Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The application provides a sodium ion battery electrolyte and a sodium ion battery, and relates to the technical field of sodium ion batteries.A sodium ion battery electrolyte comprises a sodium salt, an organic solvent and an additive.The additive is selected from one or more of a thioimide functional additive and a film-forming additive.The sodium ion battery electrolyte provided by the application can inhibit the dissolution of SEI films and CEI films, improve the cycle stability of the sodium ion battery under high pressure, and thus improve the energy density and service life of the sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more particularly to a sodium-ion battery electrolyte and a sodium-ion battery. Background Technology

[0002] With the ever-increasing demand for energy and the finite reserves of traditional fossil fuels such as oil, coal, and natural gas, the world is facing a new trend of energy transition. Secondary batteries have become a crucial technology in this transition, with lithium-ion batteries being a mature technology that dominates the market and is widely used in new energy vehicles, aerospace, and energy storage. In recent years, the demand for power batteries and energy storage has expanded rapidly, leading to a surge in global demand for lithium resources. However, lithium resources are unevenly distributed and limited in the Earth's crust, posing a technological risk that supply may not meet development needs. Sodium-ion batteries, with their similar working principle to lithium-ion batteries and abundant resources, are the most promising alternative and supplementary product to lithium-ion batteries.

[0003] Sodium-ion batteries have significant advantages in terms of material cost and resource reserves, but they still lag behind lithium-ion batteries in terms of energy density. High voltage is crucial for improving energy density, and the electrolyte, a vital component of the SEI and CEI films in sodium-ion batteries, significantly impacts their energy density. Traditional ester-based electrolytes used in lithium-ion batteries exhibit poor compatibility with the electrode interface in sodium-ion batteries. Furthermore, under high voltage conditions, some components of the SEI and CEI films formed during operation continuously dissolve, leading to poor cycle performance and a continuous decrease in capacity. Therefore, addressing the dissolution problem of the SEI and CEI films during high-voltage charging and discharging of sodium-ion batteries and developing a high-voltage electrolyte suitable for them is of paramount importance. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a sodium-ion battery electrolyte and a sodium-ion battery.

[0005] The present invention provides a sodium-ion battery electrolyte comprising sodium salt, organic solvent, and additives; wherein the additives are selected from one or more of thioimide functional additives and film-forming additives.

[0006] The sodium-ion battery electrolyte proposed in this invention helps to improve problems such as poor cycle stability and capacity decay during high-voltage charge and discharge of sodium-ion batteries.

[0007] Preferably, the sodium-ion battery electrolyte comprises, by weight, 5-40 parts sodium salt, 70-95 parts organic solvent, and 0.1-8 parts additives.

[0008] The sodium-ion battery electrolyte prepared by controlling the ratio of raw materials can form a relatively complete SEI film and CEI film, thereby improving the battery energy density and extending the battery life.

[0009] Preferably, the thioimide functional additive is N-cyclohexylthiophthalimide.

[0010] The basic imide groups in the thioimide functional additive of this invention can react with hydrofluoric acid and trace amounts of water in the electrolyte, which can effectively avoid the damage to the SEI film caused by hydrofluoric acid and trace amounts of water. Furthermore, the benzene ring and imide ring structures help to form a flat and dense SEI film on the negative electrode, which helps to improve the energy density and cycle stability of sodium-ion batteries.

[0011] Preferably, the film-forming additive is selected from one or more of 1,3-propanesulfonate lactone, fluoroethylene carbonate, ethylene sulfate, and sodium bis(trifluoromethanesulfonyl)imide.

[0012] Film-forming additives can form a flat, dense, and stable solid electrolyte interface (SEI) film on the electrode surface, effectively suppressing the occurrence of harmful side reactions and reducing electrolyte consumption, thereby improving the cycle stability of sodium-ion batteries.

[0013] Preferably, the mass ratio of the thioimide functional additive to the film-forming additive is (0.05-0.2):6.

[0014] Thioimide functional additives and film-forming additives work synergistically to prevent the electrolyte from being oxidized at the positive electrode and to inhibit the dissolution of transition metal ions; at the same time, they construct stable CEI and SEI films, avoiding the continuous consumption of electrolyte, solving the problem of continuous capacity decay during high-voltage charge-discharge cycles, and improving the service life of sodium-ion batteries.

[0015] Preferably, the organic solvent is an ether-based organic solvent; the ether-based organic solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

[0016] The electrolyte prepared by ether-based organic solvents has better compatibility with the hard carbon of the negative electrode; the weak solvation structure of ether-based organic solvents can form a uniform and stable CEI film at the positive electrode, solving the dissolution problem of the CEI film under high pressure; the ether-based organic solvents and additives work synergistically to jointly construct a uniform and stable SEI film and CEI film.

[0017] Preferably, the sodium salt is selected from one or more of sodium hexafluorophosphate and sodium perchlorate.

[0018] The combination of ether-based organic solvents and sodium salts can improve the stability of sodium-ion batteries during high-voltage charge and discharge processes, resulting in high-performance sodium-ion batteries.

[0019] The present invention also proposes a sodium-ion battery, comprising a positive electrode, a separator, a negative electrode, and the aforementioned sodium-ion battery electrolyte.

[0020] Preferably, the positive electrode sheet includes a positive current collector and a positive electrode coating coated on the positive current collector. The positive electrode coating includes the following raw materials in parts by weight: 90-96 parts of positive active material, 0.5-2 parts of oxalic acid, 1-3 parts of conductive agent, and 1-3 parts of binder.

[0021] More preferably, the positive electrode active material is selected from NaNi 1 / 3 Fe 1 / 3 Mn l / 3 O2, NaNi 0.25 Fe 0.25 Mn 0.5 One or more of O2.

[0022] More preferably, the preparation of the positive electrode sheet includes: adding positive electrode active material, oxalic acid, conductive agent and binder into a solvent, dispersing them evenly to obtain a positive electrode slurry, uniformly coating the positive electrode slurry onto a positive electrode current collector, baking and drying, rolling and die-cutting, and forming a positive electrode coating from the positive electrode slurry to obtain the positive electrode sheet.

[0023] More preferably, the solvent is N-methylpyrrolidone; the positive electrode current collector is carbon-coated aluminum foil.

[0024] Preferably, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating coated on the negative electrode current collector. The negative electrode coating includes the following raw materials in parts by weight: 90-96 parts of negative electrode active material, 1-4 parts of conductive agent and 1-5 parts of binder.

[0025] More preferably, the negative electrode active material is hard carbon.

[0026] More preferably, the preparation of the negative electrode sheet includes: adding the negative electrode active material, conductive agent and binder into a solvent, dispersing them evenly to obtain a negative electrode slurry, uniformly coating the negative electrode slurry onto the negative electrode current collector, baking and drying, rolling and die-cutting, and forming a negative electrode coating from the negative electrode slurry to obtain the negative electrode sheet.

[0027] More preferably, the solvent is water; the negative electrode current collector is carbon-coated aluminum foil.

[0028] Preferably, the diaphragm is a PP and PE mixed diaphragm.

[0029] A method for preparing a sodium-ion battery includes the following steps: stacking a positive electrode, a separator, and a negative electrode into a battery cell, encapsulating and drying the cell, injecting the sodium-ion battery electrolyte, and performing immersion, formation, aging, degassing and sealing, and capacity testing to obtain the battery.

[0030] Using the above-described method for preparing sodium-ion batteries, sodium-ion batteries with excellent charge-discharge performance and long service life can be obtained.

[0031] The beneficial effects of this invention are as follows:

[0032] The film-forming additive of this invention can form a good SEI film on the electrode surface. The thioimide functional additive, being a basic group, can bind with hydrofluoric acid and trace amounts of water in the fluorinated electrolyte, thereby removing hydrofluoric acid and water and preventing them from damaging the SEI film. Furthermore, the strong electronegativity of the sulfur atom makes it more inclined to undergo electrochemical reduction reactions, improving the film-forming effect of the SEI film in the electrolyte and reducing the occurrence of side reactions. This invention uses ether-based organic solvents to solve the problem of instability and continuous dissolution of some substances in the CEI film formed by ester-carbonate solvents at the positive electrode of sodium-ion batteries.

[0033] The sodium-ion battery electrolyte used in this invention can form a relatively complete SEI film and CEI film, inhibit the dissolution of the SEI film and CEI film, suppress the occurrence of harmful side reactions in the battery, improve the dissolution of the SEI film and CEI film under high voltage, and improve the cycle stability of the battery under high voltage, thereby improving the energy density and service life of the sodium-ion battery. Detailed Implementation

[0034] The technical solution of the present invention will be described in detail through specific embodiments.

[0035] Unless otherwise specified, all materials and reagents used in the following examples and comparative examples are commercially available.

[0036] Example 1

[0037] A method for preparing a sodium-ion battery electrolyte includes the following steps:

[0038] In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane were mixed at a mass ratio of 6:3:1 to obtain an organic solvent. Sodium hexafluorophosphate, 1,3-propanesulfonic acid lactone, fluoroethylene carbonate, and N-cyclohexylthiophthalimide were dissolved in the organic solvent to obtain a sodium-ion battery electrolyte. The concentration of sodium hexafluorophosphate in the sodium-ion battery electrolyte was 1 mol / L, the mass percentage of fluoroethylene carbonate in the total mass of the sodium-ion battery electrolyte was 5%, the mass percentage of 1,3-propanesulfonic acid lactone in the total mass of the sodium-ion battery electrolyte was 1%, and the mass percentage of N-cyclohexylthiophthalimide in the total mass of the sodium-ion battery electrolyte was 0.05%.

[0039] Example 2

[0040] A method for preparing a sodium-ion battery electrolyte includes the following steps:

[0041] In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane were mixed in a mass ratio of 6:3:1 to obtain an organic solvent. Sodium hexafluorophosphate, 1,3-propanesulfonic acid lactone, fluoroethylene carbonate, and N-cyclohexylthiophthalimide were dissolved in the organic solvent to obtain a sodium-ion battery electrolyte. The concentration of sodium hexafluorophosphate in the sodium-ion battery electrolyte was 1 mol / L, the mass percentage of fluoroethylene carbonate in the total mass of the sodium-ion battery electrolyte was 5%, the mass percentage of 1,3-propanesulfonic acid lactone in the total mass of the sodium-ion battery electrolyte was 1%, and the mass percentage of N-cyclohexylthiophthalimide in the total mass of the sodium-ion battery electrolyte was 0.1%.

[0042] Example 3

[0043] A method for preparing a sodium-ion battery electrolyte includes the following steps:

[0044] In an argon-atmosphere glove box with an oxygen content of less than 0.01 ppm, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane were mixed in a mass ratio of 6:3:1 to obtain an organic solvent. Sodium hexafluorophosphate, 1,3-propanesulfonic acid lactone, fluoroethylene carbonate, and N-cyclohexylthiophthalimide were dissolved in the organic solvent to obtain a sodium-ion battery electrolyte. The concentration of sodium hexafluorophosphate in the sodium-ion battery electrolyte was 1 mol / L, the mass percentage of fluoroethylene carbonate in the total mass of the sodium-ion battery electrolyte was 5%, the mass percentage of 1,3-propanesulfonic acid lactone in the total mass of the sodium-ion battery electrolyte was 1%, and the mass percentage of N-cyclohexylthiophthalimide in the total mass of the sodium-ion battery electrolyte was 0.2%.

[0045] Comparative Example 1

[0046] A method for preparing a sodium-ion battery electrolyte includes the following steps:

[0047] In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane were mixed in a mass ratio of 6:3:1 to obtain an organic solvent. Sodium hexafluorophosphate, 1,3-propanesulfonate lactone, and fluoroethylene carbonate were dissolved in the organic solvent to obtain a sodium-ion battery electrolyte. The concentration of sodium hexafluorophosphate in the sodium-ion battery electrolyte was 1 mol / L, the mass percentage of fluoroethylene carbonate in the total mass of the sodium-ion battery electrolyte was 5%, and the mass percentage of 1,3-propanesulfonate lactone in the total mass of the sodium-ion battery electrolyte was 1%.

[0048] Comparative Example 2

[0049] The only difference between this comparative example and comparative example 1 is that 1,3-propanesulfonic acid lactone is not added; the rest of the steps are the same as those in comparative example 1.

[0050] Comparative Example 3

[0051] The only difference between this comparative example and Comparative Example 1 is that the organic solvent is a mixture of ethylene carbonate, dimethyl carbonate and propylene carbonate in a mass ratio of 1:1:1. The remaining steps are the same as those in Comparative Example 1.

[0052] The above electrolyte is assembled with a positive electrode, a separator, and a negative electrode to obtain a sodium-ion battery, specifically:

[0053] Positive electrode preparation: NaNi 1 / 3 Fe 1 / 3 Mn l / 3 O2, oxalic acid, conductive agent SP, conductive agent GOs, and PVDF are mixed in a mass ratio of 93.5:0.5:1.75:1.25:3. N-methylpyrrolidone is added, and the mixture is stirred thoroughly according to the homogenization process to obtain a positive electrode slurry with a solid content of 57%. The slurry is then coated onto a carbon-coated aluminum foil for the positive electrode current collector to a thickness of 340 μm. After drying, rolling, and die-cutting, the positive electrode slurry forms a positive electrode coating, thus obtaining the positive electrode sheet.

[0054] Negative electrode preparation: Hard carbon, SP, CMC and SBR are mixed in a mass ratio of 94:2.4:1.4:2.4, deionized water is added, and the mixture is stirred thoroughly according to the homogenization process to obtain a negative electrode slurry with a solid content of 50%. The slurry is then coated onto the carbon-coated aluminum foil of the negative electrode current collector with a coating thickness of 150μm. After drying, rolling, and die cutting, the negative electrode slurry forms a negative electrode coating, thus obtaining the negative electrode sheet.

[0055] Sodium-ion battery preparation: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, resulting in a dry cell. The dry cell is placed in an aluminum-plastic film and dried at 80-95℃ for 15-30 hours. Then, the prepared sodium-ion battery electrolyte is injected and the cell is sealed. The cell undergoes high-temperature wetting, formation, aging, degassing and sealing, and capacity testing to obtain the final product.

[0056] The sodium-ion batteries prepared above were tested for their initial charge-discharge efficiency and capacity retention after 200 cycles at 25°C. The test results are shown in Table 1.

[0057] Table 1

[0058]

[0059] As can be seen from the data in Table 1, the sodium-ion battery prepared by this invention exhibits a high capacity retention rate under high voltage conditions. Combined with Comparative Examples 1 and 2, it can be seen that adding 1,3-propanesulfonate lactone to the sodium-ion electrolyte can improve the capacity retention rate of the sodium-ion battery. This is because 1,3-propanesulfonate lactone can prevent the electrolyte from oxidizing on the positive electrode surface, inhibit the dissolution of transition metal ions, and simultaneously construct a stable SEI film, thereby improving the cycle performance of the sodium-ion battery and extending its lifespan.

[0060] Combining Comparative Examples 1 and 3, it can be seen that sodium-ion batteries using ether-based electrolytes have better cycle stability under high voltage. This is because ether-based electrolytes have better compatibility with the hard carbon anode than ester-based electrolytes, and ether-based electrolytes help to build a stable CEI film, thereby improving the cycle stability of sodium-ion batteries under high voltage.

[0061] As can be seen from Examples 1-3 and Comparative Example 1, adding N-cyclohexylthiophthalimide to the sodium-ion electrolyte can effectively improve the capacity retention rate of sodium-ion batteries under high voltage. This is because the imide group in N-cyclohexylthiophthalimide can absorb trace amounts of hydrofluoric acid and water in the electrolyte, and the benzene ring and imide ring help to form a flat and stable SEI film, suppress the occurrence of harmful side reactions, and improve the cycle stability of sodium-ion batteries.

[0062] In summary, this invention utilizes ether-based organic solvents in combination with film-forming additives such as 1,3-propanesulfonic acid lactone, fluoroethylene carbonate, and thioimide functional additives to obtain sodium-ion batteries with stable SEI and CEI films. This effectively improves the cycle performance of sodium-ion batteries under high voltage, increases battery energy density, and extends battery life.

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A sodium-ion battery electrolyte, characterized in that, It includes sodium salt, organic solvent, and additives; the additives include thioimide functional additives and film-forming additives; the organic solvent is an ether-based organic solvent.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, The thioimide functional additive is N-cyclohexylthiophthalimide.

3. The sodium-ion battery electrolyte according to claim 1, characterized in that, The film-forming additive is selected from one or more of 1,3-propanesulfonate lactone, fluoroethylene carbonate, ethylene sulfate, and sodium bis(trifluoromethanesulfonyl)imide.

4. The sodium-ion battery electrolyte according to any one of claims 1-3, characterized in that, The mass ratio of the thioimide functional additive to the film-forming additive is (0.05-0.2):

6.

5. The sodium-ion battery electrolyte according to claim 1, characterized in that, The ether organic solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

6. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt is selected from one or more of sodium hexafluorophosphate and sodium perchlorate.

7. The sodium-ion battery electrolyte according to claim 1, characterized in that, By weight, it includes 5-40 parts sodium salt, 70-95 parts organic solvent, and 0.1-8 parts additives.

8. A sodium-ion battery, characterized in that, It includes a positive electrode, a separator, a negative electrode, and the sodium-ion battery electrolyte according to any one of claims 1-7.

9. The sodium-ion battery according to claim 8, characterized in that, The positive electrode active material in the aforementioned positive electrode sheet is selected from NaNi 1 / 3 Fe 1 / 3 Mn l / 3 O2, NaNi 0.25 Fe 0.25 Mn 0.5 One or more of O2.

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