Electrochemical reaction of lithium with cobalt fluoride thin film electrode

To extend the electrochemical reaction mechanisms of transition-metal compounds based on metal cobalt as the anode with Li, the electrochemical reaction of CoF2 with Li was first investigated. A lithium phosphorous oxynitride (Lipon) thin film coating on the surface of CoF2 was fabricated as a separator between CoF2 and liquid electrolyte to avoid a solution of CoF2. Interestingly, the electrochemical behavior of the Li/LiPF6/Lipon/CoF2 cell. was reversible. The as-deposited, lithiated, and delithiated CoF2 thin film electrode was characterized by ex situ scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy measurements. It is very difficult to understand the reversible decomposition of LiF under potentials less than 6.1 V vs. Li/Li+, so an attempt was made to theoretically analyze the reaction of LiF with metal Co. The stable formation and further dissociation of CoLiF may be one of the main pathways in the reversible electrochemical reaction of CoF2 with Li. (C) 2004 The Electrochemical Society.