A preparation method of double lithium borate oxalate

Abstract

The application discloses a preparation method of lithium bisoxalate borate, which comprises the following steps: adding lithium oxalate and boric acid into an aprotic organic solvent, adding oxalyl chloride dropwise under stirring at a certain temperature, continuing to react at the certain temperature after the dropping is completed, filtering the reaction liquid after the reaction is completed, and obtaining lithium bisoxalate borate through concentration crystallization, washing and filtering, and drying of the filtrate. The method has the advantages of low reaction temperature, no need of high-temperature dehydration, low energy consumption and cost, almost no water in the reaction system, avoidance of decomposition of the target product due to water and heat, improvement of the reaction yield, simple process, less impurities, easy purification, and high purity of the obtained product.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing lithium bis(oxalate-borate); this method for preparing lithium bis(oxalate-borate) can be used as an additive for lithium-ion battery electrolytes. Background Technology

[0002] Lithium bis(oxalate-borate) (LiBOB) is a widely used electrolyte salt for lithium-ion batteries in recent years. It has good chemical properties and stability, and its thermal decomposition temperature can reach 300℃. It can form a stable SEI film on the carbon anode to prevent the intercalation of solvent molecules. It has high conductivity and a wide electrochemical window, which can improve the stability and safety of lithium-ion batteries and extend their service life.

[0003] Lithium-ion battery electrolytes containing LiBOB exhibit no dissolution or corrosion of manganese and iron-based cathode materials, and also demonstrate high thermal stability against other cathode materials such as lithium iron phosphate, lithium manganese oxide, and ternary NCM. With the rapid development of the new energy industry, especially electric vehicles, in recent years, the demand for power lithium-ion batteries is increasing, creating a vast market for related battery materials.

[0004] According to publicly available information, the preparation methods of lithium bis(oxalate-borate) are mainly divided into two types: solid-phase method and liquid-phase method. The reaction raw materials are oxalic acid, boron source and lithium hydroxide or lithium carbonate, which produce lithium bis(oxalate-borate) and water.

[0005] German patent DE19829030C1 describes a liquid-phase method for synthesizing lithium bis(oxalateborate) using lithium hydroxide or lithium carbonate, oxalic acid, boric acid or boron oxide as raw materials and water, toluene or tetrahydrofuran as the reaction medium.

[0006] In patent CN101397305B, a solution of a lithium source compound, a boron source compound, and a compound containing oxalate is heated to obtain a solution containing lithium bis(oxalate-borate). The heating is carried out in a sealed vessel at a pressure of 0.15–8 MPa and a temperature greater than the boiling point of the solvent at atmospheric pressure but less than 250°C. The solvent is selected from one or more of water, toluene, acetonitrile, and tetrahydrofuran. After heating, the solution containing lithium bis(oxalate-borate) is subjected to vacuum distillation to obtain a suspension, which is then vacuum dried to obtain the product.

[0007] In patent CN101914110B, oxalic acid, boric acid, and lithium hydroxide are metered and mixed in a mixer for 2-5 minutes. The mixture is then placed into a sealed reactor equipped with a pressure relief device. The reactor is heated to 100-300°C and kept at that temperature for 5-10 hours. After 3 hours of holding at that temperature, water vapor inside the reactor is released. The vapor is released once every hour. After synthesis, the reactor is evacuated at 130°C for 20 hours to obtain lithium bis(oxalate-borate).

[0008] In summary, all existing technical solutions involve the generation of water during the reaction process, which then combines with lithium bis(oxalate-borate) to form crystalline hydrates. To reduce residual moisture in the product, high-temperature dehydration is often required. This process is not only energy-intensive, but also accelerates the decomposition of lithium bis(oxalate-borate) with water during heating, resulting in low product yield, high impurity content, and difficulty in purification, making it challenging to meet the application standards of the lithium-ion battery industry. Summary of the Invention

[0009] To address the aforementioned technical problems, the present invention aims to provide a method for preparing lithium bis(oxalatoborate) that is mild in reaction, simple in process, low in cost, and suitable for industrial production. This method yields lithium bis(oxalatoborate) with high yield and purity.

[0010] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0011] A method for preparing lithium dioxalate borate involves adding lithium oxalate and boric acid to an aprotic organic solvent, and then adding oxalyl chloride dropwise at a certain temperature while stirring. After the addition is complete, the reaction is continued at a certain temperature. After the reaction is complete, the reaction solution is cooled and filtered. The filtrate is concentrated, crystallized, washed, filtered, and dried to obtain lithium dioxalate borate. The tail gas generated during the reaction is absorbed by water. The chemical reaction formula is as follows: Li₂C₂O₄ + H₃BO₃ + 2C₂O₂Cl₂ → LiB(C₂O₄)₂ + LiCl + 3HCl + CO₂ + CO

[0012] In this preparation method, the molar ratio of lithium oxalate, boric acid and oxalyl chloride is 1:(0.9-1.1):(2-3), and more preferably 1:(1-1.1):(2-2.5).

[0013] Furthermore, in this method, the dropping temperature of oxalyl chloride is 10–60 °C.

[0014] Furthermore, in this method, the heat preservation reaction temperature is 40℃~80℃, and the reaction time is 1~12 hours.

[0015] In the preparation method, the aprotic organic solvent is a solvent capable of dissolving lithium dioxaborate, selected from one or a mixture of two or more of acetonitrile, propionitrile, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl ethyl ketone, 1,4-dioxane, ethylene glycol dimethyl ether, and tetrahydrofuran.

[0016] The amount of aprotic organic solvent added is 3 to 8 times the mass of lithium oxalate, as long as the solvent can fully dissolve the product generated by the reaction.

[0017] The water content of the aprotic organic solvent is less than 500 ppm, more preferably less than 300 ppm.

[0018] Furthermore, in this preparation method, the washing solvent is selected from one or a mixture of two or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, benzene, toluene, chlorobenzene, n-hexane, cyclohexane, n-heptane, n-octane, dichloromethane, 1,2-dichloroethane, trichloroethane, 1,1,2,2-tetrachloroethane, and petroleum ether.

[0019] In this preparation method, oxalyl chloride is used as a reactant to react with boric acid and lithium oxalate to produce lithium bis(oxalateborate) and lithium chloride as a byproduct. At the same time, due to the presence of oxalyl chloride, the trace amount of water generated in the intermediate process can react with oxalyl chloride in a timely manner to produce gaseous hydrogen chloride, carbon dioxide and carbon monoxide. By heating, the gaseous hydrogen chloride, carbon dioxide and carbon monoxide can be quickly expelled from the reaction system.

[0020] Furthermore, excess lithium oxalate or boric acid in the reaction raw materials, and lithium chloride, a byproduct of the reaction, are almost insoluble in the solvent provided by this preparation method and can be completely removed by cooling and filtration. Excess oxalyl chloride, due to its boiling point of only 62–65°C, can be removed by concentration.

[0021] Since the reaction system is almost anhydrous, it solves the problems of high-temperature dehydration and residual moisture in existing technologies, avoids the decomposition of lithium bis(oxalate-borate) products when exposed to water and heat, and improves the reaction yield.

[0022] The beneficial effects of this invention are:

[0023] 1) This method has a low reaction temperature, does not require high-temperature dehydration, and has low energy consumption and cost;

[0024] 2) The reaction system of this method is almost anhydrous, which avoids the decomposition of the target product by water and heat, and improves the reaction yield.

[0025] 3) This method is simple, produces few impurities, is easy to purify, and yields products with high purity. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a method for preparing lithium dioxalate borate. The specific process is as follows: lithium oxalate and boric acid are added to an aprotic organic solvent. Oxaloyl chloride is added dropwise at a temperature of 10–60°C with stirring. After the addition is complete, the reaction continues at 40–80°C for 1–12 hours. After the reaction is complete, the reaction solution is cooled to room temperature, filtered to remove insoluble solids, and the filtrate is concentrated, crystallized, washed, filtered again, and dried to obtain lithium dioxalate borate. The tail gas generated during the reaction is absorbed by water. The chemical reaction formula is as follows:

[0028] Li2C2O4+H3BO3+2C2O2Cl2→LiB(C2O4)2+LiCl+3HCl+CO2+CO

[0029] In this preparation method, the molar ratio of lithium oxalate, boric acid and oxalyl chloride is 1:(0.9-1.1):(2-3), and more preferably 1:(1-1.1):(2-2.5).

[0030] In the preparation method, the aprotic organic solvent is a solvent capable of dissolving lithium dioxaborate, selected from one or a mixture of two or more of acetonitrile, propionitrile, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl ethyl ketone, 1,4-dioxane, ethylene glycol dimethyl ether, and tetrahydrofuran. The amount of aprotic organic solvent added is 3 to 8 times the mass of lithium oxalate, as long as it ensures that the solvent can fully dissolve the product generated in the reaction. The water content of the aprotic organic solvent is less than 500 ppm, preferably less than 300 ppm.

[0031] In this preparation method, the washing solvent is selected from one or a mixture of two or more of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, benzene, toluene, chlorobenzene, n-hexane, cyclohexane, n-heptane, n-octane, dichloromethane, 1,2-dichloroethane, trichloroethane, 1,1,2,2-tetrachloroethane, and petroleum ether.

[0032] In this preparation method, oxalyl chloride is used as a reactant to react with boric acid and lithium oxalate to produce lithium bis(oxalateborate) and lithium chloride as a byproduct. At the same time, due to the presence of oxalyl chloride, the trace amount of water generated in the intermediate process can react with oxalyl chloride in a timely manner to produce gaseous hydrogen chloride, carbon dioxide and carbon monoxide. By heating, the gaseous hydrogen chloride, carbon dioxide and carbon monoxide can be quickly expelled from the reaction system.

[0033] Furthermore, excess lithium oxalate or boric acid in the reaction raw materials, and lithium chloride, a byproduct of the reaction, are almost insoluble in the solvent provided by this preparation method and can be completely removed by cooling and filtration. Excess oxalyl chloride, due to its boiling point of only 62–65°C, can be removed by concentration.

[0034] Since the reaction system is almost anhydrous, it solves the problems of high-temperature dehydration and residual moisture in existing technologies, avoids the decomposition of lithium bis(oxalate-borate) products when exposed to water and heat, and improves the reaction yield.

[0035] The present invention will be further described below through specific embodiments.

[0036] Example 1

[0037] Add 102 g (1 mol) of lithium oxalate, 62 g (1 mol) of boric acid, and 306 g of acetonitrile with a moisture content of 200 ppm to a dry three-necked flask equipped with a stirrer and reflux condenser. Maintain the temperature at 10–15 °C, and add 254 g (2 mol) of oxalyl chloride dropwise through a constant-pressure dropping funnel while stirring. During the dropwise addition, bubbles will be generated; control the dropping rate to avoid excessive instantaneous gas production. The addition is completed after 1.5 hours. Slowly raise the temperature to 40–45 °C and continue the reaction at this temperature for 12 hours. The tail gas generated during the reaction is absorbed by water.

[0038] After the reaction was completed, the reaction solution was cooled to room temperature and filtered under a nitrogen atmosphere. The filter cake was lithium chloride, a byproduct. The filtrate was concentrated and crystallized. After washing several times with dichloromethane, it was dried under reduced pressure to obtain 176g of lithium bis(oxalate-borate) solid product, with a yield of 90.7%, a purity of 99.82%, and a moisture content of 25ppm.

[0039] Example 2

[0040] 102 g (1 mol) of lithium oxalate, 68 g (1.1 mol) of boric acid, and 500 g of ethyl acetate with a water content of 95 ppm were added to a dry three-necked flask equipped with a stirrer and reflux condenser. The temperature was controlled at 50–60 °C. Under stirring, 317 g (2.5 mol) of oxalyl chloride was added dropwise through a constant-pressure dropping funnel. Bubbles were generated during the addition; the dropping rate was controlled to avoid excessive instantaneous gas production. The addition was completed after 3 hours, and the reaction was maintained at the same temperature for another hour. The tail gas produced during the reaction was absorbed with water.

[0041] After the reaction was completed, the reaction solution was cooled to room temperature and filtered under a nitrogen atmosphere. The filter cake contained lithium chloride as a byproduct and excess boric acid. The filtrate was concentrated and crystallized. It was washed several times with dimethyl carbonate and dried under reduced pressure to obtain 170g of lithium bis(oxalate-borate) solid product, with a yield of 87.6%, a purity of 99.86%, and a moisture content of 30ppm.

[0042] Example 3

[0043] Add 102 g (1 mol) of lithium oxalate, 65 g (1.05 mol) of boric acid, 600 g of 1,4-dioxane with a water content of 236 ppm, and 200 g of ethylene glycol dimethyl ether with a water content of 120 ppm to a dry three-necked flask equipped with a stirrer and reflux condenser. Maintain the temperature at 30–35 °C, and add 279 g (2.2 mol) of oxalyl chloride dropwise through a constant-pressure dropping funnel while stirring. During the dropwise addition, bubbles are generated; control the dropping rate to avoid excessive instantaneous gas production. The addition is completed after 2.5 hours, and the temperature is slowly raised to 75–80 °C and the reaction is maintained at this temperature for 5 hours. The tail gas generated during the reaction is absorbed by water.

[0044] After the reaction was complete, the reaction solution was cooled to room temperature and filtered under a nitrogen atmosphere. The filter cake was lithium chloride, a byproduct. The filtrate was concentrated and crystallized. After washing several times with petroleum ether, it was dried under reduced pressure to obtain 175 g of lithium bis(oxalate-borate) solid product, with a yield of 90.2%, a purity of 99.92%, and a moisture content of 33 ppm.

[0045] As can be seen from the above embodiments, the target product lithium bis(oxalato)borate obtained by the preparation method of the present invention has relatively high yield and purity.

[0046] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any modifications or equivalent transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing lithium bis(oxalateborate), characterized in that: Lithium oxalate and boric acid were added to... In an aprotic organic solvent, oxalyl chloride is added dropwise under stirring at a certain temperature. After the addition is complete, the reaction is continued at a certain temperature. After the reaction is completed, the reaction solution is cooled and filtered. The filtrate is concentrated, crystallized, washed, filtered, and dried to obtain lithium dioxalate borate. The molar ratio of lithium oxalate, boric acid, and oxalyl chloride is 1:(0.9~1.1):(2~3); The dropping temperature of oxalyl chloride is 10~60℃; The heat preservation reaction temperature is 40℃~80℃, and the reaction time is 1~12 hours; The aprotic organic solvent is a solvent capable of dissolving lithium dioxaborate, selected from one or more of acetonitrile, propionitrile, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl ethyl ketone, 1,4-dioxane, ethylene glycol dimethyl ether, and tetrahydrofuran. The water content of the aprotic organic solvent is less than 500 ppm.

2. The method for preparing lithium bis(oxalateborate) according to claim 1, characterized in that: The amount of aprotic organic solvent added is 3 to 8 times the mass of lithium oxalate.

3. The method for preparing lithium bis(oxalateborate) according to claim 1, characterized in that: The washing solvent is selected from one or a mixture of two or more of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, benzene, toluene, chlorobenzene, n-hexane, cyclohexane, n-heptane, n-octane, dichloromethane, 1,2-dichloroethane, trichloroethane, 1,1,2,2-tetrachloroethane, and petroleum ether.