N-doped rutile TiO2/C with significantly enhanced Na storage capacity for Na-ion batteries

Rutile TiO2 is seldom studied as anode material for Na-ion battery for its much poorer Na storage performance than anatase phase. Herein, strategies of carbon coating and nitrogen doping are proposed and achieved together by a facile ball milling method followed by a high temperature sintering process to improve its electrochemical properties. The feature of this work lies in the dual N doping, not only to the carbon layers but also to the TiO2 lattice, resulting in sufficient oxygen vaccancies and defects in TiO2/C. Although the pristine TiO2 prepared by the similar method shows only 10 mAh g(-1) capacity, the Na storage performance of N-doped TiO2/C is significantly enhanced. It demonstrates a high reversible discharge capacity of 211.2 mAh g(-1) at 16.8 mA g(-1) (0.1C). Moreover, a capacity retention of 92.3% is achieved after 500 cycles at 168 mA g(-1) (1C), verifying ultrahigh reversible capacity and excellent cycling performance for rutile TiO2. The excellent Na storage performance of N-doped TiO2/C should be ascribed to the improved electronic and ionic conductivity resulting from dual N-doping strategy and shortened Na ion diffusion length due to the particle downsizing. (C) 2017 Elsevier Ltd. All rights reserved.