Preparation method of lithium fluoroborate containing unsaturated bonds

Abstract

The invention relates to a preparation method of lithium fluoroborate containing unsaturated bonds, and belongs to the technical field of lithium ion battery additives. The preparation method comprises the following steps: carrying out reaction on organic acid lithium containing unsaturated bonds and boron trifluoride gas in a solvent at a low temperature of-10 to 0 DEG C, and carrying out solid-liquid separation to obtain a lithium fluoroborate crude product containing unsaturated bonds; the solvent is a poor solvent of lithium fluoroborate containing unsaturated bonds. According to the method, boron trifluoride gas is used as a fluorine reagent, so that introduction of water is avoided; the method has the advantages of simple operation, high product quality, high yield, low cost, full utilization of raw materials, reduction of the generation of three wastes, and suitableness for large-scale production. The yield of the obtained product can reach 96% or above, and the purity can reach 99% or above.

Description

Technical Field

[0001] The invention relates to a method for preparing lithium fluoroborate salt containing unsaturated bonds, belonging to the technical field of lithium ion battery additives. Background Art

[0002] Lithium-ion batteries are indispensable energy storage devices in modern electronic devices. The optimization of their performance has always been the focus of research and development by researchers and enterprises. In lithium-ion batteries, the electrolyte plays a vital role as a medium for transferring lithium ions. In order to improve the performance, stability and safety of batteries, researchers often add various additives to the basic electrolyte.

[0003] Vinylene carbonate (VC), lithium tetrafluoroborate (LiBF4) and lithium difluorooxalatoborate (LiODFB) are the most important additives in lithium-ion battery electrolytes. They can form a solid electrolyte membrane (SEI membrane) at the negative electrode during the initial charge and discharge process of lithium batteries, prevent direct contact between the electrode and the electrolyte, reduce the occurrence of side reactions, and thus improve the cycle life and stability of the battery. However, vinylene carbonate has disadvantages such as high production cost and complex preparation process; lithium tetrafluoroborate has disadvantages such as low room temperature ion conductivity, inability to form SEI membrane on the graphite surface when used alone, and complex preparation process; and lithium difluorooxalatoborate has disadvantages such as sensitivity to moisture, strong corrosiveness, and complex preparation process.

[0004] The Chinese invention patent with the announcement date of June 20, 2023 and the announcement number of CN110233289B discloses a high-voltage additive and an electrolyte and a battery containing the additive, and specifically discloses that the organic fluoroborate electrolyte additive is synthesized by the following steps: adding the raw material lithium salt RO-Li, boron trifluoride gas or a complex containing boron trifluoride, and the reaction solvent-dimethyl carbonate to the reactor, reacting for 2-10 hours at 20℃-40℃ and 0.1Mpa, and concentrating, crystallizing, separating, and drying the reaction liquid to obtain a high-purity organic fluoroborate finished product. However, the raw material lithium salts of the reaction are mostly organic lithium salts containing benzene rings and heterocycles, and the olefin lithium salts containing unsaturated bonds are prone to polymerization during the reaction and concentration process due to the presence of unsaturated double bonds, thereby affecting the yield and purity of the reaction product.

[0005] The Chinese invention patent with a publication date of October 18, 2022 and a publication number of CN115197259A discloses an organic alkali metal salt of trifluoroboric acid containing an unsaturated bond, and a preparation method and application thereof. Specifically, it discloses an organic alkali metal salt containing an unsaturated bond and boron trifluoride as reaction raw materials, and 2,6-di-tert-butyl-p-cresol as an inhibitor, and reacts in methyl tert-butyl ether. The prepared organic alkali metal salt of trifluoroboric acid containing an unsaturated bond contains unsaturated bonds, esters and trifluoroboric acid groups. While exerting the structural functions of MBF4 (such as LiBF4), it can also assist in the formation of an SEI film and play a similar function to VC, and can be used as a new additive for the next generation. However, the preparation method uses ether solvents, which poses a safety hazard, and an inhibitor is used in the reaction, which affects the product purity (94%) and yield (80%).

[0006] The Chinese invention patent with a publication date of September 8, 2023 and a publication number of CN116715691A discloses a method for preparing an organic lithium salt of trifluoroboric acid containing an unsaturated bond at low temperature, specifically disclosing adding an organic lithium salt containing an unsaturated bond to acetonitrile, and adding boron trifluoride acetonitrile under stirring conditions for reaction. This method has the advantages of simple synthesis, low production cost, and relatively safe, but the purity of the synthesized organic lithium salt of trifluoroboric acid containing an unsaturated bond is below 98%, and the yield is below 88%, and there are still disadvantages of low product purity and yield. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing a lithium fluoroborate salt containing an unsaturated bond, and to provide a method for preparing a lithium fluoroborate salt containing an unsaturated bond with high yield and purity.

[0008] In order to achieve the above object, the technical scheme of the preparation method of a lithium fluoroborate salt containing an unsaturated bond in the present invention is:

[0009] A preparation method of lithium fluoroborate salt containing unsaturated bonds comprises the following steps: organic acid lithium containing unsaturated bonds and boron trifluoride gas react in a solvent under low temperature conditions of -10-0°C, and then undergo solid-liquid separation to obtain a crude lithium fluoroborate salt containing unsaturated bonds; the solvent is a poor solvent for the lithium fluoroborate salt containing unsaturated bonds.

[0010] The beneficial effect of the above technical scheme is that the preparation method of lithium fluoroborate salt containing unsaturated bonds of the present invention is an improved invention. The present invention uses organic lithium salt containing unsaturated bonds and boron trifluoride gas as reaction raw materials and reacts in a poor solvent, wherein boron trifluoride gas is used as a fluorine reagent, which, on the one hand, avoids the introduction of moisture into the reaction system, and on the other hand, can make full use of the reaction raw materials and improve the yield of the product; and the poor solvent, on the one hand, provides conditions for the reaction to improve the yield of the product, and on the other hand, the crude lithium salt generated by the reaction is insoluble in the poor solvent, which is conducive to the separation and purification of the product. Moreover, after filtering the crude lithium salt, the poor solvent can be recycled.

[0011] Furthermore, the use of a poor solvent and a low temperature reaction can prevent the organic lithium salt containing an unsaturated bond from undergoing other reactions (such as addition reactions) during the reaction process, thereby improving the utilization rate of raw materials, and further improving the yield of the reaction and the purity of the reaction product. According to testing, the yield of the product obtained by the present invention can reach more than 96%, and the purity can reach more than 99%.

[0012] As a further improvement, the boron trifluoride is in excess relative to the organic acid lithium containing an unsaturated bond.

[0013] Preferably, the purity of the boron trifluoride gas is not less than 96%.

[0014] Specifically, in order to achieve a higher utilization efficiency of the raw materials, the reaction is carried out under the condition that the pressure of the boron trifluoride gas is higher than the normal pressure. Preferably, the pressure of the boron trifluoride gas is 80 to 100 kPa higher than the normal pressure.

[0015] As a further improvement, the organic acid lithium containing unsaturated bonds is a C3-C8 olefin organic acid lithium.

[0016] As a further improvement, the organic acid lithium containing unsaturated bonds is selected from one of lithium dimethyl butylate, lithium acrylate, lithium methacrylate, and lithium maleate.

[0017] As a further improvement, the poor solvent is selected from one or both of anisole and dichloromethane.

[0018] As a further improvement, the mass ratio of the organic acid lithium containing unsaturated bonds to the poor solvent is 1:(9.5-13).

[0019] As a further improvement, the preparation method comprises dissolving a crude lithium fluoroborate salt containing an unsaturated bond in a good solvent, filtering the solution, concentrating and crystallizing the filtrate, and obtaining a fine lithium fluoroborate salt containing an unsaturated bond.

[0020] As a further improvement, the good solvent is selected from one or more of dimethyl carbonate, ethyl methyl carbonate, and ethyl acetate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The NMR spectrum of lithium dimethyl butyl acrylate used in the present invention;

[0022] Figure 2 The NMR spectrum of lithium maleate used in the present invention;

[0023] Figure 3 This is the NMR spectrum of lithium boron trifluoride acrylate prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0024] Lithium batteries have the highest energy density among all commercial batteries currently available and are widely used in consumer electronics, electric vehicles, large-scale energy storage and other fields. In recent years, the development of various industries has put forward higher requirements for battery life, energy density, rate performance and safety. The electrolyte in the battery mainly plays the role of transmitting ions between the positive and negative electrodes. The composition of the electrolyte, such as electrolyte salt, directly affects the capacity and safety performance of the battery. Vinyl carbonate (VC) is one of the most important additives in lithium battery electrolytes. It can form a solid electrolyte film at the negative electrode during the initial charge and discharge process of the lithium battery, thereby improving the service life of the battery. One of the reasons for VC film formation is that it has unsaturated bonds, which can undergo polymerization reactions under certain conditions, thereby helping to form an SEI film. However, VC has the disadvantages of high production cost and complex preparation process. Lithium battery additives with better performance, such as lithium tetrafluoroborate and lithium difluoroborate oxalate, also have problems such as high production cost and complex process. Based on this, the present invention provides a method for preparing lithium fluoroborate salts with unsaturated bonds.

[0025] The preparation method of lithium fluoroborate salt containing unsaturated bonds of the present invention comprises the following steps: organic acid lithium containing unsaturated bonds and boron trifluoride gas react in a solvent under low temperature conditions of -10-0°C, and then undergo solid-liquid separation to obtain a crude lithium fluoroborate salt containing unsaturated bonds; the solvent is a poor solvent for the lithium fluoroborate salt containing unsaturated bonds.

[0026] The entire reaction process is carried out under closed conditions.

[0027] To further describe the present invention, it should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0028] A specific embodiment of the method for preparing a lithium fluoroborate salt containing an unsaturated bond of the present invention:

[0029] The lithium dimethyl butylate and lithium maleate used in the following examples of the present invention are prepared in the laboratory. The NMR spectrum of lithium dimethyl butylate ((CH3)2C=CHCH2COOLi) is as follows: Figure 1 As shown, the NMR spectrum of lithium maleate (LiOOCCH=CHCOOLi) is as follows Figure 2 shown.

[0030] The chemical reaction equation involved in the preparation method of the lithium fluoroborate salt containing unsaturated bonds of the present invention is as follows:

[0031] RO-Li+BF3——→ROBF3Li

[0032] Li-ORO-Li+2BF3——→LiBF3OROBF3Li.

[0033] Example 1

[0034] The preparation method of a lithium fluoroborate salt containing an unsaturated bond in this embodiment comprises the following steps:

[0035] (1) nitrogen replacement was performed on the high pressure glass bottle, and 30 g of lithium dimethyl butylate and 360 g of anisole were added to the high pressure glass bottle in a fume hood in a dry room, and stirred evenly;

[0036] (2) Cooling the high-pressure bottle containing the reaction solution to -10°C while stirring, and maintaining a negative pressure of -80 kPa;

[0037] (3) Slowly introduce 96.6% pure boron trifluoride gas (BF3) into the high-pressure bottle while keeping it sealed;

[0038] (4) When the pressure in the high-pressure bottle reaches 100 kPa, stop the gas supply, release the pressure in the reaction bottle to the normal pressure, and then repeat step (3). The flow meter measures the amount of boron trifluoride gas consumed. When the weight of the reaction bottle increases to 16.9 g, stop the gas supply after the reaction is completed.

[0039] (5) Filter the reaction solution of step (4) in a fume hood in a dry room to obtain 46.4 g of crude lithium salt;

[0040] (6) Dissolve the crude lithium salt in 370 g of ethyl acetate, and filter using a filter membrane after the solution is complete;

[0041] (7) The filtrate obtained in step (6) was concentrated and crystallized by rotary evaporation, and the solid after crystallization was scraped out, crushed and dried (105° C.) to finally obtain 45.5 g of a finished product. The product purity was 99.9% and the product yield was 97% after gas chromatography testing.

[0042] In other implementation situations, boron trifluoride gas can be introduced into the reaction system at a flat pressure to prepare lithium fluoroborate salt containing unsaturated bonds, and the effect is equivalent to or similar to that of this embodiment.

[0043] Example 2

[0044] The preparation method of a lithium fluoroborate salt containing an unsaturated bond in this embodiment comprises the following steps:

[0045] (1) The high-pressure glass bottle was replaced with nitrogen, and 60 g of lithium dimethyl butylate and 780 g of dichloromethane were added to the high-pressure glass bottle in a fume hood in a dry room, and stirred evenly;

[0046] (2) Cooling the high-pressure bottle containing the reaction solution to -5°C while stirring, and maintaining a negative pressure of -80 kPa;

[0047] (3) Slowly introduce 96.6% pure boron trifluoride gas (BF3) into the high-pressure bottle while keeping it sealed;

[0048] (4) When the pressure in the high-pressure bottle reaches 150 kPa, stop the gas supply first, release the pressure in the reaction bottle to the normal pressure, and then repeat step (3). The flow meter measures the amount of boron trifluoride gas consumed. When the weight of the reaction bottle increases to 33.9 g, stop the gas supply after the reaction is completed.

[0049] (5) Filter the reaction solution of step (4) in a fume hood in a dry room to obtain 92.9 g of crude lithium salt;

[0050] (6) Dissolve the crude lithium salt using 743 g of dimethyl carbonate, and filter using a filter membrane after the dissolution is complete;

[0051] (7) The filtrate obtained in step (6) was concentrated and crystallized by rotary evaporation, and the solid after crystallization was scraped out, crushed and dried (105° C.) to finally obtain 92.4 g of a finished product. The product purity was 99.8% and the product yield was 98.4% after gas chromatography testing.

[0052] Example 3

[0053] The preparation method of a lithium fluoroborate salt containing an unsaturated bond in this embodiment comprises the following steps:

[0054] (1) nitrogen replacement was performed on the high-pressure glass bottle, and 78 g of lithium acrylate and 1014 g of dichloromethane were added to the high-pressure glass bottle in a fume hood in a dry room, and stirred evenly;

[0055] (2) Cooling the high-pressure bottle containing the reaction solution to -8°C while stirring, and maintaining a negative pressure of -80 kPa;

[0056] (3) Slowly introduce 96.6% pure boron trifluoride gas (BF3) into the high-pressure bottle while keeping it sealed;

[0057] (4) When the pressure in the high-pressure bottle reaches 95 kPa, stop the gas supply first, release the pressure in the reaction bottle to the normal pressure, and then repeat step (3). The flow meter measures the amount of boron trifluoride gas consumed. When the weight of the reaction bottle increases to 67.8 g, stop the gas supply after the reaction is completed;

[0058] (5) Filter the reaction solution of step (4) in a fume hood in a dry room to obtain 145.1 g of crude lithium salt;

[0059] (6) Dissolve the crude lithium salt in 1160 g of ethyl methyl carbonate, and filter using a filter membrane after the solution is complete;

[0060] (7) The filtrate obtained in step (6) was concentrated and crystallized by rotary evaporation, and the solid after crystallization was scraped out, crushed and dried (110° C.), and finally 143 g of a finished product was obtained. The product purity was 99.9% and the product yield was 98% after gas chromatography testing.

[0061] The NMR spectrum of lithium boron trifluoride acrylate prepared in this example is as follows Figure 3 As shown, the peak position of the fluorine spectrum in the NMR test is the position of lithium boron trifluoride acrylate, and the obtained product is the target product.

[0062] Example 4

[0063] The preparation method of a lithium fluoroborate salt containing an unsaturated bond in this embodiment comprises the following steps:

[0064] (1) The high-pressure glass bottle was replaced with nitrogen, and 64 g of lithium maleate and 610 g of dichloromethane were added to the high-pressure glass bottle in a fume hood in a dry room, and stirred evenly;

[0065] (2) Cooling the high-pressure bottle containing the reaction solution to -10°C while stirring, and maintaining a negative pressure of -80 kPa;

[0066] (3) Slowly introduce 96.6% pure boron trifluoride gas (BF3) into the high-pressure bottle while keeping it sealed;

[0067] (4) When the pressure in the high-pressure bottle reaches 100 kPa, stop the gas supply first, release the pressure in the reaction bottle to the normal pressure, and then repeat step (3). The flow meter measures the amount of boron trifluoride gas consumed. When the weight of the reaction bottle increases to 67.8 g, stop the gas supply after the reaction is completed;

[0068] (5) Filter the reaction solution of step (4) in a fume hood in a dry room to obtain 94.3 g of crude lithium salt;

[0069] (6) Dissolve the crude lithium salt in 754 g of ethyl methyl carbonate, and filter using a filter membrane after the solution is complete;

[0070] (7) The filtrate obtained in step (6) was concentrated and crystallized by rotary evaporation, and the solid after crystallization was scraped out, crushed and dried (110° C.) to finally obtain 93.5 g of a finished product. The product purity was 99.8% and the product yield was 98.5% after gas chromatography testing.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 1 is that the reaction is carried out at 20° C. and comprises the following steps:

[0073] (1) nitrogen replacement was performed on the high pressure glass bottle, and 30 g of lithium dimethyl butylate and 360 g of anisole were added to the high pressure glass bottle in a fume hood in a dry room, and stirred evenly;

[0074] (2) The high-pressure bottle containing the reaction solution is kept at a temperature of 20°C while stirring, and a negative pressure of -80 kPa is maintained;

[0075] (3) Slowly introduce 96.6% pure boron trifluoride gas (BF3) into the high-pressure bottle while keeping it sealed;

[0076] (4) When the pressure in the high-pressure bottle reaches 100 kPa, stop the gas supply, release the pressure in the reaction bottle to the normal pressure, and then repeat step (3). The flow meter measures the amount of boron trifluoride gas consumed. When the weight of the reaction bottle increases to 16.9 g, stop the gas supply after the reaction is completed.

[0077] (5) Due to the high activity of boron trifluoride and the large amount of heat generated, the material will polymerize, and some yellowing and sticky blocks will appear in the reaction liquid. After post-reaction treatment, the purity of the product is 60% and the yield is about 50%.

[0078] Comparative Example 2

[0079] The difference between this comparative example and Example 1 is that dimethyl carbonate (DMC) is used as a good solvent of lithium fluoroborate salt containing unsaturated bonds, and the reaction temperature is 20° C., and the following steps are included:

[0080] (1) The high-pressure glass bottle was replaced with nitrogen, and 30 g of lithium dimethyl butylate and 360 g of dimethyl carbonate were added to the high-pressure glass bottle in a fume hood in a dry room, and stirred evenly;

[0081] (2) The high-pressure bottle containing the reaction solution is kept at a temperature of 20°C while stirring, and a negative pressure of -80 kPa is maintained;

[0082] (3) Slowly introduce 96.6% pure boron trifluoride gas (BF3) into the high-pressure bottle while keeping it sealed;

[0083] (4) When the pressure in the high-pressure bottle reaches 100 kPa, stop the gas supply, release the pressure in the reaction bottle to the normal pressure, and then repeat step (3). The flow meter measures the amount of boron trifluoride gas consumed. When the weight of the reaction bottle increases to 16.9 g, stop the gas supply after the reaction is completed.

[0084] (5) During the reaction, the reaction liquid gradually turns yellow and finally brown. The reaction liquid is concentrated, crystallized, separated, and dried to obtain a product with a purity of 90% and a yield of 20%.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the specification of the present invention should also be included in the protection scope of the present invention.

Claims

1. A method for preparing a lithium fluoroborate salt containing an unsaturated bond, characterized in that: The method comprises the following steps: an organic acid lithium containing an unsaturated bond and a boron trifluoride gas react in a solvent at a low temperature of -10 to 0°C, and then undergo solid-liquid separation to obtain a crude lithium fluoroborate salt containing an unsaturated bond; the solvent is a poor solvent for the lithium fluoroborate salt containing an unsaturated bond.

2. The method for preparing a lithium fluoroborate salt containing an unsaturated bond according to claim 1, characterized in that: The boron trifluoride is in excess relative to the organic acid lithium containing an unsaturated bond.

3. The method for preparing a lithium fluoroborate salt containing an unsaturated bond according to claim 1 or 2, characterized in that: The organic acid lithium containing unsaturated bonds is a C3-C8 olefin organic acid lithium.

4. The method for preparing the lithium fluoroborate salt containing an unsaturated bond according to claim 3, characterized in that: The organic acid lithium containing unsaturated bonds is selected from one of lithium dimethyl butylate, lithium acrylate, lithium methacrylate and lithium maleate.

5. The method for preparing a lithium fluoroborate salt containing an unsaturated bond according to claim 1 or 2, characterized in that: The poor solvent is selected from one or both of anisole and dichloromethane.

6. The method for preparing the lithium fluoroborate salt containing an unsaturated bond according to claim 5, characterized in that: The mass ratio of the organic acid lithium containing unsaturated bonds to the poor solvent is 1: (9.5-13).

7. The method for preparing lithium fluoroborate salt containing unsaturated bonds according to claim 1, characterized in that: The preparation method comprises dissolving a crude lithium fluoroborate salt containing an unsaturated bond in a good solvent, filtering the solution, concentrating the filtrate and crystallizing the solution to obtain a fine lithium fluoroborate salt containing an unsaturated bond.

8. The method for preparing the lithium fluoroborate salt containing an unsaturated bond according to claim 7, characterized in that: The good solvent is selected from one or more of dimethyl carbonate, ethyl methyl carbonate and ethyl acetate.

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