Preparation method of fluorophosphate

Abstract

The invention discloses a preparation method of fluorophosphate, which comprises the following steps: in an organic solvent, anhydrous metaphosphate and oxalyl fluoride react to generate difluorophosphate and / or hexafluorophosphate, the structural formula of the anhydrous metaphosphate is MPO3, the structural formula of the difluorophosphate is MPO2F2, the structural formula of the hexafluorophosphate is MPF6, and in the formulas, M is selected from Li, Na or K. According to the method, high-toxicity and high-irritation raw materials such as hydrofluoric acid, phosphorus pentachloride and sulfuric acid do not need to be adopted, dangerous intermediates such as phosphorus pentafluoride and hexafluorophosphoric acid are not generated in the process, the process is simple and environmentally friendly, and the prepared fluorophosphate product is high in purity, few in impurity and suitable for lithium batteries.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, and in particular to a method for preparing fluorophosphate. Background Art

[0002] Fluorophosphates are mainly represented by hexafluorophosphate and difluorophosphate, among which lithium hexafluorophosphate is the most widely used electrolyte salt in lithium-ion batteries. Lithium difluorophosphate, as an additive with excellent performance, is also widely used in lithium-ion batteries to improve the battery's high and low temperature performance, cycle stability and rate performance. Sodium hexafluorophosphate is also used as the main electrolyte salt in emerging sodium batteries. Potassium hexafluorophosphate can be used as a photocuring agent. Ammonium hexafluorophosphate can be used in catalytic synthesis and other fields.

[0003] 1. Preparation of hexafluorophosphate:

[0004] The preparation methods of hexafluorophosphate are mainly divided into hexafluorophosphate neutralization method and phosphorus pentafluoride method. The hexafluorophosphate neutralization method is only applicable to the preparation of sodium hexafluorophosphate, potassium hexafluorophosphate, and ammonium hexafluorophosphate. When preparing lithium hexafluorophosphate, serious hydrolysis problems will occur. The synthesis of lithium hexafluorophosphate generally uses the phosphorus pentafluoride method, which refers to the formation of the corresponding lithium hexafluorophosphate by phosphorus pentafluoride and metal fluoride salt. However, due to the high activity and high hazard of phosphorus pentafluoride, the synthesis process has high requirements for equipment and operation, and generally needs to be prepared and used immediately.

[0005] At present, the most widely used method for preparing solid lithium hexafluorophosphate in industry is to first prepare phosphorus pentafluoride from phosphorus pentachloride and anhydrous hydrofluoric acid, and then react with lithium fluoride in anhydrous hydrofluoric acid to generate lithium hexafluorophosphate. However, this method will produce a large amount of hydrogen chloride, and after the reaction is completed, the lithium hexafluorophosphate needs to be crystallized and separated at low temperature in anhydrous hydrofluoric acid. To prepare the carbonate solution of lithium hexafluorophosphate (also known as lithium hexafluorophosphate liquid salt, hereinafter referred to as liquid salt), pure phosphorus pentafluoride needs to be passed into the carbonate suspension of lithium fluoride. For example, U.S. Patent No. 2001041158 uses polyphosphoric acid and hydrofluoric acid to react, and adds fuming sulfuric acid as a dehydrating agent to prepare high-purity phosphorus pentafluoride. This method avoids the introduction of chlorine, but does not solve the problem of raw material danger, and produces a large amount of waste sulfuric acid that is difficult to handle; U.S. Patent No. 3592594 proposes to prepare high-purity phosphorus pentafluoride by reacting calcium fluoride, sulfuric acid, phosphoric acid, etc., and then further prepare lithium hexafluorophosphate. Although this method avoids the use of hydrofluoric acid and the introduction of chlorine, it will A large amount of calcium salt waste is produced, and highly toxic gases such as phosphorus oxyfluoride are produced during the reaction. It is rarely used at present; the document Ind.Eng.Chem.Res.2019,58,20491-20494 discloses the use of calcium fluoride and phosphorus pentachloride as raw materials to directly react to generate phosphorus pentafluoride and calcium chloride, and then react with lithium fluoride to generate lithium hexafluorophosphate. This method avoids dangerous hydrofluoric acid raw materials, and the by-product calcium chloride is relatively environmentally friendly, but the reaction temperature is as high as 350°C and the pressure reaches 0.8-1.0MPa. The reaction activity of the reaction materials is very high at this temperature, resulting in extremely high safety requirements for the equipment, and it is rarely used in practice.

[0006] 2. Preparation of difluorophosphate:

[0007] Taking lithium difluorophosphate as an example, its early preparation methods mainly include direct hydrolysis of lithium hexafluorophosphate, lithiation of difluorophosphoric anhydride and lithiation of difluorophosphate, but these methods have long routes, complex processes, many impurities, and poor product quality. After that, some new synthesis processes emerged. For example: Chinese patent CN108862232A discloses a method for preparing lithium difluorophosphate by reacting lithium hexafluorophosphate with lithium metaphosphate; Chinese patent CN103259040A discloses a method for preparing lithium difluorophosphate by an organic tin reagent method; Chinese patent CN104445133A discloses a method for preparing lithium difluorophosphate by reacting a mixed gas obtained by reacting pyrophosphate with fluorine gas and then passing it into an anhydrous hydrogen fluoride solution of lithium fluoride. The above methods either have low product purity or are prone to introduce impurities, which are not suitable for industrial applications.

[0008] At present, in the industrial production of lithium difluorophosphate, lithium hexafluorophosphate and lithium carbonate reaction process as disclosed in Chinese patent CN101208266A are often used, or lithium hexafluorophosphate and siloxane reaction process as disclosed in Chinese patent CN101507041A, the product yield and purity obtained by these two processes are relatively high. However, lithium carbonate process is used to generate a large amount of by-product lithium fluoride, although lithium fluoride can be removed through complicated separation steps, the insoluble content in the product inevitably rises, and due to purity problems, by-product lithium fluoride often cannot be directly utilized, causing waste of resources, and overall production cost is high. And the product obtained by siloxane process has the problem of silicon residue, and the by-product fluorosilane toxicity produced is relatively large, and resource utilization is difficult. Summary of the invention

[0009] In order to solve the above technical problems, the present invention proposes a method for preparing fluorophosphates with simple process, high product conversion rate, high product purity and environmental friendliness.

[0010] The objective of the present invention is achieved through the following technical solutions:

[0011] A method for preparing fluorophosphates specifically comprises the following steps: in an organic solvent, anhydrous metaphosphate and oxalyl fluoride react to generate difluorophosphate and / or hexafluorophosphate, wherein the anhydrous metaphosphate has a structural formula of MPO3, the difluorophosphate has a structural formula of MPO2F2, and the hexafluorophosphate has a structural formula of MPF6, wherein M is selected from Li, Na or K.

[0012] In the reaction of the present invention, anhydrous metaphosphate (MPO3) reacts with oxalyl fluoride (C2O2F2) to generate difluorophosphate (MPO2F2), and the difluorophosphate continues to react with oxalyl fluoride to generate hexafluorophosphate (MPF6).

[0013] When anhydrous metaphosphate and oxalyl fluoride generate difluorophosphate, the reaction equation is as shown in Formula I:

[0014] MPO3+C2O2F2 → MPO2F2+ CO2+ CO Formula Ⅰ

[0015] When further reacting to generate hexafluorophosphate, the reaction equation is shown in Formula II:

[0016] MPO2F2+2C2O2F2 → MPF6+ 2CO2+ 2CO Formula Ⅱ

[0017] Wherein, M is potassium, sodium or lithium.

[0018] Specifically, when the molar ratio of metaphosphate to oxalyl fluoride is 1:0.9 to 1:3.0, the product fluorophosphate is mainly difluorophosphate. The smaller the molar ratio of metaphosphate to oxalyl fluoride, the greater the proportion of difluorophosphate in the product fluorophosphate, but the formation of hexafluorophosphate cannot be completely avoided; when the molar ratio of metaphosphate to oxalyl fluoride is 1:3.0 to 1:3.3, the product fluorophosphate is mainly hexafluorophosphate. When the molar ratio of lithium metaphosphate to oxalyl fluoride is 1:3.3 to 1:4.5, the product fluorophosphate is completely converted into hexafluorophosphate. In addition, when the molar ratio of metaphosphate to oxalyl fluoride is <1:0.9, the raw material conversion rate is low; when the molar ratio of metaphosphate to oxalyl fluoride is >1:4.5, although no other side reactions will occur, it will cause unnecessary waste.

[0019] The two preparation methods described in the present invention can be carried out in a wide temperature range, and different reaction temperatures can be selected according to different solvent systems, different reactor types, etc. Specifically, the reaction temperature of the method described in the present invention is 0-100°C; preferably, the reaction temperature is 10-60°C. When the reaction temperature exceeds 60°C, some products such as lithium hexafluorophosphate will decompose in small amounts, resulting in a decrease in product purity; when the reaction temperature is lower than 10°C, the temperature is too low, resulting in a decrease in the solubility of the raw materials and a decrease in the reaction rate.

[0020] According to the above-mentioned preparation method of fluorophosphate, the raw material oxalyl fluoride can be commercially available, or it can be prepared by reacting oxalyl chloride with a fluoriding agent. Specifically, the fluoriding agent is selected from potassium fluoride, hydrogen fluoride, triethylamine salt of hydrogen fluoride or pyridinium salt of hydrogen fluoride. Regardless of the acquisition method, too high a chlorine content will affect the quality of the final product, and the chlorine content of the oxalyl fluoride is <50ppm; preferably, the chlorine content of the oxalyl fluoride is <5ppm. In addition, due to the low boiling point of oxalyl fluoride, the present invention adopts low-temperature reflux condensation, closed pressurization, gas absorption and other means to reduce the volatilization loss of oxalyl fluoride during the reaction, and there is no special limitation on this.

[0021] In the prior art, oxalyl fluoride exists in two planar configurations, cis and trans (Journal of Baoji University of Arts and Sciences, Vol 27, No. 1, PP. 49-53, Mar 2007), and their reaction activities differ only slightly, and both can undergo the reaction described in the present invention.

[0022] In the reaction system of the present invention, water, impurities such as hydrogen phosphate and dihydrogen phosphate in the metaphosphate will react with oxalyl fluoride to generate hydrogen fluoride, resulting in excessive acidity of the final product. Specifically, the water content of the metaphosphate is <1000ppm; preferably, the water content of the metaphosphate is <100ppm; more preferably, the water content of the metaphosphate is <10ppm. The total content of the hydrogen phosphate and dihydrogen phosphate is <1000ppm; preferably, the total content of the hydrogen phosphate and dihydrogen phosphate is <100ppm; more preferably, the total content of the hydrogen phosphate and dihydrogen phosphate is <10ppm.

[0023] The organic solvent of the present invention can be selected as long as it is an aprotic solvent that does not react with the raw materials or products. Specifically, the organic solvent is selected from at least one of chain carbonates, cyclic carbonates, aliphatic ester solvents, ether solvents, halogenated hydrocarbon solvents, or organic solvents containing heteroatoms such as N, P, and S. The chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the cyclic carbonate is selected from at least one of ethylene glycol carbonate, propylene glycol carbonate, and butylene glycol carbonate; the aliphatic ester solvent is selected from at least one of ethyl acetate, propyl acetate, and butyl acetate; the ether solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, tetrahydrofuran, dioxane, and methyltetrahydrofuran; the halogenated hydrocarbon solvent is selected from at least one of dichloromethane and dichloroethane; the organic solvent containing heteroatoms such as N, P, and S is selected from at least one of acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, methyl pyrrolidone, cyclopentane, and hexamethylphosphoric triamide.

[0024] The present invention can select different organic solvents according to different target products. When the target product is hexafluorophosphate, the organic solvent is preferably at least one of carbonate solvents, ether solvents or acetonitrile; when the target product is a liquid salt of hexafluorophosphate, the organic solvent is preferably at least one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate; when the target product is a mixture of difluorophosphate and hexafluorophosphate, the organic solvent is preferably at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether or tetrahydrofuran.

[0025] The amount of the organic solvent is not particularly limited. The moisture content of the organic solvent is <100 ppm, preferably <5 ppm.

[0026] After the reaction is completed, the product can be further separated and purified by post-treatment processes such as distillation concentration, crystallization, and filtration to obtain a solid product or a solution product directly. The present invention has no particular limitation on the post-treatment process, such as the solubility difference can be used to separate difluorophosphate and hexafluorophosphate.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The method of the present invention does not require the use of highly toxic and irritating raw materials such as hydrofluoric acid, phosphorus pentachloride, and sulfuric acid, and does not produce dangerous intermediates such as phosphorus pentafluoride and hexafluorophosphoric acid during the process. The process is simple and environmentally friendly;

[0029] 2. The product obtained by the method of the present invention has high purity and few impurities, and is suitable for lithium battery application;

[0030] 3. The present invention can prepare solid salts or solution salts of difluorophosphate and hexafluorophosphate according to demand. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0032] Example 1

[0033] Preparation of Lithium Hexafluorophosphate Solid

[0034] In a dry environment with a dew point of <-45°C, add 8.6 g (0.1 mol) of anhydrous lithium metaphosphate (water content <10 ppm) and 150 mL of anhydrous ethylene glycol dimethyl ether (water content <10 ppm) into a flask equipped with a thermometer, a reflux condenser, and a stirrer, and slowly add 32.9 g (0.35 mol) of oxalyl fluoride (chlorine content <5 ppm). Gas release can be observed. The reaction temperature is controlled at 25°C, and a reflux condenser is passed through a reflux circulating liquid with a temperature of <-25°C. After the raw materials are added within 2 hours, the reaction is stirred for 24 hours until most of the solids are dissolved.

[0035] By NMR F 19 NMR detection: In addition to the product lithium hexafluorophosphate and a small amount of raw material oxalyl fluoride, there are basically no other impurity peaks in the reaction liquid. The reaction liquid is first subjected to precise filtration to remove the residual undissolved lithium metaphosphate, and then distilled and concentrated to obtain a solid and dried to obtain 14.9g of lithium hexafluorophosphate solid, with a yield of 98.0% based on lithium metaphosphate.

[0036] Ion chromatography detection: the purity of lithium hexafluorophosphate solid is>99.9%; titration detection: the acidity of lithium hexafluorophosphate solid is 69 ppm (calculated as HF).

[0037] Example 2

[0038] The operation of this embodiment is the same as that of embodiment 1, except that the reaction temperature is lowered to 10° C. and the reaction time is extended to 36 h. The other operations remain unchanged.

[0039] Finally, 14.8 g of lithium hexafluorophosphate was obtained with a yield of 97.3%, a purity of >99.9%, and an acidity of 53 ppm (calculated as HF).

[0040] Example 3

[0041] The operation of this example is the same as that of Example 1, except that the amount of oxalyl fluoride added is increased to 37.6 g (0.4 mol), and the other operations remain unchanged.

[0042] Finally, 15.1 g of lithium hexafluorophosphate was obtained with a yield of 99.3%, a purity of >99.9%, and an acidity of 74 ppm (calculated as HF).

[0043] Example 4

[0044] Preparation of lithium hexafluorophosphate solution

[0045] In a dry environment with an ambient dew point of <-45°C, 8.6 g (0.1 mol) of anhydrous lithium metaphosphate (water content <10 ppm) and 100 g of anhydrous ethyl methyl carbonate (water content <5 ppm) were added to a flask equipped with a thermometer, a reflux condenser, and a stirrer. 31.0 g (0.33 mol) of oxalyl fluoride (chlorine content <5 ppm) was slowly added within 4 hours. Gas release was observed. The reaction temperature was controlled at 15-20°C. At the same time, a refrigeration circulating liquid <-30°C was passed through the reflux condenser. After the addition of the raw materials, the reaction was stirred at 20°C for about 30 hours until most of the solids were dissolved.

[0046] The reaction solution is first finely filtered to remove the residual undissolved lithium salt, and then purged with high-purity nitrogen bubbling for a period of time to remove the residual oxalyl fluoride.

[0047] By NMR F 19 NMR detection: except for the product lithium hexafluorophosphate, there are basically no other impurity peaks. Finally, 114g of lithium hexafluorophosphate ethyl methyl carbonate solution was obtained; the lithium content was detected by ICP, and the conversion showed that the concentration of lithium hexafluorophosphate in the solution was 13%, and the recovery rate was 97.3% based on lithium metaphosphate; and the acidity was 26ppm (based on HF) after titration.

[0048] Example 5

[0049] Preparation of lithium hexafluorophosphate solution containing a small amount of lithium difluorophosphate

[0050] The operation of this embodiment is the same as that of embodiment 2, except that the amount of oxalyl fluoride added is reduced to 28.2 g (0.3 mol), and the other operations remain unchanged.

[0051] After testing and calculation, a total of 113 g of ethyl methyl carbonate solution containing 12.8% lithium hexafluorophosphate and 0.15% lithium difluorophosphate was obtained, with a yield of 96.7% based on lithium metaphosphate, and a solution acidity of 23 ppm (based on HF).

[0052] Example 6

[0053] Preparation of lithium difluorophosphate and lithium hexafluorophosphate solids

[0054] In a dry environment with an ambient dew point of <-45°C, add 8.6g (0.1mol) of anhydrous lithium metaphosphate (water content <5ppm) and 200mL of anhydrous ethylene glycol dimethyl ether (water content <10ppm) to a flask equipped with a thermometer, a reflux condenser, and a stirrer, slowly add 10.3g (0.11mol) of oxalyl fluoride (chlorine concentration <5ppm), control the reaction temperature at 10°C, and pass a reflux condenser through a reflux condenser with a temperature of <-25°C. After adding the raw materials within 2 hours, stir and react for 24 hours until most of the solid is dissolved. Filter the reaction solution to remove the undissolved lithium salt raw material (2.0g, which can be applied to the next reaction), then distill and concentrate to obtain a solid, add 50mL of dimethyl carbonate to it, stir, filter, and dry to obtain 6.5g of solid.

[0055] After testing and calculation: the solid is lithium difluorophosphate with a purity of >99.9%, and the yield is 60.2% based on lithium metaphosphate; the filtrate can be distilled and concentrated to 5mL again, and 0.3g of ethylene glycol dimethyl ether is added with stirring, and filtered and dried again to obtain 2.0g of lithium hexafluorophosphate solid with a purity of >99.9%, with a yield of 13.1%; the mother liquor also contains about 0.5g of lithium hexafluorophosphate and lithium difluorophosphate accounting for about 2% of the mass of lithium hexafluorophosphate. The combined yield of the several parts is 76.6% (if calculated based on the converted lithium metaphosphate, the yield is 98.9%).

[0056] Example 7

[0057] Simultaneous preparation of lithium difluorophosphate solid and lithium hexafluorophosphate solution containing a small amount of lithium difluorophosphate

[0058] In a dry environment with an ambient dew point of <-45°C, add 8.6g (0.1mol) of anhydrous lithium metaphosphate (water content <10ppm) and 200mL of anhydrous ethylene glycol dimethyl ether (water content <10ppm) to a flask equipped with a thermometer, a reflux condenser, and a stirrer, slowly add 18.8g (0.2mol) of oxalyl fluoride (chlorine concentration <5ppm), control the reaction temperature at 25°C, and pass a reflux condenser through a reflux condenser with a temperature of <-25°C. After adding the raw materials for 2 hours, stir and react for 24 hours until most of the solid is dissolved. Filter the reaction solution to remove the undissolved lithium salt raw material (1.5g, which can be applied to the next reaction), then distill and concentrate to obtain a solid, add 50mL of ethyl methyl carbonate to it, stir, and filter to obtain 2.2g of solid.

[0059] After testing and calculation: the solid is lithium difluorophosphate with a purity of >99.9%, and the yield is 20.4%; the obtained solution is 56.6g in total, containing 15.9% lithium hexafluorophosphate and 0.13% lithium difluorophosphate, and the yield is 60.0%; the total yield of the two parts combined is 80.4% (if calculated based on the converted lithium metaphosphate, the yield is 97.8%).

[0060] Example 8

[0061] Preparation of solid sodium hexafluorophosphate

[0062] The operation of this embodiment is the same as that of embodiment 1, except that the type of metaphosphate is changed, and sodium metaphosphate is used instead of lithium metaphosphate, and the added amount is 10.2 g (0.1 mol). Other operations remain unchanged.

[0063] After testing and calculation: a total of 16.3 g of sodium hexafluorophosphate, a yield of 97.0%, a purity of >99.9%, and an acidity of 41 ppm.

[0064] Example 9

[0065] Preparation of Potassium Hexafluorophosphate Solid

[0066] The operation of this embodiment is the same as that of embodiment 1, except that the type of metaphosphate is changed, potassium metaphosphate is used instead of lithium metaphosphate, the added amount is 11.8 g (0.1 mol), and the reaction temperature is increased to 40° C., and other operations remain unchanged.

[0067] After testing and calculation: a total of 17.8 g of potassium hexafluorophosphate, a yield of 96.7%, a purity of >99.9%, and an acidity of 33 ppm.

Claims

1. A method for preparing a fluorophosphate, characterized in that: In an organic solvent, anhydrous metaphosphate reacts with oxalyl fluoride to generate difluorophosphate and / or hexafluorophosphate, wherein the structural formula of the anhydrous metaphosphate is MPO3, the structural formula of the difluorophosphate is MPO2F2, and the structural formula of the hexafluorophosphate is MPF6, wherein M is selected from Li, Na or K.

2. The method for preparing the fluorophosphate according to claim 1, characterized in that: When anhydrous metaphosphate and oxalyl fluoride react in a molar ratio of 1:0.9 to 1:3.3, a mixture of difluorophosphate and hexafluorophosphate is generated.

3. The method for preparing the fluorophosphate according to claim 1, characterized in that: When anhydrous metaphosphate and oxalyl fluoride react in a molar ratio of 1:3.3 to 1:4.5, hexafluorophosphate is generated.

4. The method for preparing the fluorophosphate according to claim 1, characterized in that: The reaction temperature is 0-100°C.

5. The method for preparing the fluorophosphate according to claim 1, characterized in that: The chlorine content of the oxalyl fluoride is less than 50 ppm; the water content of the metaphosphate is less than 1000 ppm, and the total content of the hydrogen phosphate and dihydrogen phosphate of the metaphosphate is less than 1000 ppm; and the water content of the organic solvent is less than 100 ppm.

6. The method for preparing the fluorophosphate according to claim 5, characterized in that: The chlorine content of the oxalyl fluoride is <5ppm; the water content of the metaphosphate is <10ppm, and the total content of the hydrogen phosphate and dihydrogen phosphate of the metaphosphate is <100ppm; the water content of the organic solvent is <5ppm.

7. The method for preparing the fluorophosphate according to claim 1, characterized in that: The organic solvent is selected from at least one of chain carbonates, cyclic carbonates, aliphatic lipid solvents, ether solvents, halogenated hydrocarbon solvents, and organic solvents containing heteroatoms such as N, P, and S.

8. The method for preparing the fluorophosphate according to claim 7, characterized in that: The chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the cyclic carbonate is selected from at least one of ethylene glycol carbonate, propylene glycol carbonate, and butylene glycol carbonate; the aliphatic ester solvent is selected from at least one of ethyl acetate, propyl acetate, and butyl acetate; the ether solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, tetrahydrofuran, dioxane, and methyltetrahydrofuran; the halogenated hydrocarbon solvent is selected from at least one of dichloromethane and dichloroethane; the organic solvent containing heteroatoms such as N, P, and S is selected from at least one of acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, methyl pyrrolidone, cyclopentane, and hexamethylphosphoric triamide.

9. The method for preparing the fluorophosphate according to claim 2, characterized in that: The organic solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether or tetrahydrofuran.

10. The method for preparing the fluorophosphate according to claim 3, characterized in that: The organic solvent is selected from at least one of a carbonate solvent, an ether solvent or acetonitrile.