KR102231049B1 - Manufacturing method for high-purity crystallization of lithium difluorophosphate with excellent solubility and Non-aqueous electrolyte for secondary battery - Google Patents

Abstract

The present invention relates to a method for preparing a lithium difluorophosphate crystal. More specifically, the present invention relates to an invention which can provide a method for preparing a lithium difluorophosphate crystal with high yield and high purity, and the high-purity lithium difluorophosphate crystal prepared thereby can be applied to various uses.

Description

Manufacturing method for high-purity crystallization of lithium difluorophosphate with excellent solubility and Non-aqueous electrolyte for secondary battery

The present invention relates to a method for producing a lithium difluorophosphate salt crystal having excellent solubility in a non-aqueous electrolyte solution with high purity, a lithium difluorophosphate salt crystal prepared by this method, and a non-aqueous electrolyte solution for a secondary battery comprising the same .

Lithium difluorophosphate salts are industrially useful compounds such as wood preservatives (refer to Patent Document 1), toothbrush disinfectants, and polymer stabilizers.

However, with the recent reduction in weight and size of electric products, the development of a secondary battery having a high energy density, such as a lithium ion secondary battery, is in progress. Further, as the field of application of this lithium ion secondary battery is expanded, improvement in battery characteristics is further desired. In order to improve battery characteristics such as load characteristics, cycle characteristics, storage characteristics, and low temperature characteristics of such lithium ion secondary batteries, various studies have been made on non-aqueous solvents and electrolytes. For example, by using an electrolytic solution containing a vinyl ethylene carbonate compound, we are manufacturing a battery that minimizes decomposition of the electrolytic solution and has excellent storage characteristics and cycle characteristics, and the existing lithium ion secondary battery contains propane sultone. A technique of increasing the recovery capacity after storage by using an electrolytic solution is disclosed.

However, the conventional lithium ion secondary battery electrolyte has an effect of improving storage characteristics and cycle characteristics to some extent, but since a film with high resistance is formed on the negative electrode side, low-temperature discharge characteristics and high-current discharge characteristics, etc. are deteriorated. there is a problem.

Accordingly, a technology was developed in which lithium difluorophosphate salt was applied as a secondary battery electrolyte component as an additive with excellent safety while improving low temperature discharge characteristics, high current discharge characteristics, high temperature storage characteristics, and cycle characteristics. There is a problem that manufacturing efficiency and purity are deteriorated.

Further, as described above, the lithium difluorophosphate salt crystal has been recently used as an electrolyte for a non-aqueous electrolyte solution for a secondary battery, but there is a problem of insufficient solubility in the non-aqueous electrolyte solution.

Japanese Laid-Open Patent No. 2002-501034 (published on January 15, 2002) Japanese Laid-Open Patent No. 2001-006729 (published on January 12, 2001)

Journal of Fluorine Chemistry (1988), 38(3), 297.

The present invention has been conceived to solve the above problems, and the problem to be solved by the present invention is to propose a new method for preparing a lithium difluorophosphate salt crystal with high purity, and the thus prepared lithium difluorophosphate salt crystal 2 It is an object to provide an electrolyte for a non-aqueous electrolyte solution such as a rechargeable battery.

The method for preparing a lithium difluorophosphate salt crystal of the present invention for solving the above problem includes the first step of synthesizing a lithium difluorophosphate salt crystal from dihalophosphate represented by the following formula (1); And a second step of purifying and recrystallizing the lithium difluorophosphate salt crystal to prepare a lithium difluorophosphate salt crystal.

[Formula 1]

In Formula 1, each of X ₁ and X ₂ is independent, and is -Cl, -Br or -I, and R is a C ₁ to C ₁₀ straight-chain alkyl group, a C ₃ to C ₁₀ pulverized alkyl group, C _{It is a 6} to C ₁₀ cycloalkyl group or a C ₆ to C ₂₀ aryl group.

As a preferred embodiment of the present invention, the first step is difluoro phosphate represented by the following formula (2) by reacting a mixture of dihalophosphate represented by Formula 1, a fluorinating agent, and a non-aqueous solvent under an inert gas. 1-1 step of synthesizing; 1-2 steps of adding and reacting the difluoro phosphate dropwise to a mixture of lithium salt, water and a non-aqueous solvent, and then evaporating the non-aqueous solvent to obtain a solid; And steps 1-3 of dissolving the solid in a non-aqueous solvent, recrystallizing it, and filtering to obtain a lithium difluorophosphate crystal.

[Formula 2]

In Formula 2, R is a C ₁ to C ₁₀ straight-chain alkyl group, a C ₃ to C ₁₀ pulverized alkyl group, a C ₆ to C ₁₀ cycloalkyl group, or a C ₆ to C ₂₀ aryl group, provided that , R in Formula 2 is the same as R in Formula 1.

As a preferred embodiment of the present invention, the reaction of step 1-1 may be carried out for 6 to 10 hours under a reaction temperature of 40°C to 150°C.

As a preferred embodiment of the present invention, the mixed solution of step 1-1 is Dihalophosphate and a fluorinating agent may be included in a molar ratio of 1: 1.5 to 3.0.

As a preferred embodiment of the present invention, the fluorinating agent is NH ₄ F (ammonium floride), NaF, KF, CeF (cesium floride), tri (C ₁ ~ C ₃ alkyl) amine trihydrofluoride salt and pyridine hydrogen fluoride It may include a single species or two or more selected from the ride salt.

As a preferred embodiment of the present invention, each of the non-aqueous solvents in steps 1-1 and 1-2 are independent, and cyclic carbonates, chain carbonates, cyclic esters, chain esters, n-hexane, cyclohexane , n-heptane, iso-heptane, benzene, xylene, acetonitrile, methyl ether, ethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetrahydrofuran 1 selected from It may contain more than one species.

As a preferred embodiment of the present invention, the lithium salt of the step 1-2 is lithium chloride, lithium bromide, lithium fluoride, lithium iodide, lithium hydroxide, lithium carbonate, lithium bicarbonate, lithium phosphate, lithium metaphosphate, lithium acetate, and sulfuric acid. It may contain at least one selected from lithium.

As a preferred embodiment of the present invention, the mixture of steps 1-2 may contain lithium salt and water in a molar ratio of 1:0.10 to 0.65.

As a preferred embodiment of the present invention, the dropwise addition of difluoro phosphate in step 1-2 may be performed dropwise in 230 to 350 parts by weight based on 100 parts by weight of the lithium salt.

As a preferred embodiment of the present invention, the non-aqueous solvent of the 1-2 step mixture may be used in an amount of 3.5 to 5 ml per 1 g of difluoro phosphate added dropwise.

As a preferred embodiment of the present invention, the yield of the lithium difluorophosphate salt crystal synthesized in step 1 may be 82% to 92% and the purity of 95% to 98%.

As a preferred embodiment of the present invention, in the method for preparing a lithium difluorophosphate salt crystal having excellent solubility of the present invention with high purity, the second step is a lithium difluorophosphate salt crystal in a reactor, a purification solvent, and the following formula: Step 2-1 of performing a purification process by adding and stirring the compound represented by 1; 2-2 step of first concentrating the purified reaction product in vacuum; 2-3 steps of concentrating the first vacuum concentrate in a second vacuum; And 2-4 steps of obtaining recrystallized lithium difluorophosphate salt crystals by cooling the second vacuum concentrate after performing a drying process.

[Formula 3]

Si(X) _a R _b

In Formula 3, X is a halogen element, R is a C1-C5 straight-chain alkyl group, a C3-C5 branched alkyl group, or a C1-C3 alkoxy group, and a and b satisfy a+b=4. Is an integer, provided that a and b are not 0.

As a preferred embodiment of the present invention, the reactor in step 2-1 may be equipped with a reactor jacket, a vacuum pump, a condenser, and a receiver.

As a preferred embodiment of the present invention, step 2-1 may be used in an amount of 350 to 480 parts by weight of the purification solvent and 5 to 30 parts by weight of the compound represented by Formula 1 based on 100 parts by weight of the lithium difluorophosphate salt crystal. have.

As a preferred embodiment of the present invention, the purification solvent may include an aqueous alcohol solution and an alkyl acetate.

As a preferred embodiment of the present invention, the purification solvent may include an aqueous alcohol solution and an alkyl acetate in a weight ratio of 1: 1.5 to 2.5.

As a preferred embodiment of the present invention, the purification process of step 2-1 is carried out under a nitrogen atmosphere and 23 to 30° C., and the first vacuum concentration of step 2-2 is performed under a pressure of 40 to 45° C. and 25 to 50 torr. And, the second vacuum concentration in step 2-3 may be performed under a pressure of 30 to 40° C. and 10 torr or less.

As a preferred embodiment of the present invention, the drying process of steps 2-4 may be performed under a vacuum atmosphere of 10 torr or less and 70 to 90°C using a rotary evaporator.

As a preferred embodiment of the present invention, the yield of the recrystallized lithium difluorophosphate crystals in steps 2-4 may be 80.0% or more, preferably 81.5% to 95.0%.

As a preferred embodiment of the present invention, the purity increase rate of Equation 1 below may be satisfied for the recrystallized lithium difluorophosphate salt crystals in steps 2-4.

[Equation 1]

3.0% ≤ (B-A)/A×100% ≤ 10.0%

In Equation 1, A is the purity (%) of the synthesized lithium difluorophosphate salt crystal in step 1, and B is the purity (%) of the recrystallized difluorophosphoric acid salt crystal in the second step.

As a preferred embodiment of the present invention, the method for preparing a lithium difluorophosphate salt crystal of the present invention may further include a third step of drying the recrystallized lithium difluorophosphate salt crystal of the second stage.

Another object of the present invention is to provide a high purity lithium difluorophosphate salt crystal prepared by the above manufacturing method and excellent in solubility.

Another object of the present invention is to provide the high-purity lithium difluorophosphate salt crystal as an electrolyte for a non-aqueous electrolyte for a secondary battery.

In addition, an object of the present invention is to provide a non-aqueous electrolyte solution for a secondary battery comprising a lithium difluorophosphate salt crystal as an electrolyte.

Another object of the present invention is to provide a high purity lithium difluorophosphate salt crystal prepared by the above manufacturing method.

As a preferred embodiment of the present invention, the lithium difluorophosphate salt crystal of the present invention has an average particle diameter of 2.000 to 5.000 μm for _{D 10 , 15.000 to 20.000 μm for D 50} , and 55.000 to 75.000 μm for D _90. have.

As a preferred embodiment of the present invention, the crystals of the lithium difluorophosphate salt of the present invention may have a tap density of 0.8500 to 0.9200 g/cm ³ .

Another object of the present invention is to provide the high-purity lithium difluorophosphate salt crystal as an electrolyte for a non-aqueous electrolyte for a secondary battery.

In addition, an object of the present invention is to provide a non-aqueous electrolyte solution for a secondary battery comprising a lithium difluorophosphate salt crystal as an electrolyte.

In the method for preparing a lithium difluorophosphate salt crystal of the present invention, a lithium difluorophosphate salt crystal can be prepared in high yield and high purity by introducing a specific reactant at an optimum composition ratio, and the prepared lithium difluorophosphate salt crystal can be prepared. It is possible to provide a nonaqueous electrolyte for a secondary battery having excellent stability by introducing it as an electrolyte for a nonaqueous electrolyte for a secondary battery. In addition, when the lithium difluorophosphate salt crystal of the present invention is prepared, purification and recrystallization using a specific purification solvent in the purification process has a specific range of particle size and density characteristics, and thus recrystallized lithium difluorophosphate salt The crystal is excellent in solubility in the secondary battery electrolyte.

Hereinafter, a method for preparing a crystal of lithium difluorophosphate having excellent solubility according to the present invention with high purity will be described in more detail.

The lithium difluorophosphate salt crystal of the present invention comprises a first step of synthesizing a _{lithium difluorophosphate salt crystal (LiPO 2} F _{2 );} And a second step of purifying and recrystallizing the lithium difluorophosphate salt crystal.

The first step is a 1-1 step of synthesizing a difluoro phosphate represented by the following formula (2) by reacting a mixture of a dihalophosphate represented by the following formula (1), a fluorinating agent, and a non-aqueous solvent; 1-2 steps of adding and reacting the difluoro phosphate dropwise to a mixture of lithium salt, water and a non-aqueous solvent, and then evaporating the non-aqueous solvent to obtain a solid; And a step 1-3 of dissolving the solid in a non-aqueous solvent, recrystallization at 0 to 25°C, and filtering to obtain a lithium difluorophosphate crystal.

[Formula 1]

In Formula 1, each of X ₁ and X ₂ is independent and is -Cl, -Br or -I, preferably -Cl or -Br, more preferably -Cl. In addition, the R in Formula 1 is a C ₁ to C ₁₀ straight-chain alkyl group, a C ₃ to C ₁₀ pulverized alkyl group, a C ₆ to C ₁₀ cycloalkyl group, or a C ₆ to C ₂₀ aryl group, Preferably, they are a C ₂ to C ₅ straight-chain alkyl group, a C ₃ to C ₅ pulverized alkyl group, a phenyl group or a benzyl group.

[Formula 2]

In Formula 2, R is a C ₁ to C ₁₀ straight-chain alkyl group, a C ₃ to C ₁₀ pulverized alkyl group, a C ₆ to C ₁₀ cycloalkyl group, or a C ₆ to C ₂₀ aryl group, preferably Preferably, it is a C ₂ to C ₅ straight-chain alkyl group, a C ₃ to C ₅ pulverized alkyl group, a phenyl group or a benzyl group. However, R in Formula 2 is the same as R in Formula 1 used in step 1-1.

The inert gas of step 1-1 is a general inert gas used in the art, and nitrogen gas or the like may be used.

Step 1-1 is a reaction temperature of 40 to 150°C, preferably 45 to 120°C, and more preferably 50 to 80°C while slowly stirring the mixture of dihalophosphate, fluorinating agent and non-aqueous solvent. After raising about 10 to 20 hours, preferably over 15 to 20 hours, reacting at an elevated reaction temperature for 6 to 10 hours, preferably for 6.5 to 9.0 hours, to synthesize phosphate with the difluoro. can do. Then, the solution (including the reaction product) subjected to the reaction is lowered to room temperature and filtered by a general method used in the art to obtain phosphate with difluoro. At this time, when heating the mixed solution to an appropriate reaction temperature, if the temperature increase rate is too fast, the reaction stability may be deteriorated. Therefore, it is preferable to gradually increase the temperature of the mixed solution to the reaction temperature. In addition, when the reaction temperature is less than 40° C., the reaction rate is too low and thus productivity decreases, and when the reaction temperature exceeds 150° C., the reaction occurs rapidly and the reaction product is chemically decomposed again.

For a specific example to aid understanding of the reaction of step 1-1 is as shown in Equation 1 below.

[Equation 1]

RPO ₂ Cl ₂ + fluorinating agent (fluoride) -> RPO ₂ F ₂ + chloride

The mixed solution of step 1-1 is The dihalophosphate and the fluorinating agent may be included in a molar ratio of 1: 1.5 to 3.0, preferably in a molar ratio of 1: 2.0 to 3.0, and more preferably in a molar ratio of 1: 2.2 to 2.7. At this time, if the molar ratio of the fluorinating agent is less than 1.5 molar ratio, the synthesis of the difluorophosphate represented by Chemical Formula 2 may be unsatisfactory, resulting in a problem that the yield of the crystals of the lithium difluorophosphate is lowered, and the content of the fluorinating agent is 3.0 molar ratio. Exceeding is uneconomical, rather, there may be a problem that unnecessary reaction products are generated due to the unreacted fluorinating agent component, and the amount of difluorophosphate synthesis is reduced.

And, the fluorinating agent is NH ₄ F (ammonium floride), NaF, KF, CeF (cesium floride), tri (C ₁ ~ C ₃ alkyl) amine trihydrofluoride salt and pyridine hydrogen fluoride salt selected from a single species or 2 It may include more than one species, preferably NH ₄ F, NaF, and may include a single species or two or more selected from the triethylamine trihydrofluoride salt.

The non-aqueous solvent in step 1-1 is cyclic carbonate, chain carbonate, cyclic ester, chain ester, n-hexane, cyclohexane, n-heptane, iso-heptane, benzene, xylene, acetonitrile, methyl ether , Ethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetrahydrofuran. In addition, the amount of the non-aqueous solvent in step 1-1 is preferably used so that the concentration of the dihalophosphate in the mixture is 7 to 9 g/ml, preferably 7.5 to 8.5 g/mol. At this time, if the concentration of dihalophosphate exceeds 7 to 9 g/ml due to too little or too much use of the non-aqueous solvent, there may be a problem that the amount of difluorophosphate synthesis decreases.

Next, step 1-2 is a step of reacting lithium salt, water, and difluoro phosphate, which is a reaction product of step 1-1, to prepare a lithium difluorophosphate salt crystal. The reaction product of lithium difluorophosphate salt crystals may be formed through a reaction as shown in Equation 2 below.

[Equation 2]

RPO ₂ F ₂ + LiX + H ₂ O → LiPO ₂ F ₂ + HX + ROH

In steps 1-2, the difluoro phosphate was added dropwise to a mixture of lithium salt, water, and a non-aqueous solvent and reacted, followed by filtration to obtain a lithium difluorophosphate salt crystal. In addition, when difluoro phosphate is added dropwise, a separate diluting solvent is not used and heat of reaction is generated, so it is preferable to slowly perform the dropwise addition.

The mixture of steps 1-2 may contain lithium salt and water in a molar ratio of 1: 0.10 to 0.65, preferably in a molar ratio of 1: 0.15 to 0.45, and more preferably in a molar ratio of 1: 0.20 to 0.35. At this time, if the molar ratio of water is less than 0.10 molar ratio _{, there may be a problem that the synthesis yield of LiPO 2} F ₂ is lowered, and even if the molar ratio of water exceeds 0.65 molar ratio, there _{is no increase in the synthesis yield of LiPO 2} F ₂ , but rather, impurities are generated by participating in the reaction. Since there may be a problem, it is recommended to use a lithium salt and water within the above range.

In step 1-2, the dropwise addition amount of difluoro phosphate is 230 to 350 parts by weight, preferably 250 to 320 parts by weight, more preferably 270 to 305 parts by weight, based on 100 parts by weight of the lithium salt. When the dropwise addition amount of rho phosphate is outside the above range, _{since the yield of LiPO 2} F ₂ synthesis may be lowered, it is preferable to add difluoro phosphate dropwise within the above range.

In step 1-2, the non-aqueous solvent of the mixed solution may be the same as or different from the non-aqueous solvent of step 1-1, and the non-aqueous solvent of step 1-2 is a cyclic carbonate, a chain carbonate, and Click ester, chain ester, n-hexane, cyclohexane, n-heptane, iso-heptane, benzene, xylene, acetonitrile, methyl ether, ethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether , Diethylene glycol dimethyl ether and tetrahydrofuran may be used alone or two or more selected from.

And, the amount of the non-aqueous solvent used in step 1-2 is 3.5 to 5 ml per 1 g of difluoro phosphate to be added dropwise, preferably 3.8 to 4.6 ml per 1 g of difluoro phosphate, and more preferably difluoro phosphate. It is recommended to use 3.8 ~ 4.4 ml per 1g.

After adding difluorophosphate dropwise while stirring the mixture in step 1-2, stirring and reaction were continuously performed at 50 to 70°C, preferably 50 to 60°C for 3 to 8 hours, preferably for 4 to 6.5 hours. Thus, a reaction product of lithium difluorophosphate salt crystals can be obtained. And, when the reaction is complete, the reaction solution containing the reaction product is decompressed to evaporate the non-aqueous solvent to obtain a solid.

Step 1-3 is a step of washing unreacted impurities, impurities, etc. from the solid. After dissolving the solid of step 1-2 in a non-aqueous solvent, recrystallization at 25 to 0°C, filtering is performed to obtain difluorophosphoric acid. This is a step of obtaining a lithium salt crystal. In this case, the non-aqueous solvent is the same as the non-aqueous solvent of the step 1-1 and/or the step 1-2.

The lithium difluorophosphate salt crystal obtained by performing steps 1-1 to 1-3 described above may have a yield of 82 to 92% and a purity of 95 to 98%, preferably, a yield of 85.0 to 92.0% and a purity of 95.20 Can be ~ 98.00%.

In the manufacturing method of the present invention, the second step is a step of purifying and recrystallizing the lithium difluorophosphate salt crystal prepared in the first step.

The second step is a 2-1 step of performing a purification process by introducing and stirring a lithium difluorophosphate salt crystal, a purification solvent, and a compound represented by the following formula (3) into a reactor; 2-2 step of first concentrating the purified reaction product in vacuum; 2-3 steps of concentrating the first vacuum concentrate in a second vacuum; And 2-4 steps of obtaining recrystallized lithium difluorophosphate salt crystals by cooling the second vacuum concentrate after performing a drying process.

[Formula 3]

Si(X) _a R _b

X in Formula 3 is a halogen element, preferably -F or -Cl, more preferably -Cl.

In addition, the R in Formula 1 is a C ₁ to C ₅ straight-chain alkyl group, a C ₃ to C ₅ pulverized alkyl group or a C ₁ to C ₃ alkoxy group, and preferably R is a C ₁ to C ₅ -chain alkyl group, C ₃ ~ C ₅ alkyl group or grinding of C ₁ ~ C ₃ alkoxy group, more preferably a preferably R is a straight-chain alkyl group of C ₁ ~ C _3. In addition, a and b in Formula 3 are integers satisfying a+b=4, provided that a and b are not 0.

The reactor of the second stage may be equipped with a reactor jacket, a vacuum pump, a condenser, a scrubber, and/or a receiver.

The purification solvent of step 2-1 is a mixture of an aqueous alcohol solution and an alkyl acetate, and by mixing an alkyl acetate, the amount of the purification solvent is reduced compared to when the aqueous alcohol solution is used alone, and the recrystallized diffle is adjusted through the adjustment of the amount of alkyl acetate. The particle size of the lithium urophosphate salt crystal can be controlled and a lithium difluorophosphate salt crystal having a specific size range can be obtained in a high yield.

In addition, the purification solvent may include an aqueous alcohol solution and an alkyl acetate in a weight ratio of 1: 1.5 to 2.5, preferably in a weight ratio of 1: 1.8 to 2.5, and more preferably in a weight ratio of 1: 1.8 to 2.3. At this time, if the amount of alkyl acetate used in the purification solvent is less than 1.5 weight ratio, the average size (D ₅₀ ) of the crystals of the recrystallized lithium difluorophosphate salt becomes too small, so that crystals of the appropriate size range to be prepared may not be obtained in high yield. In addition, the tap density decreases, and if the amount of alkyl acetate exceeds 2.5 weight ratio, there may be a problem in that the purity of the obtained lithium difluorophosphate salt is rather low, and the tap density may be too high, so it is preferable to use it within the above range.

And, the amount of the purification solvent is 350 to 480 parts by weight, preferably 380 to 460 parts by weight, more preferably 385 to 460 parts by weight of the purification solvent, based on 100 parts by weight of the lithium difluorophosphate salt crystal obtained in step 1. 450 parts by weight may be used. At this time, if the amount of the purification solvent is less than 350 parts by weight, there may be a problem that the solubility decreases and the tablet decreases, and the average particle size of the recrystallized lithium difluorophosphate salt crystals increases. Since there may be a problem of lowering economic efficiency due to an increase in cost, it is recommended to use it within the above range.

In addition, the aqueous alcohol solution of the purification solvent component may be an aqueous alcohol solution having 2 to 4 carbon atoms, preferably an aqueous alcohol solution having 2 to 4 carbon atoms, and more preferably an aqueous ethanol solution having a concentration of 99.5% to 99.8%.

In addition, the alkyl acetate of step 2-1 may include at least one selected from methyl acetate, ethyl acetate and propyl acetate, and preferably at least one selected from methyl acetate and ethyl acetate, More preferably, it may contain ethyl acetate.

When the compound represented by Formula 3 in step 2-1 is used with the purification solvent, recrystallized lithium difluorophosphate salt is performed even when the second vacuum concentration process is performed under milder conditions than when the purification solvent is used alone. Can be obtained in an equivalent to high yield and/or purity, and the recrystallized lithium difluorophosphate crystal has a small average particle diameter to recrystallize, thereby increasing the solubility of the crystal in the non-aqueous electrolyte solution of the secondary battery. Do it.

And, the amount of the compound represented by Formula 3 is 5 to 30 parts by weight, preferably 5 to 20 parts by weight, more preferably 5 to 30 parts by weight, based on 100 parts by weight of the lithium difluorophosphate salt crystal obtained in step 1. 15 parts by weight may be used. At this time, if the amount of the compound represented by Formula 3 is less than 5 parts by weight, the amount of the compound is small and there is no effect of reducing the amount of the purified solvent due to the mixed use thereof, so that the effect of reducing the yield of the recrystallized lithium difluorophosphate crystal is insufficient. If it is used in excess of 30 parts by weight, due to the presence of the compound represented by Formula 3 remaining during the purification process, the recrystallized lithium difluorophosphate salt crystal Since there may be a problem that the purity is rather lowered, it is recommended to use it within the above range.

In addition, the purification process of step 2-1 is preferably performed under a nitrogen atmosphere and 23 to 30°C, preferably under a nitrogen atmosphere and 23 to 27°C.

Next, the step 2-2 is a process of first vacuum concentrating the reactant subjected to the purification process in step 2-1, and the first vacuum concentration increases the temperature inside the reactor to 40 ~ 45 ℃, and then 25 ~ When vacuum concentration can be performed while maintaining a pressure of 50 torr, preferably 30 to 45 torr, more preferably 35 to 42 torr, and the alcohol vapor distilled from the reactor is condensed in the condenser and the liquid is not collected in the receiver You can perform up to. At this time, when the first vacuum concentration is performed at less than 40°C, there may be a problem that the solvent is not distilled, resulting in a decrease in productivity. Can occur. In addition, when the primary vacuum concentration pressure is less than 25 torr, there may be a problem in that the solvent passes to the pump, and when it exceeds 50 torr, there may be a problem that the time increases, resulting in a decrease in productivity and a decrease in purity.

Next, step 2-3 is a process of secondary vacuum concentrating the first vacuum concentrate, and is performed under a pressure of 30 to 40°C and 10 torr or less, preferably 30 to 40°C and 5 torr or less. It is better to do it under pressure. In steps 2-3, when an appropriate amount of vacuum concentrate is generated, the vacuum is removed with nitrogen to terminate the second vacuum concentration process. At this time, when the secondary vacuum concentration pressure exceeds 10 torr, there may be a problem of lowering productivity due to an increase in concentration time and a problem of low purity of the purified product.

Next, the second vacuum concentrate is dried in step 2-4, where drying can be performed using a general drying method used in the art, and a preferred embodiment is, for example, a rotary evaporator. It is good to perform rotary drying in a vacuum atmosphere of 2 torr or less and 70 to 90° C., preferably in a vacuum atmosphere of 10 torr or less and 80 to 90° C. by using the rotary drying for about 10 to 14 hours.

When the drying process is completed, the dried product is cooled to 25° C. or less, and finally recrystallized lithium difluorophosphate crystals can be obtained.

Thus, the recrystallized lithium difluorophosphate crystal of the present invention prepared by performing the first and second steps of Method 1 has a yield of 80.0% or more, preferably 81.5 to 95%, and more preferably 82.5. It may be ~ 95.0%.

In addition, the recrystallized lithium difluorophosphate salt crystal may have a purity satisfying Equation 3 below.

[Equation 3]

3.0%≦(BA)/A×100%≦10.0%, preferably 3.5%≦(BA)/A×100%≦8.0%, more preferably 3.7%≦(BA)/A×100%≦7.0 %

In Equation 3, A is the purity (%) of the synthesized lithium difluorophosphate salt crystal in step 1, and B is the purity (%) of the recrystallized difluorophosphoric acid salt crystal in the second step.

Further, the recrystallized lithium difluorophosphate salt crystal of the present invention has an average particle diameter of D ₁₀ of 2.000 to 5.000 µm, D ₅₀ of 15.000 to 20.000 µm and D ₉₀ of 55.000 to 75.000 µm, preferably The average particle diameter of D ₁₀ is 2.250 to 4.850 μm, D ₅₀ is 16.000 to 19.500 μm and D ₉₀ is 56.500 to 74.500 μm, and more preferably, the average particle diameter of D ₁₀ is 2.350 to 4.750 μm, and D ₅₀ is 17.000 ~ 19.000㎛ and D ₉₀ may satisfy 57.500 ~ 72.500㎛.

In addition, the recrystallized lithium difluorophosphate salt crystal of the present invention may have a tap density of 0.8500 to 0.9200 g/cm ³ , preferably a tap density of 0.8650 to 0.9000 g/cm ³ , and more preferably The tap density may be 0.8750 to 0.8950 g/cm ³ .

The lithium difluorophosphate salt crystal of the present invention prepared in this way can be used for various purposes, for example, it can be used as a stabilizer for a chloroethylene polymer, a catalyst for a reaction lubricant, a disinfectant for a toothbrush, a preservative for wood, etc. And, preferably, it can be used as an electrolyte for a non-aqueous electrolyte solution for a secondary battery, and more preferably, the lithium difluorophosphate salt crystal of the present invention has excellent solubility in a non-aqueous electrolyte solution for a secondary battery. It is suitable for use as an electrolyte for aqueous electrolytic solutions.

Hereinafter, the present invention will be described in more detail through examples. However, it should not be interpreted to limit the scope of the present invention by the following examples, and the following examples are intended to aid understanding of the present invention.

[Example]

Example 1: Preparation of recrystallized lithium difluorophosphate salt crystals

(1) Synthesis of lithium difluorophosphate salt crystal (LiPO ₂ F ₂ ) (step 1)

In a dried reactor under nitrogen protection, dihalophosphate 38.2 g (0.2 mol) represented by the following formula 1-1, NH ₄ F 18.52 g (0.5 mol) ammonium fluoride, tetraethylene glycol dimethyl ether (0.66 g, 0.003 mol) It was added to 300 ml of acetonitrile, which is a non-aqueous solvent, and the temperature of the reactor was slowly increased to about 55°C for 20 hours, and then stirred at about 55°C to perform the reaction for 8 hours.

After completion of the reaction, the temperature of the reactor was lowered to room temperature, filtered and distilled to obtain 24.3 g of difluoro phosphate represented by the following formula (2-1).

Next, in another dry reaction vessel, lithium chloride 8.48 g (0.2 mol), water 0.9 g (0.05 mol), and 100 ml of acetonitrile were mixed to prepare a mixture, and then the above formula (2) while stirring the mixture was stirred. Difluoro phosphate represented by -1 was added dropwise. At this time, the amount of difluoro phosphate added dropwise was 24.3 g. Then, after slowly stirring and reacting at 55° C. for 5 hours, the solvent was evaporated under reduced pressure to obtain a solid lithium difluorophosphate salt crystal.

[Formula 1-1]

In Formula 1-1, X ₁ and X ₂ are -Cl, and R is a C ₃ linear alkyl group.

[Formula 2-1]

In Formula 2-1, R is a C ₃ linear alkyl group.

(2) Preparation of recrystallized lithium difluorophosphate salt crystal (step 2)

100 parts by weight of the lithium difluorophosphate salt crystal and 420 parts by weight of a purification solvent and 8.5 parts by weight of a compound represented by the following formula 3-1 in the reactor in which the reactor jacket, vacuum pump, condenser, scrubber and/or receiver, etc. are installed Part was added and stirred, and the reactor temperature was maintained at 24° C. to 25° C., and lithium fluoride produced by-product was separated by filtration.

In this case, the purification solvent includes an aqueous ethanol solution of 99.5% ~ 99.8% concentration and ethyl acetate in a 1:2.1 weight ratio.

[Chemical Formula 3-1]

Si(X) _a R _b

In Formula 3-1, X is -Cl, R is a methyl group, and a and b are 2.

Next, hot water was added to the reactor jacket, and the vacuum pump was operated while maintaining the internal temperature of the reactor at 43 to 44°C, and the first vacuum concentration was performed while maintaining an initial pressure of about 28 torr inside the reactor. The first vacuum concentration was performed until the alcohol vapor distilled from the reactor was condensed in the condenser so that no liquid was collected in the receiver.

Next, while maintaining the internal temperature of 43℃ ~ 44℃, the pressure was reduced to 1 torr, and the remaining alcohol aqueous solution of the vacuum concentrate was concentrated in the condenser and the second vacuum was performed until no liquid was generated in the receiver. Concentration was carried out.

Next, difluorophosphoric acid was finally recrystallized by distilling with a pump having a vacuum degree of 1 torr using a rotary evaporator and completely dried for 12 hours at 85°C, and then cooled to 25°C. A lithium salt crystal was obtained (yield 87.0%, purity 99.93%).

Examples 2 to 9 and Comparative Examples 1 to 9

A recrystallized lithium difluorophosphate salt crystal was prepared in the same manner as in Example 1, but Examples 2 to 9 and Comparative Examples 1 to 9 were each prepared by varying the amount of components used as shown in Table 1 below. Implemented. In addition, the crystallized LiPO ₂ F ₂ synthesis (step 1) and the recrystallized LiPO ₂ F ₂ crystals (step 2) were measured for the increase in purity based on Equation 1 below, and are shown in Table 2 below.

[Equation 1]

Relative purity increase/decrease = ((purity of recrystallized LiPO ₂ F ₂ crystals (%)-crystallized LiPO ₂ F ₂ crystal purity without recrystallization (%)) / (crystallized crystallization without recrystallization LiPO ₂ F ₂ crystal purity (%))} × 100%

division Synthesis of Crystallized LiPO ₂ F ₂ (Step 1) Preparation of recrystallized LiPO ₂ F ₂ crystals (2nd step-purification process) Step 1-1 Step 1-2 (One) Fluorinating agent (2) (3)
(Part by weight) Stage 1
LiPO ₂ F ₂
(Part by weight) Purification solvent
(Part by weight) Chemical formula
3-1
(Part by weight) Example 1 1: 2.5 NH ₄ F 1:0.25 287 100 420 8.5 Example 2 1: 2.0 NH ₄ F 1:0.25 287 100 420 8.5 Example 3 1: 2.85 NH ₄ F 1:0.25 287 100 420 8.5 Example 4 1: 2.5 NH ₄ F 1:0.15 287 100 420 8.5 Example 5 1: 2.5 NH ₄ F 1:0.45 287 100 420 8.5 Example 6 1: 2.5 NH ₄ F 1:0.25 250 100 420 8.5 Example 7 1: 2.5 NH ₄ F 1:0.25 320 100 420 8.5 Example 8 1: 2.5 NH ₄ F 1:0.25 287 100 380 8.5 Example 9 1: 2.5 NH ₄ F 1:0.25 287 100 450 8.5 Comparative Example 1 1: 2.5 NH ₄ F 1:0.25 287 - - - Comparative Example 2 1: 1.3 NH ₄ F 1:0.25 287 100 420 8.5 Comparative Example 3 1: 3.2 NH ₄ F 1:0.25 287 100 420 8.5 Comparative Example 4 1: 2.5 NH ₄ F 1:0.09 287 100 420 8.5 Comparative Example 5 1: 2.5 NH ₄ F 1:0.68 287 100 420 8.5 Comparative Example 6 1: 2.5 NH ₄ F 1:0.25 225 100 420 8.5 Comparative Example 7 1: 2.5 NH ₄ F 1:0.25 360 100 420 8.5 Comparative Example 8 1: 2.5 NH ₄ F 1:0.25 287 100 337 8.5 Comparative Example 9 1: 2.5 NH ₄ F 1:0.25 287 100 502 8.5 (1): Molar ratio of dihalophosphate and fluorinating agent
(2): Molar ratio of lithium salt and water
(3): Dropwise amount of difluoro phosphate per 100 parts by weight of lithium salt

division Crystallized LiPO ₂ F ₂ (Step 1) Recrystallized LiPO ₂ F ₂ Crystals (Step 2) Relative purity
Increase/decrease rate (%) yield(%) water(%) yield(%) water(%) Comparative Example 1 90.2 96.1 - - - Example 1 90.2 96.1 87.0 99.93 3.99 Example 2 84.3 94.5 82.1 99.14 4.91 Example 3 89.3 95.4 86.7 99.71 4.52 Example 4 88.9 96.0 86.5 99.70 3.85 Example 5 90.3 95.8 87.4 99.82 4.20 Example 6 89.7 95.6 86.4 99.78 4.37 Example 7 88.1 94.9 86.1 99.92 5.29 Example 8 90.2 96.2 87.2 99.85 3.79 Example 9 90.2 96.3 86.0 99.94 3.78 Comparative Example 2 75.0 93.5 71.9 98.99 - Comparative Example 3 89.4 92.9 85.8 98.02 - Comparative Example 4 81.0 94.0 75.6 99.11 - Comparative Example 5 88.4 91.1 84.7 96.96 - Comparative Example 6 82.6 95.3 78.8 99.79 - Comparative Example 7 84.2 95.2 79.7 99.85 - Comparative Example 8 90.2 96.1 87.5 98.02 - Comparative Example 9 90.2 96.3 86.1 99.93 -

Looking at the yield and purity of Table 2, in the case of Examples 1 to 9 _{, the yield of crystallized LiPO 2} F ₂ (step 1) was 84% or more and purity 95% or more, and recrystallized LiPO ₂ F ₂ crystals It can be seen that (Step 2) has a yield of 82% or more and a purity of 98.5% or more.

In the case of Comparative Example 2 in which the dihalophosphate and the fluorinating agent were used in a 1:1.3 molar ratio of less than 1:1.5 in step 1-1, as compared with Examples 1 and 2, crystallized LiPO ₂ F ₂ (step 1) The yield of was very low, and as a result, there was a problem that the yield of the reaction product of the second step was also too low. And, in the case of Comparative Example 3 in which the dihalophosphate and the fluorinating agent were used in excess of 1: 3.0 molar ratio in step 1-1, there was no increase in the yield and the purity was rather low as compared with Examples 1 and 3 This occurred, which is believed to have lowered the purity of the _{crystallized LiPO 2} F ₂ due to the synthesis of unnecessary reaction products due to the unreacted fluorinating agent.

In addition, in the case of Comparative Example 4 in which lithium salt and water were used in a molar ratio of 1:0.10 or less in step 1-2, compared with Examples 1 and 4 _{, the yield of crystallized LiPO 2} F ₂ (step 1) was rapid. In the case of Comparative Example 5 in which lithium salt and water were used in excess of 1:0.65 molar ratio, when compared with Examples 1 and 5, the purity of the _{crystallized LiPO 2} F _{2 was too low.} This is believed to be due to the occurrence of many impurities due to unnecessary additional reactions.

In addition, in the case of Comparative Example 6 in which the difluorophosphate dropwise addition amount in step 1-2 was less than 230 parts by weight, compared with Examples 1 and 6, _{the yield of crystallized LiPO 2} F ₂ was not too good. In the case of Comparative Example 7, in which the difluorophosphate dropwise addition amount exceeded 350 parts by weight in step 1-2, compared with Examples 1 and 7, _{the yield of crystallized LiPO 2} F ₂ was rather lowered. There was.

And, in the case of Comparative Example 8 in which the amount of the purification solvent used was less than 350 parts by weight, compared to Example 8, there was a problem of low purity. In addition, in the case of Comparative Example 9, in which the amount of the aqueous alcohol solution used in the second-stage reaction exceeded 480 parts by weight, compared to Example 1 or Example 9, there was no increase in yield and/or purity due to excessive use of the alcohol aqueous solution in the second-stage process.

Examples 10 to 13 and Comparative Examples 10 to 14

To prepare a recrystallized lithium difluorophosphate salt crystal in the same manner as in Example 1, but in the preparation of the recrystallized lithium difluorophosphate salt crystal in the second step, an aqueous ethanol solution and an aqueous solution of ethanol in a purification solvent as shown in Table 3 below. By varying the weight ratio of ethyl acetate, Examples 10 to 11 and Comparative Examples 10 to 12 were carried out, respectively.

In addition, a recrystallized lithium difluorophosphate salt crystal was prepared in the same manner as in Example 1, but in the preparation of the recrystallized lithium difluorophosphate salt crystal in the second step, the compound represented by Formula 3-1 Examples 12 to 13 and Comparative Examples 12 to 14 were each carried out by varying the amount of use.

division Preparation of recrystallized LiPO ₂ F _{2 crystals}
(Step 2-Purification process) Phase 1 LiPO ₂ F ₂
(Part by weight) refine
menstruum
(Part by weight) Alcohol aqueous solution:
Alkyl acetate
(Weight ratio) Formula 3-1 compound used
(Part by weight) Example 1 100 420 1: 2.1 8.5 Example 10 100 420 1: 1.8 8.5 Example 11 100 420 1: 2.3 8.5 Example 12 100 420 1: 2.1 6.0 Example 13 100 420 1: 2.1 15.0 Comparative Example 10 100 420 1: 1.0 8.5 Comparative Example 11 100 485 1: 1.0 8.5 Comparative Example 12 100 420 1: 2.8 8.5 Comparative Example 13 100 420 1: 2.1 3 Comparative Example 14 100 420 1: 2.1 32

division Stage 1
Yield (%) / Purity (%) Step 2
Yield (%) / Purity (%) Purity increase rate (%) Example 1 90.2 / 96.1 87.0 / 99.93 3.99 Example 10 90.2 / 96.1 88.4 / 99.93 3.99 Example 11 90.2 / 96.1 86.5 / 99.87 3.92 Example 12 90.2 / 96.1 86.8 / 99.91 3.96 Example 13 90.2 / 96.1 87.8 / 99.97 3.99 Comparative Example 10 90.2 / 96.1 87.1 / 98.88 2.89 Comparative Example 11 90.2 / 96.1 88.3 / 99.92 3.98 Comparative Example 12 90.2 / 96.1 86.7 / 99.65 3.69 Comparative Example 13 90.2 / 96.1 85.1 / 99.04 3.06 Comparative Example 14 90.2 / 96.1 87.8 / 95.66 -

Looking at Tables 3 and 4, when compared with Example 10 (1.8 weight ratio), yield and purity of Comparative Example 10 in which the purification solvent was used in a 1.0 weight ratio of less than 1.5 weight ratio of alkyl acetate to the alcohol aqueous solution during the purification process. There was a problem of decreasing, and when the alkyl acetate was used in a weight ratio of less than 1.5, it was confirmed that a purification solvent was used to have a similar yield and purity as in Example 10 (Comparative Example 11).

And, in the case of Comparative Example 12 in which the purification solvent was used in a 2.8 weight ratio exceeding 2.5 weight ratio of the alcohol aqueous solution, compared to Example 11 (2.3 weight ratio), recrystallized lithium difluorophosphate There was a problem that the purity of the salt crystal was rather lowered.

And, in the case of Comparative Example 13 using less than 5 parts by weight of the compound of Formula 3-1, as compared with Example 1 (8.5 parts by weight) and Example 12 (6 parts by weight), recrystallized lithium difluorophosphate salt It was confirmed that the effect of preventing the decrease in the yield of crystals was inferior.

In addition, in the case of Comparative Example 14 in which the compound of Formula 3-1 was used in excess of 30 parts by weight, compared to Example 1 (8.5 parts by weight) and Example 13 (15 parts by weight), the yield reduction prevention effect was insufficient and the purity was rather There was a problem of greatly decreasing, which is believed to be because the compound represented by Formula 3-1 remained and acted as an impurity.

Example 14 and Comparative Examples 15 to 18

Recrystallized lithium difluorophosphate salt crystals were prepared in the same manner as in Example 1, but Example 14 and Comparative Examples 15 to 18 were each carried out by varying the production conditions as shown in Table 5 below. At this time, the vacuum compression conditions of the second step were different. In addition, the crystallized LiPO ₂ F ₂ synthesis (step 1) and the recrystallized LiPO ₂ F ₂ crystal (step 2) were measured for the increase in purity based on Equation 1, and are shown in Table 6 below.

division
(Part by weight) Preparation of recrystallized LiPO ₂ F ₂ crystals (step 2) At the first vacuum concentration
pressure Temperature at the first vacuum concentration At the second vacuum concentration
pressure yield(%)/
water(%) Example 1 28 torr 43 ~ 44℃ 1 torr 87.0%/99.93% Example 14 28 torr 40 ~ 41℃ 1 torr 86.3%/99.95% Comparative Example 15 28 torr 35 ~ 36℃ 1 torr 81.8%/99.91% Comparative Example 16 28 torr 48 ~ 49℃ 1 torr 87.1%/96.22% Comparative Example 17 35 torr 43 ~ 44℃ 1 torr 79.4%/98.17% Comparative Example 18 21 torr 43 ~ 44℃ 1 torr 86.8%/99.19%

division Stage 1
Yield (%) / Purity (%) Step 2
Yield (%) / Purity (%) Purity increase rate (%) Example 1 90.2 / 96.1 87.0 / 99.93 3.99 Example 14 90.2 / 96.1 86.3 / 99.95 4.00 Comparative Example 15 90.2 / 96.1 81.8 / 99.91 3.96 Comparative Example 16 90.2 / 96.1 87.1 / 96.22 1.25 Comparative Example 17 90.2 / 96.1 79.4 / 98.17 2.15 Comparative Example 18 90.2 / 96.1 86.8 / 99.17 3.21

Looking at the yield/purity of steps 1 and 2 in Table 6, in the case of Examples 1 and 14, the recrystallized LiPO ₂ F ₂ crystals showed a high yield of 85% or more and a high purity increase rate of 3.90% or more.

In addition, in the case of Comparative Example 15 in which the first vacuum concentration temperature is less than 40°C, compared with Example 14, the second yield is significantly lower than the first yield. In the case of Comparative Example 16, there was no change in yield, but there was a problem in that the purity was rather decreased.

Further, under the first hour concentrated in vacuo, 30 torr in excess of the pressure of the second-step reaction first for comparing performing a vacuum concentrated to Example 17, the recrystallized LiPO as compared to the crystallized LiPO ₂ F ₂ synthesized in Step 1, ₂ There was a problem in that the yield of the F ₂ crystal was lowered and the purity increase rate was also low, and in the case of Comparative Example 18 in which the first vacuum concentration was performed under a pressure of less than 25 torr, compared to Example 1, there was a problem in that the improvement rate of purity increase was low. .

Experimental Example 1: Analysis of particle characteristics of recrystallized lithium difluorophosphate salt crystals

The particle distribution and tap density of the recrystallized lithium difluorophosphate salt crystals prepared in Example 1, Examples 12 to 13, and Comparative Example 13 were measured, and the results are shown in Table 7 below.

division Crystal particle distribution diagram Tap density
(g/cm ³ ) D ₁₀ (㎛) D ₅₀ (㎛) D ₉₀ (㎛) Example 1 2.692 17.933 69.572 0.8852 Example 12 4.575 18.782 72.419 0.8933 Example 13 2.513 17.245 66.875 0.8694 Comparative Example 13 7.418 23.084 84.119 0.9471

Looking at the crystal particle distribution of Table 7, it was confirmed that the particle size and distribution of the recrystallized crystal tend to be different depending on the amount of the compound represented by Chemical Formula 3-1.

In the case of Comparative Example 13 in which the amount of the compound represented by Formula 3-1 was less than 5 parts by weight of the crystals, as compared with Example 1 (8.5 parts by weight) and Example 12 (6 parts by weight), the particle size of the crystal It can be seen that there is a tendency of a relatively large increase, which decreases solubility when the crystal is used as an electrolyte in a nonaqueous electrolyte.

In addition, in the case of Comparative Example 14, the tap density was much higher than that of Examples 1 and 12 to 13, and through this, the crystals of Comparative Example 14 had a relatively uneven particle surface than that of Examples 1 and 12 to 13. It is because I can't.

Through the above examples, it was confirmed that a high-purity lithium difluorophosphate salt crystal could be prepared in a high yield by using the method suggested by the present invention. The lithium difluorophosphate salt crystal of the present invention prepared by this method can be used as a composition of a stabilizer for a chloroethylene polymer, a catalyst for a reaction lubricant, a disinfectant for a toothbrush, a preservative for wood, and the like. It is possible to provide a non-aqueous electrolyte for a secondary battery having excellent stability by introducing it as an electrolyte of an aqueous electrolytic solution.

Claims (12)

1 step of synthesizing a lithium difluorophosphate salt crystal from dihalophosphate represented by the following formula (1); And
A second step of purifying and recrystallizing the lithium difluorophosphate salt crystal; and
The first step,
1-1 step of synthesizing difluoro phosphate represented by the following formula (2) by reacting a mixture of dihalophosphate represented by Chemical Formula 1, a fluorinating agent, and a non-aqueous solvent under an inert gas;
1-2 steps of adding and reacting the difluoro phosphate dropwise to a mixture of lithium salt, water and a non-aqueous solvent, and then evaporating the non-aqueous solvent to obtain a solid; And
Step 1-3 of dissolving the solid in a non-aqueous solvent, recrystallization, and filtering to obtain a lithium difluorophosphate salt crystal, and performing a process including,
In the second step, 350 to 450 parts by weight of a purification solvent and 5 to 30 parts by weight of a compound represented by the following formula (3) are added and stirred to perform a purification process based on 100 parts by weight of the lithium difluorophosphate crystal. -Stage 1;
2-2 step of first vacuum concentrating the purified reaction product under 40 ~ 45 ℃ and 25 ~ 50 torr conditions;
2-3 steps of second vacuum concentrating the first vacuum concentrate under conditions of 30 to 40° C. and 10 torr or less; And
After performing the drying process of the second vacuum concentrate, 2-4 steps of obtaining recrystallized lithium difluorophosphate salt crystals by cooling, and performing a process including,
The purification solvent contains an aqueous alcohol solution having 2 to 4 carbon atoms and an alkyl acetate in a weight ratio of 1: 1.5 to 2.5,
The lithium difluorophosphate salt crystals prepared by performing the two-step process have an average particle diameter of 2.000 to 5.000 µm for _{D 10 , 15.000 to 20.000 µm for D 50} and 55.000 to 75.000 µm for D ₉₀ .
The recrystallized lithium difluorophosphate salt crystal has a yield of 81.5 to 95.0%, and the purity increase rate satisfies Equation 3 below.
[Formula 1]

In Formula 1, each of X ₁ and X ₂ is independent, and is -Cl, -Br or -I, and R is a C ₁ to C ₁₀ straight-chain alkyl group, a C ₃ to C ₁₀ pulverized alkyl group, C _{It is a 6} to C ₁₀ cycloalkyl group or a C ₆ to C ₂₀ aryl group,
[Formula 2]

In Formula 2, R is a C ₁ to C ₁₀ straight-chain alkyl group, a C ₃ to C ₁₀ pulverized alkyl group, a C ₆ to C ₁₀ cycloalkyl group, or a C ₆ to C ₂₀ aryl group.
[Formula 3]
Si(X) _a R _b
In Formula 3, X is a halogen element, R is a C ₁ to C ₅ straight-chain alkyl group, a C ₃ to C ₅ branched alkyl group or a C ₁ to C ₃ alkoxy group, and a and b are a+b= It is an integer satisfying 4, provided that a and b are not 0,
[Equation 3]
3.5% ≤ (BA)/A×100% ≤ 7.0%
In Equation 3, A is the purity (%) of the synthesized lithium difluorophosphate salt crystal in step 1, and B is the purity (%) of the recrystallized difluorophosphoric acid salt crystal in the second step.
delete The method of claim 1,
The mixed solution of step 1-1 is It contains dihalophosphate and a fluorinating agent in a molar ratio of 1: 2.0 to 3.0,
The fluorinating agent is excellent in solubility, characterized in that it contains at least one selected _{from NH 4} F, NaF, KF, CeF, tri(C ₁ ~ C _{3 alkyl) amine trihydrofluoride salt and pyridine hydrogen fluoride salt.} A method of producing a lithium difluorophosphate salt crystal with high purity.
The method of claim 1, wherein each of the non-aqueous solvents in steps 1-1 and 1-2 is independent, and includes cyclic carbonates, chain carbonates, cyclic esters, chain esters, n-hexane, cyclohexane, n- At least one selected from heptane, iso-heptane, benzene, xylene, acetonitrile, methyl ether, ethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetrahydrofuran. A method of producing a lithium difluorophosphate salt crystal having excellent solubility, comprising a high purity.
The method of claim 1, wherein the lithium salt of step 1-2 is selected from lithium chloride, lithium bromide, lithium fluoride, lithium iodide, lithium hydroxide, lithium carbonate, lithium bicarbonate, lithium phosphate, lithium metaphosphate, lithium acetate, and lithium sulfate. Includes more than a species,
A method of producing a lithium difluorophosphate salt crystal having excellent solubility with high purity, characterized in that the mixture of steps 1-2 contains lithium salt and water in a molar ratio of 1:0.10 to 0.65.
The method of claim 1, wherein the difluoro phosphate is added in an amount of 230 to 350 parts by weight based on 100 parts by weight of the lithium salt,
A method of producing a lithium difluorophosphate salt crystal having excellent solubility with high purity, characterized in that the non-aqueous solvent of the 1-2 step mixture is used in an amount of 3.5 to 5 ml per 1 g of difluorophosphate added dropwise.
delete delete delete The method of claim 1, wherein the tap density of the recrystallized lithium difluorophosphate salt crystal in the second step is 0.8500 to 0.9200 g/cm ³ . Way.
Comprising a lithium difluorophosphate salt crystal prepared by the method of any one of claims 1, 3 to 6, and 10,
The lithium difluorophosphate salt crystal has an average particle diameter of 2.000 to 5.000 μm for _{D 10 , 15.000 to 20.000 μm for D 50} , and 55.000 to 75.000 μm for D ₉₀ . Lithium salt crystals.
A non-aqueous electrolyte for a secondary battery comprising the lithium difluorophosphate salt crystal of claim 11 as an electrolyte.