Safe preparation method of lithium tetrafluoroborate

Abstract

The invention provides a safe preparation method of lithium tetrafluoroborate, comprising: feeding through a boron trifluoride air inlet pipe and an ether feed inlet to form a complex between boron trifluoride and ether; introducing an anhydrous hydrogen fluoride solution and a boron trifluoride / ether complex into a first tank body 11 for reaction; heating and distilling the first tank body through a temperature control jacket to obtain a fluoroboric acid solution; introducing the fluoroboric acid solution into a second tank body through a fluoroboric acid feed inlet, and then uniformly adding lithium sulfate particles mixed with molecular sieves to react; after the reaction is finished or during the reaction, adding a solvent through a first solvent addition inlet to dissolve a crude lithium tetrafluoroborate product to form a crude lithium tetrafluoroborate solution; introducing nitrogen through a third nitrogen inlet for pressure filtration to slowly input the crude lithium tetrafluoroborate solution into a reduced pressure spray concentration unit; during the process of introducing nitrogen through the third nitrogen inlet for pressure filtration, simultaneously opening a spray unit for spray drying to obtain a crude lithium tetrafluoroborate product.

Description

Technical Field

[0001] The invention relates to a safe preparation method of lithium tetrafluoroborate. Background Art

[0002] At present, lithium tetrafluoroborate is mainly used as an electrolyte lithium salt in lithium-ion battery electrolytes. The classic electrolyte system currently used in lithium-ion secondary batteries is an electrolyte salt dissolved in an organic aprotic solvent. Lithium tetrafluoroborate (LiBF4) has good chemical stability and thermal stability, is insensitive to environmental moisture, and has the potential to develop into an excellent electrolyte system widely used in the field of energy storage and power lithium-ion batteries. At present, the preparation method of lithium tetrafluoroborate includes an aqueous solution method. In the preparation process of lithium tetrafluoroborate, boron trifluoride / ether complex is required, but boron trifluoride is easily deliquesced in water vapor to form fluoride, which endangers the health of operators. Summary of the invention

[0003] The present invention provides a safe preparation method of lithium tetrafluoroborate, which can effectively solve the above problems.

[0004] The present invention is achieved in that:

[0005] The present invention provides a safe preparation method of lithium tetrafluoroborate, comprising:

[0006] S11, feeding through the boron trifluoride air inlet pipe and the ether feed port, and controlling the heating jacket to heat the mixing tube to a temperature of 34.5° C. to 126° C., so that the boron trifluoride and the ether form a complex, and the step S11 is performed by the mixing unit;

[0007] S21, introducing anhydrous hydrogen fluoride solution and boron trifluoride / ether complex into the first tank 11 for reaction, wherein the molar ratio of the anhydrous hydrogen fluoride solution to boron trifluoride is 1 to 1.2:1;

[0008] S22, after the reaction is completed, heating and distilling the first tank body through the temperature control jacket to obtain a fluoroboric acid solution, wherein the temperature range of the evaporation concentration is 40 to 70° C.;

[0009] S31, passing the fluoroboric acid solution into the second tank through the fluoroboric acid feeding port, and then evenly adding lithium sulfate particles mixed with molecular sieves to react;

[0010] S32, after the reaction is completed or during the reaction, adding a solvent through the first solvent addition port to dissolve the crude lithium tetrafluoroborate to form a crude lithium tetrafluoroborate solution;

[0011] S41, introducing nitrogen through the third nitrogen inlet for pressure filtration, so that the crude lithium tetrafluoroborate solution is slowly input into the vacuum spray concentration unit;

[0012] S50, while nitrogen is introduced through the third nitrogen inlet for pressure filtration, the spray unit is simultaneously turned on for spray drying to remove most of the solvent to obtain crude lithium tetrafluoroborate.

[0013] The beneficial effects of the present invention are as follows: the safe preparation method provided by the present invention performs a complexation reaction of boron trifluoride and ether through a mixing unit, thereby preventing boron trifluoride from deliquescing in the air, which is beneficial to improving the safety of production; further, the present invention further provides a new preparation method of lithium tetrafluoroborate, which has the characteristics of simple operation, easy industrialization, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 It is a schematic structural diagram of a lithium tetrafluoroborate preparation system provided in an embodiment of the present invention.

[0016] Figure 2 It is a schematic diagram of the structure of a mixing unit in a lithium tetrafluoroborate preparation system provided in an embodiment of the present invention.

[0017] Figure 3 The present invention provides a flow chart of a safe method for preparing lithium tetrafluoroborate. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0020] Reference Figure 1 As shown, an embodiment of the present invention provides a lithium tetrafluoroborate preparation system, comprising:

[0021] The mixing unit 50 includes a barrel 51, a water filter plate 52 arranged in the middle of the barrel 51, a mixing tube 53 arranged on the upper part of the water filter plate 52, an air distribution plate 54 arranged on the top of the mixing tube 53, a fourth stirring unit 56 penetrating the air distribution plate 54, the mixing tube 53 and the water filter plate 52, and an air supply assembly 55.

[0022] Reference Figure 2 As shown, the mixing unit 50 is mainly used to automatically mix boron trifluoride and ether to form a complex, thereby preventing the danger caused by manual mixing. Boron trifluoride is easily hydrolyzed when it comes into contact with water or humid air, and produces toxic fluoride smoke that is extremely harmful to the human body. Therefore, the present invention can greatly reduce the danger caused by manual mixing in the prior art by automatically mixing boron trifluoride and ether.

[0023] The barrel 51 includes a complex sampling port 510 and a boron trifluoride discharge port 511 arranged at the bottom, a mixing chamber 512 arranged at the top of the mixing tube 53, a boron trifluoride feed port 514 and an ether feed port 513 arranged at the top, and a heating jacket 515 arranged on the periphery of the mixing tube 53.

[0024] The barrel 51 can be divided into three detachable structures: upper, middle and lower parts. Specifically, the barrel part corresponding to the mixing chamber 512, the barrel part corresponding to the mixing tube 53, and the barrel part corresponding to the lower part of the water filter plate 52 can be detachably connected by flanges, etc., so as to facilitate the cleaning and maintenance of the mixing tube 53.

[0025] The mixing chamber 512 is used to premix the introduced boron trifluoride and diethyl ether, and then feed them evenly through the gas distribution plate 54 .

[0026] The air distribution plate 54 is used to uniformly feed the material into the mixing chamber 512. The air distribution plate 54 has a plurality of uniformly distributed through-hole structures, and the hole diameter thereof is 0.1 mm to 1 mm. In one embodiment, the hole diameter of the air distribution plate 54 is about 0.2 mm.

[0027] The mixing tube 53 is an inverted cochlear structure 531, and is arranged in two rows along the vertical direction, with the top of one row of cochlear structures facing the middle of the other row of cochlear structures 531. When the boron trifluoride gas carries the ether liquid into the cochlear structure 531, due to the inverted structure of the cochlear structure 531, the gas repeatedly collides in the cochlear structure 531 to quickly form a complex.

[0028] Furthermore, in one embodiment, the cochlear structure 531 is filled with metal balls 532. The metal balls 532 can be made of inert materials such as stainless steel, and the main function of the metal balls 532 is to have a large heat capacity to prevent drastic temperature changes.

[0029] The heating jacket 515 is used to heat the mixing tube 53 to a temperature above the boiling point of ether and below the boiling point of the boron trifluoride / ether complex, that is, the heating jacket 515 is used to heat the mixing tube 53 to 34.5°C to 126°C. This is because when heated to a temperature above the boiling point of ether, the ether will vaporize and fully mix with boron trifluoride to form a complex; and heating to a temperature below the boiling point of the boron trifluoride / ether complex is to prevent the complex from vaporizing after formation and flowing to the bottom for liquid discharge. Preferably, the heating jacket 515 is used to heat the mixing tube 53 to 40°C to 100°C. More preferably, the heating jacket 515 is used to heat the mixing tube 53 to 50°C to 60°C, at which temperature the boron trifluoride gas and the ether vapor can quickly form a complex. In one embodiment, the heating jacket 515 is used to heat the mixing tube 53 to 55±1°C.

[0030] The gas supply assembly 55 includes an inert gas inlet pipe 551 , a boron trifluoride inlet pipe 552 , and an air pump 553 . The inert gas inlet pipe 551 is used to introduce nitrogen gas to drive away the water vapor in the barrel 51 .

[0031] Specifically, the control of the mixing unit 50 includes the following steps:

[0032] S10, introducing nitrogen gas through the inert gas inlet pipe 551 to drive off the water vapor in the barrel 51;

[0033] S11, feed the material through the boron trifluoride inlet pipe 552 and the ether feed port 513, and control the heating jacket 515 to heat the mixing tube 53 to a temperature of 34.5° C. to 126° C., so that the boron trifluoride and the ether form a complex.

[0034] In step S11, preferably, the heating jacket 515 is controlled to heat the mixing tube 53 to a temperature of 50° C. to 60° C. In this step, since the heating temperature reaches the boiling points of boron trifluoride and ether, the ether will vaporize and fully collide with boron trifluoride in the mixing tube 53 to form a complex with a boiling point of 126° C., and then flow to the bottom for collection.

[0035] In step S11, the following steps may be further included:

[0036] Sampling and analysis are performed through the complex sampling port 510, and after sampling and analysis, liquid is discharged.

[0037] The first reaction tank 10 comprises a first tank body 11, a temperature control jacket 12 arranged on the outer surface of the first tank body 11, and a first stirring unit 13, wherein the first tank body 11 also comprises a boron trifluoride / ether solution feeding port 110, an anhydrous hydrogen fluoride solution feeding port 111, a first exhaust port 112, a first nitrogen inlet 113, and a first discharge port 114 arranged at the bottom.

[0038] The first reaction tank 10 is used to react the boron trifluoride / ether solution with the anhydrous hydrogen fluoride solution to generate a fluoroboric acid solution. The chemical reaction equation is as follows:

[0039] HF+BF3﹒ (C2O5)2O---->HBF4+(C2O5)2O.

[0040] The theoretical molar ratio of the reaction of anhydrous hydrogen fluoride solution and boron trifluoride is 1:1. However, since the anhydrous hydrogen fluoride solution is relatively volatile under normal temperature conditions, in order to make the boron trifluoride react as much as possible, preferably, the molar ratio of the anhydrous hydrogen fluoride solution to boron trifluoride is 1 to 1.2:1. More preferably, the molar ratio of the anhydrous hydrogen fluoride solution to boron trifluoride is 1.08 to 1.1:1. In many embodiments, the molar ratios of the anhydrous hydrogen fluoride solution to boron trifluoride are 1.02:1, 1.05:1, 1.08:1 and 1.11:1, respectively.

[0041] After the reaction of the anhydrous hydrogen fluoride solution and the boron trifluoride / ether complex is completed, the solution needs to be distilled to obtain a fluoroboric acid solution. Specifically, the temperature range of the evaporation concentration is 40 to 70°C. The temperature of evaporation concentration should not be too high, as it will easily cause the decomposition of fluoroboric acid. More preferably, the temperature range of the evaporation concentration is 60 to 70°C. In several embodiments, the temperatures of the evaporation concentration are 50°C, 55°C, 60°C and 65°C, respectively.

[0042] The control of the first reaction tank 10 is as follows:

[0043] S20, introducing nitrogen through the first nitrogen inlet 113 to remove air and other water vapor in the first tank body 11;

[0044] S21, introducing anhydrous hydrogen fluoride solution and boron trifluoride / ether complex into the first tank 11 for reaction, wherein the molar ratio of the anhydrous hydrogen fluoride solution to boron trifluoride is 1 to 1.2:1;

[0045] S22, after the reaction is completed, the first tank body 11 is heated and distilled by the temperature control jacket 12 to obtain a fluoroboric acid solution, wherein the temperature range of the evaporation concentration is 40-70°C.

[0046] In step S20 , the concentration of the exhaust gas may be detected through the first exhaust port 112 , and the process ends when the concentration is lower than a set value.

[0047] In step S21, the boron trifluoride / ether complex is first introduced into the first tank 11, and then the anhydrous hydrogen fluoride solution is pumped in batches. This has the advantage that the anhydrous hydrogen fluoride solution is diluted by the boron trifluoride / ether complex to reduce the corrosion of the first tank 11 and the first stirring unit 13.

[0048] In step S22, the concentration of the exhausted ether gas can be detected through the first exhaust port 112, and when the concentration of the ether gas is lower than a set value, the heating ends.

[0049] The second reaction tank 20 includes a second tank body 21, a temperature control jacket 22 arranged on the outer surface of the second tank body 21, and a first stirring unit 23, wherein the second tank body 21 also includes a first solvent addition port 210 arranged at the top, a fluoroboric acid feed port 211, a solid feed port 212, a second exhaust port 215, a second nitrogen inlet 213, and a second discharge port 214 arranged at the bottom.

[0050] The second reaction tank 20 is mainly used for the reaction of fluoroboric acid solution with lithium sulfate solid to prepare crude lithium tetrafluoroborate. The chemical reaction equation is as follows:

[0051] Li2SO4+2HBF4---->H2O+SO3+2LiBF4.

[0052] The theoretical molar ratio of the reaction of the lithium sulfate and the fluoroboric acid is 1:2. In order to make the lithium sulfate react fully, it is preferred that the fluoroboric acid is appropriately excessive. Preferably, the molar ratio of the lithium sulfate to the fluoroboric acid is 1:2 to 2.2. More preferably, the molar ratio of the lithium sulfate to the fluoroboric acid is 1:2.05 to 2.1. In many embodiments, the molar ratio of the lithium sulfate to the fluoroboric acid is 1:2.01, 1:2.05, 1:2.08 and 1:2.10, respectively. Further, in order to promote the smooth progress of the reaction, it is preferred that an appropriate amount of molecular sieves be added as a dehydrating agent during the reaction to remove water. The mass ratio of the fluoroboric acid to the molecular sieve is 1:2 to 4. In other embodiments, the mass ratio of the fluoroboric acid to the molecular sieve is 1:2.5, 1:2.8, 1:3.0, 1:3.2, 1:3.5. The molecular sieve can be mixed in the lithium sulfate in the early stage, so that the lithium sulfate can be pre-dehydrated and can also be evenly added during the reaction.

[0053] The control of the second reaction tank 20 comprises the following steps:

[0054] S30, introducing nitrogen through the second nitrogen inlet 213 to remove air and other water vapor in the second tank body 21;

[0055] S31, passing fluoroboric acid into the second tank body 21 through the fluoroboric acid feeding port 211, and then evenly adding lithium sulfate particles mixed with molecular sieves to react;

[0056] S32, after the reaction is finished or during the reaction, a solvent is added through the first solvent addition port 210 to dissolve the crude lithium tetrafluoroborate to form a crude lithium tetrafluoroborate solution.

[0057] In step S30 , the concentration of the exhaust gas may be detected through the second exhaust port 215 , and the process ends when the concentration is lower than a set value.

[0058] In step 31, during the reaction, the sulfur trioxide gas generated by the reaction can be promptly removed by a vacuum pump to allow the reaction to proceed smoothly. As a further improvement, the concentration change of the sulfur trioxide gas can be detected to determine whether the reaction is proceeding normally or whether the reaction is completed.

[0059] In step S32, the solvent includes dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and a mixture thereof. Dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and other solvents are good solvents for lithium tetrafluoroborate, but poor solvents for lithium sulfate and dehydrating agents, so they can be removed in subsequent steps.

[0060] The filter press tank 30 includes a third tank body 31, a filter screen 33 arranged in the lower part of the third tank body 31, and a third stirring unit 32, wherein the third tank body 31 also includes a second solvent inlet 310, a lithium tetrafluoroborate mixed liquid feed inlet 311, a third nitrogen inlet 313 and a third exhaust port 314 arranged at the top, and a third discharge port 312 arranged at the bottom.

[0061] In one embodiment, at least two filter press tanks 30 arranged in parallel may be included, one of which is used for filter pressing, and the other is used as a buffer tank to store the crude lithium tetrafluoroborate solution; or one of which is used for cleaning, and the other is used as a working tank. With such an arrangement, the system of the present invention can be in a continuous production process.

[0062] The bottom and top of the third tank body 31 are both detachable structures, so as to facilitate the timely cleaning and replacement of the filter screen 33. The bottom and top of the third tank body 31 can be connected by flanges, which is not limited here.

[0063] The filter press tank 30 is used to filter the lithium tetrafluoroborate mixed solution. Specifically, the control of the filter press tank 30 includes the following steps:

[0064] S40, before the crude lithium tetrafluoroborate solution is introduced, further comprising introducing nitrogen through the third nitrogen inlet 313 to remove air and other water vapor in the third tank body 31;

[0065] S41, then introducing the crude lithium tetrafluoroborate solution, and introducing nitrogen through the third nitrogen inlet 313 for pressure filtration, so that the crude lithium tetrafluoroborate solution is slowly input into the vacuum spray concentration unit 40;

[0066] S42, when the filter press is completed, a good solvent for lithium tetrafluoroborate is introduced through the second solvent inlet 310 to dissolve the residual lithium tetrafluoroborate, and then nitrogen is introduced again through the third nitrogen inlet 313 for filter press, so that the crude lithium tetrafluoroborate solution is slowly input into the reduced pressure spray concentration unit 40 until the end.

[0067] In step S41, since solids such as lithium sulfate and molecular sieves are insoluble in solvents such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, they will stay in the filter screen 33 and be filtered. Since solid precipitates will accumulate on the screen, as the number of uses increases, during the filter press process, the flow rate of the crude lithium tetrafluoroborate solution can be used to determine whether the filter screen 33 has reached its service life or needs to be cleaned.

[0068] Specifically, during the process of pressure filtration by introducing nitrogen at a constant pressure through the third nitrogen inlet 313, the flow rate of the crude lithium tetrafluoroborate solution in the reduced pressure spray concentration unit 40 is obtained. When the flow rate is lower than the first flow rate threshold, it indicates that the filter screen 33 has been partially blocked and needs to be replaced or cleaned.

[0069] The filter press tank 30 further includes a first drain port 315 disposed at the bottom, and a second drain port 316 disposed at one side of the filter screen 33. When the filter screen 33 needs to be cleaned, the internal liquid is first drained, the solvent is introduced through the second solvent inlet 310, and the third stirring unit 32 is turned on for strong stirring, and then the second drain port 316 and the first drain port 315 are opened successively to mix the solids such as lithium sulfate and molecular sieve with the solvent and discharge from the second drain port 316. Furthermore, constant pressure nitrogen can also be introduced through the third nitrogen inlet 313, and the flow rate of the first drain port 315 is used to determine whether it is cleaned, otherwise it needs to be disassembled and replaced.

[0070] The vacuum spray concentration unit 40 is used to perform vacuum spray concentration on the crude lithium tetrafluoroborate solution in the filter press 30 to remove most of the solvent and obtain the crude lithium tetrafluoroborate.

[0071] The vacuum spray concentration unit 40 includes a fourth tank body 41, a second temperature control jacket 42 disposed on the outer surface of the fourth tank body 41, and a spray unit 43 disposed on the top of the fourth tank body 41, wherein the fourth tank body 41 also includes a vacuum port 411 disposed on the top, and a discharge port 412 disposed on the bottom. The crude lithium tetrafluoroborate formed by spray-drying the crude lithium tetrafluoroborate solution through the vacuum spray concentration unit 40 can be collected through the discharge port 412.

[0072] The control of the vacuum spray concentration unit 40 specifically includes:

[0073] S50, while nitrogen is introduced through the third nitrogen inlet 313 for pressure filtration, the spray unit 43 is simultaneously turned on for spray drying to remove most of the solvent to obtain crude lithium tetrafluoroborate.

[0074] See also Figure 3 The embodiment of the present invention further provides a safe preparation method of lithium tetrafluoroborate, comprising the following steps:

[0075] S11, feeding through the boron trifluoride inlet pipe 552 and the ether feed port 513, and controlling the heating jacket 515 to heat the mixing pipe 53 to a temperature of 34.5° C. to 126° C., so that the boron trifluoride and the ether form a complex;

[0076] S21, introducing anhydrous hydrogen fluoride solution and boron trifluoride / ether complex into the first tank 11 for reaction, wherein the molar ratio of the anhydrous hydrogen fluoride solution to boron trifluoride is 1 to 1.2:1;

[0077] S22, after the reaction is completed, the first tank body 11 is heated and distilled by the temperature control jacket 12 to obtain a fluoroboric acid solution, wherein the temperature range of the evaporation concentration is 40 to 70° C.;

[0078] S31, passing the fluoroboric acid solution into the second tank 21 through the fluoroboric acid feeding port 211, and then evenly adding lithium sulfate particles mixed with molecular sieves to react;

[0079] S32, after the reaction is completed or during the reaction, a solvent is added through the first solvent addition port 210 to dissolve the crude lithium tetrafluoroborate to form a crude lithium tetrafluoroborate solution;

[0080] S41, introducing nitrogen through the third nitrogen inlet 313 for pressure filtration, so that the crude lithium tetrafluoroborate solution is slowly input into the vacuum spray concentration unit 40;

[0081] S50, while nitrogen is introduced through the third nitrogen inlet 313 for pressure filtration, the spray unit 43 is simultaneously turned on for spray drying to remove most of the solvent to obtain crude lithium tetrafluoroborate.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A safe preparation method of lithium tetrafluoroborate, It is characterized in that include: S11, nitrogen is introduced through the inert gas inlet pipe to drive out the water vapor in the barrel, and then the material is fed through the boron trifluoride inlet pipe and the ether feed port, and the heating jacket is controlled to heat the mixing tube to a temperature of 50°C~60°C, so that boron trifluoride and ether form a complex. Step S11 is performed by a mixing unit, which includes a barrel, a water filter plate arranged in the middle of the barrel, a mixing tube arranged above the water filter plate, an air distribution plate arranged at the top of the mixing tube, a fourth stirring unit penetrating the air distribution plate, the mixing tube and the water filter plate, and an air supply component; the barrel includes a complex sampling port and a boron trifluoride discharge port arranged at the bottom, a mixing chamber arranged at the top of the mixing tube, and a trifluoride mixing chamber arranged at the top. The mixing tube is provided with a boron trifluoride feed port, an ether feed port, and a heating jacket arranged on the periphery of the mixing tube; the barrel can be divided into three detachable structures of upper, middle and lower parts as a whole; the gas distribution plate has a plurality of evenly distributed through-hole structures, and the aperture thereof is 0.1 mm to 1 mm; the mixing tube is an inverted cochlear structure, and is arranged in two rows in the vertical direction, wherein the top of one row of cochlear structures faces the middle of another row of cochlear structures; when the boron trifluoride gas carries the ether liquid into the cochlear structure, due to the inverted structure of the cochlear structure, the gas repeatedly collides in the cochlear structure to quickly form a complex; the cochlear structure is filled with metal balls; the gas supply assembly includes an inert gas inlet pipe, a boron trifluoride inlet pipe, and an air pump; S21, introducing anhydrous hydrogen fluoride solution and boron trifluoride / ether complex into the first tank for reaction, wherein the molar ratio of the anhydrous hydrogen fluoride solution to the boron trifluoride is 1-1.2:1; S22, after the reaction is completed, heating and distilling the first tank body through the temperature control jacket to obtain a fluoroboric acid solution, wherein the temperature range of evaporation and concentration is 40-70° C.; S31, passing the fluoroboric acid solution into the second tank through the fluoroboric acid feeding port, and then evenly adding lithium sulfate particles mixed with molecular sieves to react; S32, after the reaction is completed or during the reaction, a solvent is added through the first solvent addition port to dissolve the crude lithium tetrafluoroborate to form a crude lithium tetrafluoroborate solution; S41, introducing nitrogen through a third nitrogen inlet for pressure filtration, so that the crude lithium tetrafluoroborate solution is slowly input into a vacuum spray concentration unit; S50, while nitrogen is introduced through the third nitrogen inlet for pressure filtration, the spray unit is simultaneously turned on for spray drying to remove most of the solvent, thereby obtaining a crude lithium tetrafluoroborate product.

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