Electrochemical Reaction of Lithium with Cobalt Fluoride Thin Film Electrode

Abstract

To extend the electrochemical reaction mechanisms of transition-metal compounds based on metal cobalt as the anode with Li, the electrochemical reaction of CoF 2 with Li was first investigated. A lithium phosphorous oxynitride (Upon) thin film coating on the surface of CoF 2 was fabricated as a separator between CoF 2 and liquid electrolyte to avoid a solution of CoF 2 . Interestingly, the electrochemical behavior of the Li/LiPF 6 /Lipon/CoF 2 cell was reversible. The as-deposited, lithiated, and delithiated CoF 2 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 CoF 2 with Li. © 2004 The Electrochemical Society. All rights reserved.