is not in contact with the electrolyte (sodium ions are transmitted to the surface of the negative electrode current collector through the solid electrolyte), resulting in the effects of reducing battery cost and improving battery cycle life.

[0037] In some optional embodiments, the sodium solid electrolyte includes but is not limited to at least one of sodium lanthanum zirconium oxide, sodium aluminum titanium phosphide or sodium aluminum oxide, or other sodium solid electrolytes known to those skilled in the art.

[0038] In some optional embodiments, the preparation method of the solid electrolyte sheet is as follows:

[0039] The sodium solid electrolyte and polytetrafluoroethylene powder are mixed and then smelted in an open mill to prepare a solid electrolyte sheet.

[0040] The solid electrolyte sheet prepared by the above method has good density and flexibility.

[0041] In some optional embodiments, the thickness of the solid electrolyte sheet may be, for example, but not limited to, 100 μm, 125 μm or 150 μm;

[0042] The thickness of the conductive layer may be, for example, but not limited to, 1 μm, 2 μm or 3 μm;

[0043] The thickness of the liquid retaining layer may be, for example, but not limited to, 3 μm, 5 μm or 7 μm.

[0044] In some optional embodiments, before the start of refining, the sodium solid electrolyte includes, by mass percentage, 15% to 25% of a sodium solid electrolyte with a particle size of 0.5 to 1.5 microns, 25% to 35% of a sodium solid electrolyte with a particle size of 2.5 to 3.5 microns, and the remainder is a sodium solid electrolyte with a particle size of 3.5 to 4.5 microns.

[0045] By further optimizing and adjusting the particle size of the sodium solid electrolyte, the prepared solid electrolyte sheet has better density and flexibility.

[0046] In some optional embodiments, the conductive layer includes a conductive agent;

[0047] The conductive agent includes but is not limited to at least one of carbon material or metal particles;

[0048] The carbon material includes but is not limited to conductive carbon black, acetylene black or graphite;

[0049] The metal particles include, but are not limited to, metal particles or alloy particles of gold, silver, copper, iron, aluminum or tin.

[0050] In some optional embodiments, the conductive layer further includes an anionic surfactant to improve the dispersibility of the conductive agent and promote the adhesion of the conductive agent to the solid electrolyte sheet.

[0051] In some optional embodiments, the mass ratio of the conductive agent to the anionic surfactant is (9-19):1.

[0052] In some optional embodiments, the liquid retaining layer includes a liquid retaining material, a semi-solid electrolyte and a binder;

[0053] The mass ratio of the liquid retaining material, the semi-solid electrolyte and the binder may be, for example, but not limited to, 2:6:1, 4:5:1, 5:4:1 or 6:2:1.

[0054] In some optional embodiments, the liquid retaining material includes but is not limited to at least one of montmorillonite or hydrotalcite;

[0055] The semi-solid electrolyte includes but is not limited to at least one of PMMA, PEO, PEG or PAA;

[0056] The binder includes but is not limited to SBR.

[0057] In some optional embodiments, the liquid-retaining layer further comprises a dispersant;

[0058] The dispersant includes CMC (carboxymethyl cellulose).

[0059] In some optional embodiments, the mass ratio of the liquid retaining material, the semi-solid electrolyte, the binder and the dispersant may be, for example, but not limited to, 2:6:1:1, 4:5:1:1, 5:4:1:1 or 6:2:1:1.

[0060] In some optional embodiments, the negative electrode current collector includes aluminum foil, aluminum mesh or aluminum foam.

[0061] In a second aspect, the present invention provides a method for preparing the negative electrode sheet of the above-mentioned negative electrode-free sodium ion battery, comprising the following steps:

[0062] The conductive layer slurry is coated on one side of the solid electrolyte sheet, and the liquid retaining layer slurry is coated on the other side of the solid electrolyte sheet. After drying, a modified solid electrolyte sheet is obtained, and then the modified solid electrolyte sheet is compounded with the negative electrode current collector to prepare a negative electrode sheet.

[0063] The preparation method provided by the invention is simple and convenient.

[0064] In some optional embodiments, the solvent of the slurry of the conductive layer or the slurry of the liquid retaining layer includes water.

[0065] In some optional embodiments, the composite method includes rolling, so that the modified solid electrolyte sheet and the negative electrode current collector are rolled into one.

[0066] In a third aspect, the present invention provides a negative electrode-free sodium ion battery, wherein the negative electrode sheet of the negative electrode-free sodium ion battery is the negative electrode sheet of the negative electrode-free sodium ion battery;

[0067] There is no separator between the negative electrode and the positive electrode.

[0068] The negative electrode-free sodium ion battery has low cost and long service life.

[0069] In some optional embodiments, the negative electrode-free sodium ion battery is a laminated battery or a cylindrical battery.

[0070] The present invention is further described below by means of specific examples and comparative examples. However, it should be understood that these examples are only used for more detailed description and should not be construed as limiting the present invention in any form.

[0071] Example 1

[0072] A negative electrode sheet comprises a negative electrode current collector and a modified solid electrolyte sheet; the modified solid electrolyte sheet is laminated and arranged on the surface of the negative electrode current collector (aluminum foil);

[0073] The modified solid electrolyte sheet is a solid electrolyte sheet with a conductive layer (thickness 2 μm) and a liquid retaining layer (thickness 5 μm) coated on both sides respectively; the conductive layer of the modified solid electrolyte sheet is bonded to the negative electrode current collector;

[0074] The solid electrolyte sheet is composed of sodium solid electrolyte (sodium lanthanum zirconium oxide) and polytetrafluoroethylene, and the mass ratio of sodium solid electrolyte is 9:1;

[0075] The conductive layer is composed of conductive carbon black and anionic surfactant sodium dodecyl sulfate in a mass ratio of 9:1;

[0076] The liquid retaining layer is composed of liquid retaining material (montmorillonite powder), semi-solid electrolyte (PMMA), binder SBR and dispersant CMC, with a mass ratio of 6:2:1:1.

[0077] The preparation method is as follows:

[0078] ① Select three solid electrolytes with different particle sizes (1 micron, 3 microns, and 5 microns), and the weighing ratios of different particle sizes are 20%, 30%, and 50% respectively.

[0079] ② Mix the material in ① with polytetrafluoroethylene powder and mix them in a mixer for 5 hours. The mixed powder enters a high-temperature open mill and after multiple open millings, a dense and flexible solid electrolyte sheet with a thickness of 125 microns is obtained.

[0080] ③ Prepare liquid-retaining materials, semi-solid electrolytes, binders and dispersants; mix the above materials in a mixer for 5 hours, add deionized water, and homogenize using a homogenizer for 2 hours to obtain uniform slurry A.

[0081] ④ Prepare a conductive agent and anionic surfactant; mix the above materials in a mixer for 5 hours, add deionized water, and homogenize using a homogenizer for 2 hours to obtain a uniform slurry B.

[0082] ⑤ Place the solid electrolyte sheet obtained in ② in a continuous coating machine (including an oven) as a substrate, use the coating machine to coat slurry A on one side of the substrate and slurry B on the other side, and after drying, obtain a modified solid electrolyte sheet. Then roll the modified solid electrolyte sheet and the negative electrode current collector together to prepare a negative electrode sheet.

[0083] Example 2

[0084] A negative electrode sheet comprises a negative electrode current collector and a modified solid electrolyte sheet; the modified solid electrolyte sheet is laminated and arranged on the surface of the negative electrode current collector (aluminum foil);

[0085] The modified solid electrolyte sheet is a solid electrolyte sheet with a conductive layer (thickness 2 μm) and a liquid retaining layer (thickness 5 μm) coated on both sides respectively; the conductive layer of the modified solid electrolyte sheet is bonded to the negative electrode current collector;

[0086] The solid electrolyte sheet is composed of sodium solid electrolyte (sodium aluminum titanium phosphorus) and polytetrafluoroethylene, and the mass ratio of sodium solid electrolyte is 15:1;

[0087] The conductive layer is composed of conductive graphite and anionic surfactant sodium laurate in a mass ratio of 15:1;

[0088] The liquid retaining layer is composed of a liquid retaining material (hydrotalcite), a semi-solid electrolyte (PEO), a binder SBR and a dispersant CMC, with a mass ratio of 2:6:1:1.

[0089] The preparation method is as follows:

[0090] ① Three solid electrolytes with different particle sizes (0.5 microns, 2.5 microns, and 4.5 microns) were selected, and the weighing ratios of different particle sizes were 15%, 35%, and 50% respectively.

[0091] ② Mix the material in ① with polytetrafluoroethylene powder and mix them in a mixer for 5 hours. The mixed powder enters a high-temperature open mill and after multiple open millings, a dense and flexible solid electrolyte sheet with a thickness of 100 microns is obtained.

[0092] ③ Prepare liquid-retaining materials, semi-solid electrolytes, binders and dispersants; mix the above materials in a mixer for 5 hours, add deionized water, and homogenize using a homogenizer for 2 hours to obtain uniform slurry A.

[0093] ④ Prepare a conductive agent and anionic surfactant; mix the above materials in a mixer for 5 hours, add deionized water, and homogenize using a homogenizer for 2 hours to obtain a uniform slurry B.

[0094] ⑤ Place the solid electrolyte sheet obtained in ② in a continuous coating machine (including an oven) as a substrate, use the coating machine to coat slurry A on one side of the substrate and slurry B on the other side, and after drying, obtain a modified solid electrolyte sheet. Then roll the modified solid electrolyte sheet and the negative electrode current collector together to prepare a negative electrode sheet.

[0095] Example 3

[0096] A negative electrode sheet comprises a negative electrode current collector and a modified solid electrolyte sheet; the modified solid electrolyte sheet is laminated and arranged on the surface of the negative electrode current collector (aluminum foil);

[0097] The modified solid electrolyte sheet is a solid electrolyte sheet with a conductive layer (thickness 2 μm) and a liquid retaining layer (thickness 5 μm) coated on both sides respectively; the conductive layer of the modified solid electrolyte sheet is bonded to the negative electrode current collector;

[0098] The solid electrolyte sheet is composed of sodium solid electrolyte (sodium aluminum oxide) and polytetrafluoroethylene, and the mass ratio of sodium solid electrolyte is 19:1;

[0099] The conductive layer is composed of conductive carbon black and anionic surfactant sodium oleate in a mass ratio of 19:1;

[0100] The liquid retaining layer is composed of liquid retaining material (montmorillonite powder), semi-solid electrolyte (PEG), binder SBR and dispersant CMC, with a mass ratio of 3:5:1:1.

[0101] The preparation method is as follows:

[0102] ① Select three solid electrolytes with different particle sizes (4.5 microns, 3.5 microns, and 5.5 microns), and the weighing ratios of different particle sizes are 25%, 25%, and 50% respectively.

[0103] ② Mix the material in ① with polytetrafluoroethylene powder and mix them in a mixer for 5 hours. The mixed powder enters a high-temperature open mill and after multiple open millings, a dense and flexible solid electrolyte sheet with a thickness of 150 microns is obtained.

[0104] ③ Prepare liquid-retaining materials, semi-solid electrolytes, binders and dispersants; mix the above materials in a mixer for 5 hours, add deionized water, and homogenize using a homogenizer for 2 hours to obtain uniform slurry A.

[0105] ④ Prepare a conductive agent and anionic surfactant; mix the above materials in a mixer for 5 hours, add deionized water, and homogenize using a homogenizer for 2 hours to obtain a uniform slurry B.

[0106] ⑤ Place the solid electrolyte sheet obtained in ② in a continuous coating machine (including an oven) as a substrate, use the coating machine to coat slurry A on one side of the substrate and slurry B on the other side, and after drying, obtain a modified solid electrolyte sheet. Then roll the modified solid electrolyte sheet and the negative electrode current collector together to prepare a negative electrode sheet.

[0107] Example 4

[0108] A negative electrode sheet, which is different from Example 1 in that step ① in the preparation method is different, and the content of step ① is as follows:

[0109] Select a solid electrolyte with a particle size (2 to 3 microns).

[0110] Comparative Example 1

[0111] A carbon-coated aluminum foil, the preparation method is as follows:

[0112] The binder (5% by mass) was mixed with the conductive carbon black and the anionic surfactant sodium dodecyl sulfate in Example 1 to obtain a slurry, and then the slurry was coated on an aluminum foil and dried to obtain a carbon-coated aluminum foil.

[0113] Comparative Example 2

[0114] A negative electrode sheet, which is different from Example 1 in that no liquid retaining layer is coated on the solid electrolyte sheet.

[0115] Comparative Example 3

[0116] A negative electrode sheet, which is different from Example 1 in that no conductive layer is coated on the solid electrolyte sheet.

[0117] Test Example 1

[0118] The negative electrodes provided in Examples 1 to 4 and Comparative Examples 1 to 3 were used to prepare a negative electrode-free sodium ion battery, wherein the positive electrode sheet was prepared by uniformly mixing sodium ferric pyrophosphate, conductive carbon black, PVDF, and PAA in a ratio of 95:2:2:1 and adding the mixture to a solvent (NMP) to obtain a positive electrode slurry, and coating the positive electrode slurry on the surface of a carbon-coated aluminum foil to obtain a positive electrode sheet;

[0119] The electrolyte contains 1M NaPF 6 Diethylene glycol dimethyl ether:

[0120] A negative electrode-free sodium ion laminate battery was assembled in an inert atmosphere glove box according to the same preparation method, wherein a separator was required between the positive electrode sheet and the negative electrode sheet when the battery was prepared using the negative electrode sheet of Comparative Example 1.

[0121] The performance of the batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were tested respectively (including charge and discharge capacity, initial coulombic efficiency, 5C capacity retention rate (compared with 0.5C normal cycle, the percentage of capacity compared with 0.5C cycle), capacity retention rate after 100 charge and discharge cycles at 0.1C / 0.1C, gas production, and capacity retention rate after 300 charge and discharge cycles at 0.5C / 1C), and the results are shown in Table 1.

[0122] Table 1 Test results of various embodiments and comparative examples

[0123]

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet for a negative electrode-free sodium ion battery, characterized in that: It comprises a negative electrode current collector and a modified solid electrolyte sheet; the modified solid electrolyte sheet is bonded to the surface of the negative electrode current collector; The modified solid electrolyte sheet is a solid electrolyte sheet with a conductive layer and a liquid retaining layer coated on both sides respectively; the conductive layer of the modified solid electrolyte sheet is bonded to the negative electrode current collector; The solid electrolyte sheet includes a sodium solid electrolyte and polytetrafluoroethylene, and the mass ratio of the sodium solid electrolyte is (9-19):

1.

2. The negative electrode sheet of the negative electrode-free sodium ion battery according to claim 1, characterized in that: The sodium solid electrolyte includes at least one of sodium lanthanum zirconium oxide, sodium aluminum titanium phosphide or sodium aluminum oxide.

3. The negative electrode sheet of the negative electrode-free sodium ion battery according to claim 1, characterized in that: The preparation method of the solid electrolyte sheet is as follows: The sodium solid electrolyte and polytetrafluoroethylene powder are mixed and then smelted in an open mill to prepare a solid electrolyte sheet.

4. The negative electrode sheet of the negative electrode-free sodium ion battery according to claim 3, characterized in that: Before the smelting, the sodium solid electrolyte includes, by mass percentage, 15% to 25% of a sodium solid electrolyte with a particle size of 0.5 to 1.5 microns, 25% to 35% of a sodium solid electrolyte with a particle size of 2.5 to 3.5 microns, and the remainder of a sodium solid electrolyte with a particle size of 3.5 to 4.5 microns.

5. The negative electrode sheet of the negative electrode-free sodium ion battery according to claim 1, characterized in that: The conductive layer includes a conductive agent; The conductive agent includes at least one of a carbon material or metal particles; The carbon material includes conductive carbon black, acetylene black or graphite; The metal particles include metal particles or alloy particles of gold, silver, copper, iron, aluminum or tin.

6. The negative electrode sheet of the negative electrode-free sodium ion battery according to claim 1, characterized in that: The liquid retaining layer comprises a liquid retaining material, a semi-solid electrolyte and a binder; The mass ratio of the liquid retaining material, the semi-solid electrolyte and the binder is (6-2):(2-6):

1.

7. The negative electrode sheet of the negative electrode-free sodium ion battery according to claim 6, characterized in that: The liquid retaining material includes at least one of montmorillonite or hydrotalcite; The semi-solid electrolyte comprises at least one of PMMA, PEO, PEG or PAA; The binder includes SBR.

8. The method for preparing a negative electrode sheet for a negative electrode-free sodium ion battery according to any one of claims 1 to 7, characterized in that: The following steps are involved: The conductive layer slurry is coated on one side of the solid electrolyte sheet, and the liquid retaining layer slurry is coated on the other side of the solid electrolyte sheet. After drying, a modified solid electrolyte sheet is obtained, and then the modified solid electrolyte sheet is compounded with the negative electrode current collector to prepare a negative electrode sheet.

9. A negative electrode-free sodium ion battery, characterized in that: The negative electrode sheet of the negative electrode-free sodium ion battery is the negative electrode sheet of the negative electrode-free sodium ion battery according to any one of claims 1 to 7; There is no separator between the negative electrode and the positive electrode.

10. The negative electrode-free sodium ion battery according to claim 9, characterized in that: The negative electrode-free sodium ion battery is a laminated battery or a cylindrical battery.

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