A method for removing water from an aqueous bisfluorosulfonylimide metal salt

Abstract

The present application relates to the field of material and chemical industry, in particular to a method for removing water from a water-containing bistrifluoromethylsulfonylimide metal salt. The method comprises the following steps: performing electrolytic dehydration treatment on a mixed solution containing the water-containing bistrifluoromethylsulfonylimide metal salt and an organic solvent; the water-containing bistrifluoromethylsulfonylimide metal salt contains water and a bistrifluoromethylsulfonylimide metal salt. The method aims to improve the purity and stability of the bistrifluoromethylsulfonylimide metal salt, simplify the purification means, and provide high-quality electrolyte materials for subsequent electrochemical applications.

Description

Technical Field

[0001] This invention relates to the fields of materials and chemical engineering, and specifically to a method for removing water from a hydrous bis(fluorosulfonyl)imide metal salt. Background Technology

[0002] Lithium bisfluorosulfonylimide (LiFSI), a key component in cutting-edge lithium-ion battery electrolytes, is widely prepared using the direct liquid-phase method. LiFSI synthesis generally involves two-step and one-step methods, both ultimately resulting in an aqueous LiFSI solution. Given LiFSI's inherently strong hygroscopic properties, current industrial processes commonly employ solvent azeotropic dehydration technology to effectively remove moisture to meet product-grade standards. Carbonate compounds, due to their excellent hydrophilicity, good solubility in LiFSI, ease of separation from water, and direct compatibility with lithium-ion battery electrolytes, are currently recognized as the best dehydrating agents.

[0003] A patent CN116462166A, titled "A Method for Dehydration in the Synthesis of Lithium Difluorosulfonylimide," reports the dehydration of lithium difluorosulfonylimide by evaporating low-boiling-point azeotropes under negative pressure. This method avoids the introduction of thionyl chloride and prevents the introduction of acidic gases and SO3. 2- The formation of water is problematic. However, in low-boiling-point solvent systems such as carbonates, the vapor pressure of water decreases significantly, causing the dehydration efficiency to drop sharply as the water content decreases. Therefore, in the azeotropic dehydration process, a large amount of solvent circulation is required, which not only significantly increases energy consumption but also may cause side reactions between FSI and water under high-temperature conditions, forcing the process to be carried out in a low-temperature and vacuum environment, further exacerbating the system's energy consumption. For example, when the concentration of LiFSI aqueous solution is about 50%, most of the water can be efficiently removed using carbonate-based dehydrating agents (such as DMC); however, when the water content drops below 15% of the LiFSI aqueous solution concentration, the dehydration efficiency drops sharply, requiring a large amount of drying solvent for continuous azeotropic operation. This process is not only complex but also accompanied by high energy consumption and cost.

[0004] Therefore, exploring and developing a simpler and more efficient LiFSI dehydration and drying method is of urgent and significant importance for optimizing production processes, reducing energy consumption and costs, and improving the quality of LiFSI products. This method should effectively solve the problems of low efficiency and high energy consumption in current processes, providing solid technical support for the large-scale production and application of LiFSI.

[0005] To address at least one of the above problems, the present invention is proposed. Summary of the Invention

[0006] This invention provides a highly efficient dehydration and purification process for water-containing bis(fluorosulfonyl)imide metal salts using electrochemical technology.

[0007] The specific technical solution of this application is as follows:

[0008] The method includes the following steps: electrolytic dehydration treatment of a mixed solution containing a bis(fluorosulfonyl)imide metal salt and an organic solvent; wherein the aqueous bis(fluorosulfonyl)imide metal salt comprises water and the bis(fluorosulfonyl)imide metal salt.

[0009] Preferably, the anode material used in the electrolysis includes an oxygen-binding agent, and the cathode material used in the electrolysis includes a hydrogen evolution agent, so as to effectively remove the trace amounts of residual water in the solution by electrochemical decomposition.

[0010] Preferably, in the mixed solution, the mass of the alkali metal salt of bis(fluorosulfonyl)imide is A, and the mass of the water is B; the value of B / (A+B) is less than 20%.

[0011] Preferably, the mass of the organic solvent is 5-20 times the mass of the bis(fluorosulfonyl)imide metal salt.

[0012] Preferably, the operating current density for electrolysis is 1 mA / cm². 2 Up to 100mA / cm 2 Operating pressure is between 0 kPa and 50 kPa gauge pressure; operating temperature is between -15 and 80°C.

[0013] Preferably, the method is an intermittent or continuous operation;

[0014] The continuous process is operated as follows: a mixed solution containing hydrated bis(fluorosulfonyl)imide metal salt and an organic solvent is continuously fed in, and the dehydrated bis(fluorosulfonyl)imide metal salt solution is continuously discharged.

[0015] At this point, it is necessary to control the inlet and outlet flow rates according to the volume of the electrolytic cell in order to maintain a certain residence time of the mixed solution in the electrolytic cell to achieve dehydration.

[0016] Preferably, the operating voltage of the electrolytic cell is 0.2 to 10V.

[0017] Preferably, the intermittent operation includes the following steps: using an electrolytic cell for water electrolysis and performing electrolytic dehydration treatment on the mixed solution using a constant voltage method;

[0018] The initial current density is controlled within the range of 10–100 mA / cm². 2；

[0019] When the current density is less than 10 mA / cm 2 When the water content of the mixed solution is detected, it is determined whether the electrolysis endpoint has been reached; or after replacing the anode, it is determined whether the electrolysis endpoint has been reached based on whether the current density decreases.

[0020] When the water content of the mixed solution is less than 50 ppm or the current density no longer decreases after replacing the anode, the electrolysis endpoint is reached, and the mixed solution is discharged.

[0021] Electrolysis can continue if the electrolysis endpoint is not reached, or the oxidized anode can be replaced before continuing electrolysis.

[0022] Preferably, the oxidized anode can be replaced during the electrolysis process to reduce the water content in the mixed solution.

[0023] In any implementation, the reaction is carried out in a single-chamber electrolytic cell and a two-electrode system.

[0024] The aqueous bis(fluorosulfonyl)imide metal salt is obtained by azeotropic dehydration of an aqueous bis(fluorosulfonyl)imide metal salt solution, with a water content of less than 20 wt%. Specifically, the mass of the bis(fluorosulfonyl)imide alkali metal salt is A, and the mass of the water is B; the value of B / (A+B) is less than 20%. More preferably, B / (A+B) = 0.1% to 15%. The aqueous bis(fluorosulfonyl)imide metal salt originates from the aqueous bis(fluorosulfonyl)imide metal salt solution obtained during the preparation process. The purpose of this application is to further and completely remove any remaining trace amounts of water from the aqueous bis(fluorosulfonyl)imide metal salt solution.

[0025] In any embodiment, the oxygen-binding agent of the anode is one or more of the following metals: copper, zinc, aluminum, manganese, antimony, tin, and iron, or their alloys. Oxides of iron, cobalt, and nickel, or hydroxides of iron, cobalt, and nickel, may also be used. The oxygen-binding agent of the anode may also be selected from materials such as iridium oxide, ruthenium oxide, and oxidized ruthenium-supported iridium.

[0026] Without an oxygen-binding agent, the anodic dissolution is more likely to occur because the electro-oxygen generation reaction (OER) is more difficult, resulting in poor product quality.

[0027] In any embodiment, the hydrogen evolution agent at the cathode can be a catalyst with electrochemical hydrogen evolution reaction (HER) activity, including but not limited to platinum-supported catalysts such as platinum-carbon catalysts or lithium metal and other catalysts that have been proven to have excellent HER performance.

[0028] In any embodiment, a wide variety of organic solvents are used, including but not limited to dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC), all of which are commonly used organic solvents in lithium-ion battery electrolytes. Therefore, the dehydrated mixed solution is a mixture of organic solvent and bis(fluorosulfonyl)imide alkali metal salt, which can be directly used as a battery electrolyte.

[0029] The electrolysis reaction is carried out in a single-chamber electrolytic cell.

[0030] In any embodiment, the operating current density of the electrolytic cell is set to 1 mA / cm². 2 Up to 100mA / cm 2 Within the specified range; the operating pressure is set between atmospheric pressure (approximately 0 kPa gauge pressure) and 50 kPa gauge pressure; while the operating temperature is controlled within the range of room temperature (usually 20℃ ± 5℃, depending on the experimental environment) to 80℃. For example, -15 to 80℃.

[0031] In any implementation, this method is applicable to continuous reactions.

[0032] In any embodiment, the working voltage (i.e., cell voltage) of the electrolytic cell is 0.2 to 10V, while the effective cell voltage, after precise measurement and deduction of the cell resistance voltage drop, is controlled between 0.2 and 3.0V.

[0033] In any implementation, this method exhibits high versatility and is applicable to the dehydration treatment of FSI electrolyte solutions composed of metal elements including, but not limited to, sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), and calcium (Ca).

[0034] In any implementation, the electrolytic cells used for dehydration can be expanded in series, that is, multiple electrolytic cells with the same structure and function are connected sequentially through conductive materials using an electrical series connection method. Theoretically, the number of such series-connected electrolytic cells is not absolutely limited, provided that electrical and chemical balance allows it. In practical applications, the recommended range for the number of series stages is usually set to 1 to 20 stages.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. This application provides a method for dehydrating hydrous bis(fluorosulfonyl)imide metal salts. This method uses electrochemical technology to dehydrate a solution of a bis(fluorosulfonyl)imide metal salt (e.g., an alkali metal bis(fluorosulfonyl)imide, particularly lithium bis(fluorosulfonyl)imide) in an organic solvent system. During this process, an oxygen-binding agent is introduced at the anode, while a hydrogen evolution agent is used at the cathode, effectively removing trace amounts of residual water from the solution through electrochemical decomposition. This method aims to improve the purity and stability of bis(fluorosulfonyl)imide metal salt solutions, simplify purification methods, and provide high-quality electrolyte materials for subsequent electrochemical applications, yielding bis(fluorosulfonyl)imide metal salt solutions with a water content of less than 50 ppm.

[0037] 2. Electrochemical techniques are usually carried out under mild conditions (e.g., ambient temperature and pressure), and the use of electricity to replace environmentally harmful chemical reagents (e.g., stoichiometric oxidants and reductants) also gives electrochemistry the potential to improve the efficiency and sustainability of chemical reactions.

[0038] 3. Electrochemical technology enables this dehydration and purification technology to be continuous. It only requires a continuous supply of electricity and does not require any external dehydrating agent to carry out the dehydration process continuously. Detailed Implementation

[0039] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in manuals, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified. The raw materials used in the following embodiments and comparative examples are all commercially available.

[0040] Taking lithium bisfluorosulfonylimide as an example, the principle of this application is illustrated by the following example:

[0041] This application provides a method for removing trace amounts of water from lithium bis(fluorosulfonyl)imide. The method employs an electrochemical process using a single-chamber electrolytic cell. An azeotropically dehydrated and concentrated aqueous lithium bis(fluorosulfonyl)imide (LiFSI) solution is added to the electrolytic cell, wherein the water content does not exceed 15% of the total mass (the sum of the masses of water and LiFSI). An organic solvent is added to the electrolytic cell, and then an electrolytic reaction is carried out in a two-electrode system. The anode material used in the electrolysis contains an oxygen-binding agent, and the cathode material used in the electrolysis contains a hydrogen evolution agent. During this process, water is electrochemically converted into hydrogen and oxygen, which are then discharged through the exhaust system of the electrolytic cell, thereby effectively removing trace amounts of water from the LiFSI. Finally, the LiFSI product obtained after electrolytic treatment and collection has a significantly reduced water content, meeting the requirements for high-purity applications.

[0042] The aforementioned oxygen-binding agents refer to materials that can undergo oxidation or have oxygen evolution reaction activity, thereby removing oxygen from water.

[0043] The material itself is oxidized after the oxygen-binding agent is oxidized, thus requiring regeneration.

[0044] When an oxygen-binding agent exhibits oxygen evolution reaction activity, it catalyzes the reaction that produces oxygen in the water. Therefore, the oxygen-binding agent itself remains unchanged and does not require regeneration. In this case, iridium oxide, ruthenium oxide, and oxidized ruthenium and iridium-supported materials can be selected as oxygen-binding agents.

[0045] The aforementioned hydrogen evolution agent refers to a material that possesses hydrogen evolution reaction activity and can remove oxygen from water. The hydrogen evolution agent catalyzes the reaction of water to produce hydrogen gas; therefore, the hydrogen evolution agent itself does not change and does not require regeneration.

[0046] Typically, copper foam is used as the anode and platinum sheet electrodes are used as the cathode for electrolytic water purification. Under energized conditions, copper undergoes an oxygen-absorbing oxidation reaction at the anode to produce copper oxide (eq.1), and the generated hydrogen ions move towards the cathode under the influence of the electric field; a hydrogen evolution reaction occurs at the cathode (eq.2). The oxidation reactions of other metal oxygen-binding agents are similar.

[0047] Anode reaction: Cu + H₂O → 2e⁻ - =CuO + 2H + eq.1 Cathode reaction: 2H + +2e - =H2 eq.2

[0048] The general method for reusing metal oxygen binders is as follows. If an oxidation reaction occurs, reduction is required through electrochemical methods, such as hydrogen reduction or CO reduction. Specifically, when aluminum is used as an oxygen binder, simply replacing the aluminum electrode is sufficient.

[0049] When oxides of iron, cobalt, nickel, or their hydroxides are used as oxygen-binding agents, an anodizing reaction occurs (eq.3).

[0050] Anode reaction: M(OH)₂ + OH⁻ - -e - =M(OH)3eq.3

[0051] The hydrogen evolution reaction of a typical hydrogen evolution agent at the cathode follows the reaction described in eq.2. However, when lithium metal is used as the hydrogen evolution agent at the cathode, graphite can be used as the support, and the reaction equation is as follows:

[0052] Cathode reaction: 2H + +LiC6=H2+Li + +C6 eq.4

[0053] Li + +e - =LiC6 eq.5

[0054] Preferably, the operating pressure of the electrolytic cell is set between atmospheric pressure (approximately 0 kPa gauge pressure) and 50 kPa gauge pressure; while the operating temperature is controlled within the range of room temperature (usually 20℃ ± 5℃, depending on the experimental environment) to 80℃.

[0055] Example 1

[0056] 50 ml of concentrated lithium bis(fluorosulfonyl)imide (LiFSI) aqueous solution, after azeotropic dehydration, was added to the electrolytic cell. The water content was 15% of the total mass (sum of water and LiFSI). Simultaneously, 500 ml of dimethyl carbonate (DMC), an organic solvent, was added to the electrolytic cell. Electrolysis was then carried out in a two-electrode system. A copper foam electrode was used as the anode to act as an oxygen-binding agent, and a platinum sheet electrode was used as the cathode to act as a hydrogen evolution agent. The relative electrode surface area of ​​the anode and cathode was controlled to be 10 × 10 cm². -2 Electrolysis was then performed using a constant voltage of 3V, at an operating temperature of 25℃, an operating pressure of 0 kPa gauge pressure, and an initial current density of 100 mA / cm². 2 After electrolysis begins, gas is generated at the cathode, and the current density continuously decreases. When the current is less than 1 mA / cm², the current density decreases. 2 The oxygen-bound anode was replaced. However, after replacing the anode with a new foamed copper anode, the current was still less than 1 mA / cm. 2 Furthermore, the concentration stopped decreasing, therefore the electrolytic dehydration reaction was determined to be complete. At this point, the water content of the mixed solution in the electrolytic cell was less than 50 ppm. This mixed solution consists of an organic solvent and LiFSI, and can be used directly as a lithium battery electrolyte or as a raw material for electrolytes.

[0057] Example 2

[0058] Except for changing the operating temperature to 15°C, the electrolytic dehydration reaction was carried out in the same way as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0059] Example 3

[0060] Except for changing the operating temperature to 80°C, the electrolytic dehydration reaction was carried out in the same way as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0061] Example 4

[0062] Except for changing the operating pressure to 50 kPa gauge pressure, the electrolytic dehydration reaction was carried out in the same way as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0063] Example 5

[0064] Except for changing the amount of dimethyl carbonate (DMC) added to 250 ml, electrolysis was performed using a constant voltage of 1.5 V, with an initial current density of 100 mA / cm². 2 The electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0065] Example 6

[0066] Except for changing the amount of dimethyl carbonate (DMC) added to 1000 ml, and using a constant voltage method of 6V for electrolysis, the initial current density was 100 mA / cm². 2 The electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0067] Example 7

[0068] Except for changing the water content of the concentrated lithium bis(fluorosulfonyl)imide (LiFSI) aqueous solution after azeotropic dehydration to 10 wt%, electrolysis was performed using a constant voltage method at 2V with an initial current density of 75 mA / cm². 2 The electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0069] Example 8

[0070] Except for changing the water content of the concentrated lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte solution after azeotropic dehydration to 5%, electrolysis was performed at a constant voltage of 1V with an initial current density of 50mA / cm². 2 The electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0071] Example 9

[0072] Except for changing the water content of the concentrated lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte solution after azeotropic dehydration to 1%, electrolysis was performed at a constant voltage of 0.5V with an initial current density of 10 mA / cm². 2 The electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0073] Example 10

[0074] Except for changing the added organic solvent to 500 ml of ethyl methyl carbonate (EMC), the electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0075] Example 11

[0076] Except for changing the added organic solvent to 500 ml of diethyl carbonate (DEC), the electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0077] Example 12

[0078] Except for changing the added organic solvent to 500 ml of ethylene carbonate (EC), the electrolytic dehydration reaction was carried out in the same way as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0079] Example 13

[0080] Except for changing the oxygen-binding agent of the anode to metallic Zn, the electrolytic dehydration reaction was carried out in the same way as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0081] Example 14

[0082] Except for changing the oxygen-binding agent of the anode to metallic Fe, the electrolytic dehydration reaction was carried out in the same way as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0083] Example 15

[0084] Except for changing the oxygen-binding agent at the anode to ferric hydroxide, the electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0085] Example 16

[0086] Except for changing the oxygen-binding agent at the anode to iron oxide, the electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0087] Example 17

[0088] Except for changing the oxygen-binding agent at the anode to iridium oxide, the electrolytic dehydration reaction was carried out in the same manner as in Example 1. After the electrolysis started, gas was generated at the anode and gas was generated at the cathode. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0089] Example 18

[0090] Except for changing the hydrogen evolution agent of the cathode to metallic lithium supported on a graphite rod, the electrolytic dehydration reaction was carried out in the same way as in Example 1. After the electrolytic dehydration reaction was completed, the water content was measured to be less than 50 ppm.

[0091] Comparative Example 1

[0092] Except for changing both the anode and cathode to graphite rod electrodes, the electrolysis time was the same as in Example 1. Specifically, after the start of electrolysis, gas was generated at the anode, and the current density continuously decreased. When the current was less than 1 mA / cm²... 2 At that time, after the electrolytic dehydration reaction was completed, the graphite rod electrode dissolved, and the water content was measured to be 10 wt%.

[0093] This proves that inert graphite rod electrodes have almost no water removal effect, and electrodes without oxygen-binding agents are prone to dissolution.

Claims

1. A method for removing water from a hydrous difluorosulfonylimide metal salt, characterized in that, The method includes the following steps: electrolytically dehydrating a mixed solution containing an aqueous bis(fluorosulfonyl)imide metal salt and an organic solvent; wherein the aqueous bis(fluorosulfonyl)imide metal salt comprises water and the bis(fluorosulfonyl)imide metal salt.

2. The method according to claim 1, characterized in that, The anode material used in the electrolysis contains an oxygen-binding agent, and the cathode material used in the electrolysis contains a hydrogen evolution agent.

3. The method according to claim 1, characterized in that, In the mixed solution, the mass of the alkali metal salt of bis(fluorosulfonyl)imide is A, and the mass of the water is B; the value of B / (A+B) is less than 20%.

4. The method according to claim 1, characterized in that, The mass of the organic solvent is 5-20 times the mass of the bis(fluorosulfonyl)imide metal salt.

5. The method according to claim 1, characterized in that, The operating current density for electrolysis is 1 mA / cm². 2 Up to 100mA / cm 2 The operating pressure is between 0 kPa and 50 kPa gauge pressure; the operating temperature is between 15 and 80°C.

6. The method according to claim 1, characterized in that, The method can be an intermittent or continuous operation; the continuous operation is as follows: a mixed solution containing hydrated bis(fluorosulfonyl)imide metal salt and an organic solvent is continuously fed in, and the dehydrated bis(fluorosulfonyl)imide metal salt solution is continuously discharged.

7. The method according to claim 1, characterized in that, The operating voltage of the electrolytic cell is 0.2 to 10V.

8. The method according to claim 6, characterized in that, The intermittent operation includes the following steps: using an electrolytic cell for water electrolysis and employing a constant voltage method to electrolyze and dehydrate a mixed solution containing bis(fluorosulfonyl)imide metal salt, water, and organic solvent; The initial current density is controlled within the range of 10–100 mA / cm². 2 , When the current density is less than 10 mA / cm 2 When the water content of the mixed solution is detected, it is determined whether the electrolysis endpoint has been reached; or after replacing the anode, it is determined whether the electrolysis endpoint has been reached based on whether the current density decreases. When the water content of the mixed solution is less than 50 ppm or the current density no longer decreases after replacing the anode, the electrolysis endpoint is reached, and the mixed solution is discharged. Electrolysis can continue if the electrolysis endpoint is not reached, or the oxidized anode can be replaced before continuing electrolysis.

9. The method according to claim 1, characterized in that, In order to reduce the water content in the mixed solution during the electrolysis process, the oxidized anode is replaced.

10. The method according to claim 1, characterized in that, The aqueous difluorosulfonylimide metal salt is derived from the aqueous solution of difluorosulfonylimide metal salt obtained during the preparation process of difluorosulfonylimide metal salt.