Construction of TiO2/TiOF2 heterojunction as a cathode material for high-performance Mg2+/Li+ hybrid-ion batteries

Abstract

Anatase TiO₂ has attracted significant interest as a cathode material for Mg-ion batteries or Mg²⁺/Li⁺ hybrid-ion batteries. However, owing to the semiconductor property and slower Mg²⁺ diffusion kinetics it still suffers from poor electrochemical performance. Herein, a TiO₂/TiOF₂ heterojunction consisting of in situ formed TiO₂ sheets and TiOF₂ rods, was prepared by adjusting the amount of HF in the hydrothermal process, and used as cathode of Mg²⁺/Li⁺ hybrid-ion battery. The TiO₂/TiOF₂ heterojunction prepared by adding 2 mL HF (TiO₂/TiOF₂-2) 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 TiO₂ and Pure TiOF₂. The reactions of Li⁺ intercalation/detercalation in the TiO₂/TiOF₂ 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 TiO₂/TiOF₂ heterostructure is much lower than that of TiO₂ and TiOF₂, 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.

Keywords: Cathode materials; DFT calculation; Li(+) intercalation/detercalation; Mg(2+)/Li(+) hybrid-ion battery; TiO(2)/TiOF(2).