Decomposition reaction of LiPF_6-based electrolytes for lithium ion cells

摘要

The decomposition of LiPF_6 electrolytes with water was studied by measuring the water content after storage. The solvents used were ethylene carbonate (EC) + diethyl carbonate (DEC), EC + dimethyl carbonate (DMC), propylene carbonate (PC) + DEC, and PC + DMC mixed by the volume ratio 1 to 1, respectively. The experimental results were in good agreement with - d[H_2O]/dt = k[H_2O]~2[LiPF_6], We obtained Kite constants (k) from this empirical equation, with k increasing in the order of EC + DMC < EC + DEC < PC + DMC < PC + DEC. This order is in inverse proportion to the order of the dielectric constants of these solvents. Nonionized LiPF_6 dissociates to PF_5 and LiF in organic solvents, and PF_5 reacts with water. A solvent with a high dielectric constant increases the ionization of LiPF_6, thereby suppressing the reaction with water.