Preparation method of high-purity lithium difluoro (oxalato) borate

Abstract

The invention provides a preparation method of high-purity lithium difluoro (oxalato) borate, which comprises the following steps: taking a boron trifluoride complex, lithium oxalate and anhydrous oxalic acid as raw materials, simultaneously adding a composite catalyst prepared from polyaluminum chloride and silicon dioxide gel, filtering, concentrating, evaporating and crystallizing, washing and drying to obtain a lithium difluoro (oxalato) borate product. The yield of the lithium difluoro (oxalato) borate obtained by the method can reach 90% or above, and the purity of the lithium difluoro (oxalato) borate can reach 99.65% or above; meanwhile, the composite catalyst disclosed by the invention can be repeatedly utilized, and high-yield and high-purity lithium difluoro (oxalato) borate can also be obtained.

Description

Technical field:

[0001] The invention relates to the technical field of battery electrolyte materials, and more specifically to a method for preparing high-purity lithium difluorooxalatoborate. Background technology:

[0002] In lithium-ion batteries, the commonly used electrolyte lithium salts are mainly lithium hexafluorophosphate, lithium tetrafluoroborate, etc. Although lithium hexafluorophosphate has been commercialized, it is sensitive to temperature and moisture. The decomposition products produced by it when heated will corrode the positive electrode material. Although lithium tetrafluoroborate has good performance at low temperatures, the electrolyte has low ionic conductivity at high temperatures and it is difficult to form a stable SEI at the interface. These have limited the application of these two lithium salts. Therefore, it is necessary to develop a lithium salt with stable high and low temperature performance and good compatibility with positive and negative electrode materials.

[0003] As a new type of lithium salt, lithium difluorooxalatoborate has both the good cycle and rate performance of batteries using lithium dioxalatoborate electrolyte at high temperatures and the good cycle stability of batteries using lithium tetrafluoroborate electrolyte at low temperatures. At the same time, it has a large solubility in linear carbonate solvents and the electrolyte has a high ionic conductivity.

[0004] Patent CN111943969B discloses a method for preparing lithium difluorooxalate borate, which uses lithium tetrafluoroborate and lithium oxalate as main raw materials, and selects niobium pentachloride, niobium pentafluoride or antimony pentafluoride as auxiliary agents to prepare lithium difluorooxalate borate, which can initiate the reaction, accelerate the reaction process and improve the reaction conversion rate. However, in this method, lithium tetrafluoroborate is used as a raw material. Since the product lithium difluorooxalate borate is similar in structure to the raw material lithium tetrafluoroborate, the solubility difference in the solvent is small, and it is difficult to separate thoroughly. It needs to be purified by repeated recrystallization. The yield of lithium difluorooxalate borate product is low and the manufacturing cost is high.

[0005] Patent CN109232628B discloses a one-pot method for synthesizing lithium difluorooxalate borate, wherein the specific steps for preparing lithium tetrafluoroborate and lithium difluorooxalate borate crude products are: placing lithium fluoride and a solvent in a reaction device, then slowly aerating boron trifluoride gas to synthesize lithium tetrafluoroborate; then adding anhydrous oxalic acid to the device, and then slowly dropping a catalyst to obtain a crude lithium difluorooxalate borate. This method still uses lithium tetrafluoroborate as a raw material, and there is also the problem that the two are difficult to separate.

[0006] Patent CN113980045B discloses a one-step method for synthesizing lithium difluorooxalate borate, wherein a silicon-aluminum composite oxide is used as a catalyst, a boron trifluoride complex, lithium oxalate, anhydrous oxalic acid and an aprotic organic solvent are mixed for reaction, and after the reaction is completed, the lithium difluorooxalate borate product is obtained by filtration, concentration, evaporation crystallization, washing and drying; wherein the silicon-aluminum composite oxide is prepared from silicon dioxide gel and aluminum hydroxide. However, this method has the following problems: high-temperature calcination is required during the preparation of the silicon-aluminum composite oxide, and the manufacturing process is complicated. In addition, the aluminum hydroxide remaining in the silicon-aluminum composite oxide may react with anhydrous oxalic acid and the byproduct hydrofluoric acid, which affects the continued use of the catalyst.

[0007] Therefore, there is an urgent need for a method for preparing lithium difluorooxalatoborate with simple operating steps, low production cost, high purity and high yield. Summary of the invention:

[0008] The present invention provides a method for preparing high-purity lithium difluorooxalatoborate to overcome the problems of low purity of sodium fluoride, complicated operation process and high production cost in the prior art.

[0009] In order to achieve the above technical objectives and solve the above technical problems, the technical idea of ​​the present invention is as follows: using boron trifluoride complex, lithium oxalate and anhydrous oxalic acid as raw materials, and adding a composite catalyst prepared by polyaluminum chloride and silica gel, a high-purity and high-yield lithium difluorooxalate borate product is obtained.

[0010] The present invention is implemented by the following technical solutions:

[0011] Boron trifluoride complex, lithium oxalate and anhydrous oxalic acid are added to a non-protonic organic solvent, and a composite catalyst is added at the same time, and the mixture is stirred and reacted. After the reaction is completed, the mixture is filtered, concentrated, evaporated, crystallized, washed and dried to obtain a lithium difluorooxalatoborate product; wherein the composite catalyst is prepared from polyaluminium chloride and silicon dioxide gel.

[0012] The preparation method of the composite catalyst is as follows: silica gel, polyaluminium chloride powder and carbon tetrachloride are mixed in a mass ratio of 1:(1-1.5):(4-8), added thereto, refluxed at 40-60°C for 1-3 hours under stirring, cooled to room temperature, filtered, rinsed with carbon tetrachloride solvent for 2-3 times, and then dried under nitrogen atmosphere to obtain the composite catalyst.

[0013] Furthermore, in the above method, the molar ratio of the boron trifluoride complex, lithium oxalate and anhydrous oxalic acid is (2-2.5):(1-1.2):(0.9-1).

[0014] Furthermore, in the above method, the added amount of the composite catalyst is 0.5%-2% of the mass of the anhydrous oxalic acid.

[0015] Furthermore, in the above method, the amount of the non-protonic polar solvent added is 1-5 times the total mass of the boron trifluoride complex, lithium oxalate and anhydrous oxalic acid.

[0016] Preferably, the boron trifluoride complex is at least one selected from the group consisting of a boron trifluoride ether complex, a boron trifluoride acetonitrile complex, and a boron trifluoride dimethyl carbonate complex.

[0017] Preferably, the aprotic organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile, propionitrile, methyl acetate, ethyl acetate, propyl acetate, acetone and tetrahydrofuran.

[0018] Furthermore, the water content of the aprotic organic solvent is controlled within 500 ppm.

[0019] Furthermore, the reaction temperature of the method is 30-80°C, and the reaction time is 1-12 hours.

[0020] Furthermore, the tail gas generated during the reaction of the method is absorbed by alkaline solution.

[0021] Furthermore, in the method, a non-polar solvent is used in the washing process, and the non-polar solvent is selected from at least one of cyclohexane, petroleum ether, dichloromethane, dichloroethane, toluene and xylene.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The silica gel composite polyaluminium chloride catalyst used in the present invention can play a good catalytic role in the reaction of preparing lithium difluorooxalatoborate from lithium oxalate, oxalic acid and boron trifluoride, with a yield of more than 90% and a purity of more than 99.65%. At the same time, the composite catalyst of the present invention can be reused to obtain lithium difluorooxalatoborate with high yield and high purity.

[0024] (2) During the preparation process of the present invention, the ratio of the two types of oxalate sources, lithium oxalate and oxalic acid, is controlled within a certain range to ensure that the reaction as a whole advances toward a forward reaction, while reducing the generation of by-products other than hydrofluoric acid, thereby improving the yield and purity of lithium difluorooxalatoborate. Specific implementation method:

[0025] In order to make the purpose, technical scheme and advantages of the present invention more clear, the technical scheme of the present invention is further described below through specific implementation methods. Those skilled in the art should know that the embodiments are only to help understand the technical content and technical effects of the present invention and should not be regarded as limiting the present invention.

[0026] The above description only shows that the raw materials used in the embodiments of the present invention or the comparative examples are purchased from mainstream manufacturers in the market, and does not mean that the raw materials must be produced by the above-mentioned manufacturers. As long as it is conventional raw material, it can play the expected role without particular limitation. If specific conditions or operating methods are not described in the present embodiment or the comparative examples, it can be obtained according to the conditions or operating methods commonly used in the art.

[0027] Example 1

[0028] Preparation of composite catalyst: Mix silica gel, polyaluminium chloride powder and carbon tetrachloride in a mass ratio of 1:1.2:6, add it, reflux at 40°C for 2 hours with stirring, cool to room temperature, filter, rinse twice with carbon tetrachloride solvent, and then dry under a nitrogen atmosphere to obtain a composite catalyst.

[0029] Preparation of lithium difluorooxalate borate: Under nitrogen protection, add 112g (1.1mol) of lithium oxalate, 90g (1mol) of anhydrous oxalic acid, 316g of boron trifluoride carbonate dimethyl ester complex (boron trifluoride content is 43%) to a dry reaction bottle with stirring, then add 800g of dimethyl carbonate solvent with a water content of 80ppm, and add 1.5g of the prepared composite catalyst. Stir the reaction at 40°C under normal pressure, acidic gas will escape, and the tail gas will be absorbed by potassium hydroxide aqueous solution. After reacting for 2 hours, observe the materials in the reaction bottle, the solids are significantly reduced, and the reaction liquid is slightly turbid. Continue to keep the temperature for 3 hours and stop the reaction.

[0030] The reaction solution was cooled to room temperature and filtered under reduced pressure under a nitrogen atmosphere to remove the solid catalyst and unreacted solid impurities. The filtrate was concentrated and evaporated to crystallize. Dichloromethane was added thereto for stirring and washing. After filtration, it was dried under vacuum to obtain 267 g of lithium difluorooxalatoborate solid with a yield of 92.8% and a purity of 99.78%.

[0031] Example 2

[0032] The solid catalyst and unreacted solid impurities removed by filtration in Example 1 were collected, washed three times with carbon tetrachloride solvent, and then dried under a nitrogen atmosphere to obtain a composite catalyst for reuse.

[0033] Preparation of lithium difluorooxalate borate: Under nitrogen protection, add 102g (1 mol) of lithium oxalate, 90g (1 mol) of anhydrous oxalic acid, 316g of boron trifluoride carbonate dimethyl ester complex (boron trifluoride content is 43%) to a dry reaction bottle with stirring, then add 800g of dimethyl carbonate solvent with a moisture content of 80ppm, and add the recovered composite catalyst. Stir the reaction at 40°C under normal pressure, acidic gas will escape, and the tail gas will be absorbed by potassium hydroxide aqueous solution. After reacting for 2 hours, observe the materials in the reaction bottle, the solids are significantly reduced, and the reaction liquid is slightly turbid. Continue to keep the temperature for 3 hours and stop the reaction.

[0034] The reaction solution was cooled to room temperature and filtered under reduced pressure under a nitrogen atmosphere to remove the solid catalyst and unreacted solid impurities. The filtrate was concentrated and evaporated to crystallize. Dichloromethane was added thereto for stirring and washing. After filtration, it was dried under vacuum to obtain 261 g of lithium difluorooxalatoborate solid with a yield of 90.7% and a purity of 99.69%.

[0035] Example 3

[0036] Under nitrogen protection, 122.4g (1.2mol) of lithium oxalate, 90g (1mol) of anhydrous oxalic acid, and 240g of boron trifluoride acetonitrile complex (boron trifluoride content is 62%) were added to a dry reaction bottle with stirring, followed by 500g of acetonitrile solvent with a water content of 300ppm, and 2g of the composite catalyst prepared in Example 1. The reaction was stirred at 75°C under normal pressure, and the tail gas was absorbed by potassium hydroxide aqueous solution. After reacting for 1 hour, the materials in the reaction bottle were observed, and the solid content was significantly reduced. The reaction was continued for 1 hour at a temperature of 100°C, and the reaction was stopped.

[0037] The reaction solution was cooled to room temperature and filtered under reduced pressure under a nitrogen atmosphere to remove the solid catalyst and unreacted solid impurities. The filtrate was concentrated and evaporated to crystallize. Toluene was added thereto for stirring and washing. After filtration, the solution was dried under vacuum to obtain 291 g of lithium difluorooxalatoborate solid with a yield of 92.1% and a purity of 99.74%.

[0038] Comparative Example 1

[0039] (1) A silicon-aluminum composite oxide solid catalyst was prepared according to Example 1 of the scheme disclosed in CN113980045B, and the scheme for preparing lithium difluorooxalate phosphate was implemented according to Example 1 of the present invention to obtain 253 g of lithium difluorooxalate borate solid with a yield of 87.9% and a purity of 99.67%.

[0040] (2) The solid catalyst and unreacted solid impurities removed by filtration in step (1) were rinsed three times with carbon tetrachloride solvent, then dried under a nitrogen atmosphere, and reused. The preparation method of lithium difluorooxalate phosphate was carried out according to Example 1 of the present invention to obtain 237 g of lithium difluorooxalate borate solid with a yield of 82.5% and a purity of 99.04%.

[0041] Comparative Example 2

[0042] The amount of lithium oxalate in Example 1 was changed to 143 g (1.4 mol), and other conditions remained unchanged, and finally 263 g of lithium difluorooxalatoborate solid was obtained with a yield of 91.6% and a purity of 98.46%.

[0043] By comparing Examples 1-3 with Comparative Example 1, it can be found that the composite catalyst of the present invention does not react with the raw materials and the product, and can still play a good catalytic role by washing and drying to obtain high-purity and high-yield lithium difluorooxalatoborate; while the catalyst in Comparative Example 1 cannot achieve the technical effect of reuse.

[0044] By comparing Example 1 and Comparative Example 2, it can be found that when the content of lithium oxalate is increased, the amount of lithium oxalate used is too excessive compared to oxalic acid, resulting in the production of lithium fluoride in addition to hydrogen fluoride in the by-product, resulting in the low purity of the finally obtained lithium difluorooxalatoborate.

[0045] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing high-purity lithium difluorooxalatoborate, characterized in that: Boron trifluoride complex, lithium oxalate and anhydrous oxalic acid are added to a non-protonic organic solvent, and a composite catalyst is added at the same time, and the mixture is stirred and reacted. After the reaction is completed, the mixture is filtered, concentrated, evaporated, crystallized, washed and dried to obtain a lithium difluorooxalatoborate product; wherein the composite catalyst is prepared from polyaluminium chloride and silicon dioxide gel.

2. The method according to claim 1, characterized in that The preparation method of the composite catalyst is as follows: silica gel, polyaluminium chloride powder and carbon tetrachloride are mixed in a mass ratio of 1:(1-1.5):(4-8), added thereto, refluxed at 40-60°C for 1-3 hours under stirring, cooled to room temperature, filtered, rinsed with carbon tetrachloride solvent for 2-3 times, and then dried under a nitrogen atmosphere to obtain the composite catalyst.

3. The method according to claim 1, characterized in that The molar ratio of boron trifluoride complex, lithium oxalate and anhydrous oxalic acid is (2-2.5):(1-1.2):(0.9-1).

4. The method according to claim 1, characterized in that The added amount of the composite catalyst is 0.5%-2% of the mass of the anhydrous oxalic acid.

5. The method according to claim 1, characterized in that The amount of the non-protonic polar solvent added is 1-5 times the total mass of the boron trifluoride complex, lithium oxalate and anhydrous oxalic acid.

6. The method according to claim 1, characterized in that The boron trifluoride complex is at least one selected from a boron trifluoride ether complex, a boron trifluoride acetonitrile complex, and a boron trifluoride dimethyl carbonate complex.

7. The method according to claim 1, characterized in that The aprotic organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile, propionitrile, methyl acetate, ethyl acetate, propyl acetate, acetone and tetrahydrofuran; and the water content of the aprotic organic solvent is controlled within 500 ppm.

8. The method according to claim 1, characterized in that The reaction temperature is 30-80°C, and the reaction time is 1-12 hours.

9. The method according to claim 1, characterized in that: The tail gas generated during the reaction of the method is absorbed by alkaline solution.

10. The method according to claim 1, characterized in that The washing process uses a non-polar solvent, which is selected from at least one of cyclohexane, petroleum ether, dichloromethane, dichloroethane, toluene and xylene.