Revisited TiNbO as an Anode Material for Advanced Li-Ion Batteries.

TiNbO with a tunnel-type structure is considered as a perspective negative electrode material for Li-ion batteries (LIBs) with theoretical capacity of 252 mAh g corresponding to one-electron reduction/oxidation of Ti and Nb, but only ≈160 mAh g has been observed practically. In this work, highly reversible capacity of 200 mAh g with the average (de)lithiation potential of 1.5 V vs Li/Li is achieved for TiNbO with pseudo-2D layered morphology obtained via thermal decomposition of the NHTiNbO intermediate prepared by K→ H→ NH cation exchange from KTiNbO. Using synchrotron powder X-ray diffraction (SXPD), single-phase (de)lithiation mechanism with 4.8% unit cell volume change is observed. X-ray absorption near-edge structure (XANES) experiment revealed simultaneous Ti/Ti and Nb/Nb reduction/oxidation within the whole voltage range. Li migration barriers for TiNbO along [010] direction derived from density functional theory (DFT) calculations are within the 0.15-0.4 eV range depending on the Li content that is reflected in excellent C-rate capacity retention. TiNbO synthesized via the ion-exchange route appears as a strong contender to widely commercialized Ti-based negative electrode material LiTiO in the next generation of high-performance LIBs.