An electrolyte containing sodium phosphinimide and a sodium-ion battery using the same

Abstract

This invention discloses an electrolyte containing sodium phosphorimide and a sodium-ion battery using the electrolyte. The electrolyte comprises a sodium salt, an organic solvent, a basic additive, and a sodium phosphorimide additive; the structural formula of the sodium phosphorimide additive is shown in Formula I, wherein R1, R2, R... 3， R4 is selected from any one of C1-C6 fluoroalkanes, alkenes, alkynes, cyano, isocyano, isothiocyano, and fluorosulfonyl groups. Compared with the prior art, the electrolyte of this invention uses sodium phosphorimide additive, whose anion has a weak coordination structure with a negatively charged dispersion, thereby effectively improving the conductivity of the electrolyte and reducing the desolvation energy of sodium ions. Furthermore, this sodium salt has high thermal stability, is not sensitive to aqueous acids, and can participate in decomposition to form a film-forming highly stable phosphate inorganic compound. Therefore, the electrolyte of this invention containing sodium phosphorimide can significantly improve the cycle performance, high-temperature storage performance, and low-temperature discharge performance of sodium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to an electrolyte containing sodium phosphorylimide and a sodium-ion battery using the electrolyte. Background Technology

[0002] Currently, lithium-ion batteries are widely used in digital electronics, new energy vehicles, and energy storage applications. However, with the rapid expansion of the market, safety issues and the scarcity of lithium resources are becoming increasingly prominent. Sodium ions have very similar ionic radii and chemical properties to lithium ions, and sodium is more abundant in the Earth's crust. Therefore, sodium-ion batteries are expected to become a promising low-cost and safe energy storage technology to replace lithium-ion batteries.

[0003] Sodium-ion batteries and lithium-ion batteries share a high degree of technological similarity and manufacturing process compatibility. Sodium-ion batteries also achieve energy conversion and storage through the ion migration and intercalation / deintercalation reactions of sodium ions between the positive and negative electrode materials. Among them, the electrolyte of sodium-ion batteries is an important channel for the effective transport of sodium ions and is a key material affecting the performance of sodium-ion batteries. It has an important impact on the electrochemical performance of sodium-ion batteries, such as operating temperature range, cycle life, rate capability, and safety.

[0004] While targeted research on sodium-ion battery electrolytes remains limited, most studies utilize organic electrolyte systems similar to those in lithium-ion batteries. These systems employ sodium hexafluorophosphate as the lithium salt, carbonate or ether solvents as organic solvents, and vinylene carbonate and vinyl sulfate as additives. However, sodium salts like sodium hexafluorophosphate exhibit poor thermal stability and readily decompose to produce harmful substances such as HF acid. Furthermore, traditional additives suffer from poor film-forming stability, leading to various side reactions at the electrolyte-electrode interface, resulting in poor electrochemical performance of sodium-ion batteries. Therefore, exploring and developing novel sodium salt electrolyte additives is of great significance. Summary of the Invention

[0005] Based on the technical problems existing in the prior art, this invention proposes to use sodium phosphorimide as an electrolyte additive, which can significantly improve the cycle performance, high-temperature storage performance and low-temperature discharge performance of sodium-ion batteries.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, a basic additive, and a sodium phosphoryl imide additive.

[0008] The structural formula of the sodium phosphoryl imide additive is shown in formula (I).

[0009]

[0010] In formula (I), R1, R2, R3, and R4 may be the same or different, and are all independently selected from any of the following groups: C1-C5 fluoroalkyl, C2-C6 alkenyl, C2-C6 alkyne, cyano, isocyano, isothiocyano, and fluorosulfonyl.

[0011] Furthermore, the sodium phosphoryl imide additive is selected from at least one of the following compounds 1 to 4:

[0012]

[0013] Further, the base additive is selected from at least one of the following: vinylene carbonate, fluorovinyl carbonate, vinyl sulfate, vinyl sulfate, vinyl sulfite, 1,3-propane sulpholactone, 1,4-butane sulpholactone, methanedisulfonate, succinic acid nitrile, adiponitrile, 1,3,6-hexanetrionitrile, succinic anhydride, 1-propylphosphonic anhydride, N,N'-dicyclohexylcarbodiimide, triallyl phosphate, triargyl phosphate, biphenyl, cyclohexylbenzene, fluorobenzene, triphenyl phosphite, toluene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethylene sulfite, maleic anhydride, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate.

[0014] Further, the sodium salt is selected from at least one of the following: sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(oxalate-borate), sodium difluorooxalate-borate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0015] Further, the organic solvent is selected from at least one of the following: cyclic or linear carbonates, cyclic or linear carboxylic esters, and cyclic or linear ethers; even further, the organic solvent is selected from dimethyl carbonate, diethyl carbonate, methyl 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.

[0016] Furthermore, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 10-35%, organic solvent 60-85%, basic additive 0.2-15%, and sodium phosphorimide additive 1-20%.

[0017] Furthermore, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 10-30%, organic solvent 65-85%, basic additive 1-3%, and sodium phosphoryl imide additive 2-5%.

[0018] According to one embodiment of the present invention, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 14%, organic solvent 82%, basic additive 2%, and sodium phosphoryl imide additive 2%.

[0019] According to one embodiment of the present invention, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 14%, organic solvent 83%, basic additive 2%, and sodium phosphoryl imide additive 1%.

[0020] According to one embodiment of the present invention, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 14%, organic solvent 79%, basic additive 2%, and sodium phosphoryl imide additive 5%.

[0021] According to one embodiment of the present invention, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 14%, organic solvent 74%, basic additive 2%, and sodium phosphoryl imide additive 10%.

[0022] According to one embodiment of the present invention, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 14%, organic solvent 64%, basic additive 2%, and sodium phosphorimide additive 20%.

[0023] According to one embodiment of the present invention, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 14%, organic solvent 83%, basic additive 1%, and sodium phosphorimide additive 2%.

[0024] According to one embodiment of the present invention, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 14%, organic solvent 80%, basic additive 4%, and sodium phosphoryl imide additive 2%.

[0025] According to one embodiment of the present invention, the mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 14%, organic solvent 78%, basic additive 6%, and sodium phosphorimide additive 2%.

[0026] The present invention also provides a method for preparing the above-mentioned sodium-ion battery electrolyte.

[0027] The method for preparing sodium-ion battery electrolyte provided by the present invention includes the following steps: in an inert atmosphere, sodium salt is first added to the organic solvent, and after the sodium salt is completely dissolved, a basic additive and sodium phosphoryl imide additive are added to the system and mixed evenly to obtain sodium-ion battery electrolyte.

[0028] Another object of the present invention is to provide a sodium-ion battery.

[0029] The sodium-ion battery provided by the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the sodium-ion battery electrolyte provided by the present invention as described above.

[0030] Furthermore, the application of sodium phosphorimide as shown in Formula I in the preparation of sodium-ion battery electrolytes also falls within the scope of protection of this invention.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The anion of the sodium phosphorimide additive used in the present invention has a weak coordination structure with negative charge dispersion, which can effectively improve the solubility and conductivity of the lithium salt in the electrolyte and reduce the desolvation energy of sodium ions, thus improving the low-temperature performance of sodium-ion batteries; 2) The sodium phosphorimide additive used in the present invention has high thermal stability, is not sensitive to water and acid, and can participate in the decomposition to form a film to form highly stable phosphate inorganic substances, thus significantly improving the cycle performance and high-temperature storage performance of sodium-ion batteries. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the methods described are conventional methods. Unless otherwise specified, the raw materials are all available from publicly available commercial sources.

[0033] Example 1:

[0034] A sodium-ion battery electrolyte, wherein the mass percentage of each component is as follows: sodium salt (NaPF6) 14%, organic solvent 82%, basic additive (ethylene carbonate) 2%, and sodium phosphorimide additive shown in Compound 1 2%; the organic solvent is a mixed solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5.

[0035]

[0036] The electrolyte was prepared as follows: In an inert atmosphere glove box with water / oxygen levels both <0.1 ppm, NaPF6 was dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of EC:DEC:EMC = 3:2:5, with a sodium salt concentration of 1.3 mol / L. After the sodium salt was completely dissolved, 2% by mass of vinylene carbonate (basic additive) and 2% by mass of Compound 1 additive were added to the electrolyte. The mixture was stirred until homogeneous to obtain the sodium-ion battery electrolyte sample.

[0037] A sodium-ion battery, characterized in that it comprises a positive electrode, a negative electrode, a separator, and a sodium-ion battery electrolyte sample prepared above.

[0038] The sodium-ion battery was prepared as follows: Hard carbon (negative electrode material), conductive SP (conductive base), CMC (binder), and SBR (dispersant) were mixed with a suitable amount of deionized water at a mass ratio of 94.5:1.5:2:2 to form a uniform paste. This paste was then uniformly coated onto a 10μm copper foil serving as the negative electrode current collector and baked at 100℃ for 12 hours to obtain the negative electrode sheet. Na3V2(PO4)3 (positive electrode material), conductive SP (conductive base), and PVDF (binder) were mixed with a suitable amount of NMP solvent at a mass ratio of 95:2:2.5 to form a uniform paste. This paste was then uniformly coated onto a 15μm aluminum foil serving as the positive electrode current collector and baked at 110℃ for 12 hours to obtain the positive electrode sheet. The positive electrode sheet, separator, and negative electrode sheet were stacked sequentially to obtain the sodium-ion battery cell. The battery prepared in this experiment was a 1Ah soft-pack battery. After drying the cell, 9g of electrolyte was injected to obtain the corresponding battery sample.

[0039] Example 2

[0040] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that compound 2 is used instead of compound 1. The rest are the same as in Example 1 and will not be repeated here.

[0041]

[0042] Example 3

[0043] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that compound 3 is used instead of compound 1. The rest are the same as in Example 1 and will not be repeated here.

[0044]

[0045] Example 4

[0046] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that compound 4 is used instead of compound 1. The rest are the same as in Example 1 and will not be repeated here.

[0047]

[0048] Example 5

[0049] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that the amount of compound 1 added is 1%. The rest is the same as in Example 1 and will not be described again.

[0050] Example 6

[0051] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that the amount of compound 1 added is 5%. The rest are the same as in Example 1 and will not be repeated here.

[0052] Example 7

[0053] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that the amount of compound 1 added is 10%. The rest is the same as in Example 1 and will not be repeated here.

[0054] Example 8

[0055] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that the amount of compound 1 added is 20%. The rest are the same as in Example 1 and will not be described again.

[0056] Example 9

[0057] A sodium-ion 9 battery electrolyte and battery are prepared in the same way as in Example 1, except that 2% vinylene carbonate, 1% compound 1 (Example 1), and 1% compound 2 (Example 2) are added as additives. The rest are the same as in Example 1 and will not be repeated.

[0058] Example 10

[0059] A sodium-ion battery electrolyte and battery are prepared in the same way as in Example 1. The only difference is that 1% of the total mass of the electrolyte, 1% of compound 3 (Example 3), and 1% of compound 4 (Example 4) are added as additives. The rest is the same as in Example 1 and will not be repeated.

[0060] Example 11

[0061] A sodium-ion 9 battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that 2% vinylene carbonate, 2% fluoroethylene carbonate, and 2% compound 1 are added as additives according to the total mass of the electrolyte. The rest are the same as in Example 1 and will not be repeated here.

[0062] Example 12

[0063] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1. The only difference is the addition of 2% vinylene carbonate, 2% fluoroethylene carbonate, 2% ethylene sulfate, and 2% compound 1 as additives, based on the total mass of the electrolyte. The rest is the same as in Example 1 and will not be repeated here.

[0064] Comparative Example 1

[0065] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1. The only difference is that the additives contain only 2% vinylene carbonate. The rest are the same as in Example 1 and will not be described again.

[0066] Comparative Example 2

[0067] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1. The only difference is that the additives include 2% vinylene carbonate and 2% fluoroethylene carbonate. The rest are the same as in Example 1 and will not be repeated here.

[0068] Comparative Example 3

[0069] A sodium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that the additives include 2% vinylene carbonate, 2% fluoroethylene carbonate, and 2% vinyl sulfate.

[0070] Test methods: The batteries prepared in the above examples and comparative examples were subjected to room temperature cycling tests, low temperature discharge tests, and high temperature storage performance tests, respectively.

[0071] (I) 25℃ ambient temperature cycling test

[0072] The sodium-ion batteries of Examples 1-6 and Comparative Examples 1-4 were charged to 3.9V at 0.5C constant current and constant voltage at 25°C, with a cutoff current of 0.05C; then discharged to 2.0V at 0.5C constant current, and their initial discharge capacity Q0 was recorded as the initial discharge capacity. After 200 cycles of the same charge-discharge cycle while maintaining a constant ambient temperature, the discharge capacity Q of the 200th cycle was recorded. 300 If the average value of three experimental batteries is taken in parallel testing, then the room temperature discharge capacity retention rate = Q 200 / Q0*100%.

[0073] (II) High-temperature storage performance test at 60℃

[0074] Sodium-ion batteries from Examples 1-6 and Comparative Examples 1-4 were charged to 3.9V at 0.2C constant current and constant voltage at 25℃, with a cutoff current of 0.05C. They were then discharged to 2.0V at 0.2C constant current, and the discharge capacity Q0 was recorded as the initial discharge capacity. Subsequently, the batteries were charged to 3.9V at 0.2C constant current and constant voltage, with a cutoff current of 0.05C. The fully charged experimental batteries were then placed in a 60℃ oven for 7 days. After high-temperature storage, the cells were discharged to 2.0V at 0.2C constant current, and the discharge capacity Q1 was recorded. Then, the batteries were charged to 3.9V at 0.2C constant current and constant voltage, and then discharged to 2.0V at 0.2C constant current, and the discharge capacity Q2 was recorded. This process was repeated for three parallel experimental batteries, and the average value was taken. The high-temperature storage capacity retention rate = Q1 / Q0*100%, and the high-temperature storage capacity recovery rate = Q2 / Q0*100%.

[0075] (III) Low-temperature discharge performance test at -20℃

[0076] Sodium-ion batteries from Examples 1-6 and Comparative Examples 1-4 were charged to 3.9V at 25℃ using a constant current and constant voltage of 0.2C, with a cutoff current of 0.05C. They were then discharged to 2.0V using a constant current of 0.2C, and their discharge capacity Q0 was recorded as the initial discharge capacity. The battery was charged to 3.9V using a constant current and constant voltage of 0.2C, with a cutoff current of 0.05C. The sample was then placed at -20℃ for 3 hours to reach temperature equilibrium. The experimental cell was then discharged to 2.0V using a constant current of 0.2C, and its discharge capacity Q1 was recorded. This process was repeated for three parallel experimental batteries, and the average value was taken. The low-temperature discharge capacity retention rate was calculated as Q1 / Q0*100%. The test results are shown in Table 1.

[0077] Table 1. Test results of battery samples from the examples and comparative examples.

[0078]

[0079] The test data from Comparative Examples 1-4 show that using only basic additives such as vinylene carbonate, fluoroethylene carbonate, and ethylene sulfate results in poor electrolyte cycling performance. The highest capacity retention after 200 cycles at room temperature is 83.7%. High-temperature storage performance is also poor, with a highest capacity retention of only 79.6% and a highest recovery rate of 87.5%. This is mainly due to the instability of sodium hexafluorophosphate, the poor film-forming stability of conventional additives, and severe side reactions between the electrolyte and electrode materials. Furthermore, the low-temperature performance of the comparative electrolyte is also poor, with a highest capacity retention of only 76.2% at -20℃. This is primarily because conventional additives result in uneven film formation, leading to thicker films with higher impedance, thus contributing to poor low-temperature performance.

[0080] In contrast, the test data from Examples 1-12 show that using one or a combination of sodium phosphorimide additives (compounds 1-4) as additives resulted in a minimum capacity retention of 85.2% after 200 cycles at room temperature, a minimum capacity retention of 80.5% after 60°C high-temperature storage, and a minimum recovery rate of 90.1%, demonstrating significant improvements in high-temperature cycling and high-temperature storage performance. Simultaneously, the minimum capacity retention at -20°C low-temperature discharge was 77.2%, indicating that the sodium phosphorimide additive also exhibits improved low-temperature performance. Therefore, the sodium phosphorimide additive anion used in this invention possesses a weakly coordinated structure with a negatively charged dispersion, effectively improving the electrolyte conductivity and reducing the desolvation energy of sodium ions. Furthermore, this sodium salt exhibits high thermal stability, is insensitive to aqueous acids, and can participate in decomposition to form a highly stable phosphate-based inorganic compound, thereby enhancing the cycling, high-temperature storage, and low-temperature discharge performance of sodium-ion batteries, achieving the beneficial effects of this invention.

[0081] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A sodium-ion battery electrolyte, comprising a sodium salt, an organic solvent, a basic additive, and a sodium phosphorimide additive; wherein the sodium phosphorimide additive has the structural formula shown in formula (I). In formula (I), R1, R2, R3, and R4 may be the same or different, and are all independently selected from any of the following groups: cyano or fluorosulfonyl.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that: The sodium phosphoryl imide additive is selected from at least one of the following compounds 3 to 4: 。 3. The sodium-ion battery electrolyte according to claim 1 or 2, characterized in that: The base additive is selected from at least one of the following: vinylene carbonate, fluorovinyl carbonate, vinyl sulfate, vinyl sulfate, vinyl sulfite, 1,3-propane sulpholactone, 1,4-butane sulpholactone, methanedisulfonate, succinate, adiponitrile, 1,3,6 Hexanetrionitrile, succinic anhydride, 1 Propylphosphoanhydride, N,N' Dicyclohexylcarbodiimide, Triallyl phosphate, Triargyl phosphate, Biphenyl, Cyclohexylbenzene, Fluorobenzene, Triphenyl phosphite, Toluene, 1,1,2,2 Tetrafluoroethyl 2,2,3,3 Tetrafluoropropyl ether, ethylene sulfite, maleic anhydride, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate.

4. The sodium-ion battery electrolyte according to claim 1 or 2, characterized in that: The sodium salt is selected from at least one of the following: sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(oxalate)borate, sodium difluorooxalateborate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

5. The sodium-ion battery electrolyte according to claim 1 or 2, characterized in that: The organic solvent is selected from at least one of the following: cyclic or chain carbonates, cyclic or linear carboxylic esters, and cyclic or linear ethers.

6. The sodium-ion battery electrolyte according to claim 5, characterized in that: The organic solvent is selected from at least one of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl 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.

7. The sodium-ion battery electrolyte according to claim 1 or 2, characterized in that: The mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 10-35%, organic solvent 60-85%, basic additive 0.2-15%, and sodium phosphorimide additive 1-20%.

8. The sodium-ion battery electrolyte according to claim 7, characterized in that: The mass percentage of each component in the sodium-ion battery electrolyte is as follows: sodium salt 13-18%, organic solvent 65-80%, basic additive 1-3%, and sodium phosphoryl imide additive 2-5%.

9. A method for preparing a sodium-ion battery electrolyte according to any one of claims 1-8, comprising the following steps: adding a sodium salt to the organic solvent in an inert atmosphere, and after the sodium salt is completely dissolved, adding the basic additive and the sodium phosphoryl imide additive to the system, mixing evenly to obtain a sodium-ion battery electrolyte.

10. A sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein, The electrolyte is the sodium-ion battery electrolyte according to any one of claims 1-8.

11. The use of sodium phosphorimide as shown in Formula I of claim 1 in the preparation of sodium-ion battery electrolyte.

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