Sodium ion battery based on molten salt electrolyte

Abstract

The invention discloses a sodium ion battery based on molten salt electrolyte, the sodium ion battery adopts NaFSI: KFSI solid molten salt with the molar ratio of 56: 44 as NaFSI-KFSI molten salt electrolyte, the NaFSI-KFSI molten salt electrolyte is in a solid state at room temperature, and when the temperature rises to 80 DEG C, the NaFSI-KFSI molten salt electrolyte is in a liquid state; and the electrolyte for the sodium ion battery is ensured to have high sodium ion conductivity and high sodium ion transference number. Compared with a sodium-ion battery and an all-solid-state sodium-ion battery constructed based on a traditional organic solvent electrolyte, the sodium-ion battery constructed based on the molten salt electrolyte has the advantages of high working voltage, high energy density, high safety, high-temperature characteristic and good cycling stability; and meanwhile, the battery keeps a very long storage life at normal temperature, so that the sodium ion battery has a very good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and more particularly to a sodium-ion battery based on a molten salt electrolyte. Background Art

[0002] Currently, the sodium-ion battery system mainly uses organic liquid electrolytes (electrolyte salts dissolved in organic solvents), and its safety performance needs to be further improved. The all-solid-state sodium-ion battery can not only improve safety but also help increase the energy density by using a solid electrolyte to replace the liquid electrolyte. The solid electrolyte is a key technology for realizing high-performance all-solid-state sodium-ion batteries. However, existing inorganic solid electrolytes (such as oxides, sulfides, and halides) still have many limitations in terms of ionic conductivity and interfacial compatibility with electrodes (including mechanical, chemical, and electrochemical aspects), which hinder the full development of all-solid-state sodium-ion batteries. In addition, interface problems, engineering, etc. of solid sodium batteries need to be further solved.

[0003] Due to advantages such as rich resources and low cost, the sodium-ion battery system is an important development direction for future large-scale energy storage technologies and has received extensive attention in recent years. With the joint efforts of scientists from all over the world, the performance of the positive and negative electrode materials and electrolytes of sodium-ion batteries has been continuously improved, and sodium-ion batteries have gradually moved from laboratory research to large-scale industrialization. With the joint efforts of the academic and industrial communities, the industrialization process of sodium-ion batteries has been continuously promoted, and the large-scale commercial application of sodium-ion batteries is at hand.

[0004] However, at present, the vast majority of sodium-ion battery electrolytes are organic electrolytes, with sodium salts dissolved in organic solvents. Such an electrolyte system brings certain safety problems to sodium-ion batteries. Especially during overcharging or short-circuiting of the battery, the heat inside the battery quickly ignites the organic solvent, which further exacerbates the occurrence of battery combustion or thermal runaway. The all-solid-state sodium-ion battery can not only improve safety but also help increase the energy density by using a solid electrolyte to replace the liquid electrolyte. However, interface contact problems and battery preparation processes in solid-state batteries severely limit the development and industrialization of solid-state sodium-ion batteries.

[0005] CN202311100138.4 discloses a method for preparing a long-cycle full battery by regulating the N / P ratio of sodium vanadium phosphate and hard carbon. This battery system uses sodium vanadium phosphate as the positive electrode and hard carbon as the negative electrode material, and the electrolyte is an organic solvent of 1M NaPF 6 solution.

[0006] CN202210834056.1 discloses a polyoxymethylene semi-solid sodium ion battery, its preparation method and application. Without reducing the injection amount of the liquid electrolyte, this invention replaces part of the solvent of the liquid electrolyte with trioxymethylene. During the battery formation process, trioxymethylene in-situ polymerizes in the battery to form polyoxymethylene insoluble in the liquid components, thus forming a semi-solid sodium ion battery containing polyoxymethylene. This battery system uses sodium vanadium phosphate as the positive electrode and hard carbon as the negative electrode material, showing good cycle stability.

[0007] CN202311442827.3 discloses a sodium ion battery electrolyte, including sodium salt, solvent and additive. The sodium salt is an inorganic sodium salt, and the concentration of this sodium salt is 0.01 mol / L - 3.0 mol / L; the solvent is a composite solvent system with different donor numbers, including a first donor number solvent and a second donor number solvent. The first donor number solvent is a high DN (Donor number) value solvent with a donor number greater than 21, and the second donor number solvent is a low DN (Donor number) value solvent with a donor number less than 21. When this electrolyte is used in a hard carbon||Na 3 V 2 (PO 4 ) 3 full battery, it shows good electrochemical performance.

[0008] Liu et al. reported the electrochemical performance of a full battery constructed with a Na-rich type Na 3 V 2 (PO 4 ) 3 positive electrode material and a hard carbon negative electrode material. The electrolyte is a liquid organic ether electrolyte (made by dissolving NaPF 6 in diglyme), and the constructed full battery shows good cycle stability.

[0009] SEI TECHNICAL REVIEW·NUMBER 76·APRIL 2013·33 studied the electrochemical performance of a ZnNa alloy||NaCrO 2 full battery in a NaFSI-KFSI molten salt electrolyte. This battery operates at a temperature of 90 °C and shows good electrochemical performance and safety.

[0010] Electrochemistry,92(10),101001(2024) disclosed an HC / NaFSA-C3C1pyrrFSA / NaCrO 2 sodium ion full battery. This battery uses C3C1pyrrFSA; an ionic liquid as a co-salt, enabling the battery to show good electrochemical performance in the range of 25 - 60 °C.

[0011] However, the disadvantages of the above-mentioned prior art are as follows: Using an organic liquid electrolyte to construct a sodium-ion battery increases the safety and cost of the sodium-ion battery. Although prior art has reported the use of solid electrolytes and ionic liquid electrolytes in sodium-ion batteries, which can reduce the use of organic liquid solvents to a certain extent, the solid-state sodium battery constructed with solid electrolytes has problems of large interfacial contact impedance and low intrinsic ionic conductivity, which severely limits the electrochemical performance of the solid-state sodium battery. Ionic liquid-based low-temperature molten salts often have high costs. NaZn||NaCrO 2 shows good electrochemical performance in molten salt electrolytes, but due to the low discharge voltage of NaCrO 2 , the output voltage of the constructed full battery is low and the energy density is low. Therefore, NaZn||NaCrO 2 also has the defects of high cost and low energy density. Summary of the Invention

[0012] The object of the present invention is to provide a sodium-ion battery based on molten salt electrolyte, so as to solve the problems of poor performance of sodium-ion batteries with organic electrolytes and solid-state sodium-ion batteries in the prior art, and low energy density of molten salt sodium-ion batteries.

[0013] To solve the above problems, the present invention adopts the following technical solutions:

[0014] Provide a sodium-ion battery based on molten salt electrolyte. The sodium-ion battery uses a NaFSI∶KFSI solid molten salt with a molar ratio of 56:44 as the NaFSI-KFSI molten salt electrolyte. The NaFSI-KFSI molten salt electrolyte is solid at room temperature and becomes liquid when the temperature rises to 80 °C, ensuring that the sodium-ion battery has high sodium-ion conductivity and high sodium-ion transference number.

[0015] Preferably, the positive electrode material is selected from: polyanion positive electrodes, layered oxide positive electrodes, Prussian blue / white, etc.

[0016] Preferably, the negative electrode material is selected from: hard carbon, layered oxides, alloy compounds, etc.

[0017] Preferably, the NaFSI-KFSI molten salt electrolyte further includes other salts with a content of 0-20 wt%, and the salts are selected from: CsFSI, LiPF 6 , LiBF 4 , KPF 6 , KBF 4 at least one of them.

[0018] Preferably, the NaFSI-KFSI molten salt electrolyte further includes CsFSI with a content of 10 wt%.

[0019] The sodium-ion battery and the lithium-ion battery further include a separator, and the separator is selected from: PP, modified PP, PE, glass fiber, polyimide, etc.

[0020] Preferably, the operating temperature of the sodium-ion battery is 80-150 °C.

[0021] According to a preferred embodiment of the present invention, the sodium-ion battery uses hard carbon as the negative electrode material and Na 3 V 2 (PO 4 ) 3 as the positive electrode material, and uses a polyimide separator. This battery exhibits advantages such as high capacity, high efficiency, and high safety. By selecting the NaFSI–KFSI molten salt electrolyte and preferably the high-capacity positive electrode material Na 3 V 2 (PO 4 ) 3 and the high-capacity hard carbon negative electrode material, a molten salt hard carbon||Na 3 V 2 (PO 4 ) 3 sodium-ion battery can be constructed. This electrolyte has high thermal stability and non-flammability, and the constructed sodium-ion battery exhibits excellent electrochemical performance, including advantages such as high capacity, high energy density, high safety, and low self-discharge.

[0022] According to another preferred embodiment of the present invention, the sodium-ion battery uses hard carbon as the negative electrode material and Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) as the positive electrode material. The Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) positive electrode material has a lower cost compared to the Na 3 V 2 (PO 4 ) 3 positive electrode material, and the Fe raw material is more environmentally friendly and non-toxic compared to the vanadium raw material.

[0023] The present invention aims to solve the problems and challenges existing in liquid sodium-ion batteries and all-solid-state sodium-ion batteries and improve the electrochemical performance of sodium-ion batteries. A NaFSI-KFSI molten salt electrolyte prepared by mixing NaFSI and KFSI in a molar ratio of 56:44 is screened. It should be understood that this molar ratio is limited to the unique value of 56:44, which is determined by the phase diagram. This ratio directly determines the melting point of the electrolyte. If other ratios are used, it will inevitably lead to changes in the melting point, and further lead to changes in ionic conductivity, ion transference number, and activation energy, thus unable to achieve the technical effects of the present invention.

[0024] Among them, the full Chinese name of NAFSI is Sodium Bis(fluorosulfonyl)imide, CAS: 100669-96-3, chemical formula: F 2 NNaO 4 S 2 。The Chinese name of KFSI is potassiumbis(fluoromethanesulfonyl)imide, chemical formula: KN(SO 2 F) 2 。

[0025] Aiming at the problems and challenges existing in current organic liquid electrolyte-based sodium-ion batteries and all-solid-state sodium-ion batteries, the present invention uses pure salt as the electrolyte. This electrolyte is prepared by mixing NaFSI and KFSI in a molar ratio of 56:44. It is solid at room temperature and becomes liquid when the temperature rises to 80 °C, showing very high sodium ionic conductivity and sodium ion transference number. Since it does not contain organic solvents, the safety of the sodium-ion battery constructed according to the present invention is greatly improved. At 80 °C, NaFSI:KFSI becomes liquid, ensuring high sodium ionic conductivity and high sodium ion transference number of the electrolyte. The molten salt sodium-ion battery constructed thereby exhibits good electrochemical performance, including high working voltage, high energy density, high safety, high-temperature characteristics, and good cycle stability.

[0026] Compared with the prior art, the present invention has the following significant advantages:

[0027] Compared with liquid electrolytes, the NaFSI and KFSI mixed molten salt electrolyte does not use organic solvents, and the safety is greatly improved;

[0028] Compared with solid electrolytes, the NaFSI and KFSI mixed molten salt electrolyte has no interface problems, high ionic conductance, and low interface impedance;

[0029] The NaFSI and KFSI mixed molten salt system is applied to sodium-ion batteries, and the molar ratio of NaFSI:KFSI is 56:44. Compared with using ionic liquids, the salts used have the advantage of low cost;

[0030] According to a preferred embodiment of the present invention, the positive and negative electrode materials of the sodium-ion battery adopt Na 3 V 2 (PO 4 ) 3 positive electrode material and hard carbon negative electrode material. Compared with the reported Na-Zn alloy negative electrode, hard carbon has low cost. Compared with the NaCrO 2 positive electrode material, Na 3 V 2 (PO 4 ) 3 positive electrode has a higher energy density;

[0031] In addition to the above molten salt electrolyte, other salts can be added to the NaFSI and KFSI mixed molten salt electrolyte, including CsFSI, etc., which can further reduce the melting point and improve the performance;

[0032] In the NaFSI and KFSI mixed molten salt electrolyte, in addition to using Na 3 V 2 (PO 4 ) 3 positive electrode and hard carbon negative electrode, sodium iron pyrophosphate positive electrode material and layered oxide positive electrode material can also be used. The negative electrode can adopt alloying negative electrodes including Sn, Bi, Sb, etc. and their alloys, or carbon-based composite materials.

[0033] In summary, according to the present invention, a sodium-ion battery based on a molten salt electrolyte is provided. The sodium-ion battery uses a solid NaFSI∶KFSI molten salt with a molar ratio of 56:44 as the NaFSI-KFSI molten salt electrolyte. This molten salt electrolyte is solid at room temperature and becomes liquid when the temperature rises to 80 °C, ensuring that the sodium-ion battery has high sodium-ion conductivity and high sodium-ion transference number. The sodium-ion battery constructed based on this molten salt electrolyte shows many advantages compared with the sodium-ion battery constructed with traditional organic solvent electrolytes and all-solid-state sodium-ion batteries, including high working voltage, high energy density, high safety, high-temperature characteristics, and good cycle stability. At the same time, this battery maintains a very high storage life at room temperature and is a sodium-ion battery with very promising applications. Brief Description of the Drawings

[0034] Figure 1 Shows the hard carbon||Na constructed according to Example 1 of the present invention 3 V 2 (PO 4 ) 3Charge and discharge curves of molten salt sodium-ion batteries. Detailed implementation manners

[0035] The following further describes the present invention in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional operations in the art or experimental methods recommended by instrument and equipment manufacturers. The reagents and materials used in the embodiments can be obtained from commercial sources unless otherwise specified.

[0036] Example 1:

[0037] Construct hard carbon || Na 3 V 2 (PO 4 ) 3 Molten salt sodium-ion battery. Using commercial hard carbon as the negative electrode material, a slurry is prepared by mixing hard carbon, conductive agent Super P, and binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the negative electrode material is obtained. Using commercial Na 3 V 2 (PO 4 ) 3 as the positive electrode material, a slurry is prepared by mixing Na 3 V 2 (PO 4 ) 3 , conductive agent Super P, and binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the positive electrode material is obtained. Using a NaFSI∶KFSI solid molten salt with a molar ratio of 56:44 as the electrolyte.

[0038] The battery is assembled in a glove box (with water and oxygen values less than 0.5 ppm), and the temperature is maintained at 80 °C during assembly (the range can be 80 - 150 °C). The mass of the molten salt electrolyte is 150 mg. A PP separator is used. Assembled into a hard carbon || Na 3 V 2 (PO 4 ) 3 battery, and cycled at 80 °C. Its charge and discharge curves are as Figure 1 shown. Its electrochemical performance is shown in Table 1, including working voltage, energy density, cycle life, and working temperature.

[0039] Example 2:

[0040] Construct Li 4 Ti 5 O 12 ||Na 3 V 2(PO 4 ) 3 Molten salt sodium-ion battery. Using commercial Li 4 Ti 5 O 12 as the negative electrode material, Li 4 Ti 5 O 12 , conductive agent Super P, and binder sodium alginate are mixed in a mass ratio of 90:5:5 to prepare a slurry, which is then coated on an Al current collector, and after drying, rolling, cutting, and weighing, the negative electrode material is obtained. Using commercial Na 3 V 2 (PO 4 ) 3 as the positive electrode material, Na 3 V 2 (PO 4 ) 3 , conductive agent Super P, and binder PVDF are mixed in a mass ratio of 90:5:5 to prepare a slurry, which is then coated on an Al current collector, and after drying, rolling, cutting, and weighing, the positive electrode material is obtained. Using a NaFSI∶KFSI solid molten salt with a molar ratio of 56:44 as the electrolyte.

[0041] The battery is assembled in a glove box (with water and oxygen values less than 0.5 ppm), and the temperature is maintained at 80 °C during assembly. The mass of the molten salt electrolyte is 150 mg. A PP separator is used. Assembled into a Li 4 Ti 5 O 12 ||Na 3 V 2 (PO 4 ) 3 battery, and cycled at 80 °C. Its electrochemical performance is shown in Table 1, including working voltage, energy density, cycle life, and working temperature.

[0042] The difference between Example 2 and Example 1 is that commercial Li 4 Ti 5 O 12 negative electrode material is used to replace the commercial hard carbon negative electrode material, which shows that the negative electrode material of the molten salt sodium-ion battery of the present invention is not limited to the hard carbon negative electrode, but can also be Li 4 Ti 5 O 12 negative electrode material. Moreover, the sodium-ion intercalation potential of the Li 4 Ti 5 O 12 negative electrode is higher than that of the hard carbon negative electrode, there is no risk of sodium deposition, and theoretically the safety is extremely high.

[0043] Example 3:

[0044] Constructing hard carbon||Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) molten salt sodium-ion battery. Using commercial hard carbon as the negative electrode material, a slurry is prepared by mixing hard carbon, conductive agent Super P, and binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the negative electrode material is obtained. Using commercial Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) as the positive electrode material, a slurry is prepared by mixing Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 )、conductive agent Super P, and binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the positive electrode material is obtained. Using a NaFSI∶KFSI solid molten salt with a molar ratio of 56:44 as the electrolyte.

[0045] The battery assembly is carried out in a glove box (with water and oxygen values less than 0.5 ppm), and the temperature is maintained at 80 °C during assembly. The mass of the molten salt electrolyte is 150 mg. A PP separator is used. Assembled into a hard carbon||Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) battery, and cycled at 80 °C. Its electrochemical performance is shown in Table 1, including working voltage, energy density, cycle life, and working temperature.

[0046] The difference between Example 3 and Example 1 is that commercial Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) positive electrode material is used to replace the commercial Na 3 V 2 (PO 4 ) 3 positive electrode material, thus indicating that the positive electrode material of the molten salt sodium-ion battery of the present invention is not limited to Na 3 V 2 (PO4 ) 3 Positive electrode material, Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) The positive electrode material is also acceptable, and Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) Compared with the Na 3 V 2 (PO 4 ) 3 positive electrode material, the Fe-based raw material is more environmentally friendly and non-toxic compared with the vanadium-based raw material, and the cost of the positive electrode material is lower.

[0047] Example 4:

[0048] Construct a hard carbon || Na 3 V 2 (PO 4 ) 3 molten salt sodium-ion battery. Using commercial hard carbon as the negative electrode material, a slurry is prepared by mixing hard carbon, conductive agent Super P, and binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the negative electrode material is obtained. Using commercial Na 3 V 2 (PO 4 ) 3 as the positive electrode material, a slurry is prepared by mixing Na 3 V 2 (PO 4 ) 3 , conductive agent Super P, and binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the positive electrode material is obtained. Using a NaFSI∶KFSI solid molten salt with a molar ratio of 56:44 + 10% mass ratio CsFSI additive as the electrolyte.

[0049] The battery assembly is carried out in a glove box (the water and oxygen values are less than 0.5 ppm), and the temperature is maintained at 80 °C during assembly (the range can be 80 - 150 °C). The mass of the molten salt electrolyte is 150 mg. A PP separator is used. Assembled into a hard carbon || Na 3 V 2 (PO 4 ) 3 battery, and cycling is carried out at 80 °C. Its electrochemical performance is shown in Table 1, including the working voltage, energy density, cycle life, and working temperature.

[0050] The difference between Example 4 and Example 1 lies in that a 10% mass ratio of CsFSI additive is added to the NaFSI:KFSI solid molten salt with a molar ratio of 56:44. This shows that the molten salt electrolyte of the molten salt sodium-ion battery of the present invention is not limited to NaFSI:KFSI. Based on the main salts of NaFSI:KFSI, some other salts can also be added, such as the CsFSI additive. The addition of CsFSI can improve the cycle stability of the battery. The reason is that the addition of cesium changes the microstructure of the electrolyte, regulates the solid electrolyte interface characteristics, stabilizes the interface, and improves the performance.

[0051] Example 5:

[0052] Construct hard carbon||Na 3 V 2 (PO 4 ) 3 molten salt sodium-ion battery. Using commercial hard carbon as the negative electrode material, a slurry is prepared by mixing hard carbon, conductive agent Super P, and binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the negative electrode material is obtained. Using commercial Na 3 V 2 (PO 4 ) 3 as the positive electrode material, a slurry is prepared by mixing Na 3 V 2 (PO 4 ) 3 , conductive agent Super P, and binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the positive electrode material is obtained. Using a NaFSI:KFSI solid molten salt with a molar ratio of 56:44 as the electrolyte.

[0053] The battery is assembled in a glove box (with water and oxygen values less than 0.5 ppm), and the temperature is maintained at 80 °C during assembly (the range can be 80 - 150 °C). The mass of the molten salt electrolyte is 150 mg. A polyimide separator is used. Assembled into a hard carbon||Na 3 V 2 (PO 4 ) 3 battery, and cycled at 80 °C. Its electrochemical performance is shown in Table 1, including working voltage, energy density, cycle life, and working temperature.

[0054] The difference between Example 5 and Example 1 lies in that a polyimide separator is used instead of a PP separator, which shows that the separator of the molten salt sodium-ion battery of the present invention is not limited to the PP separator. Due to the high temperature involved, the separator can also be a heat-resistant polyimide separator (PI separator), and even a modified PP separator is also possible. It is found through comparison that the polyimide separator can work in this system, but in the future, the polyimide separator can be used under higher temperature conditions.

[0055] Example 6:

[0056] Construct a hard carbon || Na 3 V 2 (PO 4 ) 3 molten salt sodium-ion battery. A slurry is prepared by mixing a commercial hard carbon negative electrode material, a conductive agent Super P, and a binder PVDF in a mass ratio of 90:5:5, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the negative electrode material is obtained. Using a commercial Na 3 V 2 (PO 4 ) 3 as the positive electrode material, a conductive agent Super P, and a binder PVDF are mixed in a mass ratio of 90:5:5 to prepare a slurry, and then coated on an Al current collector. After drying, rolling, cutting, and weighing, the positive electrode material is obtained. A solid molten salt of NaFSI∶KFSI with a molar ratio of 56:44 + 10% by mass of CsFSI additive is used as the electrolyte.

[0057] The battery is assembled in a glove box (with water and oxygen values less than 0.5 ppm), and the temperature is maintained at 80 °C during assembly (the range can be 80 - 150 °C). The mass of the molten salt electrolyte is 150 mg. A polyimide separator is used. Assembled into a hard carbon || Na 3 V 2 (PO 4 ) 3 battery, and cycled at 120 °C. Its electrochemical performance is shown in Table 1, including the working voltage, energy density, cycle life, and working temperature.

[0058] The difference between Example 6 and Example 1 lies in that a 10% by mass ratio of CsFSI additive is added to the solid molten salt of NaFSI∶KFSI with a molar ratio of 56:44, and at the same time, a polyimide separator is used instead of a PP separator, enabling the battery to work stably at a high temperature of 120 °C.

[0059] Table 1 Molten salt sodium-ion batteries using different negative electrodes, electrolytes, positive electrodes, separators, and temperatures

[0060] In summary, the present invention provides a sodium-ion battery based on a molten salt electrolyte. The battery uses a solid molten salt NaFSI:KFSI as the electrolyte. At room temperature, this binary mixed molten salt is solid, and when the temperature rises to 80 °C, this binary mixed molten salt becomes liquid, thus ensuring its high sodium-ion conductivity and high sodium-ion transference number. Compared with sodium-ion batteries constructed with traditional organic solvent electrolytes and all-solid-state sodium-ion batteries, the sodium-ion battery constructed based on this molten salt exhibits many advantages, including high working voltage, high energy density, high safety, high-temperature characteristics, and good cycle stability. At the same time, the battery maintains a very high storage life at room temperature.

[0061] The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Various changes can be made to the above embodiments of the present invention. All simple, equivalent changes and modifications made according to the claims and the content of the specification of the present invention application fall within the scope of the claims of the present invention patent. What is not described in detail in the present invention is conventional technical content.

Claims

1. A sodium ion battery based on molten salt electrolyte, characterized in that: The sodium ion battery uses NaFSI:KFSI solid molten salt with a molar ratio of 56:44 as NaFSI-KFSI molten salt electrolyte. The NaFSI-KFSI molten salt electrolyte is solid at room temperature and becomes liquid when the temperature rises to 80°C, thereby ensuring that the sodium ion battery has high sodium ion conductivity and high sodium ion migration number.

2. The sodium ion battery based on molten salt electrolyte according to claim 1, characterized in that: The positive electrode material is selected from: polyanion positive electrode, layered oxide positive electrode, Prussian blue / white.

3. The sodium ion battery based on molten salt electrolyte according to claim 1, characterized in that: The negative electrode material is selected from: hard carbon, layered oxides, and alloy compounds.

4. The sodium ion battery based on molten salt electrolyte according to claim 1, characterized in that: The NaFSI-KFSI molten salt electrolyte also includes other salts with a content of 0-20wt%, and the salt is selected from at least one of CsFSI, LiPF6, LiBF4, KPF6, and KBF4.

5. The sodium ion battery based on molten salt electrolyte according to claim 4, characterized in that: The NaFSI-KFSI molten salt electrolyte further includes CsFSI in an amount of 10 wt %.

6. The sodium ion battery based on molten salt electrolyte according to claim 1, characterized in that: The lithium-ion battery further comprises a separator, and the separator is selected from: PP, modified PP, PE, glass fiber, and polyimide.

7. The sodium ion battery based on molten salt electrolyte according to claim 1, characterized in that: The operating temperature of the sodium ion battery is 80-150°C.

8. The sodium ion battery based on molten salt electrolyte according to claim 1, characterized in that: The sodium ion battery uses hard carbon as the negative electrode material, Na3V2(PO4)3 as the positive electrode material, and a polyimide separator.

9. The sodium ion battery based on molten salt electrolyte according to claim 1, characterized in that: The sodium ion battery uses hard carbon as a negative electrode material, Na4Fe3(PO4)2(P2O7) as a positive electrode material, and a polyimide separator.

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