JP6912982B2 - 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 electrolyte solution (for example, a lithium secondary battery), various additives are added to the non-aqueous electrolyte 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 of reacting lithium hexafluorophosphate and silicon dioxide in a non-aqueous solvent (see, for example, Patent Document 2).
A method for reacting lithium hexafluorophosphate with a compound having a Si—O—Si bond such as hexamethyldisiloxane (see, for example, Patent Document 3), and
A method of reacting lithium hexafluorophosphate with a phosphoric acid salt of lithium and an oxoacid anhydride of phosphorus (see, for example, Patent Document 4) is known.

Japanese Patent No. 3439085 Japanese Patent No. 4604505 Japanese Patent No. 5768801 Japanese Unexamined Patent Publication No. 2015-209341

However, according to the studies 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 yield of lithium difluorophosphate with respect to these conventional production methods.

An object of the present disclosure is to provide a method for producing lithium difluorophosphate, which can produce lithium difluorophosphate in a high yield.

Specific means for solving the above problems include the following aspects.

<1> A method for producing lithium difluorophosphate, which comprises a reaction step of obtaining lithium difluorophosphate by reacting a booxine compound represented by the following formula (I) with lithium hexafluorophosphate.

In formula (I), R ¹ , R ² , and R ³ each independently represent an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms.

<2> In the formula (I), the R ¹ , the R ² , and the R ³ are independently methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, respectively. The method for producing lithium difluorophosphate according to <1>, which is a t-butyl group, a cyclohexyl group, or a phenyl group.

<3> The difluorophosphorus according to <1> or <2>, wherein the boroxine compound represented by the formula (I) is a compound represented by the following formula (I-1) or the following formula (I-2). Method for producing lithium acid.

<4> Further, prior to the reaction step, there is a step of obtaining a boronoxine compound represented by the formula (I) by dehydrating the boronic acid compound represented by the following formula (II) <1>. The method for producing lithium difluorophosphate according to.

In formula (II), R ⁰ represents an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms.

<5> In the formula (II), the R ⁰ is a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a cyclohexyl group, or a phenyl group. The method for producing lithium difluorophosphate according to <4>.

<6> The difluoro compound according to <4> or <5>, wherein the boronic acid compound represented by the formula (II) is a compound represented by the following formula (II-1) or the following formula (II-2). Method for producing lithium phosphate.

According to the present disclosure, there is provided a method for producing lithium difluorophosphate capable of producing lithium difluorophosphate in a high yield.

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 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”) is obtained by reacting a boroxin compound represented by the following formula (I) with lithium hexafluorophosphate. , Has a reaction step to obtain lithium difluorophosphate.

In formula (I), R ¹ , R ² , and R ³ each independently represent an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms.

_{In the reaction step, lithium difluorophosphate (LiPO 2} F ₂ ) is produced by the following reaction scheme by reacting the booxine compound represented by the formula (I) with lithium hexafluorophosphate (LiPF _6). Will be done.

In the reaction step, the formation of reaction by-products (LiF, Li ₂ PO ₃ F, etc.) is suppressed, and a reaction product having a high mass fraction of lithium difluorophosphate can be obtained.
Therefore, according to the production method of the present disclosure, lithium difluorophosphate can be produced in a high yield.
In the present specification, the mass fraction of lithium difluorophosphate in the reaction product may be referred to as "purity of lithium difluorophosphate".

The booxine compound represented by the formula (I) to be reacted with lithium hexafluorophosphate (LiPF _{6) in the reaction step is as follows.}

In formula (I), R ¹ , R ² , and R ³ each independently represent an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms.

In formula (I), as the unsubstituted aryl group represented by R ^{1, R 2,} and R ^3, each independently, a phenyl group, a naphthyl group, anthracenyl group, and a phenanthryl group, a phenyl group Is preferable.

In the formula (I), the aliphatic groups having 1 to 12 carbon atoms represented by ^{R 1} , R ² , and R ^{3 may be independently linear aliphatic groups or branched.} It may be an aliphatic group of the above, or it may be an aliphatic group having a cyclic structure.
In formula (I), ^{the aliphatic groups having 1 to 12 carbon atoms represented by R 1} , R ² , and R ³ may be independently saturated aliphatic groups (that is, alkyl groups). , It may be an unsaturated aliphatic group (that is, an alkenyl group or an alkynyl group).

Specific examples of the aliphatic group having 1 to 12 carbon atoms represented by R ¹ , R ² , and R ^{3 include}
Methyl group, ethyl group, n-propyl group, isopropyl group, 1-ethylpropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, 2-methylbutyl group, 3,3-dimethylbutyl group , N-pentyl group, isopentyl group, neopentyl group, 1-methylpentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n-heptyl group, isoheptyl group, sec-heptyl group, tert Linear or branched saturated aliphatic groups such as −heptyl group, n-octyl group, isooctyl group, sec-octyl group, tert-octyl group, nonyl group, decyl group, undecyl group, dodecyl group. Alkyl group);
Vinyl group, 1-propenyl group, allyl group (2-propenyl group), isopropenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, pentenyl group, hexenyl group, 2-methyl-2-propenyl group , 1-Methyl-2-propenyl group, 2-methyl-1-propenyl group, hexenyl group, ethynyl group, 1-propynyl group, 2-propynyl group (synonymous with propargyl group), 1-butynyl group, 2-butynyl group , 3-butynyl group, 1-pentynyl group, 2-pentynyl group, 3-pentynyl group, 4-pentynyl group, 5-hexynyl group, 1-methyl-2-propynyl group, 2-methyl-3-butynyl group, 2 Linear or branched, such as −methyl-3-pentynyl group, 1-methyl-2-butynyl group, 1,1-dimethyl-2-propynyl, 1,1-dimethyl-2-butynyl group, 1-hexynyl group Unsaturated aliphatic group (ie, alkenyl group or alkynyl group);
An aliphatic group having a cyclic structure such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a 1-cyclopentenyl group, a 1-cyclohexenyl group;
And so on.

The aliphatic groups having 1 to 12 carbon atoms represented by R ¹ , R ² , and R ³ are independently methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, and isobutyl group. , T-butyl group, or cyclohexyl group is preferable, methyl group, ethyl group, or isopropyl group is more preferable, and methyl group is further preferable.

In formula (I), R ¹ , R ² and R ³ are independently methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group and cyclohexyl group, respectively. , Or a phenyl group, more preferably a methyl group, an ethyl group, an isopropyl group, or a phenyl group. It is more preferably a methyl group or a phenyl group.

The boroxine compound represented by the formula (I) is particularly preferably a compound represented by the following formula (I-1) or the following formula (I-2).

The boronoxine compound represented by the formula (I) can be obtained, for example, by dehydrating the boronic acid compound represented by the formula (II) described later.
When only one boronic acid compound represented by the formula (II) described later is used and this is dehydrated, it is represented by the formula (I) of the embodiment in which ^{R 1} , R ² and R ^{3 are the same.} Boroxine compounds are produced.
When two or more boronic acid compounds represented by the formula (II) described later are used and dehydrated, R ¹ , R ² and R ³ are represented by the formula (I) of a different embodiment. One or more boroxine compounds are produced.
Here, ^{the concept of "R 1} , R ² , and R ³ are different" includes ^{not only the states in which R 1} , R ² , and R ³ are different from each other, but also among ^{R 1} , R ² , and R ^3. A state in which two of them are the same and the remaining one is different from the other two is also included.

In the reaction step, one kind of booxine compound represented by the formula (I) may be reacted with lithium hexafluorophosphate, or two or more kinds of the boroxine compound represented by the formula (I) may be reacted. You may react with lithium hexafluorophosphate.
From the viewpoint of further improving the yield of lithium difluorophosphate, it is preferable to react one of the booxine compounds represented by the formula (I) with lithium hexafluorophosphate in the reaction step.

The reaction in the reaction step can be carried out in the presence of a solvent.
The specific embodiment in which the reaction in the reaction step is carried out in the presence of a solvent is not particularly limited.
A mode in which the booxine compound represented by the formula (I) is added to a solution in which lithium hexafluorophosphate is dissolved in a solvent, or
It is preferable to add lithium hexafluorophosphate to the solution in which the booxine compound represented by the formula (I) is dissolved in a solvent.

Solvents include, for example, acetone, ethyl acetate, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, hexane, heptane, octane, nonane, decane, toluene, xylene (ortho, meta, para), ethylbenzene, butylbenzene, pentyl. Solvents such as benzene, hexylbenzene, heptylbenzene, propylbenzene, isopropylbenzene (cumen), cyclohexylbenzene, tetraline, mesitylene methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, and cyclononane can be mentioned.

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

The reaction temperature in the reaction step is preferably 20 ° C. to 150 ° C., more preferably 20 ° C. to 100 ° C., and even more preferably 20 ° C. to 60 ° 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 suppressed, and the production rate tends to be improved.

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

There is no particular limitation on the method for taking out lithium difluorophosphate obtained in the reaction step.
For example, when a slurry in which lithium difluorophosphate is dispersed is obtained by the reaction step, the lithium difluorophosphate can be taken out by separating the solvent from the slurry and drying it.
When a solution in which lithium difluorophosphate is dissolved in a solvent is obtained by the reaction step, lithium difluorophosphate can be taken out by distilling off the solvent from the solution by heat concentration or the like.
When a solution in which lithium difluorophosphate is dissolved is obtained by the reaction step, lithium difluorophosphate is precipitated by adding a solvent in which lithium difluorophosphate is not dissolved to the solution, and then. Lithium difluorophosphate can also be removed by separating the solvent from the solution and drying it.

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 in a shelf-type dryer; a fluid drying method in a conical dryer; a method of drying using a device such as a hot plate or an oven; warm air in a dryer such as a dryer. Alternatively, a method of supplying hot air; or the like can be mentioned.

The pressure for drying the extracted lithium difluorophosphate may be normal pressure or reduced pressure.
The temperature at which the extracted lithium difluorophosphate is dried is preferably 20 ° C. to 150 ° C., more preferably 20 ° C. to 100 ° C., and even more preferably 20 ° C. to 60 ° C.
When the temperature is 20 ° C. or higher, the drying efficiency is excellent.
When the temperature is 150 ° C. or lower, lithium difluorophosphate can be taken out stably.

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

In the production method of the present disclosure, a boronoxine compound represented by the above formula (I) is further obtained by dehydrating the boronic acid compound represented by the following formula (II) before the above-mentioned reaction step. It may have a step (also referred to as "step A" in the present specification).
When the production method of the present disclosure has step A, in the reaction step, the booxine compound represented by the formula (I) obtained in step A is reacted with lithium hexafluorophosphate.
However, step A is an arbitrary step. That is, in the production method of the present disclosure, the reaction step may be carried out using a boroxine compound represented by the formula (I) prepared in advance.

In formula (II), R ⁰ represents an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms.

^{The preferred form of R 0} in formula (II) is similar to the preferred form ^{of R 1} in formula (I).

As the boronic acid compound represented by the formula (II), methylboronic acid, ethylboronic acid, isopropylboronic acid, or phenylboronic acid is preferable, and methylboronic acid or phenylboronic acid is more preferable.
Here, methylboronic acid is a compound represented by the following formula (II-1), and phenylboronic acid is a compound represented by the following formula (II-2).

In step A, one of the boronic acid compounds represented by the formula (II) may be dehydrated to obtain a boronoxine compound, or two or more of the boronic acid compounds represented by the formula (II) may be dehydrated. It may be allowed to obtain a boronoxine compound.
When two or more kinds of boronic acid compounds represented by the formula (II) are dehydrated, two or more kinds of booxine compounds represented by the formula (I) may be produced.

Step A may be carried out in the presence of a solvent.
Examples of the solvent that can be used in the step A include the same solvents as those that can be used in the reaction step.

When each of the step A and the reaction step is carried out in the presence of a solvent, the solvent in the step A and the solvent in the reaction step may be the same type or different types, but the production efficiency of lithium difluorophosphate may be improved. From the viewpoint, it is preferable that they are of the same type.

When the production method of the present disclosure includes step A, a particularly preferable form from the viewpoint of productivity of lithium difluorophosphate is that in step A, the boronic acid compound represented by the formula (II) is used as a solvent (hereinafter, solvent). By dehydrating in the presence of (also referred to as A), a solution containing the boronoxine compound represented by the formula (I) is obtained, and then in the reaction step, lithium hexafluorophosphate is added to this solution. In the presence of solvent A, the boronoxine compound represented by the formula (I) is reacted with lithium hexafluorophosphate.

The production method of the present disclosure described above is particularly suitable for producing lithium difluorophosphate as an additive added to a non-aqueous electrolyte solution for a lithium ion battery (preferably a lithium ion secondary battery).
That is, according to the production method of the present disclosure, lithium difluorophosphate can be produced in high yield, 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 electrolytic solution.

Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited to the following examples.
Hereinafter, "step A" is a step of obtaining a boronoxine compound represented by the formula (I) by dehydrating the boronic acid compound represented by the formula (II), which is provided before the reaction step as described above. Is.

[Example 1] (without step A)
After purging a 100 mL flask equipped with a stirrer, a thermometer, a gas introduction line, and an exhaust line with dry nitrogen gas, triphenylboroxin (that is, represented by the above formula (I-2)) is here. 6.85 g (0.022 mol) of compound) and 50 g of dimethyl carbonate were added, and the mixture was stirred at room temperature (25 ° C.) to dissolve triphenylboroxin. 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 triphenylboroxin with lithium hexafluorophosphate (reaction step).
The reaction solution obtained by stirring for 1 hour was a slurry in which a solid was precipitated. After cooling this slurry to room temperature (25 ° C.; the same applies hereinafter), the solid (wet cake) was separated by filtration. The obtained wet cake was dried at 60 ° C. under a reduced pressure of 10 kPa or less to obtain 3.50 g of a solid product.

The obtained solid product was analyzed to determine _{the purity of lithium difluorophosphate (LiPO 2} F ₂ ) (that is, _{the mass fraction (mass percentage) of LiPO 2} F ₂ in the solid product). As a result, 100 mass was determined. %Met.
The yield of LiPO ₂ F ₂ was 98.3 mol% (see Table 1).
Here, the purity and yield of _{LiPO 2} F _{2 were 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 : -81.0 ppm, -83.5 ppm (molecular weight: 107.9, F number: 2)
LiF: -120.0 ppm (molecular weight: 25.9, F number: 1)
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 (mass fraction) was determined by 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 parts of compound X) / (total mass parts of each compound) x 100 = mass fraction of compound X (%) ... Equation (b)

(Yield of LiPO ₂ F ₂ )
The mass of the obtained solid product was multiplied by the purity calculated above to obtain the mass of _{LiPO 2} F _{2. The number of moles of LiPO 2} F ₂ was calculated from the mass of this LiPO ₂ F ₂ , and the obtained value was defined as the number of moles 1.
_{Next, the number of moles of LiPF 6} was calculated from the mass of _{LiPF 6} charged as a raw material, and the obtained value was defined as the number of moles 2.
The yield (mol%) of LiPO ₂ F ₂ was determined as the ratio of the number of moles 1 to the number of moles 2 ((number of moles 1 / number of moles 2) × 100).

[Example 2] (with step A)
A 100 mL flask equipped with a stirrer, a thermometer, a gas introduction line, an exhaust line, and a Dean Stark tube was prepared. The Dean Stark tube was filled with toluene for removal of produced water.
After purging the 100 mL flask with dry nitrogen gas, 8.05 g (0.066 mol) of phenylboronic acid (that is, the compound represented by the formula (II-2)) and 70 g of toluene are placed therein. , The obtained liquid was heated with stirring. Further, heating and stirring of the liquid were continued so that the state in which toluene was refluxed was maintained at a temperature of 100 to 110 ° C. The heating was stopped when the refluxed toluene was no longer accompanied by water, and the liquid was cooled to room temperature (25 ° C.). As described above, the dehydration reaction of phenylboronic acid was carried out to produce triphenylboroxin (that is, the compound represented by the formula (I-2)) (above, step A).
To the liquid cooled above, 5.00 g (0.033 mol) of lithium hexafluorophosphate is added, the mixture is heated again, and the mixture is stirred at 60 ° C. for 1 hour to obtain a dehydration reaction product of phenylboronic acid. A reaction was carried out between phenylboronic acid and lithium hexafluorophosphate (reaction step).
The reaction solution obtained by stirring for 1 hour was a slurry in which a solid was precipitated. After cooling this slurry to room temperature (25 ° C.), the solid (wet cake) was separated by filtration. Then, the obtained wet cake was dried at 60 ° C. under a reduced pressure of 10 kPa or less to obtain 3.28 g of a solid product.

With respect to 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 100% by mass, and the yield of lithium difluorophosphate was 92.1 mol% (see Table 1).

[Example 3] (without step A)
6.85 g (0.022 mol) of triphenylboroxin (ie, the compound represented by the above formula (I-2)) and trimethylboroxin (ie, the compound represented by the above formula (I-1)) are added. ) The same operation as in Example 1 was performed except that the content was changed to 2.76 g (0.022 mol).
The mass of the obtained solid product was 3.52 g, the purity of lithium difluorophosphate was 100% by mass, and the yield of lithium difluorophosphate was 98.8 mol% (see Table 1).

[Example 4] (with step A)
8.05 g (0.066 mol) of phenylboronic acid (ie, the compound represented by the formula (II-2)) and 1.80 g (0) of methylboronic acid (ie, the compound represented by the formula (II-1)). The same operation as in Example 2 was performed except that the value was changed to .066 mol).
The mass of the obtained solid product was 3.32 g, the purity of lithium difluorophosphate was 100% by mass, and the yield of lithium difluorophosphate was 93.2 mol% (see Table 1).
In step A of this Example 4, a dehydration reaction of methylboronic acid was carried out to produce trimethylboroxin (that is, a compound represented by the formula (I-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, 10.72 g (0.066 mol) of hexamethyldisiloxane and 50 g of dimethyl carbonate are placed therein. , Stirred and mixed at room temperature (25 ° C.). 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 obtain hexamethyldisiloxane [(CH ₃ ) ₃ O-Si-O (CH ₃ ) ₃ ] and lithium hexafluorophosphate. Reaction was performed.
The reaction solution obtained by stirring for 1 hour was a slurry in which a solid was precipitated. After cooling this slurry to room temperature (25 ° C.), the solid (wet cake) was separated by filtration. Then, 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.

With respect to 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 96.1% by mass, and the yield of lithium difluorophosphate was 88.8 mol%. The solid product contained 3.9% by mass of LiF as a reaction by-product (see Table 1 above).

[Comparative Example 2]
A 200 mL Hastelloy C sealed reaction vessel (hereinafter simply referred to as “reaction vessel”) equipped with a thermometer, a pressure gauge, a gas introduction line and an exhaust line was placed in a glove box purged with dry nitrogen gas. .. In a glove box, a reaction vessel, lithium hexafluorophosphate 5.0 g (0.033 mol), phosphorus pentoxide _{(P 2 O 5) 3.1g (} 0.022mol), and phosphoric acid tri lithium (Li 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 stirrer at 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 (25 ° C.), 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 crude product was dissolved by stirring at 300 rpm for 1 hour with a stirrer while heating at 60 ° C. A solution 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 solvent-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.

With respect to 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 the yield of lithium difluorophosphate was 76.6 mol%. Solid products include lithium monofluorophosphate (Li ₂ PO ₃ F) (3.5% by weight), LiF (0.6% by weight), and other products (0.7% by weight) as reaction by-products. (Mass%) was included (see Table 1 above).

The results of the above Examples and Comparative Examples are summarized in Table 1 below.
In the following, (I-1), (I-2), (II-1), and (II-2) are represented by the compound represented by (I-1), (I-2), respectively. It means a compound represented by (II-1), a compound represented by (II-1), and a compound represented by (II-2).

As shown in Table 1, Example 1 in which a boroxine compound represented by the formula (I) ((I-1), (I-2)) was reacted with _{lithium hexafluorophosphate (LiPF 6).} In Nos. 4 to 4, the target product, lithium difluorophosphate (LiPO ₂ F ₂ ), was obtained in a higher yield than in Comparative Examples 1 and 2.
The reason why the yield in Examples 1 to 4 is not 100 mol% is considered to be that a loss occurred due to the volatilization of a part of the raw material. The reason why the yields of Examples 2 and 4 are lower than those of Examples 1 and 2 is that in Examples 2 and 4, the starting material is not a boroxine compound ((I-1), (I-2)) but a boronic acid. It is considered that the use of the compounds ((II-1) and (II-2)) increased the loss due to the volatilization of the raw materials as compared with Examples 1 and 2.

Claims (6)

A method for producing lithium difluorophosphate, which comprises a reaction step of reacting a boroxine compound represented by the following formula (I) with lithium hexafluorophosphate to produce lithium difluorophosphate according to the following reaction scheme.

[In formula (I), R ¹ , R ² , and R ³ each independently represent an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms. ]

In the formula (I), the R ¹ , the R ² and the R ³ are independently methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group and t-butyl. The method for producing lithium difluorophosphate according to claim 1, which is a group, a cyclohexyl group, or a phenyl group. The lithium difluorophosphate according to claim 1 or 2, wherein the booxine compound represented by the formula (I) is a compound represented by the following formula (I-1) or the following formula (I-2). Production method.

The first aspect of claim 1, further comprising a step of obtaining a boronoxine compound represented by the formula (I) by dehydrating the boronic acid compound represented by the following formula (II) before the reaction step. A method for producing lithium difluorophosphate.

[In formula (II), R ⁰ represents an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms. ] 4. In the formula (II), the R ⁰ is a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a cyclohexyl group, or a phenyl group. The method for producing lithium difluorophosphate according to. Lithium difluorophosphate according to claim 4 or 5, wherein the boronic acid compound represented by the formula (II) is a compound represented by the following formula (II-1) or the following formula (II-2). Manufacturing method.