Porosity-controlled TiNb₂O₇ microspheres with partial nitridation as a practical negative electrode for high-power lithium-ion batteries

Titanium niobium oxide (TiNb₂O₇) has been recognized as a promising anode material for lithium-ion batteries (LIBs) in view of its potential to operate at high rates with improved safety and high theoretical capacity of 387 mAh g^-1. However, it suffers from poor Li⁺ ion diffusivity and low electronic conductivity originated from its wide band gap energy (E_g > 2 eV). Here, porous TiNb₂O₇ microspheres (PTNO MSs) are prepared via a facile solvothermal reaction. PTNO MSs have a particle size of ≈1.2 μm and controllable pore sizes in the range of 5-35 nm. Ammonia gas nitridation treatment is conducted on PTNO MSs to introduce conducting Ti_1-_xNb_xN layer on the surface and form nitridated PTNO (NPTNO) MSs. The porous structure and conducting Ti_1-_xNb_xN layer enhance the transport kinetics associated with Li⁺ ions and electrons, which leads to significant improvement in electrochemical performance. As a result, the NPTNO electrode shows a high discharge capacity of ≈265 mAh g^-1, remarkable rate capability (≈143 mAh g^-1 at 100 C) and durable long-term cyclability (≈91% capacity retention over 1000 cycles at 5 C). These results demonstrate the great potential of TiNb₂O₇ as a practical high-rate anode material for LIBs. Porosity controlled TiNb₂O₇ microspheres are successfully prepared via a facile solvothermal reaction. Ammonia gas treatment is then carried out to enhance conductivity with a Ti_1-XNb_XN layer formed on the surface. These partially nitridated TiNb₂O₇ microspheres show a superior rate capability of ≈143 mAh g^-1 at 100 C and durable long-term cyclability of ≈91% capacity retention over 1000 cycles at 5 C. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.