Brief analysis of lithium battery carbonate and its properties

Lithium battery carbonate and its properties Carbonate rock is the first organic solvent used in the lithium battery industry. It is used in the lithium battery industry (including early lithium primary batteries, lithium secondary batteries, current lithium batteries, and lithium polymer batteries). Etc.) play an irreplaceable purpose. The carbonates commonly used in lithium batteries can be divided into cyclic carbonates and linear carbonates. 1 Cycle Carbonic Acid (1) Basic physical and chemical properties Propylene carbonate (PC) and ethylene carbonate (EC) are the two most important organic solvents in the rechargeable electrolyte of lithium batteries. PC is a colorless, transparent, slightly aromatic liquid at room temperature and pressure, with a relative molecular mass of 102.09, a density (25°C) of 1.198g/cm3, a freezing point of -49.27°C, and good low-temperature performance. PC has a flash point of 128°C, an ignition point of 133°C, a boiling point of 242°C, a refractive index of 1.4209~1.4218, and a relatively high dielectric constant (66.1°C at 25°C). PC is easily soluble in organic solvents such as benzene, ethanol, acetone, and has greater solubility for certain inorganic salts, carbon dioxide, hydrogen sulfide and certain organic sulfides, and can be used as a solvent for efficient desulfurization and decarbonization. In addition, PC has high chemical, electrochemical and optical stability and can be used under harsh conditions. The disadvantage is that PC has a certain degree of hygroscopicity, which may have a certain influence on the control of moisture in the electrolyte. (2) The phosgene method for preparing propylene carbonate and ethylene carbonate is the earliest industrial method to prepare PC and EC. It uses ethylene glycol or propylene glycol to synthesize phosgene. Due to its high toxicity and serious environmental pollution, phosgene has been banned from use. Another commonly used method is the transesterification method, which mainly uses ethylene glycol/propylene glycol transesterification of diethyl carbonate to prepare cyclic carbonate. The raw materials of this method are expensive, and the organotin as a catalyst is more toxic, and it is basically no longer used. (3) Other cyclic carbonate rock solvents A series of new carbonate rock solvents can be obtained by introducing -cl, -f and other functional groups at the methyl or methylene positions of PC and EC. The introduction of halogen atoms reduces the melting point of the electrolyte and increases the flash point, which is beneficial to improve the low-temperature safety of the electrolyte. The cycle efficiency and safety of the battery in the electrolyte formed by fluorocarbonic acid have also been improved. For example, TFPC formed by replacing three hydrogens with fluorine on the PC methyl group has a high flash point (134°C), which improves the fire resistance of the electrolyte. 2 Linear carbonate commonly used linear carbonate rocks are dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and methyl propyl carbonate (MPC). Because recycled carbonate rock generally has high viscosity and melting point, it is often mixed with linear carbonate rock with low viscosity and low melting point to obtain better performance. (1) The basic physical and chemical properties of linear carbonate DMC is a colorless liquid at room temperature, with a melting point of 4.6°C, a boiling point of 90°C, and a flash point of 18°C. It is a non-toxic or slightly toxic product that can form an azeotrope with water or alcohol. DMC has a unique molecular structure, containing functional groups such as carbonyl, methyl, and methoxy, and has diverse reactivity. It can be used as carbonylation, methylation reagent, gasoline additive, raw material for polycarbonate synthesis, etc. The structure of DEC is similar to DMC. It is a colorless liquid at room temperature with an extremely low melting point of -74.3°C (not the -43°C reported in general literature). The boiling point (126.8°C) and flash point (33°C) are slightly higher than DMC, and the toxicity is greater than DMC. DEC is soluble in ketones, alcohols, ethers, esters, etc., but insoluble in water. Both DMC and DEC have low viscosity (0.58mpa). And dielectric constant (3.11 and 2.82), usually not used alone as a solvent for lithium battery electrolytes, but as a co-solvent. EMC and MPC are asymmetric linear carbonates. The melting point, boiling point and flash point are similar to DMC and DEC, but the thermal stability is poor, and it is easy to generate DMC and DEC through transesterification under alkaline conditions. Different from DMC and DEC, the electrolyte with EMC or MPC as a single solvent has excellent electrochemical performance under the same conditions. In recent years, in order to improve the thermal stability of linear carbonate rocks, some or all fluorocarbonate rocks have been synthesized. These solvents have low melting points, high anode stability, good safety, and good thermal stability. However, the application prospect of this system is broad. 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 article: How to improve the low temperature performance of lithium iron phosphate battery pack?