Method for preparing electrolyte for sodium-ion battery

Abstract

The application discloses a preparation method of an electrolyte for a sodium ion battery. Methyl ferrocene formate is prepared as an additive. The methyl ferrocene formate is a double active site structure containing a substituent group, has a free radical capture site and a metal ion coordination site, and can accurately control the redox potential. The decomposition product and transition metal ion can be actively activated at a high voltage. At a normal voltage, the electrolyte can be restored and recycled through electrochemical reduction. In the process, no complex is generated, no foreign matter is deposited in the electrolyte, and the cycle stability of the battery is not affected. In addition, the electrolyte prepared by the application has a relatively low concentration and low viscosity, which effectively ensures the conductivity of the electrolyte. Moreover, the additive and the film forming agent are compounded, the design scheme can form a positive and negative double interface synergistic protection, the electrolyte decomposition and metal dissolution of the positive electrode are inhibited, the negative electrode SEI film integrity is protected, and the film damage and impedance surge are not prone to occur after long-term cycle.

Description

Technical Field

[0001] This invention relates to the field of electrolytes, and in particular to a method for preparing an electrolyte for sodium-ion batteries. Background Technology

[0002] With the acceleration of the global energy transition, developing efficient and low-cost energy storage technologies has become a key path to alleviate the crisis of traditional fossil fuels and environmental pollution. Sodium-ion batteries, due to the abundance, wide distribution, and low cost of sodium resources, have shown great potential to replace lithium-ion batteries in the field of large-scale energy storage. Traditional sodium-ion batteries have relatively low energy density, and increasing the battery cutoff voltage is a core technological direction for achieving breakthroughs in energy density. For example, increasing the cutoff voltage of a NaNi1 / 3Fe1 / 3Mn1 / 3O2 cathode sodium-ion battery from 4.0V to 4.3V can significantly increase energy density, but the high-voltage environment accelerates the oxidative degradation process of the electrolyte, generating byproducts such as CO2, CO, and small-molecule carboxylic acids. Simultaneously, it induces the dissolution of transition metal ions on the cathode surface, further catalyzing the electrolyte decomposition reaction, disrupting the charge transfer balance at the positive and negative electrode interfaces, and ultimately leading to a significant decrease in battery cycle life.

[0003] In existing technologies, most methods improve the oxidative stability of electrolytes to some extent by developing high-concentration electrolytes, locally high-concentration electrolytes, or adding film-forming additives. However, these methods have significant limitations. High-concentration electrolytes have higher viscosity, leading to decreased ionic conductivity and deterioration of battery rate performance. Furthermore, the interfacial layers formed by film-forming additives are often irreversible structures, prone to membrane damage and impedance surges after long-term cycling, and cannot actively capture electrolyte decomposition products and dissolved metal ions. Some manufacturers have begun to introduce metal ion complexing additives such as nitrile compounds. While these can inhibit transition metal dissolution to some extent, they only function within a fixed voltage range and cannot achieve the dynamic response effect of high-voltage trigger activation and reversible recovery at normal voltage. Moreover, the complexing products tend to accumulate and deposit in the electrolyte, affecting the long-term cycle stability of the battery. Therefore, it is necessary to propose a new solution to address these issues. Summary of the Invention

[0004] In view of this, the present invention addresses the deficiencies of the prior art, and its main objective is to provide a method for preparing an electrolyte for sodium-ion batteries. This method can effectively solve the problems that existing sodium battery electrolytes are prone to membrane damage and impedance surges after long-term cycling, or that complex products tend to accumulate and deposit in the electrolyte, affecting the long-term cycling stability of the battery.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an electrolyte for sodium-ion batteries includes the following steps: (1) Preparation of additives: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additives. (2) Electrolyte preparation: Dissolve NaTFSI in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. Add the additive obtained in step (1) with a mass of 0.3-1.2% of the NaTFSI mass. Add a negative electrode film-forming agent with a volume of 1.0% of the solvent volume. Stir in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries.

[0006] As a preferred embodiment, in step (1), the catalyst is concentrated sulfuric acid.

[0007] As a preferred embodiment, in step (1), the desiccant is magnesium sulfate.

[0008] As a preferred embodiment, in step (1), the vacuum degree of the vacuum distillation is 0.08 MPa, and the temperature of the vacuum distillation is 80°C.

[0009] As a preferred embodiment, in step (1), the eluent used in the silica gel column chromatography is composed of petroleum ether and ethyl acetate, with a volume ratio of petroleum ether to ethyl acetate of 5:1.

[0010] As a preferred embodiment, in step (2), the solvent is composed of EC and DEC, and the volume ratio of EC to DEC is (1-2):(1-8).

[0011] As a preferred embodiment, in step (2), the negative electrode film-forming agent is FEC.

[0012] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution: By preparing methyl ferrocene as an additive, methyl ferrocene, with its substituent-modified dual-active-site structure, possesses both free radical capture sites and metal ion coordination sites, precisely controlling the redox potential to achieve an oxidation potential of 4.1-4.2V and a reduction potential of 2.8-3.2V. Under high voltage, it can actively activate and capture decomposition products and transition metal ions; under normal voltage, it can be electrochemically reduced and recycled, overcoming the shortcomings of existing solutions such as irreversible protection and product accumulation. Simultaneously, no complexes are formed during the process, and no foreign matter is deposited in the electrolyte, thus not affecting the battery's cycle stability. Furthermore, the electrolyte prepared according to this invention has a relatively low concentration and low viscosity, effectively ensuring its conductivity. The design scheme of combining additives and film-forming agents forms a synergistic protection between the positive and negative electrodes, inhibiting both positive electrode electrolyte decomposition and metal dissolution while protecting the integrity of the negative electrode SEI film. After long-term cycling, film damage and impedance surges are less likely to occur, and it also meets dynamic protection requirements.

[0013] To more clearly illustrate the effects of the present invention, the present invention will be described in detail below with reference to several specific embodiments. Detailed Implementation

[0014] This invention discloses a method for preparing an electrolyte for sodium-ion batteries, which includes the following steps: (1) Preparation of additive: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additive. The catalyst was concentrated sulfuric acid, the desiccant was magnesium sulfate, the vacuum degree of the vacuum distillation was 0.08 MPa, the temperature of the vacuum distillation was 80 °C, and the eluent used in the silica gel column chromatography was composed of petroleum ether and ethyl acetate, with a volume ratio of petroleum ether to ethyl acetate of 5:1.

[0015] (2) Electrolyte preparation: Dissolve NaTFSI in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. Add the additive obtained in step (1) with a mass of 0.3-1.2% of the NaTFSI mass. Add a negative electrode film-forming agent with a volume of 1.0% of the solvent volume. Stir in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries. The solvent is composed of EC and DEC with a volume ratio of (1-2):(1-8). The negative electrode film-forming agent is FEC.

[0016] (3) Assemble sodium-ion batteries: Select NaNi1 / 3Fe1 / 3Mn1 / 3O2 as the positive electrode material, hard carbon as the negative electrode material, and glass fiber membrane as the separator. Inject the above electrolyte and assemble to obtain a button cell. Specifically, the button cell model is CR2032.

[0017] The following detailed description is based on specific embodiments.

[0018] Example 1 (1) Preparation of additive: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additive. The catalyst was concentrated sulfuric acid, the desiccant was magnesium sulfate, the vacuum degree of the vacuum distillation was 0.08 MPa, the temperature of the vacuum distillation was 80 °C, and the eluent used in the silica gel column chromatography was composed of petroleum ether and ethyl acetate, with a volume ratio of petroleum ether to ethyl acetate of 5:1.

[0019] (2) Electrolyte preparation: NaTFSI is dissolved in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. Add the additive obtained in step (1) with a mass of 1.2% of the NaTFSI mass. Then add the negative electrode film-forming agent with a volume of 1.0% of the solvent volume. Stir in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries. The solvent is composed of EC and DEC with a volume ratio of 1:1. The negative electrode film-forming agent is FEC.

[0020] Example 2 (1) Preparation of additive: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additive. The catalyst was concentrated sulfuric acid, the desiccant was magnesium sulfate, the vacuum degree of the vacuum distillation was 0.08 MPa, the temperature of the vacuum distillation was 80 °C, and the eluent used in the silica gel column chromatography was composed of petroleum ether and ethyl acetate, with a volume ratio of petroleum ether to ethyl acetate of 5:1.

[0021] (2) Electrolyte preparation: NaTFSI is dissolved in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. Add the additive obtained in step (1) with a mass of 0.3% of the NaTFSI mass. Then add the negative electrode film-forming agent with a volume of 1.0% of the solvent volume. Stir in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries. The solvent is composed of EC and DEC with a volume ratio of 1:1. The negative electrode film-forming agent is FEC.

[0022] Example 3 (1) Preparation of additive: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additive. The catalyst was concentrated sulfuric acid, the desiccant was magnesium sulfate, the vacuum degree of the vacuum distillation was 0.08 MPa, the temperature of the vacuum distillation was 80 °C, and the eluent used in the silica gel column chromatography was composed of petroleum ether and ethyl acetate, with a volume ratio of petroleum ether to ethyl acetate of 5:1.

[0023] (2) Electrolyte preparation: NaTFSI is dissolved in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. Add the additive obtained in step (1) with a mass of 1.2% of the NaTFSI mass. Then add the negative electrode film-forming agent with a volume of 1.0% of the solvent volume. Stir in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries. The solvent is composed of EC and DEC with a volume ratio of 2:8. The negative electrode film-forming agent is FEC.

[0024] Example 4 (1) Preparation of additive: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additive. The catalyst was concentrated sulfuric acid, the desiccant was magnesium sulfate, the vacuum degree of the vacuum distillation was 0.08 MPa, the temperature of the vacuum distillation was 80 °C, and the eluent used in the silica gel column chromatography was composed of petroleum ether and ethyl acetate, with a volume ratio of petroleum ether to ethyl acetate of 5:1.

[0025] (2) Electrolyte preparation: NaTFSI is dissolved in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. The additive obtained in step (1) is added with a mass of 1% of the NaTFSI mass. Then, a negative electrode film-forming agent is added with a volume of 1.0% of the solvent volume. The mixture is stirred in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries. The solvent is composed of EC and DEC with a volume ratio of 2:3. The negative electrode film-forming agent is FEC.

[0026] Example 5 (1) Preparation of additive: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additive. The catalyst was concentrated sulfuric acid, the desiccant was magnesium sulfate, the vacuum degree of the vacuum distillation was 0.08 MPa, the temperature of the vacuum distillation was 80 °C, and the eluent used in the silica gel column chromatography was composed of petroleum ether and ethyl acetate, with a volume ratio of petroleum ether to ethyl acetate of 5:1.

[0027] (2) Electrolyte preparation: NaTFSI is dissolved in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. The additive obtained in step (1) is added with a mass of 0.8% of the NaTFSI mass. Then, a negative electrode film-forming agent is added with a volume of 1.0% of the solvent volume. The mixture is stirred in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries. The solvent is composed of EC and DEC with a volume ratio of 1:8. The negative electrode film-forming agent is FEC.

[0028] Example 6 (1) Preparation of additive: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additive. The catalyst was concentrated sulfuric acid, the desiccant was magnesium sulfate, the vacuum degree of the vacuum distillation was 0.08 MPa, the temperature of the vacuum distillation was 80 °C, and the eluent used in the silica gel column chromatography was composed of petroleum ether and ethyl acetate, with a volume ratio of petroleum ether to ethyl acetate of 5:1.

[0029] (2) Electrolyte preparation: NaTFSI is dissolved in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. The additive obtained in step (1) is added with a mass of 0.9-0.3% of the NaTFSI mass. Then, a negative electrode film-forming agent is added with a volume of 1.0% of the solvent volume. The mixture is stirred in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries. The solvent is composed of EC and DEC with a volume ratio of 1:3. The negative electrode film-forming agent is FEC.

[0030] Comparative Example 1 (1) Electrolyte preparation: NaTFSI is added to a solvent to dissolve it. The solvent is composed of EC and DEC with a volume ratio of 1:1 to obtain the electrolyte.

[0031] The electrolytes prepared in the above embodiments and comparative examples were used to assemble batteries, and a coin cell with the model number CR22032 was obtained after assembly. The performance was then tested, and the test results are shown in Table 1.

[0032]

[0033] Table 1 Analysis of the above data sets revealed that by adding methyl ferrocene and a film-forming agent to the system, a synergistic protection between the positive and negative electrodes was formed. This not only inhibited the decomposition of the positive electrode electrolyte and metal dissolution but also protected the integrity of the negative electrode SEI film. After long-term cycling, the film was less prone to damage and impedance surge. In contrast, Comparative Example 1, which did not include methyl ferrocene and a film-forming agent, exhibited significantly lower electrochemical performance than Example 1, especially in terms of the interfacial impedance growth rate after 100 cycles, which was five times that of Example 1.

[0034] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an electrolyte for sodium-ion batteries, characterized in that: It includes the following steps: (1) Preparation of additives: Under nitrogen protection, 0.1 mol ferrocene, 0.12 mol ethyl formate and 50 mL anhydrous ethanol were added to a dry three-necked flask. After stirring evenly, 5 mL of catalyst was slowly added dropwise, the temperature was raised to 70 °C, and the reaction was refluxed for 6 h. After the reaction was completed, the reaction solution was obtained. The reaction solution was cooled to room temperature, and saturated sodium bicarbonate solution was slowly added to the reaction solution to adjust the pH of the reaction solution to neutral. After standing and separating the layers, the organic phase was taken, dried with a desiccant for 2 h, filtered, and then purified by vacuum distillation and silica gel column chromatography to obtain the additives. (2) Electrolyte preparation: Dissolve NaTFSI in a solvent to obtain an initial electrolyte solution with a NaTFSI concentration of 1.5 mol / L. Add the additive obtained in step (1) with a mass of 0.3-1.2% of the NaTFSI mass. Add a negative electrode film-forming agent with a volume of 1.0% of the solvent volume. Stir in an argon-protected glove box until completely dissolved to obtain an electrolyte for sodium-ion batteries.

2. The method for preparing the electrolyte for sodium-ion batteries according to claim 1, characterized in that: In step (1), the catalyst is concentrated sulfuric acid.

3. The method for preparing the electrolyte for sodium-ion batteries according to claim 1, characterized in that: In step (1), the desiccant is magnesium sulfate.

4. The method for preparing the electrolyte for sodium-ion batteries according to claim 1, characterized in that: In step (1), the vacuum degree of the vacuum distillation is 0.08 MPa, and the temperature of the vacuum distillation is 80°C.

5. The method for preparing the electrolyte for sodium-ion batteries according to claim 1, characterized in that: In step (1), the eluent used in the silica gel column chromatography is composed of petroleum ether and ethyl acetate, with a volume ratio of 5:

1.

6. The method for preparing the electrolyte for sodium-ion batteries according to claim 1, characterized in that: In step (2), the solvent is composed of EC and DEC, and the volume ratio of EC to DEC is (1-2):(1-8).

7. The method for preparing the electrolyte for sodium-ion batteries according to claim 1, characterized in that: In step (2), the negative electrode film-forming agent is FEC.

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