Method for producing lithium difluorophosphate, method for producing difluorophosphate ester, lithium difluorophosphate, method for producing nonaqueous electrolyte, and method for producing nonaqueous secondary battery

Abstract

The present invention provides a method for producing lithium difluorophosphate, wherein the method allows a difluorophosphate ester to react with a lithium salt compound in a non-aqueous organic solvent, wherein water is not used as a raw material in the reaction; the present invention also provides a method for producing difluorophosphate ester, which has a step of allowing a dihalogenated phosphate ester to react with a fluorinating agent containing a hydrofluoric acid concentration of less than 15 mol% in a non-aqueous organic solvent; the present invention also provides lithium difluorophosphate, wherein the value of the relationship (d90-d10) / MV represented by the particle size d90 of the volume cumulative distribution of 90%, the particle size d10 of the volume cumulative distribution of 10% and the volume average particle size MV is less than 10; the present invention also provides a method for producing a non-aqueous electrolyte using the above-mentioned production method and a method for producing a non-aqueous secondary battery.

Description

Technical Field

[0001] The present invention relates to a method for producing lithium difluorophosphate, a method for producing difluorophosphate ester, lithium difluorophosphate, a method for producing a nonaqueous electrolyte solution and a method for producing a nonaqueous secondary battery. Background Art

[0002] In recent years, the battery as an electrochemical device has attracted attention for small-sized, high-energy-density power storage systems for information-related equipment and communication equipment, i.e., computers, video cameras, digital cameras, mobile phones, smart phones, power tools, etc., or large-sized, high-power power storage systems for auxiliary power supplies and power storage for electric vehicles, hybrid vehicles, fuel cell vehicles, etc. As a candidate, non-aqueous electrolyte batteries such as lithium-ion batteries, lithium batteries, and lithium-ion capacitors can be listed.

[0003] Most of these non-aqueous electrolyte batteries have been put into practical use, but they are not durable enough for various applications. In particular, they deteriorate significantly at high temperatures above 45°C, which poses a major problem when used as vehicle batteries.

[0004] So far, as a means for improving the cycle characteristics, high temperature storage properties, and durability of non-aqueous electrolyte batteries, the optimization of various battery components including positive electrode active materials or negative electrode active materials has been studied. The technology related to non-aqueous electrolytes is no exception, and various additives have been proposed to inhibit the decomposition of the electrolyte on the surface of the active positive electrode or negative electrode and cause degradation. For example, Patent Document 1 proposes a scheme to improve battery characteristics by adding vinylene carbonate to the electrolyte. This method prevents the decomposition of the electrolyte on the surface by covering the electrode with a polymer film produced by the polymerization of vinylene carbonate, but it is also difficult for lithium ions to pass through the film, so there is a problem of increased internal resistance. In addition, it is known that the addition of lithium difluorophosphate disclosed in Patent Document 2 can effectively reduce the internal resistance.

[0005] Various synthesis methods have been developed and reported for lithium difluorophosphate used as an additive (eg, Patent Documents 3 to 7).

[0006] As a method for producing the above-mentioned lithium difluorophosphate, for example, as described in step (2) of Patent Document 7, it discloses a method for obtaining lithium difluorophosphate by reacting a difluorophosphate ester with water and a lithium salt (e.g., lithium chloride). In this method, the difluorophosphate ester is rapidly hydrolyzed in water, and the generated difluorophosphoric acid further reacts with lithium chloride to obtain lithium difluorophosphate.

[0007] For example, as described in step (1) of Patent Document 7, it is disclosed that the difluorophosphate ester as a raw material of the above production method can be obtained by allowing a dihalogenated phosphate compound and a fluorinating agent to interact in a non-aqueous solvent in the presence of a catalyst.

[0008] As a method for obtaining a difluorophosphate ester without using a catalyst, Non-Patent Document 1 discloses a method of reacting a dichlorophosphate ester (here, ethyl ester) with potassium fluoride in acetonitrile.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent No. 3438636

[0012] Patent Document 2: Japanese Patent No. 3439085

[0013] Patent Document 3: Japanese Patent No. 4604505

[0014] Patent Document 4: Japanese Patent No. 5277550

[0015] Patent Document 5: Japanese Patent No. 5893522

[0016] Patent Document 6: International Publication No. 2015 / 122511

[0017] Patent Document 7: Japanese Patent No. 6443903

[0018] Non-patent literature

[0019] Non-patent document 1: ChemPhysChem 2010, 11, 2871-2878 Summary of the invention

[0020] Technical Problems to be Solved by the Invention

[0021] Patent Document 3 states that lithium hexafluorophosphate (hereinafter referred to as LiPF6) can be produced by reacting with silicon dioxide, but it takes a very long time of up to 3 days to complete the reaction at a reaction temperature of 50°C. In order to increase the reaction rate, a method of increasing the reaction temperature is also considered, but at a temperature above 60°C, LiPF6 begins to decompose, which has the risk of increasing impurities, so this is also a problem in this method.

[0022] In addition, Patent Document 4 discloses a method for producing lithium difluorophosphate with good selectivity in a short time by reacting a halide other than a fluoride with LiPF6 and water in a non-aqueous solvent. However, this method, like the above-mentioned method using silicon dioxide, requires the removal of 4 of the 6 molecules of fluorine atoms contained in the raw material LiPF6. Therefore, in addition to the increase in its waste disposal costs, it cannot be said to be an efficient mass production method from the perspective of effectively utilizing limited fluorine resources.

[0023] As a method for improving the utilization efficiency of fluorine, patent document 5 discloses a method for obtaining lithium difluorophosphate by reacting lithium dichlorophosphate synthesized by lithium carbonate and phosphorus oxychloride with hydrofluoric acid, and in addition, patent document 6 discloses a method for obtaining lithium difluorophosphate by reacting lithium dichlorophosphate synthesized by phosphorus oxychloride and lithium hydroxide with triethylamine hydrofluorate (in terms of molar ratio, the ratio of triethylamine to hydrofluoric acid is 1:2.04), but in these methods, a side reaction of fluorine anions reacting with lithium cations to generate lithium fluoride occurs. Therefore, there is the following technical problem: in order to obtain high-purity lithium difluorophosphate, it is necessary to remove tiny lithium fluorides based on filtration, which requires a lot of labor.

[0024] As a method that improves the utilization efficiency of fluorine compared to Patent Documents 3 and 4 using LiPF6 as a raw material and does not produce lithium fluoride byproducts as described in Patent Documents 5 and 6, Patent Document 7 discloses a method for obtaining lithium difluorophosphate by reacting difluorophosphate with water and a lithium salt (e.g., lithium chloride). In this method, water is used as a necessary raw material (the embodiment discloses that water is used at a ratio of 0.8 to 1.7% by mass relative to the total amount of raw materials (difluorophosphate + lithium salt + water + non-aqueous solvent)), difluorophosphate is rapidly hydrolyzed in water, and the generated difluorophosphoric acid further reacts with lithium chloride, thereby obtaining lithium difluorophosphate.

[0025] However, the less the raw materials used in the reaction, the less time required for adding the raw materials can be spent, and the more efficient it is. Therefore, from this point of view, a new production method is sought.

[0026] In addition, according to the method shown in Non-Patent Document 1, difluorophosphate can be produced without using a special catalyst, but the selectivity of fluorination (the ratio of the target product in the group of fluorides obtained by fluorination. Hereinafter also referred to as "fluorination selectivity") may sometimes decrease depending on the manufacturer or production batch of the fluorinating agent, and therefore a method that can stably achieve a higher selectivity is strongly sought.

[0027] Furthermore, the dissolution of lithium difluorophosphate powder in a non-aqueous solvent is an exothermic reaction, but lithium hexafluorophosphate, which is a main electrolyte contained in a non-aqueous electrolyte of a lithium ion battery, decomposes at a temperature greater than 60° C. Therefore, in order to add an arbitrary amount of lithium difluorophosphate to a non-aqueous electrolyte to produce an electrolyte containing the additive, it is necessary to pay close attention to suppressing the rise in the internal temperature.

[0028] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel method for producing lithium difluorophosphate, a method for producing a nonaqueous electrolyte solution, and a method for producing a nonaqueous secondary battery, which use less raw materials in the reaction and are excellent in efficiency.

[0029] In addition, the present invention also aims to provide a method for producing a difluorophosphate ester capable of stably achieving high fluorination selectivity and yield, a method for producing lithium difluorophosphate derived from the difluorophosphate ester, a method for producing a non-aqueous electrolyte solution using the lithium difluorophosphate, and a method for producing a non-aqueous secondary battery.

[0030] Furthermore, the present invention aims to provide lithium difluorophosphate which generates less heat when dissolved in a non-aqueous electrolyte in the form of an additive.

[0031] Technical means to solve technical problems

[0032] The present invention utilizes the following scheme to solve the above technical problems.

[0033] <1>

[0034] A method for producing lithium difluorophosphate, comprising reacting a difluorophosphate ester represented by the following general formula (1A) with a lithium salt compound in a non-aqueous organic solvent, wherein:

[0035] No water is used as a starting material in the reaction,

[0036] [Chemical formula 1]

[0037]

[0038] In the general formula (1A), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

[0039] <2>

[0040] according to <1> The method for producing lithium difluorophosphate, wherein the water content in the total amount of the difluorophosphate ester represented by the general formula (1A), the lithium salt compound and the non-aqueous organic solvent before the reaction is 200 mass ppm or less.

[0041] <3>

[0042] according to <1> or <2> The method for producing lithium difluorophosphate, wherein the water content in the total amount of the difluorophosphate ester represented by the general formula (1A), the lithium salt compound and the non-aqueous organic solvent before the reaction is 145 mass ppm or less.

[0043] <4>

[0044] according to <1> ~ <3> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein the water content in the total amount of the difluorophosphate ester represented by the general formula (1A), the lithium salt compound and the nonaqueous organic solvent before the reaction is 135 ppm by mass or less.

[0045] <5>

[0046] according to <1> ~ <4> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein the lithium salt compound is at least one selected from the group consisting of lithium chloride, lithium bromide, lithium fluoride, lithium carbonate, lithium acetate, and lithium propionate.

[0047] <6>

[0048] according to <1> ~ <5> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein the nonaqueous organic solvent is at least one selected from the group consisting of carbonates, chain esters, ethers, and ketones.

[0049] <7>

[0050] according to <6> The method for producing lithium difluorophosphate, wherein the carbonate is at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate and butylene carbonate, the chain ester is at least one selected from the group consisting of ethyl acetate, methyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate, the ether is at least one selected from the group consisting of dimethoxyethane, dimethoxymethane, tetrahydrofuran and diethyl ether, and the ketone is at least one selected from the group consisting of acetone, ethyl methyl ketone and diethyl ketone.

[0051] <8>

[0052] according to <1> ~ <7> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein the reaction is carried out under protection of an inert gas.

[0053] <9>

[0054] A method for producing a non-aqueous electrolyte using <1> ~ <8> The lithium difluorophosphate obtained by any one of the production methods described above.

[0055] <10>

[0056] A method for manufacturing a non-aqueous secondary battery using <9> The non-aqueous electrolyte obtained by the above-mentioned production method.

[0057] <11>

[0058] A method for producing a difluorophosphate ester, which is a method for producing a difluorophosphate ester represented by the following general formula (2), comprising the steps of reacting a dihalogenated phosphate ester represented by the following general formula (1) with a fluorinating agent containing hydrofluoric acid at a concentration of 15 mol % or less in a non-aqueous organic solvent (a),

[0059] [Chemical formula 2]

[0060]

[0061] In the general formula (1), X represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom, and Y represents a chlorine atom, a bromine atom or an iodine atom. In the general formulas (1) and (2), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

[0062] <12>

[0063] according to <11> In the method for producing difluorophosphate, the non-aqueous organic solvent (a) is at least one selected from the group consisting of carbonates, chain esters and ketones.

[0064] <13>

[0065] according to <12> The method for producing difluorophosphate, wherein the non-aqueous organic solvent (a) is at least one selected from the group consisting of carbonates and chain esters,

[0066] The carbonates are at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate and butylene carbonate; the chain esters are at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate.

[0067] <14>

[0068] according to <11> ~ <13> The method for producing a difluorophosphate ester according to any one of the preceding claims, wherein the fluorinating agent is at least one selected from the group consisting of hydrofluoric acid salts of organic amines and inorganic fluorides.

[0069] <15>

[0070] according to <14> The method for producing difluorophosphate ester, wherein the hydrofluoric acid salt of the organic amine is at least one selected from the group consisting of triethylamine monohydrofluoric acid salt, tetramethylethylenediamine dihydrofluoric acid salt and pyridine monohydrofluoric acid salt; and the inorganic fluoride is at least one selected from the group consisting of ammonium fluoride, sodium fluoride, potassium fluoride, cesium fluoride and zinc fluoride.

[0071] <16>

[0072] according to <11> The method for producing difluorophosphate ester, wherein the fluorinating agent is at least one selected from sodium fluoride, ammonium fluoride, triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride; the non-aqueous organic solvent (a) is at least one selected from esters having a relative dielectric constant of 8 or less at 25°C, ethers having a relative dielectric constant of 8 or less at 25°C and propylene carbonate.

[0073] <17>

[0074] according to <11> ~ <16> The method for producing a difluorophosphate ester according to any one of the preceding claims, wherein no catalyst is used in the reaction of step 1.

[0075] <18>

[0076] according to <11> The method for producing difluorophosphate, wherein the fluorinating agent is at least one selected from sodium fluoride, ammonium fluoride, cesium fluoride, zinc fluoride, triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride,

[0077] The nonaqueous organic solvent (a) is at least one selected from esters having a relative dielectric constant of 8 or less at 25°C and ethers having a relative dielectric constant of 8 or less at 25°C.

[0078] <19>

[0079] according to <18> The method for producing difluorophosphate ester, wherein the ester having a relative dielectric constant of 8 or less at 25° C. is at least one selected from ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, amyl acetate, methyl propionate, ethyl propionate, propyl propionate and dibutyl phthalate.

[0080] <20>

[0081] according to <18> In the method for producing difluorophosphate, the ether having a relative dielectric constant of 8 or less at 25° C. is at least one selected from 1,2-dimethoxyethane, tetrahydrofuran, diethyl ether and diethylene glycol diethyl ether.

[0082] <21>

[0083] A method for producing lithium difluorophosphate, which has the advantages of using <11> ~ <20> Step 2 of reacting the difluorophosphate ester represented by the general formula (2) produced by the method for producing a difluorophosphate ester described in any one of the above, a lithium salt compound (b), and water in a non-aqueous organic solvent (b).

[0084] <22>

[0085] according to <21> The method for producing lithium difluorophosphate, wherein the non-aqueous organic solvent (b) is at least one selected from the group consisting of esters, n-hexane, cyclohexane, n-heptane, isoheptane, benzene, toluene, xylene, acetonitrile, dimethyl ether, diethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, diethylene glycol dimethyl ether, anisole, phenethyl ether and tetrahydrofuran.

[0086] <23>

[0087] according to <21> or <22> The method for producing lithium difluorophosphate, wherein the lithium salt compound (b) is at least one selected from the group consisting of lithium chloride, lithium bromide, lithium fluoride, lithium iodide, lithium hydroxide, lithium carbonate, lithium bicarbonate, lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, lithium metaphosphate, lithium acetate and lithium sulfate.

[0088] <24>

[0089] according to <21> ~ <23> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein the molar ratio of the difluorophosphate ester represented by the general formula (2) to the lithium salt compound (b) and water in the step 2 is 1:2:2 to 1:1:0.01.

[0090] <25>

[0091] A method for producing lithium difluorophosphate, which has the advantages of using <11> ~ <20> Step 3 of reacting the difluorophosphate represented by the general formula (2) produced by the method for producing a difluorophosphate described in any one of the preceding claims with a lithium salt compound (c) in a non-aqueous organic solvent (c),

[0092] The water content in the total amount of the difluorophosphate represented by the general formula (2), the lithium salt compound (c) and the nonaqueous organic solvent (c) before the reaction in the step 3 is 200 ppm by mass or less.

[0093] <26>

[0094] according to <25> The method for producing lithium difluorophosphate, wherein the water content in the total amount of the difluorophosphate represented by the general formula (2), the lithium salt compound (c) and the non-aqueous organic solvent (c) before the reaction in step 3 is 145 mass ppm or less.

[0095] <27>

[0096] according to <25> or <26> In the method for producing lithium difluorophosphate, the lithium salt compound (c) is at least one selected from the group consisting of lithium chloride, lithium bromide, lithium fluoride, lithium carbonate, lithium acetate and lithium propionate.

[0097] <28>

[0098] according to <25> ~ <27> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein the nonaqueous organic solvent (c) is at least one selected from the group consisting of esters, ethers, and ketones.

[0099] <29>

[0100] according to <28> The method for producing lithium difluorophosphate, wherein the non-aqueous organic solvent (c) comprises an ester,

[0101] The ester is at least one selected from the group consisting of cyclic carbonates, chain carbonates, chain esters, and cyclic esters.

[0102] <30>

[0103] A method for producing lithium difluorophosphate, comprising: using a chlorinating agent to <11> ~ <20> Step 4: after chlorinating the difluorophosphate ester represented by the general formula (2) produced by the method for producing a difluorophosphate ester described in any one of the preceding claims to convert it into difluoromonochlorophosphoric acid oxide, hydrolyzing it to synthesize difluorophosphoric acid, and further neutralizing it.

[0104] <31>

[0105] according to <30> The method for producing lithium difluorophosphate, wherein the chlorinating agent is phosphorus oxychloride.

[0106] <32>

[0107] according to <30> or <31> The method for producing lithium difluorophosphate, wherein the neutralization is performed by adding lithium hydride or lithium chloride to neutralize difluorophosphoric acid.

[0108] <33>

[0109] according to <21> ~ <32> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein at least one of the steps 1 to 4 is performed under protection of an inert gas.

[0110] <34>

[0111] A method for producing a non-aqueous electrolyte, using <21> ~ <33> The lithium difluorophosphate obtained by the method for producing lithium difluorophosphate described in any one of the above.

[0112] <35>

[0113] A method for manufacturing a non-aqueous secondary battery, using <34> A non-aqueous electrolyte obtained by the method for producing a non-aqueous electrolyte.

[0114] <36>

[0115] according to <1> ~ <8> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein the difluorophosphate represented by the general formula (1A) is produced by a method for producing difluorophosphate having the following step 1, wherein the step 1 is a step of reacting a dihalogenated phosphate represented by the general formula (1) with a fluorinating agent containing a hydrofluoric acid concentration of 15 mol % or less in a non-aqueous organic solvent (a),

[0116] [Chemical formula 3]

[0117]

[0118] In the general formula (1), X represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom, and Y represents a chlorine atom, a bromine atom or an iodine atom. In the general formula (1), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted with a halogen atom.

[0119] <37>

[0120] according to <36> In the method for producing lithium difluorophosphate, the nonaqueous organic solvent (a) is at least one selected from the group consisting of carbonates, chain esters and ketones.

[0121] <38>

[0122] according to <37> The method for producing lithium difluorophosphate, wherein the non-aqueous organic solvent (a) is at least one selected from the group consisting of carbonates and chain esters,

[0123] The carbonates are at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate and butylene carbonate, and the chain esters are at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate.

[0124] <39>

[0125] according to <36> ~ <38> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein the fluorinating agent is at least one selected from the group consisting of hydrofluoric acid salts of organic amines and inorganic fluorides.

[0126] <40>

[0127] according to <39> The method for producing lithium difluorophosphate, wherein the hydrofluoric acid salt of the organic amine is at least one selected from the group consisting of triethylamine monohydrofluoric acid salt, tetramethylethylenediamine dihydrofluoric acid salt and pyridine monohydrofluoric acid salt, and the inorganic fluoride is at least one selected from the group consisting of ammonium fluoride, sodium fluoride, potassium fluoride, cesium fluoride and zinc fluoride.

[0128] <41>

[0129] according to <36> The method for producing lithium difluorophosphate, wherein the fluorinating agent is at least one selected from sodium fluoride, ammonium fluoride, triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride, and the non-aqueous organic solvent (a) is at least one selected from esters having a relative dielectric constant of less than 8 at 25°C, ethers having a relative dielectric constant of less than 8 at 25°C and propylene carbonate.

[0130] <42>

[0131] according to <36> ~ <41> The method for producing lithium difluorophosphate according to any one of the preceding claims, wherein no catalyst is used in the reaction in step 1.

[0132] <43>

[0133] according to <36> The method for producing lithium difluorophosphate, wherein the fluorinating agent is at least one selected from sodium fluoride, ammonium fluoride, cesium fluoride, zinc fluoride, triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride,

[0134] The nonaqueous organic solvent (a) is at least one selected from esters having a relative dielectric constant of 8 or less at 25°C and ethers having a relative dielectric constant of 8 or less at 25°C.

[0135] <44>

[0136] according to <43> The method for producing lithium difluorophosphate, wherein the ester having a relative dielectric constant of 8 or less at 25° C. is at least one selected from ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, amyl acetate, methyl propionate, ethyl propionate, propyl propionate and dibutyl phthalate.

[0137] <45>

[0138] according to <43> In the method for producing lithium difluorophosphate, the ether having a relative dielectric constant of 8 or less at 25° C. is at least one selected from 1,2-dimethoxyethane, tetrahydrofuran, diethyl ether and diethylene glycol diethyl ether.

[0139] <46>

[0140] A method for producing a non-aqueous electrolyte using <36> ~ <45> The lithium difluorophosphate obtained by any one of the production methods described above.

[0141] <47>

[0142] A method for manufacturing a non-aqueous secondary battery using <46> The non-aqueous electrolyte obtained by the above-mentioned production method.

[0143] <48>

[0144] A lithium difluorophosphate, wherein the value of the relationship (d90-d10) / MV represented by the particle size d90 at 90% of the volume cumulative distribution, the particle size d10 at 10% of the volume cumulative distribution, and the volume average particle size MV is 10 or less.

[0145] <49>

[0146] according to <48> The lithium difluorophosphate is characterized in that the concentration of hydrofluoric acid mixed therein is 4000 mass ppm or less.

[0147] Effects of the Invention

[0148] According to the present invention, it is possible to provide a novel method for producing lithium difluorophosphate, a method for producing a nonaqueous electrolyte solution, and a method for producing a nonaqueous secondary battery, which use less raw materials in the reaction and are excellent in efficiency.

[0149] Furthermore, according to the present invention, there can be provided a method for producing a difluorophosphate ester capable of stably achieving high fluorination selectivity and yield, a method for producing lithium difluorophosphate derived from the difluorophosphate ester, a method for producing a nonaqueous electrolyte solution using the lithium difluorophosphate, and a method for producing a nonaqueous secondary battery.

[0150] Furthermore, according to the present invention, it is possible to provide lithium difluorophosphate which generates little heat when dissolved in a non-aqueous electrolyte solution as an additive. BRIEF DESCRIPTION OF THE DRAWINGS

[0151] Figure 1 This is a SEM (Scanning Electron Microscope) image of the lithium difluorophosphate of Example A.

[0152] Figure 2 is a SEM image of lithium difluorophosphate of Example A.

[0153] Figure 3 This is a SEM image of lithium difluorophosphate of Example C.

[0154] Figure 4 This is a SEM image of lithium difluorophosphate of Example C. DETAILED DESCRIPTION

[0155] Hereinafter, the present invention will be described in detail, but the description of the components described below is an example of an embodiment of the present invention, and the present invention is not limited to these specific contents. Various modifications can be implemented within the scope of the gist.

[0156] In the present specification, "to" means that the numerical values ​​described before and after it are the upper limit and the lower limit.

[0157] [Method for producing lithium difluorophosphate]

[0158] The present invention provides a method for producing lithium difluorophosphate, which comprises reacting a difluorophosphate ester represented by the following general formula (1A) with a lithium salt compound in a non-aqueous organic solvent, wherein water is not used as a raw material in the reaction.

[0159] [Chemical formula 4]

[0160]

[0161] In the general formula (1A), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

[0162] In the present invention, by not using water as a raw material in the reaction, the raw materials used in the reaction can be reduced compared to the production method of Patent Document 7 which requires water as an essential raw material, and the time required for adding the raw materials can be reduced, thereby improving efficiency.

[0163] In the present invention, “not using water as a raw material” means that water is not actively added as a raw material. More specifically, the water content in the system before the reaction is 7000 mass ppm or less relative to the total amount of the raw materials.

[0164] <Water content in the total amount of raw materials before reaction>

[0165] In the manufacturing method of lithium difluorophosphate of the present invention (hereinafter also referred to as the manufacturing method of the present invention), it is more preferred that the water content contained in the total amount of raw materials before the reaction is 1000 mass ppm or less, further preferably 500 mass ppm or less, and particularly preferably 200 mass ppm or less. By setting the water content in the total amount of raw materials before the reaction to 200 mass ppm or less, the side reactions shown in the following 1) to 3) can be suppressed, so that lithium difluorophosphate as the target product can be obtained with high purity.

[0166] 1) The hydrolysis of lithium difluorophosphate as the target product leads to the formation of lithium monofluorophosphate

[0167] 2) The difluorophosphate represented by the general formula (1A) reacts with water to generate alcohol (ROH) as a byproduct.

[0168] 3) The by-product alcohol (ROH) reacts with lithium difluorophosphate to generate by-product compounds (LiPO2F(OR)) and hydrofluoric acid

[0169] In addition, R in ROH and LiPO2F(OR) is the same as R in the general formula (1A).

[0170] From the viewpoint of further reducing the amount of hydrofluoric acid mixed in, the water content in the total amount of the raw materials before the reaction is preferably 145 mass ppm or less, more preferably 135 mass ppm or less.

[0171] For the method of putting down in writing in patent documentation 7, owing to use water as necessary raw material, therefore by-product alcohol and hydrochloric acid will inevitably be produced.The existence of this alcohol is a problem, even if the inventor of the present application finds that it is removed by heating under reduced pressure drying, also can be firmly added to lithium difluorophosphate by hydrogen bond, extremely difficult to remove alcohol itself fully, not only that, also there is lithium difluorophosphate and alcohol reaction to produce this serious problem of hydrofluoric acid.And, the inventor of the present application also finds that hydrolysis can not stop completely at a certain stage, can be until proceeding to the hydrolysis of difluorophosphoric acid or lithium difluorophosphate, thereby there is the problem of sneaking into monofluorophosphate body and hydrofluoric acid.

[0172] According to the above preferred aspect of the present invention, high-purity lithium difluorophosphate with a small amount of hydrofluoric acid and impurities mixed therein can be efficiently produced.

[0173] Since difluorophosphate reacts rapidly with water to be hydrolyzed, water cannot be present in difluorophosphate before the reaction. Therefore, the water content in the total amount of raw materials before the reaction can be calculated by setting the "water content in difluorophosphate before the reaction" to "0 mass ppm".

[0174] In the present invention, the amount of water contained in the total amount of raw materials before the reaction can be calculated by measuring the amount of water in the lithium salt compound and the non-aqueous organic solvent using a Karl Fischer moisture meter and summing them up. In addition, the amount of water in the lithium salt compound is a value measured by connecting a moisture vaporizer to the Karl Fischer moisture meter and setting the set temperature to 150°C.

[0175] Thus, by setting the water content in the total amount of raw materials before the reaction to 7000 mass ppm or less, more preferably to 1000 mass ppm or less, further preferably to 500 mass ppm or less, and particularly preferably to 200 mass ppm or less, it is possible to produce high-purity lithium difluorophosphate with a small amount of hydrofluoric acid mixed in, without the need for the usually required purification (mainly recrystallization) step, thereby being able to efficiently produce inexpensive and high-quality lithium difluorophosphate.

[0176] <Difluorophosphate represented by general formula (1A)>

[0177] In the production method of the present invention, a difluorophosphate ester represented by the following general formula (1A) is used as a raw material.

[0178] [Chemical formula 5]

[0179]

[0180] In the general formula (1A), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

[0181] The hydrocarbon group having 1 to 15 carbon atoms represented by R may be any of straight chain, branched chain and cyclic, and may have multiple bonds. In addition, it may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Specifically, there may be mentioned an alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, an alkynyl group having 2 to 15 carbon atoms, a cycloalkyl group having 3 to 15 carbon atoms, an aryl group having 6 to 15 carbon atoms, an aralkyl group having 7 to 15 carbon atoms, etc., preferably an alkyl group having 1 to 15 carbon atoms or an aryl group having 6 to 15 carbon atoms.

[0182] Examples of the alkyl group having 1 to 15 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, and n-dodecyl. Preferably, the alkyl group has 1 to 10 carbon atoms, and preferably, it is methyl, ethyl, n-propyl, or isopropyl.

[0183] Examples of the aryl group having 6 to 15 carbon atoms include phenyl, naphthyl, anthracenyl and the like, and phenyl is preferred.

[0184] Furthermore, any hydrogen atom in the hydrocarbon group represented by R may be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferred.

[0185] R is preferably an unsubstituted alkyl group having 1 to 15 carbon atoms or an unsubstituted aryl group having 6 to 15 carbon atoms, and more preferably an unsubstituted alkyl group having 1 to 10 carbon atoms or an unsubstituted phenyl group.

[0186] As described above, the water content in the difluorophosphate ester represented by the general formula (1A) before the reaction was set to "0 mass ppm".

[0187] The synthesis method of the difluorophosphate represented by the above general formula (1A) is not particularly limited, and various known synthesis methods can be adopted.

[0188] For example, it can be obtained by reacting a dihalogenated phosphoric acid ester such as dichlorophosphate with a known fluorinating agent (for example, potassium fluoride, hydrofluoric acid, sodium hexafluorosilicate, sodium fluoride, ammonium fluoride, cesium fluoride, triethylamine trihydrofluoride, pyridine hydrofluoride, etc.).

[0189] The difluorophosphate represented by the general formula (1A) is preferably manufactured by the method for manufacturing difluorophosphate of the present invention described later. That is, the method for manufacturing lithium difluorophosphate of the present invention is preferably that the difluorophosphate represented by the general formula (1A) in the method is manufactured by the method for manufacturing difluorophosphate containing the following step 1, wherein the step 1 is a step for reacting the dihalogenated phosphate represented by the general formula (1) with a fluorinating agent having a hydrofluoric acid concentration of 15 mol% or less in a non-aqueous organic solvent (a). The difluorophosphate represented by the general formula (1A) manufactured by the method for manufacturing difluorophosphate of the present invention is preferably excellent in terms of yield and purity.

[0190] [Chemical formula 6]

[0191]

[0192] In the general formula (1), X represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom, and Y represents a chlorine atom, a bromine atom or an iodine atom. In the general formula (1), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

[0193] The specific description and the description of the preferred embodiment of the method for producing a difluorophosphate ester having the step 1 are the same as those described below.

[0194] <Lithium Salt Compounds>

[0195] The lithium salt compound used in the production method of the present invention is not particularly limited, and examples thereof include at least one selected from the group consisting of lithium chloride, lithium bromide, lithium fluoride, lithium carbonate, lithium acetate, lithium propionate, lithium iodide, lithium hydroxide, lithium bicarbonate, lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, lithium metaphosphate and lithium sulfate.

[0196] The lithium salt compound is preferably at least one selected from the group consisting of lithium chloride, lithium bromide, lithium fluoride, lithium carbonate, lithium acetate and lithium propionate. Among them, at least one selected from the group consisting of lithium chloride, lithium acetate, lithium carbonate and lithium propionate is more preferred, and at least one selected from lithium chloride and lithium acetate is further preferred.

[0197] In addition, from the perspective of improving the yield and purity of lithium difluorophosphate, the above-mentioned lithium salt compound is preferred because lithium difluorophosphate has low solubility in by-product compounds (compounds other than lithium difluorophosphate) generated by the reaction of the lithium salt compound with the difluorophosphate ester represented by the above-mentioned general formula (1A) and the generated by-product compounds (compounds other than lithium difluorophosphate) are easy to remove. Specifically, lithium chloride is preferred.

[0198] The lithium salt compounds may be used alone or in combination of two or more.

[0199] In the production method of the present invention, among the difluorophosphate ester represented by the general formula (1A), the lithium salt compound and the non-aqueous organic solvent, the lithium salt compound is most likely to introduce water into the reaction system. Therefore, in order to set the water content in the total amount of raw materials before the reaction to 7000 mass ppm or less, it is important to reduce the water content of the lithium salt compound before the reaction.

[0200] The water content of the lithium salt compound before the reaction is preferably 3000 mass ppm or less, more preferably 2500 mass ppm or less, further preferably 2000 mass ppm or less, particularly preferably 1000 mass ppm or less, and most preferably 600 mass ppm or less.

[0201] The water content of the lithium salt compound before the reaction can be reduced by, for example, drying the lithium salt compound having a high water content under reduced pressure at a temperature of 100 to 200° C. for a certain period of time.

[0202] <Non-aqueous organic solvent>

[0203] As the nonaqueous organic solvent used in the manufacture method of the present invention, there is no particular limitation, but since carbonates, chain esters (chain carboxylates), ethers and ketones are easily available commercial products with low water content, it is preferred to be selected from at least one of the group consisting of carbonates, chain esters (chain carboxylates), ethers and ketones.

[0204] Examples of the carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate, butylene carbonate and the like, and ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate is preferred.

[0205] Examples of the chain esters include ethyl acetate, methyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate, and ethyl acetate is preferred.

[0206] Examples of the ethers include dimethoxyethane, dimethoxymethane, tetrahydrofuran, and diethyl ether, and dimethoxyethane is preferred.

[0207] Examples of the ketones include acetone, ethyl methyl ketone, and diethyl ketone, and acetone is preferred.

[0208] The non-aqueous organic solvent is preferably selected from at least one of the group consisting of carbonates, linear esters and ketones, more preferably selected from at least one of the group consisting of carbonates and linear esters, and from the perspective of improving the yield of the obtained lithium difluorophosphate, more preferably carbonates with low solubility of lithium difluorophosphate, particularly preferably ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate.

[0209] In the manufacture method of the present invention, from the angle of suppressing the generation of hydrofluoric acid, improving the purity of lithium difluorophosphate, preferably the amount of water brought into the reaction system from the non-aqueous organic solvent is few. From the angle of the amount of water in the total amount of raw materials before the reaction is set to below 7000 mass ppm, as the water content in the non-aqueous organic solvent before the reaction, preferably below 0.5 mass % (5000 mass ppm), more preferably below 0.1 mass % (1000 mass ppm), further preferably below 0.05 mass % (500 mass ppm), particularly preferably below 0.02 mass % (200 mass ppm).

[0210] <Reaction Conditions>

[0211] In the reaction of reacting the difluorophosphate ester represented by the general formula (1A) with a lithium salt compound in a non-aqueous organic solvent, the addition ratio of the difluorophosphate ester represented by the general formula (1A) to the lithium salt compound is preferably 1.0:0.7 to 1.0:1.5, more preferably 1.0:0.9 to 1.0:1.2, in terms of molar ratio.

[0212] The nonaqueous organic solvent is preferably used in such an amount that the concentration of the difluorophosphate ester represented by the general formula (1A) in the nonaqueous organic solvent is 5% by mass to 25% by mass.

[0213] Furthermore, the temperature of the reaction solution in the above reaction is preferably -10 to 120°C, more preferably 0 to 60°C.

[0214] From the perspective of suppressing the increase of the moisture content of the reaction system and thus suppressing the generation of by-products, the reaction of the difluorophosphate represented by the general formula (1A) and the lithium salt compound in the manufacturing method of the present invention in a non-aqueous organic solvent is preferably carried out under the protection of an inert gas. Specifically, carrying out the above reaction under the protection of an inert gas means that the raw materials, solvents and reaction vessels used are operated under an inert gas atmosphere. For the inert gas, the dew point is preferably below -40°C. As the inert gas, nitrogen can be preferably listed.

[0215] [Method for producing non-aqueous electrolyte solution and method for producing non-aqueous secondary battery]

[0216] The present invention also relates to a method for producing a non-aqueous electrolyte using lithium difluorophosphate obtained by the method for producing lithium difluorophosphate of the present invention, and a method for producing a non-aqueous secondary battery using the non-aqueous electrolyte obtained by the production method.

[0217] Lithium difluorophosphate is a substance added as an additive to non-aqueous electrolytes in order to improve the performance of non-aqueous electrolyte batteries such as lithium ion secondary batteries. However, due to its low solubility in solvents in non-aqueous electrolytes, its usage is usually 0.5 to 1.5% by mass relative to the non-aqueous electrolyte.

[0218] Assuming that the amount added to the non-aqueous electrolyte is set to 1.0 mass %, when the concentration of hydrofluoric acid mixed in lithium difluorophosphate is about 3000 mass ppm, the concentration of free acid (mainly hydrofluoric acid) in the non-aqueous electrolyte will increase by about 30 mass ppm.

[0219] Since the standard concentration of free acid (hydrofluoric acid) in ordinary non-aqueous electrolytes is about 40 mass ppm, if lithium difluorophosphate causes an increase of about 30 mass ppm, the allowable value of hydrofluoric acid contained in other raw materials will be greatly limited, which may cause serious obstacles to the stable production of non-aqueous electrolytes.

[0220] Therefore, the concentration of hydrofluoric acid mixed in lithium difluorophosphate is preferably as low as possible. From the viewpoint of reducing the concentration of hydrofluoric acid, the amount of water in the total amount of raw materials before the reaction is preferably as small as possible.

[0221] The manufacturing method of the nonaqueous electrolyte of the present invention preferably uses the lithium difluorophosphate obtained by the manufacturing method of the lithium difluorophosphate of the present invention, and the manufacturing method of the lithium difluorophosphate uses the difluorophosphate represented by the above-mentioned general formula (1A) manufactured by the manufacturing method of the difluorophosphate of the present invention described later as a raw material. Since the production efficiency is excellent when the nonaqueous electrolyte is obtained by this method, it is preferred.

[0222] In addition, the method for producing a non-aqueous secondary battery of the present invention preferably uses a non-aqueous electrolyte obtained by the method for producing a non-aqueous electrolyte. The method is preferably used to produce a non-aqueous secondary battery because of its excellent production efficiency.

[0223] [Lithium difluorophosphate]

[0224] The inventors of the present application conducted in-depth research to solve the above-mentioned technical problems and found that lithium difluorophosphate with a large d10 (i.e., a large primary particle size) and a small d90 (i.e., a small secondary particle size) releases little heat when dissolved in a non-aqueous electrolyte as an additive.

[0225] The lithium difluorophosphate of the present invention is a lithium difluorophosphate having a value of 10 or less for the relationship (d90-d10) / MV represented by the particle size d90 at 90% of the volume cumulative distribution, the particle size d10 at 10% of the volume cumulative distribution, and the volume average particle size MV.

[0226] It is estimated that lithium difluorophosphate is a powder composed of spherical secondary particles formed by agglomeration of primary particles at room temperature and normal pressure.

[0227] In a powder composed of primary particles and spherical secondary particles formed by agglomeration of the primary particles, two particle size peaks are shown in terms of the relative particle amount converted into volume in a particle size distribution measurement.

[0228] (Particle size of primary particles and secondary particles)

[0229] For powders composed of primary particles and secondary particles formed by agglomeration of the primary particles, the particle sizes of the primary particles and secondary particles between samples from different batches can be compared using the values ​​of d10 and d90 as indices, respectively.

[0230] The d10 of the lithium difluorophosphate of the present invention is preferably 1.3 μm or more, and more preferably 1.7 μm or more.

[0231] The d90 of the lithium difluorophosphate of the present invention is preferably 170 μm or less, and more preferably 140 μm or less.

[0232] (Width of particle size distribution)

[0233] “(d90-d10) / MV” is an index showing the width of the particle size distribution of lithium difluorophosphate. The value of (d90-d10) / MV of the lithium difluorophosphate of the present invention is 10 or less, preferably 6.5 or less, and more preferably 5.8 or less.

[0234] By setting the value of (d90-d10) / MV of lithium difluorophosphate to less than 10, the difference between the particle sizes of the secondary particles and the primary particles of lithium difluorophosphate becomes smaller, that is, the degree of aggregation of the primary particles becomes smaller, and the heat generation when dissolved in a non-aqueous electrolyte in the form of an additive can be suppressed. On the other hand, when the value of (d90-d10) / MV is greater than 10, the heat generation when dissolved in a non-aqueous electrolyte in the form of an additive increases.

[0235] (Definition of parameters for particle size distribution measurement)

[0236] In the particle size distribution measurement, d10 and d90 are the particle sizes at 10% and 90% of the volume cumulative distribution, respectively, and MV is the volume average particle size. The smaller (d90-d10) / MV is, the smaller the width of the particle size distribution is. However, considering the constraints on manufacturing, the lower limit of (d90-d10) / MV is usually about 1. In addition, d90, d10 and MV can be measured by using a laser diffraction particle size distribution analyzer according to the laser diffraction scattering method.

[0237] The concentration of hydrofluoric acid mixed in the lithium difluorophosphate of the present invention is preferably 4000 mass ppm or less, more preferably 2500 mass ppm or less.

[0238] By setting the concentration of hydrofluoric acid in lithium difluorophosphate to below 4000 mass ppm, the concentration of hydrofluoric acid in the non-aqueous electrolyte produced by adding the lithium difluorophosphate can be reduced. It is known that it is not preferred to have a large amount of acid in the electrolyte of the battery (e.g., Japanese Patent No. 5679719 Gazette, Japanese Patent Publication No. 2001-307772 Gazette, etc.).

[0239] [Method for producing difluorophosphate]

[0240] The inventors of the present application have conducted in-depth research to solve the above technical problems, and have found that the reason for the fluctuation of fluorination selectivity due to the manufacturer or production batch of the fluorinating agent is the difference in the hydrofluoric acid content in the fluorinating agent. It is also found that by fluorinating a dihalogenated phosphoric acid ester using a fluorinating agent containing a hydrofluoric acid concentration of 15 mol% or less, a difluorophosphate ester can be obtained with a high selectivity of, for example, 75 mol% or more.

[0241] Furthermore, it was confirmed that lithium difluorophosphate can be efficiently produced by synthesizing lithium difluorophosphate using the obtained difluorophosphate ester.

[0242] The inventors of the present application attempted to use hydrofluoric acid commonly used in the fluorination of halogenated phosphoric acid compounds to fluorinate the dihalogenated phosphoric acid ester represented by the general formula (1). The result was unexpectedly that due to overfluorination or uneven fluorination, a large amount of byproducts such as hexafluorophosphoric acid or diethyl monofluorophosphate were generated, and the fluorination selectivity of the difluorophosphate ester represented by the general formula (2) as the target product was reduced. In addition, it was also clarified that since it is difficult to separate the monofluorophosphate diester from the difluorophosphate ester represented by the general formula (2) in the byproducts, the amount of the byproduct of the monofluorophosphate diester increases. If the proportion of the monofluorophosphate diester in the obtained fluoride is greater than 5 mol%, the recovery rate when the difluorophosphate ester is distilled and purified decreases.

[0243] The method for producing difluorophosphate ester of the present invention can suppress the formation of by-product monofluorophosphate diester by adjusting the concentration of hydrofluoric acid contained in the fluorinating agent to 15 mol % or less, thereby achieving stable production of difluorophosphate ester represented by general formula (2) with high selectivity and high yield.

[0244] [Process 1]

[0245] The present invention provides a method for producing a difluorophosphate represented by the following general formula (2), which comprises a step 1 of reacting a dihalogenated phosphate represented by the following general formula (1) with a fluorinating agent containing hydrofluoric acid at a concentration of 15 mol % or less in a non-aqueous organic solvent (a).

[0246] <Dihalogenated phosphoric acid ester represented by general formula (1) and difluorophosphoric acid ester represented by general formula (2)>

[0247] [Chemical formula 7]

[0248]

[0249] In the general formula (1), X represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom, and Y represents a chlorine atom, a bromine atom or an iodine atom. In the general formulas (1) and (2), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

[0250] In the general formula (1), X represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom, and Y represents a chlorine atom, a bromine atom or an iodine atom. X and Y are preferably chlorine atoms.

[0251] In the general formulae (1) and (2), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

[0252] R in the general formulae (1) and (2) represents the same group.

[0253] The hydrocarbon group having 1 to 15 carbon atoms represented by R may be any of a straight chain, a branched chain, and a cyclic group, and may have a multiple bond. In addition, it may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. As the hydrocarbon group having 1 to 15 carbon atoms represented by R, specifically, there can be listed an alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, an alkynyl group having 2 to 15 carbon atoms, a cycloalkyl group having 3 to 15 carbon atoms, an aryl group having 6 to 15 carbon atoms, an aralkyl group having 7 to 15 carbon atoms, etc., preferably an alkyl group having 1 to 15 carbon atoms or an aryl group having 6 to 15 carbon atoms.

[0254] Examples of the alkyl group having 1 to 15 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, and n-dodecyl. Preferably, the alkyl group has 1 to 10 carbon atoms, and preferably, the alkyl group is methyl, ethyl, n-propyl, or isopropyl.

[0255] Examples of the aryl group having 6 to 15 carbon atoms include phenyl, naphthyl, anthracenyl and the like, and phenyl is preferred.

[0256] Furthermore, any hydrogen atom in the hydrocarbon group represented by R may be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferred.

[0257] R is preferably an unsubstituted alkyl group having 1 to 15 carbon atoms or an unsubstituted aryl group having 6 to 15 carbon atoms, and more preferably an unsubstituted alkyl group having 1 to 10 carbon atoms or an unsubstituted phenyl group.

[0258] The synthesis method of the dihalogenated phosphate represented by the general formula (1) is not particularly limited. When the synthesis method of dichlorophosphate is given as an example, for example, phosphorus oxychloride can be dissolved in a non-aqueous organic solvent, and an equimolar mixed solution of a corresponding alcohol and triethylamine is added dropwise thereto while the solution temperature is maintained at below 5° C., and then triethylamine hydrochloride is removed by filtration, and further reduced pressure distillation is performed to obtain dichlorophosphate.

[0259] If the non-aqueous organic solvent is a high boiling point solvent such as propylene carbonate (hereinafter sometimes referred to as "PC") or diethylene glycol diethyl ether (hereinafter sometimes referred to as "DGDE"), it is easy to separate the non-aqueous organic solvent from the dichlorophosphate by the above-mentioned vacuum distillation, so the type of the non-aqueous organic solvent (a) used in the later-described step 1 is not particularly limited. On the other hand, if the non-aqueous organic solvent is a solvent with a lower boiling point than the non-aqueous organic solvent (e.g., ethyl methyl carbonate (hereinafter sometimes referred to as "EMC"), etc.), it takes more time to completely separate the dichlorophosphate from the non-aqueous organic solvent by the above-mentioned vacuum distillation. Therefore, it is preferred to directly enter the later-described step 1 in a state where the non-aqueous organic solvent is not completely separated, but in this case, from the point of easy control of the solvent composition, it is preferred that the type of the non-aqueous organic solvent (a) used in the later-described step 1 is the same as the type of the non-aqueous organic solvent used when synthesizing the dichlorophosphate.

[0260] <Fluorinating Agent>

[0261] In step 1 of the method for producing difluorophosphate of the present invention, a fluorinating agent having a hydrofluoric acid concentration of 15 mol% or less is used as the fluorinating agent. The fluorinating agent having a hydrofluoric acid concentration of 15 mol% or less means a fluorinating agent having a hydrofluoric acid concentration of 15 mol% or less relative to the total amount of the fluorinating agent. In addition, the hydrofluoric acid constituting the fluorinating agent as an equimolar neutralization salt of a base and hydrofluoric acid such as triethylamine monohydrofluoride is not included in the hydrofluoric acid when calculating the above-mentioned contained hydrofluoric acid concentration.

[0262] The fluorinating agent is not particularly limited, and examples thereof include at least one selected from the group consisting of hydrofluoric acid salts of organic amines and inorganic fluorides. Since the concentration of the contained hydrofluoric acid can be easily set to 15 mol% or less, the hydrofluoric acid salt of the organic amine is preferably at least one selected from the group consisting of triethylamine monohydrofluoric acid salt, tetramethylethylenediamine dihydrofluoric acid salt and pyridine monohydrofluoric acid salt, and the inorganic fluoride is preferably at least one selected from the group consisting of ammonium fluoride, sodium fluoride, potassium fluoride, cesium fluoride and zinc fluoride.

[0263] The concentration of hydrofluoric acid in the fluorinating agent used in step 1 is 15 mol% or less. However, from the viewpoint of suppressing the formation of by-products such as monofluorophosphate diesters and further improving the selectivity and yield of the difluorophosphate ester represented by the general formula (2), the concentration of hydrofluoric acid in the fluorinating agent used in step 1 is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 1 mol% or less.

[0264] In the present invention, the concentration of hydrofluoric acid contained in the fluorinating agent is a value measured by non-aqueous neutralization titration of the fluorinating agent dissolved or dispersed in a non-aqueous organic solvent using a glass burette, triethylamine as a titration base, and bromophenol blue as an indicator.

[0265] As the nonaqueous organic solvent to be used, acetone is preferred.

[0266] The fluorinating agent may be a commercially available product or may be synthesized.

[0267] The synthesis method of the fluorinating agent is not particularly limited, and it can be obtained, for example, by reacting hydrofluoric acid with a corresponding basic compound (for example, when the fluorinating agent is triethylamine monohydrofluoride, triethylamine is used) in a reaction solvent. The reaction solvent is not particularly limited, but when it is difficult to completely separate the reaction solvent from the fluorinating agent by filtration or the like or when it takes a long time, it is preferred to use a solvent of the same type as the nonaqueous organic solvent (a) described later used in step 1 as the reaction solvent from the viewpoint of easy control of the solvent composition.

[0268] <Non-aqueous organic solvent (a)>

[0269] The reaction in step 1 is carried out in a nonaqueous organic solvent (a).

[0270] The water content in the nonaqueous organic solvent (a) causes the generation of hydrofluoric acid and is therefore preferably very small. The water content in the nonaqueous organic solvent (a) before the reaction is preferably 0.05% by mass or less.

[0271] As the above-mentioned non-aqueous organic solvent (a), esters such as carbonates or chain esters (chain carboxylic acid esters), ketones, ethers, nitriles such as acetonitrile, etc. can be listed. If it is at least one selected from the group consisting of carbonates, chain esters and ketones, it is easy to obtain the above-mentioned difluorophosphate with high selectivity, so it is preferred.

[0272] The nonaqueous organic solvent (a) is preferably at least one selected from the group consisting of carbonates and chain esters.

[0273] The carbonate ester is preferably at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate, and butylene carbonate.

[0274] The chain ester is preferably at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0275] In addition, as another preferred embodiment, in the above step 1, the fluorinating agent is preferably at least one selected from sodium fluoride, ammonium fluoride, triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride, and the non-aqueous organic solvent (a) is preferably at least one selected from esters having a relative dielectric constant of 8 or less at 25° C., ethers having a relative dielectric constant of 8 or less at 25° C. and propylene carbonate. If the fluorinating agent and the non-aqueous organic solvent (a) are combined as described above, the amount of the fluorinating agent can be further reduced and the amount of waste generated by using an excessive amount of the fluorinating agent can be reduced, so it is preferred.

[0276] Preferred examples of esters having a relative dielectric constant of less than 8 at 25°C include at least one selected from ethyl methyl carbonate (EMC), dimethyl carbonate (hereinafter sometimes referred to as "DMC"), diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, amyl acetate, methyl propionate, ethyl propionate, propyl propionate and dibutyl phthalate.

[0277] Preferred examples of the ethers having a relative dielectric constant of 8 or less at 25° C. include at least one selected from 1,2-dimethoxyethane, tetrahydrofuran, diethyl ether, and diethylene glycol diethyl ether (DGDE).

[0278] <Reaction Conditions of Step 1>

[0279] In the above step 1, the equivalent of the fluorinating agent containing hydrofluoric acid at a concentration of 15 mol% or less relative to the dihalogenated phosphate represented by the above general formula (1) is preferably 2.0 to 3.0 when the dihalogenated phosphate represented by the general formula (1) does not contain fluorine atoms, and is preferably 1.0 to 1.5 when the dihalogenated phosphate represented by the general formula (1) contains fluorine atoms (when X in the general formula (1) is a fluorine atom).

[0280] The nonaqueous organic solvent (a) is preferably used in such an amount that the concentration of the dihalogenated phosphoric acid ester represented by the general formula (1) in the nonaqueous organic solvent (a) is 0.01 g / mL to 0.4 g / mL.

[0281] In addition, the temperature of the reaction solution at this time is preferably -30 to 100°C, more preferably -10 to 50°C.

[0282] From the perspective of suppressing the increase of the moisture content of the reaction system and thus suppressing the generation of by-products, the above step 1 is preferably carried out under the protection of an inert gas. Specifically, carrying out the above reaction under the protection of an inert gas means that the raw materials, solvents and reaction vessels used are operated under an inert gas atmosphere. The inert gas preferably has a dew point of -40°C or less. Nitrogen can be preferably cited as the inert gas.

[0283] In the reaction of step 1, a catalyst may be used, but it is preferred that no catalyst be used in the reaction of step 1.

[0284] The following scheme is preferred: the fluorinating agent is at least one selected from sodium fluoride, ammonium fluoride, cesium fluoride, zinc fluoride, triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride,

[0285] The nonaqueous organic solvent (a) is at least one selected from esters having a relative dielectric constant of 8 or less at 25°C and ethers having a relative dielectric constant of 8 or less at 25°C.

[0286] The esters having a relative dielectric constant of less than 8 at 25°C are preferably at least one selected from ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, amyl acetate, methyl propionate, ethyl propionate, propyl propionate and dibutyl phthalate.

[0287] Furthermore, the ether having a relative dielectric constant of 8 or less at 25° C. is preferably at least one selected from 1,2-dimethoxyethane, tetrahydrofuran, diethyl ether, and diethylene glycol diethyl ether.

[0288] [Method for producing lithium difluorophosphate]

[0289] The present invention also provides a method for producing lithium difluorophosphate, which uses the difluorophosphate ester represented by the general formula (2) produced in the above step 1 as a raw material and comprises any one of the following steps 2 to 4.

[0290] Hereinafter, steps 2 to 4 will be described in detail.

[0291] [Process 2]

[0292] Step 2 is a step of reacting the difluorophosphate ester represented by the general formula (2) produced in step 1, a lithium salt compound (b), and water in a nonaqueous organic solvent (b).

[0293] The non-aqueous organic solvent (b) in the above step 2 is preferably at least one selected from the group consisting of esters, n-hexane, cyclohexane, n-heptane, isoheptane, benzene, toluene, xylene, acetonitrile, dimethyl ether, diethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, diethylene glycol dimethyl ether, anisole, phenethyl ether and tetrahydrofuran.

[0294] Examples of the esters include cyclic carbonates, chain carbonates, chain esters (chain carboxylic acid esters), and cyclic esters (cyclic carboxylic acid esters).

[0295] The cyclic carbonate is preferably at least one selected from the group consisting of propylene carbonate and butylene carbonate.

[0296] The linear carbonate is preferably at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0297] The chain ester is preferably at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0298] The cyclic ester is preferably at least one selected from the group consisting of γ-butyrolactone and γ-valerolactone.

[0299] The lithium salt compound (b) in the above step 2 is preferably at least one selected from the group consisting of lithium chloride, lithium bromide, lithium fluoride, lithium iodide, lithium hydroxide, lithium carbonate, lithium bicarbonate, lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, lithium metaphosphate, lithium acetate and lithium sulfate.

[0300] The molar ratio of the difluorophosphate ester represented by the general formula (2), the lithium salt compound (b) and water in the above step 2 is preferably 1:2:2 to 1:1:0.01.

[0301] In addition, the amount of the nonaqueous organic solvent (b) used in the above-mentioned step 2 is preferably used in a manner such that the concentration of the difluorophosphate represented by the general formula (2) in the nonaqueous organic solvent (b) is 0.01 g / mL to 0.4 g / mL. In addition, in step 2, the total amount of the difluorophosphate represented by the general formula (2), the lithium salt compound (b), water and the nonaqueous organic solvent (b) before the reaction is sometimes recorded as "the total amount of raw materials before the reaction in step 2".

[0302] Furthermore, the temperature of the reaction solution in step 2 is preferably -10 to 120°C.

[0303] From the viewpoint of suppressing oxidation of the nonaqueous organic solvent (b) by oxygen, the step 2 is preferably performed under protection of an inert gas. Preferred examples of the inert gas include nitrogen gas.

[0304] [Process 3]

[0305] Step 3 is a step of reacting the difluorophosphate ester represented by the general formula (2) produced in the step 1 with a lithium salt compound (c) in a non-aqueous organic solvent (c).

[0306] The water content in the total amount of the difluorophosphate ester represented by the general formula (2), the lithium salt compound (c) and the non-aqueous organic solvent (c) before the reaction in step 3 (hereinafter, this total amount is sometimes referred to as "the total amount of raw materials before the reaction in step 3") is preferably 200 mass ppm or less.

[0307] Among them, difluorophosphate reacts rapidly with water to be hydrolyzed, so water cannot be present in difluorophosphate before the reaction. Therefore, the water content in the total amount of raw materials before the reaction in step 3 can be calculated by setting "water content in difluorophosphate before the reaction" to "0 mass ppm".

[0308] The amount of water contained in the total amount of raw materials before the reaction in step 3 can be calculated by measuring the amount of water in the lithium salt compound and the non-aqueous organic solvent (c) using a Karl Fischer moisture meter and summing them up. In addition, the amount of water in the lithium salt compound is a value measured by connecting a moisture vaporizer to the Karl Fischer moisture meter and setting the set temperature to 150°C.

[0309] It is preferred that the water content in the total amount of the difluorophosphate represented by the general formula (2), the lithium salt compound (c) and the nonaqueous organic solvent (c) before the reaction in step 3 is 145 ppm by mass or less because the amount of hydrofluoric acid mixed in the lithium difluorophosphate can be reduced.

[0310] The lithium salt compound (c) in the above step 3 is preferably at least one selected from the group consisting of lithium chloride, lithium bromide, lithium fluoride, lithium carbonate, lithium acetate and lithium propionate.

[0311] In the above step 3, among the difluorophosphate represented by the general formula (2), the lithium salt compound (c) and the non-aqueous organic solvent (c), the lithium salt compound (c) having a very high hygroscopicity is most likely to introduce water into the system. Therefore, in order to set the water content in the total amount of raw materials before the reaction in step 3 to 200 mass ppm or less, it is important to reduce the water content of the lithium salt compound before the reaction.

[0312] The water content of the lithium salt compound before the reaction is preferably 3000 mass ppm or less, more preferably 2500 mass ppm or less, and even more preferably 1000 mass ppm or less.

[0313] Since hydrofluoric acid is generated, the amount of water in the nonaqueous organic solvent (c) in the above step 3 is preferably very small, and the water content in the nonaqueous organic solvent (c) before the reaction is preferably 0.05 mass % (500 mass ppm) or less.

[0314] The nonaqueous organic solvent (c) in step 3 is preferably at least one selected from the group consisting of esters, ethers and ketones, since esters, ethers and ketones are easily available as commercial products with low water content.

[0315] The nonaqueous organic solvent (c) in the above step 3 preferably contains esters.

[0316] The above-mentioned esters may be used in one kind or in two or more kinds.

[0317] Examples of the esters include cyclic carbonates, chain carbonates, chain esters, and cyclic esters.

[0318] The cyclic carbonate is preferably at least one selected from the group consisting of propylene carbonate and butylene carbonate.

[0319] The linear carbonate is preferably at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0320] The chain ester is preferably at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0321] The cyclic ester is preferably at least one selected from the group consisting of γ-butyrolactone and γ-valerolactone.

[0322] In the step 3, the equivalent of the lithium salt compound (c) relative to the difluorophosphate ester represented by the general formula (2) is preferably 0.7 to 1.5.

[0323] The nonaqueous organic solvent (c) is preferably used in an amount such that the concentration of the difluorophosphate ester represented by the general formula (2) in the nonaqueous organic solvent is 0.01 g / mL to 0.4 g / mL.

[0324] Furthermore, the reaction solution temperature is preferably -10 to 120°C.

[0325] Step 3 is the same as step 1 above, and is preferably performed under protection of an inert gas.

[0326] [Process 4]

[0327] Step 4 is a step of chlorinating the difluorophosphate ester represented by the general formula (2) produced in step 1 with a chlorinating agent to convert it into difluoromonochlorophosphoric acid oxide, hydrolyzing it to synthesize difluorophosphoric acid, and further neutralizing it.

[0328] The chlorinating agent in the above step 4 is preferably phosphorus oxychloride.

[0329] The neutralization in the above step 4 is preferably neutralization of difluorophosphoric acid by adding lithium hydride or lithium chloride.

[0330] The above-mentioned chlorination reaction, hydrolysis reaction and neutralization reaction are preferably carried out in a non-aqueous organic solvent (d).

[0331] The nonaqueous organic solvent (d) preferably comprises esters.

[0332] The above-mentioned esters may be used in one kind or in two or more kinds.

[0333] Examples of the esters include cyclic carbonates, chain carbonates, chain esters (chain carboxylic acid esters), and cyclic esters (cyclic carboxylic acid esters).

[0334] The cyclic carbonate is preferably at least one selected from the group consisting of propylene carbonate and butylene carbonate.

[0335] The linear carbonate is preferably at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0336] The chain ester is preferably at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0337] The cyclic ester is preferably at least one selected from the group consisting of γ-butyrolactone and γ-valerolactone.

[0338] The nonaqueous organic solvent (d) is preferably used in such an amount that the concentration of the difluorophosphate ester represented by the general formula (2) in the nonaqueous organic solvent is 0.01 g / mL to 0.4 g / mL.

[0339] Furthermore, the reaction solution temperature is preferably -10 to 60°C.

[0340] Step 4 is the same as step 1 above, and is preferably performed under protection of an inert gas.

[0341] Lithium difluorophosphate can be produced by various methods as shown in the above steps 2 to 4, but the production method including the above step 3 is preferred because lithium difluorophosphate can be obtained with high yield and high purity and the concentration of acid mixed in lithium difluorophosphate is low.

[0342] [Method for producing non-aqueous electrolyte, and method for producing non-aqueous electrolyte battery]

[0343] The present invention also relates to a method for producing a non-aqueous electrolyte using lithium difluorophosphate obtained by the above-mentioned production method of the present invention, and a method for producing a non-aqueous electrolyte battery using the non-aqueous electrolyte obtained by the above-mentioned production method.

[0344] Example

[0345] The present invention is specifically described below by way of examples, but the present invention is not limited to these examples. The operation of the raw materials or solvents is carried out in a nitrogen atmosphere with a dew point of -50°C or less. In addition, the fluororesin reaction container and glass reaction container used are dried at 150°C for more than 12 hours and then cooled to room temperature under a nitrogen gas flow with a dew point of -50°C or less before use.

[0346] [Synthesis of difluorophosphate represented by general formula (1A)]

[0347] According to the procedures described in the following Synthesis Examples 1 to 6, the difluorophosphate represented by the general formula (1A) was synthesized.

[0348] (Synthesis example 1)

[0349] 500 mL of acetonitrile and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction vessel, and stirred to mix thoroughly. 174.3 g (3000 mmol) of potassium fluoride was added, and stirring was continued for 12 hours at a solution temperature of 25°C. 19 F-NMR was used to confirm that the target product, ethyl difluorophosphate, was 90 mol%, potassium hexafluorophosphate was 4 mol%, and diethyl monofluorophosphate was 6 mol% in the obtained reaction solution. After removing potassium chloride by filtration, 46.8 g (360 mmol, yield 72%) of ethyl difluorophosphate was obtained by reduced pressure distillation.

[0350] (Synthesis example 2)

[0351] 500 mL of ethyl methyl carbonate (hereinafter referred to as EMC) and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction container and stirred to mix thoroughly. While maintaining the solution temperature below 20°C, 28.0 g (1400 mmol) of hydrofluoric acid was added dropwise over 30 minutes, and then the solution temperature was raised to 25°C and stirring was continued for 24 hours. 19F-NMR was used to confirm that the target product in the obtained reaction solution was 45 mol% of ethyl difluorophosphate, 30 mol% of hexafluorophosphate, and 25 mol% of diethyl monofluorophosphate. After the hydrochloric acid was removed by vacuum concentration, 22.8 g (175 mmol, yield 35%) of ethyl difluorophosphate was obtained by vacuum distillation.

[0352] (Synthesis example 3)

[0353] 81.5 g (500 mmol) of ethyl dichlorophosphate and 94.0 g (500 mmol) of sodium hexafluorosilicate were added to a 500 mL fluororesin reaction container, and stirring was continued at 60°C for 12 hours. 19 F-NMR was used to confirm that the target product in the reaction solution was 87 mol% of ethyl difluorophosphate, 8 mol% of ethyl chlorofluorophosphate, and 5 mol% of difluorophosphoric acid. 13.5 g (104 mmol, yield 21%) of ethyl difluorophosphate was obtained by vacuum distillation.

[0354] (Synthesis Example 4)

[0355] The reaction was carried out in the same manner as in Synthesis Example 1 except that the raw material was changed from 81.5 g (500 mmol) of ethyl dichlorophosphate to 74.5 g (500 mmol) of methyl dichlorophosphate. As a result, methyl difluorophosphate was obtained at a yield of 24%.

[0356] (Synthesis Example 5)

[0357] The reaction was carried out in the same manner as in Synthesis Example 1 except that the raw material was changed from 81.5 g (500 mmol) of ethyl dichlorophosphate to 88.5 g (500 mmol) of n-propyl dichlorophosphate. As a result, n-propyl difluorophosphate was obtained at a yield of 31%.

[0358] (Synthesis Example 6)

[0359] The same reaction procedure as in Synthesis Example 1 was followed except that the raw material was changed from 81.5 g (500 mmol) of ethyl dichlorophosphate to 105.5 g (500 mmol) of phenyl dichlorophosphate. As a result, phenyl difluorophosphate was obtained at a yield of 31%.

[0360] [Synthesis of lithium difluorophosphate]

[0361] The difluorophosphate esters obtained in the above Synthesis Examples 1 to 6 were reacted with a lithium salt compound in a non-aqueous organic solvent to synthesize lithium difluorophosphate according to the procedures of Examples 1 to 18 and Comparative Example 1 below.

[0362] The water content in the non-aqueous organic solvent was measured using a Karl Fischer moisture meter (coulometric titration type MKC-610) manufactured by KYOTO ELECTRONICS MANUFACTURING CO., LTD. In addition, a moisture vaporizer (ADP-611) manufactured by KYOTO ELECTRONICS MANUFACTURING CO., LTD. was connected to the Karl Fischer moisture meter to measure the water content in the lithium salt compound at a set temperature of 150°C.

[0363] pass 19 The purity of the lithium difluorophosphate obtained by the reaction was determined by F-NMR measurement. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was determined by non-aqueous neutralization titration using triethylamine as a base.

[0364] (Example 1)

[0365] 100 mL of EMC (containing 110 mass ppm of water) and 4.2 g (100 mmol) of undried anhydrous lithium chloride (containing 4850 mass ppm of water) were added to a 500 mL glass reaction container, and stirring was started at a temperature in the container of 40° C. Here, 13.0 g (100 mmol) of ethyl difluorophosphate obtained in the step of Synthesis Example 1 was added over 1 hour. The water content in the total amount of raw materials before the reaction was 270 mass ppm.

[0366] With the addition of ethyl difluorophosphate, foaming due to the generation of ethyl chloride can be seen. Then, stirring was continued for 12 hours at an internal temperature of 40°C. After the internal temperature was lowered to below 25°C, the precipitated solid was recovered by filtration, and after reduced pressure drying at 80°C, lithium difluorophosphate with a purity of 97% was obtained with a yield of 98%. The main impurities are lithium monofluorophosphate (Li2PO3F) generated by the decomposition of lithium difluorophosphate in water or lithium monofluorophosphate ethyl ester (LiPO2F(OCH2CH3)) generated by the reaction of lithium difluorophosphate with ethanol as a by-product. In addition, when the concentration of hydrofluoric acid mixed in lithium difluorophosphate was measured by non-aqueous neutralization titration, the result was 2030 mass ppm.

[0367] (Example 2)

[0368] The reaction was carried out in the same manner as in Example 1 except that the lithium chloride used was changed to lithium chloride containing 2150 mass ppm of water (the product of lithium chloride containing 4850 mass ppm of water and dried under reduced pressure at 150° C. for 2 hours). As a result, after filtration / reduced pressure drying, lithium difluorophosphate having a purity of >99% was obtained at a yield of 98%. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 910 mass ppm.

[0369] (Example 3)

[0370] The reaction was carried out in the same manner as in Example 1 except that the lithium chloride used was changed to one containing 1200 mass ppm of water (the product of drying lithium chloride containing 4850 mass ppm of water at 150° C. under reduced pressure for 3 hours). As a result, after filtration / reduced pressure drying, lithium difluorophosphate having a purity of >99% was obtained at a yield of 98%. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 420 mass ppm.

[0371] (Example 4)

[0372] The reaction was carried out in the same manner as in Example 1 except that the lithium chloride used was changed to lithium chloride containing 510 mass ppm of water (the product of lithium chloride containing 4850 mass ppm of water and dried under reduced pressure at 150° C. for 6 hours). As a result, after filtration / reduced pressure drying, lithium difluorophosphate having a purity of >99% was obtained at a yield of 98%. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 230 mass ppm.

[0373] (Example 5)

[0374] The reaction was carried out in the same steps as in Example 4 except that the ethyl difluorophosphate used was changed to the ethyl difluorophosphate obtained in the steps of Synthesis Example 2 (the water content in the total amount of raw materials before the reaction was 110 mass ppm). As a result, after filtration / reduced pressure drying, lithium difluorophosphate with a purity of >99% was obtained at a yield of 98%. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 210 mass ppm.

[0375] (Example 6)

[0376] The reaction was carried out in the same steps as in Example 4 except that the ethyl difluorophosphate used was changed to the ethyl difluorophosphate obtained in the steps of Synthesis Example 3 (the water content in the total amount of raw materials before the reaction was 110 mass ppm.), and as a result, after filtration / reduced pressure drying, lithium difluorophosphate with a purity of >99% was obtained at a yield of 98%. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 250 mass ppm.

[0377] (Example 7)

[0378] The reaction was carried out in the same manner as in Example 4 except that the solvent used was changed from EMC to dimethyl carbonate (hereinafter referred to as DMC) containing 120 mass ppm of water. (The water content of the total amount of raw materials before the reaction was 120 mass ppm.) As a result, after filtration / reduced pressure drying, lithium difluorophosphate with a purity of >99% was obtained at a yield of 98%. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 230 mass ppm.

[0379] (Example 8)

[0380] 100 mL of ethyl acetate (containing 95 mass ppm of water) and 4.2 g (100 mmol) of lithium chloride (containing 510 mass ppm of water) were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40° C. At this time, 13.0 g (100 mmol) of ethyl difluorophosphate obtained in the step of Synthesis Example 1 was added over 1 hour. The water content in the total amount of raw materials before the reaction was 100 mass ppm.

[0381] With the addition of ethyl difluorophosphate, foaming due to the generation of ethyl chloride was observed. Then, stirring was continued for 12 hours at an internal temperature of 40°C. The ethyl chloride and ethyl acetate contained in the obtained solution were removed by heating under reduced pressure, and the obtained solid was then washed with EMC. Furthermore, the solid was recovered by filtration and dried under heating under reduced pressure at 80°C, resulting in lithium difluorophosphate with a purity of >99% with a yield of 97%. In addition, when the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was determined by non-aqueous neutralization titration, the result was 200 mass ppm.

[0382] (Example 9)

[0383] The reaction was carried out in the same manner as in Example 8 except that the solvent used was changed from ethyl acetate to acetone containing 130 mass ppm of water (the water content in the total amount of the raw materials before the reaction was 130 mass ppm). As a result, after filtration / reduced pressure drying, lithium difluorophosphate having a purity of >99% was obtained at a yield of 96%. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 180 mass ppm.

[0384] (Example 10)

[0385] The reaction was carried out in the same manner as in Example 8 except that the solvent used was changed from ethyl acetate to dimethoxyethane (hereinafter referred to as DME) containing 90 mass ppm of water. (The water content in the total amount of the raw materials before the reaction was 100 mass ppm.) As a result, after filtration and reduced pressure drying, lithium difluorophosphate with a purity of 98% was obtained at a yield of 92%. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 420 mass ppm.

[0386] (Example 11)

[0387] 100 mL of EMC (containing 110 mass ppm of water) and 6.6 g (100 mmol) of lithium acetate (containing 3800 mass ppm of water) were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40°C. At this time, 13.0 g (100 mmol) of ethyl difluorophosphate obtained by the steps of Synthesis Example 1 was added over 1 hour. In addition, the water contained in the total amount of raw materials before the reaction was 300 mass ppm. Then, stirring was continued for 12 hours at an internal temperature of 40°C. Ethyl acetate as a by-product was removed by vacuum concentration, and the precipitated solid was then recovered by filtration, and after vacuum drying at 80°C, lithium difluorophosphate with a purity of 97% was obtained with a yield of 95%. The main impurities were lithium monofluorophosphate as a hydrolysis product or lithium difluorophosphate and ethyl monofluorophosphate generated by the reaction of ethanol as a by-product. In addition, when the concentration of hydrofluoric acid mixed in lithium difluorophosphate was measured by non-aqueous neutralization titration, the result was 2570 mass ppm.

[0388] (Example 12)

[0389] The reaction was carried out in the same manner as in Example 11 except that the lithium acetate used was changed to one containing 1960 mass ppm of water (the product of lithium acetate containing 3800 mass ppm of water and dried under reduced pressure at 150° C. for 2 hours). (The water content in the total amount of the raw materials before the reaction was 200 mass ppm.) As a result, lithium difluorophosphate having a purity of >99% was obtained at a yield of 96% after filtration / reduced pressure drying. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 970 mass ppm.

[0390] (Example 13)

[0391] The reaction was carried out in the same manner as in Example 11 except that the lithium acetate used was changed to one containing 950 mass ppm of water (the product of lithium acetate containing 3800 mass ppm of water and dried under reduced pressure at 150° C. for 3 hours). (The water content in the total amount of the raw materials before the reaction was 140 mass ppm.) As a result, lithium difluorophosphate having a purity of >99% was obtained at a yield of 96% after filtration / reduced pressure drying. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 530 mass ppm.

[0392] (Example 14)

[0393] The reaction was carried out in the same manner as in Example 11 except that the lithium acetate used was changed to one containing 450 mass ppm of water (the product of lithium acetate containing 3800 mass ppm of water and dried under reduced pressure at 150° C. for 6 hours). (The water content of the total amount of the raw materials before the reaction was 120 mass ppm.) As a result, lithium difluorophosphate having a purity of >99% was obtained at a yield of 95% after filtration / reduced pressure drying. In addition, the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was 280 mass ppm.

[0394] (Example 15)

[0395] 100 mL of EMC (containing 110 mass ppm of water) and 4.2 g (100 mmol) of lithium chloride (containing 510 mass ppm of water) were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40° C. At this time, 11.6 g (100 mmol) of methyl difluorophosphate obtained by the step of Synthesis Example 4 was added over 1 hour. The water content in the total amount of raw materials before the reaction was 110 mass ppm.

[0396] With the addition of methyl difluorophosphate, foaming due to the generation of methyl chloride was observed. Then, stirring was continued for 12 hours at an internal temperature of 40°C. The precipitated solid was recovered by filtration and dried under reduced pressure at 80°C to obtain lithium difluorophosphate with a purity of >99% at a yield of 98%. In addition, when the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was measured by non-aqueous neutralization titration, the result was 250 mass ppm.

[0397] (Example 16)

[0398] 100 mL of EMC (containing 110 mass ppm of water) and 4.2 g (100 mmol) of lithium chloride (containing 510 mass ppm of water) were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40° C. At this time, 14.4 g (100 mmol) of n-propyl difluorophosphate obtained in the step of Synthesis Example 5 was added over 1 hour. The water content in the total amount of raw materials before the reaction was 110 mass ppm.

[0399] Then, stirring was continued for 12 hours at an internal temperature of 40° C. The precipitated solid was recovered by filtration and dried under reduced pressure at 80° C. to obtain lithium difluorophosphate with a purity of >99% at a yield of 98%. In addition, when the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was measured by non-aqueous neutralization titration, the result was 210 mass ppm.

[0400] (Example 17)

[0401] 100 mL of EMC (containing 110 mass ppm of water) and 4.2 g (100 mmol) of lithium chloride (containing 510 mass ppm of water) were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40° C. At this time, 17.8 g (100 mmol) of phenyl difluorophosphate obtained in the step of Synthesis Example 6 was added over 1 hour. The water content in the total amount of raw materials before the reaction was 110 mass ppm.

[0402] Then, stirring was continued for 48 hours at an internal temperature of 40° C. The precipitated solid was recovered by filtration and dried under reduced pressure at 80° C. to obtain lithium difluorophosphate with a purity of 98% at a yield of 97%. In addition, when the concentration of hydrofluoric acid mixed in the lithium difluorophosphate was measured by non-aqueous neutralization titration, the result was 300 mass ppm.

[0403] (Example 18)

[0404] 100 mL of acetonitrile (containing 280 mass ppm of water) and 4.2 g (100 mmol) of lithium chloride (containing 510 mass ppm of water) were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40° C. At this time, 13.0 g (100 mmol) of ethyl difluorophosphate obtained by the step of Synthesis Example 1 was added over 1 hour. In addition, the water content in the total amount of raw materials before the reaction was 250 mass ppm.

[0405] With the addition of ethyl difluorophosphate, foaming due to the generation of ethyl chloride can be seen. Then, stirring was continued for 12 hours at an internal temperature of 40°C. The ethyl chloride and acetonitrile contained in the obtained solution were removed under heating and reduced pressure, and the obtained solid was then washed with EMC. In addition, the solid was recovered by filtration and dried under heating and reduced pressure at 80°C. As a result, lithium difluorophosphate with a purity of 96% was obtained with a yield of 95%. The main impurities were lithium monofluorophosphate generated by the decomposition of lithium difluorophosphate in water or lithium monofluorophosphate ethyl generated by the reaction of lithium difluorophosphate with ethanol as a by-product. In addition, when the concentration of hydrofluoric acid mixed in lithium difluorophosphate was measured by non-aqueous neutralization titration, the result was 2800 mass ppm.

[0406] (Comparative Example 1)

[0407] 100 mL of EMC (containing 110 mass ppm of water), 4.2 g (100 mmol) of lithium chloride (containing 510 mass ppm of water) and 0.9 g of water (50 mmol) were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40°C. At this time, 13.0 g (100 mmol) of ethyl difluorophosphate obtained by the steps of Synthesis Example 1 was added over 1 hour. In addition, the water contained in the total amount of raw materials before the reaction was 7700 mass ppm. Then, stirring was continued for 12 hours at an internal temperature of 40°C. After the internal temperature was lowered to below 25°C, the precipitated solid was recovered by filtration, and after reduced pressure drying at 80°C, lithium difluorophosphate with a purity of 83% was obtained with a yield of 96%. The main impurities are monofluoro lithium phosphate generated by the decomposition of lithium difluorophosphate in water or monofluoro lithium ethyl phosphate generated by the reaction of lithium difluorophosphate with ethanol as a by-product. In addition, when the concentration of hydrofluoric acid mixed in lithium difluorophosphate was measured by non-aqueous neutralization titration, the result was 4210 mass ppm. 1 H-NMR and 19 F-NMR confirmed that 0.5 mass % of ethanol was contained even after drying.

[0408]

[0409] The results are shown in Table 1. In Table 1, the water content in the total amount of raw materials before reaction in Comparative Example 1 indicates an amount including added water.

[0410] Since water was used as a reaction raw material in Comparative Example 1, more raw materials were used in the reaction than in Examples, and the production method was less efficient than that in Examples.

[0411] In comparison of the embodiments, it was found that in Embodiment 1 and Embodiment 11, in which the water content in the total amount of raw materials before the reaction was 270 mass ppm and 300 mass ppm, which were more than those in other embodiments (the water content in the lithium salt compound was 4850 mass ppm and 3800 mass ppm, which were more than those in other embodiments), lithium monofluorophosphate as a hydrolysis product of lithium difluorophosphate or lithium ethyl monofluorophosphate generated by the reaction of lithium difluorophosphate with by-product ethanol was present as impurities, and the selectivity was reduced, resulting in reduced purity. In addition, the amount of hydrofluoric acid mixed was also a very high value of more than 2000 mass ppm.

[0412] It is found that if the water contained in the lithium salt compound is reduced to about 2000 mass ppm so that the water contained in the total amount of raw materials before the reaction is less than 200 mass ppm, the hydrolysis of lithium difluorophosphate or the decomposition caused by the byproduct ethanol can be significantly suppressed, and if the purity is improved by reducing monofluoro lithium phosphate or monofluoro ethyl lithium phosphate, the concentration of hydrofluoric acid is reduced (Examples 2, 12). In addition, according to the results of Examples 3, 4, 13, and 14, it is found that if the water contained in the total amount of raw materials before the reaction is further reduced (if the water contained in the lithium salt compound is further reduced), the purity of lithium difluorophosphate reaches the limit of 99%, and the concentration of hydrofluoric acid is further reduced at the same time, especially if the water content in the total amount of raw materials before the reaction is set to about 100 mass ppm (if the water contained in the lithium salt compound is set to about 500 mass ppm), the concentration of hydrofluoric acid can be suppressed to a particularly low level. In addition, it can be confirmed according to these results that even if the lithium salt compound is changed from lithium chloride to lithium acetate, lithium difluorophosphate can be obtained.

[0413] In addition, it can be considered that the reason why the yield of about 95% in Examples 11 to 14 using lithium acetate is lower than that when lithium chloride is used is that the by-product ethyl acetate was not removed by reduced pressure concentration, so that part of the lithium difluorophosphate that should have been almost completely precipitated was dissolved by the ethyl acetate remaining in the solution.

[0414] In Examples 4 to 6, the water content contained in the total amount of raw materials before the reaction was fixed to 110 mass ppm (the water content of the lithium chloride used was fixed to 510 mass ppm), and the raw material ethyl difluorophosphate of different manufacturing methods was used, but the difference in the manufacturing method did not affect the yield, purity, and the concentration of the hydrofluoric acid mixed into the obtained lithium difluorophosphate. In addition, according to the results of Examples 4, 7 to 10, it can be confirmed that lithium difluorophosphate can be obtained even if the non-aqueous organic solvent is changed from EMC to DMC or ethyl acetate, acetone, DME. In addition, it can be considered that when using ethyl acetate, acetone, DME, the reason why the yield decreases compared to the result of EMC or DMC is that even if these solvents are removed after the solvent is partially residual, when the EMC is washed / filtered later, part of the lithium difluorophosphate is dissolved in these solvents, thereby being separated to the filtrate side.

[0415] Even if the raw material substrate is changed from ethyl ester to methyl ester (Example 15), n-propyl ester (Example 16), or phenyl ester (Example 17), high-purity lithium difluorophosphate of 98% or more can be obtained at a high yield of 97% or more under the same conditions. It can be said that the difference in the yield and purity of the lithiation reaction caused by the type of substrate is small.

[0416] Next, the particle size distribution of lithium difluorophosphate obtained by the production methods of Example 1, Example 8, and Comparative Example 1 (referred to as Example A, Example B, and Example C, respectively) was measured by the method described below. The results are shown in Table 2 below.

[0417] (Particle size distribution measurement)

[0418] The particle size distribution of about 10 mg of lithium difluorophosphate obtained in Example A, Example B, and Example C was measured in about 20 mL of hexane solvent using a laser diffraction particle size distribution measuring device (Shimadzu Corporation. SALD-2200). During the measurement, the measuring cell was stirred, the light intensity distribution was adjusted to 50%, and the refractive index of the target substance was set to 1.35 for evaluation. Based on the measurement results, the particle size d10 at which the volume accumulation was 10%, the particle size d90 at which the volume accumulation was 90%, and the volume average particle size MV on the side of the small particle size were obtained.

[0419] (Evaluation of heat release during dissolution of lithium difluorophosphate)

[0420] A solution was prepared by dissolving LiPF6 as an electrolyte in a non-aqueous solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio EC:EMC=3:7) at a concentration of 1.2 mol / L. The solution was divided into 20 mL portions and the temperature of each solution was adjusted to 30°C to prepare a test solution.

[0421] To each of the test solutions, lithium difluorophosphate (Example A, Example B, Example C) described in Table 2 was added so that the concentration was 1.5% by mass, and the mixture was stirred and mixed to prepare a non-aqueous electrolyte solution.

[0422] Table 2 shows the results of measuring the temperature of the non-aqueous electrolyte solution after adding lithium difluorophosphate and stirring for 5 minutes.

[0423]

[0424] According to the results in Table 2, the following conclusions can be drawn.

[0425] The (d90-d10) / MV values ​​of the lithium difluorophosphate obtained in Example A (Example 1), Example B (Example 8), and Example C (Comparative Example 1) were all 10 or less, and the heat generation when dissolved in a non-aqueous electrolyte as an additive could be suppressed.

[0426] There is a tendency that the smaller the value of (d90-d10) / MV of lithium difluorophosphate is, the more heat generation can be suppressed when it is dissolved in a non-aqueous electrolyte solution as an additive.

[0427] The lower the water content in the total amount of raw materials before the reaction, the smaller the value of (d90-d10) / MV.

[0428] When water as a raw material does not exist, the value of (d90-d10) / MV is small.

[0429] The higher the purity of the product, the smaller the value of (d90-d10) / MV.

[0430] The lower the hydrofluoric acid concentration in the product, the smaller the value of (d90-d10) / MV.

[0431] Figure 1 and Figure 2 The SEM image of the lithium difluorophosphate of Example A is shown in FIG. Figure 3 and Figure 4 A SEM image of lithium difluorophosphate of Example C is shown in FIG.

[0432] [Fluorinating agent]

[0433] Triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride can be obtained by dissolving triethylamine or tetramethylethylenediamine in a non-aqueous organic solvent with a water content of less than 50 mass ppm and keeping the solution temperature below 5 ° C, respectively adding equimolar hydrofluoric acid to these alkalis. In addition, the above-mentioned non-aqueous organic solvent is the same as the non-aqueous organic solvent (a) used in the later-described operation 1. When the concentration of hydrofluoric acid remaining in these obtained fluorinating agents is measured by non-aqueous neutralization titration using a glass burette, it is less than the specified amount lower limit (0.2 mol %) respectively. In addition, in the above-mentioned non-aqueous neutralization titration, the reaction solution is partially sampled, diluted with acetone, titrated using triethylamine as a base and bromophenol blue as an indicator, and the measured value is converted to the concentration of the hydrofluoric acid standard contained in the reaction solution. The non-aqueous neutralization titration described later is all carried out in the same manner.

[0434] In addition, hydrofluoric acid is dissolved in a non-aqueous organic solvent, and while the solution temperature is maintained at below 5°C, an equal molar amount of ammonia is charged to synthesize ammonium fluoride. In addition, the non-aqueous organic solvent is the same as the non-aqueous organic solvent (a) used in the later-described step 1. After the ammonium fluoride is recovered by filtration, the residual hydrofluoric acid concentration is measured by non-aqueous neutralization titration, and the result is less than the specified amount lower limit (0.2 mol %). The ammonium fluoride is recorded as ammonium fluoride (1) (also expressed as NH4F(1)).

[0435] In addition, hydrofluoric acid is dissolved in a non-aqueous organic solvent, and while the solution temperature is maintained at below 5°C, an equimolar amount of sodium hydroxide is slowly added to synthesize sodium fluoride. In addition, the non-aqueous organic solvent is the same as the non-aqueous organic solvent (a) used in the later-described step 1. After sodium fluoride is recovered by filtration and dried under reduced pressure, the residual hydrofluoric acid concentration is measured by non-aqueous neutralization titration, and the result is less than the specified amount lower limit (0.2 mol %). The sodium fluoride is recorded as sodium fluoride (1) (also expressed as NaF (1)).

[0436] [Preparation of a fluorinating agent containing hydrofluoric acid]

[0437] Dissolve triethylamine in a non-aqueous organic solvent with a water content of 50 mass ppm or less, and while maintaining the solution temperature at 5° C. or less, add 2 times the mole of hydrofluoric acid to obtain triethylamine dihydrofluoride. When the concentration of hydrofluoric acid contained is measured by non-aqueous neutralization titration, the result is 50 mol%. In addition, the non-aqueous organic solvent is the same as the non-aqueous organic solvent (a) used in the step 1 described later.

[0438] By adding ammonium bifluoride (containing hydrofluoric acid concentration of 50 mol%) manufactured by FUJIFILM Wako Pure Chemical Corporation to ammonium fluoride (1), ammonium fluoride (2) (also represented by NH4F(2)) (number average molecular weight 35.3) containing hydrofluoric acid concentration of 10 mol% and ammonium fluoride (3) (also represented by NH4F(3)) (number average molecular weight 33.6) containing hydrofluoric acid concentration of 20 mol% were prepared. The contained hydrofluoric acid concentration was measured by non-aqueous neutralization titration.

[0439] Furthermore, sodium fluoride (2) (also referred to as NaF (2)) (number average molecular weight 39.8) containing 10 mol% of hydrofluoric acid and sodium fluoride (3) (also referred to as NaF (3)) containing 20 mol% of hydrofluoric acid were prepared by adding sodium hydrogen fluoride manufactured by FUJIFILM Wako Pure Chemical Corporation to sodium fluoride (1). The contained hydrofluoric acid concentration was measured by non-aqueous neutralization titration.

[0440] Methyl dichlorophosphate, which is the raw material of step 1 (dihalogenated phosphoric acid ester represented by general formula (1)), can be obtained by dissolving phosphorus oxychloride in PC as a non-aqueous organic solvent, adding an equimolar mixture of the corresponding alcohol (methanol) and triethylamine dropwise thereto while keeping the solution temperature below 5°C, removing triethylamine hydrochloride by filtration, and further separating by reduced pressure distillation. Similarly, ethyl dichlorophosphate, n-propyl dichlorophosphate, and phenyl dichlorophosphate can be obtained by replacing alcohol with the corresponding ethanol, n-propanol, and phenol, respectively, and separating them.

[0441] [Comparative Example 1-1]

[0442] 500 mL of EMC and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction container and stirred to mix thoroughly. While keeping the solution temperature below 20°C, 28.0 g (1400 mmol) of hydrofluoric acid was added dropwise over 30 minutes, and then the solution temperature was raised to 25°C and stirring was continued for 24 hours. 19 F-NMR analysis of the obtained reaction solution showed that the selectivity of ethyl difluorophosphate as the target product was 45 mol%, and 30 mol% of hexafluorophosphoric acid and 25 mol% of diethyl monofluorophosphate were also produced. 31 It was confirmed by P-NMR that the ethyl dichlorophosphate as a raw material had been completely consumed.

[0443] After removing the hydrochloric acid by vacuum concentration, vacuum distillation was performed in a 10-layer distillation tower to obtain the purity of the fluorine and phosphorus components (by 19F-NMR, 31 12.0 g (92.3 mmol, yield 19%, distillation recovery rate 41%) of ethyl difluorophosphate with a concentration of 97% (P-NMR measurement). This ethyl difluorophosphate was obtained as a mixed solution with EMC. In addition, the values ​​of yield, etc. are values ​​after subtracting the contained solvent, and the same shall apply hereinafter.

[0444] [Comparative Example 1-2]

[0445] 350 mL of EMC and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction container and stirred to mix thoroughly. While keeping the solution temperature below 20°C, a mixed solution of 74.1 g (525 mmol) of triethylamine dihydrofluoride (containing a hydrofluoric acid concentration of 50 mol%) and 150 mL of EMC was added dropwise over 30 minutes, and then the solution temperature was raised to 25°C and stirring was continued for 24 hours. 19 F-NMR analysis of the obtained reaction solution showed that the selectivity of ethyl difluorophosphate as the target product was 49 mol%, and 39 mol% of hexafluorophosphoric acid and 12 mol% of diethyl monofluorophosphate were also produced. 31 It was confirmed by P-NMR that the ethyl dichlorophosphate as a raw material had been completely consumed.

[0446] After the hydrochloric acid was removed by vacuum concentration, the triethylamine hydrochloride was removed by filtration. The filtrate obtained was subjected to vacuum distillation in a 10-layer distillation tower to obtain the purity of the fluorine and phosphorus components (by 19 F-NMR, 31 12.7 g (98.0 mmol, yield 20%, distillation recovery rate 40%) of ethyl difluorophosphate with an ethyl difluorophosphate content of 98% (P-NMR measurement) was obtained. This ethyl difluorophosphate was obtained as a mixed liquid with EMC.

[0447] [Comparative Examples 1-3]

[0448] 500 mL of EMC and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction container and stirred to mix thoroughly. At this time, 29.9 g (525 mmol) of ammonium bifluoride (containing a hydrofluoric acid concentration of 50 mol%) was added and stirring was continued for 24 hours at a solution temperature of 25°C. 19 F-NMR analysis of the obtained reaction solution showed that the selectivity of ethyl difluorophosphate as the target product was 51 mol%, and in addition, 40 mol% of hexafluorophosphoric acid and 9 mol% of diethyl monofluorophosphate were also produced. 31 It was confirmed by P-NMR that the ethyl dichlorophosphate as a raw material had been completely consumed.

[0449] After the reaction, separation operation was performed in the same manner as in Comparative Example 1-2, and analysis was performed in the same manner to obtain 15.5 g (119.3 mmol, yield 23%, distillation recovery rate 45%) of ethyl difluorophosphate with a purity of 98% of fluorine and phosphorus components. In addition, the ethyl difluorophosphate was obtained in the form of a mixed solution with EMC.

[0450] [Comparative Examples 1-4]

[0451] 500 mL of EMC and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction container, and stirred and mixed thoroughly. At this time, 34.5 g (1025 mmol) of ammonium fluoride (3) was added, and stirring was continued for 24 hours at a solution temperature of 25°C. 19 F-NMR analysis of the obtained reaction solution showed that the selectivity of ethyl difluorophosphate as the target product was 69 mol%, and in addition, 26 mol% of hexafluorophosphoric acid and 5 mol% of diethyl monofluorophosphate were produced. 31 It was confirmed by P-NMR that the ethyl dichlorophosphate as a raw material had been completely consumed.

[0452] After the reaction, separation operation was performed in the same manner as in Comparative Example 1-2, and analysis was performed in the same manner to obtain 38.2 g (293.5 mmol, yield 59%, distillation recovery rate 85%) of ethyl difluorophosphate with a purity of fluorine and phosphorus components greater than 99%. The ethyl difluorophosphate was obtained in the form of a mixed solution with EMC.

[0453] [Comparative Examples 1-5]

[0454] 500 mL of EMC and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction container, and stirred to mix thoroughly. At this time, 35.5 g (1025 mmol) of sodium fluoride (3) was added, and stirring was continued for 24 hours at a solution temperature of 25°C. 19 F-NMR analysis of the obtained reaction solution showed that the selectivity of ethyl difluorophosphate as the target product was 66 mol%, and 30 mol% of hexafluorophosphoric acid and 4 mol% of diethyl monofluorophosphate were also produced. 31 It was confirmed by P-NMR that the ethyl dichlorophosphate as a raw material had been completely consumed.

[0455] After the reaction, separation operation was performed in the same manner as in Comparative Example 1-2, and analysis was performed in the same manner to obtain 37.3 g (287.0 mmol, yield 57%, distillation recovery rate 87%) of ethyl difluorophosphate with a purity of fluorine and phosphorus components>99%. The ethyl difluorophosphate was obtained in the form of a mixed solution with EMC.

[0456] [Example 1-1]

[0457] 500 mL of EMC and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction container, and stirred to mix thoroughly. At this time, 37.1 g (1050 mmol) of ammonium fluoride (2) was added, and stirring was continued for 24 hours at a solution temperature of 25°C. 19 F-NMR analysis of the obtained reaction solution showed that the selectivity of the target product, ethyl difluorophosphate, was 91 mol%, and 6 mol% of hexafluorophosphoric acid and 3 mol% of diethyl monofluorophosphate were also produced. 31 It was confirmed by P-NMR that the ethyl dichlorophosphate as a raw material had been completely consumed.

[0458] The ammonium chloride was removed by filtration, and the obtained filtrate was subjected to vacuum distillation in a 10-layer distillation tower to obtain the purity of the fluorine and phosphorus components (by 19 F-NMR, 31 55.6 g (427.5 mmol, yield 85%, distillation recovery rate 94%) of ethyl difluorophosphate >99% (P-NMR determination).

[0459] [Examples 1-2 to 1-4]

[0460] According to the steps and analysis methods shown in Example 1-1, the experiment was conducted by changing only the fluorinating agent used as shown in Table 3. As a result, it was confirmed that ethyl difluorophosphate was generated with selectivities of 90 mol%, 95 mol%, and 96 mol%, respectively. Then, through separation operation, ethyl difluorophosphate with fluorine and phosphorus component purities of >99% was obtained with yields of 85%, 90%, and 91% (distillation recovery rates of 94%, 95%, and 95%), respectively. In addition, the hydrofluoric acid concentration contained in the fluorinating agent used in Examples 1-3 and 1-4 was <0.2 mol% (less than 0.2 mol%).

[0461] [Examples 1-5]

[0462] 500 mL of EMC and 81.5 g (500 mmol) of ethyl dichlorophosphate were added to a 1 L fluororesin reaction container, and stirred to mix thoroughly. At this time, 38.9 g (1050 mmol) of ammonium fluoride (1) was added, and stirring was continued for 24 hours at a solution temperature of 25°C. 19 F-NMR analysis of the obtained reaction solution showed that the selectivity of ethyl difluorophosphate as the target product was 98 mol %, and in addition, 2 mol % of diethyl monofluorophosphate was generated. 31 It was confirmed by P-NMR that the ethyl dichlorophosphate as a raw material had been completely consumed.

[0463] The ammonium chloride was removed by filtration, and the obtained filtrate was subjected to vacuum distillation in a 10-layer distillation tower to obtain the purity of the fluorine and phosphorus components (by 19 F-NMR, 31 60.5 g (465.0 mmol, yield 93%, distillation recovery rate 95%) of ethyl difluorophosphate >99% (P-NMR determination).

[0464] [Examples 1-6 to 1-9]

[0465] According to the steps and analytical methods shown in Examples 1-5, the experiment was conducted by changing only the non-aqueous organic solvent (a) used as shown in Table 3. As a result, it was confirmed that ethyl difluorophosphate was generated with selectivities of 97 mol%, 96 mol%, 92 mol%, and 83 mol%, respectively. Then, through separation operation, ethyl difluorophosphate with fluorine and phosphorus component purities of >99% was obtained with yields of 92%, 90%, 86%, and 78%, respectively (distillation recovery rates of 95%, 94%, 94%, and 94%). In addition, "DMC" in Table 3 represents dimethyl carbonate.

[0466] [Examples 1-10]

[0467] The experiment was conducted by the same steps and analytical methods as in Example 1-5 except that the fluorinating agent was changed from ammonium fluoride (1) to sodium fluoride (1), and it was confirmed that ethyl difluorophosphate was generated with a selectivity of 96 mol %. Then, through separation operation, ethyl difluorophosphate with a purity of fluorine and phosphorus components >99% was obtained with a yield of 91% (distillation recovery rate of 95%).

[0468] [Examples 1-11, 1-12]

[0469] The experiment was carried out in the same steps as in Examples 1-10 except that the non-aqueous organic solvent (a) was changed from EMC to PC or acetonitrile. The results confirmed that ethyl difluorophosphate was generated with selectivities of 96 mol % and 80 mol %, respectively. Subsequently, through separation operation, ethyl difluorophosphate with purities of fluorine and phosphorus components both >99% was obtained with yields of 89% and 73%, respectively (distillation recovery rates of 93% and 92%).

[0470] [Comparative Examples 1-6]

[0471] The experiment was conducted by the same steps and analysis methods as in Comparative Example 1-1, except that the dihalogenated phosphate represented by the general formula (1) was changed from 81.5 g (500 mmol) of ethyl dichlorophosphate to 74.5 g (500 mmol) of methyl dichlorophosphate. The results showed that methyl difluorophosphate was generated with a selectivity of 47 mol %. Then, through separation operation, methyl difluorophosphate with a purity of 98% for fluorine and phosphorus components was obtained with a yield of 18% (distillation recovery rate of 39%).

[0472] [Examples 1-13]

[0473] The experiment was conducted by the same steps and analytical methods as Comparative Examples 1-6 except that the fluorinating agent was changed from hydrofluoric acid to ammonium fluoride (1). The results confirmed that methyl difluorophosphate was generated with a selectivity of 97 mol %. Then, through separation operation, methyl difluorophosphate with a purity of fluorine and phosphorus components >99% was obtained with a yield of 89% (distillation recovery rate of 92%).

[0474] [Examples 1-14]

[0475] The experiment was conducted with the same steps and analysis methods as in Example 1-13, except that the non-aqueous organic solvent (a) was changed from EMC to acetonitrile. The results confirmed that methyl difluorophosphate was generated with a selectivity of 78 mol %. Subsequently, through separation operation, methyl difluorophosphate with a purity of fluorine and phosphorus components >99% was obtained with a yield of 70% (distillation recovery rate of 90%).

[0476] [Comparative Examples 1-7]

[0477] The experiment was conducted by the same steps and analysis methods as in Comparative Example 1-2, except that the dihalogenated phosphate represented by the general formula (1) was changed from 81.5 g (500 mmol) of ethyl dichlorophosphate to 88.5 g (500 mmol) of n-propyl dichlorophosphate. The results showed that n-propyl difluorophosphate was generated with a selectivity of 51 mol %. Then, through separation operation, n-propyl difluorophosphate with a purity of 98% for fluorine and phosphorus components was obtained with a yield of 20% (distillation recovery rate of 40%).

[0478] [Examples 1-15]

[0479] The experiment was conducted by the same steps and analytical methods as Comparative Examples 1-7 except that the fluorinating agent was changed from triethylamine dihydrofluoride to ammonium fluoride (1). The results confirmed that n-propyl difluorophosphate was generated with a selectivity of 97 mol %. Then, through separation operation, n-propyl difluorophosphate with a purity of fluorine and phosphorus components >99% was obtained with a yield of 90% (distillation recovery rate of 93%).

[0480] [Examples 1-16]

[0481] The experiment was conducted with the same steps and analysis methods as in Example 1-15, except that the non-aqueous organic solvent (a) was changed from EMC to PC. The results confirmed that n-propyl difluorophosphate was generated with a selectivity of 96 mol%. Then, through separation operation, n-propyl difluorophosphate with a purity of fluorine and phosphorus components >99% was obtained with a yield of 88% (distillation recovery rate of 92%).

[0482] [Example 1-17]

[0483] The experiment was conducted with the same steps and analysis methods as in Example 1-15, except that the non-aqueous organic solvent (a) was changed from EMC to acetonitrile. The results confirmed that n-propyl difluorophosphate was generated with a selectivity of 77 mol %. Then, through separation operation, n-propyl difluorophosphate with a purity of fluorine and phosphorus components >99% was obtained with a yield of 69% (distillation recovery rate of 90%).

[0484] [Comparative Examples 1-8]

[0485] The experiment was conducted by the same steps and analysis methods as Comparative Examples 1-3, except that the dihalogenated phosphate represented by the general formula (1) was changed from 81.5 g (500 mmol) of ethyl dichlorophosphate to 105.5 g (500 mmol) of phenyl dichlorophosphate. The results showed that phenyl difluorophosphate was generated with a selectivity of 43 mol %. Then, through separation operation, phenyl difluorophosphate with a purity of fluorine and phosphorus components of >99% was obtained with a yield of 17% (distillation recovery rate of 39%).

[0486] [Examples 1-18]

[0487] The experiment was conducted in the same manner as in Comparative Example 1-8 except that the fluorinating agent was changed from ammonium bifluoride (containing a hydrofluoric acid concentration of 50 mol%) to ammonium fluoride (1). As a result, it was confirmed that phenyl difluorophosphate was generated at a selectivity of 89 mol%. 13 P-NMR was used to determine that phenyl dichlorophosphate, which was the raw material, remained. Therefore, the reaction time was extended by 48 hours, and the final selectivity was increased to 92 mol%. Then, through separation operation, phenyl difluorophosphate with a purity of fluorine and phosphorus components> 99% was obtained with a yield of 83% (distillation recovery rate of 90%).

[0488] The above results are shown in Table 3.

[0489]

[0490] In Table 3, Et3N is triethylamine, TMEDA is tetramethylethylenediamine, HF is hydrofluoric acid, NH4F is ammonium fluoride, and NaF is sodium fluoride.

[0491] Since hydrofluoric acid is generally used in the fluorination of halogenated phosphoric acid compounds (the halogen is chlorine or bromine), fluorination with hydrofluoric acid was first attempted as shown in Comparative Example 1-1. However, unexpectedly, the fluorination selectivity for forming the target product was as low as 45 mol %, and a large amount of by-products of hexafluorophosphoric acid or diethyl monofluorophosphate, which were believed to be produced due to overfluorination or uneven fluorination, were confirmed to be generated.

[0492] Therefore, the fluorination conditions described in paragraphs

[0079] to

[0081] of International Publication No. 2015 / 122511 were then used to attempt fluorination with triethylamine dihydrofluoride (Comparative Examples 1-2). It was predicted that a high selectivity of more than 90 mol% could be obtained, but the result showed that the selectivity was greatly reduced to 49 mol%. Even if the fluorinating agent was changed to ammonium bifluoride, the selectivity was still low (Comparative Examples 1-3).

[0493] Next, when the fluorinating agent was changed from triethylamine dihydrofluoride to triethylamine monohydrofluoride (Example 1-3), a very high result of 95 mol% selectivity was unexpectedly obtained. When the amine was changed from triethylamine to tetramethylethylenediamine and tetramethylethylenediamine dihydrofluoride was used as the fluorinating agent (Example 1-4), a very good result of 96 mol% selectivity was also obtained.

[0494] In order to confirm the relationship between the amount of hydrofluoric acid and the fluorination selectivity, when fluorination of ethyl dichlorophosphate was carried out using ammonium fluoride or sodium fluoride with a hydrofluoric acid content of less than 0.2 mol%, 10 mol%, or 20 mol% as a fluorinating agent (Comparative Examples 1-4, 1-5, Examples 1-1, 1-2, 1-5, and 1-10), it was confirmed that the lower the concentration of hydrofluoric acid contained, the higher the selectivity for forming ethyl difluorophosphate, and the less by-products such as hexafluorophosphoric acid that are believed to be generated due to overfluorination or uneven fluorination.

[0495] As shown in the results of Comparative Examples 1-2 and 1-3, even when the selectivity of forming ethyl difluorophosphate is so low as about 50 mol % during the reaction, the purity of fluorine and phosphorus components can be obtained by the separation operation after the reaction. It is 98% high-purity ethyl difluorophosphate. However, since hexafluorophosphoric acid as the main by-product can be concentrated and remain in the still during distillation, it is easy to separate from ethyl difluorophosphate, but it is difficult to separate the monoethyl phosphate generated as a by-product from ethyl difluorophosphate. (When containing 12 mol % of diethyl monofluorophosphate, the recovery rate during the distillation purification of ethyl difluorophosphate with a purity of fluorine and phosphorus components is 40%, and the distillation recovery rate is 45% when containing 9 mol %.)

[0496] In addition, in Comparative Examples 1-1 to 1-3, in order to increase the purity of ethyl difluorophosphate to 97% or more, it was necessary to use a 10-layer distillation tower for distillation purification. However, in Example 1-1 containing only 3 mol% of diethyl monofluorophosphate, diethyl monofluorophosphate was able to be removed at a distillation recovery rate of 94% even with distillation using a 5-layer distillation tower.

[0497] In addition, the dihalogenated phosphoric acid ester represented by the general formula (1) was fixed to ethyl dichlorophosphate, and the fluorinating agent was fixed to ammonium fluoride, and the influence of changing the non-aqueous organic solvent (a) was investigated (Examples 1-5 to 1-9). As a result, there was a tendency that the selectivity was best when carbonate or chain ester solvents were used, followed by DGDE, and then acetonitrile.

[0498] When the dihalogenated phosphate represented by the general formula (1) was fixed to ethyl dichlorophosphate, the fluorinating agent was fixed to sodium fluoride, and the non-aqueous organic solvent (a) was changed (Examples 1-10 to 1-12), the same tendency was found, that is, the selectivity was best when carbonates were used.

[0499] In addition, from the results of Examples 1-13 to 1-18 and Comparative Examples 1-6 to 1-8, it can be seen that even if the substituent (the group represented by R) of the dichlorophosphate ester used as the raw material is changed, the tendency of the above results remains unchanged. By using a fluorinating agent and a carbonate solvent containing a low concentration of hydrofluoric acid (here less than 0.2 mol %), a high selectivity of fluorination of more than 96 mol % can be achieved (for Example 1-18, due to the slow fluorination rate, raw material residue occurred. By further extending the reaction time, the selectivity was actually increased to more than 92 mol %).

[0500] [Examples 1-9-1, 1-12-1]

[0501] The experiments were conducted in the same manner and by the same analysis methods as in Examples 1-9 and 1-12, except that the amount of the fluorinating agent used was changed to 1.5 equivalents. The results are shown in Table 4 together with the results of Examples 1-5 to 1-8, 1-10, and 1-11.

[0502] [Examples 1-19, 1-20]

[0503] The experiment was conducted in the same procedure and analysis method as in Example 1-3 except that the amount of the fluorinating agent and the type of the nonaqueous organic solvent (a) were changed as shown in Table 4. The results are shown in Table 4 together with the results of Example 1-3.

[0504] [Examples 1-21, 1-22]

[0505] The experiment was conducted in the same procedure and analysis method as in Example 1-4 except that the amount of the fluorinating agent and the type of the nonaqueous organic solvent (a) were changed as shown in Table 4. The results are shown in Table 4 together with the results of Example 1-4.

[0506]

[0507] As shown in Table 4, in Examples 1-5 to 1-7 using esters with a relative dielectric constant of 8 or less as the non-aqueous organic solvent (a) and Example 1-8 using ethers with a relative dielectric constant of 8 or less as the non-aqueous organic solvent (a), excellent selectivity and yield can be achieved even when the amount of the fluorinating agent used is a relatively small amount of 1.05 equivalents.

[0508] On the other hand, in Example 1-9 using acetonitrile (relative dielectric constant of about 37) as the non-aqueous organic solvent (a), when the amount of the fluorinating agent is also 1.05 equivalents, the selectivity and yield are slightly lower. In order to achieve the same degree of selectivity and yield as in Examples 1-5 to 1-8, it is necessary to increase the amount of the fluorinating agent to about 1.5 equivalents as shown in Example 1-9-1. In addition, the theoretical amount (2 molar times) required for fluorination is set to 1.0 equivalent.

[0509] In addition, as shown in Table 4, in Examples 1-10 using an ester with a relative dielectric constant of less than 8 as the non-aqueous organic solvent (a) and Examples 1-11 using propylene carbonate as the non-aqueous organic solvent (a), excellent selectivity and yield can be achieved even when the amount of the fluorinating agent used is a relatively small amount of 1.05 equivalents.

[0510] On the other hand, in Example 1-12 using acetonitrile (relative dielectric constant of about 37) as the non-aqueous organic solvent (a), when the amount of the fluorinating agent was also 1.05 equivalents, the selectivity and yield were slightly lower. In order to achieve the same degree of selectivity and yield as in Examples 1-10 and 1-11, the amount of the fluorinating agent needs to be increased to about 1.5 equivalents as shown in Example 1-12-1.

[0511] The above tendency was also confirmed when the fluorinating agent was changed to triethylamine monohydrofluoride (Examples 1-3, 1-19, and 1-20) or tetramethylethylenediamine dihydrofluoride (Examples 1-4, 1-21, and 1-22).

[0512] [Example 2-1]

[0513] 100 mL of EMC and 4.2 g (100 mmol) of lithium chloride (containing 4850 mass ppm of water) were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40°C. At this time, 13.0 g (100 mmol) of ethyl difluorophosphate obtained by the steps of Example 1-5 was added over 1 hour. In addition, the water contained in lithium chloride and EMC was used as water as one of the reaction raw materials. The molar ratio between ethyl difluorophosphate, lithium chloride and water was 1:1:0.02. At this time, bubbling caused by the generation of ethyl chloride can be observed. Then, stirring was continued for 12 hours at an internal temperature of 40°C. The precipitated solid was recovered by filtration, and lithium difluorophosphate with a purity of 97% was obtained at a yield of 98% after reduced pressure drying at 80°C. The main impurity is lithium monofluorophosphate generated by the decomposition of lithium difluorophosphate in water. The acid concentration (converted to the concentration of hydrofluoric acid) mixed in the lithium difluorophosphate was measured by non-aqueous neutralization titration and found to be 2110 mass ppm.

[0514] [Examples 2-2 to 2-15]

[0515] Lithium difluorophosphate was obtained by the same procedure as in Example 2-1 except that the type of raw materials before the reaction or the amount of water contained therein was changed as shown in Table 5. In Example 2-14, the stirring time during the reaction was set to 48 hours.

[0516] [Example 2-16]

[0517] 100 mL of EMC and 18.6 g (120 mmol) of phosphorus oxychloride were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 40°C. At this time, 13.0 g (100 mmol) of ethyl difluorophosphate obtained by the steps of Example 1-5 was added over 2 hours. 9.3 g (68.3 mmol) of difluoromonochlorophosphorus was obtained by distilling and purifying the reaction solution. Next, 75 mL of EMC and 9.3 g of difluoromonochlorophosphorus were added to a 500 mL glass reaction container, and stirring was started at an internal temperature of 5°C. At this time, 1.2 g (68.3 mmol) of water was added dropwise over 1 hour. After the internal temperature was raised to 25°C, the generated hydrochloric acid was removed by decompression. Then, 2.9 g (70 mmol) of lithium chloride (the water content was 4850 mass ppm) was added, and stirred at an internal temperature of 40°C for 6 hours. The generated hydrochloric acid and solvent were removed under reduced pressure to obtain a crude product of lithium difluorophosphate. The crude product was recrystallized in dimethoxyethane to obtain 4.9 g (46.1 mmol) of lithium difluorophosphate with a purity of >99%. In addition, the acid concentration (converted to the concentration of hydrofluoric acid) mixed in the lithium difluorophosphate was measured by non-aqueous neutralization titration, and the result was 100 mass ppm.

[0518] The results are shown in Table 5.

[0519]

[0520] Industrial Applicability

[0521] According to the present invention, a novel method for producing lithium difluorophosphate, a method for producing a nonaqueous electrolyte, and a method for producing a nonaqueous secondary battery can be provided, which use less raw materials in the reaction and have excellent efficiency.

[0522] In addition, according to the present invention, there can be provided a method for producing a difluorophosphate ester that can stably achieve high fluorination selectivity and yield; a method for producing lithium difluorophosphate derived from the difluorophosphate ester; a method for producing a non-aqueous electrolyte solution using the lithium difluorophosphate; and a method for producing a non-aqueous secondary battery.

[0523] Furthermore, according to the present invention, it is possible to provide lithium difluorophosphate which generates little heat when dissolved in a non-aqueous electrolyte solution in the form of an additive.

[0524] Although the present invention has been described in detail or with reference to specific embodiments, it will be apparent to one skilled in the art that various changes or modifications can be made without departing from the technical concept of the present invention.

[0525] This application is based on a patent application filed in Japan on August 6, 2019 (Japanese Patent Application No. 2019-144873) and a patent application filed in Japan on August 6, 2019 (Japanese Patent Application No. 2019-144874), and the contents thereof are incorporated herein by reference.

Claims

1. A method for producing lithium difluorophosphate, comprising reacting a difluorophosphate ester represented by the following general formula (1A) with a lithium salt compound in a non-aqueous organic solvent, wherein: No water is used as a starting material in the reaction, In the general formula (1A), R is a hydrocarbon group having 1 to 15 carbon atoms, and any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

2. The method for producing lithium difluorophosphate according to claim 1, wherein: The water content in the total amount of the difluorophosphate represented by the general formula (1A), the lithium salt compound, and the nonaqueous organic solvent before the reaction is 200 ppm by mass or less.

3. The method for producing lithium difluorophosphate according to claim 2, wherein: The water content in the total amount of the difluorophosphate represented by the general formula (1A), the lithium salt compound, and the nonaqueous organic solvent before the reaction is 145 ppm by mass or less.

4. The method for producing lithium difluorophosphate according to claim 3, wherein: The water content in the total amount of the difluorophosphate represented by the general formula (1A), the lithium salt compound, and the nonaqueous organic solvent before the reaction is 135 ppm by mass or less.

5. The method for producing lithium difluorophosphate according to any one of claims 1 to 4, wherein The lithium salt compound is at least one selected from the group consisting of lithium chloride, lithium bromide, lithium fluoride, lithium carbonate, lithium acetate and lithium propionate.

6. The method for producing lithium difluorophosphate according to any one of claims 1 to 4, wherein The non-aqueous organic solvent is at least one selected from the group consisting of carbonates, chain esters, ethers and ketones.

7. The method for producing lithium difluorophosphate according to claim 5, wherein: The non-aqueous organic solvent is at least one selected from the group consisting of carbonates, chain esters, ethers and ketones.

8. The method for producing lithium difluorophosphate according to claim 6, wherein: The carbonates are at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate and butylene carbonate; the chain esters are at least one selected from the group consisting of ethyl acetate, methyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate; the ethers are at least one selected from the group consisting of dimethoxyethane, dimethoxymethane, tetrahydrofuran and diethyl ether; and the ketones are at least one selected from the group consisting of acetone, ethyl methyl ketone and diethyl ketone.

9. The method for producing lithium difluorophosphate according to claim 7, wherein: The carbonates are at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate and butylene carbonate; the chain esters are at least one selected from the group consisting of ethyl acetate, methyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate; the ethers are at least one selected from the group consisting of dimethoxyethane, dimethoxymethane, tetrahydrofuran and diethyl ether; and the ketones are at least one selected from the group consisting of acetone, ethyl methyl ketone and diethyl ketone.

10. The method for producing lithium difluorophosphate according to any one of claims 1 to 4, wherein The reaction is carried out under the protection of an inert gas.

11. The method for producing lithium difluorophosphate according to claim 5, wherein: The reaction is carried out under the protection of an inert gas.

12. The method for producing lithium difluorophosphate according to claim 6, wherein: The reaction is carried out under the protection of an inert gas.

13. The method for producing lithium difluorophosphate according to claim 7, wherein: The reaction is carried out under the protection of an inert gas.

14. The method for producing lithium difluorophosphate according to claim 8, wherein: The reaction is carried out under the protection of an inert gas.

15. The method for producing lithium difluorophosphate according to claim 9, wherein: The reaction is carried out under the protection of an inert gas.

16. The method for producing lithium difluorophosphate according to any one of claims 1 to 4, wherein The difluorophosphate represented by the general formula (1A) is produced by the following method for producing difluorophosphate: The method for producing difluorophosphate comprises step 1 of reacting a dihalogenated phosphate represented by the following general formula (1) with a fluorinating agent containing hydrofluoric acid at a concentration of 15 mol % or less in a non-aqueous organic solvent (a). In the general formula (1), X represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom, Y represents a chlorine atom, a bromine atom or an iodine atom, and R is a hydrocarbon group having 1 to 15 carbon atoms, wherein any hydrogen atom in the hydrocarbon group may be substituted by a halogen atom.

17. The method for producing lithium difluorophosphate according to claim 16, wherein: The non-aqueous organic solvent (a) is at least one selected from the group consisting of carbonates, chain esters and ketones.

18. The method for producing lithium difluorophosphate according to claim 17, wherein: The non-aqueous organic solvent (a) is at least one selected from the group consisting of carbonates and chain esters, The carbonates are at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate and butylene carbonate, and the chain esters are at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate.

19. The method for producing lithium difluorophosphate according to claim 16, wherein: The fluorinating agent is at least one selected from the group consisting of hydrofluoric acid salts of organic amines and inorganic fluorides.

20. The method for producing lithium difluorophosphate according to claim 19, wherein: The hydrofluoride of the organic amine is at least one selected from the group consisting of triethylamine monohydrofluoride, tetramethylethylenediamine dihydrofluoride and pyridine monohydrofluoride, and the inorganic fluoride is at least one selected from the group consisting of ammonium fluoride, sodium fluoride, potassium fluoride, cesium fluoride and zinc fluoride.

21. The method for producing lithium difluorophosphate according to claim 16, wherein: The fluorinating agent is at least one selected from sodium fluoride, ammonium fluoride, triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride, and the non-aqueous organic solvent (a) is at least one selected from esters with a relative dielectric constant of less than 8 at 25°C, ethers with a relative dielectric constant of less than 8 at 25°C and propylene carbonate.

22. The method for producing lithium difluorophosphate according to claim 16, wherein: In the reaction of step 1, no catalyst is used.

23. The method for producing lithium difluorophosphate according to any one of claims 17 to 21, wherein In the reaction of step 1, no catalyst is used.

24. The method for producing lithium difluorophosphate according to claim 16, wherein: The fluorinating agent is at least one selected from sodium fluoride, ammonium fluoride, cesium fluoride, zinc fluoride, triethylamine monohydrofluoride and tetramethylethylenediamine dihydrofluoride, The nonaqueous organic solvent (a) is at least one selected from esters having a relative dielectric constant of 8 or less at 25°C and ethers having a relative dielectric constant of 8 or less at 25°C.

25. The method for producing lithium difluorophosphate according to claim 24, wherein: The esters having a relative dielectric constant of less than 8 at 25° C. are at least one selected from ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, amyl acetate, methyl propionate, ethyl propionate, propyl propionate and dibutyl phthalate.

26. The method for producing lithium difluorophosphate according to claim 24, wherein: The ether having a relative dielectric constant of 8 or less at 25° C. is at least one selected from 1,2-dimethoxyethane, tetrahydrofuran, diethyl ether and diethylene glycol diethyl ether.

27. The method for producing lithium difluorophosphate according to claim 5, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

28. The method for producing lithium difluorophosphate according to claim 6, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

29. The method for producing lithium difluorophosphate according to claim 7, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

30. The method for producing lithium difluorophosphate according to claim 8, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

31. The method for producing lithium difluorophosphate according to claim 9, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

32. The method for producing lithium difluorophosphate according to claim 10, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

33. The method for producing lithium difluorophosphate according to claim 11, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

34. The method for producing lithium difluorophosphate according to claim 12, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

35. The method for producing lithium difluorophosphate according to claim 13, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

36. The method for producing lithium difluorophosphate according to claim 14, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

37. The method for producing lithium difluorophosphate according to claim 15, wherein: The difluorophosphate represented by the general formula (1A) is produced by the method for producing a difluorophosphate according to any one of claims 16 to 26.

38. A method for producing a non-aqueous electrolyte, characterized in that: Lithium difluorophosphate is produced by the production method according to any one of claims 1 to 37.

39. A method for manufacturing a non-aqueous secondary battery, characterized in that: A non-aqueous electrolyte is manufactured using the manufacturing method described in claim 38.

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