Sodium ion battery low-temperature electrolyte and sodium ion battery

Abstract

This invention relates to the field of batteries, and more particularly to a low-temperature electrolyte for sodium-ion batteries, its preparation method, and sodium-ion batteries themselves. This invention uses a mixed solution of carboxylic esters, carbonates, and siloxanes as the main solvent for the sodium-ion battery electrolyte. Carboxylic ester solvents have low viscosity, which helps to improve the ionic conductivity of the electrolyte; carboxylic ester solvents also have a wide liquid temperature range, which can lower the freezing point of traditional carbonate electrolytes, thereby improving the low-temperature performance of the electrolyte; siloxane molecules have good thermal stability and electrochemical compatibility, which can improve the interfacial stability and cycle performance of sodium-ion batteries. This invention, by mixing carboxylic esters with carbonates and siloxanes, can maintain the excellent film-forming properties of the electrolyte, stabilize the electrolyte and electrodes, and further improve the low-temperature performance of the electrolyte.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a low-temperature electrolyte for sodium-ion batteries, a method for preparing the same, and sodium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, new energy vehicles, and large-scale energy storage, but their low-temperature performance has always been limited. At -20°C, the performance of commercial lithium-ion batteries decreases by about half; at -30°C, commercial lithium-ion batteries can hardly function properly. Therefore, developing new energy storage technologies that can meet the operating temperature requirements of -40°C or even lower is an urgent need.

[0003] Compared to lithium ions, sodium ions have a larger radius and weaker interactions with coordinating atoms, resulting in better kinetic performance. Therefore, sodium-ion batteries have a relative advantage over lithium-ion batteries in low-temperature environments. However, the interface reaction between conventional carbonate electrolytes and hard carbon anodes in sodium-ion batteries is intense, leading to low initial efficiency and rapid capacity screening. Developing advanced electrolyte systems to stabilize the electrolyte-anode interface and fully leverage the intrinsic advantages of sodium-ion batteries under low-temperature conditions is key to promoting their application in cold environments. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-temperature electrolyte for sodium-ion batteries, a method for preparing the same, and a sodium-ion battery.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A first aspect of the present invention is to provide a low-temperature electrolyte for sodium-ion batteries, comprising: a sodium salt, a carboxylic acid ester solvent, a carbonate solvent, a siloxane solvent, and an additive; wherein the volume ratio of the carboxylic acid ester solvent ranges from 20% to 50%, the volume ratio of the carbonate solvent ranges from 20% to 40%, the volume ratio of the siloxane solvent ranges from 10% to 30%, and the mass ratio of the additive is 1% to 10%.

[0007] Preferably, the carboxylic acid ester solvent includes at least one of the following: methyl formate, methyl acetate, ethyl acetate, butyl acetate, butyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, butyl butyrate, ethyl lactate, ethyl trifluoroacetate, methyl pentafluoropropionate, and γ-butyrolactone.

[0008] The carbonate solvents include at least one of the following: ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, and fluoroethylene carbonate.

[0009] The siloxane solvents include at least one of tetramethyl-1,3-dimethoxydisiloxane, 1,2-bis(trimethylsiloxy)ethane, dimethyldimethoxysilane, and polydimethylsiloxane.

[0010] Preferably, the sodium salt comprises at least one of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, sodium hexafluoroarsenate, and sodium bis(oxaloborate).

[0011] Preferably, the concentration of the sodium salt in the low-temperature electrolyte of the sodium-ion battery is 0.5–4 mol / L.

[0012] Preferably, the additive comprises at least one of the following: ethylene carbonate, maleic anhydride, biphenyl, 1,3-propanesulfonic acid lactone, dimethyl sulfate, trimethyl phosphate, vinyl sulfate, p-dimethylbenzoic acid, and tris(trimethylsilane) phosphate.

[0013] A second aspect of the present invention is to provide a method for preparing the above-mentioned low-temperature electrolyte for sodium-ion batteries, comprising the steps of mixing sodium salt, carboxylic acid ester solvent, carbonate solvent, siloxane solvent and additives in a certain proportion to obtain the low-temperature electrolyte for sodium-ion batteries.

[0014] A third aspect of the present invention is to provide a sodium-ion battery, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the electrolyte is the above-described low-temperature electrolyte for sodium-ion batteries or a low-temperature electrolyte for sodium-ion batteries prepared by the above-described preparation method.

[0015] Preferably, the active material in the positive electrode includes at least one of sodium vanadium phosphate, sodium iron phosphate, sodium nickel iron manganese phosphate, sodium vanadium phosphate, and sodium iron sulfate.

[0016] Preferably, the sodium-ion battery operates at a temperature of -50 to 60°C.

[0017] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0018] This invention uses a mixed solution of carboxylic esters, carbonates, and siloxanes as the main solvent for sodium-ion battery electrolytes. Carboxylic ester solvents have low viscosity, which helps improve the ionic conductivity of the electrolyte; they also have a wide liquid temperature range, lowering the freezing point of traditional carbonate electrolytes and thus improving the low-temperature performance of the electrolyte. Siloxane molecules have good thermal stability and electrochemical compatibility, which can improve the interfacial stability and cycle performance of sodium-ion batteries. Furthermore, carboxylic ester molecules are partially biodegradable, making them environmentally friendly. Compared to carboxylic ester molecules, carbonate molecules, especially cyclic carbonate molecules, generally have better film-forming properties. This invention, by mixing carboxylic esters with carbonates and siloxanes, can maintain the excellent film-forming properties of the electrolyte, stabilize the electrolyte and electrodes, and further improve the low-temperature performance of the electrolyte. In summary, the electrolyte used in this invention can effectively solidify the electrolyte at low temperatures, improving the rate performance and low-temperature performance of the battery. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0021] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0022] Example 1

[0023] This embodiment provides a low-temperature electrolyte for sodium-ion batteries, its preparation method, and a sodium-ion battery.

[0024] The raw materials are ethylene carbonate (EC), diethyl carbonate (DMC), ethyl acetate (EA), dimethyl dimethoxysilane (DMMS), NaFSI, and fluoroethylene carbonate (FEC); the concentration of NaFSI is 1 mol / L; and the mass ratio of FEC is 2%.

[0025] Preparation of sodium-ion battery electrolyte: After heating EC solvent, it is mixed with DMC in a certain proportion. Then, the EC / DMC solution is mixed with EA and ACN solvents in a certain proportion and stirred for 10 min. Then, NaFSI is dissolved in the mixed solvent, FEC additive is added, and the mixture is stirred for 10 h to obtain a sodium-ion battery low-temperature electrolyte.

[0026] Preparation of negative electrode sheet: Add appropriate amount of deionized water to the negative electrode material hard carbon, conductive agent SP, thickener CMC and binder SBR in a mass ratio of 94:2:2.5:1.5, mix evenly, and uniformly coat the obtained negative electrode slurry onto the negative electrode current collector copper foil, and bake at 80℃ for 16h to obtain the negative electrode sheet.

[0027] Preparation of positive electrode sheet: Add appropriate amount of NMP solvent to the positive electrode material sodium nickel iron manganese oxide, conductive agent SP and binder PVDF in a mass ratio of 95:2.5:2.5, mix evenly, and uniformly coat the obtained positive electrode slurry onto the positive electrode current collector aluminum foil, and bake at 100℃ for 16h to obtain the positive electrode sheet.

[0028] Preparation of sodium-ion batteries: The above-prepared positive electrode sheet, separator, and above-prepared negative electrode sheet are stacked 12 times in sequence to obtain a sodium-ion battery cell with a capacity of 1.0Ah. After drying the cell, the above-prepared sodium-ion battery electrolyte is injected at a volume of 8.0g / Ah.

[0029] Examples 2-12, Comparative Examples 1-2

[0030] Only the electrolyte formulation was changed, and the specific formulation is shown in Table 1;

[0031] Table 1

[0032] Example 1 (EC / DMC):EA:DMMS=5:0:5 <![CDATA[NaPF6 1mol / L]]> FEC 2wt% Example 2 (EC / DMC):EA:DMMS=5:1:4 <![CDATA[NaPF6 1mol / L]]> FEC 2wt% Example 3 (EC / DMC):EA:DMMS=5:2:3 <![CDATA[NaPF6 1mol / L]]> FEC 2wt% Example 4 (EC / DMC):EA:DMMS=5:3:2 <![CDATA[NaPF6 1mol / L]]> FEC 2wt% Example 5 (EC / DMC):EA:DMMS=5:4:1 <![CDATA[NaPF6 1mol / L]]> FEC 2wt% Example 6 (EC / DMC):EA:DMMS=5:5:0 <![CDATA[NaPF6 1mol / L]]> FEC 2wt% Example 7 (EC / DMC):EA:DMMS=5:0:5 NaFSI 1mol / L FEC 2wt% Example 8 (EC / DMC):EA:DMMS=5:1:4 NaFSI 1mol / L FEC 2wt% Example 9 (EC / DMC):EA:DMMS=5:2:3 NaFSI 1mol / L FEC 2wt% Example 10 (EC / DMC):EA:DMMS=5:3:2 NaFSI 1mol / L FEC 2wt% Example 11 (EC / DMC):EA:DMMS=5:4:1 NaFSI 1mol / L FEC 2wt% Example 12 (EC / DMC):EA:DMMS=5:5:0 NaFSI 1mol / L FEC 2wt% Comparative Example 1 EC:DMC = 2:3 <![CDATA[NaPF6 1mol / L]]> FEC 2wt% Comparative Example 2 EC:DMC = 2:3 NaFSI 1mol / L FEC 2wt%

[0033] Note: In Examples 1-12, the EC:DMC volume ratio is 2:3.

[0034] Detection Examples

[0035] (1) Room temperature rate performance test

[0036] Sodium-ion batteries from Examples 1-12 and Comparative Examples 1-2 were charged to 3.95V at a constant current of 0.5C under 25°C conditions, and then discharged to 2.0V at a constant current of 1.0C. The discharge capacity Q0 was recorded as the initial discharge capacity. After five cycles of the same charge-discharge cycle while maintaining a constant ambient temperature, the average discharge capacity Q0 of the first five cycles was recorded. 1C The battery discharge rates were changed sequentially to 2C, 3C, 4C, 6C, 10C, and 1C, and the average discharge capacity Q of the battery was recorded. 2C Q 3C Q 4C Q 6C Q 10C Q 1C Further calculations revealed that the capacity retention rate of the sodium-ion battery under different rate conditions was Q. 2C / Q 1C Q 3C / Q 1C Q4C / Q 1C Q 6C / Q 1C Q 10C / Q 1C Q 1C ' / Q 1C The results are shown in Table 2.

[0037] Table 2

[0038] Example 1 94.3％ 86.1％ 82.3％ 74.5％ 60.2％ 98.8％ Example 2 95.0％ 87.2％ 83.9％ 76.7％ 64.9％ 99.0％ Example 3 95.6％ 88.0％ 85.5％ 78.9％ 67.5％ 99.1％ Example 4 95.1％ 87.6％ 85.1％ 78.6％ 67.0％ 99.0％ Example 5 94.9％ 87.4％ 84.2％ 78.3％ 65.3％ 98.9％ Example 6 94.2％ 86.3％ 81.9％ 75.1％ 62.31 98.7％ Example 7 95.5％ 88.1％ 85.2％ 80.1％ 68.9％ 99.0％ Example 8 96.1％ 90.4％ 86.9％ 81.2％ 70.1％ 99.3％ Example 9 96.8％ 91.0％ 88.1％ 81.9％ 71.3％ 99.5％ Example 10 96.2％ 89.9％ 86.9％ 81.7％ 70.1％ 99.4％ Example 11 95.9％ 89.2％ 86.4％ 81.2％ 69.3％ 99.3％ Example 12 95.1％ 87.5％ 85.0％ 79.7％ 68.4％ 98.7％ Comparative Example 1 90.5％ 84.2％ 80.7％ 61.2％ 40.7％ 98.5％ Comparative Example 2 92.6％ 85.3％ 80.9％ 65.4％ 45.2％ 98.1％

[0039] (2) Low-temperature capacity retention test

[0040] Sodium-ion batteries from Examples 1-12 and Comparative Examples 1-2 were charged to 3.95V at a constant current of 0.5C at 25°C; then discharged to 2.0V at a constant current of 0.1C at 25°C, 0°C, -10°C, -20°C, -30°C, -40°C, and -50°C, respectively. The average discharge capacity after 5 cycles was Q. 25℃ Q 0℃ Q -10℃ Q -20℃ Q -30℃ Q -40℃ Q -50℃ Then, the capacity retention rates of the battery under the conditions of 0℃, -10℃, -20℃, -30℃, -40℃, and -50℃ are respectively Q 0℃ / Q 25℃ Q -10℃ / Q 25℃ Q -20℃ / Q 25℃ Q -30℃ / Q 25℃ Q -40℃ / Q 25℃ Q -50℃ / Q 25℃ The results are shown in Table 3.

[0041] Table 3

[0042]

[0043]

[0044] Comparing the data from Examples 1-12 with Comparative Example 1, it is evident that the introduction of carboxylic acid ester (EA) and dimethyldimethoxysilane (DMMS) molecules can significantly improve the rate performance of sodium-ion batteries at room temperature, increasing the capacity retention at 10C from approximately 40% to over 70%. Simultaneously, the ratio of dimethyldimethoxysilane to carbonate needs optimization, with an optimal volume ratio of approximately 2:3. Similarly, carboxylic acid ester (EA) and dimethyldimethoxysilane (DMMS) molecules can also significantly improve the capacity retention of sodium-ion batteries at low temperatures, increasing the capacity retention at -40°C compared to 25°C from 30% to over 80%. Commercial electrolytes are almost inoperable at -50°C, while electrolytes containing carboxylic acid esters and siloxane solvents still maintain a capacity retention of over 70% even under the extremely harsh condition of -50°C. Comparing the data from Examples 6-12 with Comparative Example 2, it is demonstrated that carboxylic acid ester solvent molecules can exert similar effects in improving battery rate and low-temperature performance under different sodium salt (NaFSI and NaPF6) environments.

[0045] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A low-temperature electrolyte for sodium-ion batteries, characterized in that, It is composed of sodium salt, carboxylic acid ester solvent, carbonate solvent, siloxane solvent, and additives; wherein the volume ratio of the carboxylic acid ester solvent ranges from 20% to 50%, the volume ratio of the carbonate solvent ranges from 20% to 40%, the volume ratio of the siloxane solvent ranges from 10% to 30%, and the mass ratio of the additives is 1% to 10%; the carboxylic acid ester solvent is ethyl acetate; the carbonate solvent is ethylene carbonate and diethyl carbonate; and the siloxane solvent is dimethyldimethoxysilane.

2. The sodium-ion battery low-temperature electrolyte according to claim 1, characterized in that, The sodium salt includes at least one of the following: sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, sodium hexafluoroarsenate, and sodium bis(oxalatoborate).

3. The sodium-ion battery low-temperature electrolyte according to claim 1, characterized in that, In the sodium-ion battery low-temperature electrolyte, the concentration of the sodium salt is 0.5~4 mol / L.

4. The sodium-ion battery low-temperature electrolyte according to claim 1, characterized in that, The additives include at least one of the following: ethylene carbonate, maleic anhydride, biphenyl, 1,3-propanesulfonic acid lactone, dimethyl sulfate, trimethyl phosphate, vinyl sulfate, p-dimethylbenzoic acid, and tris(trimethylsilane) phosphate.

5. A method for preparing a low-temperature electrolyte for a sodium-ion battery as described in any one of claims 1-4, characterized in that, step... include: The sodium-ion battery low-temperature electrolyte is obtained by mixing sodium salt, carboxylic acid ester solvent, carbonate solvent, siloxane solvent and additives in a certain proportion.

6. A sodium-ion battery, characterized in that, include: A positive electrode, a negative electrode, a separator, and an electrolyte; wherein the electrolyte is a sodium-ion battery low-temperature electrolyte as described in any one of claims 1-4 or a sodium-ion battery low-temperature electrolyte prepared by the preparation method described in claim 5.

7. The sodium-ion battery according to claim 6, characterized in that, The positive electrode sheet contains at least one of the following active materials: sodium vanadium phosphate, sodium iron phosphate, sodium nickel iron manganese phosphate, and sodium vanadium phosphate.

8. The sodium-ion battery according to claim 6, characterized in that, The sodium-ion battery operates at a temperature of -50 to 60°C.

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