Non-aqueous electrolyte for sodium-ion battery with high and low temperature performance and application of non-aqueous electrolyte

Abstract

The invention provides a non-aqueous electrolyte for a sodium ion battery with high and low temperature performance and application of the non-aqueous electrolyte. The non-aqueous electrolyte comprises a sodium salt, a solvent and an additive, wherein the additives comprise a first additive, a second additive, a third additive and an auxiliary sodium salt additive. The auxiliary sodium salt additive for improving the low-temperature performance is added into the non-aqueous electrolyte, so that the conductivity is improved at low temperature, sodium ion transmission is promoted, impedance is reduced, and the capacity retention ratio is improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more specifically to a non-aqueous electrolyte for sodium-ion batteries that balances high and low temperature performance. Background Technology

[0002] Among numerous electrochemical energy storage technologies, lithium-ion batteries dominate the global battery market with a high market share. However, lithium resources are scarce and unevenly distributed, necessitating the search for other high-performance energy storage systems to supplement the battery market. Sodium resources are abundant and evenly distributed, leading to the successful emergence of sodium-ion batteries. Sodium-ion batteries that balance high and low temperature performance are currently the goal pursued by many application fields.

[0003] The electrolyte, serving as the channel connecting the positive and negative electrodes, is a crucial component of sodium-ion batteries and significantly impacts their performance. The high and low temperature performance of sodium-ion batteries is primarily related to the choice of solvent system, sodium salt system, and additives in the electrolyte. At high temperatures, the thermal decomposition products of electrolyte components cause gas generation, affecting battery cycling; at low temperatures, the increased electrolyte viscosity leads to decreased conductivity, affecting battery impedance. Therefore, there is an urgent need to develop electrolyte systems that offer stable cycling performance while maintaining good high and low temperature performance. Summary of the Invention

[0004] This invention provides a non-aqueous electrolyte for sodium-ion batteries and a sodium-ion battery that balances high and low temperature performance, in order to overcome the shortcomings of the prior art. The electrolyte improves interface stability and high and low temperature performance by adding functional additives.

[0005] The technical solution of the present invention is as follows:

[0006] A non-aqueous electrolyte, the non-aqueous electrolyte comprising a sodium salt, a solvent, and an additive;

[0007] The additives include a first additive, a second additive, a third additive, and an auxiliary sodium salt additive.

[0008] According to an embodiment of the present invention, the first additive is selected from p-fluorobenzonitrile.

[0009] According to an embodiment of the present invention, the content of the first additive in the non-aqueous electrolyte is 0.1-5 wt%, preferably 0.1-3 wt%, for example 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 3 wt%, or 4 wt%.

[0010] According to an embodiment of the present invention, the second additive is selected from fluoroethylene carbonate.

[0011] According to an embodiment of the present invention, the content of the second additive in the non-aqueous electrolyte is 0.1-10 wt%, preferably 0.1-5 wt%, for example 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, or 9 wt%.

[0012] According to an embodiment of the present invention, the third additive is selected from 1,3-propanesulfonyl lactone.

[0013] According to an embodiment of the present invention, the content of the third additive in the non-aqueous electrolyte is 0.1-5 wt%, preferably 0.1-3 wt%, for example 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 3 wt%, or 4 wt%.

[0014] According to an embodiment of the present invention, the auxiliary sodium salt additive is selected from at least one, two or more of sodium tetrafluoroborate, sodium difluorooxalate borate, sodium bis(oxalate borate), sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0015] According to an embodiment of the present invention, the content of the auxiliary sodium salt additive in the non-aqueous electrolyte is 0.1-3 wt%, for example, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 3 wt%.

[0016] According to an embodiment of the present invention, in the non-aqueous electrolyte, the mass ratio of the first additive, the second additive, and the third additive is 0.1-5:0.1:10:0.1-3, for example, 0.5:0.1-5:0.1-3.

[0017] According to an embodiment of the present invention, the non-aqueous organic solvent is selected from at least one or more of carbonate organic solvents, carboxylic acid ester organic solvents, and ether organic solvents.

[0018] According to an embodiment of the present invention, the carbonate organic solvent is selected from at least one, two, or more of ethylene carbonate, propylene carbonate, propylene carbonate, 1,2-butylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0019] According to an embodiment of the present invention, the carboxylic acid ester organic solvent is selected from at least one, two or more of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, and n-butyl acetate.

[0020] According to an embodiment of the present invention, the ether organic solvent is selected from at least one, two or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and 1,3-dioxolane.

[0021] According to an embodiment of the present invention, the content of the non-aqueous organic solvent in the non-aqueous electrolyte is 50-90 wt%, for example, 60 wt%, 70 wt%, or 80 wt%.

[0022] According to an embodiment of the present invention, the sodium salt is selected from at least one, two or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluorooxalate borate, sodium bis(oxalate borate), sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0023] According to an embodiment of the present invention, the sodium salt content in the non-aqueous electrolyte is 10-25 wt%, for example, 10 wt%, 15 wt%, or 20 wt%.

[0024] According to an embodiment of the present invention, in the non-aqueous electrolyte, the mass ratio of the first additive to the non-aqueous organic solvent is 0.1-5:50-90, for example, 0.1:50-90, 0.5:50-90, 1:50-90, or 2:50-90.

[0025] According to an exemplary embodiment of the present invention, the non-aqueous electrolyte comprises:

[0026] Non-aqueous organic solvent 79.5 wt%, sodium hexafluorophosphate 16 wt%, p-fluorobenzonitrile 0.5 wt%, fluoroethylene carbonate 2 wt%, 1,3-propane sulcolone 1.5 wt%, sodium difluorooxalate borate 0.5 wt%;

[0027] The non-aqueous organic solvents include propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, with a mass ratio of propylene carbonate: methyl ethyl carbonate: dimethyl carbonate of 4:3:3.

[0028] According to an exemplary embodiment of the present invention, the non-aqueous electrolyte comprises:

[0029] Non-aqueous organic solvent 79 wt%, sodium hexafluorophosphate 16 wt%, p-fluorobenzonitrile 1 wt%, fluoroethylene carbonate 2 wt%, 1,3-propane sulpholol 1.5 wt%, sodium difluorophosphate 0.5 wt%;

[0030] The non-aqueous organic solvents include propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, with a mass ratio of propylene carbonate: methyl ethyl carbonate: dimethyl carbonate of 4:3:3.

[0031] The present invention also provides the application of the above-mentioned non-aqueous electrolyte in secondary batteries, such as for sodium-ion batteries.

[0032] The present invention also provides a sodium-ion battery, wherein the sodium-ion battery comprises the above-mentioned non-aqueous electrolyte.

[0033] According to an embodiment of the present invention, the sodium-ion battery includes a positive electrode, a negative electrode, a separator, and the aforementioned non-aqueous electrolyte.

[0034] According to an embodiment of the present invention, the positive electrode comprises a positive electrode active material. Preferably, the positive electrode active material may be at least one or more of layered transition metal oxides, polyanionic compounds, and Prussian blue compounds.

[0035] According to an embodiment of the present invention, the negative electrode and the separator can be selected from materials known in the art, and the present invention does not make specific limitations.

[0036] According to an embodiment of the present invention, the sodium-ion battery retains a capacity of more than 85% after 500 cycles at 25°C, for example, 86%, 91%, 92%, 93%, 94%, or 95%.

[0037] According to an embodiment of the present invention, the sodium-ion battery retains a capacity of more than 70% after 200 cycles at 45°C, for example, 75%, 86%, 87%, 88%, 89%, 90%, 91%, or 92%.

[0038] According to an embodiment of the present invention, the capacity retention rate of the sodium-ion battery after 100 cycles at -15°C is preferably greater than 50%, for example 75%-92%, such as 80%, 85%, 90%, or 91%.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] In the non-aqueous electrolyte of the present invention, p-fluorobenzonitrile is added to improve the high-temperature cycling performance. The cyano group can complex with transition metal ions on the surface of the positive electrode material, reducing the contact between the solvent and the positive electrode, thereby slowing down the decomposition of the electrolyte and reducing the dissolution of transition metal ions from the positive electrode.

[0041] In this invention, an auxiliary sodium salt additive is added to the non-aqueous electrolyte to improve low-temperature performance, thereby increasing conductivity, promoting sodium ion transport, reducing impedance, and improving capacity retention at low temperatures.

[0042] This invention incorporates fluoroethylene carbonate and 1,3-propane sulphol to improve high-temperature or low-temperature performance, forming a stable and dense SEI film and CEI film, and inhibiting the damage of p-fluorobenzonitrile to the negative electrode material, thereby improving the high and low temperature performance of sodium-ion batteries and extending battery life. Attached Figure Description

[0043] Figure 1 The cycling performance (25°C) of Example 6 and Comparative Example 1 in a sodium-ion battery is shown.

[0044] Figure 2The cycling performance (45°C) of Example 6 and Comparative Example 1 in a sodium-ion battery is shown.

[0045] Figure 3 The cycling performance (-15°C) of Example 6 and Comparative Example 1 in a sodium-ion battery is shown. Detailed Implementation

[0046] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0047] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0048] The preparation method of the non-aqueous electrolyte in the following embodiments of the present invention is as follows:

[0049] In a glove box (O2 < 0.1 ppm, H2O < 0.1 ppm), sodium salt is slowly added to a non-aqueous organic solvent at room temperature, stirred and cooled. After the sodium salt is completely dissolved, additives are added in sequence and stirred until they are completely dissolved to obtain a non-aqueous electrolyte.

[0050] Example 1

[0051] This embodiment provides a non-aqueous electrolyte for sodium-ion batteries that balances high and low temperature performance. The concentrations of each component are as follows:

[0052] 79.5 wt% non-aqueous organic solvent (of which propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of approximately 4:3:3), 16 wt% sodium hexafluorophosphate, 0.5 wt% p-fluorobenzonitrile, 2 wt% fluoroethylene carbonate, 1.5 wt% 1,3-propanesulfonyl lactone, and 0.5 wt% sodium difluorooxalate borate.

[0053] Example 2

[0054] This embodiment provides a non-aqueous electrolyte for sodium-ion batteries that balances high and low temperature performance. The concentrations of each component are as follows:

[0055] 79 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of approximately 4:3:3), 16 wt% sodium hexafluorophosphate, 1 wt% p-fluorobenzonitrile, 2 wt% fluoroethylene carbonate, 1.5 wt% 1,3-propanesulfonyl lactone, and 0.5 wt% sodium difluorooxalate borate.

[0056] Example 3

[0057] This embodiment provides a non-aqueous electrolyte for sodium-ion batteries that balances high and low temperature performance. The concentrations of each component are as follows:

[0058] 78.5 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of approximately 4:3:3), 16 wt% sodium hexafluorophosphate, 1.5 wt% p-fluorobenzonitrile, 2 wt% fluoroethylene carbonate, 1.5 wt% 1,3-propanesulfonyl lactone, and 0.5 wt% sodium difluorooxalate borate.

[0059] Example 4

[0060] This embodiment provides a non-aqueous electrolyte for sodium-ion batteries that balances high and low temperature performance. The concentrations of each component are as follows:

[0061] 78 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of approximately 4:3:3), 16 wt% sodium hexafluorophosphate, 2 wt% p-fluorobenzonitrile, 2 wt% fluoroethylene carbonate, 1.5 wt% 1,3-propanesulfonyl lactone, and 0.5 wt% sodium difluorooxalate borate.

[0062] Example 5

[0063] This embodiment provides a non-aqueous electrolyte for sodium-ion batteries that balances high and low temperature performance. The concentrations of each component are as follows:

[0064] 79 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of approximately 4:3:3), 16 wt% sodium hexafluorophosphate, 1 wt% p-fluorobenzonitrile, 2 wt% fluoroethylene carbonate, 1.5 wt% 1,3-propanesulfonyl lactone, and 0.5 wt% sodium difluorophosphate.

[0065] Example 6

[0066] This embodiment provides a non-aqueous electrolyte for sodium-ion batteries that balances high and low temperature performance. The concentrations of each component are as follows:

[0067] 78.5 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of approximately 4:3:3), 16 wt% sodium hexafluorophosphate, 1 wt% p-fluorobenzonitrile, 2 wt% fluoroethylene carbonate, 1.5 wt% 1,3-propanesulfonyl lactone, 0.5 wt% sodium difluorophosphate, and 0.5 wt% sodium difluorooxalate borate.

[0068] Comparative Example 1

[0069] This comparative example provides a non-aqueous electrolyte for sodium-ion batteries without additives, with the following component concentrations:

[0070] 84 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of 4:3:3), 16 wt% sodium hexafluorophosphate.

[0071] Comparative Example 2

[0072] This comparative example provides a non-aqueous electrolyte for sodium-ion batteries containing a single additive, with the following component concentrations:

[0073] 83 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of 4:3:3), 16 wt% sodium hexafluorophosphate, and 1 wt% p-fluorobenzonitrile.

[0074] Comparative Example 3

[0075] This comparative example provides a non-aqueous electrolyte for sodium-ion batteries containing a single additive, with the following component concentrations:

[0076] 80.5 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of 4:3:3), 16 wt% sodium hexafluorophosphate, 2 wt% fluoroethylene carbonate, and 1.5 wt% 1,3-propanesulfonyl lactone.

[0077] Comparative Example 4

[0078] This comparative example provides a non-aqueous electrolyte for sodium-ion batteries containing a single additive, with the following component concentrations:

[0079] 83 wt% non-aqueous organic solvent (propylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a mass ratio of 4:3:3), 16 wt% sodium hexafluorophosphate, 0.5 wt% sodium difluorophosphate, and 0.5 wt% sodium difluorooxalate borate.

[0080] Application Example 1

[0081] The manufacturing process of sodium-ion batteries is as follows:

[0082] (1) Positive electrode: NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is used as the positive electrode active material, carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder. NaNi is mixed in a 90:5:5 ratio. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, carbon black, and PVDF are added to the solvent N-methylpyrrolidone (NMP) to obtain a uniform positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector and dried to obtain the positive electrode sheet.

[0083] (2) Battery assembly: In a glove box (O2 < 0.1 ppm, H2O < 0.1 ppm), button sodium-ion batteries were assembled in the following order: positive electrode shell - positive electrode plate - electrolyte - separator - electrolyte - negative electrode plate - negative electrode shell. The electrolytes used were those prepared in Examples 1-7 and Comparative Examples 1-3, respectively.

[0084] The test method is as follows, and the test results are recorded in Table 1:

[0085] 1) Room temperature cycling test: At 25°C, the assembled battery was activated at 0.2C rate for 2 weeks and then subjected to constant current charge and discharge test at 1C rate.

[0086] 2) High-temperature cycle test: After the above-assembled battery was activated at 25°C at a rate of 0.2C for 2 weeks, it was subjected to constant current charge and discharge test at 45°C at a rate of 1C.

[0087] 3) Low temperature cycle test: After the above-assembled battery is activated at 25℃ at a rate of 0.1C for 2 weeks, it is subjected to constant current charge and discharge test at -15℃ at a rate of 0.1C.

[0088] Table 1 Results of Cyclic Test

[0089]

[0090]

[0091] Table 1 shows that although Comparative Example 2, which only added the first additive such as p-fluorobenzonitrile, showed improved room temperature cycle stability compared to Comparative Example 1, its high and low temperature cycle performance was poor. Examples 1-4 show that the best results were achieved when the first additive, such as p-fluorobenzonitrile, accounted for 1 wt% of the non-aqueous electrolyte. Examples 1-6 show that the simultaneous addition of the first additive such as p-fluorobenzonitrile, the second additive such as fluoroethylene carbonate, the third additive such as 1,3-propane sulpholactone, and the auxiliary sodium salt additive exerted a synergistic effect, significantly improving both room temperature and high and low temperature performance, thus broadening the application areas of sodium-ion batteries.

[0092] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A nonaqueous electrolyte, characterized by comprising: The non-aqueous electrolyte comprises a sodium salt, a solvent and an additive. The additive comprises a first additive, a second additive, a third additive and an auxiliary sodium salt additive.

2. The nonaqueous electrolyte according to claim 1, characterized by The first additive is selected from fluoronitrobenzene. Preferably, the content of the first additive in the non-aqueous electrolyte is 0.1-5wt%.

3. The nonaqueous electrolyte according to claim 1 or 2, characterized by The second additive is selected from fluoroethylene carbonate. Preferably, the content of the second additive in the non-aqueous electrolyte is 0.1-10wt%.

4. The nonaqueous electrolyte according to any one of claims 1 to 3, characterized by The third additive is selected from 1,3-propane sultone. Preferably, the content of the third additive in the non-aqueous electrolyte is 0.1-5wt%.

5. The nonaqueous electrolyte according to any one of claims 1 to 4, characterized by The auxiliary sodium salt additive is selected from at least one, two or more of sodium tetrafluoroborate, sodium difluoro(oxalato)borate, sodium bis(oxalato)borate, sodium trifluoromethylsulfonate, sodium bis(trifluoromethylsulfonyl)imide. Preferably, the content of the auxiliary sodium salt additive in the non-aqueous electrolyte is 0.1-3wt%.

6. The nonaqueous electrolyte according to any one of claims 1 to 5, characterized by In the non-aqueous electrolyte, the mass ratio of the first additive, second additive and third additive is 0.1-5:0.1:10:0.1-3.

7. The nonaqueous electrolyte according to any one of claims 1 to 6, characterized by The non-aqueous organic solvent is selected from at least one or more of carbonate-based organic solvents, carboxylate-based organic solvents, ether-based organic solvents. Preferably, the carbonate-based organic solvent is selected from at least one, two or more of ethylene carbonate, propylene carbonate, propylene carbonate, 1,2-butylene carbonate, gamma-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate. Preferably, the carboxylate-based organic solvent is selected from at least one, two or more of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, n-butyl acetate. Preferably, the ether-based organic solvent is selected from at least one, two or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane. Preferably, the content of the non-aqueous organic solvent in the non-aqueous electrolyte is 50-90wt%.

8. The nonaqueous electrolyte according to any one of claims 1 to 7, characterized by The sodium salt is selected from at least one, two or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluoro(oxalato)borate, sodium bis(oxalato)borate, sodium trifluoromethylsulfonate, sodium bis(trifluoromethylsulfonyl)imide. Preferably, the content of the sodium salt in the non-aqueous electrolyte is 10-25wt%. Preferably, in the non-aqueous electrolyte, the mass ratio of the first additive and non-aqueous organic solvent is 0.1-5:50-90.

9. The nonaqueous electrolyte according to any one of claims 1 to 8, characterized by Use of the non-aqueous electrolyte in a secondary battery.

10. A sodium ion battery comprising the non-aqueous electrolyte of any one of claims 1-8.

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