JP7028405B2 - Method for producing lithium difluorophosphate - Google Patents

Description

The present disclosure relates to a method for producing lithium difluorophosphate.

In order to improve the performance of a battery using a non-aqueous electrolytic solution (for example, a lithium secondary battery), various additives are added to the non-aqueous electrolytic solution.
For example, as a non-aqueous electrolyte solution for a battery capable of improving the storage characteristics of a battery, a non-aqueous electrolyte solution for a battery containing at least one of lithium monofluorophosphate and lithium difluorophosphate as an additive is known (for example,). See Patent Document 1).

As a method for producing lithium difluorophosphate, for example,
A method for reacting lithium hexafluorophosphate and borate in a non-aqueous solvent (see, for example, Patent Document 2).
A method for reacting lithium hexafluorophosphate and silicon dioxide in a non-aqueous solvent (see, for example, Patent Document 3).
A method for reacting lithium hexafluorophosphate with a compound having a Si—O—Si bond such as hexamethyldisiloxane (see, for example, Patent Document 4), and
A method of reacting lithium hexafluorophosphate with a phosphate phosphate of lithium and an oxoacid anhydride of phosphorus (see, for example, Patent Document 5) is known.

Japanese Patent No. 3439085 Japanese Patent No. 4843221 Japanese Patent No. 4604505 Japanese Patent No. 5768801 JP 2015-209341A

However, according to the study by the present inventors, in these conventional methods for producing lithium difluorophosphate, not only lithium difluorophosphate, which is the main reaction product, but also lithium fluoride (LiF) and mono as reaction by-products. It was found that lithium fluorophosphate (Li ₂ PO ₃ F) and the like were also produced.
Therefore, it was found that there is room for improving the purity of the lithium difluorophosphate produced with respect to these conventional production methods.

An object of the present disclosure is to provide a method for producing lithium difluorophosphate capable of producing high-purity lithium difluorophosphate.

Specific means for solving the above problems include the following aspects.
<1> A method for producing lithium difluorophosphate, which comprises a step of producing lithium difluorophosphate by reacting boron oxide with lithium hexafluorophosphate and lithium fluoride.
<2> The method for producing lithium difluorophosphate according to <1>, wherein the reaction temperature in the reaction between the boron oxide, the lithium hexafluorophosphate and the lithium fluoride is 20 ° C. or higher.
<3> The step of producing the lithium difluorophosphate is
A step of obtaining a reaction solution containing lithium difluorophosphate by reacting the boron oxide, the lithium hexafluorophosphate and the lithium fluoride in the presence of an organic solvent.
The step of taking out the lithium difluorophosphate from the reaction solution and
The method for producing lithium difluorophosphate according to <1> or <2>.
<4> The organic solvent is acetone, ethyl acetate, acetonitrile, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, hexane, heptane, octane, nonane, decane, toluene, xylene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene, The difluorophosphorus according to <3>, which is at least one selected from the group consisting of hexylbenzene, heptylbenzene, cyclohexylbenzene, tetralin, mesitylene, methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, and cyclononane. Method for producing lithium acid.

The present disclosure provides a method for producing lithium difluorophosphate capable of producing high-purity lithium difluorophosphate.

In the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.
In the present specification, the amount of each component in the composition is the total amount of the plurality of substances present in the composition unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition. Means.
In the present specification, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. Is done.

The method for producing lithium difluorophosphate of the present disclosure (hereinafter, also referred to as “the production method of the present disclosure”) includes boron oxide (B ₂ O ₃ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium fluoride (LiF). Includes a step of producing lithium difluorophosphate (LiPO ₂ F ₂ ) by reacting with.
The reaction scheme of the above reaction is considered to be as follows.

In the above reaction, the conversion rate from lithium hexafluorophosphate (LiPF ₆ ) to lithium difluorophosphate (LiPO ₂ F ₂ ) is increased, and reaction by-products are produced (for example, residual LiF, LiF from LiPF ₆ ). , Generation of Li ₂ PO ₃ F, etc.) is suppressed.
Therefore, according to the production method of the present disclosure, high-purity lithium difluorophosphate (LiPO ₂ F ₂ ) can be produced.
As used herein, the purity of lithium difluorophosphate means the mass fraction of lithium difluorophosphate in the reaction product.

In the step of producing lithium difluorophosphate, the amount of lithium hexafluorophosphate (LiPF ₆ ) used is preferably 100 mol% to 200 mol% with respect to the amount of boron oxide ( _{B2O 3 )} used. It is more preferably 120 mol% to 180 mol%, further preferably 140 mol% to 160 mol%, and ideally 150 mol%.
In the step of producing lithium difluorophosphate, the amount of lithium fluoride (LiF) used is preferably 150 mol% to 250 mol%, more preferably more, with respect to the amount of boron oxide (B ₂ O ₃ ) used. It is 170 mol% to 230 mol%, more preferably 190 mol% to 210 mol%, and ideally 200 mol%.

The above reaction can be carried out in the presence of an organic solvent.
The specific embodiment in which the above reaction is carried out in the presence of an organic solvent is not particularly limited.
As a specific embodiment, for example,
A mode in which boron oxide and lithium fluoride are added to a solution in which lithium hexafluorophosphate is dissolved in an organic solvent (hereinafter referred to as “Phase 1”);
A mode in which lithium hexafluorophosphate is added to a dispersion liquid (for example, slurry) in which powders of boron oxide and lithium fluoride are dispersed in an organic solvent (hereinafter referred to as “Phase 2”);
And so on.
As an embodiment in which the above reaction is carried out in the presence of an organic solvent, the second embodiment is preferable from the viewpoint of further improving the production rate of the target lithium difluorophosphate.

The type of organic solvent is not particularly limited.
As the organic solvent, a single solvent composed of one kind of compound may be used, or a mixed solvent composed of two or more kinds of compounds may be used.
The organic solvent is preferably acetone, ethyl acetate, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, hexane, heptane, octane, nonane, decane, toluene, xylene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene, hexyl. It is at least one selected from the group consisting of benzene, heptylbenzene, cyclohexylbenzene, tetraline, mesitylene, methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, and cyclononane.
If isomers are present in each of these compounds, the concept of each compound includes all isomers.
For example, the concept of xylene includes ortho-xylene, meta-xylene, and para-xylene, and the concept of propylbenzene includes normal propylbenzene and isopropylbenzene (also known as cumen).

The organic solvent preferably contains at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.
In this case, the total ratio of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate to the total amount of the organic solvent is preferably 60% by mass or more, and more preferably 80% by mass or more.

The above reaction can be carried out under normal pressure or reduced pressure.
The above reaction is preferably carried out under an inert atmosphere (for example, under a nitrogen atmosphere, under an argon atmosphere, etc.) from the viewpoint of preventing contamination of a component (for example, water) that inhibits the production of lithium difluorophosphate.

The reaction temperature in the above reaction is preferably 20 ° C. or higher, preferably 20 ° C. to 150 ° C., more preferably 20 ° C. to 120 ° C., and even more preferably 20 ° C. to 100 ° C. ..
When the reaction temperature is 20 ° C. or higher, the production of lithium difluorophosphate is likely to be promoted.
When the reaction temperature is 150 ° C. or lower, the decomposition of the produced lithium difluorophosphate is further suppressed, and the production rate is likely to be improved.

The reaction time in the above reaction is preferably 30 minutes to 12 hours, more preferably 1 hour to 8 hours, from the viewpoint of efficiently advancing the reaction.

The steps for producing lithium difluorophosphate include a step of obtaining a reaction solution containing lithium difluorophosphate by reacting boron oxide, lithium hexafluorophosphate and lithium fluoride in the presence of an organic solvent, and the above-mentioned step. It may include a step of taking out lithium difluorophosphate from the reaction solution.

The preferred embodiment of the step of obtaining the reaction solution (favorable reaction conditions such as a preferable organic solvent and a preferable reaction temperature) is as described above.

In the extraction step, there is no particular limitation on the method of extracting lithium difluorophosphate from the reaction solution.
For example, when a slurry in which lithium difluorophosphate is dispersed in an organic solvent is obtained by the step of obtaining a reaction solution, the organic solvent is separated from the slurry and the residue is dried to obtain lithium difluorophosphate. Can be taken out.
When a solution in which lithium difluorophosphate is dissolved in an organic solvent is obtained by the step of obtaining the reaction solution, the lithium difluorophosphate is taken out by distilling off the organic solvent from the solution by heat concentration or the like. Can be done.
When a solution in which lithium difluorophosphate is dissolved in an organic solvent is obtained by the step of obtaining the reaction solution, lithium difluorophosphate is added to the solution by adding an organic solvent in which lithium difluorophosphate is not dissolved. Lithium difluorophosphate can also be removed by precipitating, then separating the organic solvent from the solution and drying the residue.

As a method for drying the extracted lithium difluorophosphate, a conventionally known method can be arbitrarily selected and carried out.
Examples of the drying method include a static drying method using a shelf-stage dryer; a fluid drying method using a conical dryer; a method of drying using a device such as a hot plate or an oven; warm air using a dryer such as a dryer. Alternatively, a method of supplying hot air; or the like can be mentioned.

The extracted lithium difluorophosphate can be dried under normal pressure or reduced pressure.
When drying is performed under reduced pressure, the pressure is preferably 10 kPa or less.
The drying temperature for drying the extracted lithium difluorophosphate is preferably 20 ° C to 150 ° C, more preferably 20 ° C to 100 ° C, and even more preferably 40 ° C to 80 ° C. , 50 ° C to 70 ° C, more preferably.
When the drying temperature is 20 ° C. or higher, the drying efficiency is excellent.
When the drying temperature is 150 ° C. or lower, lithium difluorophosphate can be stably taken out easily.

The extracted lithium difluorophosphate may be used as it is, for example, it may be dispersed or dissolved in an organic solvent, or it may be mixed with another solid substance and used.

The production method of the present disclosure described above is particularly suitable for producing lithium difluorophosphate as an additive added to a non-aqueous electrolytic solution for a battery (preferably a non-aqueous electrolytic solution for a lithium secondary battery). be.
That is, according to the production method of the present disclosure, high-purity lithium difluorophosphate can be produced, so that the productivity of lithium difluorophosphate is improved.
Lithium difluorophosphate produced by the production method of the present disclosure is expected to contribute to the improvement of battery characteristics when added to a non-aqueous electrolyte solution for batteries (preferably a non-aqueous electrolyte solution for lithium secondary batteries). Will be done.

Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited to the following examples.

[Example 1]
After purging a 100 mL flask equipped with a stirrer, a thermometer, a gas introduction line, and an exhaust line with dry nitrogen gas, 1.66 g (0.024 mol) of boron oxide and 1.24 g (0) of lithium fluoride were added here. .048 mol) and 23.50 g of dimethyl carbonate (referred to as “DMC” in Table 1; the same applies hereinafter) were added and stirred at room temperature (25 ° C., the same applies hereinafter) to obtain a slurry. A solution prepared by dissolving 5.45 g (0.036 mol) of lithium hexafluorophosphate in 16.35 g of dimethyl carbonate was added dropwise thereto over 1 hour to obtain a mixed solution containing all the raw materials. .. Subsequently, the reaction was carried out by stirring the mixed solution at room temperature for 12 hours to obtain a reaction solution. The obtained reaction solution was a slurry in which a solid was precipitated. By filtering this reaction solution (slurry), a wet cake was obtained as a filter medium. The obtained wet cake was washed with 20 g of dimethyl carbonate, and the washed wet cake was dried at 60 ° C. under a reduced pressure of 10 kPa or less to obtain 0.49 g of a solid product.

The obtained solid product was analyzed to determine the purity of lithium difluorophosphate (LiPO ₂ F ₂ ) (ie, the mass fraction (% by mass) of LiPO ₂ F ₂ in the solid product).
As a result, the purity of LiPO ₂ F ₂ was 100% by mass (see Table 1).
Here, the purity of LiPO ₂ F ₂ was determined as follows.

(Purity of LiPO ₂ F ₂ )
The obtained solid product was dissolved in a heavy water solvent, ¹⁹ F-NMR analysis was performed on the obtained solution, and based on the integrated value of the obtained ¹⁹ F-NMR spectrum, LiPO ₂ F ₂ was carried out by a mass-based percentage method. The purity of was calculated.
The attribution of the ¹⁹ F-NMR spectrum is as follows.
LiPF ₆ : -71.4 ppm, -73.3 ppm (molecular weight: 151.9, F number: 6)
Li ₂ PO ₃ F: -75.0 ppm, -77.5 ppm (molecular weight: 111.9, F number: 1)
LiPO ₂ F ₂ : -82.0 ppm, -84.5 ppm (molecular weight: 107.9, F number: 2)
LiF: -120.0 ppm (molecular weight: 25.9, F number: 1)
LiBF ₄ : -153.0 ppm (molecular weight: 93.7, F number: 4)
Other components: Other peaks (Molecular weight and F number are assumed to be the same as the molecular weight and F number of LiPF ₆ , respectively)

From the ¹⁹ F-NMR spectrum obtained by ¹⁹ F-NMR analysis, for each compound in the solid product, the mass fraction (% by mass) according to the above attribution and the following formulas (a) and (b), respectively. Asked. The mass fraction (mass%) of LiPO ₂ F ₂ in the solid product was taken as the purity.
In the following, one specific compound will be referred to as "Compound X". The "sum of mass parts of each compound" in the formula (b) is obtained by individually obtaining the mass parts of each compound by the formula (a) and summing up the mass parts of each obtained compound.
(Integral value of peak derived from compound X / F number of compound X) × (molecular weight of compound X) = (mass part of compound X) ... Equation (a)
((Mass part of compound X) / (sum of mass parts of each compound)) × 100 = mass fraction of compound X (%) ... Equation (b)

[Example 2]
After purging a 100 mL flask equipped with a stirrer, a thermometer, a gas introduction line, and an exhaust line with dry nitrogen gas, 1.66 g (0.024 mol) of boron oxide and 1.24 g (0) of lithium fluoride were added here. .048 mol) and 23.50 g of dimethyl carbonate were added and stirred while heating at 40 ° C. to obtain a slurry. A solution prepared by dissolving 5.45 g (0.036 mol) of lithium hexafluorophosphate in 16.35 g of dimethyl carbonate was added dropwise thereto over 1 hour to obtain a mixed solution containing all the raw materials. The reaction was subsequently carried out by stirring the mixed solution at 40 ° C. for 6 hours to obtain a reaction solution. The obtained reaction solution was a slurry in which a solid was precipitated. The reaction solution (slurry) was cooled to room temperature and then filtered to obtain a wet cake as a filter medium. The obtained wet cake was washed with 20 g of dimethyl carbonate, and the washed wet cake was dried at 60 ° C. under a reduced pressure of 10 kPa or less to obtain 0.44 g of a solid product.

For the obtained solid product, the purity of lithium difluorophosphate was determined in the same manner as in Example 1. As a result, the purity of lithium difluorophosphate was 100% by mass (see Table 1).

[Example 3]
After purging a 100 mL flask equipped with a stirrer, a thermometer, a gas introduction line, and an exhaust line with dry nitrogen gas, 1.66 g (0.024 mol) of boron oxide and 1.24 g (0) of lithium fluoride were added here. .048 mol) and 23.50 g of dimethyl carbonate were added and stirred while heating at 90 ° C. (88 ° C. reflux state) to obtain a slurry. A solution prepared by dissolving 5.45 g (0.036 mol) of lithium hexafluorophosphate in 16.35 g of dimethyl carbonate was added dropwise thereto over 1 hour to obtain a mixed solution containing all the raw materials. .. Subsequently, the reaction was carried out by stirring the mixed solution at 90 ° C. (refluxed state at 88 ° C.) for 1 hour to obtain a reaction solution. The obtained reaction solution was a slurry in which a solid was precipitated. The reaction solution (slurry) was cooled to room temperature and then filtered to obtain a wet cake as a filter medium. The obtained wet cake was washed with 20 g of dimethyl carbonate, and the washed wet cake was dried at 60 ° C. under a reduced pressure of 10 kPa or less to obtain 0.43 g of a solid product.

For the obtained solid product, the purity of lithium difluorophosphate was determined in the same manner as in Example 1. As a result, the purity of lithium difluorophosphate was 100% by mass (see Table 1).

[Example 4]
After purging a 100 mL flask equipped with a stirrer, a thermometer, a gas introduction line, and an exhaust line with dry nitrogen gas, 1.66 g (0.024 mol) of boron oxide and 23.50 g of dimethyl carbonate are placed therein. , Stirring while heating to 90 ° C. (reflux state at 88 ° C.) to obtain a slurry. A solution prepared by dissolving 5.45 g (0.036 mol) of lithium hexafluorophosphate in 16.35 g of dimethyl carbonate was added dropwise thereto over 1 hour. Immediately after all the above solutions were dropped, the slurry was changed to a uniform solution in which boron oxide was dissolved. Subsequently, 1.24 g (0.048 mol) of lithium fluoride was rapidly added thereto to obtain a mixed solution containing all the raw materials. Subsequently, the reaction was carried out by stirring the mixed solution at 90 ° C. (refluxed state at 88 ° C.) for 1 hour to obtain a reaction solution. The obtained reaction solution was a slurry in which a solid was precipitated. The reaction solution (slurry) was cooled to room temperature and then filtered to obtain a wet cake as a filter medium. The obtained wet cake was washed with 20 g of dimethyl carbonate, and the washed wet cake was dried at 60 ° C. under a reduced pressure of 10 kPa or less to obtain 0.44 g of a solid product.

For the obtained solid product, the purity of lithium difluorophosphate was determined in the same manner as in Example 1. As a result, the purity of lithium difluorophosphate was 100% by mass (see Table 1).

[Comparative Example 1]
After purging a 100 mL flask equipped with a stirrer, a thermometer, a gas introduction line, and an exhaust line with dry nitrogen gas, 1.66 g (0.024 mol) of boron oxide and 23.50 g of dimethyl carbonate are placed therein. , Stirring while heating to 90 ° C. (reflux state at 88 ° C.) to obtain a slurry. A solution prepared by dissolving 5.45 g (0.036 mol) of lithium hexafluorophosphate in 16.35 g of dimethyl carbonate was added dropwise thereto over 1 hour. Immediately after all the above solutions were dropped, the slurry was changed to a uniform solution. This solution was cooled to room temperature and kept, but no precipitation of solid products was observed, and lithium difluorophosphate was not obtained.

A solid was taken out by taking a part of the solution kept at room temperature, heating it to 60 ° C. under a reduced pressure of 10 kPa or less, distilling off the solvent from the solution, and then drying the residue.
The removed solid was dissolved in a heavy water solvent and analyzed by ¹⁹ F-NMR. The chemical shift [ppm] and (integral value (ratio)) of the obtained spectrum were as follows.
¹⁹ F-NMR: -83.0 ppm (1F), -85.5 ppm (1F), -146.5 ppm (3F).
From this result, it was suggested that the obtained solid was a compound having the following structure.

[Comparative Example 2]
After purging a 100 mL flask equipped with a stirrer, a thermometer, a gas introduction line, and an exhaust line with dry nitrogen gas, here, hexamethyldisiloxane [(CH ₃ ) ₃ Si—O—Si (CH ₃ )) ₃ ; Indicated as “HMDO” in Table 1] 10.72 g (0.066 mol) and 50 g of dimethyl carbonate were added, and the mixture was stirred and mixed at room temperature. 5.00 g (0.033 mol) of lithium hexafluorophosphate was added to the obtained solution. The obtained liquid was heated and stirred for 1 hour after reaching 60 ° C. to react the hexamethyldisiloxane with lithium hexafluorophosphate.
The reaction solution obtained by stirring for 1 hour was a slurry in which a solid was precipitated. The reaction solution was cooled to room temperature and then filtered to obtain a wet cake as a filtrate. The obtained wet cake was dried at 60 ° C. under a reduced pressure of 10 kPa or less to obtain 3.29 g of a solid product.

For the obtained solid product, the purity and yield of lithium difluorophosphate were determined in the same manner as in Example 1.
As a result, the purity of lithium difluorophosphate (reaction main product) was 96.1% by mass, and the solid product contained 3.9% by mass of LiF as a reaction by-product (above,). See Table 1).

[Comparative Example 3]
A 200 mL Hastelloy C sealed reaction vessel (hereinafter simply referred to as “reaction vessel”) equipped with a thermometer, pressure gauge, gas introduction line, and exhaust line is placed in a glove box purged with dry nitrogen gas. rice field. In the glove box, 5.0 g (0.033 mol) of lithium hexafluorophosphate, 3.1 g (0.022 mol) of diphosphorus pentoxide _{(P2 O 5 )} , and trilithium phosphate (Li) in the reaction vessel. ₃ PO ₄ ) 2.5 g (0.022 mol) of each powder was put together with a stirrer of a magnetic stirrer, and the reaction vessel was covered and sealed. Next, this reaction vessel was taken out from the glove box, and the mixture was stirred and mixed with a magnetic stirrer at a rotation speed of 300 rpm for 1 hour.
The reaction vessel after stirring and mixing for 1 hour was heated and reacted at 200 ° C. for 8 hours to obtain a crude product containing LiPO ₂ F ₂ .

After the reaction for 8 hours, the reaction vessel was cooled to room temperature, and then the inside of the reaction vessel was purged with nitrogen gas. The reaction vessel purged with nitrogen gas was placed in a glove box purged with dry nitrogen gas, and the lid of the reaction vessel was opened.
Next, 150 g of ethyl acetate was placed in the reaction vessel, the reaction vessel was covered, the glove box was taken out, and the mixture was stirred with a magnetic stirrer at 300 rpm for 1 hour while heating at 60 ° C. , A solution in which the above crude product was dissolved was obtained.

Immediately after that, the lid of the reaction vessel is opened, the solution in the reaction vessel (that is, the solution in which the crude product is dissolved) is poured into a filter equipped with a filter, and the solvent-insoluble solid content (impurity) is filtered by vacuum filtration. Separated, the solution (filtrate) was collected. The recovered solution was distilled off with an evaporator to obtain a wet cake containing LiPO ₂ F ₂ . The wet cake was dried under reduced pressure at 60 ° C. and 10 kPa or less to obtain a solid product having a mass of 8.60 g after drying.

For the obtained solid product, the purity and yield of lithium difluorophosphate were determined in the same manner as in Example 1. As a result, the purity of lithium difluorophosphate was 95.2% by mass, and as reaction by-products, lithium monofluorophosphate (Li ₂ PO ₃ F) (3.5% by mass) and LiF (0.6% by mass) were used. %) And other products (0.7% by weight) were included (see Table 1 above).

The results of the above Examples and Comparative Examples are summarized in Table 1 below.

In Table 1, "HMDO" means hexamethyldisiloxane and "DMC" means dimethyl carbonate.

As shown in Table 1, in Examples 1 to 4 in which boron oxide (B ₂ O ₃ ) was reacted with lithium hexafluorophosphate (LiPF ₆ ) and lithium fluoride (LiF), high-purity difluorophosphate was used. Lithium (LiPO ₂ F ₂ ) was obtained.
On the other hand, lithium difluorophosphate (LiPO ₂ F ₂ ) could not be obtained by the method of Comparative Example 1 (the method of reacting B ₂ O ₃ with LiPF ₆ ).
Further, even when the production method of Examples was compared with the production methods of Comparative Examples 2 and 3, lithium difluorophosphate (LiPO ₂ F ₂ ), which was the target product, was obtained with high purity.

Claims (6)

A method for producing lithium difluorophosphate, which comprises a step of producing lithium difluorophosphate by reacting boron oxide with lithium hexafluorophosphate and lithium fluoride. The method for producing lithium difluorophosphate according to claim 1, wherein the reaction temperature in the reaction between the boron oxide, the lithium hexafluorophosphate and the lithium fluoride is 20 ° C. or higher. The step of producing the lithium difluorophosphate is
A step of obtaining a reaction solution containing lithium difluorophosphate by reacting the boron oxide, the lithium hexafluorophosphate and the lithium fluoride in the presence of an organic solvent.
The step of taking out the lithium difluorophosphate from the reaction solution and
The method for producing lithium difluorophosphate according to claim 1 or 2, comprising the above. The organic solvent is acetone, ethyl acetate, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, hexane, heptane, octane, nonane, decane, toluene, xylene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene, hexylbenzene, etc. The lithium difluorophosphate according to claim 3, which is at least one selected from the group consisting of heptylbenzene, cyclohexylbenzene, tetraline, mesitylene, methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, and cyclononane. Production method. The method for producing lithium difluorophosphate according to claim 3 or 4, wherein the organic solvent comprises at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. The method for producing lithium difluorophosphate according to claim 5, wherein the total ratio of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate to the total amount of the organic solvent is 60% by mass or more.