Liquid electrolyte for lithium ion battery
The choice of solvent is mainly based on three aspects of property requirements That is, dielectric constant, viscosity and electron donor properties of solvent. Generally speaking, high dielectric constant is conducive to the dissociation of lithium salt, and strong electron donor ability will be conducive to the dissolution of electrolyte salt. The so-called electron donor property of solvent is the inherent electron loss ability of solvent molecules, which determines the solvation ability of electrolyte cations. Low viscosity can increase the fluidity of ions and help to improve the conductivity.
At present, binary and multicomponent mixed solvents composed of two or more solvents are usually used. Common organic solvents include ether, alkyl carbonate, lactone, ketal, etc.
Lithium salts are mainly used to provide effective carriers. The selection of lithium salt generally follows the following principles:
It has good stability (compatibility) with positive and negative materials, that is, during storage, the electrochemical reaction speed at the interface between electrolyte and active substances is small, so as to minimize the loss of self discharge capacity of the battery; The specific conductivity is high and the ohmic voltage drop of the solution is small; High safety performance, non-toxic and pollution-free.
Lithium salts are commonly used as follows: lithium Hexafluoroarsenate (LiPF6). Liasf6 will release toxic arsenide during charge and discharge, and the price is relatively expensive. Lithium hexafluorophosphate (LiPF6), which has been widely used in commercial batteries, has high conductivity and good compatibility with carbon materials. Its disadvantages are relatively expensive, poor stability in solid state and very sensitive to water. Lithium trifluoromethylsulfonate licf3so2 has good stability, but its conductivity is only half of that of liquid electrolyte based on LiPF6. Lithium tetrafluoroborate (LiBF4) and lithium perchlorate (licl04) are widely used salts. However, imino lithium salts containing lithium perchlorate, typically lithium difluorosulphthalide imine (Lin (CF3 SO2) 2, have conductivity comparable to that of very dry LiPF6 electrolyte and stability higher than flicf3so2.