Preparation method of (difluorophosphoryloxy) lithium trifluoroborate

Abstract

The invention discloses a preparation method of (difluorophosphoryloxy) lithium trifluoroborate, which comprises the following steps: in an organic solvent, lithium hexafluorophosphate and diboron trioxide are used as raw materials to prepare a reaction solution containing (difluorophosphoryloxy) lithium trifluoroborate, and the reaction solution does not contain lithium difluorophosphate. The product is obtained through one-step reaction, the operation is simple, the reaction steps are few, and the reaction conversion rate is high; lithium difluorophosphate does not need to be adopted as a raw material, insoluble substances are not easily generated in the reaction process, and the product is high in purity, good in quality, low in production cost and suitable for industrial application.

Description

Technical Field

[0001] The invention relates to the synthesis of electrolyte additives, in particular to a new preparation method of (difluorophosphoryloxy) lithium trifluoroborate. Background Art

[0002] As an indispensable component of lithium-ion batteries or sodium-ion batteries, electrolyte additives are mainly responsible for constructing a stable electrode / electrolyte interface film to achieve electronic insulation and facilitate the transmission of lithium ions or sodium ions. Under the influence of different functional groups of different additives, the composition and structure of the battery interface film change, ultimately affecting the battery cycle life, high-temperature storage, and low-temperature discharge performance.

[0003] Boron-containing additives can dissolve inorganic lithium salts such as LiF on the surface of the interface film due to the electron-deficient effect of boron atoms, thereby reducing the internal resistance of the battery and improving the low-temperature performance of the battery. Phosphorus-containing additives, such as phosphates and phosphates, have a strong interaction between the "P=O" functional group and the transition metal elements on the surface of the positive electrode, so they can form a stable positive electrode interface film on the surface, thereby improving the storage performance and cycle performance of the battery. In addition, phosphorus-containing additives also have a certain flame retardant effect in the electrolyte. The presence of phosphorus and boron elements in one additive can simultaneously possess the above-mentioned advantages.

[0004] Patent CN102414902A discloses an electrolyte salt containing both boron and phosphorus and a method for synthesizing the same. A product containing at least (difluorophosphoryloxy) lithium trifluoroborate is obtained by reacting lithium difluorophosphate with a boron trifluoride ether complex. Using the product as an electrolyte additive can improve the room temperature cycle performance of the battery and inhibit impedance growth during the cycle.

[0005] However, the use of lithium difluorophosphate as a raw material to prepare lithium (difluorophosphoryloxy) trifluoroborate has the following defects: 1) lithium difluorophosphate has a low solubility in most solvents, and the amount of solvent used needs to be increased during the reaction process, which will result in a high turbidity of the prepared lithium (difluorophosphoryloxy) trifluoroborate solution. Direct use as an additive will result in the electrolyte failing to meet industry standards; 2) lithium difluorophosphate has a high production cost and a complex process, and is generally obtained by crystallization, resulting in a 5-10% loss and poor economic efficiency.

[0006] Therefore, a method for preparing (difluorophosphoryloxy) lithium trifluoroborate with low turbidity, high quality and low cost is proposed, which is beneficial to the improvement of electrolyte quality and further improvement of lithium ion battery performance. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a method for preparing lithium (difluorophosphoryloxy) trifluoroborate, which reduces the turbidity of the (difluorophosphoryloxy) trifluoroborate product and improves the product quality, and at the same time has simple operation, fewer reaction steps, high reaction conversion rate, low production cost, and is suitable for industrial application.

[0008] The objective of the present invention is achieved through the following technical solutions:

[0009] A method for preparing lithium (difluorophosphoryloxy) trifluoroborate, the method comprising: using lithium hexafluorophosphate and boron trioxide as raw materials in an organic solvent to prepare a reaction solution containing lithium (difluorophosphoryloxy) trifluoroborate, the chemical reaction equation being as follows:

[0010]

[0011] The preparation method of the present invention is a one-step reaction, and the reaction solution does not contain lithium difluorophosphate.

[0012] The organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, methyl propionate, γ-butyrolactone, ethyl ether, ethylene glycol dimethyl ether, acetonitrile, benzyl cyanide or propionitrile. Preferably, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, and methyl propionate.

[0013] The mass ratio of the organic solvent to lithium hexafluorophosphate is (4-15): 1, preferably (5-12): 1. When the mass ratio of the organic solvent to lithium hexafluorophosphate is lower than 4: 1, part of the BF3 generated by the reaction may escape and not participate in the reaction, thereby causing the precipitation of lithium difluorophosphate solid precipitate, affecting the purity and quality of the product.

[0014] The molar ratio of lithium hexafluorophosphate to boron trioxide is (1.5-3): 1, and the preferred molar ratio is (1.5-2): 1. In the preparation method of the present invention, lithium hexafluorophosphate is preferably excessive, because the excess lithium hexafluorophosphate can promote the forward reaction, and the excess lithium hexafluorophosphate does not need to be removed, and only the amount of lithium hexafluorophosphate added as a lithium salt needs to be reduced accordingly when preparing the electrolyte.

[0015] In the preparation process of the above-mentioned (difluorophosphoryloxy) lithium trifluoroborate, the reaction temperature is 0-120° C., and the reaction time is 0.5-48 h; preferably, the reaction temperature is 30-90° C., and the reaction time is 0.5-8 h.

[0016] In order to improve the reaction activity, shorten the reaction time, and ensure that there is no residue of unreacted boron trioxide raw material in the reaction product, the method of the present invention also includes: adding a chain alkyl alcohol as a catalyst to the reaction system, and the chain alkyl alcohol is selected from at least one of methanol, ethanol, isopropanol, butanol or ethylene glycol.

[0017] During the reaction, the chain alkyl alcohol and boron trioxide form a boric acid monoester intermediate, which has high solubility in organic solvents, and reacts with lithium hexafluorophosphate to form (difluorophosphoryloxy) lithium trifluoroborate, and then releases the chain alkyl alcohol to continue to catalyze subsequent reactions. Therefore, adding a small amount of chain alkyl alcohol can greatly increase the reaction activity, shorten the reaction time, and reduce the turbidity of the product. Specifically, the amount of the catalyst is 0.1-2% of the molar amount of lithium hexafluorophosphate, preferably 0.2-1.5%, and more preferably 0.5-1.0%.

[0018] Regardless of whether the reaction of the present invention is carried out in the presence of a catalyst, boron trifluoride gas is generated during the reaction. Therefore, in order to suppress the problem of increased product turbidity and reduced product purity caused by the generation of lithium difluorophosphate impurities in the product (especially when the reaction temperature is high), the reaction of the present invention is carried out in a closed container or an open container equipped with a condensation reflux component.

[0019] Since two molecules of lithium (difluorophosphoryloxy) trifluoroborate can generate one molecule of bis (difluorophosphoryloxy) trifluoroborate lithium and LiBF4, the reaction formula is as follows:

[0020]

[0021] The reaction is a reversible reaction and the forward reaction activity is relatively low. Therefore, although the reaction solution prepared by the present invention contains (difluorophosphoryloxy) lithium trifluoroborate, bis(difluorophosphoryloxy) lithium trifluoroborate and LiBF4 at the same time, (difluorophosphoryloxy) lithium trifluoroborate is still the main component. Specifically, based on the total mass of the product (excluding the solvent), the reaction solution contains at least 60wt% of (difluorophosphoryloxy) lithium trifluoroborate, preferably at least 70wt% of (difluorophosphoryloxy) lithium trifluoroborate, and more preferably at least 80wt% of (difluorophosphoryloxy) lithium trifluoroborate.

[0022] In order to obtain the (difluorophosphoryloxy) lithium trifluoroborate product, the preparation method of the present invention also includes: removing the organic solvent, catalyst and boron trifluoride gas in the reaction solution by atmospheric distillation or reduced pressure distillation to obtain the (difluorophosphoryloxy) lithium trifluoroborate product. Due to the solvation of (difluorophosphoryloxy) lithium trifluoroborate, the (difluorophosphoryloxy) lithium trifluoroborate product is a concentrated solution (containing an organic solvent). Therefore, the organic solvent of the present invention is preferably an organic solvent commonly used in an electrolyte, so that the (difluorophosphoryloxy) lithium trifluoroborate product (concentrated solution) can be directly used for the preparation of an electrolyte. Moreover, when the (difluorophosphoryloxy) lithium trifluoroborate product is applied to an electrolyte as an additive, the small amount of bis(difluorophosphoryloxy) lithium trifluoroborate and lithium tetrafluoroborate contained therein have little effect on battery performance and can be ignored.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention proposes a new method for preparing lithium (difluorophosphoryloxy) trifluoroborate in one step using lithium hexafluorophosphate and diboron trioxide as raw materials. The method is simple in operation and has few reaction steps, and no lithium difluorophosphate is required as a raw material. The reaction process does not produce insoluble matter to increase the turbidity of the product. The product has high purity, good quality, low production cost, and is very suitable for industrial application.

[0025] 2. In the present invention, a small amount of chain alkyl alcohol is added as a catalyst during the reaction process to further improve the reaction activity, greatly shorten the reaction time, ensure that there is no unreacted boron trioxide in the product, reduce the turbidity of the product and improve the product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The 1# lithium salt prepared in Example 1 of the present invention 19 F-NMR spectrum;

[0027] Figure 2 The 1# lithium salt prepared in Example 1 of the present invention 31 P-NMR spectrum;

[0028] Figure 3 The 1# control lithium salt prepared in Comparative Example 1 of the present invention is 19 F-NMR spectrum;

[0029] Figure 4 The 1# control lithium salt prepared in Comparative Example 1 of the present invention is 31 P-NMR spectrum. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0031] The structures and contents of the products and control samples prepared in Examples 1 to 9 and Comparative Examples 1 to 4 of the present invention were determined by 400M nuclear magnetic resonance fluorine spectroscopy ( 19 F-NMR) and 400M NMR phosphorus spectra ( 31 P-NMR) was used for characterization and confirmation, and the characterization method was as follows: a small amount of the product was added to a nuclear magnetic tube, and an appropriate amount of diethyl carbonate was added for dilution, and the solution height was not higher than 1 / 3 of the height of the nuclear magnetic tube. Since the NMR spectra of the same substance are basically consistent and the peak position shift is extremely small in the same solvent environment, the detailed NMR spectra and results are only described in Example 1 and Comparative Example 1.

[0032] Example 1

[0033] This embodiment provides the preparation of lithium (difluorophosphoryloxy) trifluoroborate, which specifically includes the following steps:

[0034] S1. In a drying room with a dew point of -40°C, add 0.15 mol (22.8 g, purity 99%) of lithium hexafluorophosphate, 0.1 mol (6.96 g, purity 99%) of diboron trioxide, and 0.0015 mol (0.05 g) of methanol as a reaction catalyst, add 200 ml of ethyl methyl carbonate as a solvent (the mass ratio of the solvent to LiPF6 is 8.77), start stirring in a closed environment to mix the system evenly, react at 50°C for 2 hours, and obtain a ethyl methyl carbonate solution containing (difluorophosphoryloxy) trifluoroborate lithium. There is no insoluble matter, indicating that the diboron trioxide is completely reacted;

[0035] S2. Use reduced pressure distillation to remove most of the solvent and all the remaining boron trifluoride and methanol in the reaction solution. The reduced pressure distillation temperature is controlled at 60°C and the time is controlled at 0.5h to obtain a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate, which is recorded as 1# lithium salt.

[0036] The product is colorless and transparent. The turbidity is 5.23NTU when analyzed by turbidity meter.

[0037] Attached Figure 1 and attached Figure 2 They are given 1 # Lithium salt 19 F-NMR and 31 P-NMR spectrum, by Figure 1 , Figure 2 It can be seen that:

[0038] The NMR F spectrum of 1# lithium salt is as follows:

[0039] (Difluorophosphoryloxy) lithium trifluoroborate: δ = -92.41 ppm (d, J = 958.5 Hz), δ = -157.57 ppm (s)

[0040] Lithium bis(difluorophosphoryloxy) trifluoroborate: δ = -92.00 ppm (d, J = 963.1 Hz), δ = -151.88 ppm (s)

[0041] The NMR P spectrum of 1# lithium salt is as follows:

[0042] Lithium (difluorophosphoryloxy) trifluoroborate: δ = -27.91 ppm (t, J = 958.3 Hz)

[0043] Lithium bis(difluorophosphoryloxy) trifluoroborate: δ = -29.26 ppm (t, J = 963.1 Hz)

[0044] By integrating the peak area of ​​the nuclear magnetic resonance F spectrum, it can be seen that the integrated area ratio of lithium (difluorophosphoryloxy) trifluoroborate (marked by the symbol "■"), bis (difluorophosphoryloxy) trifluoroborate (marked by the symbol "●"), and lithium tetrafluoroborate (marked by the symbol "Δ") is 3.11:1.00:0.84, which is converted into a molar ratio of 1:0.16:0.068, and further converted into a mass ratio of 1:0.24:0.036. Therefore, based on the total amount of fluorine-containing lithium salt as 100wt%, it is converted that the 1# lithium salt contains 78.7wt% of lithium (difluorophosphoryloxy) trifluoroborate, 18.5wt% of bis (difluorophosphoryloxy) trifluoroborate, and 2.8wt% of lithium tetrafluoroborate. Further area integration conversion through the P spectrum found that the results were uniform and the calculation reliability was high.

[0045] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0046] Example 2

[0047] The operation of this example is the same as that of Example 1, except that the amount of methanol added is adjusted from 0.0015 mol to 0.003 mol, and a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate is obtained, which is recorded as 2# lithium salt.

[0048] The product is colorless and transparent. The turbidity is 5.16NTU when analyzed by turbidity meter.

[0049] By integrating and calculating the peak area of ​​the NMR F spectrum, it can be seen that in the 2# lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 2# lithium salt contains 84.9wt% of (difluorophosphoryloxy) lithium trifluoroborate, 13.9wt% of bis(difluorophosphoryloxy) lithium trifluoroborate and 1.2wt% of lithium tetrafluoroborate. Further area integration and conversion through the P spectrum found that the results were consistent and the calculation reliability was high.

[0050] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0051] Example 3

[0052] The operation of this example is the same as that of Example 1, except that methanol is replaced by ethanol to obtain a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate, which is recorded as 3# lithium salt.

[0053] The product is colorless and transparent. The turbidity is 5.22NTU when analyzed by turbidity meter.

[0054] By integrating and calculating the peak area of ​​the nuclear magnetic resonance F spectrum, it can be seen that in the 3# lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 3# lithium salt contains 80.2wt% of (difluorophosphoryloxy) lithium trifluoroborate, 17.4wt% of bis(difluorophosphoryloxy) lithium trifluoroborate and 2.4wt% of lithium tetrafluoroborate. Further area integration and conversion through the P spectrum found that the results were consistent and the calculation reliability was high.

[0055] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0056] Example 4

[0057] The operation of this embodiment is the same as that of embodiment 1, except that methanol is replaced by isopropanol to obtain a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate, which is recorded as 4# lithium salt.

[0058] The product is colorless and transparent. The turbidity is 5.28NTU when analyzed by turbidity meter.

[0059] By integrating and calculating the peak area of ​​the NMR F spectrum, it can be seen that in the 4# lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 4# lithium salt contains 80.7wt% of (difluorophosphoryloxy) lithium trifluoroborate, 17.1wt% of bis(difluorophosphoryloxy) lithium trifluoroborate and 2.2wt% of lithium tetrafluoroborate. Further area integration and conversion through the P spectrum found that the results were consistent and the calculation reliability was high.

[0060] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0061] Example 5

[0062] The operation of this example is the same as that of Example 1, except that the amount of lithium hexafluorophosphate added is adjusted from 0.15 mol to 0.20 mol, to obtain a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate, which is recorded as 5# lithium salt.

[0063] The product is colorless and transparent. The turbidity is 5.20 NTU when analyzed by turbidity meter.

[0064] By integrating and calculating the peak area of ​​the nuclear magnetic resonance F spectrum, it can be seen that in the 5# lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 5# lithium salt contains 22.4wt% unreacted lithium hexafluorophosphate, 61.0wt% lithium (difluorophosphoryloxy) trifluoroborate, 14.4wt% bis (difluorophosphoryloxy) trifluoroborate, and 2.20wt% lithium tetrafluoroborate. Further area integration and conversion by P spectrum showed that the results were uniform and the calculation was highly reliable.

[0065] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0066] Example 6

[0067] The operation of this embodiment is the same as that of Example 1, except that: methanol is not added to the reaction, the reaction time is extended from 2 h to 12 h, and after step S1, a methyl ethyl carbonate solution containing (difluorophosphoryloxy) lithium trifluoroborate is obtained. The solution contains insoluble matter, and the turbidity test is 52.3 NTU. After filtration, 1.25 g of insoluble matter is obtained, which is unreacted boron trioxide. After the filtrate is subjected to step S2, a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate is obtained, which is recorded as 6# lithium salt.

[0068] By integrating and calculating the peak area of ​​the nuclear magnetic resonance F spectrum, it can be seen that in the 6# lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 6# lithium salt contains 15.9wt% of unreacted raw material lithium hexafluorophosphate, 68.0wt% of (difluorophosphoryloxy) lithium trifluoroborate, 14.2wt% of bis(difluorophosphoryloxy) lithium trifluoroborate and 1.90wt% of lithium tetrafluoroborate. Further area integration and conversion by P spectrum showed that the results were uniform and the calculation reliability was high.

[0069] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0070] Example 7

[0071] The operation of this embodiment is the same as that of Example 6, except that the reaction time is extended from 12 h to 24 h. After step S1, a solution of ethyl methyl carbonate containing (difluorophosphoryloxy) lithium trifluoroborate is obtained. The solution contains insoluble matter, and the turbidity test is 39.5 NTU. After filtration, 0.84 g of insoluble matter is obtained, which is unreacted boron trioxide. After the filtrate is subjected to step S2, a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate is obtained, which is recorded as 7# lithium salt.

[0072] By integrating and calculating the peak area of ​​the nuclear magnetic resonance F spectrum, it can be seen that in the 7# lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 7# lithium salt contains 10.4wt% of unreacted raw material lithium hexafluorophosphate, 72.3wt% of (difluorophosphoryloxy) lithium trifluoroborate, 15.3wt% of bis(difluorophosphoryloxy) lithium trifluoroborate and 2.00wt% of lithium tetrafluoroborate. Further area integration and conversion by P spectrum showed that the results were uniform and the calculation reliability was high.

[0073] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0074] Example 8

[0075] The operation of this embodiment is the same as that of Example 6, except that the reaction time is extended from 12 h to 36 h. After step S1, a methyl ethyl carbonate solution containing (difluorophosphoryloxy) lithium trifluoroborate is obtained. The solution contains insoluble matter, and the turbidity test is 38.9 NTU. After filtration, 0.77 g of insoluble matter is obtained, which is unreacted boron trioxide. After the filtrate is subjected to step S2, a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate is obtained, which is recorded as 8# lithium salt.

[0076] By integrating and calculating the peak area of ​​the nuclear magnetic resonance F spectrum, it can be seen that in the 8# lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 8# lithium salt contains 9.50wt% of unreacted raw material lithium hexafluorophosphate, 73.0wt% of lithium (difluorophosphoryloxy) trifluoroborate, 15.5wt% of bis (difluorophosphoryloxy) trifluoroborate and 2.00wt% of lithium tetrafluoroborate. Further area integration and conversion by P spectrum, it is found that the results are uniform and the calculation credibility is high.

[0077] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0078] Example 9

[0079] The operation of this embodiment is the same as that of Example 6, except that the reaction solvent is changed from ethyl methyl carbonate to diethyl carbonate, the reaction temperature is increased from 50°C to 80°C, and after step S1, a ethyl methyl carbonate solution containing (difluorophosphoryloxy) lithium trifluoroborate is obtained. The solution contains insoluble matter, and the turbidity test shows that it is 48.6 NTU. After filtration, 1.04 g of insoluble matter is obtained, which is unreacted boron trioxide. After the filtrate is subjected to step S2, a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate is obtained, which is recorded as 9# lithium salt.

[0080] By integrating and calculating the peak area of ​​the nuclear magnetic resonance F spectrum, it can be seen that in the 9# lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 9# lithium salt contains 13.0wt% of unreacted raw material lithium hexafluorophosphate, 70.1wt% of (difluorophosphoryloxy) lithium trifluoroborate, 14.9wt% of bis(difluorophosphoryloxy) lithium trifluoroborate and 2.00wt% of lithium tetrafluoroborate. Further area integration and conversion by P spectrum were found to be consistent and the calculation reliability was high.

[0081] In this embodiment, no peak of lithium difluorophosphate was detected in both the NMR F spectrum and the NMR P spectrum.

[0082] Comparative Example 1

[0083] The operation of this comparative example is the same as that of Example 1, except that the amount of reaction solvent added is reduced from 200 ml to 80 ml. After step S1, a solution of ethyl methyl carbonate containing (difluorophosphoryloxy) lithium trifluoroborate is obtained. The solution contains insoluble matter, and the turbidity test is 73.9 NTU. After filtration, 3.03 g of insoluble matter is obtained, which is the by-product lithium difluorophosphate. After the filtrate is subjected to step S2, a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate is obtained, which is recorded as 1# control lithium salt.

[0084] The peak of lithium difluorophosphate was detected in both the nuclear magnetic F spectrum and the nuclear magnetic P spectrum (marked by the symbol "◇"). By integrating and calculating the peak area of ​​the nuclear magnetic F spectrum, it can be known that in the 1# control lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 1# control lithium salt contains 73.9wt% of (difluorophosphoryloxy) lithium trifluoroborate, 10.9wt% of bis(difluorophosphoryloxy) lithium trifluoroborate, 3.6wt% of lithium tetrafluoroborate and 11.6wt% of lithium difluorophosphate. Further area integration conversion was performed through the P spectrum, and it was found that the results were uniform and the calculation reliability was high.

[0085] Comparative Example 2

[0086] The operation of this comparative example is the same as that of Example 1, except that the reaction container is replaced by an open container from a closed container, and after step S1, a solution of ethyl methyl carbonate containing (difluorophosphoryloxy) lithium trifluoroborate is obtained, the solution contains insoluble matter, and the turbidity test is 66.8 NTU. After filtration, 2.21 g of insoluble matter is obtained, which is the generated by-product lithium difluorophosphate. After the filtrate is subjected to step S2, a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate is obtained, which is recorded as 2# control lithium salt.

[0087] The peak of lithium difluorophosphate was detected in both the nuclear magnetic resonance F spectrum and the nuclear magnetic resonance P spectrum of this comparative example. By integrating and calculating the peak area of ​​the nuclear magnetic resonance F spectrum, it can be known that in the 2# control lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 2# control lithium salt contains 70.2wt% of (difluorophosphoryloxy) lithium trifluoroborate, 12.1wt% of bis(difluorophosphoryloxy) lithium trifluoroborate, 4.8wt% of lithium tetrafluoroborate and 12.9wt% of lithium difluorophosphate. Further area integration conversion was performed through the P spectrum, and it was found that the results were uniform and the calculation credibility was high.

[0088] Comparative Example 3

[0089] In this comparative example, a methyl ethyl carbonate complex of lithium difluorophosphate and boron trifluoride is used as a raw material to prepare a methyl ethyl carbonate solution containing (difluorophosphoryloxy) lithium trifluoroborate, and a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate is obtained after reduced pressure distillation, which specifically includes the following steps:

[0090] S1. In a drying room with a dew point of -40°C, add 0.15 mol of lithium difluorophosphate (purity 99%) and 0.15 mol of boron trifluoride methyl ethyl carbonate complex (purity 99%) to a reaction bottle, add 200 ml of methyl ethyl carbonate as a solvent, start stirring in a closed environment to mix the system evenly, react at 50°C for 12 hours, and obtain a methyl ethyl carbonate solution containing (difluorophosphoryloxy) lithium trifluoroborate. The solution contains a small amount of insoluble matter, which may be undissolved lithium difluorophosphate. The turbidity is 12.55 NTU when analyzed by a turbidity meter. After filtration, a clear and transparent reaction solution is obtained;

[0091] S2. Use reduced pressure distillation to remove most of the solvent in the reaction solution. The reduced pressure distillation temperature is controlled at 60°C and the time is controlled at 0.5h to obtain a product concentrate of (difluorophosphoryloxy) lithium trifluoroborate, which is recorded as 3# control lithium salt.

[0092] By integrating and calculating the peak area of ​​the NMR F spectrum, it can be seen that in the 3# control lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 3# control lithium salt contains 61.4wt% of (difluorophosphoryloxy) lithium trifluoroborate, 34.3wt% of bis(difluorophosphoryloxy) lithium trifluoroborate and 4.3wt% of lithium tetrafluoroborate. Further area integration and conversion by P spectrum showed that the results were consistent and the calculation was highly reliable.

[0093] Comparative Example 4

[0094] The operation of this comparative example is the same as that of comparative example 1, except that after step S2, a poor solvent 1,2-dichloroethane is added to the product concentrate of (difluorophosphoryloxy)trifluoroborate lithium at a volume ratio of 1:1, and the mixture is kept at -20°C for 24 hours to precipitate crystals. A solid product and a filtrate are obtained after filtration, and the obtained filtrate is further subjected to reduced pressure distillation to obtain a new product concentrate of (difluorophosphoryloxy)trifluoroborate lithium, which is recorded as 4# control lithium salt.

[0095] The precipitated crystals were tested by nuclear magnetic resonance F spectrum, and the results showed that it was lithium tetrafluoroborate, not lithium difluorophosphate. The peak area of ​​the nuclear magnetic resonance F spectrum of the 4# control lithium salt was integrated and calculated: in the 4# control lithium salt, based on the total amount of fluorine-containing lithium salt as 100wt%, the 4# control lithium salt contained 38.2wt% of (difluorophosphoryloxy) lithium trifluoroborate and 61.8wt% of bis(difluorophosphoryloxy) lithium trifluoroborate. Further area integration and conversion by P spectrum were found to be consistent and the calculation credibility was high.

[0096] By comparing the reaction results of Examples 1 to 5 and Examples 6 to 9 of the present invention, it can be seen that when a chain alkyl alcohol is added as a catalyst in the reaction, it can not only promote the complete reaction of the raw materials and improve the reaction yield, but also avoid the residual boron trioxide and reduce the turbidity of the reaction solution, thereby eliminating the filtration step to achieve the effect of simplifying the process, and can also increase the reaction activity and greatly shorten the reaction time. In addition, the catalyst can be removed in the subsequent distillation process without affecting the product quality.

[0097] By comparing Example 1 of the present invention with Comparative Examples 1 to 2, it can be seen that when the reaction solvent is reduced or the reaction vessel is changed from a closed container to an open container, a large amount of by-product lithium difluorophosphate will be generated, which will produce solid precipitation, reduce the reaction yield, and increase the filtration process; on the other hand, lithium difluorophosphate impurities are introduced into the product. It is speculated that the reason is that during the reaction process, the reduction of the solvent and the change of the reaction vessel cause the intermediate product boron trifluoride to escape in large quantities, which cannot effectively enter the reaction system to generate the target product (difluorophosphoryloxy) lithium trifluoroborate, thereby leading to the generation of lithium difluorophosphate.

[0098] By comparing Comparative Example 1 and Comparative Example 4, it can be seen that the (difluorophosphoryloxy) lithium trifluoroborate reaction solution is concentrated and a poor solvent is introduced to crystallize to obtain lithium tetrafluoroborate rather than lithium difluorophosphate, indicating that the BO bond binding energy in (difluorophosphoryloxy) lithium trifluoroborate is high, the material has high chemical stability, and the concentration and crystallization process cannot decompose lithium (difluorophosphoryloxy) trifluoroborate to produce lithium difluorophosphate.

[0099] Therefore, the process for preparing lithium (difluorophosphoryloxy) trifluoroborate of the present invention, especially when a chain alkyl alcohol is added as a catalyst, can avoid the lithium difluorophosphate crystallization process, improve the raw material utilization rate, and improve the production efficiency, and can greatly reduce the cost, which is very suitable for industrial application.

Claims

1. A method for preparing lithium (difluorophosphoryloxy) trifluoroborate, characterized in that: The preparation method comprises: in an organic solvent, using lithium hexafluorophosphate and boron trioxide as raw materials to prepare a reaction solution containing (difluorophosphoryloxy) lithium trifluoroborate.

2. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 1, characterized in that: The organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, methyl propionate, γ-butyrolactone, ethyl ether, ethylene glycol dimethyl ether, acetonitrile, benzyl cyanide or propionitrile.

3. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 2, characterized in that: The mass ratio of the organic solvent to lithium hexafluorophosphate is (4-15):

1.

4. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 1, characterized in that: The molar ratio of lithium hexafluorophosphate to boron trioxide is (1.5-3):

1.

5. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 1, characterized in that: The reaction temperature is 0-120°C, and the reaction time is 0.5-48h.

6. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to any one of claims 1 to 5, characterized in that: The preparation method further comprises: adding a chain alkyl alcohol as a catalyst to the reaction system, wherein the chain alkyl alcohol is selected from at least one of methanol, ethanol, isopropanol, butanol or ethylene glycol.

7. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 6, characterized in that: The amount of the catalyst used is 0.1-2% of the molar amount of lithium hexafluorophosphate.

8. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 1 or 6, characterized in that: The reaction is carried out in a closed container or an open container equipped with a condensation reflux component.

9. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 1 or 6, characterized in that: The reaction solution contains at least 60 wt % of (difluorophosphoryloxy) lithium trifluoroborate.

10. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 9, characterized in that: The reaction solution also contains lithium bis(difluorophosphoryloxy)trifluoroborate and lithium tetrafluoroborate.

11. The method for preparing lithium (difluorophosphoryloxy) trifluoroborate according to claim 10, characterized in that: The preparation method further comprises: removing the organic solvent, catalyst and boron trifluoride gas in the reaction solution by atmospheric distillation or reduced pressure distillation to obtain the (difluorophosphoryloxy) lithium trifluoroborate product.

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