Background technology
In recent years, with the rapid development of the lithium-ion battery industry, the research and development of electrolyte lithium salts has become increasingly popular. New lithium salts with new structures and functions are constantly being reported. At present, the comprehensive review of performance, price, technology, etc. Consider that the most representative and promising product on the market is lithium difluoroxalate borate (LiODFB). It combines the advantages of lithium tetrafluoroborate (LiBF4) and lithium bisoxaloborate (LiBOB), with a thermal decomposition temperature as high as 240°C, basically no corrosion to electrode materials, good cycle performance, low moisture sensitivity, and good high and low temperature resistance. Performance, rate capability and compatibility of positive and negative electrodes are superior to lithium hexafluorophosphate currently used in lithium-ion batteries in all aspects, and may replace it as the main salt of lithium battery electrolytes in the future.
The raw material for preparing lithium difluoroxaloborate is lithium oxalate. The purity and performance indicators of lithium oxalate affect the quality of lithium difluoroxaloborate, thereby affecting the lithium ion battery capacity and cycle of the lithium difluoroxaloborate electrolyte system. The frequency and safety performance have a direct impact. Because of this, it is very necessary to produce high-purity lithium oxalate with excellent performance. The current traditional method of preparing lithium oxalate is mainly to neutralize lithium carbonate or lithium hydroxide with oxalic acid. The purity of the produced lithium oxalate is not high, and the process The process is difficult to control, is not suitable for large-scale production, and cannot meet the demand for the production of lithium difluoroxalate borate.
Content of the invention
In view of the shortcomings of the existing process technology, the purpose of the present invention is to provide a preparation method of high-purity lithium oxalate, which has a simple process, strong implementability, safety and environmental protection, high product purity, and can be produced continuously on a large scale.
In order to achieve the above objectives, the present invention provides a method for preparing high-purity lithium oxalate, using industrial grade lithium hydroxide as raw material, including the following steps:
(1) Dissolve industrial grade lithium hydroxide monohydrate and pure water in a container at a mass ratio of 1:5, stir until the solution is clear, and obtain an industrial grade lithium hydroxide solution; at the same time, weigh the industrial grade monohydrate Oxalic acid with a lithium element molar ratio of 1:2 in lithium hydroxide is stirred and dissolved in 90-100°C pure water with 1-1.5 times the mass of oxalic acid in a container to obtain an oxalic acid solution, and then 10%-20% is taken from the oxalic acid solution Slowly add the industrial grade lithium hydroxide solution, stir until the reaction is complete, let it stand for 10-30 minutes, filter and remove impurities until the solution is clear, and obtain a filtered lithium hydroxide solution.
(2) Add 20-30% of the remaining oxalic acid solution in step (1) into the reaction kettle, stir, and then slowly add the filtered lithium hydroxide solution obtained in step (1) until there is a small amount of white precipitate at the bottom Generate, stop adding the filtered lithium hydroxide solution to allow full reaction; then use homogeneous synthesis, slowly add the remaining filtered lithium hydroxide solution and the remaining oxalic acid solution into the reaction kettle at the same time, continue stirring during the addition process, the temperature Control it between 50-80°C. After adding, adjust the pH value of the reaction system to 7.0-7.5 with lithium hydroxide or oxalic acid, and continue stirring for 10-30 minutes.
(3) Control the temperature of the lithium oxalate solution obtained in step (2) to drop to normal temperature at a rate of 5-15°C/h, and let it stand until all the white precipitated lithium oxalate sinks to the bottom. The supernatant can be collected and returned to step ( 1) Recycling as a solvent instead of pure water.
(4) Use a PTFE-lined centrifuge to spin dry the lithium oxalate obtained in step (3), and dry the wet material at 100-200°C for 3-6 hours to obtain a high-purity lithium oxalate finished product.
The oxalic acid is oxalic acid with a mass content of 299.9%.
Compared with the existing technology, the advantages and beneficial effects of the present invention are:
(1) The present invention uses industrial-grade lithium hydroxide monohydrate as raw material, uses a small amount of oxalic acid to remove impurities and calcium first, and at the same time optimizes various process control parameters, adopts a homogeneous synthesis method to prepare lithium oxalate, and controls the crystallization temperature The produced lithium oxalate crystal particles are larger and more stable, thus ensuring the high purity of the lithium oxalate product produced. Both the mother liquor and the washing liquid during the reaction can be recycled, thus greatly reducing the production cost and improving the utilization rate of lithium.
(2) The reaction is carried out under conventional conditions, with low energy consumption, simple process flow, no environmentally harmful gases and waste residues, and is suitable for large-scale continuous production.
(3) The raw materials are cheap and easy to obtain, the products produced have high purity, low content of impurity elements, high element utilization rate in the entire process, and the product quality meets the requirements for preparing lithium difluoroxaloborate electrolyte for lithium-ion batteries.
Detailed implementation
A method for preparing high-purity lithium oxalate, the steps are as follows:
(1) Add 300kg of industrial grade lithium hydroxide monohydrate into 1500L of pure water, dissolve it in a plastic container, and stir until the solution is clear to obtain an industrial grade lithium hydroxide solution. Weigh 450kg of oxalic acid (mass content 299.9%) with a molar ratio of 1:2 to lithium, stir and dissolve it in an enamel container with 450L of pure water at a temperature of 90°C to obtain an oxalic acid solution, take 90kg of the oxalic acid solution and slowly add industrial grade lithium hydroxide solution, stir until complete reaction, let stand for 10 minutes, filter and remove impurities until the solution is clear, and obtain a filtered lithium hydroxide solution.
(2) Add 162kg from the remaining oxalic acid solution in step (1) into the reaction kettle, stir, and then slowly add the filtered lithium hydroxide solution obtained in step (1) until a small amount of white precipitate forms at the bottom, stop adding The filtered lithium hydroxide solution is allowed to fully react; then homogeneous synthesis is used, and the remaining filtered lithium hydroxide solution and the remaining oxalic acid solution are slowly added at the same time.into the reaction kettle, stir continuously during the addition process, and control the temperature at about 50°C. After the addition, use lithium hydroxide or oxalic acid to adjust the pH value of the reaction system to 7.0, and continue stirring for 10 minutes.
(3) Control the temperature of the lithium oxalate solution obtained in step (2) in a water bath at a speed of 5°C/h to normal temperature, let it stand until all the white precipitated lithium oxalate sinks to the bottom, collect the supernatant and return to step (1) Used as a solvent instead of pure water for recycling in the next reaction.
(4) Use a PTFE-lined centrifuge to spin dry the lithium oxalate obtained in step (3), and dry the wet material at 100tC for 6 hours to obtain 203kg of high-purity lithium oxalate finished product.
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