Low-temperature sodium ion electrolyte based on carboxylic ester-based solvent and sodium ion battery

Abstract

According to the low-temperature sodium ion electrolyte based on the carboxylic ester-based solvent and the sodium ion battery, the carboxylic ester-based mixed solvent is used, the excellent low melting point, relatively high oxidation stability, proper dielectric constant and low viscosity of the carboxylic ester-based mixed solvent are utilized, high ionic conductivity is achieved at the low temperature, and meanwhile the low-temperature sodium ion electrolyte and the sodium ion battery based on the carboxylic ester-based solvent are obtained. According to the invention, electrolyte components are further improved, sodium 4, 5-dicyano-2-(trifluoromethyl) imidazolate is introduced, and other organic solvents and additives are mutually matched and synergistic, so that the interface of the electrolyte has excellent stability, the electrolyte also has good electrochemical performance in a low-temperature environment, and the electrolyte can be applied to an environment of-85-25 DEG C, and can be applied to the field of lithium ion batteries. Good application prospects are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a low-temperature sodium ion electrolyte and a sodium ion battery based on a carboxylate-based solvent. Background Art

[0002] Sodium-ion batteries are expected to become an important supplement to lithium-ion batteries due to their abundant sodium reserves, low cost, high safety and environmental friendliness, and play an important role in future energy storage and utilization. + Stokes radius Smaller than Li + Stokes radius Sodium ion electrolytes generally show stronger ion diffusion capacity than lithium ion batteries, which makes sodium ion batteries more promising for low temperature applications. However, in low temperature environments, the viscosity of the electrolyte increases and the ion conductivity decreases. + The migration kinetics of sodium ion batteries slow down, sodium salt precipitation, electrolyte solidification, poor compatibility between electrolyte and positive and negative electrodes, and increased desolvation energy lead to increased polarization, severe electrolyte decomposition, and dendrite growth, which seriously affect the electrochemical performance of sodium ion batteries at low temperatures, causing severe capacity decay and even failure. Therefore, optimizing the electrolyte is crucial for the performance of sodium ion batteries at low temperatures. Carboxylates have low melting points and are suitable for use in low-temperature environments. Introducing carboxylates into sodium ion battery electrolytes is expected to improve the performance of sodium ion batteries in low-temperature environments.

[0003] However, carboxylates have poor compatibility with battery electrodes and many side reactions. A high proportion of carboxylates poses great challenges to the battery electrode interface. How to optimize the components of sodium ion electrolytes and improve the stability of the battery interface so that it has excellent electrochemical performance and stability even in low temperature environments is an urgent problem that needs to be solved. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a low-temperature sodium ion electrolyte and a sodium ion battery based on a carboxylate-based solvent.

[0005] The technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a low-temperature sodium ion electrolyte based on a carboxylate-based solvent, comprising the following components: an organic solvent, a sodium salt and an additive,

[0006] The organic solvent includes a carboxylate organic solvent, wherein the carboxylate organic solvent is a carboxylate containing a -RCOOR'- group, wherein R is C n H 2n+1 , R' is C n H 2n+1 ;

[0007] The volume ratio of the carboxylate organic solvent to the electrolyte is 45-85%,

[0008] The organic solvent further comprises at least one of a carbonate ester and a phosphate ester,

[0009] The additives include one or more of film-forming additives, flame-retardant additives, and overcharge protection additives, and the concentration of the additives is 0.1%-5.0%.

[0010] Preferably, the additive further comprises sodium 4,5-dicyano-2-(pentafluoroethyl)imidazolate.

[0011] Preferably, the mass ratio of sodium 4,5-dicyano-2-(pentafluoroethyl)imidazolate to the electrolyte is 1-2%.

[0012] Preferably, the carbonate is one or more of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; the phosphate is one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, 2-fluoro-2-phosphorylacetic acid triethyl ester, and tris(2,2,2-trifluoroethyl) phosphate.

[0013] Preferably, the film-forming additive is one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and vinyl sulfate; the flame retardant additive is one or more of dimethyl methylphosphonate, ethoxy (pentafluoro) cyclotriphosphazene and perfluoro (2-methyl-3-pentanone); the overcharge protection additive is one or more of biphenyl, terephthalonitrile and para-dimethylbenzoic acid.

[0014] Preferably, the sodium salt is one or more of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium tetrafluoroborate, sodium difluorophosphate, sodium difluorooxalatoborate, and sodium nitrate.

[0015] Preferably, the concentration of the sodium salt in the electrolyte is 0.3-2.0 mol / L.

[0016] A second aspect of the present invention provides a sodium ion battery, comprising a positive electrode material, a negative electrode material and a separator, and also comprising a low-temperature sodium ion electrolyte based on a carboxylate-based solvent as described above.

[0017] Preferably, the positive electrode is one of a sodium-containing transition metal oxide, a Prussian blue compound, and a polyanion compound.

[0018] Preferably, the negative electrode is one or more of a carbon-based material, a titanium-based material, an alloy material and an organic compound; the diaphragm is one or more of a glass fiber diaphragm, a polyethylene diaphragm and a polypropylene diaphragm.

[0019] The beneficial effects of the present invention are as follows: the present invention uses a carboxylate-based mixed solvent and utilizes its excellent low melting point, relatively high oxidation stability, suitable dielectric constant and low viscosity to achieve high ionic conductivity at low temperatures. At the same time, the present invention further improves the electrolyte components by introducing sodium 4,5-dicyano-2-(trifluoromethyl)imidazolate, and through the mutual coordination and synergistic effect of various other organic solvents and additives, the interface has excellent stability, so that it also has good electrochemical properties in a low temperature environment, can be used in an environment of -85-25°C, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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 or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0021] Figure 1 The differential scanning calorimetry curves of the electrolytes of Comparative Example 1, Example 1 and Example 12 are shown.

[0022] Figure 2 Graphs showing the ionic conductivity of the electrolytes used in Comparative Example 1, Example 1, and Example 12.

[0023] Figure 3 This is a long cycle diagram of a sodium ion full battery assembled with the electrolytes of Comparative Example 1, Example 1, and Example 12 matched with the sodium vanadium phosphate positive electrode at -40°C.

[0024] Figure 4 This is a diagram of the first-cycle discharge specific capacity of a sodium-ion full battery assembled using the electrolyte of Example 12 and a sodium vanadium phosphate positive electrode at -85°C. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] In order to make the contents described in the present invention easier to understand, the technical solutions described in the present invention are further described and explained in conjunction with specific implementation methods below. However, the present invention is not limited to this. All technologies realized based on the above contents of the present invention are included in the scope that the present invention is intended to protect.

[0027] Example 1

[0028] According to the stoichiometric ratio, sodium bis(fluorosulfonyl)imide was weighed, and the solvent was methyl acetate / fluoroethylene carbonate in a mol ratio of 3:2, and a 1 M sodium bis(fluorosulfonyl)imide electrolyte was prepared to obtain the electrolyte of Example 1.

[0029] Example 2

[0030] According to the stoichiometric ratio, sodium bis(fluorosulfonyl)imide was weighed, and the solvent was methyl acetate / fluoroethylene carbonate / ethyl methyl carbonate in a mol ratio of 4:3:1, and a 1 M sodium bis(fluorosulfonyl)imide electrolyte was prepared to obtain the electrolyte of Example 2.

[0031] Example 3

[0032] Sodium hexafluorophosphate was weighed according to the stoichiometric ratio, and the solvent was ethyl acetate / ethyl methyl carbonate with a mol ratio of 5:2, and a 1M sodium hexafluorophosphate electrolyte was prepared to obtain the electrolyte of Example 3.

[0033] Example 4

[0034] According to the stoichiometric ratio, sodium bis(fluorosulfonyl)imide was weighed, and the solvent was ethyl propionate / diethyl carbonate with a mol ratio of 3:1, and a 1 M sodium bis(fluorosulfonyl)imide electrolyte was prepared to obtain the electrolyte of Example 4.

[0035] Example 5

[0036] Sodium hexafluorophosphate was weighed according to the stoichiometric ratio, and the solvent was methyl propionate / triethyl phosphate with a mol ratio of 5:1, and a 0.5 M sodium hexafluorophosphate electrolyte was prepared to obtain the electrolyte of Example 5.

[0037] Example 6

[0038] Sodium trifluoromethanesulfonate was weighed according to the stoichiometric ratio, and the solvent was ethyl formate / triethyl phosphate / ethylene carbonate in a mol ratio of 4:1:3, and a 1.5 M sodium trifluoromethanesulfonate electrolyte was prepared to obtain the electrolyte of Example 6.

[0039] Example 7

[0040] Sodium perchlorate was weighed according to the stoichiometric ratio, and the solvent was ethyl acetate / propylene carbonate with a molar ratio of 3:2 to prepare a 1M sodium perchlorate electrolyte. Then, 3% by mass of 1,3-propane sultone and 1% by mass of perfluoro(2-methyl-3-pentanone) were added as additives to obtain the electrolyte of Example 7.

[0041] Example 8

[0042] According to the stoichiometric ratio, sodium bis(fluorosulfonyl)imide was weighed, and the solvent was methyl acetate / fluoroethylene carbonate in a mol ratio of 3:2, a 1M sodium bis(fluorosulfonyl)imide electrolyte was prepared, and then 3% of vinyl sulfate and 2% of biphenyl were added as additives in a mass ratio to obtain the electrolyte of Example 8.

[0043] Example 9

[0044] According to the stoichiometric ratio, sodium bis(fluorosulfonyl)imide was weighed, and the solvent was methyl acetate / fluoroethylene carbonate / ethyl methyl carbonate in a mol ratio of 4:3:1, and a 1M sodium bis(fluorosulfonyl)imide electrolyte was prepared. Then, 2% by mass of vinyl sulfate and 3% by mass of 1,3-propane sultone were added as additives to obtain the electrolyte of Example 9.

[0045] Example 10

[0046] According to the stoichiometric ratio, sodium bis(fluorosulfonyl)imide was weighed, the solvent was ethyl propionate / diethyl carbonate with a mol ratio of 3:1, a 1M sodium bis(fluorosulfonyl)imide electrolyte was prepared, and then 1% by mass of sodium 4,5-dicyano-2-(trifluoromethyl)imidazolate was added as an additive to obtain the electrolyte of Example 10.

[0047] Embodiment 11

[0048] According to the stoichiometric ratio, sodium bis(fluorosulfonyl)imide was weighed, and the solvent was methyl acetate / fluoroethylene carbonate / ethyl methyl carbonate in a mol ratio of 4:3:1. A 1M sodium bis(fluorosulfonyl)imide electrolyte was prepared, and then 0.5% sodium nitrate and 1% sodium difluorophosphate were added as additives in a mass ratio to obtain the electrolyte of Example 11.

[0049] Example 12

[0050] According to the stoichiometric ratio, sodium bis(fluorosulfonyl)imide was weighed, and the solvent was methyl acetate / fluoroethylene carbonate / ethyl methyl carbonate in a mol ratio of 4:3:1. A 1M sodium bis(fluorosulfonyl)imide electrolyte was prepared, and then 2% by mass of sodium 4,5-dicyano-2-(trifluoromethyl)imidazole was added as an additive to obtain the electrolyte of Example 12.

[0051] Example 13

[0052] Sodium hexafluorophosphate was weighed according to the stoichiometric ratio, and the solvent was methyl acetate / ethyl methyl carbonate with a molar ratio of 4:1 to prepare a 1M sodium hexafluorophosphate electrolyte. Then, 2% by mass of sodium 4,5-dicyano-2-(trifluoromethyl)imidazole and 0.2% by mass of sodium nitrate were added as additives to obtain the electrolyte of Example 13.

[0053] Embodiment 14

[0054] Sodium perchlorate was weighed according to the stoichiometric ratio, and the solvent was ethyl acetate / propylene carbonate with a molar ratio of 3:2 to prepare a 1M sodium perchlorate electrolyte. Then, 1% perfluoro(2-methyl-3-pentanone) and 1% sodium 4,5-dicyano-2-(trifluoromethyl)imidazole were added as additives in a mass ratio to obtain the electrolyte of Example 14.

[0055] Comparative Example 1

[0056] According to the stoichiometric ratio, 1 mol / L sodium perchlorate was weighed, and the solvent was propylene carbonate / ethylene carbonate with a mol ratio of 1:1, and a 1M sodium perchlorate electrolyte was prepared. After fully mixing, the electrolyte of Comparative Example 1 was obtained.

[0057] Table 1 Cyclic performance test results of sodium ion batteries assembled with electrolytes matching sodium vanadate in different comparative examples and embodiments

[0058]

[0059] It can be seen from Table 1 that the sodium ion full battery assembled by using the sodium ion battery electrolyte based on carboxylate solvent prepared by the present invention and matching the sodium vanadium phosphate positive electrode has a higher initial capacity than the control example.

[0060] Figure 1 From the differential scanning calorimeter curves of the electrolytes of Comparative Example 1, Example 1, and Example 12, it can be seen that the electrolyte containing the carboxylate-based solvent has a lower freezing point, so its electrolyte can operate stably in extreme low-temperature environments.

[0061] Figure 2 The ionic conductivity diagrams of the electrolytes of Comparative Example 1, Example 1, and Example 12 at -40°C show that the electrolytes containing carboxylate-based solvents maintain high ionic conductivity at low temperatures and have fast ion transport capabilities, thereby improving the electrochemical performance in low temperature environments.

[0062] Figure 3 This is a long cycle diagram of a sodium ion full battery assembled with the electrolytes of Comparative Example 1, Example 1, and Example 12 matched with the sodium vanadium phosphate positive electrode at -40°C. It can be seen from the figure that the full battery assembled with the electrolyte containing sodium 4,5-dicyano-2-(trifluoromethyl)imidazolate exhibits a higher discharge specific capacity and a higher capacity retention rate.

[0063] Figure 4This is a diagram of the first-cycle discharge specific capacity of a sodium ion full battery assembled using the electrolyte of Example 12 and a sodium vanadium phosphate positive electrode at -85°C. It can be seen from the figure that the full battery assembled with an electrolyte containing sodium 4,5-dicyano-2-(trifluoromethyl)imidazolate can operate stably in an extreme low-temperature environment and exhibit a high discharge specific capacity.

[0064] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A low-temperature sodium ion electrolyte based on a carboxylate-based solvent, characterized in that It includes the following components: organic solvent, sodium salt and additives, The organic solvent includes a carboxylate organic solvent, wherein the carboxylate organic solvent is a carboxylate containing a -RCOOR'- group, wherein R is C n H 2n+1 , R' is C n H 2n+1 ; The volume ratio of the carboxylate organic solvent to the electrolyte is 45-85%, The organic solvent further comprises at least one of a carbonate ester and a phosphate ester, The additives include one or more of film-forming additives, flame-retardant additives, and overcharge protection additives, and the concentration of the additives is 0.1%-5.0%.

2. A low-temperature sodium ion electrolyte based on a carboxylate-based solvent according to claim 1, characterized in that: The additive also includes sodium 4,5-dicyano-2-(pentafluoroethyl)imidazolate.

3. A low-temperature sodium ion electrolyte based on a carboxylate-based solvent according to claim 2, characterized in that: The mass ratio of 4,5-dicyano-2-(pentafluoroethyl)imidazolate sodium to the electrolyte is 1-2%.

4. A low-temperature sodium ion electrolyte based on a carboxylate-based solvent according to claim 1, characterized in that: The carbonate is one or more of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; the phosphate is one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, 2-fluoro-2-phosphorylacetic acid triethyl ester, and tris(2,2,2-trifluoroethyl) phosphate.

5. A low-temperature sodium ion electrolyte based on a carboxylate-based solvent according to claim 1, characterized in that: The film-forming additive is one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and vinyl sulfate; the flame retardant additive is one or more of dimethyl methylphosphonate, ethoxy (pentafluoro) cyclotriphosphazene and perfluoro (2-methyl-3-pentanone); the overcharge protection additive is one or more of biphenyl, terephthalonitrile and p-dimethylbenzoic acid.

6. A low-temperature sodium ion electrolyte based on a carboxylate-based solvent according to claim 1, characterized in that: The sodium salt is one or more of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium tetrafluoroborate, sodium difluorophosphate, sodium difluorooxalatoborate, and sodium nitrate.

7. A low-temperature sodium ion electrolyte based on a carboxylate-based solvent according to claim 6, characterized in that: The concentration of the sodium salt in the electrolyte is 0.3-2.0 mol / L.

8. A sodium ion battery comprising a positive electrode material, a negative electrode material and a separator, characterized in that: It also includes a low-temperature sodium ion electrolyte based on a carboxylate-based solvent as described in any one of claims 1 to 7.

9. A sodium ion battery according to claim 8, characterized in that: The positive electrode is one of a sodium-containing transition metal oxide, a Prussian blue compound, and a polyanion compound.

10. A sodium ion battery according to claim 8, characterized in that: The negative electrode is one or more of a carbon-based material, a titanium-based material, an alloy material and an organic compound; the diaphragm is one or more of a glass fiber diaphragm, a polyethylene diaphragm and a polypropylene diaphragm.

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