High-conductivity sodium ion battery low-temperature electrolyte and sodium ion battery

Abstract

The invention discloses a high-conductivity sodium ion battery low-temperature electrolyte and a sodium ion battery, the electrolyte comprises a sodium salt, a solvent and an additive, the solvent is a sulfate solvent or a combination of the sulfate solvent and a carbonate solvent; the sulfate solvent is one or more than two of dimethyl sulfite, diethyl sulfite and ethylene sulfite, and the carbonate solvent is one or more than two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The high-conductivity sodium ion battery low-temperature electrolyte and the sodium ion battery have the characteristics of low freezing point, high low-temperature conductivity and good cycling stability.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery low-temperature electrolyte with high electrical conductivity and a sodium ion battery. Background Art

[0002] Sodium-ion batteries have become a powerful energy storage technology after lithium-ion batteries due to their advantages such as abundant sodium reserves and low cost. They have been applied to many fields. However, in these applications, they are usually affected by extreme temperatures and their application is limited. Currently, the performance of commercial sodium-ion batteries decreases significantly below 0°C and is accompanied by severe capacity attenuation. Therefore, it is very important to broaden the operating temperature range of sodium-ion batteries.

[0003] To improve the electrochemical performance of batteries under low temperature conditions, optimization can be carried out from aspects such as electrode materials, electrolytes, and interface modifications. Among them, the low-temperature performance of electrode materials is determined by the intrinsic ionic conductivity and other properties of the materials, and it is difficult to significantly improve it. The interface modification process is relatively complicated and will increase the interface impedance. Therefore, optimizing the composition of the electrolyte becomes a relatively economical and efficient method.

[0004] The electrolyte greatly affects the low-temperature performance of the battery. The challenges faced by the electrolyte under low-temperature conditions are: the viscosity of the electrolyte increases, the conductivity decreases, and the ion transport performance decreases under low-temperature conditions; + Desolvation is difficult and SEI impedance increases; for example, Na + Migrate slowly in SEI and CEI membranes.

[0005] The low-temperature electrolytes currently used mainly include sodium salts and ethylene carbonate with a high dielectric constant, which has a good dissociation effect on sodium salts. At the same time, some linear carbonates are introduced to reduce the viscosity of the system, such as dimethyl carbonate and diethyl carbonate, and finally a small amount of film-forming additives are added. Usually, ester low-temperature electrolytes use a blend of multiple solvents to achieve a wide liquid range and low viscosity of the electrolyte. Some electrolytes even contain four or five or more organic solvents.

[0006] This method not only increases the cost of the electrolyte, but also consumes more time and labor costs in the process of optimizing the composition of the electrolyte. As the temperature decreases, more solvent enters the inner solvation shell, and this solvation structure causes a slow desolvation process.

[0007] In addition, the film formation of the electrolyte under low temperature conditions is also particularly critical. Currently, most electrolytes rely on a small amount of film-forming additives such as fluoroethylene carbonate and vinylene carbonate, but their film-forming quality is often poor. Summary of the invention

[0008] The purpose of the present invention is to provide a sodium ion battery low-temperature electrolyte with high conductivity and a sodium ion battery, which have the characteristics of low freezing point, high low-temperature conductivity and good cycle stability.

[0009] The present invention can be implemented by the following technical solutions: The invention discloses a sodium ion battery low-temperature electrolyte with high conductivity, comprising sodium salt, solvent and additive, wherein the solvent comprises a sulfate solvent or a combination of a sulfate solvent and a carbonate solvent; the sulfate solvent is one or more of dimethyl sulfite, diethyl sulfite and ethylene sulfite, the carbonate solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, the proportion of the sulfate solvent in the electrolyte is 50%-100%, and the proportion of the carbonate solvent in the electrolyte is 0%-50%. With this solvent system, more anions will enter the solvation shell, showing an anion-dominated solvation structure, which can effectively regulate the electrochemical deposition process, especially the sulfate solvent can promote the formation of a sulfide-rich CEI film, which has properties such as low impedance and high modulus, shows high interface stability and good transmission dynamics, and improves low-temperature performance. Sulfate solvents have lower viscosity than carbonate solvents, effectively reducing the viscosity of the electrolyte.

[0010] Further, the additive is a composite additive, and the composite additive includes a first film-forming additive and a second film-forming additive, wherein the first film-forming additive is one or more of fluoroethylene carbonate, vinylene carbonate, vinylene sulfate, vinyl sulfite, and sodium difluorooxalate borate; the second film-forming additive is one or more of methoxyacetonitrile, succinonitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,2,3-tris(2-cyanoethoxy)propane. The first film-forming additive is basically a traditional additive, which mainly decomposes into a film in the first few weeks of circulation to avoid more side reactions caused by contact between the positive electrode material and the electrolyte. However, the CEI film formed by traditional additives is uneven, which will lead to incomplete CEI film, and this problem will be aggravated under low temperature conditions. The second type of film-forming additive belongs to nitrile additives, which can inhibit the dissolution of transition metal ions, consume and remove trace water in the electrolyte, and improve the oxidation resistance of the electrolyte, but nitrile additives are more reactive and will produce side reactions when used alone at low potential of the negative electrode. The simultaneous use of two types of additives can promote the formation of fluoride-rich CEI membranes, reduce the content of organic components in the CEI membranes, make the CEI membranes thin and dense, and effectively inhibit the decomposition of the electrolyte. At the same time, the decomposition of nitrile additives to produce nitrides can also promote sodium ion conduction.

[0011] Furthermore, the amount of the first film-forming additive is 0.1-10wt% of the total mass of the electrolyte; the amount of the second film-forming additive is 0.1-10wt% of the total mass of the electrolyte. If the additive content is too much, the film on the electrode surface will be too thick, the impedance will increase during the battery cycle, and the battery cycle life will be reduced; if the additive content is too little, the film on the electrode surface is not complete and dense enough, the active material and the electrolyte are frequently in contact and continue to produce side reactions, causing the battery cycle performance to deteriorate.

[0012] Further, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide, wherein the concentration of the sodium salt is 0.2-2.0 mol / L. If the sodium salt concentration is too high, the viscosity of the electrolyte will increase, the wettability between the electrolyte and the diaphragm and the positive and negative electrodes will decrease, the sodium ion transmission will be poor, and the low temperature performance will be further deteriorated. If the sodium salt concentration is too low, the conductivity will be too low, increasing the battery impedance.

[0013] Another aspect of the present invention is to protect a low-temperature electrolyte for a sodium ion battery, wherein the sodium ion battery is added with the low-temperature electrolyte of any one of claims 1 to 4.

[0014] Furthermore, the positive electrode material of the sodium ion battery is a Prussian blue / white material, a layered oxide material or a polyanion positive electrode material.

[0015] Furthermore, the polyanion positive electrode material is one or more of a phosphate positive electrode material, a pyrophosphate positive electrode material, a sulfate positive electrode material, a silicate positive electrode material, and a borate positive electrode material.

[0016] Furthermore, the negative electrode material of the sodium ion battery is a hard carbon and / or alloy negative electrode.

[0017] Furthermore, the sodium ion battery is a soft-pack sodium ion battery, an aluminum shell sodium ion battery or a steel shell sodium ion battery.

[0018] The present invention provides a sodium ion battery low-temperature electrolyte with high conductivity and a sodium ion battery, which have the following beneficial effects: In the electrolyte system of the present invention, the electrolyte system with sulfate ester as the main solvent has a solvation structure formed in the electrolyte. The sulfate ester solvent has a weak binding ability with sodium ions, a moderate dielectric constant and a solvation ability, which can fully dissociate the sodium salt, but will not have an excessively strong binding ability with sodium ions, resulting in difficulty in desolvation under low temperature conditions, thereby reducing the viscosity of the system to the greatest extent and facilitating rapid desolvation under low temperature conditions.

[0019] The present invention uses a composite film-forming additive and two types of additives at the same time, which can promote the formation of a fluoride-rich CEI film, reduce the content of organic components in the CEI film, make the CEI film thin and dense, and effectively inhibit the decomposition of the electrolyte. At the same time, the decomposition of the nitrile additive to produce nitride can also promote sodium ion conduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The test results of the cycle performance of Example 6 are as follows; Figure 2 The specific capacity test curves of Example 6 and Comparative Example 1 are shown; Figure 3 The cyclic performance test curves of Example 6 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below in conjunction with embodiments.

[0022] The invention discloses a sodium ion battery low-temperature electrolyte with high conductivity. The electrolyte comprises a sodium salt, a solvent and an additive. The solvent is a sulfate solvent or a combination of a sulfate solvent and a carbonate solvent. The sulfate solvent is one or more of dimethyl sulfite, diethyl sulfite and ethylene sulfite. The carbonate solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The proportion of the sulfate solvent in the electrolyte is 50%-100%, and the proportion of the carbonate solvent in the electrolyte is 0%-50%.

[0023] Furthermore, the additive is a composite additive, which includes a first film-forming additive and a second film-forming additive, the first film-forming additive is one or more of fluoroethylene carbonate, vinylene carbonate, vinylene sulfate, vinyl sulfite, and sodium difluorooxalatoborate; the second film-forming additive is one or more of methoxyacetonitrile, succinonitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,2,3-tris(2-cyanoethoxy)propane.

[0024] Furthermore, the amount of the first film-forming additive is 0.1-10 wt % of the total mass of the electrolyte; the amount of the second film-forming additive is 0.1-10 wt % of the total mass of the electrolyte.

[0025] Furthermore, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide, wherein the concentration of the sodium salt is 0.2-2.0 mol / L.

[0026] Another aspect of the present invention is to protect a low-temperature electrolyte for a sodium ion battery, wherein the sodium ion battery is added with the low-temperature electrolyte of any one of claims 1 to 4.

[0027] Furthermore, the positive electrode material of the sodium ion battery is a Prussian blue / white material, a layered oxide material or a polyanion positive electrode material.

[0028] Furthermore, the polyanion positive electrode material is one or more of a phosphate positive electrode material, a pyrophosphate positive electrode material, a sulfate positive electrode material, a silicate positive electrode material, and a borate positive electrode material.

[0029] Furthermore, the negative electrode material of the sodium ion battery is a hard carbon and / or alloy negative electrode.

[0030] Furthermore, the sodium ion battery is a soft-pack sodium ion battery, an aluminum shell sodium ion battery or a steel shell sodium ion battery.

[0031] Example 1 The present embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity, wherein the electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.

[0032] In this embodiment, the sodium salt used is sodium hexafluorophosphate, and the concentration is 1 mol / L. The carbonate solvents used are ethylene carbonate and ethyl methyl carbonate (ethylene carbonate: ethyl methyl carbonate = 2:1), and the volume ratio of the carbonate solvent in the electrolyte is 20%. The sulfate solvents used are diethyl sulfite and ethylene sulfite (diethyl sulfite: ethylene sulfite = 1:1), and the volume ratio of the sulfate in the electrolyte is 80%. The first additive is fluoroethylene carbonate, the second additive is succinonitrile, and the amount of the film-forming additive added is 4 wt% of the total mass of the low-temperature electrolyte.

[0033] Example 2 The present embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity, wherein the electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.

[0034] The sodium salts used are sodium hexafluorophosphate and sodium bis(trifluoromethylsulfonyl)imide (0.7 mol / L sodium hexafluorophosphate, 0.3 mol / L sodium bis(trifluoromethylsulfonyl)imide), with a concentration of 1 mol / L. The carbonate solvents used are ethylene carbonate and ethyl methyl carbonate (ethylene carbonate: ethyl methyl carbonate = 1:1), and the volume ratio of carbonate solvents in the electrolyte is 30%. The sulfate solvents used are diethyl sulfite and vinyl sulfite (diethyl sulfite: vinyl sulfite = 1:1), and the volume ratio of sulfate in the electrolyte is 70%. The first additive is fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 1:1 (mass ratio)), the second additive is 1,3,6-hexanetrinitrile, and the amount of film-forming additive added is 4 wt% of the total mass of the low-temperature electrolyte.

[0035] Example 3 The present embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity, wherein the electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.

[0036] The sodium salts used are sodium hexafluorophosphate and sodium difluorooxalate borate (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium difluorooxalate borate), with a concentration of 1 mol / L. The carbonate solvents used are ethylene carbonate and ethyl methyl carbonate (ethylene carbonate: ethyl methyl carbonate = 3:2), and the volume ratio of carbonate solvents in the electrolyte is 40%. The sulfate solvents used are dimethyl sulfite and diethyl sulfite (dimethyl sulfite: diethyl sulfite = 1:4), and the volume ratio of sulfate in the electrolyte is 60%. The first additive is fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 1:1 (mass ratio)), the second additive is 1,3,6-hexane trinitrile, and the amount of film-forming additive added is 4 wt% of the total mass of the low-temperature electrolyte.

[0037] Example 4 The present embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity, wherein the electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.

[0038] The sodium salts used are sodium hexafluorophosphate and sodium difluorooxalate borate (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium difluorooxalate borate), with a concentration of 1 mol / L. The carbonate solvents used are ethylene carbonate and ethyl methyl carbonate (ethylene carbonate: ethyl methyl carbonate = 1:1), and the volume ratio of carbonate solvents in the electrolyte is 45%. The sulfate solvents used are diethyl sulfite and vinyl sulfite (diethyl sulfite: vinyl sulfite = 1:1), and the volume ratio of sulfate in the electrolyte is 55%. The first additive is fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 1:1 (mass ratio)), and the second additive is methoxyacetonitrile. The amount of film-forming additive is 4wt% of the total mass of the low-temperature electrolyte.

[0039] Example 5 The present embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity, wherein the electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.

[0040] The sodium salts used are sodium hexafluorophosphate and sodium perchlorate (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium perchlorate), with a concentration of 1 mol / L. The carbonate solvents used are ethylene carbonate and ethyl methyl carbonate (ethylene carbonate: dimethyl carbonate = 1:1), and the volume ratio of carbonate solvents in the electrolyte is 50%. The sulfate solvents used are dimethyl sulfite, diethyl sulfite, and vinyl sulfite (dimethyl sulfite: diethyl sulfite: vinyl sulfite = 1:1:1), and the volume ratio of sulfate in the electrolyte is 50%. The first additive is fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 2:1 (mass ratio)), and the second additive is 1,2,3-tri(2-cyanoethoxy)propane, and the amount of film-forming additive is 5 wt% of the total mass of the low-temperature electrolyte.

[0041] Example 6 The present embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity, wherein the electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.

[0042] The sodium salts used are sodium hexafluorophosphate and sodium perchlorate (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium bis(fluoroethoxy)sulfonyl)imide), with a concentration of 1 mol / L. The carbonate solvent used is ethyl methyl carbonate, and the volume ratio of the carbonate solvent in the electrolyte is 30%. The sulfate solvents used are dimethyl sulfite and diethyl sulfite (dimethyl sulfite: diethyl sulfite = 1:1), and the volume ratio of the sulfate in the electrolyte is 70%. The first additive is fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 2:1 (mass ratio)), and the second additive is 1,2,3-tri(2-cyanoethoxy)propane and 1,2-di(2-cyanoethoxy)ethane, with a mass ratio of 1:1, and the amount of film-forming additive is 4 wt% of the total mass of the low-temperature electrolyte. In this example, the obtained electrolyte was assembled into a sodium iron pyrophosphate / hard carbon soft-pack battery to test its room temperature long cycle performance.

[0043] The cycle performance test results of this embodiment are as follows Figure 1 As shown in the figure, the soft pack battery has very good cycle stability at 25°C, and the capacity retention rate is 95.92% after 300 stable cycles. At the same time, the electrolyte can also be used in button half-cells for stable cycling at -20°C. The results are shown in the figure. Figure 3 shown.

[0044] Comparative Example 1 This embodiment relates to a low-temperature sodium ion battery electrolyte, the electrolyte comprising sodium salt, carbonate solvent, a first additive, and a second additive. The electrolyte composition is different from that of Example 6 in that no sulfate solvent is added in Comparative Example 1.

[0045] The sodium salts used are sodium hexafluorophosphate and sodium bis(2-fluoroethoxy)sulfonyl imide (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium bis(2-fluoroethoxy)sulfonyl imide), with a concentration of 1 mol / L. The carbonate solvents used are ethylene carbonate and ethyl methyl carbonate (ethylene carbonate: dimethyl carbonate = 1:1). The first additive is fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 2:1 (mass ratio)), and the second additive is 1,2,3-tri(2-cyanoethoxy)propane and 1,2-bis(2-cyanoethoxy)ethane, with a mass ratio of 1:1, and the amount of film-forming additive added is 4 wt% of the total mass of the low-temperature electrolyte. The same electrolyte was used to install a button half-cell for charge and discharge under low temperature conditions. Figure 2 It can be seen that the capacity is significantly lower than that of Example 6 when charging and discharging at -20°C.

[0046] Comparative Example 2 This embodiment relates to a low-temperature sodium ion battery electrolyte, the electrolyte comprising sodium salt, carbonate solvent, sulfate solvent, and film-forming additive. The electrolyte composition is different from that of Example 6 in that only the first additive is added in Comparative Example 2.

[0047] The sodium salts used are sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium bis(fluorosulfonyl)imide), with a concentration of 1 mol / L. The carbonate solvent used is ethyl methyl carbonate, and the volume ratio of the carbonate solvent in the electrolyte is 30%. The sulfate solvents used are dimethyl sulfite and diethyl sulfite (dimethyl sulfite: diethyl sulfite = 1:1), and the volume ratio of the sulfate in the electrolyte is 70%. The first additive is fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 2:1 (mass ratio)), and the amount of the film-forming additive added is 2 wt% of the total mass of the carbonate low-temperature electrolyte. The same electrolyte is used to install a button half-cell for charge and discharge cycles at -20°C. It can be seen that its capacity retention rate is significantly inferior to that of Example 6.

[0048] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A high-conductivity sodium ion battery low-temperature electrolyte, comprising a sodium salt, a solvent and an additive, characterized in that: The solvent includes a sulfate solvent or a combination of a sulfate solvent and a carbonate solvent; the sulfate solvent is one or more of dimethyl sulfite, diethyl sulfite, and ethylene sulfite; the carbonate solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the proportion of the sulfate solvent in the electrolyte is 50%-100%, and the proportion of the carbonate solvent in the electrolyte is 0%-50%.

2. The high-conductivity sodium ion battery low-temperature electrolyte according to claim 1, characterized in that: The additive is a composite additive, which includes a first film-forming additive and a second film-forming additive. The first film-forming additive is one or more of fluoroethylene carbonate, vinylene carbonate, vinylene sulfate, vinyl sulfite, and sodium difluorooxalatoborate; the second film-forming additive is one or more of methoxyacetonitrile, succinonitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,2,3-tris(2-cyanoethoxy)propane.

3. The high-conductivity sodium ion battery low-temperature electrolyte according to claim 2, characterized in that: The amount of the first film-forming additive is 0.1-10wt% of the total mass of the electrolyte; the amount of the second film-forming additive is 0.1-10wt% of the total mass of the electrolyte.

4. The high-conductivity sodium ion battery low-temperature electrolyte according to claim 1, characterized in that: The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide, wherein the concentration of the sodium salt is 0.2-2.0 mol / L.

5. A sodium ion battery, characterized in that: The low-temperature electrolyte according to any one of claims 1 to 4 is added.

6. The sodium ion battery according to claim 5, characterized in that: The positive electrode material of the sodium ion battery is a Prussian blue / white material, a layered oxide material or a polyanion positive electrode material.

7. The high conductivity sodium ion battery according to claim 6, characterized in that: The polyanion positive electrode material is one or more of a phosphate positive electrode material, a pyrophosphate positive electrode material, a sulfate positive electrode material, a silicate positive electrode material, and a borate positive electrode material.

8. The sodium ion battery according to claim 5, characterized in that: The negative electrode material of the sodium ion battery is a hard carbon and / or alloy negative electrode.

9. The sodium ion battery according to claim 8, characterized in that: The sodium ion battery is a soft-pack sodium ion battery, an aluminum shell sodium ion battery or a steel shell sodium ion battery.

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