A low-temperature resistant sodium-ion battery electrolyte and a sodium-ion battery

Abstract

The present invention discloses a low-temperature resistant sodium-ion battery electrolyte and a sodium-ion battery. The electrolyte comprises the following components: an organic solvent, a sodium salt electrolyte, and a low-melting-point linear carboxylic acid ester additive. The low-melting-point linear carboxylic acid ester additive is a carboxylic acid ester containing a -RCOOR- group, and the low-melting-point linear carboxylic acid ester accounts for 1-30% of the volume of the low-temperature resistant sodium-ion battery electrolyte. The low-temperature resistant sodium-ion battery electrolyte of the present invention has the characteristics of good low-temperature conductivity, good interfacial stability, and excellent rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and specifically refers to a low-temperature resistant sodium-ion battery electrolyte and a sodium-ion battery. Background Art

[0002] Sodium-ion batteries are rich in resource reserves and have low costs, and are expected to be widely used in the energy storage field. However, for sodium-ion batteries used for energy storage, due to the differences in the application environment from lithium-ion batteries, there are relatively high requirements for the high and low temperature charge and discharge capabilities, rate performance, and cycle stability of sodium-ion batteries.

[0003] Currently, commercial sodium-ion battery electrolytes mostly consist of sodium hexafluorophosphate as the sodium salt, ethylene carbonate with high viscosity and high freezing point (<36.4 °C), and low-viscosity linear carbonate solvents. Among them, ethylene carbonate will be reductively decomposed on the surface of the negative electrode at a relatively low potential (~2.71 V vs SHE) to form a dense SEI film, thereby weakening the continuous decomposition of the electrolyte and avoiding gas generation and swelling of the sodium-ion battery. However, the relatively high freezing point of ethylene carbonate causes it to precipitate at low temperatures (<0 °C), affecting the normal use of sodium-ion batteries. In addition, ethylene carbonate will be oxidatively decomposed at a relatively high potential (>4.3 V), generating a large amount of gas, and in severe cases, it will cause safety accidents. To solve this problem, in recent years, propylene carbonate, as an electrolyte component with high antioxidant properties, has been widely used in lithium-ion / sodium-ion battery electrolytes. However, propylene carbonate will be nucleophilically attacked by sodium ions at a relatively low potential (~2.71 V vs SHE), resulting in a nucleophilic addition ring-opening reaction and continuous decomposition of propylene carbonate. Therefore, reasonably adjusting the ratio of ethylene carbonate and propylene carbonate in the electrolyte can, to a certain extent, weaken the reduction reaction on the negative electrode side and the oxidation side reaction on the positive electrode side of the electrolyte. However, ethylene carbonate and propylene carbonate both belong to the cyclic carbonate type, and they have the characteristics of high dielectric constant and high viscosity. At relatively low temperatures (<-40 °C), the high viscosity and high freezing point characteristics of cyclic carbonates lead to low sodium-ion conductivity, seriously affecting the diffusion of sodium ions and resulting in poor rate performance and low-temperature performance of sodium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-temperature resistant sodium-ion battery electrolyte and a sodium-ion battery, which have the characteristics of good low-temperature conductivity, good interfacial stability, and excellent rate performance.

[0005] The present invention can be realized by the following technical solutions:

[0006] The present invention discloses a low-temperature resistant sodium-ion battery electrolyte, which comprises the following components: an organic solvent, a sodium salt electrolyte, and a low-melting-point linear carboxylic acid ester additive. The low-melting-point linear carboxylic acid ester additive is a carboxylic acid ester containing the -RCOOR- group, and the low-melting-point linear carboxylic acid ester accounts for 1-30% of the volume of the low-temperature resistant sodium-ion battery electrolyte.

[0007] In the present invention, by reasonably optimizing the proportions of the organic solvent, the sodium salt, and the low-melting-point linear carboxylic acid ester additive, the rate performance, low-temperature performance, and cycle stability of the sodium-ion battery are improved. The low-temperature performance, rate performance, and cycle stability are crucial for the large-scale application of sodium-ion batteries. The present invention forms a technical solution aiming at the defect that the commercially available electrolyte formulations are difficult to simultaneously meet the above conditions. The present invention mixes the organic solvent, the sodium salt electrolyte, and the low-melting-point linear carboxylic acid ester additive in a specific proportion, and an electrolyte with high ionic conductivity and good stability under low-temperature conditions can be obtained to meet the needs of sodium-ion batteries, effectively solving the following problems:

[0008] 1. The cyclic carbonates used in the electrolyte have high melting points and generally large viscosities > 1.9. At room temperature, the sodium-ion diffusion coefficient is relatively low. At low temperatures (< -50°C), the cyclic carbonates are prone to precipitation, causing the separation of the organic solvent and the sodium salt electrolyte, affecting sodium-ion diffusion, and causing the inactivation of the sodium-ion battery.

[0009] 2. Ethylene carbonate in the cyclic carbonates used in the electrolyte will undergo oxidative decomposition at a relatively high charging potential (> 4.0 V vs SHE) to generate a large amount of flammable olefins, alkanes, hydrogen and other gases, posing a safety hazard. And propylene carbonate in the cyclic carbonates undergoes a nucleophilic ring-opening reaction with sodium ions at a relatively low discharge potential (-2.71 V vs SHE) to generate a linear alkyl carbonate, which is then reductively decomposed into propylene and oxygen under the action of free radicals, resulting in the swelling and damage of the battery.

[0010] 3. The dielectric constants of the weakly polar organic solvents in the electrolyte are generally relatively low < 3.2, which cannot effectively dissolve the sodium salt, resulting in a relatively large internal resistance of the electrolyte, and it is prone to redox reactions at a relatively high charging potential (> 4.0 V vs SHE) / a relatively low discharge potential (-2.71 V vs SHE), causing gas generation and swelling of the sodium-ion battery.

[0011] Furthermore, the carboxylic acid ester is one or more of ethylhexyl sebacate, dioctyl sebacate, dioctyl phthalate, ethyl butyrate, ethyl acetate, and / or butyl acetate.

[0012] Further, the organic solvent is a cyclic carbonate and / or a weakly polar organic solvent; the cyclic carbonate is ethylene carbonate and / or propylene carbonate; the weakly polar organic solvent is one or a mixture of two or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, trimethyl borate, triethyl borate, tripropyl borate, ethylene glycol dimethyl ether, methyl ethyl ether, methyl butyl ether, and / or ethyl butyl ether.

[0013] Further, it also contains a film-forming additive, and the film-forming additive is one or a mixture of two or more of fluoroethylene carbonate, vinylene sulfite, vinylene carbonate, trifluoropropylene carbonate, and / or 1,3-propane sultone.

[0014] Further, the volume ratio of the cyclic carbonate in the low-temperature-resistant sodium-ion battery electrolyte is 10% - 75%; the volume ratio of the weakly polar organic solvent in the low-temperature-resistant sodium-ion battery electrolyte is 10% - 50%; the volume ratio of the film-forming additive in the low-temperature-resistant sodium-ion battery electrolyte is 1 - 20%.

[0015] Further, the sodium salt of the electrolyte is one or more of sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium trifluoromethanesulfonate.

[0016] Further, the concentration of the sodium salt of the electrolyte in the low-temperature-resistant sodium-ion battery electrolyte is 0.5 - 1.2 mol / L.

[0017] Further, the density of the low-temperature-resistant sodium-ion battery electrolyte is 1.0 - 1.5 g / cm3, and the conductivity is 6 - 12 mS / cm.

[0018] Another aspect of the present invention is to protect a sodium-ion battery using the above low-temperature-resistant sodium-ion battery electrolyte.

[0019] A low-temperature-resistant sodium-ion battery electrolyte and a sodium-ion battery of the present invention have the following beneficial effects:

[0020] First, it has good low-temperature conductivity. The linear carboxylic acid ester in the low-temperature-resistant organic electrolyte has characteristics such as low melting point and low viscosity. Its mutual chelation with the cyclic carbonate can ensure that the electrolyte does not solidify at a lower temperature (< -50 °C), ensuring that sodium ions have good electronic conductivity at low temperatures, thereby improving the low-temperature discharge performance of the sodium-ion battery.

[0021] Second, the interface has good stability. In the low-temperature-resistant organic electrolyte, ethyl hexyl sebacate, dioctyl sebacate, and dioctyl phthalate will preferentially undergo reduction decomposition reactions on the negative electrode side at low temperatures, forming a dense and stable SEI film, which can then prevent the decomposition of cyclic carbonates / linear carbonates on the negative electrode side, effectively improving the electrode interface stability. Ethyl butyrate, ethyl acetate, and butyl acetate in the low-temperature-resistant organic electrolyte will adsorb on the surface of the positive electrode side at low temperatures and decompose under the catalytic action of transition metal atoms in the positive electrode material to form a stable CEI layer, effectively avoiding the occurrence of other side reactions, thereby improving the cycle stability of sodium-ion batteries.

[0022] Third, the rate performance is excellent. The radius of the Na ion is relatively large, and the nuclear charge distribution is less. Therefore, the coordination number of linear carboxylic esters with Na+ is relatively low at low temperatures in the low-temperature-resistant organic electrolyte, and the desolvation energy is relatively low. The rate of sodium desorption on the electrode surface is relatively fast, which can effectively improve the kinetics of sodium ions at the electrode interface, thereby improving the rate performance of sodium-ion batteries. In addition, the appropriate ratio of linear carboxylic esters to organic solvents and sodium salts of electrolytes in the low-temperature-resistant organic electrolyte plays an effective synergistic role, which can further ensure the low-temperature charge-discharge characteristics and excellent rate performance of sodium-ion batteries. Description of the Drawings

[0023] Figure 1 It is the rate performance curve of the sodium iron pyrophosphate / hard carbon system soft-pack battery in Application Example 1 (1C = 110 mAh / g);

[0024] Figure 2 It is the high and low temperature performance curve of the sodium iron pyrophosphate / hard carbon system soft-pack battery in Application Example 2;

[0025] Figure 3 It is the cycle stability curve of the sodium iron pyrophosphate / hard carbon system soft-pack battery in Application Example 3. Detailed Embodiments

[0026] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the products of the present invention will be further described in detail below with reference to the embodiments and the drawings.

[0027] The present invention discloses a low-temperature-resistant sodium-ion battery electrolyte, which includes the following components: an organic solvent, a sodium salt of an electrolyte, and a low-melting-point linear carboxylic ester additive. The low-melting-point linear carboxylic ester additive is a carboxylic ester containing the -RCOOR- group, and the volume ratio of the low-melting-point linear carboxylic ester in the low-temperature-resistant sodium-ion battery electrolyte is 1% to 30%.

[0028] Furthermore, the carboxylic ester is one or more of ethyl hexyl sebacate, dioctyl sebacate, dioctyl phthalate, ethyl butyrate, ethyl acetate, and / or butyl acetate.

[0029] Furthermore, the organic solvent is a cyclic carbonate and / or a weakly polar organic solvent; the cyclic carbonate is ethylene carbonate and / or propylene carbonate; the weakly polar organic solvent is one or a mixture of two or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, trimethyl borate, triethyl borate, tripropyl borate, ethylene glycol dimethyl ether, methyl ethyl ether, methyl butyl ether, and / or ethyl butyl ether.

[0030] Furthermore, it further contains a film-forming additive, and the film-forming additive is one or a mixture of two or more of fluoroethylene carbonate, vinylene sulfite, vinylene carbonate, trifluoropropylene carbonate, and / or 1,3-propane sultone.

[0031] Furthermore, the volume ratio of the cyclic carbonate in the low-temperature resistant sodium-ion battery electrolyte is 10% - 75%; the volume ratio of the weakly polar organic solvent in the low-temperature resistant sodium-ion battery electrolyte is 10% - 50%; the volume ratio of the film-forming additive in the low-temperature resistant sodium-ion battery electrolyte is 1 - 20%.

[0032] Furthermore, the sodium salt of the electrolyte is one or more of sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium trifluoromethanesulfonate.

[0033] Furthermore, the concentration of the sodium salt of the electrolyte in the low-temperature resistant sodium-ion battery electrolyte is 0.5 - 1.2 mol / L.

[0034] Furthermore, the density of the low-temperature resistant sodium-ion battery electrolyte is 1.0 - 1.5 g / cm3, and the conductivity is 6 - 12 mS / cm.

[0035] Another aspect of the present invention is to protect a sodium-ion battery using the above-mentioned low-temperature resistant sodium-ion battery electrolyte.

[0036] In the present invention, by introducing a low-melting-point and low-viscosity linear carboxylic acid ester additive into the electrolyte, the average viscosity of the electrolyte is reduced, the diffusion coefficient of sodium ions in the electrolyte is increased, and the rate performance and low-temperature performance of the sodium-ion battery are improved. In addition to the above solvents, the present invention also introduces common linear organic solvents (including low-viscosity organic solvents such as linear carbonates, ethers, and borate esters) and film-forming additives to further optimize the electrolyte formula and improve the cycle stability of the sodium-ion battery. Examples

[0037] A low-temperature resistant organic electrolyte, and the concentrations of each component in the electrolyte are as follows:

[0038] The volume ratio of cyclic carbonate is 30% (propylene carbonate / ethylene carbonate is 1.5:1.5), the volume ratio of low melting point linear carboxylic acid ester is 40% (ethylhexyl sebacate 2.0, dioctyl sebacate 2.0), the volume ratio of weakly polar organic solvent is 25% (diethyl carbonate), the volume ratio of film-forming additive is 5% (fluoroethylene carbonate), and the concentration of electrolyte sodium salt is 0.8 mol / L (sodium hexafluorophosphate). Example

[0039] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0040] The volume ratio of cyclic carbonate is 30% (propylene carbonate / ethylene carbonate is 1.5:1.5), the volume ratio of low melting point linear carboxylic acid ester is 40% (ethyl butyrate 3.0, dioctyl phthalate 1.0), the volume ratio of weakly polar organic solvent is 20% (diethyl carbonate / dimethyl carbonate is 1.0:1.0), the volume ratio of film-forming additive is 10% (fluoroethylene carbonate / vinyldene carbonate is 0.5:0.5), and the concentration of electrolyte sodium salt is 0.8 mol / L (sodium hexafluorophosphate). Example

[0041] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0042] The volume ratio of cyclic carbonate is 40% (propylene carbonate / ethylene carbonate is 2.0:2.0), the volume ratio of low melting point linear carboxylic acid ester is 30% (ethylhexyl sebacate 2.0, ethyl acetate 1.0), the volume ratio of weakly polar organic solvent is 15% (diethyl carbonate / dimethyl carbonate / ethyl methyl carbonate is 0.5:0.5:0.5), the volume ratio of film-forming additive is 15% (fluoroethylene carbonate / 1,3-propane sultone is 1.0:0.5), and the concentration of electrolyte sodium salt is 1 mol / L (sodium hexafluorophosphate is 0.7 mol / L, sodium perchlorate is 0.3 mol / L). Example

[0043] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0044] The volume ratio of cyclic carbonate is 40% (propylene carbonate / ethylene carbonate is 2.0:2.0), the volume ratio of low melting point linear carboxylic acid ester is 30% (butyl acetate 1.5, dioctyl phthalate 1.5), the volume ratio of weakly polar organic solvent is 15% (diethyl carbonate / dimethyl carbonate / ethyl methyl carbonate is 0.5:0.5:0.5), the volume ratio of film-forming additive is 15% (fluoroethylene carbonate / 1,3-propane sultone / vinylene carbonate is 0.5:0.5:0.5), and the concentration of electrolyte sodium salt is 1 mol / L (sodium hexafluorophosphate is 0.5 mol / L, sodium perchlorate is 0.3 mol / L, sodium bis(fluorosulfonyl)imide is 0.2 mol / L). Example

[0045] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0046] The volume ratio of cyclic carbonate is 50% (propylene carbonate / ethylene carbonate is 3:2), the volume ratio of low melting point linear carboxylic acid ester is 30% (ethylhexyl sebacate 1.0, ethyl butyrate 1.0, dioctyl sebacate 1.0), the volume ratio of weakly polar organic solvent is 10% (trimethyl borate), the volume ratio of film-forming additive is 10% (fluoroethylene carbonate), and the concentration of electrolyte sodium salt is 1 mol / L (sodium hexafluorophosphate). Example

[0047] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0048] The volume ratio of cyclic carbonate is 50% (propylene carbonate / ethylene carbonate is 3:2), the volume ratio of low melting point linear carboxylic acid ester is 30% (ethylhexyl sebacate 1.0, dioctyl phthalate 1.0, butyl acetate 1.0), the volume ratio of weakly polar organic solvent is 10% (trimethyl borate / triethyl borate is 1:0.5:0.5), the volume ratio of film-forming additive is 10% (fluoroethylene carbonate / vinylene carbonate is 0.7:0.3), and the concentration of electrolyte sodium salt is 1 mol / L (sodium hexafluorophosphate is 0.7 mol / L, sodium trifluoromethanesulfonate 0.3 mol / L). Example

[0049] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0050] The volume ratio of cyclic carbonate is 60% (propylene carbonate / ethylene carbonate is 4:2), the volume ratio of low melting point linear carboxylic acid ester is 20% (ethylhexyl sebacate 0.5, ethyl acetate 0.5, dioctyl sebacate 0.5, dioctyl phthalate 0.5), the volume ratio of weakly polar organic solvent is 10% (trimethyl borate / triethyl borate / tripropyl borate is 0.2:0.3:0.5), the volume ratio of film-forming additive is 10% (fluoroethylene carbonate / vinylene carbonate / vinyl sulfite is 0.5:0.3:0.2), and the concentration of electrolyte sodium salt is 0.8 mol / L (sodium hexafluorophosphate is 0.6 mol / L, sodium perchlorate is 0.1 mol / L, sodium trifluoromethanesulfonate 0.1 mol / L). Example

[0051] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0052] The volume ratio of cyclic carbonate is 60% (propylene carbonate / ethylene carbonate is 4:2), the volume ratio of low melting point linear carboxylic acid ester is 25% (ethylhexyl sebacate 1.0, dioctyl sebacate 0.75, dioctyl phthalate 0.75), the volume ratio of weakly polar organic solvent is 10% (ethylene glycol dimethyl ether), the volume ratio of film-forming additive is 5% (fluoroethylene carbonate), and the concentration of electrolyte sodium salt is 0.8 mol / L (sodium hexafluorophosphate). Example

[0053] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0054] The volume ratio of cyclic carbonate is 70% (propylene carbonate / ethylene carbonate is 4:3), the volume ratio of low melting point linear carboxylic acid ester is 20% (ethyl butyrate 1.0, ethyl acetate 0.5, butyl acetate 0.5), the volume ratio of weakly polar organic solvent is 5% (ethylene glycol dimethyl ether / methyl ethyl ether is 0.25:0.25), the volume ratio of film-forming additive is 5% (fluoroethylene carbonate / vinyl sulfite is 0.3:0.2), and the concentration of electrolyte sodium salt is 1 mol / L (sodium perchlorate is 0.5 mol / L, sodium bis(trifluoromethylsulfonyl)imide is 0.5 mol / L). Example

[0055] A low-temperature resistant organic electrolyte, and the concentrations of the components in the electrolyte are as follows:

[0056] The volume ratio of cyclic carbonate is 70% (propylene carbonate / ethylene carbonate is 4:3), the volume ratio of low-melting-point linear carboxylic acid ester is 20% (ethylhexyl sebacate 0.5, dioctyl sebacate 0.25, dioctyl phthalate 0.25, ethyl butyrate 0.25, ethyl acetate 0.5, butyl acetate 0.25), the volume ratio of weakly polar organic solvent is 5% (diethyl carbonate / ethylene glycol dimethyl ether / triethyl borate is 0.1:0.2:0.2), the volume ratio of film-forming additive is 5% (fluoroethylene carbonate / vinylene carbonate / vinyl sulfite is 0.3:0.1:0.1), and the concentration of electrolyte sodium salt is 1 mol / L (sodium hexafluorophosphate is 0.5 mol / L, sodium perchlorate is 0.3 mol / L, sodium bis(trifluoromethylsulfonyl)imide is 0.1 mol / L, sodium trifluoromethanesulfonate 0.1 mol / L).

[0057] In a glove box filled with argon, the low-melting-point linear carboxylic acid ester: cyclic carbonate: linear organic solvent were mixed evenly according to the volume ratio of 40%:38%:18%, and then 2% fluoroethylene carbonate and 2% 1,3-propane sultone were added. Finally, sodium hexafluorophosphate was added to obtain an electrolyte with a concentration of 0.8 mol / L. The electrolyte was injected into a soft-pack battery with sodium iron pyrophosphate phosphate as the positive electrode, hard carbon as the negative electrode, and a capacity of 3500 mAh to test its rate performance, low-temperature performance, and cycle stability. As Figure 1 shown in the rate performance of the NFPP / HC soft-pack battery, its capacity retention rate at a super-high rate of 20C (1C = 110 mAh / g) is 82.3% of that at 0.2C, demonstrating excellent fast charge and discharge capabilities. Figure 2 The high and low temperature performance of the NFPP / HC soft-pack battery is shown. Its capacity utilization rate reaches 80.5% of that at room temperature under the low temperature condition of -40°C, showing extremely high environmental adaptability. Figure 3 The cycle stability of the NFPP / HC soft-pack battery was further tested. After up to 1000 cycles, the battery system still has a capacity retention rate as high as 84.2%.

[0058] In a glove box filled with argon, the low-melting-point linear carboxylic acid ester: cyclic carbonate: linear organic solvent were mixed evenly according to the volume ratio of 45%:40%:10%, and then 3% fluoroethylene carbonate and 2% vinylene carbonate were added. Finally, sodium hexafluorophosphate was added to obtain an electrolyte with a concentration of 1 mol / L. The electrolyte was injected into a soft-pack battery with sodium iron pyrophosphate phosphate as the positive electrode and hard carbon as the negative electrode to test its rate performance, low-temperature performance, and cycle stability. The data are shown in Table 1.

[0059] In a glove box filled with argon gas, a low-melting-point linear carboxylic acid ester, a cyclic carbonate, and a linear organic solvent were mixed evenly at a volume ratio of 40%:40%:15%. Then, 2% fluoroethylene carbonate, 2% vinylene carbonate, and 1% 1,3-propane sultone were added. Finally, sodium hexafluorophosphate and sodium bis(trifluoromethylsulfonyl)imide (molar ratio 0.4:0.4) were added to obtain an electrolyte with a concentration of 0.8 mol / L. This electrolyte was injected into a soft-pack battery with sodium vanadium phosphate as the positive electrode and hard carbon as the negative electrode, and its rate performance, low-temperature performance, and cycle stability were tested. The data are shown in Table 1.

[0060] In a glove box filled with argon gas, a low-melting-point linear carboxylic acid ester, a cyclic carbonate, and a linear organic solvent were mixed evenly at a volume ratio of 45%:35%:15%. Then, 2% fluoroethylene carbonate, 2% vinylene carbonate, and 1% 1,3-propane sultone were added. Finally, sodium hexafluorophosphate, sodium perchlorate, and sodium bis(trifluoromethylsulfonyl)imide (molar ratio 0.6:0.2:0.2) were added to obtain an electrolyte with a concentration of 1 mol / L. This electrolyte was injected into a soft-pack battery with sodium vanadium phosphate as the positive electrode and hard carbon as the negative electrode, and its rate performance, low-temperature performance, and cycle stability were tested. The data are shown in Table 1.

[0061] In a glove box filled with argon gas, a low-melting-point linear carboxylic acid ester, a cyclic carbonate, and a linear organic solvent were mixed evenly at a volume ratio of 35%:45%:20%. Then, 5% fluoroethylene carbonate was added. Finally, sodium hexafluorophosphate and sodium perchlorate (molar ratio 0.7:0.4) were added to obtain an electrolyte with a concentration of 1.1 mol / L. This electrolyte was injected into a soft-pack battery with sodium iron sulfate as the positive electrode and hard carbon as the negative electrode, and its rate performance, low-temperature performance, and cycle stability were tested. The data are shown in Table 1.

[0062] In a glove box filled with argon gas, a cyclic carbonate and a linear carbonate were mixed evenly at a volume ratio of 78%:18%. Then, 2% fluoroethylene carbonate and 2% 1,3-propane sultone were added. Finally, sodium hexafluorophosphate was added to obtain an electrolyte with a concentration of 0.8 mol / L. This electrolyte was injected into a soft-pack battery with sodium iron pyrophosphate as the positive electrode and hard carbon as the negative electrode, and its rate performance, low-temperature performance, and cycle stability were tested. The data are shown in Table 1.

[0063] In a glove box filled with argon gas, a cyclic carbonate and a linear carbonate were mixed evenly at a volume ratio of 85%:10%. Then, 3% fluoroethylene carbonate and 2% vinylene carbonate were added. Finally, sodium hexafluorophosphate was added to obtain an electrolyte with a concentration of 1 mol / L. This electrolyte was injected into a soft-pack battery with sodium iron pyrophosphate as the positive electrode and hard carbon as the negative electrode, and its rate performance, low-temperature performance, and cycle stability were tested. The data are shown in Table 1.

[0064] In a glove box filled with argon gas, cyclic carbonate and linear carbonate were mixed evenly at a volume ratio of 80%:15%, and then 2% fluoroethylene carbonate, 2% vinylene carbonate, and 1% 1,3-propane sultone were added. Finally, sodium hexafluorophosphate and sodium bis(trifluoromethylsulfonyl)imide (molar ratio 0.4:0.4) were added to obtain an electrolyte with a concentration of 0.8 mol / L. This electrolyte was injected into a soft-pack battery with sodium vanadium phosphate as the positive electrode and hard carbon as the negative electrode, and its rate performance, low-temperature performance, and cycle stability were tested. The data are shown in Table 1.

[0065] In a glove box filled with argon gas, cyclic carbonate and linear carbonate were mixed evenly at a volume ratio of 80%:15%, and then 2% fluoroethylene carbonate, 1% vinylene carbonate, 1% ethylene sulfite, and 1% 1,3-propane sultone were added. Finally, sodium hexafluorophosphate, sodium perchlorate, and sodium bis(trifluoromethylsulfonyl)imide (molar ratio 0.6:0.2:0.2) were added to obtain an electrolyte with a concentration of 1 mol / L. This electrolyte was injected into a soft-pack battery with sodium vanadium phosphate as the positive electrode and hard carbon as the negative electrode, and its rate performance, low-temperature performance, and cycle stability were tested. The data are shown in Table 1.

[0066] In a glove box filled with argon gas, 95% cyclic carbonate and 5% fluoroethylene carbonate were mixed evenly. Finally, sodium hexafluorophosphate and sodium perchlorate (molar ratio 0.7:0.4) were added to obtain an electrolyte with a concentration of 1.1 mol / L. This electrolyte was injected into a soft-pack battery with sodium iron sulfate as the positive electrode and hard carbon as the negative electrode, and its rate performance, low-temperature performance, and cycle stability were tested. The ratio of each above-mentioned embodiment is shown in detail in Table 1, and the test results of its electrochemical performance are shown in Table 2.

[0067] Table 1 Solvent ratios of the examples and their corresponding material systems

[0068]

[0069] Table 2 Test results of electrochemical performance

[0070]

[0071] The above-mentioned embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these obvious substitution forms all belong to the protection scope of the present invention.

Claims

1. A low-temperature resistant sodium-ion battery electrolyte, characterized in that It includes the following components: an organic solvent, a sodium salt electrolyte, and a low-melting-point linear carboxylic ester additive. The low-melting-point linear carboxylic ester additive is a carboxylic ester containing the -RCOOR- group, and the volume ratio of the low-melting-point linear carboxylic ester in the low-temperature-resistant sodium-ion battery electrolyte is 35%, 40%, or 45%. The carboxylic ester includes at least one of ethylhexyl sebacate, dioctyl sebacate, and dioctyl phthalate and at least one of ethyl butyrate, ethyl acetate, and butyl acetate.

2. The low-temperature resistant sodium-ion battery electrolyte according to claim 1, characterized in that: The organic solvent is a cyclic carbonate and / or a weakly polar organic solvent; The cyclic carbonate is ethylene carbonate and / or propylene carbonate; The weakly polar organic solvent is one or a mixture of two or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, trimethyl borate, triethyl borate, tripropyl borate, ethylene glycol dimethyl ether, methyl ethyl ether, methyl butyl ether, and / or ethyl butyl ether.

3. The low-temperature resistant sodium ion battery electrolyte according to claim 2, characterized in that: It also contains a film-forming additive, and the film-forming additive is one or a mixture of two or more of fluoroethylene carbonate, vinylene sulfite, vinylene carbonate, trifluoropropylene carbonate, and / or 1,3-propane sultone.

4. The low-temperature resistant sodium ion battery electrolyte according to claim 3, wherein: The sodium salt electrolyte is one or more of sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium trifluoromethanesulfonate.

5. The low-temperature resistant sodium-ion battery electrolyte according to claim 4, characterized in that: The concentration of the sodium salt electrolyte in the low-temperature-resistant sodium-ion battery electrolyte is 0.5 - 1.2 mol / L.

6. The low-temperature resistant sodium-ion battery electrolyte according to claim 5, characterized in that: The density of the low-temperature-resistant sodium-ion battery electrolyte is 1.0 - 1.5 g / cm3, and the conductivity is 6 - 12 mS / cm.

7. A sodium-ion battery using the low-temperature-resistant sodium-ion battery electrolyte according to any one of claims 1 - 6.

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