Innovative lithium storage enhancement in cation-deficient anatase via layered oxide hydrothermal transformation

The soft-chemistry synthetic routes of anatase phases for energy conversion and storage usually employ expensive and air-sensitive amorphous alkoxides, which hardly access the electrochemically active cationic vacancy defects in the cationic donor-substituted anatase compositions. Here we demonstrate an innovative way of using layered K₃Ti₅NbO₁₄ as a cost-effectively crystalline precursor to synthesize cation-deficient Nb-doped TiO₂ (NTO, formulated as Ti_0.8Nb_0.16□_0.04O₂) anatase by a one-pot hydrothermal route. When used as an anode in lithium ion batteries, the NTO electrode displayed initial discharge and charge capacities of 618 and 384.6 mA h g^-1 at a current density of 0.2C respectively, with a remarkable discharge capacity of ~246.8 mA h g^-1 retained after 100 cycles, representing the highest value among those reported for Nb-doped TiO₂ anatases at low current density. A discharge capacity of 137.1 mA h g^-1 was obtained even at a high current density of 2C. A full cell, fabricated using the NTO electrode as the anode and a commercial LiCoO₂ cathode, is shown to deliver a discharge capacity of 220.2 mA h g^-1 after 57 cycles, which exceeds those of most previously reported full cells based on the TiO₂ anode and makes this NTO material a promising anode candidate for LIBs. These results present a practical synthetic strategy for tuning cationic vacancies through aliovalent cationic substitution to improve the electrochemical performance of actual LIBs and possibly to develop further relevant devices.