A method for synthesizing lithium tetrafluoroborate, an electrolyte

Abstract

The application belongs to the field of new energy, and discloses a synthesis method of lithium tetrafluoroborate, which comprises the following steps: step 1: adding lithium halide into a non-aqueous organic solvent, and introducing boron trichloride to obtain a solution containing lithium haloborate; and step 2: introducing hydrogen fluoride into the solution obtained in step 1 to obtain a solution containing lithium tetrafluoroborate. The method is synthesized by using a solvent method, and any available lithium halide and boron trichloride are used to react to obtain an intermediate product, and then the intermediate product is fluorinated to obtain lithium tetrafluoroborate, and various lithium halides can be selected to realize the scheme of the application, the raw materials are rich in selectivity, and the production cost is significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of new energy, specifically relating to a method for synthesizing lithium tetrafluoroborate and an electrolyte. Background Technology

[0002] The main methods for preparing LiBF4 include solid-phase-gas phase contact method (CN101863489), non-aqueous solution method (CN115260239A), aqueous solution method (US6623717), and ion exchange method (CN104030310). The solid-phase-gas phase contact method synthesizes LiBF4 at high temperatures using basic lithium salts as raw materials. This method requires sophisticated equipment, strict process control, is difficult to synthesize, has low reaction efficiency, and is difficult to scale up. The non-aqueous solution method involves forming a suspension of lithium fluoride in an organic solvent, which then reacts with BF3 to generate LiBF4. However, this method requires sophisticated equipment, has difficult-to-obtain raw materials, and has high production costs. The aqueous solution method uses boric acid to react with HF aqueous solution to prepare tetrafluoroboric acid, which is then reacted with carbonate to obtain lithium tetrafluoroborate solution. After concentration, crystallization, and drying, the product is obtained. However, in this method, lithium tetrafluoroborate exists in monohydrate or trihydrate form, resulting in low product purity and difficulties in drying and dehydration. The ion exchange method utilizes the difference in solubility between potassium tetrafluoroborate and lithium tetrafluoroborate to obtain a crude product, which is then further recrystallized to obtain a qualified product.

[0003] Solid-phase-gas phase contact, aqueous solution, and ion exchange methods are no longer widely used due to preparation difficulties, equipment requirements, and purification requirements. Currently, non-aqueous solution methods and rheological phase methods are more popular. See the following scheme for details:

[0004] Non-aqueous solution method:

[0005] D1: CN115260239A discloses lithium difluorooxalate phosphate and its preparation method, including: S1. Mixing a solvent, anhydrous lithium fluoride and boron trifluoride solution, stirring and filtering to obtain lithium tetrafluoroborate solution; S2. Adding anhydrous oxalic acid and silicon tetrachloride to the lithium tetrafluoroborate solution and reacting to obtain crude lithium difluorooxalate phosphate; S3. Purifying the crude lithium difluorooxalate phosphate to obtain refined lithium difluorooxalate phosphate.

[0006] D2: CN114477201A discloses a method for preparing lithium tetrafluoroborate, comprising: dissolving a complex of lithium fluoride (LiF) and boron trifluoride in DMC and reacting it at 64-80°C.

[0007] Rheological phase method:

[0008] D3: CN107585776A discloses a method for synthesizing lithium tetrafluoroborate by rheophase method. Boron trichloride is used as raw material, and the intermediate product boron trifluoride is obtained by fluorination with anhydrous hydrofluoric acid. Then, it is reacted with a rheophase material made of high-purity lithium fluoride solid powder and anhydrous hydrofluoric acid. After concentration, crystallization, separation and purification, the finished product lithium tetrafluoroborate is obtained.

[0009] Regardless of whether it's a non-aqueous solution method, a rheotropic phase method, or the less commonly used solid-gas phase contact method, aqueous solution method, or ion exchange method, the raw materials generally used contain at least lithium fluoride and / or boron trifluoride. In particular, CN107585776A emphasizes the use of high-purity lithium fluoride solid powder. All of the above methods share the following common technical problems:

[0010] 1. The raw material source is singular. CN101863489, CN115260239A, CN114477201A, and CN107585776A all use boron trifluoride and lithium fluoride. A singular source of raw materials means that the purity of the raw materials must be very high. For example, CN107585776A clearly states that high-purity lithium fluoride solid powder must be used. If other halogenated lithiums are mixed in the powder, impurities will be generated, affecting the purity of the product. At the same time, a singular source of raw materials means that it is very likely that the cheaper materials will be used instead of the more expensive ones.

[0011] 2. Expensive: Boron trifluoride and lithium chloride are more expensive than boron trichloride and lithium chloride; for schemes using rheophase as the reaction system, the price of the rheophase is higher than that of other solvent systems.

[0012] 3. High equipment requirements: The scheme with rheological phase as the reaction system has high corrosion protection requirements.

[0013] Therefore, the technical problems to be solved in this project are: how to make the selection of raw materials more diverse and how to reduce production costs during the production of lithium tetrafluoroborate. Summary of the Invention

[0014] To address the shortcomings of existing technologies, the present invention aims to provide a method for synthesizing lithium tetrafluoroborate. This method employs a solvent synthesis approach, first reacting any available lithium halide with boron trichloride to obtain an intermediate product, which is then uniformly fluorinated to obtain lithium tetrafluoroborate. Various lithium halides can be selected to achieve the scheme of the present invention, thus enriching the selectivity of raw materials and significantly reducing production costs.

[0015] The basis of the process route of synthesis followed by fluorination in this invention is that boron trichloride is more reactive than boron trifluoride. Boron trifluoride can only react with lithium fluoride, while boron trichloride can react with any lithium halide. Based on this characteristic, combined with the subsequent fluorination operation, lithium tetrafluoroborate with high purity and high yield can be produced.

[0016] Furthermore, this invention can use not only various lithium halides as raw materials, but also mixtures of various lithium halides as raw materials, which significantly reduces the purity requirements of the raw materials and further reduces production costs. At the same time, the process of this invention allows manufacturers to flexibly use raw materials according to the price difference of lithium halides, so that the product cost remains at the lowest level in the industry.

[0017] To achieve this objective, the present invention employs the following technical solution: a method for synthesizing lithium tetrafluoroborate, comprising the following steps:

[0018] Step 1: Add lithium halide to a non-aqueous organic solvent, pass boron trichloride through, and react to obtain a solution containing lithium haloborate;

[0019] Step 2: Pass hydrogen fluoride into the solution obtained in Step 1, and react to obtain a solution containing lithium tetrafluoroborate.

[0020] The reaction equations for steps 1 and 2 are as follows:

[0021]

[0022] X = F, Cl, Br, l

[0023] a = 1, 2, 3, 4

[0024] b = 3, 2, 1, 0.

[0025] In the above-described method for synthesizing lithium tetrafluoroborate, the lithium halide is one or a combination of lithium fluoride, lithium chloride, lithium bromide, and lithium iodide.

[0026] In the above-described method for synthesizing lithium tetrafluoroborate, the molar ratio of lithium halide to boron trichloride is 1:0.9 to 1.1.

[0027] In actual production, too much boron trichloride wastes raw materials, while too little boron trichloride affects reaction efficiency and results in incomplete reaction. Therefore, theoretically speaking, if only the basic purpose of preparing lithium tetrafluoroborate is considered, any ratio of lithium halide to boron trichloride is applicable to this invention.

[0028] In practical applications, to maximize the yield, a slight excess of boron trichloride is recommended. This slight excess means that the amount of boron trichloride used is more than 1 mole but less than 1.1 moles compared to 1 mole of lithium halide.

[0029] The yield described in this invention is calculated based on the Li element. If the molar ratio of lithium halide to boron trichloride is 1:1, the theoretical yield of lithium tetrafluoroborate is considered to be 1 mole; if the molar ratio of lithium halide to boron trichloride is 1:0.9 or 0.9:1, the theoretical yield of lithium tetrafluoroborate is considered to be 0.9 moles.

[0030] In some implementations, the molar ratio of lithium halide to boron trichloride is 1:0.9, 1:0.92, 1:0.94, 1:0.96, 1:0.98, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, or 1:1.1.

[0031] In the above-described method for synthesizing lithium tetrafluoroborate, the mass ratio of lithium halide to anhydrous hydrogen fluoride is 1:2 to 10.

[0032] In actual production, too little hydrogen fluoride will result in incomplete fluorination, affecting product quality, while too much hydrogen fluoride will waste raw materials and increase the workload of recycling. If only the basic purpose of preparing lithium tetrafluoroborate is considered, any ratio of lithium halide to anhydrous hydrogen fluoride is applicable to this invention.

[0033] In some implementations, the mass ratio of lithium halide to anhydrous hydrogen fluoride is 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10.

[0034] In the above-mentioned method for synthesizing lithium tetrafluoroborate, the non-aqueous organic solvent is any combination of one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinylene carbonate, propylene carbonate, methyl carbonate, 1-fluoroethylene carbonate, ethyl acetate, butyl acetate, and diethyl ether.

[0035] In practical use, the purity of the non-aqueous organic solvent is greater than 99.95%, and the water content is less than 10 ppm.

[0036] In the above-mentioned method for synthesizing lithium tetrafluoroborate, the reaction temperature in step 1 is 10–90°C, and the reaction time is 1–24 h.

[0037] More specifically, the reaction temperature conditions in step 1 of this invention are very mild, and it is generally recommended to carry out the reaction at room temperature; the reaction in step 1 can be completed in a relatively short time.

[0038] Preferably, the reaction temperature in step 1 is 10–40°C, and the reaction time is 1–5 h.

[0039] In some implementation examples, the reaction temperature in step 1 is 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, or 90℃; the reaction time is 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 15h, 18h, 20h, or 24h.

[0040] In the above-described method for synthesizing lithium tetrafluoroborate, the reaction temperature in step 2 is 0–90°C, and the reaction time is 3–10 h. Generally, a higher temperature results in a faster reaction rate. However, excessively high temperatures may lead to product decomposition, resulting in a lower yield. Conversely, excessively low temperatures result in a slower reaction rate and a lower yield. This invention recommends a reaction temperature of room temperature.

[0041] In the above-described method for synthesizing lithium tetrafluoroborate, the reaction pressure in step 2 is 1–10 atm. Higher pressure allows for a correspondingly higher reaction temperature and a faster reaction rate. Conversely, lower pressure limits the upper limit of the reaction temperature, slows the reaction rate, and reduces the yield. Therefore, this invention preferably operates under pressure; however, it does not oppose operation at atmospheric pressure, and atmospheric pressure is also suitable for this invention when yield is not a concern.

[0042] In the above-mentioned method for synthesizing lithium tetrafluoroborate, step 3 specifically involves: concentrating the solution obtained in step 2 to obtain crude lithium tetrafluoroborate, and recrystallizing the crude lithium tetrafluoroborate to obtain lithium tetrafluoroborate crystals.

[0043] In the above-mentioned method for synthesizing lithium tetrafluoroborate, the method for concentrating the solution obtained in step 2 is as follows: the solution obtained in step 2 is concentrated by heating under reduced pressure, and crude lithium tetrafluoroborate is precipitated from the solution and filtered to obtain crude lithium tetrafluoroborate.

[0044] The method for recrystallizing crude lithium tetrafluoroborate to obtain lithium tetrafluoroborate crystals is as follows:

[0045] The crude lithium tetrafluoroborate was dissolved in a good solvent, and then a poor solvent was added to precipitate lithium tetrafluoroborate crystals. The crystals were then dried under reduced pressure to obtain lithium tetrafluoroborate crystals.

[0046] The good solvent is any combination of one or more of the following: ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinylene carbonate, propylene carbonate, methyl carbonate, 1-fluoroethylene carbonate, ethyl acetate, butyl acetate, and diethyl ether.

[0047] The undesirable solvent is one or more of toluene, xylene, trimethylbenzene, dichloromethane, dichloroethane, n-hexane, cyclohexane, and n-heptane, or any combination thereof.

[0048] The preferred mass ratio of undesirable solvent to good solvent during recrystallization is 2–10:1. Adding too much undesirable solvent results in a high product yield but compromises purity and increases the system volume, thus increasing the workload of solvent recovery. Adding too little undesirable solvent reduces the product yield.

[0049] Meanwhile, the present invention also discloses an electrolyte containing an organic solvent and a lithium salt; at least a portion of the lithium salt is lithium tetrafluoroborate prepared by any of the methods described above.

[0050] In the electrolyte described above, the concentration of the lithium salt is 0.5–1.5 M.

[0051] It should be noted that M represents moles per liter.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) The solvent method is used to synthesize the product. First, any available lithium halide and boron trichloride are reacted to obtain an intermediate product, and then fluorinated to obtain lithium tetrafluoroborate. Various lithium halides can be selected to realize the scheme of the present invention. The raw materials can be selectively enriched, and the production cost is significantly reduced.

[0054] The basis of the process route of synthesis followed by fluorination in this invention is that boron trichloride is more reactive than boron trifluoride. Boron trifluoride can only react with lithium fluoride, while boron trichloride can react with any lithium halide. Based on this characteristic, combined with the subsequent fluorination operation, lithium tetrafluoroborate with high purity and high yield can be produced.

[0055] Furthermore, this invention can use not only various lithium halides as raw materials, but also mixtures of various lithium halides as raw materials, which significantly reduces the purity requirements of the raw materials and further reduces production costs. At the same time, the process of this invention allows manufacturers to flexibly use raw materials according to the price difference of lithium halides, so that the product cost remains at the lowest level in the industry.

[0056] (2) The present invention has low overall production cost. The present invention can select the lowest priced lithium halide according to market price fluctuations. At the same time, the price of boron trichloride used in the present invention is much lower than that of boron trifluoride. In addition, the present invention does not need to use too much hydrogen fluoride. The combination of these factors can reduce the cost of the present invention by about 30% compared with CN107585776A.

[0057] (3) Compared with the rheological phase system, the present invention uses only a small amount of hydrogen fluoride in the post-fluorination step, which can significantly reduce the corrosion protection requirements of the equipment. Attached Figure Description

[0058] Figure 1 The nuclear magnetic resonance (B-NMR) spectrum of the product of Example 1;

[0059] Figure 2 The fluorine nuclear magnetic resonance (F-NMR) spectrum of the product of Example 1;

[0060] Figure 3 The nuclear magnetic resonance (B-NMR) spectrum of the product of Example 2;

[0061] Figure 4 The fluorine nuclear magnetic resonance (F-NMR) spectrum of the product in Example 2 is shown. Detailed Implementation

[0062] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0063] The raw materials, solvents, and reaction apparatus used in this application have all undergone dehydration treatment.

[0064] Example 1

[0065] At room temperature, 500 g of dehydrated methyl ethyl carbonate and 42.4 g (1 mol) of lithium chloride were added to a 1 L reactor. The mixture was stirred for 0.5 h, then 117.2 g (1 mol) of boron trichloride was introduced, and the reaction was stirred for 2 h to obtain a mixed solution of lithium tetrachloroborate. Then, 127.2 g of anhydrous hydrogen fluoride was introduced, and the temperature was raised to 60 °C. The reaction was carried out for 3 h at a pressure of 2 atm. The reaction mixture was filtered, and the filtrate was concentrated and dried under reduced pressure at 60 °C to obtain 94.2 g of crude lithium tetrafluoroborate. 350 g of methyl ethyl carbonate was added, and the mixture was heated to dissolve at 60 °C. The solution was filtered while hot to remove insoluble matter. 1050 g of toluene was added to the filtrate, and a solid precipitated. After filtration and drying under reduced pressure at 100 °C, 85.8 g of lithium tetrafluoroborate product was obtained, with a yield of 91.5% and a purity of 99.87%.

[0066] The NMR spectrum of the product can be referenced. Figure 1 and Figure 2 , Figure 1 The image shows a nuclear magnetic resonance (B-NMR) spectrum. Figure 2 The image shows the fluorine nuclear magnetic resonance (F-NMR) spectrum of the product from Example 1.

[0067] Example 2

[0068] At room temperature, 500 g of dehydrated diethyl carbonate and 26.0 g (1 mol) of lithium fluoride were added to a 1 L reactor. The mixture was heated to 40 °C and stirred for 0.5 h. Then, 118.0 g (1 mol) of boron trichloride was introduced, and the mixture was stirred for 2 h to obtain a mixed solution of lithium monofluoroborate. 105 g of anhydrous hydrogen fluoride was then introduced, and the mixture was heated to 70 °C and reacted at 3.5 atm for 3 h. The reaction mixture was then filtered, and the filtrate was concentrated and dried under reduced pressure at 70 °C to obtain 93.8 g of crude lithium tetrafluoroborate. 300 g of dimethyl carbonate was added, and the mixture was heated to 70 °C to dissolve the crude product. The solution was filtered while hot to remove insoluble matter. 1000 g of dichloromethane was added to the filtrate, and a solid precipitated. After filtration and drying under reduced pressure at 100 °C, 88.2 g of lithium tetrafluoroborate product was obtained, with a yield of 94.1% and a purity of 99.79%.

[0069] The NMR spectrum of the product can be referenced. Figure 3 and Figure 4 , Figure 3The nuclear magnetic resonance (B-NMR) spectrum of the product of Example 2; Figure 4 The fluorine nuclear magnetic resonance (F-NMR) spectrum of the product in Example 2 is shown.

[0070] Example 3

[0071] At room temperature, 500 g of dehydrated propylene carbonate and 86.8 g (1 mol) of lithium bromide were added to a 1 L reactor. The mixture was heated to 45 °C and stirred for 0.5 h. Then, 118.0 g (1 mol) of boron trichloride was introduced, and the mixture was stirred for 2 h to obtain a mixed solution of lithium monobromotrichloroborate. 105 g of anhydrous hydrogen fluoride was then introduced, and the mixture was heated to 60 °C and reacted at 1.5 atm for 4 h. The reaction mixture was then filtered, and the filtrate was concentrated and dried under reduced pressure at 65 °C to obtain 93.8 g of crude lithium tetrafluoroborate. 300 g of propylene carbonate was added, and the mixture was heated to 80 °C to dissolve the crude product. The solution was filtered while hot to remove insoluble matter. 1000 g of n-hexane was added to the filtrate, and a solid precipitated. After filtration and drying under reduced pressure at 90 °C, 90.2 g of lithium tetrafluoroborate product was obtained, with a yield of 96.2% and a purity of 98.62%.

[0072] Example 4

[0073] At room temperature, 500 g of dehydrated methyl ethyl carbonate and 38.2 g (0.9 mol) of lithium chloride were added to a 1 L reactor. The mixture was stirred for 0.5 h, then 117.2 g (1 mol) of boron trichloride was introduced, and the reaction was stirred for 2 h to obtain a mixed solution of lithium tetrachloroborate. 127.2 g of anhydrous hydrogen fluoride was then introduced, and the mixture was heated to 30 °C and reacted at 4 atm for 3 h. The reaction was then complete. The reaction mixture was filtered, and the filtrate was concentrated and dried under reduced pressure at 60 °C to obtain 86.2 g of crude lithium tetrafluoroborate. 350 g of methyl ethyl carbonate was added, and the mixture was heated to 60 °C to dissolve the crude product. The solution was filtered while hot to remove insoluble matter. 1050 g of toluene was added to the filtrate, and a solid precipitated. 78.5 g of lithium tetrafluoroborate product was obtained by filtration and drying under reduced pressure at 100 °C, with a yield of 93.0% and a purity of 98.63%.

[0074] Example 5

[0075] At room temperature, 500 g of dehydrated methyl ethyl carbonate and 46.6 g (1.1 mol) of lithium chloride were added to a 1 L reactor. The mixture was stirred for 1 h, then 117.2 g (1 mol) of boron trichloride was introduced, and the reaction was stirred for 2 h to obtain a mixed solution of lithium tetrachloroborate. Then, 127.2 g of anhydrous hydrogen fluoride was introduced, the temperature was lowered to 0 °C, and the reaction was carried out at a pressure of 6 atm for 3 h. The reaction mixture was filtered, and the filtrate was concentrated and dried under reduced pressure at 60 °C to obtain 95.5 g of crude lithium tetrafluoroborate. 350 g of methyl ethyl carbonate was added, and the mixture was heated to dissolve at 60 °C. The solution was filtered while hot to remove insoluble matter, and 1050 g of n-heptane was added to the resulting filtrate, precipitating a solid. After filtration and drying under reduced pressure at 100 °C, 86.4 g of lithium tetrafluoroborate product was obtained, with a yield of 92.2% and a purity of 99.11%.

[0076] Example 6

[0077] At room temperature, 500 g of dehydrated methyl ethyl carbonate and 44.5 g (1.05 mol) of lithium chloride were added to a 1 L reactor. The mixture was stirred for 1 h, then 117.2 g (1 mol) of boron trichloride was introduced, and the reaction was stirred for 2 h to obtain a mixed solution of lithium tetrachloroborate. Then, 127.2 g of anhydrous hydrogen fluoride was introduced, and the temperature was raised to 80 °C. The reaction was carried out at 4 atm for 3 h, after which the reaction was complete. The reaction mixture was filtered, and the filtrate was concentrated and dried under reduced pressure at 60 °C to obtain 96.1 g of crude lithium tetrafluoroborate. 350 g of methyl ethyl carbonate was added, and the mixture was heated to dissolve at 60 °C. The solution was filtered while hot to remove insoluble matter, and 1050 g of cyclohexane was added to the resulting filtrate, precipitating a solid. After filtration and drying under reduced pressure at 100 °C, 85.4 g of lithium tetrafluoroborate product was obtained, with a yield of 91.1% and a purity of 99.35%.

[0078] Example 7

[0079] At room temperature, 500g of dehydrated methyl ethyl carbonate and 40.3g (0.95mol) of lithium chloride were added to a 1L reactor. The mixture was stirred for 1 hour, then 117.2g (1mol) of boron trichloride was introduced, and the reaction was stirred for 2 hours to obtain a mixed solution of lithium tetrachloroborate. 127.2g of anhydrous hydrogen fluoride was then introduced, and the mixture was heated to 90℃ and reacted at 5 atm for 3 hours. The reaction was then complete. The reaction mixture was filtered, and the filtrate was concentrated and dried under reduced pressure at 60℃ to obtain 90g of crude lithium tetrafluoroborate. 350g of methyl ethyl carbonate was added, and the mixture was heated to 60℃ to dissolve the crude product. The solution was filtered while hot to remove insoluble matter. 1050g of cyclohexane was added to the resulting filtrate, precipitating a solid. 82.7g of lithium tetrafluoroborate product was obtained by filtration and drying under reduced pressure at 100℃, yielding a yield of 92.8% and a purity of 98.97%.

[0080] Comparative Example 1

[0081] At room temperature, 500 g of dehydrated ethyl methyl carbonate and 42.4 g (1.0 mol) of lithium chloride were added to a 1 L reactor. The mixture was stirred for 1 h, then 68.0 g (1.0 mol) of boron trifluoride was introduced, and the reaction was stirred for 2 h to obtain a solid-liquid mixture. Then, 127.2 g of anhydrous hydrogen fluoride was introduced, and the mixture was heated to 90 °C and reacted at 6 atm for 3 h. The reaction was then complete. The reaction mixture was filtered, and the filtrate was concentrated and dried under reduced pressure at 60 °C to obtain 28 g of crude product. 350 g of ethyl methyl carbonate was added, and the mixture was heated to 60 °C, where it remained essentially insoluble. 1050 g of cyclohexane was added to the resulting mixture, and a solid precipitated. The solid was filtered and dried under reduced pressure at 100 °C to obtain 25.4 g of solid. The product was identified as lithium fluoride.

[0082] The product was tested using the method described in GB / T 22660.1-2008. The content of free F in the sample was determined according to Part 3: Determination of fluorine content by distillation-thorium nitrate volumetric method. The element Li was detected by inductively coupled plasma (ICP) method, which confirmed that the substance in the product was lithium fluoride.

[0083] Results analysis:

[0084] 1. As can be seen from Example 1 and Comparative Example 1, boron trichloride is more reactive than boron trifluoride. Boron trifluoride cannot react with lithium chloride, while boron trichloride can react with any lithium halide. Based on this characteristic, combined with the fluorination operation, lithium tetrafluoroborate with high purity and high yield can be produced.

[0085] 2. As can be seen from Examples 5 and 6, an excess of lithium halide is undesirable as it leads to material waste, but this does not hinder the smooth implementation of the present invention. As can be seen from Examples 1, 4, and 7, an appropriate excess of boron trichloride can help to moderately improve the yield.

[0086] 3. As can be seen from Examples 1-7, the entire reaction process of the present invention can be carried out under extremely mild temperature conditions. The fluorination operation only accompanies the latter half of the reaction of the present invention and is not a rheo-phase reaction of hydrogen fluoride. Therefore, its overall reaction conditions are much milder than those of the prior art, providing a feasible basis for industrial scaling.

[0087] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, nor does it mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for synthesizing lithium tetrafluoroborate, characterized in that, Includes the following steps: Step 1: Add lithium halide to a non-aqueous organic solvent, pass boron trichloride through, and react to obtain a solution containing lithium haloborate; Step 2: Pass hydrogen fluoride into the solution obtained in Step 1, and react to obtain a solution containing lithium tetrafluoroborate; The reaction equations for steps 1 and 2 are as follows: ； Where X is F, Cl, Br or I; a is 1, 2 or 3; b is 1, 2 or 3.

2. The method for synthesizing lithium tetrafluoroborate according to claim 1, characterized in that, The molar ratio of lithium halide to boron trichloride is 1:0.9~1.

1.

3. The method for synthesizing lithium tetrafluoroborate according to claim 1, characterized in that, The mass ratio of lithium halide to anhydrous hydrogen fluoride is 1:2~10.

4. The method for synthesizing lithium tetrafluoroborate according to claim 1, characterized in that, The non-aqueous organic solvent is any combination of one or more of the following: ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinylene carbonate, propylene carbonate, methyl carbonate, 1-fluoroethylene carbonate, ethyl acetate, butyl acetate, and diethyl ether.

5. The method for synthesizing lithium tetrafluoroborate according to claim 1, characterized in that, The reaction temperature in step 1 is 10~90℃, and the reaction time is 1~24h.

6. The method for synthesizing lithium tetrafluoroborate according to claim 1, characterized in that, The reaction temperature in step 2 is 0~90℃, and the reaction time is 3~10h.

7. The method for synthesizing lithium tetrafluoroborate according to claim 1, characterized in that, The reaction pressure in step 2 is 1~10 atm.

8. The method for synthesizing lithium tetrafluoroborate according to claim 1, characterized in that, It also includes step 3, which specifically involves: concentrating the solution obtained in step 2 to obtain crude lithium tetrafluoroborate, and recrystallizing the crude lithium tetrafluoroborate to obtain lithium tetrafluoroborate crystals.

9. The method for synthesizing lithium tetrafluoroborate according to claim 8, characterized in that, The method for concentrating the solution obtained in step 2 is as follows: the solution obtained in step 2 is concentrated by heating under reduced pressure, and crude lithium tetrafluoroborate is precipitated from the solution. The crude lithium tetrafluoroborate is obtained by filtration. The method for recrystallizing crude lithium tetrafluoroborate to obtain lithium tetrafluoroborate crystals is as follows: The crude lithium tetrafluoroborate was dissolved in a good solvent, and then a poor solvent was added to precipitate lithium tetrafluoroborate crystals. The crystals were then dried under reduced pressure to obtain lithium tetrafluoroborate crystals. The good solvent is any combination of one or more of the following: ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinylene carbonate, propylene carbonate, methyl carbonate, 1-fluoroethylene carbonate, ethyl acetate, butyl acetate, and diethyl ether. The undesirable solvent is one or more of toluene, xylene, trimethylbenzene, dichloromethane, dichloroethane, n-hexane, cyclohexane, and n-heptane, or any combination thereof.

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