Phosphorus-doped TiO 2 mesoporous nanocrystals for anodes in high-current-rate lithium ion batteries.

Limited by the intrinsic low electronic conductivity and inferior electrode kinetics, the use of TiO 2 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 TiO 2 mesoporous nanocrystals (P-TMC) with ultrafine size of 2-8 nm and high specific surface area (234.164 m 2 g -1 ) has been synthesized. It is formed through a hydrothermal process and NaBH 4 assisted heat treatment for anatase defective TiO 2 (TiO 2-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.