Safety improvement of lithium ion batteries by organo-fluorine compounds

Thermal stability, electrochemical oxidation stability and charge/discharge characteristics of natural graphite powder were investigated by mixing of five fluoro-carbonates with 1 mol/L LiClO₄–EC/DEC/PC (1:1:1 vol.). DSC study revealed that thermal stability of the electrolyte solution was improved by mixing of fluoro-carbonates by 10.0–33.3 vol.%. Electrochemical oxidation stability was also improved. Oxidation currents for Pt electrode significantly decreased by mixing of fluoro-carbonates. In the fluoro-carbonate-mixed electrolyte solutions, electrochemical reduction of PC decreased with increasing concentration of fluoro-carbonate and current density. As a result, first coulombic efficiency for natural graphite electrode increased, that is, irreversible capacity decreased in the fluoro-carbonate-mixed solutions.