Sodium-ion electrolyte and preparation method thereof

Abstract

The application relates to the technical field of batteries, and particularly discloses a sodium ion electrolyte and a preparation method thereof. The sodium ion electrolyte comprises a sodium salt, a solvent and an additive; the solvent comprises ether solvents and ionic liquids, wherein the ether solvents comprise glycol dimethyl ether and ethylene glycol dimethyl ether, and the ionic liquids comprise ether group-containing piperidine ionic liquids; and the additive comprises at least one of vinyl ethylene sulfite, dimethyl succinate and methylphenyl diphenyl phosphate. The sodium ion electrolyte system has good electrical properties, can help improve the coulomb efficiency of a sodium ion battery, and has the advantages of high safety.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a sodium ion electrolyte and its preparation method. Background Technology

[0002] Since its invention, the lithium-ion battery has been widely used in daily life, serving as an ideal energy storage device with numerous advantages such as high energy density, high voltage, long cycle life, and being environmentally friendly and pollution-free. However, its large-scale application is limited by the scarcity and high price of lithium resources. Sodium-ion batteries, on the other hand, are abundant in the Earth's crust, widely distributed, and inexpensive. Furthermore, sodium and lithium belong to the same group but different periods, sharing similar electrochemical characteristics, making sodium-ion batteries a popular energy storage system today.

[0003] As an important component of a battery, the electrolyte acts as a bridge between the positive and negative electrodes, responsible for the transport of charge carriers between them. It is a major factor affecting battery safety and also has a significant impact on the battery's energy density, cycle life, and rate performance.

[0004] Currently, sodium-ion batteries primarily use organic carbonate electrolytes. However, carbonate solvents have a low flash point, causing the internal temperature of the battery to rise under conditions such as overcharging, over-discharging, high temperature, or short circuits. The accumulated heat inside the battery leads to electrolyte decomposition, producing large amounts of toxic and harmful gases. This causes a rapid increase in internal pressure, potentially leading to explosions or fires, posing a significant safety hazard. Non-flammable ionic liquids can mitigate these issues; however, ionic liquids have high viscosity and low conductivity, and their electrochemical performance needs further improvement. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a sodium-ion electrolyte and its preparation method, which can effectively improve the electrical performance of the electrolyte system, increase the coulombic efficiency of sodium-ion batteries, and has the advantage of high safety.

[0006] In a first aspect, the present invention provides a sodium ion electrolyte comprising a sodium salt, a solvent, and an additive;

[0007] The solvents include ether solvents and ionic liquids, wherein the ether solvents include glycol dimethyl ether and ethylene glycol dimethyl ether, and the ionic liquids include piperidine ionic liquids containing ether groups;

[0008] The additives include at least one of vinyl sulfite, dimethyl succinate, and toluene diphenyl phosphate.

[0009] The sodium ion electrolyte according to embodiments of the present invention has at least the following beneficial effects:

[0010] This invention selects a mixed system of ether-based solvents and ether-containing piperidine ionic liquids as solvents. The two have good compatibility, and the resulting electrolyte meets both safety requirements and exhibits good electrochemical performance. Applying ether-based solvents to sodium metal batteries can generate a uniform electrolyte interface (SEI) to suppress sodium dendrite formation. The ether-based electrolyte has good compatibility with the negative electrode, especially for high-surface-area carbon, improving the initial coulombic efficiency of high-specific-surface-area carbon. Ionic liquids possess low vapor pressure, good thermal stability, and excellent electrochemical performance. Specifically, using glycol dimethyl ether and ethylene glycol dimethyl ether as ether solvents results in a thinner and more uniform SEI film. The SEI film effectively inhibits the dissolution of transition metal ions and prevents the co-intercalation of solvent molecules, improving the cycle stability and lifespan of the working electrode. An excessively thick SEI film consumes a large amount of sodium ions from the electrode and electrolyte, leading to low initial cycle coulombic efficiency. The thinner SEI film formed by this invention helps improve the electrochemical performance of sodium-ion batteries.

[0011] By adding additives with different functions to the electrolyte, battery performance can be significantly improved in various aspects. Ethylene sulfite and dimethyl succinate can form a high-quality SEI film, reducing solvent-electrode contact and enhancing battery performance. Toluene diphenyl phosphate can improve electrolyte safety and battery cycle stability, and has good compatibility with sodium-ion battery cathode and anode materials.

[0012] According to some embodiments of the present invention, the molar concentration of the sodium salt in the sodium ion electrolyte is 0.5 to 5 mol / L, including but not limited to 0.5 to 4.5 mol / L, 0.5 to 4 mol / L, 0.5 to 3.5 mol / L, 0.5 to 3 mol / L, 1 to 5 mol / L, 1 to 4.5 mol / L, 1 to 4 mol / L, 1 to 3.5 mol / L, and 1 to 3 mol / L.

[0013] According to some preferred embodiments of the present invention, the molar concentration of the sodium salt in the sodium ion electrolyte is 1 to 3 mol / L.

[0014] This concentration of sodium salt can ensure high ionic conductivity, improve ion conduction rate, reduce battery internal resistance, and is beneficial to improving the cycle performance of sodium-ion batteries.

[0015] According to some embodiments of the present invention, the sodium salt includes at least one of sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrachloroaluminate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium cyanide, and sodium thiocyanate.

[0016] According to some preferred embodiments of the present invention, the sodium salt includes at least one of sodium nitrate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, and sodium trifluoromethanesulfonate.

[0017] According to some preferred embodiments of the present invention, the sodium salt includes at least one of sodium nitrate, sodium tetrafluoroborate, and sodium bis(trifluoromethanesulfonyl)imide.

[0018] According to some embodiments of the present invention, the volume ratio of the ether solvent to the ionic liquid is 2 to 5:1, including but not limited to 2 to 4:1, 2 to 3:1, 3 to 5:1, 3 to 4:1, 4 to 5:1, 2:1, 3:1, 4:1, and 5:1; preferably 3 to 5:1.

[0019] If the volume ratio of ionic liquid is too large, the conductivity of sodium ion electrolyte will decrease; conversely, if the volume ratio of ether solvent is too large, the poor oxidation resistance of ether solvent will easily lead to problems such as deterioration of cycle performance, capacity loss and safety hazards.

[0020] According to some embodiments of the present invention, the volume ratio of glycol dimethyl ether to ethylene glycol dimethyl ether in the ether solvent is 0.5 to 4:1, including but not limited to: 0.5 to 3.5:1, 0.5 to 3:1, 1 to 4:1, 1 to 3.5:1, and 1 to 3:1.

[0021] According to some preferred embodiments of the present invention, the volume ratio of glycol dimethyl ether to ethylene glycol dimethyl ether in the ether solvent is 1 to 3:1.

[0022] According to some embodiments of the present invention, the ether-containing piperidine ionic liquid is prepared by the following steps:

[0023] 2-[2-(2-methoxy-ethoxy)-ethoxy]-ethanol is converted into an ether-containing haloalkane by halogenation, and then reacted with pyridine by quaternization to obtain the final product.

[0024] According to some embodiments of the present invention, the raw materials for the halogenation reaction also include thionyl chloride.

[0025] According to some embodiments of the present invention, the reagent for the halogenation reaction is chloroform.

[0026] According to some embodiments of the present invention, the temperature of the halogenation reaction is 120°C to 150°C.

[0027] According to some embodiments of the present invention, the halogenation reaction takes 2 to 6 hours.

[0028] According to some embodiments of the present invention, the temperature of the quaternization reaction is 60°C to 80°C.

[0029] According to some embodiments of the present invention, the quaternization reaction takes 36-72 hours.

[0030] According to some embodiments of the present invention, the mass concentration of the additive in the sodium ion electrolyte is 1% to 5%, including but not limited to 1% to 4.5%, 1% to 4%, 1.5% to 5%, 1.5% to 4.5%, 1.5% to 4%, 2% to 5%, 2% to 4.5%, and 2% to 4%.

[0031] According to some preferred embodiments of the present invention, the mass concentration of the additive in the sodium ion electrolyte is 2% to 4%.

[0032] According to some embodiments of the present invention, the additive comprises toluene diphenyl phosphate and vinyl sulfite in a mass ratio of 1:1 to 5.

[0033] Test results show that toluene diphenyl phosphate and vinyl sulfite in a mass ratio of 1:1 to 5 have a more significant effect on improving electrochemical performance when used as additives.

[0034] According to some preferred embodiments of the present invention, the additive comprises toluene diphenyl phosphate and vinyl sulfite in a mass ratio of 1:2 to 3.

[0035] A second aspect of the present invention provides a method for preparing the above-mentioned sodium ion electrolyte, comprising the following steps:

[0036] The sodium salt, solvent, and additives are mixed to obtain the final product.

[0037] A third aspect of the present invention provides a sodium-ion battery comprising the sodium-ion electrolyte described above.

[0038] According to some embodiments of the present invention, the positive electrode, separator, and negative electrode of the sodium-ion battery are all conventional in the art.

[0039] Beneficial effects:

[0040] This invention uses a combination of glycol dimethyl ether and ethylene glycol dimethyl ether as an ether-based electrolyte. This ether solvent can form a thin and ordered SEI film in a sodium battery system, and has little impact on the composition of the SEI film. It is then combined with a piperidine-containing ionic liquid containing ether groups, which has good compatibility with ether solvents, and a variety of solvents are mixed to improve electrochemical performance. The addition of additives can further improve the cycle stability, coulombic efficiency and safety of the battery.

[0041] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0042] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0043] Example

[0044] The preparation method of the ether-containing piperidine ionic liquid in this invention is as follows:

[0045] 15.8 g of pyridine (0.2 mol) and 36.2 g of 2-[2-(2-methoxy-ethoxy)-ethoxy]-ethanol (0.22 mol) were dissolved in 350 mL of chloroform. The mixture was stirred, and 35.7 g of thionyl chloride (0.3 mol) was added dropwise to the reaction system. The mixture was refluxed (130 °C) and stirred for 3 hours, then concentrated under reduced pressure. 7.2 g of pyridine was added to the concentrated product, and the mixture was stirred at 70 °C for 48 hours. The reaction mixture was extracted and dried to obtain an ether-containing piperidine ionic liquid.

[0046] Example 1

[0047] The electrolyte formulation for Example 1 is shown in Table 1. The preparation steps of the electrolyte are as follows:

[0048] Ethylene glycol dimethyl ether, glycol dimethyl ether, and ether-containing piperidine ionic liquid were mixed uniformly in a volume ratio of 1:3:1. 1 kg of this mixture was taken, 20 g of vinyl sulfite was added, and then NaNO3 was added until the molar concentration of NaNO3 was 0.5 mol / L. After stirring, the mixture was completely dissolved to obtain the electrolyte.

[0049] Examples 2-10

[0050] The electrolyte formulations for Examples 2-10 are shown in Table 1. The preparation steps for the electrolytes are the same as those for Example 1.

[0051] Table 1 Electrolyte formulations for Examples 1-10

[0052]

[0053]

[0054] Comparative Example 1

[0055] The formulation and preparation steps of the electrolyte are the same as in Example 8, except that the solvent is replaced with dimethyl carbonate.

[0056] Comparative Example 2

[0057] The formulation and preparation steps of the electrolyte are the same as in Example 8, except that it does not contain glycol dimethyl ether, that is, the solvent is ethylene glycol dimethyl ether: ether-containing piperidine ionic liquid = 4:1.

[0058] Comparative Example 3

[0059] The electrolyte formulation and preparation steps are the same as in Example 8, except that it does not contain ionic liquid.

[0060] Comparative Example 4

[0061] The electrolyte formulation and preparation steps are the same as in Example 8, except that no additives are used.

[0062] Test case

[0063] Using electrolytes with different formulations from Examples 1-10 and Comparative Examples 1-4 as electrolytes for sodium-ion batteries, NaFePO4 as the positive electrode active material, and biomass hard carbon as the negative electrode, sodium-ion soft-pack batteries were assembled, and battery performance was tested respectively.

[0064] The test items are as follows:

[0065] (1) Initial charge-discharge efficiency: Under a voltage range of 1.0 to 4.2V and a current density of 0.1C, charge-discharge was performed at room temperature and low temperature (-20℃), and the initial charge-discharge efficiency was recorded;

[0066] (2) Capacity retention: At room temperature, charge at a constant current of 1C to 4.0V, then charge at a constant voltage to a current of 0.05C, and then discharge at a constant current of 1 / 3C to 1.0V. Calculate the capacity retention after 100 cycles by repeating this charge / discharge cycle.

[0067] (3) High temperature thickness expansion rate: At 25°C, take a sodium-ion battery and charge it to 4.0V with a constant current of 0.5C. Then charge it to 0.05C with a constant voltage at 4.0V to make it fully charged at 4.0V. Test the thickness of the fully charged sodium-ion battery before storage and record it as D0. Then place the fully charged sodium-ion battery in a 60°C oven. After 7 days, take it out and immediately test the thickness of the sodium-ion battery after storage. Calculate the thickness expansion rate.

[0068] The performance test results of sodium-ion batteries and their electrolytes in Examples 1-10 and Comparative Examples 1-4 are shown in Table 2.

[0069] Table 2 Performance test results of Examples 1-10 and Comparative Examples 1-4

[0070] First charge / discharge efficiency (%) Capacity retention rate (%) High-temperature thickness expansion rate (%) Example 1 87.5 92.4 3.4 Example 2 88.7 92.2 3.5 Example 3 91.6 94.5 3.2 Example 4 91.6 95.9 3.3 Example 5 88.1 93.4 3.3 Example 6 91.7 94.9 3.2 Example 7 92.0 95.6 3.3 Example 8 95.2 99.0 3.1 Example 9 89.5 90.8 3.2 Example 10 91.2 90.6 3.3 Comparative Example 1 90.6 91.2 4.6 Comparative Example 2 88.5 84.8 3.3 Comparative Example 3 86.4 82.6 3.9 Comparative Example 4 89.6 87.2 3.4

[0071] As can be seen from the test results in Table 2, the sodium-ion battery electrolytes prepared in Examples 1 to 10 of this application use ether solvents, ionic liquids and additives, are not easily reduced, can form a thinner SEI film on the negative electrode surface, inhibit the decomposition of the electrolyte, and reduce solvent consumption; the sodium-ion batteries have higher initial efficiency and better cycle performance, and good thermal stability.

[0072] In Comparative Example 1, during the use of carbonate solvent, the electrolyte continuously decomposes as the cycle continues, and the decomposition products of the electrolyte accumulate on the surface of the carbon negative electrode, resulting in a slightly thicker SEI film than in Example 8. Therefore, the electrochemical performance is worse than that of Example 8.

[0073] Comparative Example 2 reduced the amount of ether solvent, resulting in a decrease in the electrochemical performance of the battery.

[0074] Compared with Example 8, Comparative Example 3 omitted the ionic liquid, resulting in a decrease in the battery's initial charge-discharge efficiency and cycle performance, as well as poorer safety.

[0075] Compared with Example 8, Comparative Example 4 omitted the additives, which accelerated the decomposition of the electrolyte. The results showed that the cycle performance and coulombic efficiency of the sodium-ion battery were worse.

[0076] The above description provides a detailed account of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

Claims

1. A sodium ion electrolyte, characterized in that, The sodium ion electrolyte comprises sodium salt, solvent, and additives; The solvent includes ether solvents and ionic liquids, wherein the ether solvents include glycol dimethyl ether and ethylene glycol dimethyl ether, and the ionic liquids include piperidine ionic liquids containing ether groups; the volume ratio of the ether solvent to the ionic liquid is 2~5:1; The additive includes at least one of vinyl sulfite, dimethyl succinate, and diphenyl methyl phosphate, and includes at least diphenyl methyl phosphate; The ether-containing piperidine ionic liquid is prepared by the following steps: 2-[2-(2-methoxy-ethoxy)-ethoxy]-ethanol is converted into an ether-containing haloalkane by halogenation, and then reacted with pyridine by quaternization to obtain the final product.

2. The sodium ion electrolyte according to claim 1, characterized in that, The molar concentration of the sodium salt in the sodium ion electrolyte is 0.5~5 mol / L.

3. The sodium ion electrolyte according to claim 1, characterized in that, The sodium salt includes at least one of sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrachloroaluminate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium cyanide, and sodium thiocyanate.

4. The sodium ion electrolyte according to claim 1, characterized in that, In the ether solvent, the volume ratio of glycol dimethyl ether to ethylene glycol dimethyl ether is 0.5~4:

1.

5. The sodium ion electrolyte according to claim 1, characterized in that, The additive has a mass concentration of 1% to 5% in the sodium ion electrolyte.

6. The sodium ion electrolyte according to claim 1, characterized in that, The additives include toluene diphenyl phosphate and vinyl sulfite in a mass ratio of 1:1 to 5.

7. The method for preparing the sodium ion electrolyte according to any one of claims 1 to 6, characterized in that, Includes the following steps: The sodium salt, solvent, and additives are mixed to obtain the final product.

8. A sodium-ion battery, characterized in that, Includes the sodium ion electrolyte according to any one of claims 1 to 6.

Images