Interstitial and substitutional V5+-doped TiNb2O7 microspheres: A novel doping way to achieve high-performance electrodes

Dual improvement on electronic conductivity and ionic conductivity of TiNb2O7 (TNO) is of great significance for realizing high-performance lithium-ion batteries. In this work, the V5+-doped TNO microspheres (denoted as Vx-TNOMs, x = 0, 0.015, 0.030 and 0.045) were synthesized via a simple solvothermal approach. X-ray diffraction coupled with Rietveld refinements and Raman spectra analyses verified that V5+ not simply possessed substitution doping mode but also inserted into the interstices of the TNOMs lattice. The density functional theory (DFT) calculations indicated that the improved electronic conductivity could originate from the formation of impurity bands after the V5+ doping. Meanwhile, the climbing image-nudged elastic band (CI-NEB) demonstrated that a TNOMs framework with faster ion transport pathways is achieved by the V5+ doping. Served as anode material of lithium-ion batteries, the V0.030-TNOMs electrode presents an impressive discharge capacity of 163.5 mAh/g at 10 C and long cycle life up to 2000 cycles with a capacity fading of merely 0.014% per cycle. Furthermore, the full battery employing V0.030-TNOMs as an anode and commercial LiCoO2 as a cathode exhibits superior electrochemical performances with promising application prospect. Our present study sheds new light on constructing high-performance electrodes for electrochemical energy storage.