Construction of TiO/TiOF heterojunction as a cathode material for high-performance Mg/Li hybrid-ion batteries.

Anatase TiO has attracted significant interest as a cathode material for Mg-ion batteries or Mg/Li hybrid-ion batteries. However, owing to the semiconductor property and slower Mg diffusion kinetics it still suffers from poor electrochemical performance. Herein, a TiO/TiOF heterojunction consisting of in situ formed TiO sheets and TiOF rods, was prepared by adjusting the amount of HF in the hydrothermal process, and used as cathode of Mg/Li hybrid-ion battery. The TiO/TiOF heterojunction prepared by adding 2 mL HF (TiO/TiOF-2) exhibits high electrochemical performance, with a high initial discharge capacity (378 mAh/g at 50 mA/g), an outstanding rate performance (128.8 mAh/g at 2000 mA/g), and good cycle stability (capacity retention of 54 % after 500 cycles), which is much superior to that of Pure TiO and Pure TiOF. The reactions of Li intercalation/detercalation in the TiO/TiOF heterojunction are revealed by investigating the evolution of the hybrids during different electrochemical states. Moreover, theoretical calculations prove that the Li formation energy in the TiO/TiOF heterostructure is much lower than that of TiO and TiOF, demonstrating that the heterostructure plays a crucial role in the enhanced electrochemical performance. This work provides a novel method to design cathode materials with high performance by constructing heterostructure.