High conductivity sodium ion battery low temperature electrolyte and sodium ion battery
By using sulfate ester solvents and composite film-forming additives to optimize sodium-ion battery electrolytes, the problems of decreased conductivity and poor film formation quality under low temperature conditions were solved, and sodium-ion battery performance with high conductivity and good cycle stability was achieved.
Patent Information
- Application Number
- CN202411941752.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-26
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2044-12-26
AI Technical Summary
Existing sodium-ion batteries have decreased conductivity and increased viscosity under low temperature conditions, which reduces ion transport performance and leads to poor film formation quality, resulting in battery performance degradation. In addition, the electrolyte composition is complex and the cost is high.
An electrolyte system based on sulfate ester solvents is used, combined with composite film-forming additives, including traditional and nitrile additives, to form a dense fluoride-rich CEI membrane, optimize the sodium salt concentration and additive ratio, and promote sodium ion conduction.
Maintain high conductivity under low temperature conditions, improve battery transmission performance, reduce viscosity, improve cycle stability, simplify electrolyte composition and reduce costs.
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Figure CN119542552B_ABST
Abstract
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, with their advantages of abundant sodium reserves and low cost, have become a powerful energy storage technology after lithium-ion batteries and have been applied in many fields. However, their applications in these fields are often affected by extreme temperatures, which limits their application. Currently, the performance of commercial sodium-ion batteries decreases significantly below 0°C and is accompanied by severe capacity decay. 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 make significant improvements. The interface modification process is relatively complex 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: such as the increase in electrolyte viscosity, the decrease in conductivity, and the reduction in ion transport performance under low temperature conditions; such as Na + Desolvation is difficult and SEI impedance increases; for example, Na + Migrate slowly in SEI and CEI membranes.
[0005] The currently used low-temperature electrolytes primarily consist of sodium salts and ethylene carbonate, a high-dielectric constant material that has a good dissociation effect on sodium salts. Linear carbonates, such as dimethyl carbonate and diethyl carbonate, are also introduced to reduce the viscosity of the system. Finally, a small amount of film-forming additives is added. Typically, ester-based low-temperature electrolytes utilize a blend of multiple solvents to achieve a wide electrolyte range and low viscosity. Some electrolytes even contain four or five or more organic solvents.
[0006] This approach not only increases the cost of the electrolyte, but also consumes more time and labor in optimizing the electrolyte composition. As the temperature decreases, more solvent enters the inner solvation shell, and this solvation structure causes the desolvation process to slow down.
[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 present invention aims to provide a sodium ion battery low-temperature electrolyte with high electrical conductivity and a sodium ion battery, which have the characteristics of low freezing point, high low-temperature electrical conductivity and good cycle stability.
[0009] The present invention can be achieved through the following technical solutions:
[0010] The present invention discloses a high-conductivity, low-temperature electrolyte for sodium-ion batteries, comprising a sodium salt, a solvent, and an additive. 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, and the carbonate solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The sulfate solvent accounts for 50%-100% of the electrolyte, while the carbonate solvent accounts for 0%-50% of the electrolyte. This solvent system allows more anions to enter the solvation shell, resulting in an anion-dominated solvation structure that effectively regulates the electrochemical deposition process. In particular, the sulfate solvent promotes the formation of sulfide-rich CEI films, which exhibit low impedance, high modulus, high interfacial stability, good transport kinetics, and improved low-temperature performance. Sulfate solvents have lower viscosity than carbonate solvents, effectively reducing electrolyte viscosity.
[0011] 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. 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. However, nitrile additives are highly reactive and will produce side reactions when used alone at low potentials 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.
[0012] 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. If the additive content is too high, the film formed on the electrode surface will be too thick, which will increase the impedance during battery cycling and shorten the battery cycle life. If the additive content is too low, the film formed on the electrode surface will not be complete and dense, resulting in frequent contact between the active material and the electrolyte, causing continuous side reactions and deteriorating battery cycle performance.
[0013] Furthermore, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)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 separator and the positive and negative electrodes will decrease, the sodium ion transmission will be poor, and the low-temperature performance will further deteriorate. If the sodium salt concentration is too low, the conductivity will be too low, increasing the battery impedance.
[0014] 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 according to any one of claims 1 to 4.
[0015] Furthermore, the sodium ion battery positive electrode material is a Prussian blue / white material, a layered oxide material or a polyanion positive electrode material.
[0016] Furthermore, the polyanionic 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.
[0017] Furthermore, the negative electrode material of the sodium ion battery is a hard carbon and / or alloy negative electrode.
[0018] 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.
[0019] The present invention provides a high-conductivity low-temperature electrolyte for sodium ion batteries and a sodium ion battery, which have the following beneficial effects:
[0020] 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, and a moderate dielectric constant and solvation ability. It can fully dissociate the sodium salt without having too strong a binding ability with sodium ions, which makes desolvation difficult under low temperature conditions. It reduces the viscosity of the system to the greatest extent, which is conducive to rapid desolvation under low temperature conditions.
[0021] 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
[0022] Figure 1 The test results of the cycle performance of Example 6 are as follows;
[0023] Figure 2 The specific capacity test curves of Example 6 and Comparative Example 1 are shown;
[0024] Figure 3 The graphs are the cycle performance test curves of Example 6 and Comparative Example 1. DETAILED DESCRIPTION
[0025] 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 with reference to embodiments.
[0026] The invention discloses a low-temperature electrolyte for a sodium ion battery 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%.
[0027] 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.
[0028] 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.
[0029] Furthermore, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide, wherein the concentration of the sodium salt is 0.2-2.0 mol / L.
[0030] 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 according to any one of claims 1 to 4.
[0031] Furthermore, the sodium ion battery positive electrode material is a Prussian blue / white material, a layered oxide material or a polyanion positive electrode material.
[0032] Furthermore, the polyanionic 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.
[0033] Furthermore, the negative electrode material of the sodium ion battery is a hard carbon and / or alloy negative electrode.
[0034] 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.
[0035] Example 1
[0036] This embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity. The electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.
[0037] In this example, the sodium salt used is sodium hexafluorophosphate at a concentration of 1 mol / L. The carbonate solvents used are ethylene carbonate and ethyl methyl carbonate (ethylene carbonate:ethyl methyl carbonate = 2:1), with the carbonate solvent accounting for 20% of the electrolyte by volume. The sulfate solvents used are diethyl sulfite and ethylene sulfite (diethyl sulfite:ethylene sulfite = 1:1), with the sulfate accounting for 80% of the electrolyte by volume. The first additive is fluoroethylene carbonate, and the second additive is succinonitrile. The film-forming additive is added in an amount of 4 wt% of the total mass of the low-temperature electrolyte.
[0038] Example 2
[0039] This embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity. The electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.
[0040] The sodium salts used were 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 were ethylene carbonate and ethyl methyl carbonate (ethylene carbonate:ethyl methyl carbonate = 1:1), with the carbonate solvent accounting for 30% by volume of the electrolyte. The sulfate solvents used were diethyl sulfite and ethylene sulfite (diethyl sulfite:ethylene sulfite = 1:1), with the sulfate accounting for 70% by volume of the electrolyte. The first additive was fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate:vinylene carbonate = 1:1 (mass ratio)), and the second additive was 1,3,6-hexanetrinitrile. The film-forming additive was added in an amount of 4 wt% of the total mass of the low-temperature electrolyte.
[0041] Example 3
[0042] This embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity. The electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.
[0043] The sodium salts used were sodium hexafluorophosphate and sodium difluorooxalatoborate (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium difluorooxalatoborate), with a concentration of 1 mol / L. The carbonate solvents used were ethylene carbonate and ethyl methyl carbonate (ethylene carbonate:ethyl methyl carbonate = 3:2), with the carbonate solvent accounting for 40% of the electrolyte volume. The sulfate solvents used were dimethyl sulfite and diethyl sulfite (dimethyl sulfite:diethyl sulfite = 1:4), with the sulfate accounting for 60% of the electrolyte volume. The first additive was fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate:vinylene carbonate = 1:1 (mass ratio)), and the second additive was 1,3,6-hexanetrinitrile. The film-forming additive was added in an amount of 4 wt% of the total mass of the low-temperature electrolyte.
[0044] Example 4
[0045] This embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity. The electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.
[0046] The sodium salts used were sodium hexafluorophosphate and sodium difluorooxalatoborate (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium difluorooxalatoborate), with a concentration of 1 mol / L. The carbonate solvents used were ethylene carbonate and ethyl methyl carbonate (ethylene carbonate:ethyl methyl carbonate = 1:1), with the carbonate solvent accounting for 45% by volume of the electrolyte. The sulfate solvents used were diethyl sulfite and ethylene sulfite (diethyl sulfite:ethylene sulfite = 1:1), with the sulfate accounting for 55% by volume of the electrolyte. The first additive was fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate:vinylene carbonate = 1:1 (mass ratio)), and the second additive was methoxyacetonitrile. The film-forming additive was added in an amount of 4 wt% based on the total mass of the low-temperature electrolyte.
[0047] Example 5
[0048] This embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity. The electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.
[0049] The sodium salts used were 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 were ethylene carbonate and ethyl methyl carbonate (ethylene carbonate: dimethyl carbonate = 1:1), with the carbonate solvent accounting for 50% of the electrolyte volume. The sulfate solvents used were dimethyl sulfite, diethyl sulfite, and ethylene sulfite (dimethyl sulfite: diethyl sulfite: ethylene sulfite = 1:1:1), with the sulfate accounting for 50% of the electrolyte volume. The first additives were fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 2:1 (mass ratio)), and the second additive was 1,2,3-tris(2-cyanoethoxy)propane. The film-forming additive was added in an amount of 5 wt% of the total mass of the low-temperature electrolyte.
[0050] Example 6
[0051] This embodiment relates to a low-temperature sodium ion battery electrolyte with high conductivity. The electrolyte includes a sodium salt, a carbonate solvent, a sulfate solvent, a first additive, and a second additive.
[0052] The sodium salts used were sodium hexafluorophosphate and sodium perchlorate (0.5 mol / L sodium hexafluorophosphate and 0.5 mol / L sodium bis(2-fluoroethoxy)sulfonyl)imide), with a concentration of 1 mol / L. The carbonate solvent used was ethyl methyl carbonate, with the carbonate solvent accounting for 30% by volume of the electrolyte. The sulfate solvents used were dimethyl sulfite and diethyl sulfite (dimethyl sulfite: diethyl sulfite = 1:1), with the sulfate accounting for 70% by volume of the electrolyte. The first additive was fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 2:1 (mass ratio)), and the second additive was 1,2,3-tris(2-cyanoethoxy)propane and 1,2-bis(2-cyanoethoxy)ethane, with a mass ratio of 1:1. The film-forming additive was added in an amount of 4 wt% of the total mass of the low-temperature electrolyte. In this example, the obtained electrolyte was also assembled into a sodium iron pyrophosphate / hard carbon soft-pack battery to test its room temperature long cycle performance.
[0053] 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℃, 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℃. Figure 3 shown.
[0054] Comparative Example 1
[0055] This embodiment relates to a low-temperature sodium ion battery electrolyte, the electrolyte comprising a sodium salt, a carbonate solvent, a first additive, and a second additive. The electrolyte composition differs from that of Example 6 in that no sulfate solvent is added in Comparative Example 1.
[0056] The sodium salts used are sodium hexafluorophosphate and sodium bis(2-fluoroethoxy)imide (0.5 mol / L sodium hexafluorophosphate, 0.5 mol / L sodium bis(2-fluoroethoxy)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-tris(2-cyanoethoxy)propane and 1,2-bis(2-cyanoethoxy)ethane with a mass ratio of 1:1. 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 and 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.
[0057] Comparative Example 2
[0058] This embodiment relates to a low-temperature sodium ion battery electrolyte, which includes a sodium salt, a carbonate solvent, a sulfate solvent, and a film-forming additive. The electrolyte composition differs from that of Example 6 in that only the first additive is added in Comparative Example 2.
[0059] The sodium salts used were 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 was ethyl methyl carbonate, with the carbonate solvent accounting for 30% by volume of the electrolyte. The sulfate solvents used were dimethyl sulfite and diethyl sulfite (dimethyl sulfite: diethyl sulfite = 1:1), with the sulfate accounting for 70% by volume of the electrolyte. The first additive was fluoroethylene carbonate and vinylene carbonate (fluoroethylene carbonate: vinylene carbonate = 2:1 (mass ratio)), with the film-forming additive added in an amount of 2 wt% of the total mass of the carbonate low-temperature electrolyte. A button-type half-cell was assembled using the same electrolyte and subjected to charge and discharge cycles at -20°C. It was found that the capacity retention was significantly inferior to that of Example 6.
[0060] The above embodiments are merely specific embodiments of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the scope of the present invention, and such obvious alternatives are all within the scope of protection of the present invention.
Claims
1. A high-conductivity low-temperature electrolyte for sodium ion batteries, comprising a sodium salt, a solvent, and an additive, characterized in that: The solvent is 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 20%-50%; The additive is a composite additive, comprising 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 difluorooxalatoborate; and 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 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; The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide, wherein the concentration of the sodium salt is 0.2-2.0 mol / L.
2. A sodium ion battery, characterized in that: The low-temperature electrolyte according to claim 1 is added.
3. The sodium ion battery according to claim 2, wherein: The positive electrode material of the sodium ion battery is a Prussian blue material, a Prussian white material, a layered oxide material or a polyanion positive electrode material.
4. The sodium ion battery according to claim 3, wherein: 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.
5. The sodium ion battery according to claim 2, wherein: The negative electrode material of the sodium ion battery is hard carbon and / or alloy negative electrode.
6. The sodium ion battery according to claim 5, 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.