A method for preparing lithium difluorooxalate borate

Abstract

This invention relates to a method for preparing lithium difluorooxalate borate, belonging to the field of lithium-ion battery material technology. The preparation method includes the following steps: reacting lithium difluorooxalate borate and boron fluoride in a lithium fluoride hydrogen fluoride solution to obtain lithium difluorooxalate borate. This invention utilizes the reaction of lithium difluorooxalate borate and boron fluoride in a lithium fluoride hydrogen fluoride solution to generate lithium difluorooxalate borate. This one-step reaction is simple to operate and has high reactant utilization, resulting in a high product yield. Furthermore, the reaction of this invention does not generate byproducts, reducing the need for impurity removal and improving product purity. The solvent used in the reaction is hydrogen fluoride, which is easy to recover and reuse after the reaction. The absence of water in the reaction process results in a low water content in the obtained lithium difluorooxalate borate product, meeting battery-grade requirements.

Description

Technical Field

[0001] This invention relates to a method for preparing lithium difluorooxalate borate, belonging to the field of lithium-ion battery material technology. Background Technology

[0002] Currently, the electrolytes commonly used in lithium-ion batteries are lithium hexafluorophosphate (LiPF6), lithium bis(oxalate-borate) (LiBOB), and lithium tetrafluoroborate (LiBF4). LiPF6 has a pyrolysis temperature of only 200℃ and poor thermal stability, which is one of the reasons for frequent lithium battery fires. LiBF4, as a lithium salt, has a low charge transfer resistance, giving the battery good low-temperature performance, but it is unstable in water and has difficulty forming an SEI film on the negative electrode surface, resulting in poor cycle performance of the assembled battery. LiBOB has excellent film-forming properties and thermal stability, but it still has disadvantages such as low solubility, low ionic conductivity, and poor low-temperature performance. Lithium difluorooxalate-borate (LiODFB), because its molecular structure contains half LiBF4 and half LiBOB, combines the advantages of both lithium salts. LiODFB exhibits excellent high and low temperature performance, demonstrating good electrochemical performance at both -20℃ and 60℃. It also possesses excellent film-forming properties, helping to form a stable, low-resistance SEI film in the electrolyte, effectively improving the cycle life and rate performance of the battery, and showing great promise for application in lithium-ion batteries.

[0003] Chinese invention patent CN107226821B discloses a synthetic process for preparing lithium difluorooxalatoborate from lithium bis(oxalato)borate. The process involves reacting lithium bis(oxalato)borate with fluorine-, boron-, and lithium-containing compounds under solvent conditions, followed by crystallization and drying to obtain lithium difluorooxalatoborate. However, the yield is low (90-95%) and the water content is high (100-180 ppm), making it difficult to meet battery-grade requirements. Furthermore, the solvent used is an organic solvent, which is consumed in large quantities, difficult to recycle, and easily causes environmental pollution. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing lithium difluorooxalate borate, which solves the problems of low yield, high water content and difficulty in organic solvent recovery in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing lithium difluorooxalate borate includes the following steps: reacting lithium difluorooxalate borate and boron fluoride in a solution of lithium fluoride in hydrogen fluoride to obtain lithium difluorooxalate borate.

[0007] This invention utilizes the reaction of lithium difluorooxalateborate and boron fluoride in a lithium fluoride hydrogen fluoride solution to produce lithium difluorooxalateborate. This one-step reaction is simple to operate and has high reactant utilization, resulting in a high product yield. Furthermore, the reaction produces no byproducts, reducing the need for impurity removal and improving product purity. The solvent used in the reaction is hydrogen fluoride, which is easily recyclable after the reaction. The absence of water in the reaction process results in a low water content in the obtained lithium difluorooxalateborate product, meeting battery-grade requirements.

[0008] The chemical reaction involved in the preparation process of this invention is: LiF + LiB(C2O4)2 + BF3 = 2LiBF2C2O4.

[0009] To ensure complete reaction of the reactants, reduce product impurities, simplify the process, and improve product purity, the molar ratio of lithium fluoride, lithium bis(oxalato)borate, and boron fluoride is preferably 1:1:(1.0–1.2). To ensure complete dissolution of lithium fluoride in the hydrogen fluoride solution, the molar ratio of lithium fluoride to hydrogen fluoride is preferably 1:(20–30).

[0010] Preferably, the reaction temperature is -5℃ to 0℃, and the reaction time is 8 to 16 hours. This temperature ensures a stable reaction rate and allows for a more complete reaction.

[0011] Preferably, the pressure of the reaction is 0.08 to 0.25 MPa.

[0012] Preferably, the reaction involves first adding lithium bis(oxalato)borate to a lithium fluoride hydrogen fluoride solution, then introducing boron fluoride gas, and collecting the gas on the liquid surface and circulating it back into the lithium fluoride hydrogen fluoride solution.

[0013] Preferably, after the reaction, hydrogen fluoride is converted into a gas to obtain solid lithium difluorooxalate borate. This not only improves the purity of the lithium difluorooxalate borate product but also promotes the recycling of hydrogen fluoride and reduces costs. Preferably, the temperature at which the hydrogen fluoride is converted into a gas is 14–18°C. At this temperature, the hydrogen fluoride evaporates quickly, and subsequent condensation and recovery are also easier.

[0014] More preferably, the lithium difluorooxalate borate solid is further descaled to remove residual solvent from its surface. Drying is preferred. The drying temperature is 100–130°C, and the time is 1.5–2.5 h.

[0015] Preferably, the lithium fluoride hydrogen fluoride solution is obtained by reacting lithium fluoride with anhydrous hydrogen fluoride.

[0016] More preferably, the reaction temperature between lithium fluoride and anhydrous hydrogen fluoride is -10 to -30°C.

[0017] To remove excess hydrogen fluoride solvent, preferably, the hydrogen fluoride is converted into gas by vacuum concentration. Attached Figure Description

[0018] Figure 1 The infrared spectrum of lithium difluorooxalate borate prepared in Example 1 of this invention is shown. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0020] I. Specific embodiments of the preparation method of lithium difluorooxalatoborate of the present invention are as follows:

[0021] Example 1

[0022] The preparation method of lithium difluorooxalatoborate in this embodiment adopts the following steps:

[0023] In a reactor, 25.94 g (1.0 mol) of lithium fluoride was reacted with 600 g (30.0 mol) of anhydrous hydrogen fluoride at -30 °C for 4 h to obtain a lithium fluoride hydrogen fluoride solution. The temperature was raised to 0 °C, and 193.79 g (1.0 mol) of lithium difluorooxalate borate was added to the reactor. The mixture was stirred and dispersed for 40 min at 600 rpm. 69.16 g (1.0 mol) of boron fluoride gas was introduced from the bottom of the container, and the gas was collected at the top and then returned to the bottom. This cycle was repeated, maintaining a pressure of 0.08 MPa, and the reaction was carried out for 16 h. The temperature was then raised to 16 °C, and the reaction solution was concentrated to zero at -0.085 MPa. The resulting solid was then dried at 120 °C for 2 h to obtain 284.7 g of lithium difluorooxalate borate, with a yield of 99.0%, a purity of 99.96%, and a water content of 12.0 ppm. Infrared spectroscopy was performed on the product of this example, and the results are as follows: Figure 1 As shown.

[0024] Example 2

[0025] The preparation method of lithium difluorooxalatoborate in this embodiment adopts the following steps:

[0026] In a reactor, 25.94 g (1.0 mol) of lithium fluoride was reacted with 500 g (25.0 mol) of anhydrous hydrogen fluoride at -20 °C for 4 h to obtain a lithium fluoride hydrogen fluoride solution. The temperature was raised to -5 °C, and 193.79 g (1.0 mol) of lithium difluorooxalate borate was added to the reactor. The mixture was stirred and dispersed for 40 min at a speed of 600 rpm. 74.59 g (1.1 mol) of boron fluoride gas was introduced from the bottom of the container, and the gas was collected at the top of the container and then returned to the bottom of the container. This cycle was repeated, maintaining a gas pressure of 0.15 MPa, and the reaction was carried out for 10 h. Then the temperature was raised to 16 °C, and the reaction solution was concentrated to the point where no gas was present at -0.085 MPa. The resulting solid was then dried at 120 °C for 2 h to obtain 285.2 g of lithium difluorooxalate borate, with a yield of 99.2%, a purity of 99.93%, and a water content of 11.0 ppm.

[0027] Example 3

[0028] The preparation method of lithium difluorooxalatoborate in this embodiment adopts the following steps:

[0029] In a reactor, 25.94 g (1.0 mol) of lithium fluoride was reacted with 400 g (20 mol) of anhydrous hydrogen fluoride at -10 °C for 4 h to obtain a lithium fluoride hydrogen fluoride solution. The temperature was raised to -5 °C, and 193.79 g (1.0 mol) of lithium difluorooxalate borate was added to the reactor. The mixture was stirred and dispersed for 40 min at 600 rpm. 81.37 g (1.2 mol) of boron fluoride gas was introduced from the bottom of the container, and the gas was collected at the top of the container and then returned to the bottom. This cycle was repeated, maintaining a gas pressure of 0.25 MPa, and the reaction was carried out for 8 h. The temperature was raised to 16 °C, and the reaction solution was concentrated to the point where no gas was present under a pressure of -0.085 MPa. The resulting solid was then dried at 120 °C for 2 h to obtain lithium difluorooxalate borate with a yield of 99.5%, a purity of 99.95%, and a water content of 12.0 ppm.

[0030] II. Comparative Example

[0031] The preparation method of lithium difluorooxalatoborate in this comparative example adopts the following steps:

[0032] In a reactor, 28.53 g of lithium fluoride (1.1 mol) was reacted with 400 g of anhydrous hydrogen fluoride (20.0 mol) at -10 °C for 4 h to obtain a lithium fluoride hydrogen fluoride solution. The temperature was raised to -5 °C, and 193.79 g of lithium difluorooxalate borate (1.0 mol) was added to the reactor. The mixture was stirred and dispersed for 40 min at 600 rpm. 81.37 g of boron fluoride gas (1.2 mol) was introduced from the bottom of the container. The gas was collected at the top of the container and then returned to the bottom. This cycle was repeated, maintaining a gas pressure of 0.25 MPa, and the reaction was carried out for 8 h. The temperature was then raised to 16 °C, and the reaction solution was concentrated to the point of no gas emission at -0.085 MPa. The resulting solid was then dried at 120 °C for 2 h to obtain 296.50 g of a mixture of lithium difluorooxalate borate and lithium tetrafluoroborate, of which 286.6 g was lithium difluorooxalate borate with a purity of 96.66% and a water content of 12.0 ppm.

[0033] Therefore, when the molar ratio of lithium fluoride to lithium difluorooxalate borate is greater than 1:1, a mixture of lithium difluorooxalate borate and lithium tetrafluoroborate will be generated, reducing the purity of the product.

Claims

1. A process for the preparation of lithium bisfluorosulfonylborate, characterized in that, The method comprises the following steps: The lithium fluoride, the lithium difluorophosphate and the boron fluoride are reacted to obtain the lithium difluorophosphate; the molar ratio of the lithium fluoride, the lithium difluorophosphate and the boron fluoride is 1:1:(1.0-1.2); the reaction is that the lithium difluorophosphate is first added into the lithium fluoride hydrogen fluoride solution, then the boron fluoride gas is introduced, and the gas on the liquid surface is collected and introduced into the lithium fluoride hydrogen fluoride solution; the reaction temperature is-5-0 ℃; and the reaction pressure is 0.08-0.25 MPa.

2. The method of preparing lithium bisfluorooxalato borate according to claim 1, characterized in that, The molar ratio of the lithium fluoride and the hydrogen fluoride is 1:(20-30).

3. The method of preparing lithium bisfluorooxalato borate according to claim 1, characterized in that, The reaction time is 8-16 h.

4. The method of preparing lithium bisfluorooxalato borate according to claim 3, characterized in that, The reaction pressure is 0.15-0.25 MPa.

5. Process for the preparation of lithium bisfluorosulfonylborate according to any one of claims 1 to 4, characterized in that, After the reaction, the hydrogen fluoride is converted into gas to obtain the lithium difluorophosphate solid.

6. Process for the preparation of lithium bisfluorosulfonylborate according to any one of claims 1 to 4, characterized in that, The lithium fluoride hydrogen fluoride solution is obtained by reacting the lithium fluoride and the anhydrous hydrogen fluoride.

7. The method of preparing lithium bisfluorooxalato borate according to claim 6, characterized in that, The reaction temperature of the lithium fluoride and the anhydrous hydrogen fluoride is-10--30 ℃.

8. The method of preparing lithium bisfluorooxalato borate according to claim 5, wherein, The conversion of the hydrogen fluoride into gas is realized by means of pressure reduction concentration.

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