Structural evolution and lithium-storage mechanism of the FeTiO3@Fe2TiO5 endogenous heterojunction

Constructing heterojunctions is an effective strategy for improving the migration of electronic charge carriers and enhancing electronic conductivity. Herein, polyvinylpyrrolidone crosslinked with graphene oxide was used as a template to construct a FeTiO3@Fe2TiO5 endogenous heterojunction anode material (hetero-FTO) anode. The initial electrochemical capacity of the hetero-FTO anode (1207 mA h g−1 at 100 mA g−1) was approximately twice that of FTO (600 mA h g−1 at 100 mA g−1). Electrochemical kinetics and density functional theory calculations demonstrated that the built-in electric field formed at the interface of the endogenous heterojunction increased the electronic conductivity and effectively improved the conversion rate. The structural evolution of the heterojunction during cycling was tracked using in situ XPS and ex situ HRTEM and calculation of Gibbs free energies. After 100 cycles, the FeTiO3@Fe2TiO5 heterojunction structures transformed into cubic phase γ-Fe2O3; however, the capacity still increased to 865 mA h g−1. This ingenious heterogeneous-structure-design strategy and analysis of the heterogeneous structural evolution are crucial for improving the lithium-storage performance of batteries, especially those containing titanium-based conversion-type anode materials.