Lithium difluorobis(oxalato)phosphate, its preparation method and use

Abstract

This application discloses lithium difluorobis(oxalato)phosphate, its method of preparation and uses. [Means] The preparation method includes the steps of: (1) mixing oxalyl chloride, lithium hexafluorophosphate, and a non-aqueous solvent, adding siloxane, and reacting to obtain a lithium difluorobis(oxalato)phosphate solution; and (2) adding a poor solvent to the lithium difluorobis(oxalato)phosphate solution and performing a crystallization process to obtain the lithium difluorobis(oxalato)phosphate. The present application prepares difluorobis(oxalato)phosphate using raw materials such as lithium hexafluorophosphate, oxalyl chloride, and hexamethyldisiloxane, and the method of the present application has few side reactions, few impurities, a high product purity, and is easy to realize for industrial production.

Description

[Technical field]

[0001] The present application relates to the field of chemical synthesis, for example, lithium difluorobis(oxalato)phosphate, its method of preparation and uses. [Background technology]

[0002] Lithium ion batteries are mainly composed of a positive electrode, a negative electrode, a separator, an electrolyte, etc., and the electrolyte is mainly composed of electrolytes and organic solvents. The electrolyte is an active component that connects the positive electrode and the negative electrode, and is an important factor in battery performance. The electrolyte additive is the most important component in the electrolyte of a lithium ion battery other than the electrolyte and the organic solvent, and a suitable additive can play an important role in enhancing the performance of a lithium battery. Lithium difluorobis(oxalato)phosphate is mainly applied to non-aqueous electrolytes such as lithium ion batteries and lithium ion capacitors. Lithium difluorobis(oxalato)phosphate can improve the high temperature resistance of the electrolyte, and can form a more stable solid electrolyte interface film (SEI film) with the positive electrode material, thereby improving the cycle charge and discharge performance of the battery.

[0003] Among the currently disclosed methods for preparing lithium difluorobis(oxalato)phosphate, most of the methods involve reacting lithium hexafluorophosphate and silicon tetrachloride as raw materials. However, during the reaction process, lithium hexafluorophosphate is prone to partially decompose into phosphorus pentafluoride or to react with other oxygen-containing substances to produce lithium difluorophosphate, making it difficult to remove impurities. In addition, during the reaction process using a silicon-based auxiliary, large amounts of silicon tetrafluoride and hydrogen chloride gas are generated, which are difficult to separate and utilize, resulting in a high safety risk for the technical solution and significant difficulties in industrialization.

[0004] CN102216311B discloses a method for preparing lithium difluorobis(oxalato)phosphate solution, which uses hexafluorophosphoric acid, lithium oxalate, and silicon tetrachloride as raw materials to prepare lithium difluorobis(oxalato)phosphate; the method generates a large amount of hydrogen chloride and silicon fluoride, which are highly corrosive acid gases that have very high requirements for devices and are difficult to separate from the product, and the chloride ion content and acid value in the product are difficult to control, and the method has concerns and risks in terms of safety and reliability.

[0005] CN111690010A discloses a method for preparing lithium tetrafluoro(oxalato)phosphate and lithium difluorobis(oxalato)phosphate, which comprises reacting lithium hexafluorophosphate, oxalic acid, and silazane to prepare lithium difluorobis(oxalato)phosphate. The method produces two types of gases, ammonia gas and fluorosilane, which are difficult to separate, and the post-treatment is complicated, and the amount of the three wastes produced is large, which is disadvantageous for industrial production.

[0006] The above methods have problems such as low safety, poor reliability, and large amount of waste generated, which are disadvantageous for industrial production. Therefore, there is a great need to develop a method for preparing lithium difluorobis(oxalato)phosphate that is safe, reliable, environmentally friendly, and advantageous for industrial production. Summary of the Invention [Problem to be solved by the invention]

[0007] The following is a brief summary of the subject matter described in greater detail in the present text. This summary does not limit the scope of the claims.

[0008] One embodiment of the present application provides lithium difluorobis(oxalato)phosphate, its preparation method and use, the preparation method including: (1) mixing oxalyl chloride, lithium hexafluorophosphate and a non-aqueous solvent, adding siloxane, and reacting to obtain a lithium difluorobis(oxalato)phosphate solution; and (2) adding a poor solvent to the lithium difluorobis(oxalato)phosphate solution to perform crystallization to obtain the lithium difluorobis(oxalato)phosphate. The present application prepares difluorobis(oxalato)phosphate using raw materials such as lithium hexafluorophosphate, oxalyl chloride, hexamethyldisiloxane, etc., and the method of the present application has few side reactions, few impurities, high product purity, and is easy to realize industrial production. [Means for solving the problem]

[0009] In aspect 1, one embodiment of the present application comprises: (1) mixing oxalyl chloride, lithium hexafluorophosphate, and a non-aqueous solvent, adding siloxane, and reacting to obtain a lithium difluorobis(oxalato)phosphate solution; and (2) adding a poor solvent to the lithium difluorobis(oxalato)phosphate solution to perform crystallization to obtain the lithium difluorobis(oxalato)phosphate. A method for preparing lithium difluorobis(oxalato)phosphate is provided.

[0010] The present invention uses raw materials such as lithium hexafluorophosphate, oxalyl chloride, and hexamethyldisiloxane to prepare difluorobis(oxalato)phosphate, which has fewer side reactions, fewer impurities, and higher product purity than other related methods, making it easier to realize industrial production. The reaction process is as follows:

[0011] [ka]

[0012] In this reaction, siloxane bonds very strongly with the fluorine atoms in the lithium hexafluorophosphate, and can provide oxygen atoms for the formation of lithium difluorobis(oxalato)phosphate, without generating waste gases such as ammonia gas, resulting in little waste.

[0013] Preferably, the non-aqueous solvent described in step (1) comprises any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, ethyl acetate, or acetonitrile.

[0014] Preferably, the purity of the non-aqueous solvent described in step (1) is greater than 99.9%, such as 99.9%, 99.92%, 99.95%, 99.98%, or 100%.

[0015] Preferably, the water content of the non-aqueous solvent described in step (1) is less than 10 ppm, such as, for example, 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 7 ppm, or 9 ppm.

[0016] If the purity of the non-aqueous solvent is lower than 99.9%, the impurities are too much, which leads to a decrease in the purity of the product; if the water content of the non-aqueous solvent is higher than 10 ppm, lithium hexafluorophosphate will be partially decomposed, the acid value will increase, and the yield will decrease.

[0017] Preferably, the mass ratio of the non-aqueous solvent in step (1) to the lithium hexafluorophosphate is (10-20):1, such as 10:1, 12:1, 15:1, 18:1, or 20:1.

[0018] Preferably, the siloxane described in step (1) comprises any one or a combination of at least two of hexamethyldisiloxane, hexaethyldisiloxane, difluorotetramethyldisiloxane, difluorotetraethyldisiloxane, dichlorotetramethyldisiloxane, or dichlorotetraethyldisiloxane.

[0019] Preferably, the method of adding the siloxane comprises dropwise addition.

[0020] In the present invention, the siloxane is slowly added dropwise and stirred to prevent vigorous gas evolution.

[0021] Preferably, the molar ratio of lithium hexafluorophosphate, oxalyl chloride, and siloxane described in step (1) is 1:(2.0-2.4):(4.0-4.5), such as 1:2:4, 1:2.2:4, 1:2.3:4.4, 1:2.1:4.3, 1:2.3:4.5, or 1:2.4:4.5.

[0022] By controlling the molar ratio of lithium hexafluorophosphate, oxalyl chloride and siloxane within the above range, it is possible to produce lithium difluorobis(oxalato)phosphate with good performance.For 1.0 mol of lithium hexafluorophosphate, if the molar amount of oxalyl chloride is less than 2.0 mol, the reaction of lithium hexafluorophosphate is incomplete, the price of lithium hexafluorophosphate is high, the preparation cost increases, and it is difficult to remove, and it may decompose and generate impurities; if the molar amount of oxalyl chloride is more than 2.4 mol, the amount of oxalyl chloride used is too large, so it is difficult to remove, which affects the purity of the product; if the molar amount of siloxane is less than 4.0 mol, lithium hexafluorophosphate and oxalyl chloride are excessive, the preparation cost increases, and the purity of the product decreases; if the molar amount of siloxane is more than 4.5 mol, siloxane is excessive, and the reaction yield does not further increase.

[0023] Preferably, the reaction described in step (1) includes stirring.

[0024] Preferably, the reaction temperature is 30 to 60°C, such as 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C.

[0025] Preferably, the reaction time is 6 to 12 hours, such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

[0026] If the reaction temperature is lower than 30℃, the reaction will be incomplete, the conversion rate will be low, and the product yield and purity will be affected; if the reaction temperature is higher than 60℃, the decomposition of lithium hexafluorophosphate will be accelerated, phosphorus pentafluoride and hydrogen fluoride will be generated, the product acid value will increase, and side reactions will increase; if the reaction time is lower than 6h, the reaction will be incomplete; if it is higher than 12h, the reaction yield will not increase further, and the cost will increase.

[0027] Preferably, the mixing described in step (1) is carried out under an inert atmosphere.

[0028] Preferably, both steps (1) and (2) are carried out under an inert atmosphere.

[0029] Preferably, the gas in the inert atmosphere includes at least one of nitrogen gas, helium gas, neon gas, and argon gas.

[0030] Preferably, the moisture content of the inert atmosphere is less than 10 ppm, such as 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 7 ppm, or 9 ppm.

[0031] The lower the moisture content of the inert atmosphere, the better. If the moisture content is higher than 10 ppm, it is easy to react with lithium hexafluorophosphate, which will increase the acid value and reduce the yield.

[0032] Preferably, the anti-solvent described in step (2) comprises any one or a combination of at least two of n-hexane, dichloromethane, 1,2-dichloroethane, toluene, or ethylbenzene.

[0033] Preferably, the mass ratio of the poor solvent to the lithium hexafluorophosphate is (8 to 30):1, for example, 8:1, 10:1, 15:1, 20:1, 25:1, or 30:1.

[0034] If the mass ratio of the poor solvent to the lithium hexafluorophosphate is lower than 8:1, the crystallization of lithium difluorobis(oxalato)phosphate in the concentrated solution is incomplete, leading to a decrease in the product yield; if the mass ratio of the poor solvent to the lithium hexafluorophosphate is higher than 30:1, the poor solvent becomes excessive, increasing the cost and not further increasing the yield.

[0035] Preferably, after step (1) and before carrying out the crystallization treatment in step (2), the lithium difluorobis(oxalato)phosphate solution is filtered.

[0036] Preferably, the crystallization treatment described in step (2) is followed by filtration, washing and drying.

[0037] Preferably, the drying comprises vacuum drying.

[0038] Preferably, the drying temperature is 40 to 120°C, for example, 40°C, 50°C, 80°C, 100°C, or 120°C, and is preferably 60 to 100°C.

[0039] Preferably, the drying time is from 2 to 12 hours, for example, 2 hours, 5 hours, 8 hours, 10 hours, or 12 hours, etc., and preferably from 4 to 8 hours.

[0040] If the drying temperature is too low, the drying will be insufficient and the remaining raw materials, moisture and solvent cannot be removed, if the drying temperature is too high, the product will be partially decomposed under high temperature conditions, if the drying time is too short, the drying will be insufficient and the remaining raw materials, moisture and solvent cannot be removed, if the drying time is too long, the moisture content etc. cannot be further reduced, and the preparation cost will be high.

[0041] In an embodiment, the present application provides, in an aspect 2, lithium difluorobis(oxalato)phosphate produced by the method according to the aspect 1.

[0042] Preferably, the lithium difluorobis(oxalato)phosphate has a chloride ion content of 0 to 5 ppm, such as 1 ppm, 2 ppm, 3 ppm, 4 ppm, or 5 ppm.

[0043] Preferably, the lithium difluorobis(oxalato)phosphate has a metal impurity ion content of 0 to 10 ppm, such as 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 7 ppm, or 9 ppm.

[0044] Preferably, the water content of the lithium difluorobis(oxalato)phosphate is 0 to 10 ppm, for example, 1 ppm, 3 ppm, 5 ppm, 8 ppm, or 10 ppm, and is preferably 7.5 ppm or less.

[0045] Preferably, the acid value of the lithium difluorobis(oxalato)phosphate is 0 to 10 ppm, such as 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 7 ppm, or 9 ppm.

[0046] Preferably, the purity of the lithium difluorobis(oxalato)phosphate is ≧99.9%, such as 99.9%, 99.92%, 99.95%, 99.98%, or 100%.

[0047] In an embodiment, the present application provides an electrolyte solution comprising the lithium difluorobis(oxalato)phosphate according to the embodiment.

[0048] In an aspect 4, an embodiment of the present application further provides a lithium ion battery comprising the electrolyte solution according to the aspect 3. Effect of the Invention

[0049] Compared with the related art, the embodiments of the present application have the following beneficial effects:

[0050] (1) The method according to the embodiment of the present application uses inexpensive raw materials to prepare lithium difluorobis(oxalato)phosphate, and the method is easy to operate, has few reaction steps, and has few impurities, avoiding the disadvantages of other methods that are complicated in operation and have many impurities in the product, ensuring the purity and quality of the product, and obtaining high-quality and high-purity products, which is suitable for industrial production.

[0051] (2) The yield of the lithium difluorobis(oxalato)phosphate prepared by the method according to the embodiment of the present application can reach 89.2% or more, and the purity of the lithium difluorobis(oxalato)phosphate prepared by the method according to the embodiment of the present application can reach 99.55% or more, the moisture content of the product can reach 19 ppm or less, the free acid content can reach 22.1 ppm or less, the chloride ion content can reach 30.2 ppm or less, and the metal impurity ion content can reach 10.8 ppm or less. By adjusting the composition ratio of each component and the reaction conditions, the prepared lithium difluorobis(oxalato)phosphate can reach 91.5% or more, the purity can reach 99.94% or more, the moisture content of the product can reach 7.5 ppm or less, the free acid content can reach 8.8 ppm or less, the chloride ion content can reach 4.8 ppm or less, and the metal impurity ion content can reach 8.9 ppm or less.

[0052] Other aspects may be understood upon reading and understanding the drawings and detailed description. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] The technical solution of the present application will be further described below by means of specific embodiments. Those skilled in the art will appreciate that the above examples are merely for the purpose of understanding the present application, and should not be regarded as specific limitations of the present application.

[0054] The raw materials or reagents used in the examples and comparative examples of the present application are all purchased from mainstream manufacturers in the market, and those without a specified manufacturer or concentration are all commonly available raw materials or reagents of analytical purity (Analytical Reagent), and there is no particular restriction as long as they can perform the intended function. The equipment such as glove boxes used in the examples and comparative examples of the present application are all purchased from major manufacturers in the market, and there is no particular restriction as long as they can perform the intended function. If specific techniques or conditions are not specified in the examples and comparative examples of the present application, they will be performed according to the techniques or conditions described in the literature in this field or according to the product instructions.

[0055] [Example 1] This embodiment provides lithium difluorobis(oxalato)phosphate, and the preparation method of the lithium difluorobis(oxalato)phosphate is as follows:

[0056] (1) In a nitrogen atmosphere glove box with a water content of less than 10 ppm, 250 g of dimethyl carbonate dehydrated to 8 ppm was added to a three-necked reaction flask, 15.19 g (0.1 mol) of lithium hexafluorophosphate and 25.38 g (0.2 mol) of oxalyl chloride were added, the three-necked reaction flask was taken out of the glove box, placed on a thermostatic magnetic stirrer, and heated to 30°C. 64.95 g (0.4 mol) of hexamethyldisiloxane was added dropwise to the three-necked reaction flask using a constant pressure dropping funnel, and the molar ratio of lithium hexafluorophosphate, oxalyl chloride, and hexamethyldisiloxane was 1:2:4. The mixture was thoroughly stirred to react, and the trimethylfluorosilane gas generated during the reaction was introduced into an alkaline solution such as a potassium hydroxide solution and absorbed. After reacting for 6 hours, the reaction was terminated, and a lithium difluorobis(oxalato)phosphate solution was obtained.

[0057] (2) The reaction liquid was filtered, and the filtrate was concentrated under reduced pressure to remove most of the solvent and trimethylchlorosilane. 150 g of dichloromethane was added to the obtained concentrated liquid to perform crystallization, and the liquid was filtered, washed twice with 50 g of dichloromethane, and dried at 60°C under a relative vacuum of -0.09 MPa for 8 hours to obtain 23.13 g (0.0918 mol) of the product lithium difluorobis(oxalato)phosphate, with a product yield of 91.8%.

[0058] [Example 2] This embodiment provides lithium difluorobis(oxalato)phosphate, and the preparation method of the lithium difluorobis(oxalato)phosphate is as follows:

[0059] (1) In a nitrogen atmosphere glove box with a water content of less than 10 ppm, 152 g of diethyl carbonate dehydrated to 7 ppm was added to a three-necked reaction flask, 15.19 g (0.1 mol) of lithium hexafluorophosphate and 30.46 g (0.24 mol) of oxalyl chloride were added, the three-necked reaction flask was taken out of the glove box, placed on a thermostatic magnetic stirrer, and heated to 60°C. 73.07 g (0.45 mol) of hexamethyldisiloxane was added dropwise to the three-necked reaction flask using a constant pressure dropping funnel, and the molar ratio of lithium hexafluorophosphate, oxalyl chloride, and hexamethyldisiloxane was 1:2.4:4.5. The mixture was thoroughly stirred to react, and the trimethylfluorosilane gas generated during the reaction was introduced into an alkaline solution such as potassium hydroxide solution and absorbed. After reacting for 12 hours, the reaction was terminated, and a lithium difluorobis(oxalato)phosphate solution was obtained.

[0060] (2) The reaction liquid was filtered, and the filtrate was concentrated under reduced pressure to remove most of the solvent and trimethylchlorosilane. 300 g of 1,2-dichloroethane was added to the resulting concentrated liquid to perform crystallization, and the liquid was filtered, washed twice with 80 g of 1,2-dichloroethane, and dried at 100°C under a relative vacuum of -0.08 MPa for 4 hours to obtain 23.60 g (0.0937 mol) of the product lithium difluorobis(oxalato)phosphate, with a product yield of 93.7%.

[0061] [Example 3] This embodiment provides lithium difluorobis(oxalato)phosphate, and the preparation method of the lithium difluorobis(oxalato)phosphate is as follows:

[0062] (1) In a nitrogen atmosphere glove box with a water content of less than 10 ppm, 300 g of ethyl methyl carbonate dehydrated to 6 ppm was added to a three-necked reaction flask, 15.19 g (0.1 mol) of lithium hexafluorophosphate and 27.92 g (0.22 mol) of oxalyl chloride were added, the three-necked reaction flask was taken out of the glove box, placed on a thermostatic magnetic stirring device, and heated to 40°C. 68.20 g (0.42 mol) of hexamethyldisiloxane was dropped into the three-necked reaction flask using a constant pressure dropping funnel, and the molar ratio of lithium hexafluorophosphate, oxalyl chloride, and hexamethyldisiloxane was 1:2.2:4.2. The mixture was thoroughly stirred to react, and the trimethylfluorosilane gas generated during the reaction was introduced into an alkaline solution such as potassium hydroxide solution and absorbed. After reacting for 8 hours, the reaction was terminated, and a lithium difluorobis(oxalato)phosphate solution was obtained.

[0063] (2) The reaction liquid was filtered, and the filtrate was concentrated under reduced pressure to remove most of the solvent and trimethylchlorosilane. 160 g of dichloromethane was added to the resulting concentrated liquid to perform crystallization. The liquid was filtered, washed twice with 60 g of dichloromethane, and dried at a relative vacuum of -0.09 MPa and 70°C for 7 hours to obtain 23.25 g (0.0923 mol) of the product lithium difluorobis(oxalato)phosphate, with a product yield of 92.3%.

[0064] [Example 4] This embodiment provides lithium difluorobis(oxalato)phosphate, and the preparation method of the lithium difluorobis(oxalato)phosphate is as follows:

[0065] (1) In a nitrogen atmosphere glove box with a water content of less than 10 ppm, 250 g of ethyl acetate dehydrated to 9 ppm was added to a three-necked reaction flask, 15.19 g (0.1 mol) of lithium hexafluorophosphate and 25.38 g (0.2 mol) of oxalyl chloride were added, the three-necked reaction flask was taken out of the glove box, placed on a thermostatic magnetic stirrer, and heated to 50°C. 106.01 g (0.43 mol) of hexaethyldisiloxane was added dropwise to the three-necked reaction flask using a constant pressure dropping funnel, and the molar ratio of lithium hexafluorophosphate, oxalyl chloride, and hexaethyldisiloxane was 1:2:4.3. The mixture was thoroughly stirred to react, and the reaction was terminated after 10 hours of reaction, to obtain a lithium difluorobis(oxalato)phosphate solution.

[0066] (2) The reaction liquid was filtered, and the filtrate was concentrated under reduced pressure to remove most of the solvent, triethylfluorosilane liquid, and triethylchlorosilane liquid. 180 g of dichloromethane was added to the resulting concentrated liquid to perform crystallization, and the liquid was filtered, washed twice with 70 g of dichloromethane, and dried at a relative vacuum of -0.09 MPa and 80°C for 6 hours to obtain 23.20 g (0.0921 mol) of the product lithium difluorobis(oxalato)phosphate, with a product yield of 92.1%.

[0067] [Example 5] This embodiment provides lithium difluorobis(oxalato)phosphate, and the preparation method of the lithium difluorobis(oxalato)phosphate is as follows:

[0068] (1) In a nitrogen atmosphere glove box with a water content of less than 10 ppm, 250 g of dimethyl carbonate dehydrated to 5 ppm was added to a three-necked reaction flask, 15.19 g (0.1 mol) of lithium hexafluorophosphate and 25.38 g (0.2 mol) of oxalyl chloride were added, the three-necked reaction flask was taken out of the glove box, placed on a thermostatic magnetic stirrer, heated to 50°C, and 81.28 g (0.4 mol) of dichlorotetramethyldisiloxane was dropped into the three-necked reaction flask using a constant pressure dropping funnel, the molar ratio of lithium hexafluorophosphate, oxalyl chloride and dichlorotetramethyldisiloxane was 1:2:4, and the mixture was thoroughly stirred to react, and the dimethylfluorochlorosilane gas generated during the reaction was introduced into an alkaline solution such as a potassium hydroxide solution and absorbed, and the reaction was terminated after 10 hours of reaction, to obtain a lithium difluorobis(oxalato)phosphate solution.

[0069] (2) The reaction liquid was filtered, and the filtrate was concentrated under reduced pressure to remove most of the solvent and dichlorodimethylsilane. 210 g of dichloromethane was added to the resulting concentrated liquid to perform crystallization. The liquid was filtered, washed twice with 80 g of dichloromethane, and dried at a relative vacuum of -0.09 MPa at 90°C for 5 hours to obtain 23.05 g (0.0915 mol) of the product lithium difluorobis(oxalato)phosphate, with a product yield of 91.5%.

[0070] [Example 6] The only difference between this example and Example 1 is that the amount of oxalyl chloride added in step (1) is 22.842 g (0.18 mol); the other conditions and parameters are exactly the same as those in Example 1.

[0071] [Example 7] The only difference between this example and Example 1 is that the amount of oxalyl chloride added in step (1) is 31.725 g (0.25 mol); the other conditions and parameters are exactly the same as those in Example 1.

[0072] [Example 8] The only difference between this example and Example 1 is that the amount of hexamethyldisiloxane added in step (1) is 61.7 g (0.38 mol); the other conditions and parameters are exactly the same as those in Example 1.

[0073] [Example 9] The only difference between this example and Example 1 is that the amount of hexamethyldisiloxane added in step (1) is 77.94 g (0.48 mol); the other conditions and parameters are exactly the same as those in Example 1.

[0074] [Example 10] The only difference between this embodiment and Example 1 is that the reaction temperature described in step (1) is 25° C.; the other conditions and parameters are exactly the same as those in Example 1.

[0075] [Example 11] The only difference between this embodiment and Example 1 is that the reaction temperature described in step (1) is 70° C.; the other conditions and parameters are exactly the same as those in Example 1.

[0076] [Example 12] The only difference between this embodiment and Example 1 is that in step (2), 120 g of dichloromethane was added to the obtained concentrated liquid to perform crystallization. The other conditions and parameters were exactly the same as those in Example 1.

[0077] [Example 13] The only difference between this embodiment and Example 1 is that the drying temperature described in step (2) is 30° C.; the other conditions and parameters are exactly the same as those in Example 1.

[0078] [Example 14] The only difference between this embodiment and Example 1 is that the drying temperature described in step (2) is 130° C.; the other conditions and parameters are exactly the same as those in Example 1.

[0079] [Comparative Example 1] This comparative example provides lithium difluorobis(oxalato)phosphate, and the preparation method of the lithium difluorobis(oxalato)phosphate is as follows:

[0080] (1) In a nitrogen atmosphere glove box with a water content of less than 10 ppm, 250.0 g of dimethyl carbonate dehydrated to 6 ppm was added to a three-necked reaction flask, 18.02 g (0.20 mol) of oxalic acid was added, and 32.3 g (0.2 mol) of hexamethyldisilazane was further added. The mixture was stirred for 30 minutes to mix uniformly. 50.0 g of dimethyl carbonate dehydrated to 6 ppm was added to the flask, and 15.2 g (0.1 mol) of lithium hexafluorophosphate was added while stirring and fully dissolved to prepare a lithium hexafluorophosphate solution. The three-necked reaction flask was taken out of the glove box, placed on a thermostatic magnetic stirrer, heated to 60°C, and the lithium hexafluorophosphate solution in the flask was gradually dropped into the three-necked reaction flask using a constant pressure dropping funnel, and the mixture was thoroughly stirred to react. The gas generated by the reaction was introduced into an alkaline solution such as a potassium hydroxide solution and absorbed, and the reaction was terminated after 6 hours of reaction.

[0081] (2) The reaction liquid was filtered, and the filtrate was concentrated under reduced pressure to remove most of the solvent. 150 g of dichloromethane was added to the resulting concentrated liquid to perform crystallization. The crystallization was then performed by filtering, washing twice with 50 g of dichloromethane, and drying at 60°C under a relative vacuum of -0.09 MPa for 8 hours to obtain 22.43 g (0.0890 mol) of the product lithium difluorobis(oxalato)phosphate, with a product yield of 89.0%.

[0082] Performance Test: Performance tests were carried out using the lithium difluorobis(oxalato)phosphate obtained in Examples 1 to 14 and Comparative Example 1. The purity of the product was measured using an ion chromatograph (930 model, Metrohm), the water content was measured using a moisture meter (917 model, Metrohm), the acid value was measured using a potentiometer (888 model, Metrohm), the chloride ion content was measured using an ion chromatograph (930 model, Metrohm), and the metal impurity ion content was measured using an ICP-OES (PQ-9000 model, Analytik Jena). The test results are shown in Table 1.

[0083] [Table 1]

[0084] As can be seen from Table 1, according to Examples 1 to 14, the yield of lithium difluorobis(oxalato)phosphate prepared by the method of the present application can reach 89.2% or more, the purity of lithium difluorobis(oxalato)phosphate prepared by the method of the present application can reach 99.55% or more, the moisture content of the product can reach 19 ppm or less, the free acid content can reach 22.1 ppm or less, the chloride ion content can reach 30.2 ppm or less, and the metal impurity ion content can reach 10.8 ppm or less. By adjusting the blending ratio of each component and the reaction conditions, the prepared lithium difluorobis(oxalato)phosphate can reach 91.5% or more, the purity can reach 99.94% or more, the moisture content of the product can reach 7.5 ppm or less, the free acid content can reach 8.8 ppm or less, the chloride ion content can reach 4.8 ppm or less, and the metal impurity ion content can reach 8.9 ppm or less.

[0085] Comparison of Example 1 with Examples 6-7 shows that by controlling the ratio of lithium hexafluorophosphate and oxalyl chloride to 1:(2.0-2.4), the yield and purity of the produced lithium difluorobis(oxalato)phosphate are high; if the ratio is less than 1:2, the reaction of lithium hexafluorophosphate is incomplete, and the preparation cost increases due to the high price of lithium hexafluorophosphate, and it is difficult to remove, and there is a possibility that it will decompose and generate impurities; if the ratio is more than 1:2.4, the amount of oxalyl chloride used is too large, which is difficult to remove, affecting the purity of the product.

[0086] Comparison of Example 1 with Examples 8 and 9 shows that by controlling the ratio of lithium hexafluorophosphate and siloxane to 1:(4.0-4.5), the yield and purity of the produced lithium difluorobis(oxalato)phosphate are high; if the ratio is less than 1:4, lithium hexafluorophosphate and oxalyl chloride become excessive, the preparation cost increases, and the purity of the product decreases; if the ratio is more than 1:4.5, siloxane becomes excessive, and the reaction yield does not increase further.

[0087] A comparison of Example 1 with Examples 10 and 11 shows that the temperature of the reaction described in step (1) affects the yield and purity of the produced lithium difluorobis(oxalato)phosphate, and that by controlling the reaction temperature to 30 to 60°C, lithium difluorobis(oxalato)phosphate can be prepared in high yield and purity.

[0088] Comparison between Example 1 and Example 12 shows that the amount of the anti-solvent added partially affects the yield and purity of the produced lithium difluorobis(oxalato)phosphate, and by controlling the mass ratio of the anti-solvent to the lithium hexafluorophosphate to (8-30):1, it is possible to stabilize the cost and maximize the crystallization of lithium difluorobis(oxalato)phosphate.

[0089] Comparison of Example 1 with Examples 13 and 14 shows that the drying temperature described in step (2) can affect the yield and purity of the produced lithium difluorobis(oxalato)phosphate, and by controlling the drying temperature to 40 to 120°C, decomposition of lithium difluorobis(oxalato)phosphate can be avoided and the remaining raw materials, moisture and solvent can be removed.

[0090] A comparison between Examples 1 to 5 and Comparative Example 1 shows that the lithium difluorobis(oxalato)phosphate prepared by the method of the present application is superior to Comparative Example 1 in terms of purity, water content, acid value, chloride ion content, and metal impurity ion content.

[0091] In the preparation method of lithium difluorobis(oxalato)phosphate of the present application, oxalyl chloride, lithium hexafluorophosphate, and siloxane are reacted, and the reaction activity of oxalyl chloride is better, which is favorable for the progress of the reaction, and siloxane has a strong bond with the fluorine atoms in lithium hexafluorophosphate and provides oxygen atoms for the formation of lithium difluorobis(oxalato)phosphate, so no waste gas such as ammonia gas is generated and the three wastes are reduced.

[0092] The preparation method of the present application is easy to operate, has few reaction steps, has a high conversion rate, and has few impurities, avoiding the disadvantages of other methods that are complicated in operation and have many impurities, ensuring the purity and quality of the product, and obtaining high-quality and high-purity products, which is suitable for industrial large-scale production.

[0093] The applicant declares that the above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto, and that any modification or replacement that a person skilled in the art can easily conceive within the technical scope disclosed in the present application should be understood to be included in the scope of protection and disclosure of the present application.

Claims

1. A process for preparing lithium difluorobis(oxalato)phosphate comprising the steps of: (1) mixing oxalyl chloride, lithium hexafluorophosphate and a non-aqueous solvent, adding siloxane, and reacting to obtain a lithium difluorobis(oxalato)phosphate solution; and (2) adding a poor solvent to the lithium difluorobis(oxalato)phosphate solution to perform crystallization to obtain the lithium difluorobis(oxalato)phosphate. Method for the preparation of lithium difluorobis(oxalato)phosphate.

2. The non-aqueous solvent described in step (1) includes any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, ethyl acetate, or acetonitrile; 2. The method of claim 1.

3. The purity of the non-aqueous solvent described in step (1) is greater than 99.9%; 2. The method of claim 1.

4. The water content of the non-aqueous solvent described in step (1) is less than 10 ppm; 2. The method of claim 1.

5. The mass ratio of the non-aqueous solvent described in step (1) to the lithium hexafluorophosphate is (10 to 20): 1; 2. The method of claim 1.

6. 2. The process of claim 1, wherein the siloxane in step (1) comprises any one or a combination of at least two of hexamethyldisiloxane, hexaethyldisiloxane, difluorotetramethyldisiloxane, difluorotetraethyldisiloxane, dichlorotetramethyldisiloxane, or dichlorotetraethyldisiloxane.

7. The method of claim 1, wherein the method of adding the siloxane comprises dropwise addition.

8. The molar ratio of lithium hexafluorophosphate, oxalyl chloride, and siloxane described in step (1) is 1:(2.0-2.4):(4.0-4.5); 2. The method of claim 1.

9. The reaction described in step (1) includes stirring, The reaction temperature is 30 to 60° C. The preparation method according to claim 1, wherein the reaction time is 6-12 h.

10. Step (1) and step (2) are both carried out under an inert atmosphere; The gas in the inert atmosphere includes at least one of nitrogen gas, helium gas, neon gas, and argon gas; The moisture content of the inert atmosphere is less than 10 ppm; 2. The method of claim 1.

11. The preparation method according to claim 1, wherein the anti-solvent in step (2) comprises any one or a combination of at least two of n-hexane, dichloromethane, 1,2-dichloroethane, toluene, or ethylbenzene.

12. The mass ratio of the poor solvent to the lithium hexafluorophosphate is (8 to 30):

1.

2. The method of claim 1.

13. 2. The method according to claim 1, wherein after step (1) and before carrying out the crystallization treatment in step (2), the lithium difluorobis(oxalato)phosphate solution is filtered.

14. After the crystallization treatment described in step (2), filtration, washing and drying are performed, The drying comprises vacuum drying; The drying temperature is 40 to 120° C. The drying time is 2 to 12 hours.

2. The method of claim 1.

Images