Sodium-ion battery electrolyte suitable for ultralow-temperature charging

Abstract

The invention relates to the technical field of sodium-ion battery electrolyte preparation, in particular to an electrolyte suitable for ultralow-temperature charging. The low-temperature electrolyte comprises a sodium salt, a non-aqueous solvent and a film-forming additive, the low-temperature electrolyte comprises the following components in percentage by mass: 10%-30% of sodium salt, 10%-30% of a nitrile solvent, 30%-80% of a chain carboxylic ester solvent and 1%-10% of a film-forming additive. Compared with the traditional electrolyte, the electrolyte disclosed by the invention has the advantages that the capacity retention rate can reach 56.6% at-40 DEG C, the capacity retention rate can reach 77.9% at-30 DEG C, and the capacity retention rate can reach 89.1% at-20 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery electrolyte preparation, and in particular to the preparation and application of an electrolyte suitable for ultra-low temperature charging. Background Art

[0002] As an ideal candidate for the next generation of large-scale energy storage technology, sodium-ion batteries have attracted widespread attention from the industry due to their cost advantages. However, their performance in practical applications is severely limited by geographical environmental factors. Under certain extreme conditions, the low-temperature performance problems faced by sodium-ion batteries have become an urgent technical obstacle, which urgently needs major technological innovations to overcome. Under low-temperature conditions, the electrochemical reaction kinetics of SIBs slow down significantly, the stability of the electrode-electrolyte interface is challenged, and the diffusion rate of sodium ions in the electrode material is reduced, which together lead to the decline of the overall performance of the battery. Therefore, optimizing the low-temperature performance of sodium-ion batteries and rationally designing and optimizing the electrolyte system and electrode materials have become a crucial task, which has far-reaching significance for promoting their widespread application. Therefore, from the perspective of improving the safety and cycle life of sodium-ion batteries, improving the low-temperature charging performance of sodium-ion batteries is of great significance, but the current research on low-temperature charging of sodium-ion batteries is obviously lagging behind. Summary of the invention

[0003] The object of the present invention is to provide an electrolyte suitable for ultra-low temperature charging, thereby solving the problems existing in the above-mentioned technology.

[0004] In order to solve the problem that sodium ion batteries are difficult to charge normally at low temperatures, the technical solution adopted by the present invention is as follows:

[0005] The present invention discloses an electrolyte suitable for ultra-low temperature charging, which includes a sodium salt, a non-aqueous solvent and a film-forming additive; wherein the non-aqueous solvent is composed of one of the nitrile substances shown in the following formula I and one or more of the chain carboxylic acid esters shown in the following formula II.

[0006]

[0007] Preferably, in terms of mass percentage, the sodium salt in the low-temperature electrolyte is 10% to 30%, the nitrile solvent is 10% to 30%, the chain carboxylic acid ester solvent is 30% to 80%, and the film-forming additive is 1% to 10%.

[0008] Further preferably, the low temperature electrolyte comprises sodium salt, non-aqueous solvent and film-forming additive, wherein, by weight percentage, sodium salt is 15% to 20%, nitrile solvent is 15% to 20%, and chain carboxylic acid ester solvent is 40% to 70%.

[0009] 0%, and film-forming additives are 1% to 8%.

[0010] Preferably, the sodium salt is selected from one or more of sodium tetrafluoroborate, sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide.

[0011] More preferably, the sodium salt is selected from bis(fluorosulfonyl)imide sodium salt.

[0012] Preferably, the film-forming additive is one or more of methyl (3-(methylsulfonyl)propyl) carbonate, 3-(methylsulfonyl)propyl acetate, 2-(methylsulfonyl)ethyl carbonate isopropyl (2-(methylsulfonyl)ethyl) carbonate, and ethyl 3 (methylsulfonyl)propyl) carbonate, and its chemical formula is shown in Formula III below.

[0013]

[0014] More preferably, the content of methyl (3-(methylsulfonyl)propyl) carbonate in the film-forming additive is controlled at 2% to 5%.

[0015] The beneficial effects of the present invention are as follows: the low-temperature electrolyte suitable for ultra-low-temperature charging of sodium ion batteries disclosed in the present invention comprises a sodium salt, a non-aqueous solvent and a film-forming additive, wherein the non-aqueous solvent comprises a nitrile substance and one or more chain carboxylate substances. Compared with the traditional electrolyte, the electrolyte of the present invention can achieve a capacity retention rate of 56.6% at -40 degrees Celsius, a capacity retention rate of 77.9% at -30 degrees Celsius, and a capacity retention rate of 89.1% at -20 degrees Celsius. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the capacity-voltage curve of Example 1 of the present invention at -40°C and 0.2c.

[0017] Figure 2 This is the capacity-voltage curve of Example 1 of the present invention at -30°C and 0.2C.

[0018] Figure 3 This is the capacity-voltage curve of Example 1 of the present invention at -20°C and 0.2C. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] Example 1

[0021] A sodium ion battery electrolyte, in a standard glove box, is filled with high-purity argon gas (water, oxygen content ≤1 pp m), butyronitrile (AN) and ethyl acetate (EA) are used as non-aqueous solvents, sodium bis(fluorosulfonyl)imide (NaFSI) is used as sodium salt, and methyl (3-(methylsulfonyl)propyl) carbonate and 3-(methylsulfonyl)propyl acetate are used as film-forming additives. The preparation method is as follows: 4.5 g of butyronitrile and 19.5 g of ethyl acetate (EA) are mixed, and then 0.9 g of methyl (3-(methylsulfonyl)propyl) carbonate, 0.6 g of 3-(methylsulfonyl)propyl acetate, and 4.5 g of sodium bis(fluorosulfonyl)imide (NaFSI) are added to the solution, and the mixture is stirred evenly to obtain a low-temperature electrolyte NB666.

[0022] The above-configured NB666 was used as the electrolyte, sodium nickel iron manganese oxide was used as the positive electrode, and hard carbon was used as the negative electrode to configure a 1.1Ah soft-pack battery for electrochemical testing. Figure 1 The capacity-voltage curve of this type of electrolyte at -40°C is shown. When discharged at a constant current of 0.2c, its charging capacity is 56.6% of its normal temperature capacity. Its -30°C low temperature capacity-voltage curve is shown in Figure 1. Figure 2 As shown, at a constant current discharge of 0.2c, the NB666 electrolyte can release 77.9% of its room temperature capacity at a low temperature of -30°C. Figure 3 The -20°C capacity-voltage curve of NB666 electrolyte is shown, with a capacity retention of 89.1%.

[0023] Example 2

[0024] A sodium ion battery electrolyte, in a standard glove box, after high-purity argon gas is filled (water, oxygen content ≤1 pp m), butyronitrile (AN) and chain carboxylic acid ester are used as non-aqueous solvents, sodium tetrafluoroborate is used as sodium salt, and methyl (3-(methylsulfonyl) propyl) carbonate and ethyl 3 (methylsulfonyl) propyl) carbonate are used as film-forming additives. The preparation method is as follows: 5.0 g of butyronitrile and 18.0 g of chain carboxylic acid ester are mixed, and then 0.8 g of methyl (3-(methylsulfonyl) propyl) carbonate, 0.5 g of ethyl 3 (methylsulfonyl) propyl) carbonate, and 10.0 g of sodium tetrafluoroborate are added to the solution, and the mixture is stirred evenly to obtain a low-temperature electrolyte NB667.

[0025] The above-configured NB667 was used as the electrolyte, sodium nickel iron manganese oxide was used as the positive electrode, and hard carbon was used as the negative electrode. A 1.1Ah soft-pack battery was configured for electrochemical testing. At -40°C, the discharge capacity was 55.5% of the normal temperature capacity at a constant current of 0.2c. At -30°C, the discharge capacity was 75.1% of the normal temperature capacity at a constant current of 0.2c. At -20°C, the capacity was maintained at 88.3%.

[0026] Example 3

[0027] A sodium ion battery electrolyte, in a standard glove box, after high-purity argon gas is filled (water, oxygen content ≤ 1ppm), butyronitrile (AN) and ethyl acetate (EA) are used as non-aqueous solvents, sodium bis(trifluoromethylsulfonyl)imide is used as sodium salt, and 3-(methylsulfonyl)propyl acetate and 2-(methylsulfonyl)ethyl carbonate isopropyl (2-(methylsulfonyl)ethyl) carbonate are used as film-forming additives. The preparation method is as follows: 6.5g butyronitrile and 17.5g ethyl acetate (EA) are mixed, and then 1.0g 3-(methylsulfonyl)propyl acetate, 0.7g 2-(methylsulfonyl)ethyl carbonate isopropyl (2-(methylsulfonyl)ethyl) carbonate, 4.0g sodium bis(trifluoromethylsulfonyl)imide are added to the solution, and the mixture is stirred evenly to obtain a low-temperature electrolyte NB668.

[0028] The above-configured NB668 was used as the electrolyte, sodium nickel iron manganese oxide was used as the positive electrode, and hard carbon was used as the negative electrode. A 1.1Ah soft-pack battery was configured for electrochemical testing. At -40°C, the discharge capacity was 56.2% of the normal temperature capacity at a constant current of 0.2c. At -30°C, the discharge capacity was 76.3% of the normal temperature capacity at a constant current of 0.2c. At -20°C, the capacity remained at 86.2%.

Claims

1. An electrolyte suitable for ultra-low temperature charging, characterized in that: The electrolyte comprises a sodium salt, a non-aqueous solvent and a film-forming additive; wherein the non-aqueous solvent is composed of one of the nitrile substances shown in the following formula I and one or more of the chain carboxylic acid esters shown in the following formula II:

2. The electrolyte suitable for ultra-low temperature charging according to claim 1, characterized in that: The electrolyte comprises sodium salt, non-aqueous solvent and film-forming additive, wherein, by mass percentage, sodium salt is 10% to 30%, nitrile solvent is 10% to 30%, chain carboxylic acid ester solvent is 30% to 80%, and film-forming additive is 1% to 10%.

3. The electrolyte suitable for ultra-low temperature charging according to claim 2, characterized in that: The electrolyte comprises sodium salt, non-aqueous solvent and film-forming additive, wherein, by mass percentage, sodium salt is 15% to 20%, nitrile solvent is 15% to 20%, chain carboxylic acid ester solvent is 40% to 70%, and film-forming additive is 1% to 8%.

4. An electrolyte suitable for ultra-low temperature charging according to claim 1 or 2, characterized in that: The sodium salt is selected from one or more of sodium tetrafluoroborate, sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide.

5. The electrolyte suitable for ultra-low temperature charging according to claim 4, characterized in that: The sodium salt is selected from bis(fluorosulfonyl)imide sodium salt.

6. An electrolyte suitable for ultra-low temperature charging according to claim 1 or 2, characterized in that: The film-forming additive is one or more of methyl (3-(methylsulfonyl)propyl) carbonate, 3-(methylsulfonyl)propyl acetate, 2-(methylsulfonyl)ethyl carbonate isopropyl (2-(methylsulfonyl)ethyl) carbonate, and ethyl 3 (methylsulfonyl)propyl) carbonate, and its chemical formula is shown in the following formula III:

7. The electrolyte suitable for ultra-low temperature charging according to claim 6, characterized in that: The content of methyl (3-(methylsulfonyl)propyl) carbonate in the film-forming additive is controlled at 2% to 5%.

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