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.