Explain the development status of lithium battery electrolyte in detail

In order to meet the requirements of the future development of the lithium battery industry, it is necessary to develop electrolyte materials with high safety and high environmental adaptability. It is important to consider the choice of electrolyte solvent, solute and additives: (1) Try to choose a solvent with a wide operating temperature range. The melting point of the solvent should be below -40℃, and the boiling point should be above 150℃ or higher. , The solvent with a wide electrochemical window can better guard against the redox reaction of the electrolyte in the charged state, and at the same time can improve the cycle stability of the battery. For example, ionic liquids, new solvents, multi-component solvents, etc. can be considered to deal with battery safety and environmental adaptability. (2) Choose a suitable solute to improve the environmental adaptability of the battery. At present, the commonly used LiPF6 (lithium hexafluorophosphate) has a low analysis temperature, and a small amount of analysis starts from 60°C. Under higher temperatures or harsh environments, the proportion of analysis is greatly increased, and HF (hydrofluoric acid) appears. Free acid, so that the electrolyte is acidified, eventually leading to the damage of the electrode material and the rapid deterioration of the battery performance. (3) It can be considered to add an appropriate amount of flame retardant additives, redox shuttle additives, protective positive and negative electrode film forming additives, etc. The use of flame-retardant additives can ensure that when the internal heat of the battery is out of control, the electrolyte will not burn and ignite, so that the safety of the battery can be guaranteed. The use of redox shuttle additives is to be wary that when batteries, especially power lithium-ion battery packs, have abnormal conditions during use, the single cells will often be overcharged or overdischarged, which will lead to the rapid deterioration of battery performance, and then Affect the performance and use of the entire battery pack, and even bring about potential safety hazards. The use of the positive and negative electrode film-forming additives is to effectively protect the positive and negative electrode materials from the contact reaction with the electrolyte in the charged state, and isolate the highly active positive and negative electrodes from the electrolyte through the form of film formation, thereby Watch out for the reaction of the electrolyte on the electrode surface. The key raw material for the electrolyte is lithium hexafluorophosphate, which accounts for about 50% of the cost of the electrolyte. Its processing cost is 100,000 yuan/ton, the price is 400,000 yuan/ton, and the gross profit margin is as high as 75%. Lithium hexafluorophosphate is difficult to synthesize. The entire processing process involves high temperature, low temperature, vacuum, high pressure, strong corrosive, flammable, explosive and highly toxic chemicals, which requires high equipment and personnel, and the process is extremely difficult. Morita Chemical built a plant with an annual output of 300 tons of lithium hexafluorophosphate in Zhangjiagang and copied the mature equipment and technology of the Japanese plant. It still took 3 years to reach production stably, showing the high degree of process difficulty. The difficulty lies in impurity control. The electrolyte requires extremely high purity of lithium hexafluorophosphate, and industry standards require that the moisture content is less than 30ppm and the free acid is less than 10ppm. Because lithium hexafluorophosphate itself has moisture absorption, impurity control and product purification during the acquisition and processing of high-purity raw materials are key factors. The high technical threshold has led to a very high market concentration. The market is urgently monopolized by several Japanese companies such as Kanto Electrochemical Industry, STELLA, and Morita Chemical. At present, only Tianjin Jinniu can realize industrialized processing in China, with an output of about 80 tons, and all products are for self-use and not for external sales. Jiangsu Cathay Pacific and Fluoride are currently undergoing pilot production. Development trend: In the long run, the development of new electrolyte systems will be the general trend. The thermal stability of lithium hexafluorophosphate material is poor, and there are a small amount of analysis from 60℃. Under higher temperature or harsh environment, the proportion of analysis is greatly increased. The presence of free acids such as hydrofluoric acid will acidify the electrolyte, and finally This results in damage to the electrode material and rapid deterioration of battery performance. At the same time, lithium hexafluorophosphate is easy to deliquesce, and moisture is the enemy of the electrolyte. In recent years, the use of lithium oxalate borate in electrolyte has gradually attracted attention. The electrolyte prepared with lithium oxalate borate salt has the functions of anti-overcharge and flame-retardant, and the formed SEI film is very stable, meeting the high safety requirements of power lithium-ion batteries. In the longer term, polymer lithium batteries may become the future development direction of lithium batteries. Since solid electrolytes are used instead of liquid electrolytes, compared with liquid lithium batteries, polymer lithium batteries have the advantages of being thinner, arbitrarily large, and arbitrarily shaped, and will not cause safety problems such as liquid leakage, combustion and explosion. , So the shell material can be lighter, which can increase the specific capacity of the entire battery. In addition, polymer lithium batteries have improved operating voltage and charge-discharge cycle life compared to general lithium batteries. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Is the lithium battery of low-speed electric vehicles really inferior to lead-acid batteries?