Phosphorus-doped TiO2 mesoporous nanocrystals for anodes in high-current-rate lithium ion batteries

Abstract

Limited by the intrinsic low electronic conductivity and inferior electrode kinetics, the use of TiO2 as an anode material for lithium ion batteries (LIBs) is hampered. Nanoscale surface-engineering strategies of morphology control and particle size reduction have been devoted to increase the lithium storage performances. It is found that the ultrafine nanocrystal with mesoporous framework plays a crucial role in achieving the excellent electrochemical performances due to the surface area effect. Herein, a promising anode material for LIBs consisting of phosphorus-doped TiO2 mesoporous nanocrystals (P-TMC) with ultrafine size of 2–8 nm and high specific surface area (234.164 m2 g–1) has been synthesized. It is formed through a hydrothermal process and NaBH4 assisted heat treatment for anatase defective TiO2 (TiO2–x) formation followed by a simple gas phosphorylation process in a low-cost reactor for P-doping. Due to the merits of the large specific surface area for providing more reaction sites for Li+ ions to increase the storage capacity and the presence of oxygen vacancies and P-doping for enhancing material’s electronic conductivity and diffusion coefficient of ions, the as-designed P-TMC can display improved electrochemical properties. As a LIB anode, it can deliver a high reversible discharge capacity of 187 mAh g–1 at 0.2 C and a good long cycling performance with ∼82.6% capacity retention (101 mAh g–1) after 2500 cycles at 10 C with an average capacity loss of only 0.007% per cycle. Impressively, even the current rate increases to 100 times of the original rate, a satisfactory capacity of 104 mAh g−1 can be delivered, displaying good rate capacity. These results suggest the P-TMC a viable choice for application as an anode material in LIB applications. Also, the strategy in this work can be easily extended to the design of other high-performance electrode materials with P-doping for energy storage.