Low-temperature sodium ion electrolyte with flame retardant property and sodium ion battery

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a low-temperature sodium ion electrolyte with flame retardant property and a sodium ion battery. The low-temperature sodium ion electrolyte comprises a sodium salt, a short-chain linear carboxylic ester compound, a phosphazene compound and an additive, the volume ratio of the short-chain linear carboxylic ester compound to the phosphazene compound is (0.5-10): 1; according to the invention, the short-chain linear carboxylic ester compound and the phosphazene compound are used as the sodium-ion electrolyte solvent according to a certain proportion to be applied to a sodium-ion battery system, so that stable work of the sodium-ion battery at a low temperature is ensured, combustion can be effectively isolated, and the safety of the sodium-ion battery operating under a low-temperature working condition is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion batteries, and in particular relates to a low-temperature sodium ion electrolyte with flame retardancy and a sodium ion battery. Background Art

[0002] The use of fossil energy has caused environmental pollution and other problems, and the development and utilization of new energy is imminent. However, new energy has the problems of spatial imbalance and temporal instability. The application of chemical energy storage batteries provides an important premise for the large-scale use of renewable energy. Sodium resources are abundant, cheap and non-toxic, and sodium-ion batteries have the same structure and working principle as lithium-ion batteries. They are considered to be an ideal choice to replace lithium-ion batteries in the future in areas such as large-scale energy storage. However, although sodium-ion batteries have broad prospects, once they are operated under low-temperature conditions, the capacity and power of the battery are often severely reduced. Usually, a large amount of solvents with low melting points and high saturated vapor pressure are used in low-temperature electrolytes, so that the electrolyte as a whole will not solidify under low-temperature conditions and can still remain liquid. However, this type of solvent also has a lower boiling point, has a higher risk of combustion and explosion, and increases safety hazards. Therefore, it is crucial to develop flame-retardant or non-flammable low-temperature sodium-ion electrolytes. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a low-temperature sodium ion electrolyte with flame retardant properties to improve the safety of sodium ion batteries operating under low-temperature working conditions.

[0004] The invention provides a low-temperature sodium ion electrolyte with flame retardant properties. The low-temperature sodium ion electrolyte comprises sodium salt, short-chain linear carboxylic acid ester compounds, phosphazene compounds and additives; the volume ratio of the short-chain linear carboxylic acid ester compounds to the phosphazene compounds is 0.5-10:1.

[0005] Preferably, the sodium salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide and sodium tetrafluoroborate.

[0006] Preferably, based on the total mass of the electrolyte, the concentration of the sodium salt is 0.1-1.5 mol / L.

[0007] Preferably, based on the total mass of the electrolyte, the concentration of the sodium salt is 0.3-0.8 mol / L.

[0008] Preferably, the short-chain linear carboxylic acid ester compound includes one or more of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate and methyl butyrate.

[0009] Preferably, the phosphazene compound includes one or more of perfluorocyclotriphosphazene, methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, n-propoxypentafluorocyclotriphosphazene, isopropyloxypentafluorocyclotriphosphazene and phenoxypentafluorocyclotriphosphazene.

[0010] Preferably, the volume ratio of the short-chain linear carboxylic acid ester compound to the phosphazene compound is 1-4:1.

[0011] Preferably, the additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, and sodium difluorooxalatoborate.

[0012] Preferably, based on the total mass of the electrolyte, the mass percentage content of the fluoroethylene carbonate is 0% to 10%, the mass percentage content of vinylene carbonate is 0% to 3%, the mass percentage content of 1,3-propane sultone is 0% to 3%, the mass percentage content of vinyl sulfate is 0% to 3%, and the mass percentage content of sodium difluorooxalatoborate is 0% to 3%.

[0013] The present invention also provides a sodium ion battery, which includes the low-temperature sodium ion electrolyte described in the above technical solution.

[0014] Beneficial effects of the present invention: The present invention uses short-chain linear carboxylic acid ester compounds with low melting point, low viscosity, high ionic conductivity and low cost as the main solvent, which can effectively improve the overall low-temperature performance of the electrolyte. At the same time, phosphazene compounds with high vapor pressure and high flame retardant efficiency are used as diluents with flame retardant function, which can effectively inhibit the combustion of the electrolyte while ensuring the overall low-temperature performance of the electrolyte, thereby achieving high-efficiency flame retardancy.

[0015] In the diluent of the present invention, the phosphazene compound has a non-solvation property, which can prevent the co-embedding of the solvent and cause the destruction of the negative electrode structure; in addition, the solid electrolyte interface film (SEI) derived from the electrolyte containing the phosphazene compound is rich in NaF, which can prevent the decomposition of the solvent and further enhance the stability of the electrolyte.

[0016] The short-chain linear carboxylic acid ester main solvent and the phosphazene diluent are combined to form a diluted high-concentration electrolyte, so that the electrolyte can still show higher conductivity and lower viscosity at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 This is a photo of the PP diaphragm soaked with the sodium ion battery electrolyte prepared in Example 4 before ignition; Figure 2 This is a photo of the PP diaphragm soaked with the sodium ion battery electrolyte prepared in Example 4 after being ignited; Figure 3 The specific discharge capacity and charge-discharge efficiency of the sodium ion battery electrolyte prepared in Example 2 after being assembled into a sodium ion layered oxide positive electrode full battery; Figure 4 The specific discharge capacity and charge-discharge efficiency of the sodium ion battery electrolyte prepared in Example 4 after being assembled into a sodium ion layered oxide positive electrode full battery; Figure 5 The discharge curves of the sodium ion battery electrolyte prepared in Example 4 at 0.2C at 25°C and -20°C after being assembled into a sodium ion layered oxide positive electrode full battery; Figure 6 The discharge curves of the sodium ion battery electrolyte prepared in Example 6 at 0.2C at 25°C and -20°C after being assembled into a sodium ion layered oxide positive electrode full battery; Figure 7 The discharge curves of the sodium ion battery electrolyte prepared in Comparative Example 2 at 0.2C at 25°C and -20°C respectively after being assembled into a sodium ion layered oxide positive electrode full battery. DETAILED DESCRIPTION

[0019] The invention provides a low-temperature sodium ion electrolyte with flame retardant properties. The low-temperature sodium ion electrolyte comprises sodium salt, short-chain linear carboxylic acid ester compounds, phosphazene compounds and additives; the volume ratio of the short-chain linear carboxylic acid ester compounds to the phosphazene compounds is 0.5-10:1.

[0020] In the present invention, the volume ratio of the short-chain linear carboxylic acid ester compound to the phosphazene compound is 0.5 to 10: 1, more preferably 1 to 4: 1, and more preferably 1: 1 or 2: 1 or 4: 1. The present invention applies the short-chain linear carboxylic acid ester compound and the phosphazene compound as sodium ion electrolyte solvents in a certain ratio to the sodium ion battery system, which can stably work at low temperatures and isolate combustion, thereby significantly improving the safety of the sodium ion battery operating under low temperature working conditions.

[0021] The sodium salt of the present invention preferably includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide and sodium tetrafluoroborate; based on the total mass of the electrolyte, the concentration of the sodium salt is preferably 0.1-1.5 mol / L, and more preferably 0.3-0.8 mol / L. The present invention can optimize the kinetic performance of the sodium ion battery and reduce the cost by controlling the concentration of the sodium salt, while increasing the operating temperature window, enhancing the stability of the electrolyte and improving the low temperature performance, thereby improving the overall performance and application range of the sodium ion battery.

[0022] In the present invention, the short-chain linear carboxylic acid ester compound preferably includes one or more of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate and methyl butyrate; the phosphazene compound preferably includes one or more of perfluorocyclotriphosphazene, methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, n-propoxypentafluorocyclotriphosphazene, isopropyloxypentafluorocyclotriphosphazene and phenoxypentafluorocyclotriphosphazene.

[0023] The additive of the present invention comprises one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, and sodium difluorooxalate borate; based on the total mass of the electrolyte, the mass percentage content of the fluoroethylene carbonate is preferably 0% to 10%, the mass percentage content of vinylene carbonate is preferably 0% to 3%, the mass percentage content of 1,3-propane sultone is preferably 0% to 3%, the mass percentage content of vinyl sulfate is preferably 0% to 3%, and the mass percentage content of sodium difluorooxalate borate is preferably 0% to 3%.

[0024] The present invention also provides a sodium ion battery, which includes the low-temperature sodium ion electrolyte described in the above technical solution.

[0025] In the present invention, the sodium ion battery is preferably composed of a positive electrode plate, a separator, the low-temperature flame-retardant sodium ion electrolyte of the present invention, and a negative electrode plate.

[0026] The positive electrode sheet material of the present invention is preferably Prussian blue, polyanionic materials sodium vanadium phosphate and sodium iron pyrophosphate, and layered oxide NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 ; The separator is preferably glass fiber or polypropylene; the negative electrode plate material is preferably hard carbon.

[0027] The flame-retardant low-temperature sodium ion electrolyte provided by the present invention can maintain high ionic conductivity and low viscosity at low temperatures. It is verified by examples that a sodium ion battery assembled using the low-temperature sodium ion electrolyte also exhibits better capacity utilization. In addition, the low-temperature sodium ion electrolyte can also effectively isolate combustion, significantly improving the safety of sodium ion batteries operating under low-temperature conditions.

[0028] In order to further illustrate the present invention, a low-temperature sodium ion electrolyte with flame retardant properties and a sodium ion battery provided by the present invention are described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0029] The Chinese and English names of the nouns used in the embodiments of the present invention are as follows: Sodium hexafluorophosphate (NaPF 6 ), sodium difluorooxalatoborate (NaDFOB), methyl acetate (MA), propyl acetate (PA), ethoxypentafluorocyclotriphosphazene (PFPN), fluoroethylene carbonate (FEC), ethylene carbonate (EC), diethyl carbonate (DEC).

[0030] Example 1 In an argon-protected glove box (water content <1 ppm, oxygen content <1 ppm), MA and PFPN were mixed at a volume ratio of 2:1, and NaPF 6 , making the final concentration 0.6 mol / L, and then adding 5% FEC of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0031] Example 2 In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), MA and PFPN were mixed at a volume ratio of 4:1, and NaPF 6 , making the final concentration 0.6 mol / L, and then adding 5% FEC of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0032] Example 3 In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), PA and PFPN were mixed in a volume ratio of 1:1, and NaPF 6 , making the final concentration 0.6 mol / L, and then adding 5% FEC of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0033] Example 4 In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), PA and PFPN were mixed at a volume ratio of 2:1, and NaPF6 , making the final concentration 0.6 mol / L, and then adding 5% FEC of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0034] Example 5 In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), PA and PFPN were mixed at a volume ratio of 2:1, and NaPF 6 , making the final concentration 0.6 mol / L, and then adding 5% FEC and 1% NaDFOB of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0035] Example 6 In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), PA and PFPN were mixed at a volume ratio of 4:1, and NaPF 6 , making the final concentration 0.6 mol / L, and then adding 5% FEC of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0036] Example 7 In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), PA and PFPN were mixed at a volume ratio of 2:1, and NaPF 6 , making the final concentration 0.3 mol / L, and then adding 5% FEC of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0037] Comparative Example 1 In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), EC and DEC were mixed in a volume ratio of 1:1, and NaPF 6 , making the final concentration 0.6 mol / L, and then adding 5% FEC of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0038] Comparative Example 2 In an argon-protected glove box (water content <1ppm, oxygen content <1ppm), EC, DEC, and PFPN were mixed in a volume ratio of 2:2:1, and NaPF 6 , making the final concentration 0.6 mol / L, and then adding 5% FEC of the total mass of the electrolyte. After stirring evenly, the sodium ion battery electrolyte was obtained.

[0039] Test Example 1 The sodium ion layered oxide positive electrode full cells were assembled with the sodium ion battery electrolytes prepared in Examples 1 to 7, Comparative Example 1 and Comparative Example 2, and their performances were tested. The results are shown in Tables 1 and Figure 1~Figure 5 shown; Figure 1 and Figure 2 The following are photos of the PP diaphragm soaked in the sodium ion battery electrolyte prepared in Example 4 before and after ignition. Figure 3~Figure 7 The performance of the sodium ion battery electrolytes prepared in Example 4, Example 6 and Comparative Example 2 are demonstrated in turn.

[0040] Table 1 Performance test results of sodium ion battery electrolytes prepared in Examples 1 to 7, Comparative Examples 1 and 2 Depend on Figure 1 and Figure 2 It can be seen that after the PP diaphragm soaked with the sodium ion battery electrolyte prepared in Example 4 was ignited, only a small amount of smoke was generated, and the diaphragm did not deform.

[0041] Combination Figure 3~Figure 7 It can be seen that when charging and discharging at 0.2C at -20°C, the capacity retention of the sodium ion battery electrolyte in each embodiment is significantly higher than that in the comparative example. Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all embodiments. People can also obtain other embodiments based on this embodiment without inventiveness, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A low-temperature sodium ion electrolyte with flame retardancy, characterized in that: The low-temperature sodium ion electrolyte comprises sodium salt, short-chain linear carboxylic acid ester compound, phosphazene compound and additive; the volume ratio of the short-chain linear carboxylic acid ester compound to the phosphazene compound is 0.5-10:

1.

2. The low-temperature sodium ion electrolyte according to claim 1, characterized in that The sodium salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide and sodium tetrafluoroborate.

3. The low-temperature sodium ion electrolyte according to claim 1, characterized in that Based on the total mass of the electrolyte, the concentration of the sodium salt is 0.1-1.5 mol / L.

4. The low-temperature sodium ion electrolyte according to claim 3, characterized in that Based on the total mass of the electrolyte, the concentration of the sodium salt is 0.3-0.8 mol / L.

5. The low-temperature sodium ion electrolyte according to claim 1, characterized in that The short-chain linear carboxylic acid ester compound includes one or more of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate and methyl butyrate.

6. The low-temperature sodium ion electrolyte according to claim 1, characterized in that: The phosphazene compound includes one or more of perfluorocyclotriphosphazene, methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, n-propoxypentafluorocyclotriphosphazene, isopropyloxypentafluorocyclotriphosphazene and phenoxypentafluorocyclotriphosphazene.

7. The low-temperature sodium ion electrolyte according to claim 1, characterized in that The volume ratio of the short-chain linear carboxylic acid ester compound to the phosphazene compound is 1-4:

1.

8. The low-temperature sodium ion electrolyte according to claim 1, characterized in that The additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, and sodium difluorooxalatoborate.

9. The low-temperature sodium ion electrolyte according to claim 8, characterized in that Based on the total mass of the electrolyte, the mass percentage content of the fluoroethylene carbonate is 0% to 10%, the mass percentage content of vinylene carbonate is 0% to 3%, the mass percentage content of 1,3-propane sultone is 0% to 3%, the mass percentage content of vinyl sulfate is 0% to 3%, and the mass percentage content of sodium difluorooxalatoborate is 0% to 3%.

10. A sodium ion battery, characterized in that: The sodium ion battery comprises the low-temperature sodium ion electrolyte according to any one of claims 1 to 9.

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