Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The invention provides a sodium-ion battery electrolyte and a sodium-ion battery, and relates to the technical field of sodium-ion batteries. The sodium-ion battery electrolyte comprises sodium salt, an organic solvent, a basic additive and a combined additive, the combined additive comprises a fluorine-containing phosphazene compound and a bromine-containing benzene ring compound. The combined additive in the sodium-ion battery participates in the film forming reaction on the surface of the electrode material to form an electrolyte film containing sodium fluoride and sodium bromide, so that the Na < + > transmission performance and the interfacial film stability are improved, the precipitation of sodium dendrites is inhibited, and the high-temperature shelving and normal-high-temperature cycle performance of the sodium-ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery electrolyte and a sodium ion battery. Background Art

[0002] With the extensive use of fossil energy, global air pollution has gradually worsened. Therefore, the development of green renewable energy has received widespread attention. Among them, lithium-ion and sodium-ion batteries responsible for storing green energy have developed rapidly and have been successfully applied in many fields. Compared with lithium batteries, sodium batteries have more abundant reserves in domestic resources, are more widely distributed, and are cheap and stable. Therefore, sodium batteries have been considered an excellent alternative in recent years.

[0003] However, the formation of sodium dendrites during the continuous charge and discharge process will cause the cycle life to decrease. Therefore, how to inhibit the formation of sodium dendrites and improve the electrolyte stability and cycle life is an urgent problem to be solved. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a sodium ion battery electrolyte and a sodium ion battery.

[0005] The invention discloses a sodium ion battery electrolyte, comprising a sodium salt, an organic solvent, a basic additive and a combined additive; the combined additive comprises a fluorine-containing phosphazene compound and a bromine-containing benzene ring compound.

[0006] The sodium ion electrolyte of the present invention includes a combination of additives, which can form a solid electrolyte interface layer on the surface of the positive and negative electrodes to inhibit the growth of sodium dendrites, thereby improving the electrochemical performance of the sodium ion battery.

[0007] Preferably, the fluorine-containing phosphazene compound has a structural formula as shown in Formula I,

[0008]

[0009] In the formula I, R is selected from one or more of an alkoxy group, a phenoxy group, and a fluorine atom.

[0010] More preferably, the fluorophosphazene-containing compound is selected from any one of compounds 1 to 3:

[0011]

[0012] Preferably, the bromine-containing benzene ring compound is selected from any one of compounds 4 to 6:

[0013]

[0014] The electrolyte of the present invention uses a combination of additives. When a fluorine-containing phosphazene compound and a bromine-containing benzene ring compound are used together, a solid electrolyte membrane containing sodium fluoride and sodium bromide is formed. On the one hand, the mechanical strength and stability of the interface membrane are improved, and the diffusion rate of sodium ions is increased. On the other hand, the deposition morphology of sodium is changed by sodium bromide and sodium fluoride makes sodium deposited uniformly. The combined action inhibits the formation of sodium dendrites, thereby improving the stability of the battery and the normal and high temperature cycle performance.

[0015] Preferably, the basic additive is selected from one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, 1,4-butane sultone, methylene methanesulfonate, vinyl ethylene carbonate, and styrene carbonate.

[0016] The function of the basic additive is to form a SEI / CEI film at the positive or negative electrode interface, prevent the oxidation or reduction of the solvent or sodium salt during the charge and discharge process, broaden the electrochemical window of the electrolyte, and improve the high voltage performance of the battery.

[0017] Preferably, the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(oxalatoborate), sodium difluorooxalatoborate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0018] The selection of sodium salt helps to improve the conductivity of the electrolyte, thereby improving the capacity and efficiency of the battery.

[0019] Preferably, the organic solvent is selected from one or more of cyclic or linear carbonates, cyclic or linear carboxylates, and cyclic or linear ethers.

[0020] The function of organic solvents is to dissolve sodium salts, increase the dielectric constant of the electrolyte, reduce the viscosity of the electrolyte, increase the conductivity of the electrolyte liquid phase, reduce the internal resistance of the battery, and improve the battery cycle performance.

[0021] Preferably, the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, ethyl propionate, methyl butyrate, butyl acetate, methyl propionate, propyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0022] A sodium ion battery electrolyte comprises, by weight percentage, 6-40% sodium salt, 65-85% organic solvent, 0.5-10% basic additive, and 1-12% combined additive.

[0023] The mass percentage of raw materials in the sodium ion battery electrolyte is within a certain range, which helps to balance the various physical and electrical properties, making the electrolyte have a wide operating temperature range, a high dielectric constant, low viscosity, and uniform film formation on the positive and negative electrode interfaces, which can ensure that the high-temperature shelf and cycle performance are improved without sacrificing capacity and initial efficiency.

[0024] Preferably, the mass of the fluorophosphazene-containing compound in the combined additive accounts for 0.5-6% of the total mass of the electrolyte; the mass of the bromine-containing benzene ring compound in the combined additive accounts for 0.5-6% of the total mass of the electrolyte.

[0025] Controlling the quality of fluorophosphazene-containing compounds and bromine-containing benzene ring compounds within a certain range will help improve Na + The transmission performance and interface film stability can inhibit the precipitation of sodium dendrites, which can achieve better protection of the positive and negative electrodes and complete consumption of additives, thereby improving the high-temperature storage and normal high-temperature cycle performance of sodium-ion batteries.

[0026] A sodium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and the sodium ion battery electrolyte mentioned above.

[0027] The beneficial effects of the present invention are:

[0028] The sodium ion battery of the present invention uses a combination additive of a fluorine-containing phosphazene compound and a bromine-containing benzene ring compound. The combination additive participates in a film-forming reaction on the surface of an electrode material to form an electrolyte membrane containing sodium fluoride and sodium bromide, which not only improves the mechanical strength and stability of the interface membrane and the sodium ion diffusion rate, but also the sodium bromide in the membrane can adjust the deposition morphology of sodium, and the sodium fluoride makes the sodium deposited uniformly, which jointly inhibits the formation of sodium dendrites, improves the stability of the sodium ion battery in a high temperature environment, and improves the high-temperature shelf and normal and high-temperature cycle electrical performance. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is described in detail through specific embodiments.

[0030] Unless otherwise specified, the materials, reagents, etc. used in the following examples and comparative examples can be obtained from commercial sources.

[0031] Compound 1 (CAS: 33027-66-6), Compound 2 (CAS: 15599-91-4), Compound 3 (CAS: 33027-68-8), Compound 4 (CAS: 583-53-9), Compound 5 (CAS: 108-36-1), Compound 6 (CAS: 106-37-6).

[0032] Example 1

[0033] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 5wt% compound 1 and 3wt% compound 4 are added, and the mixture is mixed and stirred to obtain a sodium ion battery electrolyte.

[0034] Example 2

[0035] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 5wt% compound 1 and 3wt% compound 5 are added, and the mixture is mixed and stirred to obtain a sodium ion battery electrolyte.

[0036] Example 3

[0037] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 5wt% compound 1 and 3wt% compound 6 are added, and the mixture is mixed and stirred to obtain a sodium ion battery electrolyte.

[0038] Comparative Example 1

[0039] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, the mixture is mixed and stirred to obtain a sodium ion battery electrolyte.

[0040] Comparative Example 2

[0041] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 5wt% compound 1 is added, and the mixture is mixed and stirred to obtain a sodium ion battery electrolyte.

[0042] Comparative Example 3

[0043] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 5wt% compound 2 is added, and the mixture is mixed and stirred evenly to obtain a sodium ion battery electrolyte.

[0044] Comparative Example 4

[0045] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 5wt% compound 3 is added, and the mixture is mixed and stirred to obtain a sodium ion battery electrolyte.

[0046] Comparative Example 5

[0047] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 3wt% compound 4 is added, and the mixture is mixed and stirred to obtain a sodium ion battery electrolyte.

[0048] Comparative Example 6

[0049] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 3wt% compound 5 is added, and the mixture is mixed and stirred to obtain a sodium ion battery electrolyte.

[0050] Comparative Example 7

[0051] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen indicators all less than 0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and after mixing, 12wt% NaPF6 and 1wt% VC are added. After the sodium salt is completely dissolved, 3wt% compound 6 is added, and the mixture is mixed and stirred evenly to obtain a sodium ion battery electrolyte.

[0052] The sodium ion electrolyte obtained above is assembled with the positive electrode sheet, the separator, and the negative electrode sheet to obtain a sodium ion battery, as follows:

[0053] The preparation method of a sodium ion battery comprises: adding an appropriate amount of deionized water to a negative electrode material hard carbon, a conductive base SP, a binder CMC, and a dispersant SBR according to a mass ratio of 94.5:1.5:2:2, mixing into a uniform paste, uniformly coating the paste on a copper foil of a negative electrode current collector, and baking at 100°C for 12 hours to obtain a negative electrode sheet; 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2, conductive agent SP, and binder PVDF are mixed in a mass ratio of 95:2:2.5, and an appropriate amount of NMP solvent is added. The mixture is mixed into a uniform paste, and the mixture is evenly coated on the aluminum foil of the positive electrode collector and baked at 110°C for 12 h to obtain the positive electrode sheet; the positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence to obtain a sodium ion battery cell. The battery prepared in the experiment is a 1.8Ah soft-pack battery. After the cell is dried, 14g of the above-mentioned sodium ion battery electrolyte is injected to obtain a sodium ion battery.

[0054] The sodium ion battery was subjected to normal and high temperature cycle tests and high temperature shelf performance tests, respectively. The test results are shown in Table 1. (1) 25°C / 45°C high temperature cycle test: At 25°C / 45°C, the sodium ion battery was charged to 3.9V using a constant current and constant voltage of 0.5C and a cut-off current of 0.05C; then discharged to 2.0V using a constant current of 0.5C, and its discharge capacity Q0 was recorded as the initial discharge capacity. After 1000 cycles of the same charge and discharge method with the ambient temperature kept unchanged, the 1000th discharge capacity Q was recorded. 1000 , then the room temperature discharge capacity retention rate = Q 1000 / Q0*100%. (2) 45℃ high temperature storage performance test: At 25℃, the above sodium ion batteries were charged to 3.9V with 0.2C constant current and constant voltage, and the cut-off current was 0.05C; then discharged to 2.0V with 0.2C constant current, and the discharge capacity Q0 was recorded as the initial discharge capacity. Subsequently, the fully charged experimental battery was charged to 3.9V with 0.2C constant current and constant voltage, and the cut-off current was 0.05C. The fully charged experimental battery was then placed in a 45℃ oven for 28 days. The experimental battery cell after high temperature storage was taken out and discharged to 2.0V with 0.2C constant current, and the discharge capacity Q1 was recorded. The three experimental batteries were tested in parallel and the average value was taken. The high temperature storage capacity retention rate = Q1 / Q0*100%.

[0055] Table 1

[0056]

[0057] From the comparison between the above embodiments and comparative examples, it can be seen that the combined additives of the present invention can effectively improve the normal and high temperature cycle retention rates and enhance the high temperature shelf performance. Combined with the data of comparative examples 1 to 4, the addition of fluorine-containing phosphazene compounds alone can significantly improve the normal temperature cycle retention rate and high shelf retention rate and recovery rate, and the addition of compound 1 has the most obvious effect; combined with the data of comparative examples 5 to 7 and comparative example 1, the addition of bromine-containing benzene ring compounds alone can greatly improve the high cycle retention rate, slightly improve the normal cycle and high shelf retention rate and recovery rate, and the addition of compound 4 has the best improvement effect; combined with the data of embodiments 1 to 3 and comparative examples 1 to 7, the fluorine-containing phosphazene compounds and bromine-containing benzene ring compounds play a synergistic role in combining to significantly improve the normal and high temperature cycle retention rate, and can also significantly improve the high shelf retention rate and recovery rate.

[0058] In summary, the sodium ion battery assembled with the electrolyte provided by the present invention has excellent normal and high temperature capacity retention rates.

[0059] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A sodium ion battery electrolyte, characterized in that: It includes sodium salt, organic solvent, basic additive and combined additive; the combined additive includes fluorine-containing phosphazene compound and bromine-containing benzene ring compound.

2. The electrolyte according to claim 1, characterized in that The fluorine-containing phosphazene compound has a structural formula as shown in Formula I, In the formula I, R is selected from one or more of an alkoxy group, a phenoxy group, and a fluorine atom.

3. The electrolyte according to any one of claims 1 to 2, characterized in that The fluorine-containing phosphazene compound is selected from any one of compounds 1 to 3:

4. The electrolyte according to claim 1, characterized in that The bromine-containing benzene ring compound is selected from any one of compounds 4 to 6:

5. The electrolyte according to claim 1, characterized in that The basic additive is selected from one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, 1,4-butane sultone, methylene methane sulfonate, vinyl ethylene carbonate, and styrene carbonate.

6. The electrolyte according to claim 1, characterized in that The sodium salt is selected from one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(oxalatoborate), sodium difluorooxalatoborate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

7. The electrolyte according to claim 1, characterized in that The organic solvent is selected from one or more of cyclic or chain carbonates, cyclic or linear carboxylates, and cyclic or linear ethers.

8. The electrolyte according to claim 1, characterized in that Calculated by mass percentage, it includes 6-40% sodium salt, 65-85% organic solvent, 0.5-10% basic additive and 1-12% combined additive.

9. The electrolyte according to claim 8, characterized in that The mass of the fluorophosphazene-containing compound in the combined additive accounts for 0.5-6% of the total mass of the electrolyte; the mass of the bromine-containing benzene ring compound in the combined additive accounts for 0.5-6% of the total mass of the electrolyte.

10. A sodium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 9.

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