JP6740424B1 - Preparation method of high-purity lithium salt by mixing in a predetermined ratio and its application - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high purity lithium salt and a lithium ion battery containing the lithium salt. SOLUTION: A step of purifying industrial lithium oxalate and a step of reacting lithium oxalate with boron trifluoride/ethyl ether to obtain a mixed reaction solution of lithium difluoro(oxalato)borate and lithium tetrafluoroborate are obtained. Then, a step of a synthetic reaction of purifying with a purification auxiliary filtration membrane, a step of concentrating and crystallizing the reaction solution, and a step of purifying and drying the mixed lithium salt are included. The high-purity lithium salt of the present invention is a mixed lithium salt containing lithium difluoro(oxalato)borate and lithium tetrafluoroborate at a predetermined molar ratio of 1:1 and can be applied to a non-aqueous electrolytic solution for a lithium ion battery. [Selection diagram] Figure 1

Description

TECHNICAL FIELD The present invention relates to the field of lithium-ion battery manufacturing technology, and more specifically, to a method for preparing a high-purity lithium salt by mixing in a predetermined ratio and its application.

The lithium battery electrolyte is a carrier that transports ions in the battery. It usually consists of a lithium salt and an organic solvent. The electrolytic solution plays a role of conducting ions between the positive electrode and the negative electrode of the lithium battery, and imparts advantages such as high voltage and high specific energy to the lithium ion battery. The electrolytic solution is usually prepared by using a raw material such as a high-purity organic solvent, an electrolyte lithium salt, and necessary additives under a certain condition at a predetermined ratio. Conventionally, the most common electrolyte lithium salt is lithium hexafluorophosphate (LiPF ₆ ), and lithium hexafluorophosphate occupies 50%-60% of the cost of the electrolyte in the process of manufacturing the electrolyte. It is mainly used in lithium-ion power batteries and lithium-ion energy storage batteries, and has the advantages of excellent cycle efficiency, thermal stability, and high conductivity.

On the other hand, lithium hexafluorophosphate as an electrolyte lithium salt has the drawback of being poor in high temperature resistance and hydrolysis resistance, and hydrogen fluoride generated destroys battery materials such as electrode materials and SEI films, This may cause a reduction in the lithium battery capacity and a shortened service life. By taking advantage of the different physicochemical properties of various lithium salts, and combining different types of lithium salts, the advantages of each lithium salt can be combined to effectively improve the characteristics of lithium batteries. ..

Compared with lithium hexafluorophosphate, lithium tetrafluoroborate (LiBF ₄ ) has a wider operating temperature range and stronger hydrolysis resistance, but has low ion mobility and poor film-forming ability by itself. There is a drawback that. Lithium difluoro(oxalato)borate (LiODFB) is a novel lithium salt, has excellent film forming performance, and has excellent thermal stability, high-low temperature performance, electrochemical stability, and the like.

CN107698611A discloses a method for synthesizing difluoro(oxalato)borate, which is an electrolyte lithium salt lithium. Step 1) of reacting a silane compound with oxalic acid to obtain a condensate of silane oxalic acid, and lithium tetrafluoroborate. And a silane oxalic acid condensate are reacted in a solvent to obtain a crude product 2), and the crude product is recrystallized to obtain lithium difluoro(oxalato)borate 3).

In CN101684893A, a synthetic process for simultaneously producing lithium difluoro(oxalato)borate and lithium tetrafluoroborate having excellent performance is disclosed. The reaction is carried out in a reaction medium at a reaction pressure of 0 to 100° C. and 0.1 to 1 MPa, and the molar ratio of lithium element, fluorine element, boron element and oxalate root ion is set to 2 to 3:5 to 6:2:1. Step (1) of producing a reaction liquid containing lithium difluoro(oxalato)borate and lithium tetrafluoroborate, preliminarily separating lithium difluoro(oxalato)borate and lithium tetrafluoroborate in the reaction liquid, and then lithium difluoroborate Lithium difluoro(oxalato)borate for a battery, which is subjected to extraction and separation using an organic solvent capable of extracting (oxalato)borate or lithium tetrafluoroborate, and recrystallization and vacuum drying. And a step (3) of obtaining lithium tetrafluoroborate.

In the conventional process, lithium tetrafluoroborate has a structure similar to that of lithium difluoro(oxalato)borate, and both solutions have high viscosities, making it difficult to separate the two, making it difficult for equipment and technology. Is high and the purity of both mixed salts produced is low, which increases the cost of the mixed salt electrolyte. For this reason, the prior art has room for improvement.

The object of the present invention is to carry out processes such as purification, synthesis, and concentration using industrial lithium oxalate as a raw material, and to produce lithium difluoro(oxalato)borate and lithium tetrafluoroborate in a predetermined molar ratio of 1:1. The mixed lithium salt can be obtained and used for the production of lithium ion batteries, the complicated process of recrystallization and the solid-liquid separation (filtration) operation after crystallization in the prior art can be omitted, and the product yield and purity can be improved. It is to provide a method for preparing a high-purity lithium salt by mixing a predetermined ratio, which can simplify the process flow, reduce the production cost, and the like, and its application.

In order to achieve the above object, the present invention adopts the following technical solutions.
A method for preparing a high-purity lithium salt by mixing a predetermined ratio,
Pure water is added to industrial lithium oxalate and stirred to prepare a lithium oxalate suspension, and then an aqueous metal chelating agent solution is added to the lithium oxalate suspension, stirred for 30 min, and suction filtered. To obtain a lithium oxalate solid, then wash the lithium oxalate solid with ultrapure water 3 to 5 times and suction filter, and finally, wash with ethanol, filter and dry to obtain a solid white solid. Obtaining purified lithium oxalate as a powder, purifying lithium oxalate (1),
While stirring, lithium oxalate was added to the organic solvent to prepare a lithium oxalate suspension, and boron trifluoride/diethyl ether was prepared until the prepared lithium oxalate suspension became transparent. Add dropwise to a lithium suspension and stir until the reaction is complete to obtain a mixed reaction solution of lithium difluoro(oxalato)borate and lithium tetrafluoroborate, and then purify with a purification auxiliary filtration membrane. Reaction step (2),
A step of concentrating and crystallization of the reaction solution, in which a mixed reaction solution of lithium difluoro(oxalato)borate and lithium tetrafluoroborate after purification is concentrated in vacuum and then crystallized to obtain a crystallized crude product of a mixed lithium salt. (3),
After washing the crystallized crude product with a poor solvent of lithium difluoro(oxalato)borate and lithium tetrafluoroborate, the brown solution in the upper layer or the lower layer is removed, and the poor solvent is further added. The solution of the upper layer or the lower layer is clarified by washing 3 to 4 times, and the solid is dried in a vacuum to obtain a high-purity lithium salt (a molar ratio of lithium difluoro(oxalato)borate and lithium tetrafluoroborate of 1 by mixing in a predetermined ratio). 1), and in the washing process, the crystallized solid becomes a viscous to fluffy crystal, the color changes from light brown to white, and the mixed lithium salt is purified and dried (4) ..

According to the above aspect, when purifying the lithium oxalate, the metal chelating agent is ethylenediaminetetraacetic acid (EDTA) and the drying temperature is 120°C.

According to the above aspect, in the synthesis reaction, the solvent is dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, acetonitrile, tetrahydrofuran, toluene, ethyl acetate, ethylene glycol dimethyl ether, ethyl ether, dimethylformamide or acetone, the reaction temperature is It is 70-90°C, and the reaction time is 10-24h.

According to the above embodiment, ethanol, polyethylene glycol diacrylate, 1,1′-(methylenebis-4,1-phenylene)bis[2-hydroxy-2-methyl-1- Acetone], lanthanum trifluoromethanesulfonate, 2-(3-nitro-2-pyridine)dimethylmalonate, potassium benzofuran-2-trifluoroborate 100:100-150:4-10:0.1-0. The mixture was charged into the reactor at a mass ratio of 3:0.1-0.4:0.2-0.5, kept at 60-80° C., nitrogen gas was introduced, and the mixture was stirred for 60-150 min, and the mixture was added. To a glass plate, then cover the quartz glass plate above the mixture, control the thickness of the mixture to 100-300 μm, irradiate with ultraviolet rays for 30-120 s, wash with acetone for 6-24 h, and leave it still. Place and dry to obtain a purification auxiliary filtration membrane.

According to the above aspect, the degree of vacuum is g-0.01 MPaG and the temperature is 60 to 90° C. when the reaction liquid is concentrated, and the temperature is -20° C. when the reaction liquid is crystallized.

According to the above aspect, when purifying the mixed lithium salt, the poor solvent is a low-boiling halogenated alkane, a nonpolar-weakly polar organic solvent, or a mixed organic solvent of both, when vacuum drying, The degree of vacuum is −0.01 MPaG and the temperature is 80 to 100° C.

According to the above aspect, the low-boiling halogenated alkane is carbon tetrachloride, trichloromethane, dichloromethane, dichloroethane or chloropropane, and the nonpolar-weakly polar organic solvent is cyclohexane, n-hexane, benzene, pentane or Petroleum ether.

A non-aqueous electrolyte solution for a lithium ion battery, which contains 0.5% by mass to 20% by mass of a high-purity lithium salt mixed in a predetermined ratio.

A lithium-ion battery, wherein a non-aqueous electrolyte for a lithium-ion battery containing 0.5% by mass to 20% by mass of a high-purity lithium salt obtained by mixing in a predetermined ratio is dried, and the molar ratio of nickel:cobalt:manganese is 6%. : Injected into a 2:2 4.2V NCM/graphite pouch battery and manufactured by conventional lithium-ion manufacturing technology (after being left at 45°C, chemical conversion using a high-temperature jig and secondary sealing, etc.) It will be done.

In the present invention, industrial lithium oxalate is used as a raw material, and it is necessary to purify lithium oxalate in order to reduce the industrial production cost. The amount of metal ions in industrial lithium oxalate is excessive, soluble metal ions such as Na ⁺ and K ⁺ can be washed with ethanol, and other soluble metal ions can be removed in the subsequent washing process, while insoluble metal such as Ca ^2+. Ions are removed by washing with a chelating reagent such as EDTA.

The beneficial effects of the present invention are as follows.
1) In the present invention, since the steps of separating and purifying lithium difluoro(oxalato)borate and lithium tetrafluoroborate are reduced, the production process is greatly simplified and the cost is reduced.
2) The present invention provides a method for purifying a mixed lithium salt, improving the purity and yield of the mixed lithium salt, allowing the prepared mixed lithium salt to be directly applied to a lithium ion battery, The cost.
3) In the present invention, by mixing a lithium salt in a predetermined ratio of 1:1 it is possible to effectively improve the room temperature and high temperature cycle characteristics of a lithium ion battery, and it is promising as a substitute for lithium hexafluorophosphate. Yes, further, by adding LiODFB or LiBF ₄ alone, mixed lithium salts with various ratios can be produced and applied to the formulation of various electrolytic solutions, and the cost can be reduced.
4) In the present invention, industrial lithium oxalate is purified to prepare a mixed lithium salt, thereby satisfying electric performance and further reducing production cost.

3 is an ¹¹ B NMR spectrum of the mixed lithium salt prepared in Example 1 of the present invention. It is a ¹⁹ F NMR spectrum of the mixed lithium salt prepared in Example 1 of the present invention. 3 is a ¹³ C NMR spectrum of the mixed lithium salt prepared in Example 1 of the present invention. It is a room temperature (25 degreeC) cycle (100 cycles) characteristic figure of the electrolyte solution containing the mixed lithium salt prepared in Example 1 of this invention. It is a cycle (100 cycles) characteristic diagram of the electrolytic solution containing the mixed lithium salt prepared in Example 1 of the present invention at a high temperature (45°C). 3 is an IR spectrum of the purification auxiliary filtration membrane produced in Example 1 of the present invention.

Hereinafter, a technical solution of the present invention will be described with reference to the drawings and embodiments.

Example 1
As shown in FIGS. 1-6,
The present invention provides a method for preparing a high-purity lithium salt by mixing in a predetermined ratio,
An appropriate amount of ultrapure water was added to 150 g of industrial lithium oxalate and stirred to prepare a lithium oxalate suspension, 0.4 g of ethylenediaminetetraacetic acid (EDTA) was weighed and dissolved in a small amount of ultrapure water. Then, the EDTA aqueous solution is added to the lithium oxalate suspension, stirred for 30 minutes, suction filtered to obtain a lithium oxalate solid, and the lithium oxalate solid is washed three times with ultrapure water and suction filtered. Finally, washing with ethanol, filtering, placing in an oven at 120° C. and drying to obtain purified lithium oxalate (96 wt %) as a solid white powder, a step (1) for purifying lithium oxalate,
Added dimethyl carbonate (DMC) 500 mL three-necked reaction flask, with vigorous stirring lithium oxalate 102g added while, 1h stirring the temperature was raised to 85 ° C., to prepare a lithium oxalate suspension trifluoride Weigh 284 g of boron iodide /diethyl ether and slowly add it to the lithium oxalate suspension over 2 h while stirring. After the addition is complete, when the suspension becomes clear, stir for another 22 h and react. Then, a mixed reaction solution of lithium difluoro(oxalato)borate and lithium tetrafluoroborate is obtained, and then purified by a purification auxiliary filtration membrane, and a synthetic reaction step (2),
The mixed reaction liquid of lithium difluoro(oxalato)borate and lithium tetrafluoroborate after purification was vacuum concentrated under the conditions of a vacuum degree of -0.01 MPaG and a temperature of 80°C, and then the reaction flask was kept at -20°C. A step (3) of concentrating the reaction solution and crystallization, which is allowed to crystallize under the conditions to obtain a crude crystallization product of a mixed lithium salt;
The reaction flask after crystallization was taken out to obtain a viscous solid-liquid system, 200 mL of carbon tetrachloride was added to the reaction flask, and after sufficiently stirring, the lower layer brown carbon tetrachloride phase solution was removed, and The carbon tetrachloride phase solution of the lower layer was made a clear solution by washing repeatedly, and the crystallized solid of the upper layer was changed from brown to white solid by suction filtration to remove carbon tetrachloride. A mixed lithium salt, which is dried at a pressure of 0.01 MPaG and a temperature of 100° C. for 24 hours to obtain a high-purity lithium salt (molar ratio of lithium difluoro(oxalato)borate and lithium tetrafluoroborate 1:1) by mixing in a predetermined ratio. Purification and drying step (4).

The obtained solid product was analyzed by ¹⁹ F NMR, ¹¹ B NMR, and ¹³ C NMR (see FIGS. 1 to 3, respectively), and the product was a molar ratio of lithium difluoro(oxalato)borate and lithium tetrafluoroborate. Is a 1:1 mixed lithium salt (calculated by integrated area of NMR), yield 85.6%, purity 99.1% (characterization by nuclear magnetic resonance), water content 120 ppm, acidity 200 ppm, insoluble matter 102 ppm, It was confirmed that the turbidity was 1.5.

Further, as a process for producing the purification auxiliary filtration membrane, ethanol, polyethylene glycol diacrylate, 1,1′-(methylenebis-4,1-phenylene)bis[2-hydroxy-2-methyl-1-acetone], trifluoromethane A mass ratio of lanthanum sulfonate, 2-(3-nitro-2-pyridine)dimethylmalonate, and potassium benzofuran-2-trifluoroborate to 100:100:7:0.1:0.1:0.2. Then, the mixture was put into a reactor, kept at 70° C., introduced nitrogen gas, stirred for 100 min, poured the mixture into a glass plate, and then covered the quartz glass plate above the mixture to give a thickness of the mixture. Was controlled to 100 μm, irradiated with ultraviolet rays for 75 s, washed with acetone for 15 h, allowed to stand and dried to obtain the above-mentioned purified auxiliary filtration membrane.

The product of this example was subjected to related characterization and the results are shown in FIGS. FIG. 1 is an ¹¹ B NMR spectrum of the mixed lithium salt prepared in this example, FIG. 2 is a ¹⁹ F NMR spectrum of the mixed lithium salt prepared in this example, and FIG. 3 is a preparation of this example. FIG. 4 is a ¹³ C NMR spectrum of the prepared mixed lithium salt, FIG. 4 is a room temperature (25° C.) cycle (100 cycles) characteristic diagram of the electrolyte solution containing the mixed lithium salt prepared in this example, and FIG. FIG. 6 is a characteristic diagram of a cycle (100 cycles) at high temperature (45° C.) of an electrolytic solution containing a mixed lithium salt prepared in this example, and FIG. 6 is an IR spectrum of the purified auxiliary filtration membrane produced in Example 1. Is. From the results, the following conclusions were obtained.
(1) Since there is only one boron atom in LiODFB and LiBF ₄ , each ¹¹ B NMR spectrum shows a single peak, while in the ¹¹ B NMR spectrum, the area ratio of two single peaks is 1: Since it is 1, it can be judged that the molar ratio of LiODFB and LiBF ₄ is 1:1. Similarly, in LiODFB, since the chemical environment of the fluorine atom is the same, the chemical shift appearing in the ¹⁹ F NMR spectrum is Are the same, and since the chemical environment of the fluorine atom is the same also in LiBF ₄ , peaks occur at the same chemical shift, and the ratio of the chemical shifts at the two positions in the ¹⁹ F NMR spectrum indicates that LiODFB is It can be confirmed that the molar ratio of LiBF ₄ is 1:1. This is because the molar ratio of LiODFB and LiBF ₄ produced by the reaction is 1:1 and the poor solvent used in the purification process is insoluble in both LiODFB and LiBF ₄ , and therefore, in the mixed salt after purification, This is because the ratio of LiODFB and LiBF ₄ is not changed.
(2) In the ¹³ C NMR spectrum, there is only a peak that is a peak of carbon atoms in LiODFB, and since LiBF ₄ does not contain carbon atoms, no peak occurs in the ¹³ C NMR spectrum.
(3) As is clear from FIG. 4, the mixed salt can effectively improve the room temperature (25° C.) cycle characteristics of the lithium ion battery, and is most effective at the added amounts of 1.5% and 3%.
(4) As is clear from FIG. 5, the mixed salt can effectively improve the cycle characteristics of the lithium ion battery at high temperature (45° C.), and is effective at the added amounts of 1.5% and 0.5%. Is the highest. On the other hand, as a result of storing at 60° C. for 9 days, the gas generation can be effectively suppressed by adding the mixed salt, and the capacity retention rate is 79.8% to 86.67% at the addition amount of 1.5%. The corresponding capacity recovery rate can be improved from 82.04% to 88.88%.
Such a mixed lithium salt has great advantages in terms of both cost and effect, and can be promising as a main salt of an electrolytic solution instead of lithium hexafluorophosphate.
(5) FIG. 6 shows the chemical composition of the purification auxiliary filtration membrane. 907 and 1030 are characteristic peaks of sulfonic acid group, 1260 is a characteristic peak of C—S bond, From this, it becomes clear that lanthanum trifluoromethanesulfonate participates in the reaction and is taken into the absorption film. 1500-1650 is a characteristic peak of a nitro group, 1576, 1468 and 1434 are characteristic absorption peaks of a pyridine ring, 994 is a bending vibration absorption peak of a pyridine ring, and 1700 is O=C- This is a strong absorption peak at 0, and from this, it is clear that 2-(3-nitro-2-pyridine)dimethylmalonate participates in the reaction and is incorporated into the absorption film, and 1600 is a characteristic of the benzene ring skeleton. Is a peak, 900 is a C-H bending vibration peak of the benzene ring, and 1000 is a characteristic peak of a C-F bond. From this, potassium benzofuran-2-trifluoroborate is involved in the reaction. It becomes clear that they are involved and are taken up by the absorption film.

Preparation of Lithium Ion Battery Non-Aqueous Electrolyte Using Mixed Lithium Salt Prepared in this Example In a glove box, vinyl carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) were added at 30:45:25. And mixed with lithium hexafluorophosphate and then dissolved to prepare an electrolytic solution having a lithium hexafluorophosphate concentration of 1M. Then, 0.5 wt%, 1.0 wt%, 1.5 wt% and 3 wt% of the mixed lithium salt samples prepared in the examples were added to the electrolyte.

The prepared non-aqueous electrolyte for a lithium-ion battery was poured into a sufficiently dried 4.2 V NCM (nickel:cobalt:manganese=6:2:2)/graphite pouch battery and left at 45° C., After the steps such as chemical conversion using a high temperature jig and secondary sealing, the battery performance was tested.

1) Normal temperature cycle characteristics Under normal temperature (25° C.) conditions, the lithium ion battery was charged to 4.2 V at 1 C constant current and constant voltage, and then discharged to 3.0 V at 1 C constant current. After 100 cycles of charge and discharge, the capacity retention rate at the 100th cycle was calculated.

2) High-temperature cycle characteristics Under the conditions of high temperature (45°C), the lithium ion battery was charged to 4.2V at 1C constant current and constant voltage, and then discharged to 3.0V at 1C constant current. After 100 cycles of charge/discharge, the capacity retention rate after 100 cycles was calculated.

Example 2
The present invention provides a method for preparing a high-purity lithium salt by mixing in a predetermined ratio,
A step (1) for purifying lithium oxalate, which is the same as in Example 1,
The addition of ethyl acetate (EA) 500 mL three-necked reaction flask, with vigorous stirring lithium oxalate 102g added while, 1h stirring the temperature was raised to 85 ° C., to prepare a lithium oxalate suspension trifluoride Weigh 284 g of boron iodide /diethyl ether and slowly add it to the lithium oxalate suspension over 2 h while stirring. After the addition is complete, when the suspension becomes clear, stir for another 22 h and react. Then, a mixed reaction solution of lithium difluoro(oxalato)borate and lithium tetrafluoroborate is obtained, and then purified by a purification auxiliary filtration membrane, and a synthetic reaction step (2),
The purified reaction mixture of lithium difluoro(oxalato)borate and lithium tetrafluoroborate was concentrated under vacuum at a vacuum degree of -0.01 MPaG and a temperature of 60°C, and then the reaction flask was kept at -20°C. A step (3) of concentrating the reaction solution and crystallization, which is allowed to crystallize under the conditions to obtain a crude crystallization product of a mixed lithium salt;
After taking out the reaction flask after crystallization, a viscous solid-liquid system was obtained, 200 mL of dichloromethane was added to the reaction flask, and after sufficiently stirring, the brown dichloromethane phase solution of the upper layer was removed, and washed 4 times repeatedly. Then, the dichloromethane layer solution of the upper layer is made into a clear solution, at this time, the crystallized solid of the lower layer changes from brown to a white solid, and suction filtration is performed to remove dichloromethane, and the vacuum degree is -0.01 MPaG , 100°C. Step (4) of purification and drying of the mixed lithium salt to obtain a high-purity lithium salt (molar ratio of lithium difluoro(oxalato)borate and lithium tetrafluoroborate 1:1) by mixing in a predetermined ratio for 24 hours. Including and

Further, as a process for producing the purification auxiliary filtration membrane, ethanol, polyethylene glycol diacrylate, 1,1′-(methylenebis-4,1-phenylene)bis[2-hydroxy-2-methyl-1-acetone], trifluoromethane The lanthanum sulfonate, 2-(3-nitro-2-pyridine)dimethylmalonate, and potassium benzofuran-2-trifluoroborate were added in a mass ratio of 100:125:7:0.2:0.25:0.35. Then, the mixture was charged into the reactor, kept at 80° C., introduced nitrogen gas, stirred for 120 min, poured the mixture into a glass plate, and then covered the quartz glass plate above the mixture to give a thickness of the mixture. Was controlled to 200 μm, irradiated with ultraviolet rays for 120 s, washed with acetone for 20 h, allowed to stand and dried to obtain the purification auxiliary filtration membrane.

The obtained solid was subjected to ¹⁹ F NMR, ¹¹ B NMR, and ¹³ C NMR analysis. It was confirmed that the yield was 87.6%, the purity was 99.9% (characterization by nuclear magnetic resonance), the water content was 112 ppm, the acidity was 148 ppm, the insoluble matter was 95 ppm, and the turbidity was 1.5. did.

Example 3
The present invention provides a method for preparing a high-purity lithium salt by mixing in a predetermined ratio,
A step (1) for purifying lithium oxalate, which is the same as in Example 1,
Add 500 mL of acetonitrile to a three-neck reaction flask, add 102 g of lithium oxalate with vigorous stirring, raise the temperature to 85° C., and stir for 1 h to prepare a lithium oxalate suspension, and then add boron trifluoride/diethyl 284 g of ether was weighed and gradually added to the lithium oxalate suspension over 2 h while stirring, and when the suspension became clear after stirring, the mixture was further stirred for 22 h to react with lithium difluoro. A step (2) of the synthetic reaction, in which a mixed reaction solution of (oxalato)borate and lithium tetrafluoroborate is obtained and then purified with a purification auxiliary filtration membrane;
The mixed reaction liquid of lithium difluoro(oxalato)borate and lithium tetrafluoroborate after purification was vacuum concentrated under the conditions of a vacuum degree of -0.01 MPaG and a temperature of 70°C, and then the reaction flask was kept at -20°C. A step (3) of concentrating the reaction solution and crystallization, which is allowed to crystallize under the conditions to obtain a crude crystallization product of a mixed lithium salt;
The reaction flask after crystallization was taken out to obtain a viscous solid-liquid system, 200 mL of cyclohexane was added to the reaction flask, and after sufficiently stirring, the brown cyclohexane phase solution of the upper layer was removed and washed 4 times repeatedly. Then, the upper layer brown cyclohexane phase solution was made into a clear solution, at this time, the lower layer crystallized solid changed from brown to pure white solid, and cyclohexane was removed by suction filtration to obtain a -0.01 MPaG vacuum degree, 100. The mixture is dried at a temperature of 24° C. for 24 hours to obtain a high-purity lithium salt (molar ratio of lithium difluoro(oxalato)borate and lithium tetrafluoroborate 1:1) by mixing in a predetermined ratio. ) And.

Further, as a process for producing the purification auxiliary filtration membrane, ethanol, polyethylene glycol diacrylate, 1,1′-(methylenebis-4,1-phenylene)bis[2-hydroxy-2-methyl-1-acetone], trifluoromethane A mass ratio of lanthanum sulfonate, 2-(3-nitro-2-pyridine)dimethylmalonate, potassium benzofuran-2-trifluoroborate to 100:150:10:0.3:0.4:0.5. Then, the mixture was charged into a reactor, kept warm at 78° C., introduced nitrogen gas, stirred for 150 min, poured the mixture into a glass plate, and then covered the quartz glass plate above the mixture to give a thickness of the mixture. Was controlled to 300 μm, irradiated with ultraviolet rays for 120 s, washed with acetone for 24 h, allowed to stand and dried to obtain the purified auxiliary filtration membrane.

The obtained solid was subjected to ¹⁹ F NMR, ¹¹ B NMR, and ¹³ C NMR analysis. It was confirmed that the yield was 85.4%, the purity was 99.9% (characterization by nuclear magnetic resonance), the water content was 65 ppm, the acidity was 127 ppm, the insoluble matter was 78 ppm, and the turbidity was 1.5. did.

Example 4
The present invention provides a method for preparing a high-purity lithium salt by mixing in a predetermined ratio, and is substantially the same as Example 3 except that tetrahydrofuran is used as the organic solvent in the synthetic reaction.

The obtained solid was subjected to ¹⁹ F NMR, ¹¹ B NMR, and ¹³ C NMR analysis. It was confirmed that the yield was 86.2%, the purity was 98.4% (characterization by nuclear magnetic resonance), the water content was 98 ppm, the acidity was 239 ppm, the insoluble matter was 184 ppm, and the turbidity was 1.5. did.

Example 5
The present invention provides a method for preparing a high-purity lithium salt by mixing in a predetermined ratio, wherein ethanol, polyethylene glycol diacrylate, 1,1′-(methylenebis-4,1-phenylene)bis is used as a manufacturing process of a purification auxiliary filtration membrane. [2-hydroxy-2-methyl-1-acetone], lanthanum trifluoromethanesulfonate, 2-(3-nitro-2-pyridine)dimethylmalonate, potassium benzofuran-2-trifluoroborate, 100:150: It was charged into a reactor at a mass ratio of 10:0.4:0.5, kept at 75° C., introduced nitrogen gas, stirred for 130 min, poured the mixture onto a glass plate, and then poured the mixture into a mixture. Except that the quartz glass plate was covered above, the thickness of the mixture was controlled to 300 μm, the mixture was irradiated with ultraviolet rays for 100 s, washed with acetone for 20 h, and allowed to stand to dry to obtain the purification auxiliary filtration membrane. It was almost the same as 3.

The obtained solid was subjected to ¹⁹ F NMR, ¹¹ B NMR, and ¹³ C NMR analysis. It was confirmed that the yield was 86.1%, the purity was 98.7% (characterization by nuclear magnetic resonance), the water content was 81 ppm, the acidity was 174 ppm, the insoluble matter was 91 ppm, and the turbidity was 1.5. did.

Example 6
The present invention provides a method for preparing a high-purity lithium salt by mixing in a predetermined ratio, wherein ethanol, polyethylene glycol diacrylate, 1,1′-(methylenebis-4,1-phenylene)bis is used as a manufacturing process of a purification auxiliary filtration membrane. [2-hydroxy-2-methyl-1-acetone], lanthanum trifluoromethanesulfonate, 2-(3-nitro-2-pyridine)dimethylmalonate, potassium benzofuran-2-trifluoroborate, 100:150: It was charged into a reactor at a mass ratio of 10:0.3:0.5, kept at 78° C. and introduced with nitrogen gas, stirred for 150 min, poured the mixture into a glass plate, and then mixed with the mixture. Except that the quartz glass plate was covered above, the thickness of the mixture was controlled to 300 μm, the mixture was irradiated with ultraviolet rays for 120 s, washed with acetone for 20 h, and allowed to stand to dry to obtain the purification auxiliary filtration membrane. It was almost the same as 3.

The obtained solid was subjected to ¹⁹ F NMR, ¹¹ B NMR, and ¹³ C NMR analysis. It was confirmed that the yield was 85.6%, the purity was 98.9% (characterization by nuclear magnetic resonance), the water content was 77 ppm, the acidity was 145 ppm, the insoluble matter was 91 ppm, and the turbidity was 1.5. did.

Example 7
The present invention provides a method for preparing a high-purity lithium salt by mixing in a predetermined ratio, wherein ethanol, polyethylene glycol diacrylate, 1,1′-(methylenebis-4,1-phenylene)bis is used as a manufacturing process of a purification auxiliary filtration membrane. [2-hydroxy-2-methyl-1-acetone], lanthanum trifluoromethanesulfonate, 2-(3-nitro-2-pyridine)dimethylmalonate, potassium benzofuran-2-trifluoroborate, 100:150: It was charged into a reactor at a mass ratio of 10:0.3:0.4, kept at 75° C., introduced nitrogen gas, stirred for 150 min, poured the mixture onto a glass plate, and then poured the mixture into a mixture. Example except that a quartz glass plate was covered above, the thickness of the mixture was controlled to 300 μm, the mixture was irradiated with ultraviolet rays for 120 s, washed with acetone for 24 h, and allowed to stand to dry to obtain the purification auxiliary filtration membrane. It was the same as 3.

The obtained solid was subjected to ¹⁹ F NMR, ¹¹ B NMR, and ¹³ C NMR analysis, and as a result, the product was a mixed lithium salt (NMR) in which the molar ratio of lithium difluoro(oxalato)borate and lithium tetrafluoroborate was 1:1. It was confirmed that the yield was 85.6%, the purity was 98.8% (characterization by nuclear magnetic resonance), the water content was 81 ppm, the acidity was 194 ppm, the insoluble matter was 93 ppm, and the turbidity was 1.5. did.

Comparative Example 1
A method for preparing a high-purity lithium salt by mixing a predetermined ratio,
Add 500 mL of acetonitrile to a three-neck reaction flask, add 102 g of lithium oxalate with vigorous stirring, raise the temperature to 85° C., and stir for 1 h to prepare a lithium oxalate suspension, and then add boron trifluoride/diethyl 284 g of ether was weighed and gradually added to the lithium oxalate suspension over 2 h while stirring, and when the suspension became clear after stirring, the mixture was further stirred for 22 h to react with lithium difluoro. A synthetic reaction step (1) for obtaining a mixed reaction solution of (oxalato)borate and lithium tetrafluoroborate;
A mixed reaction solution of lithium difluoro(oxalato)borate and lithium tetrafluoroborate was concentrated under vacuum at a vacuum degree of -0.01 MPaG and a temperature of 70°C, and then the reaction flask was left at -20°C. And crystallize to obtain a crude crystallized product of a mixed lithium salt, the step (2) of concentrating and crystallization of the reaction solution,
The reaction flask after crystallization was taken out to obtain a viscous solid-liquid system, 200 mL of cyclohexane was added to the reaction flask, and after sufficiently stirring, the brown cyclohexane phase solution of the upper layer was removed and washed 4 times repeatedly. Then, the upper layer brown cyclohexane phase solution was made into a clear solution, at this time, the lower layer crystallized solid changed from brown to pure white solid, and cyclohexane was removed by suction filtration to obtain a -0.01 MPaG vacuum degree, 100. A step (3) of purifying and drying the mixed lithium salt to obtain a mixed lithium salt (molar ratio of lithium difluoro(oxalato)borate and lithium tetrafluoroborate 1:1) by drying at a temperature of 24° C. for 24 hours.

The obtained solid was subjected to ¹⁹ F NMR, ¹¹ B NMR, and ¹³ C NMR analysis. It was confirmed that the yield was 77.4% and the purity was 85.1% (characterization by nuclear magnetic resonance).

The above examples are merely for explaining the technical solution of the present invention, and are not limitative, and the present invention has been described in detail in the above examples, but those skilled in the art can modify or modify the present invention. It is understood that equivalent substitutions can be made, and that modifications and partial substitutions made without departing from the spirit and scope of the invention are covered by the claims of the invention.

Claims (7)

A method for preparing a high-purity lithium salt by mixing a predetermined ratio,
Pure water is added to industrial lithium oxalate and stirred to prepare a lithium oxalate suspension, and then an aqueous metal chelating agent solution is added to the lithium oxalate suspension, stirred for 30 min, and suction filtered. To obtain a lithium oxalate solid, then wash the lithium oxalate solid with ultrapure water 3 to 5 times and suction filter, and finally, wash with ethanol, filter and dry to obtain a solid white solid. Obtaining purified lithium oxalate as a powder, purifying the purified lithium oxalate (1),
While stirring, purified lithium oxalate was added to the organic solvent to prepare a lithium oxalate suspension, and boron trifluoride/diethyl ether was prepared until the prepared lithium oxalate suspension became transparent. Dropwise into the lithium acid suspension and stirred until the reaction is complete to obtain a mixed reaction solution of lithium difluoro(oxalato)borate and lithium tetrafluoroborate, and then purify with a purification auxiliary filtration membrane, A synthetic reaction step (2),
A step of concentrating and crystallization of the reaction solution, in which a mixed reaction solution of lithium difluoro(oxalato)borate and lithium tetrafluoroborate after purification is concentrated in vacuum and then crystallized to obtain a crystallized crude product of a mixed lithium salt. (3),
After washing the crystallized crude product with a poor solvent of lithium difluoro(oxalato)borate and lithium tetrafluoroborate, the brown solution in the upper layer or the lower layer is removed, and the poor solvent is further added. The solution of the upper layer or the lower layer is clarified by washing 3 to 4 times, and the solid is dried in a vacuum to obtain a high-purity lithium salt (a molar ratio of lithium difluoro(oxalato)borate and lithium tetrafluoroborate of 1 by mixing in a predetermined ratio). Step (4) of refining and drying the mixed lithium salt to obtain 1)). The method for preparing a high-purity lithium salt according to claim 1, wherein the metal chelating agent is ethylenediaminetetraacetic acid and the drying temperature is 120° C. when the lithium oxalate is purified. In the synthetic reaction, the solvent is dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, acetonitrile, tetrahydrofuran, toluene, ethyl acetate, ethylene glycol dimethyl ether, ethyl ether, dimethylformamide or acetone, the reaction temperature is 70-90 ° C., The method for preparing a high purity lithium salt according to claim 1, wherein the reaction time is 10-24 h. As the manufacturing process of the purification auxiliary filtration membrane, ethanol, polyethylene glycol diacrylate, 1,1-(methylenebis-4,1-phenylene)bis[2-hydroxy-2-methyl-1-acetone], lanthanum trifluoromethanesulfonate , 2-(3-nitro-2-pyridine)dimethylmalonate, potassium benzofuran-2-trifluoroborate at 100:100-150:4-10:0.1-0.3:0.1-0. The mixture was put in a reactor at a mass ratio of 4:0.2-0.5, kept at 60-80° C., nitrogen gas was introduced, the mixture was stirred for 60-150 min, and the mixture was poured onto a glass plate. Then, cover the quartz glass plate above the mixture, control the thickness of the mixture to 100-300 μm, irradiate with ultraviolet rays for 30-120 s, wash with acetone for 6-24 h, let stand and dry to aid purification. A method for preparing a high-purity lithium salt by mixing in a predetermined ratio according to claim 1, wherein a filtration membrane is obtained. The vacuum degree is −0.01 MPaG , the temperature is 60 to 90° C. when the reaction liquid is concentrated, and the temperature is −20° C. when the reaction liquid is crystallized. 1. A method for preparing a high-purity lithium salt by mixing a predetermined ratio according to 1. When purifying the mixed lithium salt, the poor solvent is a low-boiling halogenated alkane, a nonpolar-weakly polar organic solvent, or a mixed organic solvent of both, and when vacuum-dried, the degree of vacuum is -0.01. It is MPaG and temperature is 80-100 degreeC , The preparation method of the high purity lithium salt by predetermined ratio mixing of Claim 1 characterized by the above-mentioned. The low boiling halogenated alkane is carbon tetrachloride, trichloromethane, dichloromethane, dichloroethane or chloropropane, and the nonpolar-weakly polar organic solvent is cyclohexane, n-hexane, benzene, pentane or petroleum ether. The method for preparing a high-purity lithium salt by mixing in a predetermined ratio according to claim 1.