Sodium-ion battery non-aqueous electrolyte

Abstract

The invention discloses a non-aqueous electrolyte for a sodium ion battery. The non-aqueous electrolyte comprises the following components in parts by weight: 70-85 parts of an organic solvent, 10-20 parts of an electrolyte, 0.5-5 parts of a first film-forming additive and 0.5-5 parts of a second film-forming additive, the first film-forming additive is selected from any one or more of 1, 3-propene sultone, 1, 3-propane sultone, methylene methanedisulfonate and 1, 4-butane sultone, and the second film-forming additive is selected from any one or more of 1, 3-propene sultone, 1, 3-propane sultone, methylene methanedisulfonate and 1, 4-butane sultone; the second film-forming additive is selected from any one or more of fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, vinylene sulfate and ethylene sulfite; the electrolyte is composed of sodium hexafluorophosphate, sodium bis (oxalato) borate, sodium bis (fluorosulfonyl) imide and sodium tetrafluoroborate according to the weight ratio of (14-24): (0-1): (0-1): (0-1). By adding the first film-forming additive and the second film-forming additive, the battery film formation is facilitated, the cycle performance is improved, the service life of the sodium battery can be more effectively prolonged, and the sodium battery can be better applied to the fields of energy storage, low-speed vehicles and passenger vehicles.

Description

Technical Field

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

[0002] Sodium-ion batteries (SIBs) are considered to be the most promising battery technology in the post-lithium era due to their abundant sodium reserves. Sodium is one of the elements with higher content in the earth's crust, and its abundance is 2-3 orders of magnitude higher than that of lithium. Both sodium-ion batteries and lithium-ion batteries use the "rocking chair" charging and discharging working principle. The chemical properties of sodium are similar to those of lithium. Although compared with lithium-ion batteries, the sodium charge-to-mass ratio, specific capacity, and capacity density are lower than those of lithium, making the energy density upper limit of sodium-ion batteries lower than that of lithium-ion batteries. However, sodium-ion batteries have several major advantages: (1) Obvious cost advantage, with the total material cost being 30% to 40% lower than that of lithium batteries. The positive electrode materials in sodium-ion batteries are almost free from the dependence on the low-abundance and expensive Co and Ni elements, and have a wider range of choices. At present, hundreds of sodium-ion battery positive electrode materials have been announced. The commonly used Fe, Mn, and Al elements are abundant in the earth's crust, and the annual mineral output is considerable. Among them, the cost of sodium-copper-iron-manganese ternary materials with great potential is only about 1 / 2 of that of lithium iron phosphate, which makes the cost of sodium-ion batteries have a significant competitive advantage; (2) Sodium batteries use coal-based carbon as the negative electrode material, and do not require the negative electrode graphitization process. Compared with the traditional lithium-ion battery graphite negative electrode, the cost is less than 1 / 10. (3) Sodium battery current collectors can be replaced by cheap aluminum foil. Since sodium ions and aluminum will not undergo alloying reaction at low potential, the sodium ion positive electrode current collector can be replaced by cheaper aluminum foil instead of the expensive copper foil current collector in traditional lithium-ion batteries, further reducing battery costs; at the same time, the density of aluminum metal is lower than that of copper, and its weight is 1 / 10 lower than that of copper foil.

[0003] The performance of sodium-ion batteries is complementary to that of lithium-ion batteries, and they are expected to replace lithium-ion batteries such as lithium iron phosphate in some areas. Although the energy density and cycle life of sodium-ion batteries are not as good as those of lithium-ion batteries, their better cost-effectiveness, rate performance, low-temperature performance and more stable electrochemical performance determine that they have better comparative advantages in the energy storage, low-speed vehicles and passenger car segments. However, sodium batteries also have problems such as the generation of a large amount of gas during the conventional capacity division process, the dissolution of positive electrode metal ions during the subsequent cycle process, and the oxidation of the electrolyte at the positive electrode. Summary of the invention

[0004] In view of the technical problems that a large amount of gas is generated in the existing sodium battery during the capacity division and circulation process, and the electrolyte is oxidized at the positive electrode, the present invention provides a sodium ion battery non-aqueous electrolyte to solve the above problems and solve the problem of high cost of current lithium batteries.

[0005] To achieve the above object, the technical solution adopted by the present invention is a sodium ion battery non-aqueous electrolyte, which is composed of the following components in parts by weight: 70-85 parts of an organic solvent, 10-20 parts of an electrolyte, 0.5-5 parts of a first film-forming additive, and 0.5-5 parts of a second film-forming additive; The organic solvent is selected from two or more of cyclic carbonates, chain carbonates and chain ethers; The first film-forming additive is selected from any one or more of 1,3-propylene sultone, 1,3-propane sultone, methylene disulfonate, and 1,4-butane sultone; The second film-forming additive is selected from any one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinylene sulfate, and ethylene sulfite; The electrolyte is composed of sodium hexafluorophosphate, sodium bis(oxalatoborate), sodium bis(fluorosulfonyl)imide and sodium tetrafluoroborate in a weight ratio of (14-24):(0-1):(0-1):(0-1).

[0006] Preferably, the electrolyte is composed of the following components in parts by weight: 80-85 parts of an organic solvent, 14-18 parts of an electrolyte, 0.5-3 parts of a first film-forming additive, and 1-5 parts of a second film-forming additive.

[0007] Preferably, the organic solvent is selected from two or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate, and ethylene glycol diethyl ether.

[0008] Further preferably, the organic solvent is composed of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a weight ratio of (30-50):(10-20):(10-20):(5-40).

[0009] The beneficial effects of the present invention are as follows: by adding sodium bis(oxalatoborate), sodium bis(fluorosulfonylimide) and sodium tetrafluoroborate to the electrolyte sodium hexafluorophosphate, the ionic conductivity and sodium ion migration number of the electrolyte can be further improved, the ionic capacity of the electrolyte can be enhanced, and the battery cycle can be improved. By adding the first film-forming additive and the second film-forming additive, the formation of polycarbonate compounds (SEI film components) can be promoted, and the impedance of the SEI film on the negative electrode surface can be reduced, and it is helpful to improve the low-temperature performance of the battery. It can also inhibit the decomposition of the positive electrode surface that may occur during high-temperature cycling, and prevent the oxidation reaction of the electrolyte solution, thereby improving the output characteristics and swelling characteristics after high-temperature storage, and improving the cycle performance. The non-aqueous electrolyte of the present invention can more effectively extend the service life of the sodium battery, and can be better used in the fields of energy storage, low-speed vehicles and passenger vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1The electrical performance test results of the embodiments and comparative examples are shown in FIG. DETAILED DESCRIPTION

[0011] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0012] The preparation method of the non-aqueous electrolyte for sodium ion batteries in the following examples and comparative examples is as follows: use a glove box, require the working gas to use 99.999% argon or nitrogen, the moisture content of the glove box environment is less than 10ppm, the oxygen content is less than 10ppm, the organic solvent purity is required to be greater than 99.99%, and the moisture content is required to be less than 5ppm. Weigh each material in the glove box according to the mass ratio. When preparing, pay attention to adding organic solvents and additives (first film-forming additives, second film-forming additives) first, and then add electrolytes. Pay attention to cooling before adding additives and electrolytes. The temperature is required to be less than 10°C, and then mix and stir for 1h to detect moisture, free acid, conductivity, and density. Then inject 18650-1600mAh and test the battery's first efficiency, cycle, rate discharge and other performance.

[0013] Example 1 Weigh 600 g of dimethyl carbonate, 100 g of ethylene carbonate, 200 g of ethyl methyl carbonate, 780 g of propylene carbonate, 230 g of sodium hexafluorophosphate, 10 g of sodium bis(oxalatoborate), 10 g of sodium bis(fluorosulfonyl)imide, 10 g of sodium tetrafluoroborate, 40 g of fluoroethylene carbonate, 10 g of 1,3-propylene sultone, and 10 g of vinylene carbonate to prepare an electrolyte in a glove box.

[0014] Example 2 Weigh 600 g of dimethyl carbonate, 100 g of ethylene carbonate, 200 g of ethyl methyl carbonate, 730 g of propylene carbonate, 240 g of sodium hexafluorophosphate, 10 g of sodium bis(fluorosulfonyl)imide, 10 g of sodium tetrafluoroborate, 60 g of fluoroethylene carbonate, 40 g of 1,3-propylene sultone, and 10 g of vinylene carbonate, and prepare an electrolyte in a glove box.

[0015] Example 3 Weigh 600 g of dimethyl carbonate, 100 g of ethylene carbonate, 200 g of ethyl methyl carbonate, 780 g of propylene carbonate, 240 g of sodium hexafluorophosphate, 10 g of sodium bis(oxalatoborate), 10 g of sodium bis(fluorosulfonyl)imide, 40 g of fluoroethylene carbonate, 10 g of 1,3-propylene sultone, and 10 g of vinylene carbonate to prepare an electrolyte in a glove box.

[0016] Example 4 Weigh 600 g of dimethyl carbonate, 100 g of ethylene carbonate, 200 g of ethyl methyl carbonate, 780 g of propylene carbonate, 240 g of sodium hexafluorophosphate, 10 g of sodium bis(fluorosulfonyl)imide, 10 g of sodium tetrafluoroborate, 40 g of fluoroethylene carbonate, 10 g of 1,3-propylene sultone, and 10 g of vinylene carbonate to prepare an electrolyte in a glove box.

[0017] Comparative Example 5 600 g of dimethyl carbonate, 100 g of ethylene carbonate, 200 g of ethyl methyl carbonate, 780 g of propylene carbonate, 240 g of sodium hexafluorophosphate, 40 g of fluoroethylene carbonate, 10 g of 1,3-propylene sultone, and 10 g of vinylene carbonate were weighed to prepare an electrolyte in a glove box.

[0018] Comparative Example 6 600 g of dimethyl carbonate, 100 g of ethylene carbonate, 200 g of ethyl methyl carbonate, 840 g of propylene carbonate, and 260 g of sodium hexafluorophosphate were weighed to prepare an electrolyte in a glove box.

[0019] Then the battery of the above embodiment and comparative example was injected with liquid in the glove box, and each battery was injected with 5.8±0.1g liquid and aged for 24h to test the electrical performance: 1: 0.2C constant current charging for 120min, stand for 5min, 0.5C constant current charging for 120min, cut-off voltage 3.85V, vacuum seal and then perform capacity division: constant current and constant voltage charging 0.5C constant current and constant voltage charging to 4V; stand for 5min; constant current discharge to 1.5V, then cycle constant current and constant voltage charging 0.5C; constant current and constant voltage charging to 4V, calculate the first efficiency: the first discharge capacity after capacity division / the total charge before discharge*100%.

[0020] 2: 25℃ cycle project: 1C constant current constant voltage charge to 4.0V, cut-off current 0.02C, stand for 2min, 3C constant current discharge to 1.5V, stand for 2min. Cycle 1500 times and calculate the capacity retention rate. 1500-week capacity retention rate (%) = 1500th week discharge capacity / first discharge capacity*100%.

[0021] The test results are shown in Table 1 and Figure 1 shown.

[0022] Table 1

[0023] It can be seen from Table 1 that: under the cycle performance charge and discharge test, the battery efficiency of the electrolyte of Comparative Example 6 in which no additives are added to the electrolyte is cycled at 25°C for the first time, and decays rapidly with the increase of the number of charge and discharge times. Without additives, the formation of the SEI film is unstable, which is not conducive to cycling.

[0024] The electrolyte with additives, such as Comparative Example 5, has improved cycle performance compared with Comparative Example 6, indicating that the addition of sodium bis(oxalatoborate), sodium bis(fluorosulfonyl)imide, and sodium tetrafluoroborate can further improve the battery cycle performance by using additives such as fluoroethylene carbonate, 1,3-propylene sultone, and vinylene carbonate. Fluorinated ethylene carbonate, 1,3-propylene sultone, and vinylene carbonate help the battery film to form and improve the cycle performance.

[0025] The first effect and cycle of Examples 1 and 3 are better than those of other groups, indicating that sodium bis(fluorosulfonyl)imide exhibits rate cycling performance; and it can form a film preferentially when combined with bis(oxalylboric acid) to protect the negative electrode. It is rich in a large number of boron-oxygen bonds, which are beneficial to improving the cycle and the later gas production problem of sodium ions.

Claims

1. A non-aqueous electrolyte for sodium ion batteries, characterized in that The invention is composed of the following components in parts by weight: 70-85 parts of an organic solvent, 10-20 parts of an electrolyte, 0.5-5 parts of a first film-forming additive, and 0.5-5 parts of a second film-forming additive; The organic solvent is selected from two or more of cyclic carbonates, chain carbonates and chain ethers; The first film-forming additive is selected from any one or more of 1,3-propylene sultone, 1,3-propane sultone, methylene disulfonate, and 1,4-butane sultone; The second film-forming additive is selected from any one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinylene sulfate, and ethylene sulfite; The electrolyte is composed of sodium hexafluorophosphate, sodium bis(oxalatoborate), sodium bis(fluorosulfonyl)imide and sodium tetrafluoroborate in a weight ratio of (14-24):(0-1):(0-1):(0-1).

2. The non-aqueous electrolyte for sodium ion batteries according to claim 1, characterized in that: The electrolyte solution is composed of the following components in parts by weight: 80-85 parts of an organic solvent, 14-18 parts of an electrolyte, 0.5-3 parts of a first film-forming additive, and 1-5 parts of a second film-forming additive.

3. The non-aqueous electrolyte for sodium ion batteries according to claim 1, characterized in that: The organic solvent is selected from two or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate, and ethylene glycol diethyl ether.

4. The non-aqueous electrolyte for sodium ion batteries according to claim 3, characterized in that: The organic solvent is composed of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a weight ratio of (30-50):(10-20):(10-20):(5-40).

Images