Lithium-ion battery electrolyte has conditions
The electrolyte used in the lithium ion battery is an ionic conductor in which an electrolyte lithium salt is dissolved in an organic solvent. Generally, the organic electrolyte as a practical lithium ion battery should have the following properties:
(1) The ionic conductivity is high, generally should reach 10-3~2*10-3S/cm; the lithium ion migration number should be close to 1;
(2) Electrochemically stable potential range is wide; there must be an electrochemical stability window of 0~5V;
(3) Good thermal stability and wide temperature range;
(4) The chemical properties are stable, and there is no chemical reaction with the current collector and the inert substance in the battery;
(5) Safe and low toxicity, preferably biodegradable.
Suitable solvents require high dielectric constant and low viscosity. Commonly used alkyl carbonates such as PC, EC have strong polarities, high dielectric constant, but high viscosity, large intermolecular forces, and lithium ions move in them. Slow. Linear esters such as DMC (dimethyl carbonate) and DEC (diethyl carbonate) have low viscosity but low dielectric constant. Therefore, in order to obtain a solution having high ionic conductivity, it is generally used. PC+DEC, EC+DMC and other mixed solvents. These organic solvents have some flavors, but in general, they are all RoHS compliant, REACH requirements, and are materials that are less toxic and environmentally friendly.
The inorganic anion conductive salts currently developed mainly include LiBF4, LiPF6 and LiAsF6. Their order of electrical conductivity, thermal stability and oxidation resistance are as follows:
Thermal stability: LiAsF6>LiBF4>LiPF6
Oxidation resistance: LiAsF6≥LiPF6≥LiBF4>LiClO4
LiAsF6 has very high conductivity, stability and battery charge and discharge rate, but its application is limited by the toxicity of arsenic. Currently the most commonly used is LiPF6.