CN114843450A - Sodium ion battery - Google Patents

Abstract

The invention belongs to the technical field of secondary batteries, and particularly provides a sodium ion battery. The sodium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte; the negative electrode contains a negative electrode active material, and the mass fraction a of the negative electrode active material in the negative electrode, the specific surface area b of the negative electrode active material, the density x of the nonaqueous electrolytic solution, and the molar conductivity y of the nonaqueous electrolytic solution satisfy 0.3. ltoreq. a x b x/y. ltoreq.1.5. The invention creatively designs the electrolyte from multiple aspects of comprehensive consideration of the mass fraction a of the negative active material in the negative electrode, the specific surface area b of the negative active material, the density x of the non-aqueous electrolyte and the molar conductivity y, and can effectively reduce the internal resistance of the sodium-ion battery and increase the battery capacity, so that the sodium-ion battery has the advantages of low internal resistance, good cycling stability and the like.

Description

A sodium-ion battery

technical field

The invention belongs to the technical field of secondary batteries, and in particular relates to a sodium ion battery.

Background technique

Due to the limited global reserves of lithium resources, the cost of lithium-ion batteries has increased significantly. However, the abundance of sodium resources is higher, the material cost is lower, and it can technically achieve similar functions to lithium-ion batteries. Therefore, the development of high-performance sodium-ion batteries can help alleviate the resource problems in the new energy industry. Different from the graphite negative electrode of lithium ion battery, the negative electrode of sodium ion battery usually uses amorphous carbon material with a relatively large area as the negative electrode, such as hard carbon, because the larger the specific surface area of the electrode active material, the more electrolyte is consumed in the battery, so The electrolyte design of sodium-ion batteries is quite different from that of lithium-ion batteries.

Due to the use of amorphous carbon with a large specific surface area as the negative electrode, the sodium-ion battery consumes more electrolyte during the battery formation stage, and the film is thicker, resulting in higher battery internal resistance and lower battery capacity.

SUMMARY OF THE INVENTION

Based on this, the purpose of the present invention is to provide a sodium-ion battery, which has the advantages of low internal resistance and good cycle stability.

In order to achieve the above object, the present invention adopts the following technical solutions.

A sodium ion battery, the sodium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte; the negative electrode comprises a negative electrode active material, the mass fraction a of the negative electrode active material in the negative electrode, the specific surface area b of the negative electrode active material, the non-aqueous electrode active material The density x of the aqueous electrolyte and the molar conductivity y of the non-aqueous electrolyte satisfy 0.3≤a×b×x/y≤1.5.

In some embodiments, the a, b, x, and y satisfy 0.4≤a×b×x/y≤1.3.

In some embodiments, the mass fraction a of the negative electrode active material in the negative electrode is 90%-99%.

In some embodiments, the specific surface area b of the negative electrode active material is 3˜7 g/m ² .

In some embodiments, the density x of the non-aqueous electrolyte solution is 0.8˜1.4 g/cm ³ . Preferably, the density x of the non-aqueous electrolyte solution is 0.9˜1.3 g/cm ³ .

In some embodiments, the molar conductivity y of the non-aqueous electrolyte is 5-12 S·cm ² /mol. Preferably, the molar conductivity y of the non-aqueous electrolyte is 6-11 S·cm ² /mol.

In some embodiments, the negative electrode active material is selected from at least one of hard carbon, soft carbon, graphite, graphene, and mesocarbon microspheres.

In some embodiments, the non-aqueous electrolyte contains an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt is selected from the group consisting of sodium hexafluorophosphate, sodium bistrifluoromethanesulfonimide, sodium bisfluorosulfonimide, sodium perchlorate, sodium trifluoromethanesulfonate, and tetrafluoromethanesulfonate At least one of sodium fluoroborate.

In some embodiments, the solvent is selected from at least one of C3-C5 carbonates, C2-C6 carboxylates, and C4-C10 ethers.

In some embodiments, the positive electrode includes a positive electrode active material selected from at least one of sodium-containing layered oxides, sodium-containing polyanionic compounds, and sodium-containing Prussian blue compounds.

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

Aiming at the problems of high internal resistance and low battery capacity of sodium ion batteries, the present invention innovatively proposes to determine the mass fraction a of the negative electrode active material in the negative electrode, the specific surface area b of the negative electrode active material, the density x of the non-aqueous electrolyte and the non-aqueous electrolyte. The molar conductivity y is considered to design the sodium-ion battery comprehensively: for the carbon negative electrode with a large specific surface area, reducing the density of the non-aqueous electrolyte can reduce the content of the non-aqueous electrolyte adsorbed per unit volume of the negative electrode, and reduce the participation in the film formation process. The non-aqueous electrolyte consumed by side reactions; increasing the molar conductivity of the non-aqueous electrolyte is beneficial to improve the carrier utilization rate of the film formation process, reduce the participation of anions in the film formation, and form a thinner interface film. Through further research, it is found that when the mass fraction a of the negative electrode active material in the negative electrode, the specific surface area b of the negative electrode active material, the density x of the non-aqueous electrolyte, and the molar conductivity y of the non-aqueous electrolyte satisfy 0.3≤a× When b×x/y≤1.5, it can effectively reduce the internal resistance of the sodium-ion battery while increasing the battery capacity, making it have the advantages of low internal resistance and good cycle stability.

Detailed ways

The experimental methods that do not specify specific conditions in the following examples of the present invention are usually in accordance with conventional conditions, or in accordance with the conditions suggested by the manufacturer. Various common chemical reagents used in the examples are all commercially available products.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used in the description of the present invention are only for the purpose of describing specific embodiments, and are not used to limit the present invention.

The terms "comprising" and "having" and any variations thereof of the present invention are intended to cover a non-exclusive inclusion. For example, a process, method, apparatus, product or device comprising a series of steps is not limited to the listed steps or modules, but optionally also includes unlisted steps, or optionally also includes steps for these processes, other steps inherent in the method, product or device.

The "plurality" mentioned in the present invention means two or more. "And/or", which describes the association relationship of the associated objects, means that there can be three kinds of relationships, for example, A and/or B, which can mean that A exists alone, A and B exist at the same time, and B exists alone. The character "/" generally indicates that the associated objects are an "or" relationship.

This embodiment provides a sodium-ion battery, the sodium-ion battery includes a positive electrode, a negative electrode and a non-aqueous electrolyte; the negative electrode includes a negative electrode active material, the mass fraction a of the negative electrode active material in the negative electrode, the mass fraction of the negative electrode active material The specific surface area b, the density x of the non-aqueous electrolyte solution, and the molar conductivity y of the non-aqueous electrolyte solution satisfy 0.3≦a×b×x/y≦1.5.

After research, the inventor found that when the value of a×b×x/y is higher than 1.5, the negative electrode adsorbs more electrolyte per unit volume, and consumes more electrolyte; the molar conductivity is low, and the kinetic process of film formation is slow. Anions participate in the film formation more, forming a thicker interface film, resulting in a large internal resistance of the battery; when the value of a×b×x/y is lower than 0.3, the amount of electrolyte adsorbed per unit volume of the negative electrode is too small, the film formation is insufficient, and the formation of ineffective Stabilize the interface film; the molar conductivity of the electrolyte is higher, the kinetic process of film formation is faster, and the anions participate in the film formation less, the mechanical strength of the formed interface film is unstable, and the cycle stability of the battery is reduced.

In some preferred embodiments, the a, b, x, and y satisfy 0.4≤a×b×x/y≤1.3.

Specifically, the value of a×b×x/y is 0.25, 0.28, 0.3, 0.4, 0.43, 0.45, 0.5, 0.65, 0.75, 0.8, 0.82, 0.9, 0.98, 1, 1.2, 1.25, 1.3, 1.4, 1.5, 1.65, 1.86.

In some embodiments, the mass fraction a of the negative electrode active material in the negative electrode is 90%-99%.

In some embodiments, the specific surface area b of the negative electrode active material is 3˜7 g/m ² .

In some embodiments, the density x of the non-aqueous electrolyte solution is 0.8˜1.4 g/cm ³ .

In some preferred embodiments, the density x of the non-aqueous electrolyte is 0.9-1.3 g/cm ³ .

In some embodiments, the molar conductivity y of the non-aqueous electrolyte is 5-12 S·cm ² /mol.

In some preferred embodiments, the molar conductivity y of the non-aqueous electrolyte is 6-11 S·cm ² /mol.

In some embodiments, the negative electrode active material is selected from at least one of hard carbon, soft carbon, graphite, graphene, and mesocarbon microspheres.

In some embodiments, the non-aqueous electrolyte contains an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt is selected from the group consisting of sodium hexafluorophosphate, sodium bistrifluoromethanesulfonimide, sodium bisfluorosulfonimide, sodium perchlorate, sodium trifluoromethanesulfonate, and tetrafluoromethanesulfonate At least one of sodium fluoroborate.

In some embodiments, the solvent is selected from at least one of C3-C5 carbonates, C2-C6 carboxylates, and C4-C10 ethers.

In some preferred embodiments, the solvent is selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, ethylene glycol At least one of glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

In some embodiments, the positive electrode includes a positive active material including, but not limited to, at least one of transition metal oxides, Prussian-based materials, phosphates, sulfates, and titanate materials. Wherein, the chemical formula of the transition metal oxide can be Na _z M _x O _y , M can be selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V, more Preferably, the transition metal oxide is NaNi _m Fe _n Mn _p O ₂ (m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1) or NaNi _m Co _n Mn _p O ₂ (m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1); the molecular formula of the Prussian material is Na _x M[M'(CN) ₆ ] _y ·zH ₂ O, wherein M is a transition metal, M' is a transition metal, 0<x≤2, 0.8≤y<1, 0<z≤20, more preferably, the Prussian material is Na _x Mn[Fe(CN) ₆ ] _y ·nH ₂ O (0<x≤2, 0<y≤1, 0<z≤10) or Na _x Fe[Fe(CN) ₆ ] _y ·nH ₂ O(0 <x≤2, 0<y≤1, 0<z≤10); the chemical formula of the phosphate is Na ₃ (MO _{1- x} PO ₄ ) ₂ F _1+2x , 0≤x≤1, M is selected from At least one of Al, V, Ge, Fe, Ga, more preferably, the phosphate is Na ₃ (VPO ₄ ) ₂ F ₃ or Na ₃ (VOPO ₄ ) ₂ F; the chemical formula of the phosphate is Na ₂ MPO ₄ F, M is selected from at least one of Fe and Mn, more preferably, the phosphate is Na ₂ FePO ₄ F or Na ₂ MnPO ₄ F; the titanate material can be selected from At least one of Na ₂ Ti ₃ O ₇ , Na ₂ Ti ₆ O ₁₃ , Na ₄ Ti ₅ O ₁₂ , Li ₄ Ti ₅ O ₁₂ , NaTi ₂ (PO ₄ ) ₃ ; the chemical formula of the sulfate is Na ₂ M(SO ₄ ) ₂ ·2H ₂ O, M may be selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

In some embodiments, the positive electrode further includes a positive electrode binder and a positive electrode conductive agent.

The positive electrode binder includes polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene- Perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichloroethylene copolymer Copolymers, vinylidene fluoride-vinyl fluoride copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, thermoplastic polyimides, thermoplastic resins such as polyethylene and polypropylene; acrylic resins; and benzene At least one of ethylene butadiene rubber.

The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

In some embodiments, the negative electrode further includes a negative electrode binder and a negative electrode conductive agent. The negative electrode binder and the negative electrode conductive agent may be the same as the positive electrode adhesive and the positive electrode conductive agent, respectively, and will not be repeated here.

In some embodiments, the method for preparing the positive electrode is as follows: uniformly mixing the positive electrode active material, the positive electrode binder, the positive electrode conductive agent and the positive electrode solvent, coating the substrate on the substrate, and removing the positive electrode solvent to obtain the positive electrode. The cathode solvent is a conventional choice, for example, it can be nitrogen methyl pyrrolidone (NMP).

In some embodiments, the preparation method of the negative electrode is as follows: the negative electrode active material, the negative electrode binder, the negative electrode conductive agent and the negative electrode solvent are uniformly mixed, coated on the substrate, and the negative electrode solvent is removed to obtain the negative electrode. The negative electrode solvent is a conventional choice, such as pure water.

In some embodiments, the sodium-ion battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

The separator can be an existing conventional separator, which can be a ceramic separator, a polymer separator, a non-woven fabric, an inorganic-organic composite separator, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), Diaphragms such as double-layer PP/PE, double-layer PP/PP and triple-layer PP/PE/PP.

In some embodiments, the preparation method of the sodium ion battery is a general preparation method of a secondary battery, that is, a positive electrode, a separator and a negative electrode are combined and injected into a non-aqueous electrolyte to obtain a sodium ion battery.

The following description will be given in conjunction with specific embodiments.

Example 1

This embodiment provides a sodium-ion battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte.

The non-aqueous electrolyte preparation method is as follows: ethylene carbonate, propylene carbonate, dimethyl carbonate and ethyl methyl carbonate are prepared into a mixed solvent according to a mass ratio of 25:10:30:35, and 100 g of a mixed solvent is mixed with 14 g of a mixed solvent. Sodium hexafluorophosphate was prepared into a solution to obtain a solution with a density x of 1.2 g/cm ³ and a molar conductivity y of 7 S·cm ² /mol.

The negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent; the negative electrode active material is hard carbon, the mass fraction a of the hard carbon in the negative electrode is 95%, and the specific surface area b of the hard carbon is 6 g/m ² ; The mass fraction of the negative electrode binder in the negative electrode is 3%; the mass fraction of the negative electrode conductive agent in the negative electrode is 2%.

The positive electrode includes a positive electrode active material, a positive electrode binder and a positive electrode conductive agent; the positive electrode active material is NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ ; the positive electrode active material, the positive electrode binder and the positive electrode are The mass ratio of the conductive agent is 96:2:2.

In this embodiment, the value of a×b×x/y is 0.98.

Example 2

This embodiment provides a sodium-ion battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte.

The preparation method of the non-aqueous electrolyte is as follows: ethylene carbonate, propylene carbonate, dimethyl carbonate and ethyl methyl carbonate are prepared into a mixed solvent according to a mass ratio of 25:10:30:35, and 100 g of the mixed solvent is mixed with 14.7 g sodium hexafluorophosphate was prepared into a solution to obtain a solution with a density x of 1.2 g/cm ³ and a molar conductivity y of 6.5 S·cm ² /mol.

The negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent; the negative electrode active material is hard carbon, the mass fraction a of the hard carbon in the negative electrode is 97%, and the specific surface area b of the hard carbon is 7 g/m ² ; The mass fraction of the negative electrode binder in the negative electrode is 2%; the mass fraction of the negative electrode conductive agent in the negative electrode is 1%.

The positive electrode is the same as that of Example 1.

In this embodiment, the value of a×b×x/y is 1.25.

Example 3

This embodiment provides a sodium-ion battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte.

The preparation method of the non-aqueous electrolyte is as follows: ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate are prepared into a mixed solvent in a mass ratio of 20:10:60:10, and 100 g of the mixed solvent is mixed with 9.5 g sodium hexafluorophosphate was prepared into a solution to obtain a solution with a density x of 1.1 g/cm ³ and a molar conductivity y of 9.5 S·cm ² /mol.

The negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent; the negative electrode active material is hard carbon, the mass fraction a of the hard carbon in the negative electrode is 93%, and the specific surface area b of the hard carbon is 4 g/m ² ; The mass fraction of the negative electrode binder in the negative electrode is 4%; the mass fraction of the negative electrode conductive agent in the negative electrode is 3%.

The positive electrode is the same as that of Example 1.

In this embodiment, the value of a×b×x/y is 0.43.

Comparative Example 1:

The present comparative example provides a sodium-ion battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte.

The preparation method of the non-aqueous electrolyte is as follows: ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are prepared into a mixed solvent according to a mass ratio of 80:5:15, and 100 g of the mixed solvent and 21.8 g of sodium hexafluorophosphate are prepared into a solution to obtain a solution with a density x of 1.4 g/cm ³ and a molar conductivity y of 5 S·cm ² /mol.

The negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent; the negative electrode active material is hard carbon, the mass fraction a of the hard carbon in the negative electrode is 95%, and the specific surface area b of the hard carbon is 7 g/m ² ; The mass fraction of the negative electrode binder in the negative electrode is 3%; the mass fraction of the negative electrode conductive agent in the negative electrode is 2%.

The positive electrode is the same as that of Example 1.

The value of a×b×x/y in this comparative example is 1.86.

Comparative Example 2:

The present comparative example provides a sodium-ion battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte.

The non-aqueous electrolyte preparation method is as follows: propylene carbonate, diethyl carbonate, and propyl propionate are prepared into a mixed solvent according to a mass ratio of 10:5:85, and 100 g of a mixed solvent and 4 g of sodium hexafluorophosphate are prepared into a mixed solvent. solution to obtain a solution with a density x of 0.9 g/cm ³ and a molar conductivity y of 12 S·cm ² /mol.

The negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent; the negative electrode active material is hard carbon, the mass fraction a of the hard carbon in the negative electrode is 93%, and the specific surface area b of the hard carbon is 4 g/m ² ; The mass fraction of the negative electrode binder in the negative electrode is 4%; the mass fraction of the negative electrode conductive agent in the negative electrode is 3%.

The positive electrode is the same as that of Example 1.

The value of a×b×x/y in this comparative example is 0.28.

The performance of the sodium-ion batteries in Examples 1-3 and Comparative Examples 1-2 was tested: the cyclic charge-discharge test was performed in the voltage range of 1.50-3.95V, and the internal resistance of the battery and the capacity retention rate of 200 cycles were recorded.

The results are shown in Table 1:

Table 1 Performance test results

The above results show that the sodium ion battery of the present invention has lower internal resistance and higher capacity retention rate, and has better battery performance.

Compared with Example 1, the negative electrode active material used in the sodium-ion battery of Comparative Example 1 has higher specific surface area, higher density of non-aqueous electrolyte, lower molar conductivity, and a×b×x/y value of 1.86, If it is greater than 1.50, the negative electrode absorbs more electrolyte per unit volume, and consumes more non-aqueous electrolyte; the molar conductivity is low, the kinetics of film formation is slow, anions participate in film formation more, and the interface film is thicker, resulting in battery Internal resistance is large.

Compared with Example 1, the negative electrode active material used in Comparative Example 2 has lower specific surface area, lower density of non-aqueous electrolyte, higher molar conductivity, a×b×x/y value of 0.28, less than 0.30, The amount of non-aqueous electrolyte adsorbed per unit volume of the negative electrode is too small, the film formation is insufficient, and an unstable interface film is formed; the molar conductivity of the non-aqueous electrolyte is higher, the kinetic process of film formation is faster, and the anions are less involved in film formation, forming an interface film. The mechanical strength is unstable, the battery cycle stability is reduced, and the battery capacity retention rate is low.

Example 2 is compared with Comparative Example 1. When a negative electrode active material with a higher specific surface area is used, the value of x is decreased and the value of y is increased, so that the a, b, x, and y satisfy 0.3≤a×b×x/ y≤1.5, lower impedance can be obtained.

Example 3 is compared with Comparative Example 2. When a negative electrode active material with a lower specific surface area is used, the value of x is increased and the value of y is decreased, so that the a, b, x, and y satisfy 0.3≤a×b×x/ y≤1.5, better cycle performance can be obtained.

In summary, the present invention optimizes the mass fraction a of the negative electrode active material of the sodium ion battery in the negative electrode, the specific surface area b of the negative electrode active material, the density x of the non-aqueous electrolyte, and the molar conductivity y of the non-aqueous electrolyte, so that the Said a, b, x, and y satisfy 0.3≤a×b×x/y≤1.5, which can effectively improve the cycle stability of the sodium-ion battery and reduce the internal resistance of the battery. When the value of a×b×x/y is not within the scope of the present invention, the performance of the prepared sodium-ion battery is obviously reduced.

The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the patent of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims (10)

1. a sodium ion battery, the sodium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte; it is characterized in that, the negative electrode comprises a negative electrode active material, and the negative electrode active material is at the mass fraction a of the negative electrode, the negative electrode active material The specific surface area b, the density x of the non-aqueous electrolyte, and the molar conductivity y of the non-aqueous electrolyte satisfy 0.3≤a×b×x/y≤1.5. 2 . The sodium-ion battery of claim 1 , wherein the a, b, x, and y satisfy 0.4≦a×b×x/y≦1.3. 3 . 3 . The sodium-ion battery according to claim 1 , wherein the mass fraction a of the negative electrode active material in the negative electrode is 90% to 99%. 4 . 4 . The sodium-ion battery according to claim 1 , wherein the specific surface area b of the negative electrode active material is 3˜7 g/m ² . 5 . The sodium-ion battery according to claim 1 , wherein the density x of the non-aqueous electrolyte solution is 0.8-1.4 g/cm ³ . 6 . The sodium-ion battery according to claim 1 , wherein the molar conductivity y of the non-aqueous electrolyte solution is 5-12 S·cm ² /mol. 7 . 7. The sodium-ion battery of claim 1, wherein the negative electrode active material is selected from at least one of hard carbon, soft carbon, graphite, graphene, and mesocarbon microspheres. 8. The sodium-ion battery according to claim 1, wherein the non-aqueous electrolyte contains an electrolyte salt and a solvent. 9. The sodium-ion battery of claim 8, wherein the electrolyte salt is selected from the group consisting of sodium hexafluorophosphate, sodium bistrifluoromethanesulfonimide, sodium bisfluorosulfonimide, perchloric acid At least one of sodium, sodium trifluoromethanesulfonate and sodium tetrafluoroborate; and/or, the solvent is selected from C3-C5 carbonate, C2-C6 carboxylate and C4-C10 ether at least one of. 10. The sodium-ion battery according to any one of claims 1 to 9, wherein the positive electrode comprises a positive electrode active material selected from the group consisting of sodium-containing layered oxides, sodium-containing polyanions At least one of a compound and a sodium-containing Prussian blue compound.