Electrode Based on Oxyphosphates as Anode Materials for High Energy Density Lithium-ion Batteries

Abstract

Lithium-ion batteries (Li-ion) are interesting devices for electrochemical energy storage for most emerging green technologies such as wind and solar technologies or hybrid and plug-in electric vehicles or for classical electrical devices such as laptops, phones or other electronic tools. Nevertheless, the oxygen release at high potentials in the present commercialized electrode materials (e.g. LiCoO2) leads to high thermal instability of these oxides and thus to many safety problems. This safety problem is more pronounced for stationary applications for which large size batteries were needed. Polyanionic materials in general, and particularly phosphates were well renowned by their high structural stability which are essential to overcome the above mentioned safety issue. Here, we present the structural and the electrochemical performances of three oxyphosphates M0.5TiOPO4 (M: Ni, Co, Fe). More than 300 mAh/g discharge capacity could be delivered by these phosphates under relatively high cycling rate. The lithium insertion/extraction mechanism is composed from an intercalation process for low lithium content to a conversion mechanism for higher lithium concentration leading to the extrusion of the transition metal M from the structure.