Improved sodium-ion storage performance of TiO2 nanotubes by Ni2+ doping

TiO2 is a promising anode for sodium-ion batteries (SIBs) due to its inherent safety, low cost, good structural stability during the sodium-ion storage process and appropriate voltage platform. However, unsatisfactory electrical conductivity hinders its applications. Here we demonstrate that doping TiO2 nanotubes with Ni2+ via an initial sol-gel method, subsequent hydrothermal process and final thermal treatment can balance the high conductivity and good structural stability of TiO2 to improve the sodium-ion storage performance. The resultant sample exhibits a high charge capacity of 286 mA h g(-1) after 100 cycles at a current density of 50 mA g(-1) and even at a high current density of 5 A g(-1), a capacity of 123 mA h g(-1) is maintained after 2000 cycles. It is believed that the strategy in this work can provide a useful pathway towards enhancing the electrochemical performance of TiO2 anodes for SIBs.