KR102596526B1 - Manufactuiring method for crystallization of lithium difluorophosphate and Crystallization of lithium difluorophosphate - Google Patents

Abstract

The present invention relates to a method for producing lithium difluorophosphate salt crystals. More specifically, lithium hexafluorophosphate is used as a starting material and reacted with a specific compound to produce lithium difluorophosphate salt crystals. , It relates to a method of producing highly economical lithium difluorophosphate salt crystals that can produce high purity lithium difluorophosphate salt crystals in excellent yield.

Description

Method for manufacturing lithium difluorophosphate salt crystals and lithium difluorophosphate salt crystals produced by the method {Manufactuiring method for crystallization of lithium difluorophosphate and Crystallization of lithium difluorophosphate}

The present invention relates to a method for efficiently producing lithium difluorophosphate salt crystals with high purity and to lithium difluorophosphate salt crystals prepared by this method.

In recent years, the basic research and application development of lithium-ion batteries has become one of the major technologies of interest in the new energy field, and all developed countries in the world are developing and researching it as a breakthrough for the next generation of emerging industries.

Anode materials, cathode materials, electrolyte materials and _separator materials are the four main materials of lithium-ion batteries, and common electrolyte materials are mainly LiPF ₆ , LiBF _{4 , LiClO 4} , LiAsF ₆ , LiCF ₃ SO ₃ , LiN, (CF ₃ SO ₂ ) ₂ , etc., this electrolyte is dissolved and a non-aqueous electrolyte solution is mixed in a carbonate-based organic solvent, and LiPF ₆ is currently the most widely used electrolyte.

Lithium-ion batteries using non-aqueous electrolyte solutions differ significantly in terms of battery characteristics because the reactivity of the electrode surface changes depending on the composition of the non-aqueous electrolyte solution. Specifically, the decomposition and side reactions of the electrolyte affect the durability of lithium-ion batteries (e.g., cycling and high temperature storage, etc.), and attempts are made to suppress the decomposition of the electrolyte on the active anode or cathode surface by adding various additives to the electrolyte. There was.

Recently, research has shown that adding lithium difluorophosphate to the electrolyte can improve battery performance, including low-temperature characteristics, cycle characteristics, and storage characteristics of lithium-ion secondary batteries. In fact, lithium-ion secondary batteries using lithium difluorophosphate Manufactured and sold. For example, a technology has been disclosed using at least one non-aqueous electrolyte solution selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate (LiPO ₂ F ₂ ) as an additive, in which the The reaction between the additive and lithium forms a coating film at the interface between the anode and the cathode, suppressing decomposition of the electrolyte upon contact with the anode active material and the cathode active material, thus suppressing self-discharge and improving memory characteristics after charging. It is disclosed to be effective. Additionally, Japanese Patent No. 3439085 discloses improving high-temperature cycle characteristics by adding lithium difluorophosphate to an electrolyte solution and forming a film at the electrolyte interface.

In this way, the development and production of lithium-ion secondary batteries with the addition of lithium difluorophosphate salt to the electrolyte are increasing, and the demand for lithium difluorophosphate is increasing accordingly, and lithium difluorophosphate salt is used efficiently. Various manufacturing methods are being attempted.

Japanese Patent Publication No. 2002-501034 (publication date 2002.01.15.) Japanese registered patent number 3439085 (announcement date 2003.08.25.)

Hydrolysis in the system LiPF6-propylene carbonate-dimethyl carbonate-H2O(Journal of Fluorine Chemistry 126 (2005)27-31)

The problem that the present invention aims to solve is to present a new method for producing lithium difluorophosphate salt crystals efficiently, with high yield and high purity, and to use the lithium difluorophosphate salt crystals thus prepared as a non-aqueous electrolyte for lithium ion secondary batteries. We would like to provide

The method for producing lithium difluorophosphate salt crystals of the present invention to solve the above problem is to react lithium hexafluorophosphate (LiPF ₆ ), lithium metaborate, and crown ether compound in an organic solvent to produce lithium difluorophosphate ( LiPO ₂ F ₂ ) A process for synthesizing salt crystals is performed.

As a preferred embodiment of the present invention, the production method of the present invention may further perform purification and recrystallization processes on the synthesized lithium difluorophosphate salt crystals.

As a preferred embodiment of the present invention, in the production method of the present invention, the process of synthesizing the lithium difluorophosphate salt crystal includes lithium hexafluorophosphate (LiPF ₆ ), lithium metaborate, and an organic crown ether compound. Step 1-1 of preparing a mixed solution by adding a solvent and stirring; Steps 1-2 of introducing the mixed solution into the reactor, converting the inside of the reactor to an inert atmosphere, and then performing the reaction; And after completion of the reaction, steps 1-3 of obtaining lithium difluorophosphate salt crystals by performing filtration, washing, and drying.

As a preferred embodiment of the present invention, in the production method of the present invention, the crown ether compound is a substituted or unsubstituted crown ether compound, and is 1,4,7,10-tetraoxacyclododecane (1,4, 7,10-Tetraoxacyclododecane), 1,4,7,10,13-pentaoxacyclopentadecane (1,4,7,10,13-pentaoxacyclopentadecane), 1,4,7,10,13,16-hexa One type selected from oxacyclooctadecane (1,4,7,10,13,16-hexaoxacyclooctadecane) and 4,13-diaza-18-crown-6-ether (diaza-18-crown-6-ether) It may include more.

As a preferred embodiment of the present invention, in the production method of the present invention, the organic solvent is a carbonate-based solvent containing at least one selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinyl carbonate, and methyl propionate. can be used.

As a preferred embodiment of the present invention, in the production method of the present invention, the organic solvent may be a mixed solvent of the carbonate-based solvent and acetone.

As a preferred embodiment of the present invention, in the production method of the present invention, the amount of lithium hexafluorophosphate, lithium metaborate, and crown ether compound added to the organic solvent in step 1-1 is lithium hexafluorophosphate, lithium metaborate, and crown ether compound. Lithium and crown ether compounds can be added at a molar ratio of 1:0.5 to 1.0:0.3 to 0.8.

As a preferred embodiment of the present invention, the mixed solution in step 1-1 may further include a reaction catalyst.

As a preferred embodiment of the present invention, in the production method of the present invention, the purification and recrystallization process is performed by adding and stirring one or more solvents selected from lithium difluorophosphate salt crystals and ester solvents. Perform step 2-1; Step 2-2 of performing filtration to obtain a filtrate; And steps 2-3 of heat treating and cooling the filtrate to obtain recrystallized lithium difluorophosphate salt.

As a preferred embodiment of the present invention, in the production method of the present invention, the ester-based solvent is dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, trimethyl phosphate, trimethyl phosphate. It may include one or more selected from ethyl ester, trimethyl phosphite, and triethyl methyl phosphite.

As a preferred embodiment of the present invention, lithium difluorophosphate salt crystals obtained by recrystallization may have a yield of 82.0 to 93.0% and a purity of 94.0 to 99.8%.

Another object of the present invention is to provide lithium difluorophosphate salt crystals prepared by the above-described production method.

Another object of the present invention is to provide the lithium difluorophosphate salt crystal prepared by the above method as an electrolyte for a non-aqueous electrolyte solution for a secondary battery.

Another object of the present invention is to provide a non-aqueous electrolyte solution for secondary batteries containing the lithium difluorophosphate salt crystals as an electrolyte.

The method for producing lithium difluorophosphate salt crystals of the present invention is capable of producing high purity lithium difluorophosphate salt crystals with high productivity without a special advanced purification process, and the produced lithium difluorophosphate salt crystals can be produced in 2 steps. By introducing it as an electrolyte for a non-aqueous electrolyte solution for secondary batteries, it is possible to provide a non-aqueous electrolyte solution for secondary batteries with excellent stability.

Hereinafter, the method for producing the lithium difluorophosphate salt crystal of the present invention will be described in detail.

The lithium difluorophosphate salt crystal of the present invention is synthesized by reacting lithium hexafluorophosphate (LiPF ₆ ), lithium metaborate and a crown ether compound in an organic solvent to synthesize lithium difluorophosphate (LiPO ₂ F ₂ ) salt crystal. It is manufactured by performing the following process, and more specifically, step 1-1 of preparing a mixed solution by adding and stirring lithium hexafluorophosphate (LiPF ₆ ), lithium metaborate, and crown ether compound to an organic solvent; Step 1-2 of adding the mixed solution to the reactor, converting the inside of the reactor to an inert atmosphere, raising the temperature, and performing the reaction while stirring; And after completion of the reaction, steps 1-3 of performing filtration, washing and drying to obtain lithium difluorophosphate salt crystals.

The amount of lithium hexafluorophosphate, lithium metaborate and crown ether compound added to the organic solvent in step 1-1 is lithium hexafluorophosphate, lithium metaborate and crown ether compound at a molar ratio of 1:0.5 to 1.0:0.3 to 0.8. Preferably, the molar ratio is 1:0.6 to 1.0:0.4 to 0.8, and more preferably, the molar ratio is 1:0.7 to 1.0:0.5 to 0.8 in terms of minimizing by-products due to side reactions and the yield of lithium difluorophosphate salt crystals. Good from the side.

In addition, the crown ether compound uses a substituted or unsubstituted crown ether compound, and the crown ether compound is 1,4,7,10-Tetraoxacyclododecane (1,4,7,10-Tetraoxacyclododecane), 1 ,4,7,10,13-pentaoxacyclopentadecane (1,4,7,10,13-pentaoxacyclopentadecane), 1,4,7,10,13,16-hexaoxacyclooctadecane (1, 4,7,10,13,16-hexaoxacyclooctadecane) and 4,13-diaza-18-crown-6-ether (diaza-18-crown-6-ether), preferably It may include at least one selected from 1,4,7,10-tetraoxacyclododecane and 1,4,7,10,13-pentaoxacyclopentadecane, more preferably 1,4 , 7,10-tetraoxacyclododecane can be used.

And, when the crown ether compound has a substituent, the substituent is one C ₁ to C ₃ straight-chain hydroxyalkyl group (-ROH, where R is a C ₁ to C ₃ straight-chain alkylene group) as a substituent. It may contain two or more.

In addition, the organic solvent may be a carbonate-based solvent, and the carbonate solvent may include one or more selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinyl carbonate, and methyl propionate, preferably It may include one or more types selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, and more preferably, it may include one or more types selected from dimethyl carbonate and diethyl carbonate. In terms of improving the solubility and reactivity of the reactant, it is advantageous to use a mixture of acetone and the carbonate-based solvent as the organic solvent. Preferably, the carbonate-based solvent and acetone are mixed in a weight ratio of 1:0.05 to 0.20, more preferably. It is recommended to mix and use at a weight ratio of 1:0.08 to 0.15.

In addition, the mixed solution of step 1-1 may further include a reaction catalyst, and the reaction catalyst may be one that promotes the reaction between LiPF ₆ and lithium metaborate while promoting ring opening of the crown ether compound, and is preferably used. Typically, one or more types selected from SeO ₂ F ₂ and SeO ₂ Cl ₂ may be used, and more preferably, SeO ₂ F ₂ may be used in a small amount. For a preferred example, the reaction catalyst may be added at a molar ratio of 0.001 to 0.020 per mole of lithium hexafluorophosphate.

Additionally, the inert atmosphere in steps 1 and 2 can be formed by adding an inert gas such as nitrogen gas or argon gas.

The reaction in steps 1-2 is performed by converting the inside of the reactor to an inert atmosphere, heating until the internal temperature of the reactor reaches 50 to 80°C, preferably 55 to 70°C, and more preferably 55 to 65°C. It can be performed for 8 to 20 hours, preferably for 10 to 16 hours, while maintaining the temperature and stirring slowly. At this time, if the reaction temperature is less than 50℃, the yield of lithium difluorophosphate salt may be low, and even if the reaction temperature exceeds 80℃, the yield no longer increases. Rather, unwanted impurities due to side reactions are generated and the synthesized difluorophosphate salt yield is low. Since the purity of the lithium fluorophosphate salt may be lowered, it is advantageous to carry out the reaction under the above temperature. And, the reaction time is an appropriate time for synthesizing lithium difluorophosphate salt with high yield and purity at the above temperature.

In steps 1-3, after completion of the reaction, filtration is performed using a membrane filter, etc. to obtain crystals, and then the filtering method can be used without limitation using a common method used in the industry.

Then, after washing the crystals obtained by filtering, drying them and evaporating the washing liquid, lithium difluorophosphate salt crystals can be obtained. At this time, solvents in which the lithium difluorophosphate salt does not dissolve can be used without limitation for washing, and drying methods can be used without limitation. However, drying must be done at a temperature of 90°C or higher to prevent discoloration of the lithium difluorophosphate salt. It is desirable to perform it in a range that does not apply.

Through this method, lithium difluorophosphate salt crystals can be obtained with a yield of 84.0 to 95.0% and a purity of 90.0 to 98.0%, preferably with a yield of 85.0 to 94.0% and a purity of 92.0 to 97.0%.

In addition, the method for producing lithium difluorophosphate salt crystals of the present invention may further perform purification and recrystallization processes to improve the purity of the previously prepared lithium difluorophosphate salt crystals.

The purification process can be performed through a general process used in the industry, but to prevent a decrease in yield and increase purity, purification is performed by adding and stirring one or more solvents selected from lithium difluorophosphate salt crystals and ester solvents. Step 2-1 of performing the process; Step 2-2 of performing filtration to obtain a filtrate; and steps 2-3 of heat-treating and cooling the filtrate to obtain recrystallized lithium difluorophosphate salt.

The purification process of step 2-1 is a process of dissolving the previously prepared lithium difluorophosphate salt crystals using a solvent in which only the lithium difluorophosphate salt crystals are dissolved and impurities are not dissolved.

It is recommended to use an ester-based solvent as the solvent, and the ester-based solvent is dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, ethylene carbonate, trimethyl phosphate, triethyl phosphate, and phosphorous acid. It may contain one or more types selected from trimethyl ester and triethylmethyl phosphite, and preferably one type selected from dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, trimethyl phosphate, and trimethyl phosphorous acid. It may include the above, and more preferably, a mixture of dimethyl carbonate and trimethyl phosphate ester in a weight ratio of 1:0.5 to 1.0 can be used.

In terms of dissolution, it is appropriate to use a solvent that is 5 to 30 times the weight ratio of the lithium difluorophosphate salt crystal, and preferably 5 to 15 times the weight ratio of the lithium difluorophosphate salt crystal.

In addition, it is appropriate to carry out the purification process at a temperature of 40 to 70°C, preferably 50 to 60°C while stirring, in terms of rapid dissolution of the lithium difluorophosphate salt crystals. If the temperature is too low, the purification process will be too long and , exceeding 70℃ is uneconomical.

In addition, step 2-2 is a process of filtering the solution in which the lithium difluorophosphate salt dissolved in step 2-1 is filtered using a membrane filter, etc. to obtain a filtrate from which impurities have been removed. At this time, filtration is performed by removing sugar. It can be performed using common filtration methods used in the industry.

And, steps 2-3 are a process of heat-treating the filtrate to distill off the ester-based solvent used for purification to obtain recrystallized white lithium difluorophosphate salt crystals. At this time, the heat treatment is performed by applying heat to a temperature exceeding the boiling point of the ester solvent used.

The yield of the lithium difluorophosphate salt crystals obtained by performing this purification process is somewhat lower than that of the lithium difluorophosphate salt crystals prepared through steps 1-1 to 1-3, but the purity can be improved, and it is preferable Preferably, recrystallized lithium difluorophosphate salt crystals can be obtained with a yield of 82.0 to 93.0% and a purity of 94.0 to 99.8%, preferably with a yield of 84.0 to 93.0% and a purity of 95.0 to 99.5%.

The lithium difluorophosphate salt crystal of the present invention prepared by the method described above can be used for various purposes, for example, it can be used as an electrolyte in a non-aqueous electrolyte solution for secondary batteries.

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

[Example]

Example 1: Preparation of lithium difluorophosphate salt crystals

(1) Preparation of lithium difluorophosphate salt crystals (step 1)

After adding lithium hexafluorophosphate, lithium metaborate, 1,4,7,10-tetraoxacyclododecane, selenonyl fluoride (reaction catalyst), and dimethyl carbonate (organic solvent) into the dried reactor. , It was sealed, and then argon gas was introduced. At this time, the molar ratio of lithium hexafluorophosphate, lithium metaborate, and 1,4,7,10-tetraoxacyclododecane was 1:0.85:0.60, and the molar ratio of reaction catalyst was 1 mole of lithium hexafluorophosphate. The molar ratio was 0.005. And, the organic solvent used was a mixed solvent in which dimethyl carbonate and acetone were mixed at a weight ratio of 1:0.1.

Then, the temperature was raised to 57-59°C under an argon gas atmosphere, and the reaction was performed for 12 hours while maintaining this temperature and stirring slowly.

After the reaction was completed, the reactor temperature was lowered to room temperature, and then the reaction solution was filtered using a membrane filter to obtain crystals.

Then, the obtained crystals were washed with dimethyl carbonate, dried using a rotary evaporator in an atmosphere at 70°C, and then cooled to obtain lithium difluorophosphate salt crystals.

The yield of the synthesized lithium difluorophosphate salt crystals was 89.75%, and the purity was 95.33%.

(2) Purification process (step 2)

In order to increase the purity of the lithium difluorophosphate salt crystals, an additional purification process was performed.

A mixed solvent was prepared by mixing dimethyl carbonate and trimethyl phosphate at a weight ratio of 1:0.65. After heating the mixed solvent to about 55°C, the previously prepared lithium difluorophosphate salt crystals were added and stirred to prepare a solution in which the lithium difluorophosphate salt crystals were dissolved in the mixed solvent.

Next, the solution was filtered using a membrane filter, and then a filtrate was obtained.

Next, the filtrate was dried using a rotary evaporator under a temperature atmosphere of 70°C, and then cooled to obtain recrystallized lithium difluorophosphate salt crystals.

The yield of recrystallized lithium difluorophosphate salt crystals was 87.93%, and the purity was 98.72%.

Examples 2 to 4

Lithium difluorophosphate salt crystals were prepared in the same manner as in Example 1, and a purification process was performed, except that instead of 1,4,7,10-tetraoxacyclododecane, the crown ether compound was used as shown in Table 1 below. Each lithium difluorophosphate salt crystal was prepared and Examples 2 to 5 were respectively performed.

Examples 6 to 7

Lithium difluorophosphate salt crystals were prepared in the same manner as in Example 1, and a purification process was performed, except that instead of dimethyl carbonate, a mixed solvent containing diethyl carbonate or methyl ethyl carbonate with acetone was used as the organic solvent. Examples 6 and 7 were carried out.

Examples 8 to 9

Lithium difluorophosphate salt crystals were prepared in the same manner as in Example 1, and a purification process was performed, except that dimethyl carbonate alone or trimethyl phosphate alone was used as the solvent used in the purification process, rather than a mixed solvent. Example 8 and Example 9 were carried out.

division LiPO ₂ F ₂ synthesis (step 1) Refining process (step 2) crown
ether
compound organic solvent Yield (%)/Purity (%) menstruum Yield (%)/Purity (%) Example 1 (One) dimethyl
carbonate,
acetone 89.75/95.33 Mixed solvent ⁽⁶⁾ 87.93/98.74 Example 2 (2) 89.97/96.28 87.77/99.10 Example 3 (3) 87.26/94.82 85.52/97.76 Example 4 (4) 90.50/95.91 88.84/99.42 Example 5 (5) 92.13/94.94 89.14/99.35 Example 6 (One) diethyl
carbonate,
acetone 86.47/95.02 84.56/97.03 Example 7 (One) methyl ethyl carbonate,
acetone 87.51/95.17 84.96/98.40 Example 8 (One) dimethyl
carbonate,
acetone 89.75/95.33 dimethyl
carbonate sole 88.05/98.40 Example 9 (One) Trimethyl phosphate
ester
single 86.44/98.47 (1): 1,4,7,10-tetraoxacyclododecane
(2): 1,4,7,10,13-pentaoxacyclopentadecane
(3): 1,4,7,10,13,16-hexaoxacyclooctadecane
(4): 4,13-diaza-18-crown-6-ether
(5): 2,5,8,11,14-methyl hydroxide-1,4,7,10,13-pentaoxacyclopentadecane
(6): Contains dimethyl carbonate and trimethyl phosphate in a weight ratio of 1:0.65.

Looking at the yield and purity measurement results in Table 1, it can be seen that the lithium difluorophosphate salt crystals prepared in the LiPO ₂ F ₂ synthesis (step 1) process have an overall yield of over 85.00% and a high purity of over 90.0%. I was able to confirm. In addition, it was confirmed that the yield of LiPO ₂ F ₂ crystals obtained by purification and recrystallization was somewhat lower, but the purity was greatly improved, and the overall purity of LiPO ₂ F ₂ crystals obtained by recrystallization was 95.00% or more. It was confirmed that it could be obtained with high purity.

In particular, in the case of Examples 1 to 2 and 4 in the LiPO ₂ F ₂ synthesis (step 1) process, LiPO ₂ F ₂ crystals were obtained with relatively higher yield and purity than Example 3. In addition, although the purity of Example 5 was somewhat lower than that of Examples 1 to 4, it was confirmed that LiPO ₂ F ₂ crystals could be obtained in high yield.

In addition, when looking at the yield and purity measurement results of Example 1 and Examples 6 to 7, it was confirmed that using dimethyl carbonate was relatively more advantageous in terms of yield and purity than diethyl carbonate and methylethyl carbonate.

In addition, it was confirmed that using a mixture of dimethyl carbonate and trimethyl phosphate as a purification solvent during the purification process is relatively more advantageous in terms of increasing purity than using them alone.

Examples 10 to 11 and Comparative Examples 1 to 4

Lithium difluorophosphate salt crystals were prepared in the same manner as in Example 2, and a purification process was performed, except that lithium hexafluorophosphate and the crown ether compound 1,4,7,10,13-pentaoxacyclopentade were used. Recrystallized lithium difluorophosphate salt crystals were prepared by performing Examples 10 to 11 and Comparative Examples 1 to 2, respectively, by varying the molar ratio of cane used as shown in Table 2 below.

In addition, Examples 12 to 13 and Comparative Examples 3 to 4 were respectively performed by varying the molar ratio of lithium metaborate as shown in Table 2 below to prepare recrystallized lithium difluorophosphate salt crystals.

Examples 12 to 13 and Comparative Examples 3 and 4

Lithium difluorophosphate salt crystals were prepared using the same method as in Example 2, and purification and recrystallization processes were performed, but the molar ratio of lithium metaborate used was changed as shown in Table 2 below, Examples 12 to 12. 13 and Comparative Examples 3 to 4 were performed respectively to prepare lithium difluorophosphate salt crystals and recrystallized lithium difluorophosphate salt crystals.

division LiPO ₂ F ₂ synthesis (step 1) Refining process (step 2) LiPF ₆ : Lithium metaborate:
crown
molar ratio of ether compounds Yield (%)/Purity (%) menstruum Yield (%)/Purity (%) Example 2 1:0.85:0.60 89.97/96.28 mixed solvent 87.77/99.10 Example 10 1:0.85:0.40 86.64/96.23 84.57/99.11 Example 11 1:0.85:0.80 91.02/94.87 87.85/98.24 Example 12 1:0.50:0.60 87.75/95.14 85.28/98.83 Example 13 1:1.00:0.60 90.12/96.30 87.81/99.12 Comparative Example 1 1:0.85:0.25 82.33/96.32 80.55/99.15 Comparative Example 2 1:0.85:1.05 90.94/92.72 87.81/97.82 Comparative Example 3 1:0:0.60 82.81/93.79 79.93/96.93 Comparative Example 4 1:1.20:0.60 90.18/95.37 86.27/98.65

Looking at the yield and purity measurement results in Table 2, in the case of Comparative Example 1, in which the crown ether compound was used at a molar ratio of less than 0.30 during LiPO ₂ F ₂ crystal synthesis (step 1), when compared to Examples 2 and 10, The purity was similar, but the yield was significantly lower.

In addition, in the case of Comparative Example 2, in which the crown ether compound was used in a mole ratio exceeding 0.80 when synthesizing LiPO ₂ F ₂ crystals (step 1), compared to Examples 2 and 11, the yield improvement was almost equal, but the purity was higher. The results showed a significant drop.

Through this, it can be confirmed that when synthesizing LiPO ₂ F ₂ crystals (step 1), it is preferable to use the crown ether compound at an input molar ratio of 0.30 to 0.80 to LiPF ₆ in terms of securing appropriate yield and purity. there was.

In addition, in the case of Comparative Example 3 in which lithium metaborate was not used, it was confirmed that there was a problem of a relatively large decrease in yield compared to Examples 2 and 12, and in Comparative Example 4 in which an excessive amount of lithium metaborate was used. In the case of, compared to Example 2 and Example 13, the yield was somewhat higher, but there was a problem of relatively lower purity. Through this, it was confirmed that when synthesizing LiPO ₂ F ₂ crystals (step 1), it is preferable to use an input molar ratio of lithium metaborate to LiPF ₆ in the range of 0.50 to 1.00 in terms of securing appropriate yield and purity.

Preparation Examples 1 to 13: Preparation of non-aqueous electrolyte solution for secondary batteries

Lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte was dissolved at a ratio of 1.1 mol/L in a non-aqueous solvent containing ethylene carbonate (EC) and ethylmethyl carbonate (EMC) mixed at a volume ratio of 3:7. Preparation Example 1 was performed by adding 1% by weight of lithium difluorophosphate purified in Example 1 to the solution to prepare a non-aqueous electrolyte.

In addition, a non-aqueous electrolyte solution for a secondary battery was prepared in the same manner as Preparation Example 1, but each of the lithium difluorophosphate salt crystals prepared in Examples 2 to 13 was added instead of Example 1 to produce a non-aqueous electrolyte solution for a secondary battery. were prepared and Preparation Examples 2 to 12 were carried out, respectively.

Through the above examples, it was confirmed that pure lithium difluorophosphate salt crystals can be produced in high yield using the method proposed by the present invention. The lithium difluorophosphate salt crystal of the present invention prepared by this method can be introduced as an electrolyte of a non-aqueous electrolyte solution for secondary batteries to provide a non-aqueous electrolyte solution for secondary batteries with excellent stability.

Claims (10)

A process for synthesizing lithium difluorophosphate (LiPO ₂ F ₂ ) salt crystals by reacting lithium hexafluorophosphate (LiPF ₆ ), lithium metaborate and a crown ether compound in an organic solvent. Method for producing lithium fluorophosphate salt crystals.
The method of claim 1, further comprising purifying and recrystallizing the synthesized lithium difluorophosphate salt crystals.
The method of claim 1, wherein the process of synthesizing lithium difluorophosphate salt crystals comprises:
Step 1-1 of preparing a mixed solution by adding and stirring lithium hexafluorophosphate (LiPF ₆ ), lithium metaborate, and crown ether compound into an organic solvent;
Steps 1-2 of adding the mixed solution to the reactor, converting the inside of the reactor to an inert atmosphere, and then performing the reaction while stirring at an internal temperature of 50 to 80°C; and
A method for producing lithium difluorophosphate salt crystals, characterized in that a process comprising steps 1-3 of obtaining lithium difluorophosphate salt crystals by performing filtration, washing and drying after completion of the reaction.
The method of claim 1, wherein the crown ether compound is a substituted or unsubstituted crown ether compound,
1,4,7,10-Tetraoxacyclododecane (1,4,7,10-Tetraoxacyclododecane), 1,4,7,10,13-pentaoxacyclopentadecane (1,4,7,10, 13-pentaoxacyclopentadecane), 1,4,7,10,13,16-hexaoxacyclooctadecane (1,4,7,10,13,16-hexaoxacyclooctadecane) and 4,13-diaza-18-crown- A method for producing a lithium difluorophosphate salt crystal, comprising at least one selected from 6-ether (diaza-18-crown-6-ether).
The method of claim 1, wherein the organic solvent is a carbonate-based solvent containing at least one selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinyl carbonate, and methyl propionate, or
A method for producing lithium difluorophosphate salt crystals, characterized in that using a mixed solvent of the carbonate-based solvent and acetone.
The method of claim 3, wherein the mixed solution in step 1-1 further includes a reaction catalyst,
The amount of lithium hexafluorophosphate, lithium metaborate, and crown ether compound added to the organic solvent in step 1-1 is lithium hexafluorophosphate, lithium metaborate, and crown ether compound at a molar ratio of 1:0.5 ~ 1.0: 0.3 ~ 0.8. A method for producing lithium difluorophosphate salt crystals.
The method of claim 2, wherein the purification and recrystallization process,
Step 2-1 of performing a purification process by adding and stirring one or more solvents selected from lithium difluorophosphate salt crystals and ester solvents;
Step 2-2 of performing filtration to obtain a filtrate; and
Steps 2-3 of heat treating and cooling the filtrate to obtain recrystallized lithium difluorophosphate salt;
A method for producing lithium difluorophosphate salt crystals, characterized in that performing a process comprising:
The method of claim 7, wherein the ester-based solvent is dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, ethylene carbonate, trimethyl phosphate, triethyl phosphate, trimethyl phosphite, and triethylmethyl phosphite. A method for producing lithium difluorophosphate salt crystals, comprising at least one selected from esters.
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