KR102300438B1 - Manufacturing method for high-purity crystallization of lithium difluorophosphate with excellet solubility and Non-aqueous electrolyte for secondary battery - Google Patents

Abstract

The present invention relates to a method for manufacturing a lithium difluorophosphate salt crystal. More specifically, provide is a method for manufacturing a lithium difluorophosphate salt crystal with high yields and high purity, wherein the manufactured high purity lithium difluorophosphate salt crystal can be applied to various uses.

Description

A method for manufacturing a high-purity lithium difluorophosphate salt crystal having excellent solubility and a non-aqueous electrolyte solution for a secondary battery using the same

The present invention relates to a method for preparing a crystal of a lithium difluorophosphate salt and to a non-aqueous electrolyte for a secondary battery comprising the same.

Lithium difluorophosphate salt is an industrially useful compound such as a wood preservative (see Patent Document 1), a toothbrush disinfectant, and a polymer stabilizer.

By the way, development of the secondary battery which has a high energy density, for example, a lithium ion secondary battery is advancing with weight reduction and miniaturization of electrical appliances in recent years. Moreover, as the field of application of this lithium ion secondary battery expands, the improvement of battery characteristics is still more 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 electrolyte containing a vinyl ethylene carbonate compound, the decomposition of the electrolyte is minimized, and a battery with excellent storage and cycle characteristics is manufactured. A technique for increasing the recovery capacity after storage by using an electrolytic solution is disclosed.

However, conventional lithium ion secondary battery electrolytes exhibit the 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 large-current discharge characteristics are lowered. there is a problem.

Accordingly, a technology has been developed in which lithium difluorophosphate salt is 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 in that manufacturing efficiency and purity are lowered.

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

The present invention has been devised to solve the above problems, and the problem to be solved by the present invention is to present a new method for producing a high purity lithium difluorophosphate salt crystal, and to prepare the lithium difluorophosphate salt crystal 2 An object of the present invention is to provide it as an electrolyte for a secondary battery or the like.

The method for preparing lithium difluorophosphate crystals of the present invention for solving the above problems is to _{react with lithium hexafluorophosphate (LiPF 6} ), chloride, silicon-based compound, and water in the absence of a solvent to form lithium difluorophosphate crystals Step 1 of synthesizing (LiPO ₂ F _{2 );} and a second step of purifying and recrystallizing the lithium difluorophosphate salt crystal to prepare a lithium difluorophosphate salt crystal.

As a preferred embodiment of the present invention, the silicone-based compound may include a silicone-based compound represented by the following formula (1).

[Formula 1]

In Formula 1, R _{1 To} R ₃ Each is independent, C _{1 To} C ₅ A straight-chain alkyl group, C _{3 To} C ₅ A pulverized alkyl group, C _{6 To} C ₈ A cycloalkyl group, C _{1 To} C ₁₀ Of an alkoxy group, a C ₁ ~ C ₅ straight-chain alkyl group including a halide group, a C ₃ ~ C ₅ pulverized alkyl group including a halide group, an aryl group or an aryl group including a halide group,

Each of R ₄ to R ₇ is independent, and includes a hydrogen atom, a C ₁ to C ₅ straight-chain alkyl group, a C ₃ to C ₅ pulverized alkyl group, a C ₁ to C ₁₀ alkoxy group or an aryl group, and X is an integer from 0 to 10.

As a preferred embodiment of the present invention, the first step of the method 1 is step 1-1 of preparing a mixed pulverized product by pulverizing and mixing lithium hexafluorophosphate, chloride and a silicon-based compound; 1-2 steps of introducing the mixed pulverized material into the reactor and then venting nitrogen gas through the reactor to replace the air inside the reactor with nitrogen gas; After performing the reaction by introducing and bubbling steam into the reactor, steps 1-3 of filtering the reaction product to obtain a reaction product; may be performed.

As a preferred embodiment of the present invention, the Lithium hexafluorophosphate, chloride, and silicon compound may be ground and mixed in a molar ratio of 1: 2.8 to 4.5: 0.2 to 0.7.

As a preferred embodiment of the present invention, in steps 1-2 of Method 1, nitrogen gas may be introduced for 20 to 50 minutes under 40 to 55° C. to replace the inside of the reactor with nitrogen gas.

As a preferred embodiment of the present invention, the temperature of the steam in steps 1-3 of method 1 may be 50 ~ 80 ℃.

As a preferred embodiment of the present invention, the amount of steam input in step 1-3 may be introduced in a molar ratio of 3.5 to 4.5 with respect to 1 mole of lithium hexafluorophosphate in step 1-1. In this case, the molar ratio of the steam means the molar ratio based on the water contained in the steam.

As a preferred embodiment of the present invention, the yield of the crystals of the lithium difluorophosphate synthesized in step 1 may be 85 to 99.9%.

As a preferred embodiment of the present invention, the second step is step 2-1 of performing a purification process by introducing and stirring lithium difluorophosphate crystals and a purification solvent into a reactor; Step 2-2 of first vacuum-concentrating the purified reactant; 2-3 step of second vacuum concentration of the first vacuum concentrate; and 2-4 steps of obtaining recrystallized crystals of a lithium difluorophosphate salt by cooling the secondary vacuum concentrate after performing a drying process;

As a preferred embodiment of the present invention, the reactor of 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, the purification solvent in step 2-1 may be used in an amount of 400 to 500 parts by weight based on 100 parts by weight of the lithium difluorophosphate crystal.

As a preferred embodiment of the present invention, the purification solvent of step 2-1 may include an aqueous alcohol solution having 2 to 4 carbon atoms and an alkyl acetate.

As a preferred embodiment of the present invention, the purification solvent of step 2-1 may include the alcohol aqueous solution and the 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 performed under a nitrogen atmosphere and 23° C. to 30° C., and the first vacuum concentration in step 2-2 is 40° C. to 45° C. and 25 to 30 It is carried out under a torr pressure, and the second vacuum concentration of steps 2-3 may be performed at 40° C. to 45° C. and a pressure of 2 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 2 torr or less and 70° C. 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 to 95%.

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

[Equation 1]

3.8% ≤ (B-A)/Ax100% ≤ 10%

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 difluorophosphate lithium salt complex in step 2.

As a preferred embodiment of the present invention, a third step of drying the recrystallized two-step recrystallized lithium difluorophosphate crystal; may further include.

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

As a preferred embodiment of the present invention, the crystals of the lithium difluorophosphate salt of the present invention have an average particle diameter of D ₁₀ of 2.500 ~ 6.000㎛, D ₅₀ of 21.000 ~ 26.000㎛, and D ₉₀ may satisfy 67.500 ~ 88.000㎛ .

As a preferred embodiment of the present invention, in the crystal of the lithium difluorophosphate salt of the present invention, the apparent density and tap density of the crystal may satisfy Equation 2 below.

[Equation 2]

0.580 ≤ (apparent density)/(tap density) ≤ 0.610

In Equation 2, the apparent density is the apparent density (g/cm ³ ) of the crystals of the lithium difluorophosphate salt, and the tap density is the tap density (g/cm ³ ) of the crystals of the lithium difluorophosphate salt.

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

The method for preparing lithium difluorophosphate salt crystals of the present invention is a solvent-free synthesis method, which can provide high-purity lithium difluorophosphate salt crystals in a high yield, and the prepared lithium difluorophosphate salt crystals can be used as a non-toxic compound for secondary batteries. It is possible to provide a non-aqueous electrolyte solution for a secondary battery having excellent stability by introducing it as an electrolyte of an aqueous electrolyte solution. In addition, when the crystals of the lithium difluorophosphate salt of the present invention are prepared, when purified and recrystallized using a specific purification solvent in the purification process, the crystals have particle size and density characteristics within a specific range, and thus recrystallized lithium difluorophosphate salt The crystal has excellent solubility in the secondary battery electrolyte.

1 is a graph of the measurement result of the crystal particle distribution of lithum difluorophosphate salt of Example 1. FIG.

Hereinafter, a method for preparing the crystals of the lithium difluorophosphate salt of the present invention with high purity will be described in more detail.

The crystals of the lithium difluorophosphate salt of the present invention can be prepared in the absence of a solvent.

Specifically, the first step of synthesizing a _{lithium difluorophosphate crystal (LiPO 2} F ₂ ) by reacting with lithium hexafluorophosphate (LiPF ₆ ), chloride, a silicon-based compound, and water in the absence of a solvent; and a second step of purifying and recrystallizing the crystals of the lithium difluorophosphate salt.

The first step is a process of synthesizing semi-finished, unrefined lithium difluorophosphate crystals, step 1-1 of preparing a mixed pulverized product by pulverizing and mixing lithium hexafluorophosphate, chloride and a silicon-based compound; 1-2 steps of introducing the mixed pulverized material into the reactor and then venting nitrogen gas through the reactor to replace the air inside the reactor with nitrogen gas; And after performing the reaction while introducing and bubbling the vapor (water in gaseous form) in the reactor to the reactor, and then filtration to obtain a reaction product; Steps 1-3; may be performed.

In step 1-1 above, Lithium hexafluorophosphate, chloride and silicon-based compound are 1:2.8 to 4.5: 0.2 to 1.0 molar ratio, preferably 1:3.0 to 4.0: 0.4 to 0.8 molar ratio, more preferably 1:3.4 to 3.8: 0.5 to It can be pulverized and mixed in a molar ratio of 0.7. At this time, if the molar ratio of chloride is less than 2.8 molar ratio, there may be a problem in that the yield is greatly reduced, and if the molar ratio of chloride exceeds 4.5 molar ratio, there may be a problem of not only an increase in by-products but also a decrease in price economics, and the final product, purified difluoro There may be a problem in that the average particle size of the lithium lyophosphate crystals increases. And, if the amount of the silicon-based compound used is less than 0.2 molar ratio, the particle distribution of the purified lithium difluorophosphate salt crystal is formed widely, and the D ₉₀ value is too large, so there is a problem that the crystal is not homogeneous and the yield is reduced. And, if the molar ratio exceeds 1.0, there may be a problem in that the purity of the purified lithium difluorophosphate crystals is reduced, while there is no increase in yield.

Examples of the chloride include alkali metal salts such as lithium chloride, sodium chloride, potassium chloride and cesium chloride, magnesium chloride, calcium chloride, strontium chloride, barium chloride, aluminum chloride, ammonium chloride, silicon tetrachloride, iron(II) chloride, iron(III) chloride, chloride Nickel, titanium tetrachloride, chromium (III) chloride, manganese chloride, and copper chloride may be used alone or two or more selected from the group consisting of, preferably lithium chloride, sodium chloride, potassium chloride, cesium chloride, magnesium chloride, calcium chloride, strontium chloride, chloride A single type or two or more types selected from barium and aluminum chloride can be used, and lithium chloride is more preferably used because it does not contain a cation as an impurity.

In addition, the silicone-based compound may include a silicone-based compound represented by Formula 1 below.

[Formula 1]

In Formula 1, R _{1 To} R ₃ Each is independent, C _{1 To} C ₅ A straight-chain alkyl group, C _{3 To} C ₅ A pulverized alkyl group, C _{6 To} C ₈ A cycloalkyl group, C _{1 To} C _{A C 1} ~ C _{5 linear alkyl group containing a 10} alkoxy group, a halide group, a C ₃ ~ C ₅ pulverized alkyl group containing a halide group, an aryl group or an aryl group containing a halide group, preferably is a C ₁ to C ₅ straight-chain alkyl group, C ₃ to C ₅ pulverized alkyl group, C ₁ to C ₅ alkoxy group, C ₁ to C ₃ straight-chain alkyl group including a halide group, C _{3 including a halide group} ~ C ₅ includes a phenyl group including a pulverized alkyl group, a phenyl group, a benzyl group or a halide group, more preferably a C ₁ ~ C ₃ straight-chain alkyl group, C ₃ ~ C ₅ A pulverized alkyl group or C ₁ ~ C The alkoxy group of _{3 is included.}

In Formula 1, each of R ₄ to R ₇ is independent, and a hydrogen atom, a C ₁ to C ₅ linear alkyl group, a C ₃ to C ₅ pulverized alkyl group, a C ₁ to C ₁₀ alkoxy group or an aryl group and preferably a hydrogen atom, a C ₁ to C ₅ straight-chain alkyl group, a C ₃ to C ₅ pulverized alkyl group, a phenyl group or a benzyl group, more preferably a C ₁ to C ₃ straight-chain alkyl group or C ₃ ~ C ₅ may include a pulverized alkyl group.

And, X in Formula 1 is an integer of 0 to 10, preferably an integer of 0 to 5, more preferably an integer of 1 to 3.

Next, in steps 1-2, after the recovered mixed pulverized material is put into the reactor, nitrogen gas is introduced into the reactor at 40 to 55° C. for 20 to 50 minutes, preferably at 45 to 52° C. for 20 to 50 minutes. It is a process in which the air inside the reactor is replaced with nitrogen gas by venting for a minute.

Next, in steps 1-3, the temperature of the steam may be supplied to the reactor at 50 to 80°C, preferably at 65°C to 80°C, more preferably at 65 to 80°C. At this time, if the temperature of the steam is less than 50 ℃, the yield and purity of the reaction product may fall, and if it exceeds 80 ℃, the temperature in the reactor is too high, the reaction proceeds rapidly, and there may be a problem in stability.

And, the steam of step 1-3 can be supplied in a molar ratio of 3.5 to 5.0, preferably in a molar ratio of 3.8 to 5.0, more preferably in a molar ratio of 4.2 to 5.0, with respect to 1 mole of lithium hexafluorophosphate in step 1-1. have. At this time, if the steam supply amount is less than 3.5 molar ratio, there may be a problem in that the yield is lowered, and if it exceeds 5.0 molar ratio, the hydrolysis reaction proceeds and the monofluorophosphate is further hydrolyzed, so there is a problem that the phosphate is by-produced. can In this case, the molar ratio of the steam is expressed based on the amount of water contained in the steam.

In addition, in steps 1-3, lithium hexafluorophosphate, chloride, silicon-based compound and A lithium difluorophosphate salt, which is a reaction product obtained by reacting and synthesizing water, can be prepared.

And, filtration may be performed by a general filtration method in the art, and for a specific example, the synthesized reaction solution after the synthesis reaction may be cooled to 10° C. to 15° C., preferably by performing brine cooling After cooling, it is possible to obtain crystals of lithium difluorophosphate salt by filtration (or filtering) to separate solids and liquids from the cooled synthesized reaction solution.

The yield of the crystals of the lithium difluorophosphate salt obtained through steps 1-1 to 1-3 may be preferably 85.0% to 99.9%, more preferably 91.0% to 99.0%.

The second step is a second step of purifying and recrystallizing the crystals of the lithium difluorophosphate salt prepared in the first step;

The second step is a 2-1 step of performing a purification process by introducing and stirring lithium difluorophosphate salt crystals and a purification solvent into a reactor; Step 2-2 of first vacuum-concentrating the purified reactant; 2-3 step of second vacuum concentration of the first vacuum concentrate; and 2-4 steps of obtaining recrystallized crystals of a lithium difluorophosphate salt by cooling the secondary vacuum concentrate after drying.

In the second stage of the reactor, a reactor jacket, a vacuum pump, a condenser, a scrubber, and/or a receiver may be installed.

The purification solvent of step 2-1 is used by mixing an aqueous alcohol solution and an alkyl acetate, and by using a mixture of alkyl acetate, the amount of the purified solvent is reduced compared to when the aqueous alcohol solution is used alone, and recrystallized by adjusting the amount of alkyl acetate used. By controlling the particle size of the crystals of the lithium difluorophosphate, it is possible to obtain homogeneous crystals of the crystals of the lithium difluorophosphate in a specific size range in high yield.

And, 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, more preferably in a weight ratio of 1: 1.8 to 2.3. At this time, if the amount of alkylacetate used in the purification solvent is less than 1.5 weight ratio, the average crystal size (D ₅₀ ) of the recrystallized lithium difluorophosphate salt becomes too small, so it may not be possible to obtain crystals in the appropriate size range to be prepared in high yield. , the tap density is reduced, and when the amount of alkylacetate used exceeds 2.5 weight ratio, there may be problems in that the purity of the obtained lithium difluorophosphate salt is rather low and the tap density is too high, so it is preferable to use it within the above range.

The amount of the purification solvent used is 400 to 500 parts by weight, preferably 420 to 500 parts by weight, more preferably 440 to 480 parts by weight, based on 100 parts by weight of the lithium difluorophosphate salt crystal. In this case, if the amount of the purification solvent used is less than 400 parts by weight, there may be a problem in that the solubility is lowered and the tablet is deteriorated, and if it is used in excess of 500 parts by weight, it is uneconomical.

As the aqueous alcohol solution in step 2-1, an aqueous alcohol solution having 2 to 4 carbon atoms, preferably an aqueous alcohol solution having 2 to 3 carbon atoms, and more preferably an aqueous ethanol solution having a concentration of 99.5% to 99.8% may be used.

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 include at least one selected from methyl acetate and ethyl acetate, More preferably, ethyl acetate may be included.

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

Next, step 2-2 is a process of first vacuum-concentrating the reactants subjected to the purification process in step 2-1. The first vacuum concentration is after increasing the reactor internal temperature to 40° C. to 45° C., 25 The vacuum concentration can be carried out while maintaining the pressure of ~ 30 torr, and the alcohol vapor distilled from the reactor is condensed in the condenser and the liquid is not collected in the receiver. At this time, when the primary vacuum concentration is performed at less than 40 ℃, there may be a problem that the solvent is not distilled and the productivity is lowered. can occur And, if the primary vacuum concentration pressure is less than 25 torr, there may be a problem that the solvent is passed over to the pump, and if it exceeds 30 torr, there may be a problem that the time increases and productivity is lowered.

Next, step 2-3 is a process of secondarily vacuum-concentrating the primary vacuum concentrate, and is preferably carried out at 40° C. to 45° C. and under a pressure of 2 torr or less, preferably 40° C. to 45° C. and 1 torr. It is recommended to carry out under the following pressure. In step 2-3, when an appropriate amount of vacuum concentration is generated, the vacuum is broken with nitrogen to terminate the second vacuum concentration process. At this time, when the secondary vacuum concentration pressure exceeds 2 torr, there may be a problem in that the concentration time increases and productivity decreases.

Next, the secondary vacuum concentrate is dried in steps 2-4, wherein the drying can be performed using a general drying method used in the art, and a preferred embodiment, for example, a rotary evaporator (rotary evaporator) It is good to perform rotary drying for about 10 to 14 hours under a vacuum atmosphere of 2 torr or less and 70°C to 90°C, preferably under a vacuum atmosphere of 1 torr or less and 80°C to 90°C.

When the drying process is completed, the dried product may be cooled to 25° C. or less to finally obtain recrystallized crystals of the lithium difluorophosphate salt.

The recrystallized lithium difluorophosphate crystals of the present invention prepared by performing the first and second steps in this way have a yield of 80% or more, preferably 80 to 95%, more preferably 85.0 to 95.0% in yield. can be

In addition, the recrystallized crystals of the lithium difluorophosphate salt may have a purity satisfying Equation 1 below.

[Equation 1]

3.8% ≤ (B-A)/AХ100% ≤ 10%, preferably 4.4% ≤ (B-A)/AХ100% ≤ 8.8%, more preferably 4.8% ≤ (B-A)/AХ100% ≤ 8.0%

In Equation 1, A is the purity (%) of the crystals of the lithium difluorophosphate synthesized in the first step, and B is the purity (%) of the recrystallized difluorophosphate lithium salt complex in the second step.

In addition, the crystals of the lithium difluorophosphate salt of the present invention may _{satisfy the average particle diameter D 10} of 2.500 ~ 6.000 μm, D ₅₀ of 21.000 ~ 26.000 μm and D ₉₀ of 67.500 ~ 88.000 μm when the particle distribution is measured. may satisfy 2.800 ~ 6.000㎛ _{D 10 , 21.000 ~ 25.900㎛ D 50} , and 68.000 ~ 88.000㎛ D ₉₀ .

In addition, in the crystal of the lithium difluorophosphate salt of the present invention, the apparent density and tap density of the crystal may satisfy Equation 2 below.

[Equation 2]

0.5800 ≤ (apparent density)/(tap density) ≤ 0.6100, preferably 0.5820 ≤ (apparent density)/(tap density) ≤ 0.6050

In Equation 2, the apparent density is the apparent density (g/cm ³ ) of the crystals of the lithium difluorophosphate salt, and the tap density is the tap density (g/cm ³ ) of the crystals of the lithium difluorophosphate salt.

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

Hereinafter, the present invention will be described in more detail through examples. However, it should not be construed as limiting the scope of the present invention by the following examples, and the following examples are provided to aid understanding of the present invention.

[Example]

Example 1: Preparation of recrystallized lithium difluorophosphate salt crystals

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

In a reactor of perfluoroalkoxy alkane (PFA) material at a dew point temperature of less than 50° C., lithium hexafluorophosphate, lithium chloride as a chloride, and a silicon-based compound represented by the following Chemical Formula 1-1 were mixed 1: 3.43: After grinding and mixing at a weight ratio of 0.52, the inside of the reactor was heated to 50° C., and then nitrogen gas was vented for 30 minutes to replace the inside of the reactor with a nitrogen atmosphere, and then the temperature was raised to 50° C. for 30 minutes.

Next, while stirring, 28 g of steam at 70° C. was introduced into the reactor and bubbling, and the reaction was performed at 50° C. for 9 hours, and then the inside of the reactor was cooled to 12 to 13° C. At this time, the steam was introduced into the reactor by bubbling nitrogen gas in hot water of 70 ℃.

Next, the cooled synthesized reaction solution was filtered to obtain crystals of a lithium difluorophosphate salt (yield 94.7%, purity 95.50%).

(2) Preparation of recrystallized lithium difluorophosphate crystals (Step 2)

100 parts by weight of the lithium difluorophosphate crystal and 478 parts by weight of a purified solvent are added and stirred in a reactor in which a reactor jacket, a vacuum pump, a condenser, a scrubber and/or a receiver are installed, and the reactor temperature is adjusted to 24° C. to 25 ℃ was maintained, and lithium fluoride as a by-product was separated by defiltration.

At this time, the purification solvent contains an aqueous solution of ethanol and ethyl acetate having a concentration of 99.5% to 99.8% in a weight ratio of 1:2.1.

Next, hot water was put into the reactor jacket, and the vacuum pump was operated while maintaining the reactor internal temperature of 43 to 44° C., and the primary vacuum concentration was performed while maintaining the 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 and no liquid was collected in the receiver.

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

Next, using a rotary evaporator, difluorophosphoric acid finally recrystallized by distilling with a pump having a vacuum degree of 1 torr and completely dried under 85° C. for 12 hours, and then cooled to 25° C. A lithium salt crystal was obtained (yield 91.8%, purity 99.95%).

Examples 2 to 7 and Comparative Examples 1 to 6

Recrystallized lithium difluorophosphate crystals were prepared in the same manner as in Example 1, but Examples 2 to 7 and Comparative Examples 1 to 6 were prepared by varying the amount of the component as shown in Table 1 below. carried out. In addition, _{the purity increase rate of the crystallized LiPO 2} F ₂ synthesis (step 1) and the recrystallized LiPO ₂ F ₂ crystal (step 2) was measured based on Equation 1 below and shown in Table 2 below.

division Crystallized LiPO ₂ F ₂ Synthesis (Step 1) Recrystallized LiPO ₂ F ₂ Crystalline Preparation
(Step 2 - Purification process) LiPF ₆
(mole) chloride
(mole) silane
compound
(mole) water
(vapor pressure fraction, mole) _{LiPO 2} F _{2 in} step 1
(parts by weight) refine
menstruum
(parts by weight) Aqueous alcohol solution:
alkyl acetate
(weight ratio) Example 1 One 3.42 0.52 3.93 100 478 1: 2.1 Example 2 One 3.42 0.40 3.93 100 478 1: 2.1 Example 3 One 3.42 0.80 3.93 100 478 1: 2.1 Example 4 One 3.42 0.52 4.75 100 478 1: 2.1 Example 5 One 3.42 0.52 3.65 100 478 1: 2.1 Example 6 One 3.42 0.52 3.93 100 420 1: 2.1 Example 7 One 3.42 0.52 3.93 100 478 1: 1.8 Example 8 One 3.42 0.52 3.93 100 478 1:2.3 Comparative Example 1 One 4.22 - 3.93 100 604 1: 0 Comparative Example 2 One 5.60 - 3.93 100 604 1: 0 Comparative Example 3 One 3.42 0.18 3.93 100 478 1: 2.1 Comparative Example 4 One 3.42 1.20 3.93 100 478 1: 2.1 Comparative Example 5 One 3.42 0.52 5.10 100 478 1: 2.1 Comparative Example 6 One 3.42 0.52 3.31 100 478 1: 2.1 Comparative Example 7 One 3.42 0.52 3.93 100 540 1: 2.1 Comparative Example 8 One 3.42 0.52 3.93 100 375 1: 2.1 Comparative Example 9 One 3.42 0.52 3.93 100 478 1: 1.0 Comparative Example 10 One 3.42 0.52 3.93 100 478 1:2.8

division Step 1
Yield (%) / Purity (%) Step 2
Yield (%) / Purity (%) Purity increase rate (%) Example 1 94.7 / 95.5 91.8 / 99.94 4.65 Example 2 95.2 / 95.3 90.3 / 99.91 4.83 Example 3 92.8 / 95.0 90.2 / 99.63 4.87 Example 4 87.3 / 94.8 85.4 / 99.72 5.19 Example 5 90.4 / 95.0 87.1 / 99.85 5.10 Example 6 94.7 / 95.5 88.8 / 99.80 4.50 Example 7 94.7 / 95.5 92.3 / 99.93 4.64 Example 8 94.7 / 95.5 90.5 / 99.82 4.52 Comparative Example 1 95.5 / 95.2 93.2 / 99.90 4.94 Comparative Example 2 80.2 / 94.2 77.5 / 99.53 5.66 Comparative Example 3 95.3 / 95.2 91.3 / 99.93 4.97 Comparative Example 4 92.8 / 93.4 88.9 / 96.54 3.36 Comparative Example 5 85.0 / 94.0 82.2 / 98.23 4.50 Comparative Example 6 87.2 / 95.2 84.0 / 99.92 4.96 Comparative Example 7 94.7 / 95.5 91.8 / 99.92 4.63 Comparative Example 8 94.7 / 95.5 83.4 / 98.10 2.72 Comparative Example 9 94.7 / 95.5 92.8 / 99.91 4.62 Comparative Example 10 94.7 / 95.5 90.7 / 99.63 4.32

Looking at Tables 1 and 2, when comparing Comparative Examples 1 to 2 and Example 1 in which the silane-based compound was not used in the first step, a lithium difluorophosphate salt using a silane-based compound together with a chloride in the first step synthesizing, the yield was somewhat decreased, but the purity was rather slightly increased.

In addition, in the case of Comparative Example 3, in which the silane-based compound was used in a molar ratio of 0.18, which is less than 0.2 molar ratio, with respect to 1 mole of _{LiPF 6 in step 1, there was no increase in purity and the yield was rather decreased compared to Examples 1 and 2} . And, in the case of Comparative Example 4 in which the silane-based compound was used in a molar ratio of 1.20 in excess of 1.0 molar ratio to 1 mole of _{LiPF 6 in step 1, compared with Example 3, the purity tended to decrease.}

In addition, in the case of Comparative Example 5, in which the number of vapor pressure fractions, that is, water, which is steam, was used in excess of 5.0 molar ratio with respect to _{6 moles of LiPF in step 1, when compared with Example 4, a side reaction occurred and both yield and purity were somewhat lowered.} There was, and in the case of Comparative Example 6, in which steam was added at a molar ratio of less than 3.5, there was a problem in that the yield decreased when compared to Example 5.

And, in the case of Comparative Example 7, in which the amount of the purification solvent used in the two-step reaction exceeded 500 parts by weight, there was a problem in that there was no increase in yield due to excessive use of the purification solvent in the two-step process, compared to Example 1. In addition, in the case of Comparative Example 8, in which the amount of the purification solvent used was less than 400 parts by weight, there was a problem in that the yield in the second step was too significantly lowered to 83.4% than the yield in the first step of 94.7%, and there was a problem in that the purity was lowered relatively too much. .

In addition, in the case of Comparative Example 9 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, compared with Example 7 (1.8 weight ratio), there was no significant difference. And, in the case of Comparative Example 10 in which the purifying solvent was used in a 2.8 weight ratio exceeding 2.5 weight ratio with respect to the alcohol aqueous solution as the purification solvent, compared with Example 8 (2.3 weight ratio), recrystallized lithium difluorophosphate There was a problem in that the purity of the salt crystal was rather lowered.

Example 9 and Comparative Examples 11 to 15

Recrystallized lithium difluorophosphate crystals were prepared in the same manner as in Example 1, but Example 9 and Comparative Examples 11 to 15 were performed by changing the production conditions as shown in Table 3 below. At this time, the vacuum compression conditions of the two steps were different. And, _{the purity increase rate of the crystallized LiPO 2} F ₂ synthesis (step 1) and the recrystallized LiPO ₂ F ₂ crystal (step 2) were measured based on Equation 1, and are shown in Table 4 below.

division
(parts by weight) Recrystallized LiPO ₂ F ₂ Crystals Preparation (Step 2) 1st vacuum concentration
pressure Temperature at the time of primary vacuum concentration 2nd vacuum concentration
pressure transference number(%)/
water(%) Example 1 28 torr 43 ~ 44℃ 1 torr 93%/99.9% Example 9 28 torr 40 ~ 41℃ 1 torr 92%/99.9% Comparative Example 11 28 torr 35 ~ 36℃ 1 torr 92%/96.9% Comparative Example 12 28 torr 48 ~ 49℃ 1 torr 92%/99.8% Comparative Example 13 35 torr 43 ~ 44℃ 1 torr 88%/99.8% Comparative Example 14 1 torr 43 ~ 44℃ 1 torr 83%/97.0% Comparative Example 15 21 torr 43 ~ 44℃ 1 torr 85%/97.1%

division Step 1
Yield (%) / Purity (%) Step 2
Yield (%) / Purity (%) Purity increase rate (%) Example 1 94.7 / 95.5 91.8 / 99.94 4.61 Example 9 94.7 / 95.5 91.0 / 99.97 4.68 Comparative Example 11 94.7 / 95.5 89.7 / 96.29 0.83 Comparative Example 12 94.7 / 95.5 91.9 / 99.90 4.61 Comparative Example 13 94.7 / 95.5 85.4 / 99.77 4.47 Comparative Example 14 94.7 / 95.5 84.2 / 99.81 4.51 Comparative Example 15 94.7 / 95.5 85.1 / 97.04 1.62

Looking at the yield/purity of steps 1 and 2 in Table 2, in the case of Examples 1 and 10, the recrystallized LiPO ₂ F ₂ crystals showed a high yield of 85% or more and a high purity increase rate of 4.5% or more.

In addition, in the case of Comparative Example 11 in which the primary vacuum concentration temperature was less than 40 °C, compared with Example 10, the secondary yield was significantly lower than the primary yield, and the primary vacuum concentration temperature exceeded 45 °C. In the case of Comparative Example 12, there was no change in yield, but there was a problem in that the purity was rather decreased.

In addition, in the case of Comparative Example 13 in which the first vacuum concentration was performed under a pressure exceeding 30 torr during the first vacuum concentration of the two-step reaction, the recrystallized LiPO _{2 compared to the crystallized LiPO 2} F _{2 synthesized in the first step} The yield of F ₂ crystals was low, and there was a problem that the purity increase rate was also low, and in the case of Comparative Example 15, in which the primary vacuum concentration was performed under a pressure of less than 25 torr, there was a problem that the improvement of the purity increase rate was low compared to that of Example 1. .

And, in the case of Comparative Example 14, in which the first and second vacuum concentration was performed under the same pressure (1 torr) and temperature (43 to 44° C.), and not substantially multi-stage vacuum concentration, but a single step vacuum concentration, the yield was There was a problem with a significant decrease.

Experimental Example 1: Particle Characterization of Recrystallized Lithium Difluorophosphate Crystals

The particle distribution, apparent density, and tap density of the recrystallized lithium difluorophosphate crystals prepared in Examples 1, 7 to 8 and Comparative Examples 9 to 10 were measured, and the results are shown in Table 5 and Tables below. 6 is shown. And, the particle distribution measurement graph of Example 1 is shown in FIG. 1 .

division Crystal particle distribution diagram D ₁₀ (μm) D ₅₀ (μm) D ₉₀ (μm) Example 1 2.875 25.13 85.70 Example 2 5.530 21.11 68.68 Example 3 4.274 25.89 87.52 Comparative Example 1 2.452 31.07 95.24 Comparative Example 3 2.652 29.85 92.31 Comparative Example 4 7.213 26.02 80.88

division Apparent density
(g/cm ³ ) tap density
(g/cm ³ ) Apparent Density/Tap Density Example 1 0.5288 0.8937 0.5917 Example 2 0.5276 0.8735 0.6040 Example 3 0.5297 0.9095 0.5824 Comparative Example 1 0.5134 0.8142 0.6306 Comparative Example 3 0.5251 0.8371 0.6273 Comparative Example 4 0.5302 0.9344 0.5674

Referring to Tables 5 and 6, in the case of Comparative Example 1 without using a silicone compound and Comparative Example 3 using a silicone-based compound in a 0.18 molar ratio that is less than 0.2 in the first-step reaction, the particle distribution is very wide and the crystals are homogeneous It was confirmed that the density of the recrystallized crystals was generally low.

On the other hand, in the case of Examples 1 to 3 _{, it can be seen that the difference between D 10} and D ₉₀ is smaller than Comparative Examples 1 and 2, and it can be confirmed that crystals of a homogeneous size can be obtained through this.

Through the above examples, it was confirmed that high-purity lithium difluorophosphate crystals could be prepared in high yield by using the method presented by the present invention. The crystals of the lithium difluorophosphate salt of the present invention prepared in this way can be used as a composition of a chloroethylene polymer stabilizer, a catalyst for reaction lubricating oil, a toothbrush sterilizer and a wood preservative, etc. 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 electrolyte.

Claims (14)

delete delete delete delete delete delete delete delete delete delete delete When the particle distribution is measured, lithium difluorophosphate with excellent solubility, characterized in that the _{average particle diameter of the D 10} value is 2.500 ~ 6.000 μm, the D ₅₀ value is 21.000 ~ 26.000 μm, and the D _{90 value is 67.500 ~ 88.000 μm} salt crystals.
A non-aqueous electrolyte for a secondary battery comprising the lithium difluorophosphate salt crystal of claim 12 as an electrolyte.
[13] The lithium difluorophosphate crystal according to claim 12, wherein the lithium difluorophosphate crystal has an apparent density and a tap density satisfying Equation 2 below;
[Equation 2]
0.5800 ≤ (apparent density)/(tap density) ≤ 0.6100
In Equation 2, the apparent density is the apparent density (g/cm ³ ) of the crystals of the lithium difluorophosphate salt, and the tap density is the tap density (g/cm ³ ) of the crystals of the lithium difluorophosphate salt.

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