Intercalation and conversion reactions in Ni0.5TiOPO4 Li-ion battery anode materials

The Ni0.5TiOPO4/C composite Li-ion battery anode material has been prepared by a sol–gel method with a subsequent pyrolysis step for the formation of C-coating. The resulting sub-micronsized particles displayed a narrow particle size distribution and a corresponding high electrochemical activity which, in turn, facilitates in-depth analysis of the electrochemical behavior of the material. It is shown that by limiting the degree of lithiation in the material, the redox potential in subsequent cycles is substantially affected. Ex-situ XRD reveals a gradual evolution of the structure during cycling of the material, with lower crystallinity after the first discharge cycle. By correlating the electrochemical properties with the structural studies, new insights into the electrochemical behavior of the Ni0.5TiOPO4/C anode material are achieved, suggesting a combination of intercalation and conversion reactions.

► Ni0.5TiOPO4 anode material was synthesized by sol–gel method directly from H3PO4 acid. ► The small particle size and the carbon coating of Ni0.5TiOPO4 lead to enhanced electrochemical performance. ► Ex-situ XRD analysis during the first discharge shows an amorphization of this anode material. ► A model explaining the anomalous 1st discharge capacity and the amorphization of this phosphate was proposed.