Electrochemical Reactions of Lithium with Transition Metal Nitride Electrodes

Novel transition metal nitrides of Co 3 N and Fe 3 N thin films have been successfully fabricated by combining reactive pulsed laser deposition and DC discharge in a nitrogen ambient. The electrochemical reactions of lithium with Co 3 N and Fe 3 N thin film electrodes were first investigated by the galvanostatic discharge and charge, cyclic voltammetry, and the in-situ spectroelectrochemical measurements. These thin film electrodes exhibited reversible discharge capacities ranging from 324 mAh/g to 420mAh/g. The structure, morphology, and composition of the as-deposited, lithiated, and delithiated Co 3 N and Fe 3 N thin films have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The observed diffraction peaks from metal Co(111) and Fe(110) in the lithiated thin films showed well crystallinity of transition metallic Co and Fe formed by Li reacted with Co 3 N and Fe 3 N, respectively, which could further be confirmed by their XPS spectra. We proposed a new reaction mechanism, in which part of the transition metallic Co and Fe formed during the first discharging is nitrided and another part as an active spectator may play a major role in driving the decomposition and formation of Li 3 N during the subsequent electrochemical reaction.