Method for producing lithium difluorophosphate

Abstract

Lithium difluorophosphate and its preparation method and application, which uses lithium hexafluorophosphate and silicon tetrachloride to produce lithium difluorotetrachlorophosphate, and then reacts lithium difluorotetrachlorophosphate with lithium carbonate to obtain a mixture of lithium difluorophosphate and lithium chloride, and then purifies to obtain high purity lithium difluorophosphate, which has simple steps, low cost, short reaction time and high conversion rate.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion battery technology, and specifically to a method for manufacturing lithium difluorophosphate.

Background Art

[0002] As a new type of portable power source, lithium-ion batteries have a higher specific capacity and discharge voltage than conventional lead-acid batteries and alkaline dry batteries, and have less environmental pollution. Currently, lithium-ion batteries are mainly used as portable mobile power sources and mobile phone batteries, and are widely applied to electric vehicles, automobiles, etc. as power batteries. Due to the strong support of national policies and the accumulation of lithium-ion battery technology in recent years, the lithium-ion battery industry has developed significantly. However, currently, there are still many defects in lithium-ion batteries. In the development of lithium salts, conventional lithium hexafluorophosphate cannot meet the use under extreme conditions of lithium-ion batteries. Lithium difluorophosphate can improve the high and low temperature performance of lithium-ion batteries, significantly improve its cycle stability at -20°C, and can form a more stable SEI film under high temperature conditions, effectively preventing the electrolyte from corroding the electrode and current collector, thereby improving the high and low temperature performance of lithium-ion batteries. In addition, lithium difluorophosphate has better stability than lithium hexafluorophosphate and is significantly more resistant to water and oxygen than lithium hexafluorophosphate. Therefore, lithium difluorophosphate has great industrial value as an additive for new lithium salts.

[0003] There are many methods for the production method of lithium difluorophosphate, which are roughly classified into three routes: the lithium difluorophosphate route method, the lithium hexafluorophosphate route method, and other methods. However, the existing production methods of lithium difluorophosphate have a complex process, high requirements for production equipment, many by-products, and difficulty in generating solids, etc., which are very disadvantageous for the industrialization and popularization of lithium difluorophosphate.

[0004] In Patent Document 1, it mentions manufacturing lithium difluorophosphate products by reacting lithium phosphate with phosphorus pentafluoride and phosphoryl fluoride. The technical route used involves using highly expensive, highly toxic, and highly dangerous phosphorus pentafluoride gas. The process is complex, has strict requirements for production equipment, and the product cost is high.

[0005] In Patent Document 2, it manufactures lithium difluorophosphate by reacting lithium hexafluorophosphate with water, and can decompose halogenated siloxane compounds. However, when adopting this method for production, it is easy to cause the decomposition of lithium hexafluorophosphate, and moreover, it is difficult to control the reaction process, there are many by-products, which is very disadvantageous for production.

[0006] In Patent Document 3, a method for manufacturing lithium difluorophosphate in an aprotic solvent by using lithium hexafluorophosphate and lithium carbonate is described. However, this method has a long reaction time and a low conversion rate. Moreover, this method can only obtain a non-aqueous solution of lithium difluorophosphate and cannot obtain high-purity lithium difluorophosphate, which is very disadvantageous for the popularization of lithium difluorophosphate. And in this salt solution, there are more or less organic impurities and lithium fluoride, and these impurities may have an adverse effect on the performance of the battery.

[0007] In Patent Document 4, a manufacturing method of lithium difluorophosphate is disclosed. Among them, lithium hexafluorophosphate, oxalate, and silicon tetrachloride are reacted in an organic solvent, and the reaction is carried out under a protective atmosphere. However, the yield of this method is low, especially the acid value is high, which affects the performance of the electrolyte. In this method, an alkaline solution is not used to neutralize the acidity, and lithium oxalate has almost no alkalinity in the organic solvent.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] Regarding the defects existing in the prior art, the object of the present invention is to provide a method for manufacturing lithium difluorophosphate solid with a simple manufacturing process, low cost, short reaction time, high conversion rate, easy control of the whole process, no generation of water, and no by-product impurities after purification.

Means for Solving the Problems

[0010] The present invention provides a method for manufacturing lithium difluorophosphate, In the case of basically no water, lithium hexafluorophosphate and silicon tetrachloride are stirred and reacted in a first non-aqueous solvent, degassed to remove impurities, and step (1) of obtaining a lithium tetrachloride difluorophosphate solution; The obtained lithium tetrachloride difluorophosphate solution is dropped into a lithium carbonate dispersion for reaction, filtered to obtain a filtration cake mixture of lithium difluorophosphate and lithium chloride, step (2); The filtration cake mixture is disintegrated with ethyl acetate, the insoluble matter is removed by filtration, the disintegrated solution is concentrated, and a non-polar solvent is further added for crystallization to obtain lithium difluorophosphate, step (3), which is characterized by including.

[0011] Preferably, based on the above method for manufacturing lithium difluorophosphate, the charged molar ratio of lithium hexafluorophosphate, silicon tetrachloride, and lithium carbonate is 1:(1 to 1.5):(2 to 2.5).

[0012] Preferably, based on the method for producing lithium difluorophosphate, in step (1), the molar concentration of lithium hexafluorophosphate is 1.5 to 4.0 mol / L, preferably 1.5 to 2.5 mol / L.

[0013] Preferably, based on the method for producing lithium difluorophosphate, in step (1), the reaction temperature of lithium hexafluorophosphate and silicon tetrachloride in the first non-aqueous solvent is 20 to 100 °C, preferably 50 to 90 °C, more preferably 70 to 90 °C.

[0014] Preferably, based on the method for producing lithium difluorophosphate, in step (1), the gas used for degassing to remove impurities is an inert gas, preferably one or more of nitrogen gas, argon gas, helium gas, etc., and the temperature for degassing to remove impurities is 60 to 120 °C, preferably 70 to 100 °C, more preferably 85 to 100 °C.

[0015] Preferably, based on the method for producing lithium difluorophosphate, in step (2), the reaction temperature of lithium tetrachlorodifluorophosphate and lithium carbonate is 30 to 80 °C, preferably 50 to 80 °C.

[0016] Preferably, based on the method for producing lithium difluorophosphate, in step (2), the lithium carbonate dispersion is prepared by mixing lithium carbonate and a second non-aqueous solvent, and the mass ratio of lithium carbonate to the second non-aqueous solvent is 1:(3 to 5), preferably 1:(4.2 to 5).

[0017] Preferably, based on the method for producing lithium difluorophosphate, the first non-aqueous solvent and the second non-aqueous solvent are each independently one or more of a cyclic carbonate, a chain carbonate, and a cyclic ether, and preferably, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, 1,4-dioxane, tetrahydrofuran, or one or more thereof.

[0018] Preferably, based on the method for producing lithium difluorophosphate, in step (3), the mass ratio of the filter cake mixture to ethyl acetate is 1:(1 to 2), preferably 1:(1.90 to 2), and the time for pulping the filter cake mixture with ethyl acetate is 3 to 5 h.

[0019] Preferably, based on the method for producing lithium difluorophosphate, in step (3), the concentration and pulping liquid is completed by vacuum distilling the filtrate, and the vacuum distillation temperature is 40 to 80°C, preferably 45 to 65°C, more preferably 50 to 65°C.

[0020] Preferably, based on the method for producing lithium difluorophosphate, in step (3), the non-polar solvent is one or more of n-hexane, n-pentane, cyclohexane, heptane, dichloromethane, chloroform, 1,2-dichloroethane.

[0021] Preferably, based on the method for producing lithium difluorophosphate, in step (3), the crystallization temperature is 0 to 5°C, preferably 0 to 3.5°C.

[0022] Preferably, based on the method for producing lithium difluorophosphate, in step (3), after crystallization, filtration is further performed to obtain a filter cake, and the filter cake is dried to obtain lithium difluorophosphate. The temperature for drying the filter cake is 80 to 120 °C, preferably 100 to 120 °C.

[0023] Preferably, based on the method for producing lithium difluorophosphate, in steps (1) and (2), the reactions are both carried out in an atmosphere of an inert gas, and the inert gas is one or more of nitrogen gas, argon gas, and helium gas.

[0024] The present invention further provides lithium difluorophosphate, which is produced by the production method according to any one of claims 1 to 14. Among them, the purity of the lithium difluorophosphate is ≥ 99.8%, the content of free acid is ≤ 50 ppm, preferably ≤ 25 ppm.

[0025] Preferably, based on the above lithium difluorophosphate, the water content is ≤ 10 ppm, the Cl - content is ≤ 1 ppm, preferably ≤ 0.8 ppm, and the sum of the contents of impurity metal ions is ≤ 2 ppm, preferably ≤ 1.5 ppm.

[0026] The present invention further provides a non-aqueous electrolyte battery including a positive electrode, a negative electrode, and an electrolyte containing the above-mentioned lithium difluorophosphate.

[0027] It is for use in the production of the above non-aqueous electrolyte battery of lithium difluorophosphate.

Advantages of the Invention

[0028] Compared with the existing technology, the present invention has the following advantages and effects.

[0029] The method for manufacturing lithium difluorophosphate solid provided by the present invention adopts a two-step reaction, with a simple process. The raw materials are common lithium hexafluorophosphate, silicon tetrachloride, and lithium carbonate, all of which are common and inexpensive bulk chemicals, and the manufacturing cost is low. In the reaction process of the first step, an intermediate LiPF 2 Cl 4 is generated. Its structure contains four chlorine atoms. The atomic radius of the chlorine atom is large, and the binding force with the phosphorus element is smaller than that of the fluorine atom. The chlorine atom is more likely to desorb, so it is easier to generate lithium difluorophosphate, with a faster speed, a shorter reaction time, and no water involved in the entire reaction process, avoiding the problem of low purity caused by the generation of impurities due to the hydrolysis of the product. In the present invention, lithium carbonate is used as a reaction raw material, which is inexpensive, widely sourced, and slightly excessive. Usually, it is used alone for acid removal in an organic solvent. Therefore, in the present invention, free acid can be neutralized and the acid value can be reduced.

Embodiments for Carrying Out the Invention

[0030] To better understand the above technical solution, the following specific examples are used to elaborate the technical solution of the present application in detail. The examples of the present application and the specific features in the examples are detailed descriptions of the technical solution of the present application and do not limit the technical solution of the present application. It should be understood that when there is no contradiction, the technical features in the examples of the present application and the examples can be combined with each other.

[0031] The manufacturing method of lithium difluorophosphate provided by the present invention is a two-step reaction method, and its corresponding chemical reaction formula is as follows.

[0032] LiPF 6 +SiCl 4 →LiPF 2 Cl 4 +SiF 4 ↑ LiPF 2 Cl 4 +2Li 2 CO 3→LiPO 2 F 2 +2CO 2 ↑+4LiCl

[0033] In its specific preferred means, the specific steps of the manufacturing method of the present invention are as follows.

[0034] (1) In the case of basically no water, under the protection of an inert gas, lithium hexafluorophosphate is reacted with silicon tetrachloride to produce a lithium tetrachloride difluorophosphate solution. After the reaction of this step is completed, it is necessary to degas to remove impurities. The purpose is to remove silicon tetrafluoride and prevent the remaining silicon tetrafluoride from affecting the reaction of the next step.

[0035] (2) The prepared lithium tetrachloride difluorophosphate solution is dropped into a lithium carbonate dispersion and reacted to obtain a mixture of lithium difluorophosphate and lithium chloride.

[0036] (3) The above filter cake is disintegrated with ethyl acetate, filtered, the disintegrated solution is collected, further concentrated, and then a non-aqueous solvent is added for crystallization to obtain a filter cake. After drying, lithium difluorophosphate is obtained.

[0037] In step (1), the reaction is carried out in a first non-aqueous solvent. The first non-aqueous solvent is one or a mixture of two or more of cyclic carbonates, chain carbonates, cyclic esters, chain esters, and cyclic ethers, preferably one or a mixture of two or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, 1,4-dioxane, and tetrahydrofuran, more preferably dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. The molar ratio of lithium hexafluorophosphate to silicon tetrachloride is 1:(1 to 1.5), with silicon tetrachloride being in excess to ensure complete reaction of lithium hexafluorophosphate. If the molar ratio is lower than 1:1, a large amount of lithium hexafluorophosphate remains in the reaction solution. If it is higher than 1:1.5, a large amount of silicon tetrachloride remains, resulting in high costs for subsequent removal. The concentration of lithium hexafluorophosphate is 1.5 to 4.0 mol / L. If the concentration is lower than 1.5 mol / L, it affects the reaction rate. If it is higher than 4.0 mol / L, the solution is prone to discoloration, affecting the final product. The reaction temperature is 20 to 100 °C, preferably 50 to 90 °C, more preferably 70 to 90 °C. If the reaction temperature is too low, the reaction rate is low. If it is too high, the decomposition of lithium hexafluorophosphate speeds up, and by-products and impurities are likely to occur. The temperature for degassing to remove impurities is 60 to 120 °C, preferably 70 to 100 °C, more preferably 85 to 100 °C. If the degassing temperature is lower than 60 °C, the concentration of chlorine compounds in the reaction solution is high, and it cannot be used as a non-aqueous electrolyte additive. If the degassing temperature is higher than 120 °C, it causes bumping of the solution, resulting in material loss. The gas used for degassing to remove impurities is an inert gas, preferably one or a mixture of two or more of nitrogen gas, argon gas, helium gas, etc.

[0038] In step (2), the reaction is carried out under an inert gas protection. The lithium carbonate dispersion is prepared from lithium carbonate and a second non-aqueous solvent, and the mass ratio of lithium carbonate to the second non-aqueous solvent is 1:(3 - 5), preferably 1:(4.2 - 5). If the mass ratio is lower than 1:3, a normal slurry-like homogeneous dispersion of lithium carbonate cannot be formed, and the reaction may be insufficient. If the mass ratio is greater than 1:5, it will result in waste of the solvent. The second non-aqueous solvent is one or a mixture of two or more of cyclic carbonates, chain carbonates, cyclic esters, chain esters, and cyclic ethers. Preferably, it is one or a mixture of two or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, 1,4-dioxane, and tetrahydrofuran. More preferably, it is dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. The molar ratio of lithium hexafluorophosphate to lithium carbonate is 1:(2 - 2.5). This limiting value is to ensure the complete reaction of lithium tetrachlorophosphate difluoride. If it is higher than 1:2.5, it will result in waste of lithium carbonate. If it is lower than 1:2, the reaction cannot be carried out completely. The reaction temperature is 20 - 80°C, preferably 30 - 80°C. If the temperature is lower than 20°C, the reaction rate is too slow. If the temperature is too high, side reactions will occur to easily generate PO 3 - , PO 4 3- to be generated.

[0039] In steps (1) and (2), the inert gas is one or two or more of nitrogen gas, argon gas, and helium gas.

[0040] In step (3), the weight of ethyl acetate is 1 to 2 times the weight of the filter cake mixture, preferably 1.90 to 2 times. If it is lower than 1 time, the extraction of the product is likely to be incomplete, resulting in a decrease in yield. If it exceeds 2 times, the solvent will be wasted. The beating time is 3 to 5 h to fully dissolve lithium difluorophosphate in the ethyl acetate solution. Collecting and concentrating the beaten liquid is completed by vacuum distillation of the filtrate. The vacuum distillation temperature is 40 to 80°C, preferably 45 to 65°C, more preferably 50 to 65°C. If it is lower than 40°C, the distillation rate is slow. If it is higher than 80°C, lithium difluorophosphate may be carried into the solvent, resulting in a certain loss in yield.

[0041] For the crystallization solvent, a weakly polar or non-polar solvent is selected for crystallization. Preferably, it is one or more of n-hexane, n-pentane, cyclohexane, heptane, dichloromethane, chloroform, 1,2-dichloroethane. The crystallization temperature is 0 to 5°C, and the crystallization time is 2 to 5 h. The drying temperature of the filter cake is 80 to 120°C, preferably 100 to 120°C, and the drying time is 8 to 15 h, preferably 12 to 15 h. There are no particular limitations on them as long as the desired crystallization effect can be achieved.

[0042] The lithium difluorophosphate obtained by manufacturing with the method of the present invention has a purity of ≥99.8%, a free acid content of ≤50 ppm, a water content of ≤10 ppm, and a Cl - content of ≤1 ppm, preferably ≤0.8 ppm, and the sum of the contents of impurity metal ions is ≤2 ppm, preferably ≤1.5 ppm.

[0043] (Example) The raw materials or reagents used in the present invention were all purchased from mainstream manufacturers in the market. When the production manufacturer or concentration is not specified, they are all secondary-standard raw materials or reagents that are readily available daily, and are not particularly limited as long as they can achieve the desired effect. The instrumentation and equipment used in this example were all purchased from major manufacturers in the market and are not particularly limited as long as they can play the desired role. In this example, when specific techniques or conditions are not specified, they were carried out according to the techniques or conditions described in the literature within the art or according to the product specifications.

[0044] Regarding raw materials and instruments, The glove box was purchased from Microna, and the model number is Siemens S7. The vacuum drying box was purchased from Shanghai Yiheng, and the model number is DZF-6050. Ion chromatography adopted Metrohm 833 type high-pressure ion chromatography. The inductively coupled plasma optical emission spectrometer (ICP-OES) adopted Jitian Instrument ICP-5000 inductively coupled plasma optical emission spectrometer. The Karl Fischer method test was carried out for moisture test using Jingtai SF-3 Karl Fischer moisture tester. Dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, and silicon tetrachloride were purchased from Aladdin Reagent Net. Lithium hexafluorophosphate was purchased from Morita New Energy (Zhangjiagang). Lithium carbonate was purchased from Ganfeng Lithium.

[0045] (Example 1) (1) In a glove box with a water content lower than 10 ppm by mass, a 250 ml three-necked flask was prepared. 150 ml of dimethyl carbonate with a water content of 10 ppm by mass or less was added into the flask. The three-necked flask was placed in the refrigerator of the glove box and frozen. Subsequently, 45.0 g of lithium hexafluorophosphate (0.296 mol, molecular weight 151.9 g / mol) was weighed, and the molar concentration of lithium hexafluorophosphate was adjusted to 1.97 mol / L. It was slowly dissolved in the frozen dimethyl carbonate solvent, and the solution temperature during the dissolution process was controlled at 5 - 10 °C. After the operation was completed, the above three-necked flask was transferred out of the glove box and placed in a normal temperature oil bath pot. 50.29 g of silicon tetrachloride (0.296 mol, molecular weight of silicon tetrachloride 169.9 g / mol) was weighed and rapidly added into a constant voltage dropping funnel. Subsequently, a condenser tube and a constant voltage dropping funnel were attached, and the system was protected with nitrogen gas. Subsequently, the oil bath temperature was slowly raised to 50 °C, and at the same time, silicon tetrachloride was slowly dropped into the three-necked flask for reaction, and the exhaust gas was introduced into an aqueous sodium hydroxide solution through a conduit for absorption. When the reaction occurred until no bubbles appeared at the tail suction port, it was subsequently re-reacted for 2 - 3 h, and the reaction was completed. At this time, the temperature of the reaction solution was raised to 80 °C, a bubbler was inserted into the three-necked flask, and it was slowly bubbled with nitrogen gas. The bubbled gas was absorbed by an aqueous sodium hydroxide solution, indicating that the remaining silicon tetrachloride and silicon tetrafluoride gas were completely discharged until the wet pH test paper became neutral when contacting the bubbled gas. At this time, LiPF 2 Cl 4 The solution was cooled to room temperature, rapidly introduced into a constant voltage dropping funnel, sealed, and prepared for use.

[0046] (2) 140 ml of a dimethyl carbonate solvent with a water content lower than 10 ppm by mass was added to another 500 ml three-necked flask, placed in an oil bath pot, and stirred at room temperature. 45.8 g of lithium carbonate (0.62 mol, molecular weight of lithium carbonate 73.9 g / mol) was weighed and rapidly added into the three-necked flask and stirred uniformly to form a dimethyl carbonate slurry of lithium carbonate. LiPF obtained in the previous step (1)2 Cl 4 Attach a constant-voltage dropping funnel containing the solution and a condenser tube to the three-necked flask in step (2), perform nitrogen gas protection, and at 30 °C, LiPF 2 Cl 4 Drop the solution slowly, introduce the generated carbon dioxide gas into the exhaust gas absorption bottle, absorb it with sodium hydroxide solution, and react until no bubbles appear in the exhaust gas absorption bottle. The reaction is completed. Cool to room temperature, filter rapidly to obtain 118 g of a wet solid mixture (filter cake mixture), and transfer this to a flask.

[0047] (3) Add 160 ml (144.32 g) of ethyl acetate to the filter cake mixture obtained in step (2), knead at room temperature, filter after kneading for 3.5 h, collect the kneading solution, perform vacuum distillation at 50 °C, distill to an appropriate saturation state, stop the vacuum distillation, cool to about 0 °C, add dichloromethane and perform stirring crystallization. The crystallization time is 3 h. After filtration, a pure white powdery filter cake is obtained, which is placed in a vacuum drying box and dried at 120 °C for 10 h to obtain 29.5 g of a pure white powdery lithium difluorophosphate solid, and the yield is 93.2%.

[0048] The high-purity lithium difluorophosphate is a high-purity white powdery solid. It is detected by ion chromatography that its purity is ≥99.9%, detected by titration method that the free acid is 20 ppm, measured by Karl Fischer method that the water content is ≤10 ppm, and tested by titration method that the content of Cl - is 0.3 ppm, and measured by ICP-OES method that the sum of the contents of impurity metal ions is 0.5 ppm. Specifically, refer to Table 3.

[0049] (Examples 2 to 6) Except for selecting various substances and their usage amounts, condition parameters, etc. according to Table 1 and Table 2, the others were the same as in Example 1.

[0050] (Comparative Example 1) Lithium difluorophosphate was produced according to the technical route of "lithium hexafluorophosphate + lithium carbonate + anhydrous and oxygen-free state → lithium difluorophosphate" disclosed in the specification of Chinese Patent Application Publication No. 107381531.

[0051] 600 ml of diethyl carbonate (DEC) was added to a 1 L container, 1.0 mol of lithium carbonate was added, the temperature was raised to 62 °C, and then 0.5 mol of lithium hexafluorophosphate was slowly added. The temperature was controlled at 68 °C. After the addition, the temperature was raised to 73 °C and stirred for 2 h. The resulting reaction solution was filtered. After filtration, 102 g of wet solid of the filter cake was obtained. 153 g of ethyl acetate was added and pounded for 5 h. Subsequently, the insoluble filter residue was removed by filtration. The obtained filtrate was vacuum distilled at 60 °C to an appropriate saturated state, placed in an ice bath at 0 °C, and poor solvent dichloromethane was added and stirred for crystallization. The crystallization time was 4 h. The obtained lithium difluorophosphate product was placed in a vacuum drying box and dried at 120 °C for 10 h to obtain 39.42 g of lithium difluorophosphate solid. The yield was 73.0%. The relevant parameter tests are shown in Table 3.

[0052] (Comparative Example 2) Lithium difluorophosphate was produced according to the technical route of "lithium hexafluorophosphate + lithium carbonate + ultrapure water → lithium difluorophosphate" disclosed in the specification of Chinese Patent Application Publication No. 108128764.

[0053] 152 g (1.0 mol) of lithium hexafluorophosphate was dissolved in 1000 ml of dimethyl carbonate, 0.5 g of ultrapure water was added, the temperature was raised to 80 °C, then 148 g (2.0 mol) of lithium carbonate was added, and the mixture was stirred and reacted for 1.5 h. After filtration, 235 g of wet solid of the filter cake was obtained. 329 g of ethyl acetate was added and the mixture was pulped for 5 h. Subsequently, the insoluble filter residue was removed by filtration. The obtained filtrate was vacuum distilled at 60 °C to an appropriate saturated state, placed in an ice bath at 0 °C, and poor solvent dichloromethane was added and stirred for crystallization. The crystallization time was 5 h. The obtained lithium difluorophosphate product was placed in a vacuum drying box and dried at 120 °C for 12 h to obtain 98.5 g of lithium difluorophosphate solid. The yield was 92.1%, and the related parameter tests are shown in Table 3.

[0054] (Comparative Example 3) Lithium difluorophosphate was produced according to the methods of "Lithium hexafluorophosphate + chloride + water (solvent-free) → Lithium difluorophosphate" disclosed in Japanese Patent Publication No. 6226643 and "Lithium hexafluorophosphate + chloride (lithium chloride, silicon tetrachloride, etc.) + water vapor (supplying oxygen element from water) → Lithium difluorophosphate" disclosed in Korean Registered Patent No. 10-2218938.

[0055] 152 g (1.0 mol) of LiPF6 and 258.1 g (2.0 mol) of dimethyldichlorosilane were dissolved in 505 g of ethyl methyl carbonate and cooled to 0 °C. Next, 36 g (2 mol) of water was slowly added dropwise, then the temperature was raised to 25 °C and stirred for 3 h. Subsequently, the temperature was raised to 30 °C. First, vacuum preliminary degassing was performed, and then main degassing was carried out at 30 °C and an absolute pressure of 30 Pa. The obtained slurry was filtered to obtain 217 g of wet filter cake. 325.5 g of ethyl acetate was added and the mixture was pulped for 4 h. Subsequently, the insoluble filter residue was removed by filtration. The obtained filtrate was vacuum distilled at 60 °C to an appropriate saturated state, placed in an ice bath at 0 °C, and poor solvent dichloromethane was added and stirred for crystallization. The crystallization time was 4 h. The obtained lithium difluorophosphate product was placed in a vacuum drying box and dried at 120 °C for 10 h to obtain 94.7 g of lithium difluorophosphate solid. The yield was 87.7%, and the related parameter tests are shown in Table 3.

[0056]

Table 1

[0057] Note: DMC is dimethyl carbonate, DEC is diethyl carbonate, and EMC is ethyl methyl carbonate.

[0058]

Table 2

[0059]

Table 3

[0060] As shown in Table 3, when analyzing the test results of Examples 1-6 and Comparative Examples 1, 2, and 3, it was found that in Examples 1-6, compared with Comparative Examples 1, 2, and 3, there were excellent effects in terms of yield, and significant advantages in terms of product purity. In the reaction system of the present invention, since it does not contain water and does not generate water, it was found that there were absolute advantages in terms of product purity and water content.

[0061] From the test results, it was found that Examples 2, 4, and 6 had higher effects in terms of purity and yield, and it was more advantageous and preferable that the addition amount of the beating solvent was relatively large.

[0062] In short, the present invention first reacts lithium hexafluorophosphate with silicon tetrachloride to produce an intermediate, and further uses the intermediate to react with lithium carbonate to produce lithium difluorophosphate. The intermediate can react more thoroughly with lithium carbonate, directly expressing that the product purity and yield are higher than those of the comparative examples. Also, the present invention can reduce the chlorine ion content to less than 1 ppm by dechlorination to remove impurities. In the reaction system of the present invention, it does not contain water and does not generate water, and the water content of the obtained products can all be reduced to less than 10 ppm, meeting the actual requirements of lithium battery applications.

[0063] The above descriptions are only specific embodiments of the present invention. However, the protection scope of the present invention is not limited thereto. The above is only to explain the present invention by applying specific examples and is only for helping the understanding of the present invention, not for limiting the present invention. Those skilled in the technical field to which the present invention pertains can make several simple inferences, modifications or substitutions based on the concept of the present invention. These means of inference, modification or substitution are also included in the scope of the claims of the present invention.

[0064] (Appendix) (Appendix 1) When there is basically no water, step (1) of stirring and reacting lithium hexafluorophosphate and silicon tetrachloride in a first non-aqueous solvent, degassing to remove impurities, and obtaining a lithium tetrachlorodifluorophosphate solution; Step (2) of dropping the obtained lithium tetrachlorodifluorophosphate solution into a lithium carbonate dispersion for reaction, and filtering to obtain a filtration cake mixture of lithium difluorophosphate and lithium chloride; Step (3) of pounding the filtration cake mixture with ethyl acetate, removing insoluble matters by filtration, concentrating the pounding solution, further adding a non-polar solvent for crystallization, and obtaining lithium difluorophosphate, including A method for producing lithium difluorophosphate, characterized in that.

[0065] (Appendix 2) The charged molar ratio of lithium hexafluorophosphate, silicon tetrachloride and lithium carbonate is 1:(1 - 1.5):(2 - 2.5). A method for producing lithium difluorophosphate according to Appendix 1, characterized in that.

[0066] (Appendix 3) In step (1), the molar concentration of lithium hexafluorophosphate is 1.5 - 4.0 mol / L, preferably 1.5 - 2.5 mol / L. A method for producing lithium difluorophosphate according to Appendix 1 or 2, characterized in that.

[0067] (Appendix 4) In step (1), the reaction temperature of lithium hexafluorophosphate and silicon tetrachloride in the first non-aqueous solvent is 20 to 100 °C, preferably 50 to 90 °C, more preferably 70 to 90 °C, or In step (1), the gas used for degassing to remove impurities is an inert gas, preferably one or more of nitrogen gas, argon gas, helium gas, etc. The temperature for degassing to remove impurities is 60 to 120 °C, preferably 70 to 100 °C, more preferably 85 to 100 °C. A method for producing lithium difluorophosphate according to any one of Appendices 1 to 3, characterized in that.

[0068] (Appendix 5) In step (2), the reaction temperature of the lithium tetrachlorodifluorophosphate and lithium carbonate is 30 to 80 °C, preferably 50 to 80 °C, or In step (2), the lithium carbonate dispersion is obtained by mixing lithium carbonate and a second non-aqueous solvent. The mass ratio of lithium carbonate to the second non-aqueous solvent is 1:(3 to 5), preferably 1:(4.2 to 5). A method for producing lithium difluorophosphate according to any one of Appendices 1 to 4, characterized in that.

[0069] (Appendix 6) The first non-aqueous solvent and the second non-aqueous solvent are each independently one or more of cyclic carbonates, chain carbonates, and cyclic ethers, preferably one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, 1,4-dioxane, and tetrahydrofuran. A method for producing lithium difluorophosphate according to any one of Appendices 1 to 5, characterized in that.

[0070] (Appendix 7) In step (3), the mass ratio of the filter cake mixture to ethyl acetate is 1:(1 - 2), preferably 1:(1.90 - 2). The time for defibrating the filter cake mixture with ethyl acetate is 3 - 5 h, or In step (3), the concentrated defibrated solution is completed by subjecting the filtrate to vacuum distillation. The vacuum distillation temperature is 40 - 80 °C, preferably 45 - 65 °C, more preferably 50 - 65 °C. The method for producing lithium difluorophosphate according to any one of appendices 1 - 6, characterized by the above.

[0071] (Appendix 8) In step (3), the nonpolar solvent is one or more of n - hexane, n - pentane, cyclohexane, heptane, dichloromethane, chloroform, 1,2 - dichloroethane. The method for producing lithium difluorophosphate according to any one of appendices 1 - 7, characterized by the above.

[0072] (Appendix 9) In step (3), the crystallization temperature is 0 - 5 °C, preferably 0 - 3.5 °C. The method for producing lithium difluorophosphate according to any one of appendices 1 - 8, characterized by the above.

[0073] (Appendix 10) In step (3), after crystallization, further filtration is carried out to obtain a filter cake, and the filter cake is dried to obtain lithium difluorophosphate. The temperature for drying the filter cake is 80 - 120 °C, preferably 100 - 120 °C. The method for producing lithium difluorophosphate according to any one of appendices 1 - 9, characterized by the above.

[0074] (Appendix 11) In steps (1) and (2), the reactions are both carried out in an inert gas atmosphere. The inert gas is one or more of nitrogen gas, argon gas, helium gas. The method for producing lithium difluorophosphate according to any one of Appendices 1 to 10, characterized in that...

[0075] (Appendix 12) Produced by the production method according to any one of Appendices 1 to 11, wherein the purity of the lithium difluorophosphate is ≥99.8%, the content of free acid is ≤50 ppm, preferably ≤25 ppm. Lithium difluorophosphate.

[0076] (Appendix 13) The water content is ≤10 ppm, the Cl - content is ≤1 ppm, preferably ≤0.8 ppm, and the sum of the contents of impurity metal ions is ≤2 ppm, preferably ≤1.5 ppm. Lithium difluorophosphate according to Appendix 12, characterized in that...

[0077] (Appendix 14) A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode, and an electrolyte containing the lithium difluorophosphate according to Appendix 12 or 13. Non-aqueous electrolyte battery.

[0078] (Appendix 15) Use in the production of a non-aqueous electrolyte battery of the lithium difluorophosphate according to Appendix 12 or 13.

Claims

**Claim 1**: In an atmosphere with a water content lower than 10 ppm by mass, lithium hexafluorophosphate and silicon tetrachloride are subjected to a stirring reaction in a first non-aqueous solvent, degassed to remove impurities, and a step (1) of obtaining a lithium tetrachlorodifluorophosphate solution; A step (2) of dropping the obtained lithium tetrachlorodifluorophosphate solution into a lithium carbonate dispersion for reaction, and filtering to obtain a filter cake mixture of lithium difluorophosphate and lithium chloride; A step (3) of pulping the filter cake mixture with ethyl acetate, removing insoluble matters by filtration, concentrating the pulping solution, further adding a non-polar solvent for crystallization to obtain lithium difluorophosphate, and A method for producing lithium difluorophosphate, characterized by comprising the above steps. **Claim 2** The charged molar ratio of lithium hexafluorophosphate, silicon tetrachloride, and lithium carbonate is 1:(1 - 1.5):(2 - 2.5), The method for producing lithium difluorophosphate according to claim 1, characterized by the above. **Claim 3** In step (1), the molar concentration of lithium hexafluorophosphate is 1.5 - 4.0 mol / L, The method for producing lithium difluorophosphate according to claim 1 or 2, characterized by the above. **Claim 4** In step (1), the molar concentration of lithium hexafluorophosphate is 1.5 - 2.5 mol / L, The method for producing lithium difluorophosphate according to claim 1 or 2, characterized by the above. **Claim 5** In step (1), the reaction temperature of lithium hexafluorophosphate and silicon tetrachloride in the first non-aqueous solvent is 20 - 100 °C, or In step (1), the gas used for degassing to remove impurities is an inert gas, and the temperature for degassing to remove impurities is 60 - 120 °C, The method for producing lithium difluorophosphate according to any one of claims 1 - 4, characterized by the above. **Claim 6** In step (1), the reaction temperature of lithium hexafluorophosphate and silicon tetrachloride in the first non-aqueous solvent is 50 - 90 °C, or In step (1), the gas used for degassing to remove impurities is an inert gas, and the temperature for degassing to remove impurities is 70 - 100 °C, The method for producing lithium difluorophosphate according to any one of claims 1 - 4, characterized by the above. **Claim 7** In step (2), the reaction temperature between the lithium tetrachlorophosphate difluoride and lithium carbonate is 30 to 80 °C, or In step (2), the lithium carbonate dispersion is prepared by mixing lithium carbonate and a second non-aqueous solvent, and the mass ratio of lithium carbonate to the second non-aqueous solvent is 1:(3 to 5). The method for producing lithium difluorophosphate according to any one of claims 1 to 6, characterized in that.

8. In step (2), the reaction temperature between the lithium tetrachlorophosphate difluoride and lithium carbonate is 50 to 80 °C, or In step (2), the lithium carbonate dispersion is prepared by mixing lithium carbonate and a second non-aqueous solvent, and the mass ratio of lithium carbonate to the second non-aqueous solvent is 1:(4.2 to 5). The method for producing lithium difluorophosphate according to any one of claims 1 to 6, characterized in that.

9. The first non-aqueous solvent and the second non-aqueous solvent are each independently one or more of a cyclic carbonate, a chain carbonate, and a cyclic ether. The method for producing lithium difluorophosphate according to any one of claims 1 to 8, characterized in that.

10. The first non-aqueous solvent and the second non-aqueous solvent are each independently one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, 1,4-dioxane, and tetrahydrofuran. The method for producing lithium difluorophosphate according to any one of claims 1 to 8, characterized in that.

11. In step (3), the mass ratio of the filter cake mixture to ethyl acetate is 1:(1 to 2), and the time for pulping the filter cake mixture with ethyl acetate is 3 to 5 h, or In step (3), the concentration of the pulping liquid is completed by vacuum distilling the filtrate, and the vacuum distillation temperature is 40 to 80 °C. The method for producing lithium difluorophosphate according to any one of claims 1 to 10, characterized in that.

12. In step (3), the mass ratio of the filter cake mixture to ethyl acetate is 1:(1.90 to 2), and the time for pulping the filter cake mixture with ethyl acetate is 3 to 5 h, or In step (3), the concentration of the pulping liquid is completed by vacuum distilling the filtrate, and the vacuum distillation temperature is 45 to 65 °C. The method for producing lithium difluorophosphate according to any one of claims 1 to 10, characterized in that...

13. In step (3), the non-polar solvent is one or more of n-hexane, n-pentane, cyclohexane, heptane, dichloromethane, chloroform, 1,2-dichloroethane. The method for producing lithium difluorophosphate according to any one of claims 1 to 12, characterized in that...

14. In step (3), the temperature of crystallization is 0 to 5°C. The method for producing lithium difluorophosphate according to any one of claims 1 to 13, characterized in that...

15. In step (3), after crystallization, filtration is further performed to obtain a filter cake, and the filter cake is dried to obtain lithium difluorophosphate. The temperature for drying the filter cake is 80 to 120°C. The method for producing lithium difluorophosphate according to any one of claims 1 to 14, characterized in that...

16. In steps (1) and (2), the reaction is carried out in an atmosphere of an inert gas. The inert gas is one or more of nitrogen gas, argon gas, and helium gas. The method for producing lithium difluorophosphate according to any one of claims 1 to 15, characterized in that...

Images