A process for the preparation of difluorooxalate borate

Abstract

The application provides a preparation method of difluorooxalate borate, comprising the following steps: (1) taking boron single substance and metal single substance, mixing uniformly, then adding anhydrous oxalic acid and a fluorinated metal salt corresponding to the metal single substance to obtain a mixture; the molar ratio of the metal single substance, the boron single substance, the anhydrous oxalic acid and the fluorinated metal salt is (0.90-1.10):1:(2.05-3.0):(1.90-2.10); (2) under a nitrogen atmosphere, the mixture is added into a ball milling device, a phase transfer catalyst is added, nitrogen is continuously filled, then ball milling reaction is carried out to obtain a difluorooxalate borate crude product. The preparation method uses boron single substance, anhydrous oxalic acid, a fluorinated metal salt and a metal single substance as raw materials, adopts one-step synthesis, does not need to use raw materials such as boron trifluoride and hydrogen fluoride, the process is simple, safe and environmentally friendly, the raw material conversion rate is high, high-purity and high-yield battery-grade difluorooxalate borate can be quickly and efficiently obtained without complex post-treatment steps, and the needs of industrial scale production are fully met.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology, specifically relating to a method for preparing difluorooxalate borate. Background Technology

[0002] Currently, commercially available secondary ion batteries are widely used as portable power sources in mobile phones, laptops, and cameras due to their advantages such as high operating voltage, high energy density, low self-discharge rate, no memory effect, long cycle life, and lightweight convenience. Difluorooxalate borate, as a novel electrolyte salt, exhibits good thermal and chemical stability, excellent low-temperature performance, high conductivity, and a wide electrochemical window, making it a promising next-generation electrolyte to replace hexafluorophosphate. Therefore, its synthesis research has attracted widespread attention.

[0003] Conventional synthesis of difluorooxalate borate typically involves boron trifluoride or hydrogen fluoride, which imposes stringent equipment requirements and poses significant safety risks. Therefore, providing a simple, pollution-free, and high-purity difluorooxalate borate has become a pressing issue for those skilled in the art. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a method for preparing difluorooxalate borate, wherein the preparation method adopts a one-step synthesis, which is simple, safe and environmentally friendly, and has high purity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] A method for preparing difluorooxalate borate includes the following steps: (1) taking boron and a metal element, mixing them, and then adding anhydrous oxalic acid and the corresponding fluorinated metal salt of the metal element to obtain a mixture; the molar ratio of the metal element, boron element, oxalic acid and fluorinated metal salt is (0.90~1.10):1:(2.05~3.0):(1.90~2.10); (2) adding the mixture to a ball milling device under a nitrogen atmosphere, adding a phase transfer catalyst, continuing to purge with nitrogen, and then performing a ball milling reaction to obtain crude difluorooxalate borate.

[0007] In some embodiments, nitrogen is continued to be introduced in step (2) until the pressure inside the ball milling device is 1 MPa to 5 MPa.

[0008] In some embodiments, the temperature of the ball milling reaction in step (2) is 100°C to 150°C.

[0009] In some embodiments, the ball milling reaction time is 6h to 12h.

[0010] In some embodiments, the mass of the phase transfer catalyst is 0.5% to 5% of the total mass of the boron element, anhydrous oxalic acid, fluorinated metal salt, and metal element.

[0011] In some embodiments, the elemental metal is selected from any one of sodium, zinc, magnesium, iron, and calcium; the metal ion in the fluorinated metal salt is selected from any one of sodium, zinc, magnesium, iron, and calcium ions.

[0012] In some embodiments, the phase transfer catalyst is selected from one or more of 15-crown ether-5, 18-crown ether-6, 24-crown ether-8, trimethylbenzylammonium chloride, and polyether-chain polyethylene glycol.

[0013] In some embodiments, the preparation method further includes the following steps: (3) adding a polar solvent to the crude difluorooxalate borate for extraction, concentration and crystallization, and drying.

[0014] In some embodiments, the drying conditions are: vacuum degree of 15 Pa to 1500 Pa, drying at 100°C to 120°C for 12 h to 24 h.

[0015] In some embodiments, the mass ratio of the polar solvent to crude difluorooxalate borate is (2-15):1.

[0016] In some embodiments, after extraction, the organic phase is concentrated to 20% to 40% of its original volume for crystallization.

[0017] In some embodiments, the polar solvent is selected from one or more of chain carbonates, cyclic carbonates, chain aliphatic esters, cyclic aliphatic esters, and halogenated hydrocarbons.

[0018] Preferably, the polar solvent is selected from one or more of dichloromethane, trichloromethane, tetrachloromethane, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, diethyl carbonate, ethylene carbonate, butene carbonate, ethyl propyl carbonate, ethyl acetate, butyl acetate, ethyl butyrate, ethyl formate, methyl acetate, propyl acetate, and ethyl propionate.

[0019] This invention provides a method for preparing difluorooxalate borate. The method employs a one-step synthesis using elemental boron, anhydrous oxalic acid, a fluorinated metal salt, and an elemental metal as raw materials. First, elemental boron is directly combined with the elemental metal to form a metal boride. Then, it undergoes a ball milling reaction with anhydrous oxalic acid and the fluorinated metal salt under the catalysis of a phase transfer catalyst. This overcomes the problem of small contact area between solid and solid reactants, which makes the reaction difficult. This method eliminates the need for raw materials such as boron trifluoride and hydrogen fluoride, resulting in a simple process, controllable conditions, and safety and environmental friendliness. Furthermore, the entire preparation process is solvent-free, achieving high raw material conversion rates. It allows for the rapid and efficient production of high-purity and high-yield battery-grade difluorooxalate borate without complex post-processing steps, fully meeting the needs of large-scale industrial production. Detailed Implementation

[0020] Unless otherwise specified, the experimental methods described in the following embodiments of the present invention are generally performed under conventional conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the embodiments are commercially available products.

[0021] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0022] The terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product, or device that includes a series of steps is not limited to the steps or modules listed, but may optionally include steps not listed, or may optionally include other steps inherent to such process, method, product, or device.

[0023] In this invention, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0024] This embodiment provides a method for preparing difluorooxalate borate, comprising the following steps: (1) taking boron and a metal element, mixing them, and then adding anhydrous oxalic acid and the corresponding fluorinated metal salt of the metal element to obtain a mixture; the molar ratio of the metal element, boron element, anhydrous oxalic acid and fluorinated metal salt is (0.90~1.10):1:(2.05~3.0):(1.90~2.10); (2) adding the mixture to a ball milling device under a nitrogen atmosphere, adding a phase transfer catalyst, continuing to purge with nitrogen, and then performing a ball milling reaction to obtain crude difluorooxalate borate.

[0025] The preparation reaction formula of this invention is: nB + 2nH₂C₂O₄ + 2XFn + X → XBF₂(C₂O₄) + nX 2 / n C2O4 + 2nH2. Wherein, XF is a fluoride metal salt, and the metal ion is selected from any one of sodium, zinc, magnesium, iron, and calcium ions; X is any one of sodium, zinc, magnesium, iron, and calcium elements; n is 1 or 2, when X is sodium, n = 1; when X is zinc, magnesium, iron, or calcium, n = 2.

[0026] This invention discloses a one-step synthesis method for preparing difluorooxalate borate. Using elemental boron, anhydrous oxalic acid, a fluorinated metal salt, and an elemental metal as raw materials, elemental boron is first directly combined with the elemental metal to form a metal boride. Then, it undergoes a ball milling reaction with anhydrous oxalic acid and the fluorinated metal salt under the catalysis of a phase transfer catalyst. This method overcomes the problem of small contact area between solid and solid reactants, which makes the reaction difficult. The ball milling apparatus is equipped with a constant-pressure one-way valve, which allows the generated gases to be discharged in an inert atmosphere into an activated carbon absorption column before being vented into a fume hood, ensuring the safety of the reaction process.

[0027] In the preparation method of this invention, anhydrous oxalic acid should be used in slight excess. If the oxalic acid is not in slight excess, a small amount of oxalic acid may sublimate and decompose in the reactor during the heating and calcination process, resulting in incomplete reaction of the boron elemental raw material. If the molar ratio of oxalic acid exceeds 3.0, it will cause significant waste of raw materials, resulting in a large amount of oxalic acid being discarded after failing to participate in the reaction.

[0028] In some embodiments, the mass of the phase transfer catalyst is 0.5% to 5% of the total mass of the boron, anhydrous oxalic acid, fluorinated metal salt, and metal element. Preferably, the mass of the phase transfer catalyst is 1% to 5% of the total mass of the boron, oxalic acid, fluorinated metal salt, and metal element. If the amount of phase transfer catalyst added is less than 0.5%, the optimal catalytic effect and the highest yield cannot be achieved. If it is higher than 5%, it will result in waste of the phase transfer catalyst and may inhibit the reaction, leading to a decrease in yield and reaction rate.

[0029] In some embodiments, the method further includes the following steps: (3) adding a polar solvent to the crude difluorooxalate borate for extraction, concentration and crystallization, and drying.

[0030] Preferably, the drying conditions are: a vacuum of 15 Pa to 1500 Pa, drying at 100°C to 120°C for 12 to 24 hours. Temperatures below 100°C cannot completely remove any water of crystallization that may be present in difluorooxalate borate, while temperatures above 120°C may cause a small portion of the product to decompose, thus reducing purity and yield.

[0031] It should be noted that the presence of water in the reaction system will cause it to combine with the reactants to form sodium hydroxide, affecting the purity and yield of the prepared difluorooxalate borate. Therefore, to ensure purity, all raw materials and reaction apparatus involved in this invention undergo dehydration treatment and are protected with inert gas.

[0032] The following description is based on specific embodiments.

[0033] Example 1

[0034] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0035] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:2.10:1.95 to obtain a homogeneous mixture. This mixture was then placed in a ball milling flask under a high-purity nitrogen atmosphere, and 1% of 18-crown ether-6 (solid mass) was added. The ball milling flask was purged with nitrogen to 3 MPa, and then heated to 110°C for ball milling for 12 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, propylene carbonate (3 times the mass of the crude sodium difluorooxalate borate) was added under a nitrogen atmosphere to extract the residue from the reaction vessel and concentrate it to 30% of its original volume for crystallization. The resulting crystals were filtered and placed in a 110°C, 30 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0036] Example 2

[0037] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0038] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:2.5:2.0 to obtain a homogeneous mixture. This mixture was then placed in a ball mill flask under a high-purity nitrogen atmosphere, and 1% of 18-crown ether-6 (solid mass) was added. The ball mill flask was purged with nitrogen to 3 MPa, and then heated to 110°C for ball milling for 12 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, propylene carbonate (3 times the mass of the crude sodium difluorooxalate borate) was added under a nitrogen atmosphere to extract the residue from the reactor and concentrate it to 30% of its original volume for crystallization. The obtained crystals were filtered and placed in a 110°C, 30 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0039] Example 3

[0040] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0041] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:2.5:2.0 to obtain a homogeneous mixture. This mixture was then placed in a ball milling flask under a high-purity nitrogen atmosphere, and 5% of 18-crown ether-6 (solid mass) was added. The ball milling flask was purged with nitrogen to 3 MPa, and then heated to 110°C for ball milling for 12 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, propylene carbonate (3 times the mass of the crude sodium difluorooxalate borate) was added under a nitrogen atmosphere to extract the residue from the reactor and concentrate it to 30% of its original volume for crystallization. The obtained crystals were filtered and placed in a 110°C, 30 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0042] Example 4

[0043] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0044] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:3.0:2.0 to obtain a homogeneous mixture. This mixture was then placed in a ball mill flask under a high-purity nitrogen atmosphere, and 1% of 18-crown ether-6 (solid mass) was added. The ball mill flask was purged with nitrogen to 3 MPa, and then heated to 110°C for ball milling for 12 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, propylene carbonate (3 times the mass of the crude sodium difluorooxalate borate) was added under a nitrogen atmosphere to extract the residue from the reactor and concentrate it to 30% of its original volume for crystallization. The resulting crystals were filtered and placed in a 110°C, 20 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0045] Example 5

[0046] This embodiment provides a method for preparing sodium difluorooxalate borate, including the following steps:

[0047] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:2.2:2.0 to obtain a homogeneous mixture. This mixture was then placed in a ball mill flask under a high-purity nitrogen atmosphere, and 3% of 15-crown ether-5 (solid mass) was added. The ball mill flask was purged with nitrogen to 2 MPa, and then heated to 130°C for ball milling for 10 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, 8 times the mass of the crude sodium difluorooxalate borate was added to the residue in a nitrogen atmosphere to extract and concentrate it to 20% of its original volume for crystallization. The obtained crystals were filtered and placed in a 120°C, 50 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0048] Example 6

[0049] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0050] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:2.7:2.05 to obtain a homogeneous mixture. This mixture was then placed in a ball mill flask under a high-purity nitrogen atmosphere, and 2% (solid mass) of trimethylbenzylammonium chloride was added. The ball mill flask was purged with nitrogen to 4 MPa, and then heated to 150°C for ball milling for 8 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, ethyl formate (10 times the weight of the crude sodium difluorooxalate borate) was added under a nitrogen atmosphere to extract the residue from the reaction vessel and concentrate it to 20% of its original volume for crystallization. The obtained crystals were filtered and placed in a vacuum drying oven at 115°C and 30 Pa overnight to obtain pure sodium difluorooxalate borate.

[0051] Example 7

[0052] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0053] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:2.5:2.0 to obtain a homogeneous mixture. This mixture was then placed in a ball mill flask under a high-purity nitrogen atmosphere, and 0.5% of 18-crown ether-6 (solid mass) was added. The ball mill flask was purged with nitrogen to 3 MPa, and then heated to 110°C for ball milling for 12 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, propylene carbonate (3 times the mass of the crude sodium difluorooxalate borate) was added under a nitrogen atmosphere to extract the residue from the reactor and concentrate it to 30% of its original volume for crystallization. The obtained crystals were filtered and placed in a 110°C, 30 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0054] Example 8

[0055] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0056] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:2.10:1.95 to obtain a homogeneous mixture. This mixture was then placed in a ball mill flask under a high-purity nitrogen atmosphere, and 1% of 18-crown ether-6 (solid mass) was added. The ball mill flask was purged with nitrogen to 0.3 MPa, and then heated to 110°C for ball milling for 12 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, propylene carbonate (3 times the mass of the crude sodium difluorooxalate borate) was added under a nitrogen atmosphere to extract the residue from the reaction vessel and concentrate it to 30% of its original volume for crystallization. The obtained crystals were filtered and placed in a 110°C, 30 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0057] Example 9

[0058] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0059] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:2.10:1.95 to obtain a homogeneous mixture. This mixture was then placed in a ball milling flask under a high-purity nitrogen atmosphere, and 1% of 18-crown ether-6 (solid mass) was added. The ball milling flask was purged with nitrogen to 3 MPa, and then heated to 90°C for ball milling for 12 hours to obtain crude sodium difluorooxalate borate. After cooling to room temperature, propylene carbonate (3 times the mass of the crude sodium difluorooxalate borate) was added under a nitrogen atmosphere to extract the residue from the reaction vessel and concentrate it to 30% of its original volume for crystallization. The resulting crystals were filtered and placed in a 110°C, 30 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0060] Example 10

[0061] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0062] Boron and sodium metal were first weighed and mixed in a 1:1 molar ratio under inert gas conditions at room temperature. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a 1:2.5:2.0 molar ratio for boron. The mixture was then placed into a ball milling flask under a high-purity nitrogen atmosphere, and 0.3% of 18-crown ether-6 (solid mass) was added. The ball milling flask was purged with nitrogen to 3 MPa, and then heated to 110°C for ball milling for 12 hours. After cooling to room temperature, propylene carbonate (3 times the mass of the product) was added under a nitrogen atmosphere to extract the residue from the flask and concentrate it to 30% of the original volume for crystallization. The obtained crystals were filtered and placed in a 110°C, 30 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0063] Example 11

[0064] This embodiment provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0065] Boron and sodium metal were first weighed and mixed in a 1:1 molar ratio at room temperature and under inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a 1:2.5:2.0 molar ratio for boron. The mixture was then placed into a ball milling flask under a high-purity nitrogen atmosphere, and 1% of 18-crown ether-6 by solid mass was added. The ball milling flask was purged with nitrogen to 3 MPa, and then heated to 110°C for ball milling for 12 hours. After cooling to room temperature, propylene carbonate (1 times the mass of the product) was added under a nitrogen atmosphere to extract the residue from the flask and concentrate it to 30% of the original volume for crystallization. The obtained crystals were filtered and placed in a 60°C, 30Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0066] Comparative Example 1

[0067] This comparative example provides a method for preparing sodium difluorooxalate borate, comprising the following steps:

[0068] Boron and sodium metal were first weighed and mixed in a molar ratio of 1:1 under room temperature and inert gas conditions. Then, anhydrous oxalic acid and anhydrous sodium fluoride were weighed and mixed thoroughly in a molar ratio of 1:1.52:1.95 to obtain a homogeneous mixture. This mixture was then placed in a ball milling flask under a high-purity nitrogen atmosphere, and 1% of 18-crown ether-6 (solid mass) was added. The ball milling flask was purged with nitrogen to 3 MPa, and then heated to 110°C for ball milling for 12 hours. After cooling to room temperature, propylene carbonate (3 times the mass of the product) was added under a nitrogen atmosphere to extract the residue from the flask and concentrate it to 30% of the original volume for crystallization. The obtained crystals were filtered and placed in a 110°C, 30 Pa vacuum drying oven overnight to obtain pure sodium difluorooxalate borate.

[0069] The purity, yield, free acid, moisture, turbidity, and color of the products from the above examples and comparative examples were tested.

[0070] Product purity was determined using high-performance liquid chromatography (HPLC) and nuclear magnetic resonance spectroscopy (NMR); free acidity was determined using an organic method, titrated with tripropylamine / propylene carbonate solution; moisture content was determined according to GB / T 6283 standard; turbidity was determined using a 1% difluorooxalate borate / methyl ethyl carbonate solution and a Hach turbidimeter; and color was determined by comparing a 10% difluorooxalate borate / propylene carbonate solution with a standard colorimetric tube. Test results are recorded in Table 1.

[0071] Table 1

[0072]

[0073]

[0074] The above results demonstrate that the present invention can successfully prepare difluorooxalate borate in one step, with a simple, safe, environmentally friendly, and pollution-free preparation process. In particular, the methods described in Examples 1-7 can prepare high-purity difluorooxalate borate with low free acid, moisture content, turbidity, and color, and a high yield, meeting the quality requirements for battery-grade products.

[0075] By comparing Examples 1 and 8, it can be seen that when the ball milling reaction pressure is too low, the yield of difluorooxalate borate also decreases significantly, indicating that the decrease in pressure reduces the chance of intermolecular contact, which in turn leads to a decrease in yield.

[0076] By comparing Examples 1 and 9, it can be seen that when the ball milling reaction temperature is too low, the yield decreases significantly, indicating that the reaction requires a certain activation energy to catalyze the reaction.

[0077] By comparing Example 2 and Example 10, it can be seen that a high product yield cannot be obtained when the amount of phase transfer catalyst added is insufficient.

[0078] By comparing Example 2 and Example 11, it can be seen that when the vacuum drying temperature is below 100°C, the measured free acid content of the finished product is higher. This may be due to a small amount of oxalic acid that cannot be decomposed.

[0079] By comparing Example 2 with Comparative Example 1, it can be seen that when the amount of oxalic acid added is insufficient, the reaction yield will be affected. This is because a small amount of oxalic acid will also decompose during the heating reaction.

[0080] In summary, this invention uses boron, oxalic acid, fluorinated metal salts, and metal elements as raw materials. First, boron and metal elements are mixed and directly combined to form metal borides. Then, high-purity difluorooxalate borate is synthesized by reacting boron with anhydrous oxalic acid and fluorinated metal salts in a phase transfer catalyst step. The quality meets the requirements of battery-grade materials, and the preparation process is simple, safe, environmentally friendly, and has a high yield.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing difluorooxalate borate, characterized in that, Includes the following steps: (1) Take boron and metal elements, mix them, and then add anhydrous oxalic acid and the corresponding fluorinated metal salt of the metal element to obtain a mixture; the molar ratio of the metal element, boron element, oxalic acid and fluorinated metal salt is (0.90~1.10):1:(2.05~3.0):(1.90~2.10); (2) Add the mixture to a ball milling device under a nitrogen atmosphere, add a phase transfer catalyst, continue to purge with nitrogen, and then carry out a ball milling reaction to obtain crude difluorooxalate borate; The metallic element is sodium; the metal ion in the fluorinated metal salt is sodium. The phase transfer catalyst is selected from one or more of 15-crown ether-5, 18-crown ether-6, 24-crown ether-8, trimethylbenzylammonium chloride, and polyether chain polyethylene glycol; In step (2), nitrogen is continued to be introduced until the pressure inside the ball mill device is 1 MPa to 5 MPa; The ball milling reaction temperature in step (2) is 100℃~150℃.

2. The method for preparing difluorooxalate borate as described in claim 1, characterized in that, The ball milling reaction time is 6h~12h.

3. The method for preparing difluorooxalate borate as described in claim 1, characterized in that, The mass of the phase transfer catalyst is 0.5% to 5% of the total mass of boron, anhydrous oxalic acid, fluorinated metal salt, and metal element.

4. The method for preparing difluorooxalate borate according to any one of claims 1 to 3, characterized in that, It also includes the following steps: (3) Add a polar solvent to the crude difluorooxalate borate for extraction, concentrate and crystallize, and dry; The polar solvent is selected from one or more of the following: chain carbonates, cyclic carbonates, chain aliphatic esters, cyclic aliphatic esters, and halogenated hydrocarbons.

5. The method for preparing difluorooxalate borate as described in claim 4, characterized in that, The drying conditions are: vacuum degree of 15Pa~1500Pa, drying at 100℃~120℃ for 12h~24h.

6. The method for preparing difluorooxalate borate as described in claim 4, characterized in that, The mass ratio of the polar solvent to the crude difluorooxalate borate is (2~15):1.

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