Negative-electrode-free sodium ion battery current collector, application thereof and negative-electrode-free sodium ion battery

Abstract

The invention provides a negative-electrode-free sodium ion battery current collector, application thereof and a negative-electrode-free sodium ion battery, and relates to the technical field of batteries. The negative-electrode-free sodium ion battery current collector provided by the invention comprises a base material and a coating coated on the surface of the base material, the coating comprises porous nitrogen-doped carbon particles and a binder; the porous nitrogen-doped carbon particles are loaded with fluorine-containing sodium salt and a metal catalyst, and the surfaces of the porous nitrogen-doped carbon particles are coated with polymers. According to the current collector, in-situ construction and dynamic repair of NaF-rich SEI are promoted through the core-shell structure design, long-term, uniform and stable deposition of sodium ions on the current collector can be achieved, the coulombic efficiency of a negative-electrode-free sodium battery is improved, and the cycle life of the negative-electrode-free sodium battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a current collector for a sodium ion battery without an anode, an application thereof, and a sodium ion battery without an anode. Background Art

[0002] With the explosive growth of large-scale energy storage and electric vehicles in recent years, concerns about lithium resource shortages have become increasingly serious. Therefore, the development of resource-rich, high-performance rechargeable batteries is of great significance. Sodium metal batteries (SMBs) use metallic Na as the anode. Due to the abundance and cost-effectiveness of sodium resources, sodium-ion-based batteries have become a potential alternative to lithium-ion batteries.

[0003] Sodium metal has an extremely high theoretical specific capacity of 1166 mAh g -1 , but the energy density of sodium metal batteries has always been limited by the high N / P ratio. Therefore, the use of ultra-thin sodium metal anodes or even anode-free structures can effectively reduce the N / P ratio, which is an effective way to achieve high energy density sodium metal batteries. However, during the sodium deposition / stripping process, anode-free sodium metal batteries are susceptible to interference from dendrite formation, resulting in rapid performance degradation and even thermal runaway. Among them, the sodium deposition / stripping behavior is closely related to the physical and chemical properties of the SEI film formed on the surface of the anode. The ideal SEI film should be thin and uniform, and have high ionic conductivity and elastic modulus. The SEI film is decomposed from the electrolyte and is composed of organic and inorganic components. Its inherent heterogeneity and instability make it unable to meet the requirements of long-life Na metal anodes.

[0004] Among the components of the SEI membrane, NaF, due to its low sodium ion diffusion barrier, high interfacial energy, excellent chemical stability, and mechanical strength, promotes uniform sodium ion deposition during the cycling of anode-free batteries and enhances the battery's cycling stability. Therefore, constructing a NaF-rich SEI membrane is crucial for the stable and safe operation of anode-free sodium-ion batteries. NaF is derived from F-containing solutes, solvents, and additives. Currently, a NaF-rich SEI layer can be constructed through pre-coating or catalytic regulation, but dynamic repair is difficult to achieve.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a current collector for a negative electrode-free sodium ion battery, which promotes the in-situ construction and dynamic repair of a NaF-rich SEI through a core-shell structure design, and can achieve long-term uniform and stable deposition of sodium ions on the current collector, thereby improving the coulombic efficiency and cycle life of the negative electrode-free sodium battery to solve the above-mentioned technical problems.

[0007] The second object of the present invention is to provide an application of the above-mentioned negative electrode-free sodium ion battery current collector in a negative electrode-free sodium ion battery.

[0008] A third object of the present invention is to provide a negative electrode-free sodium ion battery.

[0009] In order to achieve the above objectives, the following technical solutions are adopted:

[0010] In a first aspect, the present invention provides a negative electrode-free sodium ion battery current collector, comprising a substrate and a coating applied on the surface of the substrate;

[0011] The coating comprises porous nitrogen-doped carbon particles and a binder;

[0012] The porous nitrogen-doped carbon particles are loaded with fluorine-containing sodium salt and metal catalyst, and the surface is coated with a polymer;

[0013] The metal catalyst is used to catalyze the cleavage of the PF bond of NaPF6 to generate NaF.

[0014] As a further technical solution, the substrate includes aluminum foil, copper foil, carbon-coated aluminum foil or carbon-coated copper foil.

[0015] As a further technical solution, the binder includes at least one of CMC (carboxymethyl cellulose), PAA (polyacrylic acid) or PEO (polyethylene oxide);

[0016] In the coating, the mass proportion of the binder is 5%-10%.

[0017] As a further technical solution, the fluorine-containing sodium salt includes NaF;

[0018] The metal catalyst includes at least one of Fe, Pt or Ni;

[0019] The polymer includes at least one of PVA, polypyrrole or polyethylene glycol;

[0020] The thickness of the polymer coating is 1-10 nm.

[0021] As a further technical solution, the method for preparing the porous nitrogen-doped carbon particles includes:

[0022] a. The mesoporous silica, carbon source and nitrogen source are mixed in water, and then subjected to hydrothermal treatment, high temperature carbonization treatment and HF etching treatment to obtain nitrogen-doped core-shell carbon;

[0023] b. Immersing the nitrogen-doped core-shell carbon obtained in step a into an aqueous solution of a fluorine-containing sodium salt, drying to obtain a nitrogen-doped core-shell carbon loaded with a fluorine-containing sodium salt, and then immersing the nitrogen-doped core-shell carbon loaded with a fluorine-containing sodium salt into a polymer solution for coating to obtain a nitrogen-doped core-shell carbon with a surface-coated polymer;

[0024] c. Immerse the nitrogen-doped core-shell carbon with the surface coated polymer obtained in step b in a salt solution of a metal catalyst, and then add a reducing agent to reduce the metal catalyst to obtain porous nitrogen-doped carbon particles.

[0025] As a further technical solution, the carbon source includes at least one of glucose, fructose or cellulose;

[0026] The nitrogen source comprises at least one of urea, pyrrole or aniline;

[0027] The mass ratio of the carbon source to the nitrogen source is (5-10):1.

[0028] As a further technical solution, the temperature of the hydrothermal treatment is 180-220°C and the time is 3-5h;

[0029] The temperature of the high-temperature carbonization treatment is 750-850° C., and the time is 1.5-2.5 hours.

[0030] As a further technical solution, the mass concentration of the fluorine-containing sodium salt in the aqueous solution of the fluorine-containing sodium salt is 18%-22%;

[0031] In the salt solution of the metal catalyst, the mass concentration of the metal catalyst salt is 0.5-1.5 mol / L.

[0032] In a second aspect, the present invention provides an application of the above-mentioned negative electrode-free sodium ion battery current collector in a negative electrode-free sodium ion battery.

[0033] In a third aspect, the present invention provides a negative electrode-free sodium ion battery, using the negative electrode-free sodium ion battery current collector as the negative electrode of the negative electrode-free sodium ion battery.

[0034] Compared with the prior art, the negative electrode-free sodium ion battery current collector provided by the present invention has the following beneficial effects:

[0035] 1. Core-shell confined carbon skeleton:

[0036] The porous carbon shell provides a conductive network, accelerates the transmission of sodium ions, reduces the interface impedance, and the mesopore confinement promotes the uniform nucleation of NaF and inhibits the formation of dendrites. The shell anchors the catalyst particles and catalyzes the F - The generation of NaF is promoted by adjusting the thickness of the protective layer. + and F - The release rate is adjusted to regulate the uniform growth of NaF.

[0037] 2. Dynamic in-situ repair of NaF:

[0038] By adjusting the thickness of the protective layer and the working conditions of the battery, the Na content of the inner layer containing F sodium salt can be adjusted during the cycle. + and F - The release rate can achieve in-situ dynamic repair of the NaF layer damaged by dendrites and volume expansion, and can also replenish the Na consumed during the cycle. + . DETAILED DESCRIPTION

[0039] Below in conjunction with embodiment and example, embodiment of the present invention is described in detail, but those skilled in the art will appreciate that the following embodiment and example are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiment in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the scope of protection of the present invention. Unspecified conditions are carried out according to the conditions of normal conditions or manufacturer's recommendations. Reagents used or instruments not specified by the manufacturer are conventional products that can be purchased commercially.

[0040] In a first aspect, the present invention provides a negative electrode-free sodium ion battery current collector, comprising a substrate and a coating applied on the surface of the substrate;

[0041] The coating comprises porous nitrogen-doped carbon particles and a binder;

[0042] The porous nitrogen-doped carbon particles are loaded with fluorine-containing sodium salt and metal catalyst, and the surface is coated with a polymer;

[0043] The metal catalyst is used to catalyze the cleavage of the PF bond of NaPF6 to generate NaF.

[0044] The current collector provided by the present invention promotes the in-situ construction and dynamic repair of NaF-rich SEI through core-shell structure design, can achieve long-term uniform and stable deposition of sodium ions on the current collector, and improve the coulombic efficiency and cycle life of the negative electrode-free sodium battery.

[0045] In some optional embodiments, the substrate includes but is not limited to aluminum foil, copper foil, carbon-coated aluminum foil or carbon-coated copper foil.

[0046] In some optional embodiments, the binder includes but is not limited to CMC, PAA or PEO, or other binders well known in the art;

[0047] In the coating, the mass proportion of the binder may be, for example, but not limited to, 5%, 8% or 10%.

[0048] In some optional embodiments, the fluorine-containing sodium salt includes but is not limited to NaF, or other fluorine-containing sodium salts well known in the art are selected;

[0049] The metal catalyst includes but is not limited to Fe, Pt or Ni;

[0050] The polymer includes but is not limited to at least one of PVA, polypyrrole or polyethylene glycol;

[0051] The thickness of the polymer coating may be, for example, but not limited to, 1 nm, 5 nm or 10 nm.

[0052] In some optional embodiments, the porous nitrogen-doped carbon particles are loaded with a fluorine-containing sodium salt inside, and are coated with a polymer layer on the surface, and the metal catalyst is loaded on the polymer layer.

[0053] In some optional embodiments, the method for preparing the porous nitrogen-doped carbon particles comprises:

[0054] a. Using a template method, mesoporous silica, a carbon source, and a nitrogen source are mixed in water, and then subjected to hydrothermal treatment, high-temperature carbonization treatment, and HF etching treatment to obtain nitrogen-doped core-shell carbon;

[0055] b. Immersing the nitrogen-doped core-shell carbon obtained in step a into an aqueous solution of a fluorine-containing sodium salt, drying to obtain a nitrogen-doped core-shell carbon loaded with a fluorine-containing sodium salt, and then immersing the nitrogen-doped core-shell carbon loaded with a fluorine-containing sodium salt into a polymer solution for coating to obtain a nitrogen-doped core-shell carbon with a surface-coated polymer;

[0056] c. Immerse the nitrogen-doped core-shell carbon with the surface coated polymer obtained in step b in a salt solution of a metal catalyst, and then add a reducing agent to reduce the metal catalyst to obtain porous nitrogen-doped carbon particles.

[0057] In some optional embodiments, the carbon source includes but is not limited to at least one of glucose, fructose or cellulose, or other carbon sources well known to those skilled in the art;

[0058] The nitrogen source includes but is not limited to at least one of urea, pyrrole or aniline, or other nitrogen sources known to those skilled in the art;

[0059] The mass ratio of the carbon source to the nitrogen source may be, for example, but not limited to, 5:1, 8:1 or 10:1.

[0060] In some optional embodiments, the temperature of the hydrothermal treatment may be, but not limited to, 180° C., 190° C., or 220° C., and the time may be, but not limited to, 3 h, 4 h, or 5 h. The carbon source is pre-carbonized by the hydrothermal treatment.

[0061] The temperature of the high-temperature carbonization treatment may be, for example, but not limited to, 750° C., 800° C., or 850° C., and the time may be, for example, but not limited to, 1.5 h, 2 h, or 2.5 h.

[0062] In some optional embodiments, the mass concentration of the fluorine-containing sodium salt in the aqueous solution of the fluorine-containing sodium salt may be, for example, but not limited to, 18%, 20% or 22%;

[0063] In the salt solution of the metal catalyst, the concentration of the metal catalyst salt may be, for example, but not limited to, 0.5 mol / L, 1 mol / L or 1.5 mol / L.

[0064] In some optional embodiments, the reducing agent includes but is not limited to NaBH4, or other reducing agents well known to those skilled in the art.

[0065] In a second aspect, the present invention provides an application of the above-mentioned negative electrode-free sodium ion battery current collector in a negative electrode-free sodium ion battery.

[0066] The negative electrode-free sodium ion battery current collector provided by the present invention is used in sodium ion batteries and can effectively improve the coulombic efficiency and cycle life of the sodium ion battery.

[0067] In a third aspect, the present invention provides a negative electrode-free sodium ion battery, using the negative electrode-free sodium ion battery current collector as the negative electrode of the negative electrode-free sodium ion battery.

[0068] The sodium ion battery has good safety, high coulombic efficiency and long cycle life.

[0069] The present invention is further described below by means of specific examples and comparative examples. However, it should be understood that these examples are merely provided for more detailed description and are not to be construed as limiting the present invention in any form.

[0070] Example 1

[0071] A negative electrode-free sodium ion battery current collector, comprising a substrate (carbon-coated aluminum foil) 14 μm thick and a coating 10 μm thick applied on the surface of the substrate;

[0072] The coating consists of porous nitrogen-doped carbon particles and a binder (PAA), with the binder accounting for 10% by weight;

[0073] Porous nitrogen-doped carbon particles are loaded with NaF and metal catalyst (Fe), and the surface is coated with polymer (PVA) with a thickness of 5 nm.

[0074] The preparation method is as follows:

[0075] 1. Mesoporous SiO2 was dispersed in an aqueous solution of 10 g of carbon source (glucose) and 1 g of nitrogen source (urea), hydrothermally treated at 200 ° C for 4 h, centrifuged and filtered, washed three times with anhydrous ethanol and deionized water, then dried at 80 ° C for 6 h, carbonized at 800 ° C for 2 h, etched with 5% HF solution for 24 h, removed the template, and washed with deionized water until neutral to obtain N-doped core-shell carbon (material A).

[0076] 2. Encapsulation containing sodium F salt

[0077] Place material A in a vacuum dryer and pump to 10 -3 Pa, inject a 20% sodium fluoride aqueous solution, let it stand for 12 hours, and then vacuum dry it at 60°C for 24 hours to remove the residual liquid. The above material was immersed in a 1% polymer (PVA) ethanol solution and stirred for 6 hours to form a protective layer, obtaining a porous carbon material encapsulated with sodium fluoride (Material B).

[0078] 3. Catalyst loading

[0079] Material B was immersed in a metal catalyst salt solution (Fe) and vacuum impregnated for 12 hours. Then, a 0.1-0.5 mol / L reducing agent solution (NaBH4\formaldehyde\ethylene glycol) was added and stirred at room temperature for 2 hours. The product was collected by centrifugation, washed, and dried at 60°C to obtain porous nitrogen-doped carbon particles.

[0080] 4. Current Collector Preparation

[0081] The porous nitrogen-doped carbon particles are mixed with a binder (PAA) to prepare a slurry, which is then coated on the surface of a substrate, dried, and rolled to obtain a metal-doped porous carbon current collector.

[0082] Example 2

[0083] A negative electrode-free sodium ion battery current collector, comprising a substrate (carbon-coated aluminum foil) 14 μm thick and a coating 15 μm thick applied on the surface of the substrate;

[0084] The coating consists of porous nitrogen-doped carbon particles and a binder (CMC), with the binder accounting for 10% by mass;

[0085] The porous nitrogen-doped carbon particles are loaded with NaF and metal catalyst (Pt) and coated with polymer (PVA) with a thickness of 5 nm.

[0086] The preparation method is as follows:

[0087] 1. Mesoporous SiO2 was dispersed in an aqueous solution of 8 g of carbon source (fructose) and 1 g of nitrogen source (pyrrole), hydrothermally treated at 200 ° C for 4 h, centrifuged and filtered, washed three times with anhydrous ethanol and deionized water, then dried at 80 ° C for 6 h, carbonized at 800 ° C for 2 h, etched with 5% HF solution for 24 h, removed the template, and washed with deionized water until neutral to obtain N-doped core-shell carbon (material A).

[0088] 2. Encapsulation containing sodium F salt

[0089] Place material A in a vacuum dryer and pump to 10 -3 Pa, inject a 20% sodium fluoride aqueous solution, let it stand for 12 hours, and then vacuum dry it at 60°C for 24 hours to remove the residual liquid. The above material is immersed in a 1% polymer (PVA) ethanol solution and stirred for 6 hours to form a 1-10nm protective layer, obtaining a porous carbon material encapsulated with sodium fluoride (Material B).

[0090] 3. Catalyst loading

[0091] Material B was immersed in a metal catalyst salt solution (Pt) and vacuum impregnated for 12 hours. Then, a 0.1-0.5 mol / L reducing agent solution (NaBH4\formaldehyde\ethylene glycol) was added and stirred at room temperature for 2 hours. The product was collected by centrifugation, washed, and dried at 60°C to obtain porous nitrogen-doped carbon particles.

[0092] 4. Current Collector Preparation

[0093] The porous nitrogen-doped carbon particles are mixed with a binder (CMC) to prepare a slurry, which is then coated on the surface of a substrate, dried, and rolled to obtain a metal-doped porous carbon current collector.

[0094] Example 3

[0095] A negative electrode-free sodium ion battery current collector, comprising a 14 μm substrate (aluminum foil) and a 20 μm coating applied on the surface of the substrate;

[0096] The coating consists of porous nitrogen-doped carbon particles and a binder (PEO), with the binder accounting for 10% by weight;

[0097] The porous nitrogen-doped carbon particles are loaded with NaF and metal catalyst (Ni) and coated with polymer (PVA) with a thickness of 10 nm.

[0098] The preparation method is as follows:

[0099] 1. Mesoporous SiO2 was dispersed in an aqueous solution of 5 g of carbon source (cellulose) and 1 g of nitrogen source (aniline), hydrothermally treated at 200 ° C for 4 h, centrifuged and filtered, washed three times with anhydrous ethanol and deionized water, then dried at 80 ° C for 6 h, carbonized at 800 ° C for 2 h, etched with 5% HF solution for 24 h, removed the template, and washed with deionized water until neutral to obtain N-doped core-shell carbon (material A).

[0100] 2. Encapsulation containing sodium F salt

[0101] Place material A in a vacuum dryer and pump to 10 -3 Pa, inject a 20% sodium fluoride aqueous solution, let it stand for 12 hours, and then vacuum dry it at 60°C for 24 hours to remove the residual liquid. The above material is immersed in a 1% polymer (PVA) ethanol solution and stirred for 6 hours to form a 1-10nm protective layer, obtaining a porous carbon material encapsulated with sodium fluoride (Material B).

[0102] 3. Catalyst loading

[0103] Material B was immersed in a metal catalyst salt solution (Ni) and vacuum impregnated for 12 hours. Then, a 0.1-0.5 mol / L reducing agent solution (NaBH4\formaldehyde\ethylene glycol) was added and stirred at room temperature for 2 hours. The product was collected by centrifugation, washed, and dried at 60°C to obtain porous nitrogen-doped carbon particles.

[0104] 4. Current Collector Preparation

[0105] The porous nitrogen-doped carbon particles are mixed with a binder (PEO) to prepare a slurry, which is then coated on the surface of a substrate, dried, and rolled to obtain a metal-doped porous carbon current collector.

[0106] Comparative Example 1

[0107] A current collector, which differs from Example 1 in that NaF is not loaded in the porous nitrogen-doped carbon particles.

[0108] Comparative Example 2

[0109] A current collector, which differs from Example 1 in that no metal catalyst is loaded in the porous nitrogen-doped carbon particles.

[0110] Comparative Example 3

[0111] A current collector, which differs from Example 1 in that the surface of the porous nitrogen-doped carbon particles is not coated with a polymer.

[0112] Test Example 1

[0113] The current collectors provided in the above examples and comparative examples were used as negative electrodes to prepare negative electrode-free sodium ion batteries, wherein the positive electrode sheet was composed of sodium iron pyrophosphate, PVDF, and conductive carbon black in a ratio of 95.4:1.8:2.8;

[0114] The electrolyte was: diethylene glycol dimethyl ether containing 1 M NaPF6;

[0115] Diaphragm: PP diaphragm.

[0116] The negative electrode-free sodium ion battery was assembled in an inert atmosphere glove box according to the same preparation method.

[0117] The first coulombic efficiency and cycle performance of the negative electrode-free sodium metal batteries prepared in each embodiment and comparative example were tested. The specific testing methods are as follows:

[0118] First coulombic efficiency test of the battery: After the assembled battery is set aside for 10 hours, it is charged to 3.5V at a constant current and constant voltage of 0.2C. After another 0.5 hour, it is discharged to 2.0V at a constant current of 0.5C. The ratio of the battery discharge capacity to the charge capacity is calculated as CE.

[0119] Cycle life test: After the assembled battery was left for 10 hours, it was charged at a constant current and constant voltage of 0.5C to 3.5V at room temperature (25°C). After 0.5 hours, it was discharged at a constant current of 1C to 2.0V. This cycle was repeated 100 times, and the capacity retention rate was recorded. The test results are shown in Table 1.

[0120] Table 1

[0121] Group First coulombic efficiency (%) 100-cycle capacity retention rate (%) Example 1 97.4 99.1 Example 2 96.8 98.5 Example 3 96.2 98.1 Comparative Example 1 84.2 78.5 Comparative Example 2 81.6 77.4 Comparative Example 3 88.3 82.7

[0122] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 current collector for a sodium ion battery without a negative electrode, characterized in that: It includes a substrate and a coating applied on the surface of the substrate; The coating comprises porous nitrogen-doped carbon particles and a binder; The porous nitrogen-doped carbon particles are loaded with fluorine-containing sodium salt and metal catalyst, and the surface is coated with a polymer; The metal catalyst is used to catalyze the cleavage of the PF bond of NaPF6 to generate NaF.

2. The negative electrode-free sodium ion battery current collector according to claim 1, characterized in that The substrate includes aluminum foil, copper foil, carbon-coated aluminum foil or carbon-coated copper foil.

3. The negative electrode-free sodium ion battery current collector according to claim 1, characterized in that: The binder includes at least one of CMC, PAA or PEO; In the coating, the mass proportion of the binder is 5%-10%.

4. The negative electrode-free sodium ion battery current collector according to claim 1, characterized in that The fluorine-containing sodium salt includes NaF; The metal catalyst includes at least one of Fe, Pt or Ni; The polymer includes at least one of PVA, polypyrrole or polyethylene glycol; The thickness of the polymer coating is 1-10 nm.

5. The negative electrode-free sodium ion battery current collector according to claim 1, characterized in that: The method for preparing the porous nitrogen-doped carbon particles comprises: a. The mesoporous silica, carbon source and nitrogen source are mixed in water, and then subjected to hydrothermal treatment, high temperature carbonization treatment and HF etching treatment to obtain nitrogen-doped core-shell carbon; b. Immersing the nitrogen-doped core-shell carbon obtained in step a into an aqueous solution of a fluorine-containing sodium salt, drying to obtain a nitrogen-doped core-shell carbon loaded with a fluorine-containing sodium salt, and then immersing the nitrogen-doped core-shell carbon loaded with a fluorine-containing sodium salt into a polymer solution for coating to obtain a nitrogen-doped core-shell carbon with a surface-coated polymer; c. Immerse the nitrogen-doped core-shell carbon with the surface coated polymer obtained in step b in a salt solution of a metal catalyst, and then add a reducing agent to reduce the metal catalyst to obtain porous nitrogen-doped carbon particles.

6. The negative electrode-free sodium ion battery current collector according to claim 5, characterized in that: The carbon source includes at least one of glucose, fructose or cellulose; The nitrogen source comprises at least one of urea, pyrrole or aniline; The mass ratio of the carbon source to the nitrogen source is (5-10):

1.

7. The negative electrode-free sodium ion battery current collector according to claim 5, characterized in that: The hydrothermal treatment temperature is 180-220°C and the time is 3-5h; The temperature of the high-temperature carbonization treatment is 750-850° C., and the time is 1.5-2.5 hours.

8. The negative electrode-free sodium ion battery current collector according to claim 7, characterized in that: The mass concentration of the fluorine-containing sodium salt in the aqueous solution is 18%-22%; In the salt solution of the metal catalyst, the concentration of the metal catalyst salt is 0.5-1.5 mol / L.

9. Use of the negative electrode-free sodium ion battery current collector according to any one of claims 1 to 8 in a negative electrode-free sodium ion battery.

10. A negative electrode-free sodium ion battery, characterized in that: The negative electrode-free sodium ion battery current collector according to any one of claims 1 to 8 is used as the negative electrode of the negative electrode-free sodium ion battery.