A method for preparing lithium difluoro(oxalato)borate by gas-liquid reaction

Abstract

The present invention belongs to the field of electrochemistry, and particularly relates to a method for preparing lithium difluorooxalate borate by gas-liquid reaction. The method includes: 1) Dissolving lithium tetrafluoroborate and oxalic acid in a lower-carbon alcohol solvent to prepare a reaction solution, and placing it in an airtight container. The airtight container is provided with an inlet pipe and an outlet for dynamically controlling the air pressure in the airtight container ≥ 1.2 atm and realizing gas circulation; 2) Setting the inlet pipe to extend to the bottom of the reaction solution, and introducing high-temperature silicon tetrafluoride gas into the inlet pipe. After the molar amount of the introduced silicon tetrafluoride gas ≥ 1.2 times the molar amount required for the theoretical reaction, stop and filter to remove solid impurities in the reaction solution, and concentrate and crystallize to obtain lithium difluorooxalate borate. Through the contact thermal reaction between the high-temperature gas and the reaction solution, the present invention can greatly improve the reaction efficiency and make the reaction more complete. At the same time, by using a special solvent in combination with a special reaction scheme, the decomposition of lithium tetrafluoroborate is inhibited, the generation of impurities is reduced, and the purity of the product is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and particularly relates to a gas-liquid reaction preparation method of lithium difluorooxalate borate. Background Art

[0002] Lithium difluorooxalate borate (LiDFOB) is a new type of conductive lithium salt with excellent performance, mainly used in lithium battery electrolytes. Compared with the commonly used lithium hexafluorophosphate at present, it has better chemical stability and heat resistance. Moreover, lithium hexafluorophosphate is prone to decompose and generate impurities or even fatal defects when contacting with proton solvents, resulting in poor actual service life of existing lithium batteries. However, the solubility, chemical and temperature stability of lithium difluorooxalate borate are significantly better, and it can effectively extend the service life of lithium batteries when used in lithium batteries.

[0003] There are currently two process routes for LiDFOB in patents. Among them, in the process route using lithium tetrafluoroborate as the raw material, the catalyst is mainly silicon tetrachloride or aluminum chloride, which is dissolved in the reaction solution and mixed and reacted at a temperature up to 50 °C to prepare lithium difluorooxalate borate. However, this method has the defect of low reaction efficiency, and usually requires a reaction time of about 12 - 18 h. It has been found through research that by increasing the reaction temperature, the reaction rate can be increased to a great extent. Usually, for every 5 °C increase in the reaction temperature, the reaction rate can be increased. However, with the increase of temperature, a large amount of decomposition of the raw material lithium tetrafluoroborate will occur, resulting in a significant decrease in the actual product yield and purity. Therefore, the production efficiency of the traditional preparation process of lithium tetrafluoroborate is greatly limited at present. Summary of the Invention

[0004] To solve the problems of low reaction efficiency in the existing liquid-phase chemical method for preparing lithium difluorooxalate borate, and if the reaction efficiency is to be improved by increasing the temperature, the product yield and purity will be significantly decreased, etc., the present invention provides a gas-liquid reaction preparation method of lithium difluorooxalate borate.

[0005] The purpose of the present invention is as follows:

[0006] 1. To improve the preparation efficiency of lithium difluorooxalate borate;

[0007] 2. To ensure that the product purity of the prepared lithium difluorooxalate borate is relatively high;

[0008] 3. To avoid a significant decrease in the product yield of lithium difluorooxalate borate.

[0009] To achieve the above purpose, the present invention adopts the following technical solutions.

[0010] A gas-liquid reaction preparation method of lithium difluorooxalate borate,

[0011] The method includes:

[0012] 1) Prepare a reaction solution by dissolving lithium tetrafluoroborate and oxalic acid in a lower-carbon alcohol solvent. Place the reaction solution in an airtight container, which is equipped with an inlet pipe and an outlet for dynamically controlling the air pressure in the airtight container ≥ 1.2 atm and realizing air circulation.

[0013] 2) Set the inlet pipe to extend to the bottom of the reaction solution, and introduce high-temperature silicon tetrafluoride gas into the inlet pipe. After the molar amount of the introduced silicon tetrafluoride gas ≥ 1.2 times the molar amount required for the theoretical reaction, terminate the reaction and recover the reaction solution. After filtering to remove the solid impurities in the reaction solution, concentrate and crystallize the filtrate to obtain lithium difluorooxalate borate.

[0014] Compared with the traditional liquid-phase chemical method for preparing lithium difluorooxalate borate, the present invention innovatively adopts a gas-liquid reaction method, uses high-temperature silicon tetrafluoride gas for contact reaction, and selects a lower-carbon alcohol solvent to inhibit the overall temperature rise of the reaction solution. In addition, by controlling the air pressure in the container, the contact time between silicon tetrafluoride gas and the reaction solution is prolonged, and the effective utilization rate of silicon tetrafluoride gas is improved, so as to save materials or increase the yield and purity of the product. In addition, the tail gas discharged from the outlet enters a conventional tail gas absorption system, and a secondary falling-film caustic solution absorption and a primary packed caustic spray waste gas treatment system are adopted, and are converted into sodium salts such as sodium chloride, sodium fluoride, and sodium silicate and enter the wastewater treatment system for desalination.

[0015] Adopting a high-temperature gas-liquid contact reaction method can quickly form the target product lithium difluorooxalate borate with extremely high thermal stability through contact reaction. At the same time, when the gas is released through the inlet pipe reaching the bottom of the reaction solution, the bubbling stirs the reaction solution to improve the reaction uniformity and make the reaction more sufficient. On the other hand, the volatilization of the lower-carbon alcohol solvent can inhibit the overall temperature rise trend of the reaction solution and prevent lithium tetrafluoroborate from decomposing into lithium fluoride. After the reaction, a small amount of by-product lithium fluoride generated by decomposition can be quickly removed by filtration, and the recovered filtrate can obtain lithium difluorooxalate borate with extremely high purity through concentration and crystallization.

[0016] Preferably,

[0017] The outlet of the airtight container in step 1) is connected to a tail gas treatment device.

[0018] The air pressure in the airtight container is dynamically controlled to be 1.2 - 1.3 atm.

[0019] The tail gas treatment device includes a conventional secondary falling-film caustic solution absorption and a primary packed caustic spray waste gas treatment system as described above. The present invention prolongs the contact time between silicon tetrafluoride gas and the reaction solution by controlling the pressure in the airtight container, and improves the effective utilization rate of silicon tetrafluoride gas. However, when the air pressure is too high, the volatilization of the lower-carbon alcohol solvent is inhibited, resulting in an obvious increase in the overall temperature rise trend of the reaction solution, and then an increase in the content of by-product impurities and a decrease in the product yield.

[0020] Preferably,

[0021] In step 1), the lower alcohol solvent is a mixed solvent of ethanol and methanol with a volume ratio of (8 - 10):1.

[0022] For the technical solution of the present invention, both methanol and ethanol can effectively remove the main impurity lithium fluoride, and ethanol plays a greater role as a solvent, while methanol, due to its low boiling point, has the effect of maintaining the reaction solution at a relatively low temperature. If only ethanol is used, the yield of the product will decrease significantly, and if only methanol is used, a large amount of the solvent will be lost during the reaction, resulting in poor actual reaction effects.

[0023] Preferably,

[0024] In step 2), the temperature of the silicon tetrafluoride gas is 80 - 85°C.

[0025] The rapid thermal decomposition temperature of lithium tetrafluoroborate is generally recognized as about 80°C. However, through the solvent adjustment and reaction mode cooperation of the technical solution of the present invention, the yield of the product can be maintained at a relatively high level at 80 - 85°C, and the reaction is more complete. When a lower gas temperature is used, the reaction is likely to be incomplete, resulting in the generation of lithium tetrafluoroborate impurities, and when the temperature is too high, the yield of the product will be significantly reduced.

[0026] Preferably,

[0027] When the silicon tetrafluoride gas is introduced, ethanol vapor with a molar amount of 5 - 10% of it is introduced simultaneously.

[0028] As the reaction proceeds, methanol gradually volatilizes and is consumed, and it is necessary to replenish the solvent to prevent the product from crystallizing out prematurely. Moreover, the content of lithium tetrafluoroborate gradually decreases, and the overall solvent temperature can be slightly increased to enable the reaction solution to contact and react with the silicon tetrafluoride gas in the airtight container, further improving the raw material utilization rate.

[0029] Preferably, the molar amount required for the theoretical reaction is n th , n th = 0.5 × n min , n min is the minimum value of the molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0030] Through the above calculation, materials can be saved.

[0031] Preferably,

[0032] In step 2), the silicon tetrafluoride gas is bubbled in within 6 - 8 minutes.

[0033] The present invention can significantly shorten the reaction time, and the reaction can be completed within 6 - 8 minutes. It shortens the original high-pressure reaction that originally required at least 12 hours into a relatively low-pressure reaction in minutes, greatly improving the reaction efficiency.

[0034] Preferably, after the silicon tetrafluoride gas is completely introduced, the inlet pipe and the outlet of the airtight container are sealed, and the reaction is maintained for 5 - 10 minutes.

[0035] After the gas injection is completed, the utilization rate of the materials can be further improved through a closed reaction, and at the same time, the yield and purity of the product are improved.

[0036] The beneficial effects of the present invention are as follows:

[0037] Through the thermal reaction of the high-temperature gas in contact with the reaction liquid, the reaction efficiency can be greatly improved, the reaction time can be shortened by dozens of times, and the effective utilization rate of the gas-phase raw materials can be improved, making the reaction more complete, realizing the improvement of the product yield. At the same time, a special solvent is used in combination with a special reaction scheme to inhibit the decomposition of lithium tetrafluoroborate, reduce the generation of impurities, greatly improve the purity of the product, and realize the preparation of lithium difluoro(oxalato)borate efficiently and effectively. Specific Embodiments

[0038] The following further clearly and detailedly describes the present invention in combination with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0039] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available or raw materials that can be obtained by those skilled in the art; unless otherwise specified, the methods used in the embodiments of the present invention are all methods mastered by those skilled in the art.

[0040] Example 1

[0041] A method for preparing lithium difluoro(oxalato)borate by gas-liquid reaction, the specific steps of which include:

[0042] 1) Lithium tetrafluoroborate and oxalic acid are dissolved in a lower-carbon alcohol solvent at a molar ratio of 1:1 to prepare a reaction solution with a concentration of 4 mol / L. The lower-carbon alcohol solvent is prepared from ethanol and methanol with a volume ratio of 9:1. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. The reaction solution is placed in a high-pressure atmosphere reaction kettle. The high-pressure atmosphere reaction kettle is equipped with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet and outlet pipes cooperate to dynamically control the air pressure in the airtight container to be 1.2 - 1.3 atm and achieve air circulation;

[0043] 2) Set the inlet pipe to extend to the bottom of the reaction solution, and introduce silicon tetrafluoride gas preheated to 80 °C into the reaction solution through the inlet pipe. The total amount of introduced gas is 6 mol, and it is introduced evenly within 8 minutes. During the introduction of silicon tetrafluoride gas, a total of 0.5 mol of ethanol vapor is introduced evenly at the same time. Terminate the reaction and recover the reaction solution. After filtering to remove the solid impurities in the reaction solution, the filtrate is concentrated and crystallized at 60 °C to obtain lithium difluorooxalate borate.

[0044] Calculate the yield of lithium difluorooxalate borate and perform high-performance liquid chromatography characterization.

[0045] The yield calculation formula is as follows:

[0046]

[0047] In the formula: P is the product yield, m LiDFOB is the mass of the obtained product, m LiDFOB is the molar mass of the target product LiDFOB, n min is the minimum value of the molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0048] Through calculation and characterization, the yield of the product obtained in this example is 99.6%, and the product purity is about 99.3%.

[0049] Example 2

[0050] A method for preparing lithium difluorooxalate borate by gas-liquid reaction, the specific steps thereof include:

[0051] 1) Lithium tetrafluoroborate and oxalic acid are dissolved in a lower-carbon alcohol solvent at a molar ratio of 1:1 to prepare a reaction solution with a concentration of 4 mol / L. The lower-carbon alcohol solvent is prepared from ethanol and methanol with a volume ratio of 10:1. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. The reaction solution is placed in a high-pressure atmosphere reaction kettle. The high-pressure atmosphere reaction kettle is equipped with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet and outlet pipes cooperate to dynamically control the air pressure in the airtight container to be 1.2 - 1.3 atm and achieve air circulation;

[0052] 2) Set the inlet pipe to extend to the bottom of the reaction solution, and introduce silicon tetrafluoride gas preheated to 80 °C into the inlet pipe. The total gas introduction volume is 6 mol, and it is introduced uniformly within 8 min. During the introduction of silicon tetrafluoride gas, a total of 0.3 mol of ethanol vapor is introduced uniformly at the same time. Terminate the reaction and recover the reaction solution. After filtering to remove the solid impurities in the reaction solution, concentrate and crystallize the filtrate at 60 °C to obtain lithium difluoro(oxalato)borate.

[0053] Calculate the yield of lithium difluoro(oxalato)borate and perform high performance liquid chromatography characterization.

[0054] The formula for calculating the yield is as follows:

[0055]

[0056] In the formula: P is the product yield, m LiDFOB is the mass of the obtained product, m LiDFOB is the molar mass of the target product LiDFOB, n min is the minimum value of the molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0057] Through calculation and characterization, the yield of the product obtained in this example is 99.2%, and the product purity is about 99.1%.

[0058] Example 3

[0059] A method for preparing lithium difluoro(oxalato)borate by gas-liquid reaction, the specific steps of which include:

[0060] 1) Dissolve lithium tetrafluoroborate and oxalic acid in a low-carbon alcohol solvent at a molar ratio of 1:1 to prepare a reaction solution with a concentration of 4 mol / L. The low-carbon alcohol solvent is prepared from ethanol and methanol with a volume ratio of 8:1. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. Place the reaction solution in a high-pressure atmosphere reaction kettle. The high-pressure atmosphere reaction kettle is provided with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet pipe and the outlet pipe cooperate to dynamically control the air pressure in the airtight container to be 1.2 - 1.3 atm and achieve air circulation;

[0061] 2) Set the inlet pipe to extend to the bottom of the reaction solution, and introduce silicon tetrafluoride gas preheated to 80 °C into the inlet pipe. The total gas introduction volume is 6 mol, and it is introduced uniformly within 8 min. During the introduction of silicon tetrafluoride gas, a total of 0.6 mol of ethanol vapor is introduced uniformly at the same time. Terminate the reaction and recover the reaction solution. After filtering to remove the solid impurities in the reaction solution, concentrate and crystallize the filtrate at 60 °C to obtain lithium difluoro(oxalato)borate.

[0062] Calculate the yield of lithium difluoro(oxalato)borate and perform high performance liquid chromatography (HPLC) characterization.

[0063] The formula for calculating the yield is as follows:

[0064]

[0065] Where: P is the product yield, m LiDFOB is the mass of the obtained product, M LiDFOB is the molar mass of the target product LiDFOB, n min is the minimum value of the molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0066] Through calculation and characterization, the yield of the product obtained in this example is 99.5%, and the product purity is approximately 99.4%.

[0067] Example 4

[0068] A method for preparing lithium difluoro(oxalato)borate by gas-liquid reaction, the specific steps of which include:

[0069] 1) Dissolve lithium tetrafluoroborate and oxalic acid in a molar ratio of 1:1 in a lower aliphatic alcohol solvent to prepare a reaction solution with a concentration of 4 mol / L. The lower aliphatic alcohol solvent is prepared from ethanol and methanol with a volume ratio of 9:1. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. Place the reaction solution in a high-pressure gas reaction kettle. The high-pressure gas reaction kettle is equipped with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet and outlet pipes cooperate to dynamically control the air pressure in the airtight container to be 1.2 - 1.3 atm and achieve gas circulation;

[0070] 2) Set the inlet pipe to extend to the bottom of the reaction solution, and introduce silicon tetrafluoride gas preheated to 85°C through the inlet pipe. The total gas introduction amount is 6 mol, and it is introduced uniformly within 6 min. During the introduction of silicon tetrafluoride gas, a total of 0.5 mol of ethanol vapor is introduced uniformly at the same time. Terminate the reaction and recover the reaction solution. After filtering to remove the solid impurities in the reaction solution, concentrate and crystallize the filtrate at 60°C to obtain lithium difluoro(oxalato)borate.

[0071] Calculate the yield of lithium difluoro(oxalato)borate and perform high performance liquid chromatography (HPLC) characterization.

[0072] The formula for calculating the yield is as follows:

[0073]

[0074] Where: P is the product yield, m LiDFOB is the mass of the obtained product, M LiDFOB is the molar mass of the target product LiDFOB, n minis the minimum molar amount of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0075] Through calculation and characterization, the yield of the product obtained in this example is 99.5%, and the product purity is about 99.5%.

[0076] Example 5

[0077] A method for preparing lithium difluorooxalate borate by gas-liquid reaction, the specific steps thereof include:

[0078] 1) Dissolve lithium tetrafluoroborate and oxalic acid in a molar ratio of 1:1 in a lower-carbon alcohol solvent to prepare a reaction solution with a concentration of 4 mol / L. The lower-carbon alcohol solvent is prepared from ethanol and methanol with a volume ratio of 9:1. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. Place the reaction solution in a high-pressure atmosphere reaction kettle. The high-pressure atmosphere reaction kettle is provided with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet and outlet pipes cooperate to dynamically control the air pressure in the airtight container to be 1.2 - 1.3 atm and achieve gas circulation;

[0079] 2) Set the inlet pipe to extend to the bottom of the reaction solution, and introduce silicon tetrafluoride gas preheated to 80°C through the inlet pipe. The total gas injection volume is 6 mol, and it is evenly injected within 8 minutes. During the injection of silicon tetrafluoride gas, a total of 0.5 mol of ethanol vapor is evenly injected at the same time. Then, seal the inlet pipe and the outlet pipe, maintain for 5 minutes, terminate the reaction, and recover the reaction solution. After filtering to remove the solid impurities in the reaction solution, concentrate and crystallize the filtrate at 60°C to obtain lithium difluorooxalate borate.

[0080] Calculate the yield of lithium difluorooxalate borate and perform high-performance liquid chromatography characterization.

[0081] The yield calculation formula is:

[0082]

[0083] In the formula: P is the product yield, m LiDFOB is the mass of the obtained product, M LiDFOB is the molar mass of the target product LiDFOB, n min is the minimum molar amount of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0084] Through calculation and characterization, the yield of the product obtained in this example is 99.7%, and the product purity is about 99.5%.

[0085] Example 6

[0086] A method for preparing lithium difluorooxalate borate by gas-liquid reaction, the specific steps thereof include:

[0087] 1) Lithium tetrafluoroborate and oxalic acid are dissolved in a lower-carbon alcohol solvent at a molar ratio of 1:1 to prepare a reaction solution with a concentration of 4 mol / L. The lower-carbon alcohol solvent is prepared from ethanol and methanol with a volume ratio of 9:1. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. The reaction solution is placed in a high-pressure atmosphere reaction kettle, which is equipped with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet pipe and the outlet pipe cooperate to dynamically control the air pressure in the airtight container to be 1.2 - 1.3 atm and achieve air circulation;

[0088] 2) The inlet pipe is set to extend to the bottom of the reaction solution, and silicon tetrafluoride gas preheated to 80 °C is introduced through the inlet pipe. The total amount of introduced gas is 6 mol, and it is introduced evenly within 8 min. During the introduction of silicon tetrafluoride gas, a total of 0.5 mol of ethanol vapor is introduced evenly. Subsequently, the inlet pipe and the outlet pipe are sealed. After maintaining for 10 min, the reaction is terminated and the reaction solution is recovered. After filtering to remove solid impurities in the reaction solution, the filtrate is concentrated and crystallized at 60 °C to obtain lithium difluorooxalate borate.

[0089] Calculate the yield of lithium difluorooxalate borate and perform high-performance liquid chromatography characterization.

[0090] The formula for calculating the yield is as follows:

[0091]

[0092] In the formula: P is the product yield, m LiDFOB is the mass of the obtained product, M LiDFOB is the molar mass of the target product LiDFOB, n min is the minimum value of the molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0093] Through calculation and characterization, the yield of the product obtained in this example is 99.7%, and the product purity is about 99.6%.

[0094] It can be clearly seen from the above Examples 1 - 6 that the technical solution of the present invention can effectively and efficiently achieve the preparation of lithium difluorooxalate borate, greatly improving the preparation efficiency of lithium difluorooxalate borate. On the other hand, the yields of the recovered products can all reach more than 99%, with extremely high industrial preparation cost performance and higher product purity. In Examples 1 - 3, the main impurity component is lithium tetrafluoroborate, mainly due to the poor sufficiency of the reaction. In Example 4, the main impurity components are lithium tetrafluoroborate and lithium fluoride, while in Examples 5 - 6, the main impurity components are very small amounts of silicon tetrafluoride, silicon tetrachloride, and lithium fluoride. Such impurities can be easily further removed by recrystallization to improve the product purity, achieving an excellent preparation effect.

[0095] Comparative Example 1

[0096] A method for preparing lithium difluorooxalate borate by gas-liquid reaction, the specific steps of which include:

[0097] 1) Lithium tetrafluoroborate and oxalic acid are dissolved in a lower-carbon alcohol solvent at a molar ratio of 1:1 to prepare a reaction solution with a concentration of 4 mol / L. The lower-carbon alcohol solvent is an ethanol solvent. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. The reaction solution is placed in a high-pressure atmosphere reaction kettle. The high-pressure atmosphere reaction kettle is provided with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet pipe and the outlet pipe cooperate to dynamically control the air pressure in the airtight container to be 1.2-1.3 atm and achieve gas circulation;

[0098] 2) The inlet pipe is set to extend to the bottom of the reaction solution, and silicon tetrafluoride gas preheated to 80 °C is introduced into the inlet pipe. The total gas introduction amount is 6 mol, and it is introduced uniformly within 8 minutes. During the introduction of silicon tetrafluoride gas, a total of 0.5 mol of ethanol vapor is introduced uniformly at the same time. The reaction is terminated and the reaction solution is recovered. After filtering to remove solid impurities in the reaction solution, the filtrate is concentrated and crystallized at 60 °C to obtain lithium difluorooxalate borate.

[0099] The yield of lithium difluorooxalate borate is calculated and characterized by high performance liquid chromatography.

[0100] The yield calculation formula is:

[0101]

[0102] In the formula: P is the product yield, m LiDFOB is the mass of the obtained product, M LiDFOB is the molar mass of the target product LiDFOB, n min is the minimum value of the molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0103] Through calculation and characterization, the yield of the product obtained in this example is 98.2%, and the product purity is about 98.4%. And through characterization, the main impurity component in this scheme is lithium fluoride. Because although filtration can remove a large amount of solid lithium fluoride impurities, due to the relatively high overall temperature rise of the reaction solution and the gas introduction reaction method, the generation amount is relatively large, and it is easy to generate extremely small micron-sized or even nanometer-sized particle impurities, resulting in easy impurity residue during actual vacuum filtration and poor preparation effect.

[0104] Comparative Example 2

[0105] A method for preparing lithium difluorooxalate borate by gas-liquid reaction, the specific steps of which include:

[0106] 1) Lithium tetrafluoroborate and oxalic acid are dissolved in a lower alcohol solvent at a molar ratio of 1:1 to prepare a reaction solution with a concentration of 4 mol / L. The lower alcohol solvent is a methanol solvent. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. The reaction solution is placed in a high-pressure atmosphere reaction kettle. The high-pressure atmosphere reaction kettle is equipped with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet pipe and the outlet pipe cooperate to dynamically control the air pressure in the airtight container to be 1.2 - 1.3 atm and achieve air circulation;

[0107] 2) The inlet pipe is set to extend to the bottom of the reaction solution, and silicon tetrafluoride gas preheated to 80 °C is introduced into the reaction solution. The total amount of gas introduced is 6 mol, and it is introduced uniformly within 8 min. During the introduction of silicon tetrafluoride gas, a total of 0.5 mol of methanol vapor is introduced uniformly at the same time. The reaction is terminated and the reaction solution is recovered. After filtering to remove the solid impurities in the reaction solution, the filtrate is concentrated and crystallized at 60 °C to obtain lithium difluorooxalate borate.

[0108] The yield of lithium difluorooxalate borate is calculated and characterized by high performance liquid chromatography.

[0109] The formula for calculating the yield is as follows:

[0110]

[0111] In the formula: P is the product yield, M LiDFOB is the mass of the obtained product, M LiDFOB is the molar mass of the target product LiDFOB, n min is the minimum value of the molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0112] Through calculation and characterization, the yield of the product obtained in this example is 96.9%, and the product purity is about 95.8%.

[0113] It can be found by comparing the above Comparative Example 1 and Comparative Example 2 with Example 1 that the present invention has a specific selection for the solvent. Using only ethanol or methanol alone cannot achieve good preparation. This is because for the technical solution of the present invention, both methanol and ethanol have their unique functions. Methanol is used to control the temperature of the reaction solution to relatively maintain the overall temperature constant, while ethanol serves as the main reaction carrier to achieve the formation of the product and the removal of impurities.

[0114] Comparative Example 3

[0115] A gas-liquid reaction preparation method of lithium difluorooxalate borate, the specific steps thereof include:

[0116] 1) Lithium tetrafluoroborate and oxalic acid are dissolved in dimethyl carbonate solvent at a molar ratio of 1:1 to prepare a reaction solution with a concentration of 4 mol / L. The molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution are both 10 mol. The reaction solution is placed in a high-pressure atmosphere reaction kettle. The high-pressure atmosphere reaction kettle is provided with an inlet pipe and an outlet pipe. The outlet pipe is connected to a tail gas treatment device to eliminate the emission pollution of harmful gases such as silicon tetrafluoride, silicon tetrachloride, and hydrogen chloride. The inlet and outlet pipes cooperate to dynamically control the air pressure in the airtight container to be 1.2 - 1.3 atm and achieve air circulation;

[0117] 2) The inlet pipe is set to extend to the bottom of the reaction solution, and silicon tetrafluoride gas preheated to 80 °C is introduced into the reaction solution through the inlet pipe. The total amount of gas introduced is 6 mol, and it is introduced uniformly within 8 min. During the introduction of silicon tetrafluoride gas, a total of 0.5 mol of ethanol vapor is introduced uniformly at the same time. The reaction is terminated and the reaction solution is recovered. After filtering to remove solid impurities in the reaction solution, the filtrate is concentrated and crystallized at 60 °C to obtain lithium difluorooxalate borate.

[0118] Calculate the yield of lithium difluorooxalate borate and perform high performance liquid chromatography characterization.

[0119] The formula for calculating the yield is as follows:

[0120]

[0121] In the formula: P is the product yield, m LiDFOB is the mass of the obtained product, m LiDFOB is the molar mass of the target product LiDFOB, n min is the minimum value of the molar amounts of lithium tetrafluoroborate and oxalic acid in the reaction solution.

[0122] Through calculation and characterization, the yield of the product obtained in this example is 98.4%, and the product purity is about 95.1%.

[0123] It can also be found from the comparison between the above comparative example and Example 1 that using other conventional organic solvents will also not produce good preparation effects.

Claims

1. A method for preparing lithium difluorooxalate borate by gas-liquid reaction, characterized in that, The method includes: 1) Dissolve lithium tetrafluoroborate and oxalic acid in a lower alcohol solvent to prepare a reaction solution, and place the reaction solution in an airtight container. The airtight container is provided with an inlet pipe and an outlet for dynamically controlling the air pressure in the airtight container ≥ 1.2 atm and realizing air circulation; 2) Set the inlet pipe to extend to the bottom of the reaction solution, and introduce silicon tetrafluoride gas at 80 - 85 °C into the inlet pipe. After the molar amount of the introduced silicon tetrafluoride gas is ≥ 1.2 times the molar amount required for the theoretical reaction, terminate the reaction and recover the reaction solution. After filtering to remove solid impurities in the reaction solution, concentrate and crystallize the filtrate to obtain lithium difluorooxalate borate; In step 1), the lower alcohol solvent is a mixed solvent of ethanol and methanol with a volume ratio of (8 - 10):

1.

2. The method for preparing lithium difluorooxalate borate by gas-liquid reaction according to claim 1, characterized in that, In step 1), the outlet of the airtight container is connected to a tail gas treatment device; The air pressure in the airtight container is dynamically controlled to be 1.2 - 1.3 atm.

3. The method for preparing lithium difluorooxalate borate by gas-liquid reaction according to claim 1, characterized in that, When introducing the silicon tetrafluoride gas, introduce ethanol vapor with a molar amount of 5 - 10% of it at the same time.

4. The method for preparing lithium difluorooxalate borate by gas-liquid reaction according to claim 1, characterized in that, In step 2), the silicon tetrafluoride gas is introduced completely within 6 - 8 minutes.

5. The method for preparing lithium difluorooxalate borate by gas-liquid reaction according to claim 4, characterized in that, After the silicon tetrafluoride gas is introduced completely, seal the inlet pipe and the outlet of the airtight container, and keep the reaction for 5 - 10 minutes.

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