Designing a high-performance nitrogen-doped titanium dioxide anode material for lithium-ion batteries by unravelling the nitrogen doping effect

Despite its great potential, the use of TiO2 in lithium-ion batteries has been hampered by its intrinsically low electrical and ionic conductivities. Although nitrogen doping (N-doping) has been widely practiced to address this issue, a comprehensive understanding of how N-doping improves those poor intrinsic properties is still lacking. For this work, we performed a computational study and found that the N-doping effect relies intimately on where the N is implanted in the TiO2 lattice: interstitial N is more beneficial than substitutional N in enhancing those conductivities. Therefore, we devised a new N-doping strategy based on a self-N-doping route that enables subtle tuning of the nitrogen distribution in TiO2. Unlike conventional N-doping methods that leave the doped N predominantly on the surface, our new approach enables the preferential implantation of interstitial N into the interior of TiO2. In-depth electrochemical analyses combined with physical characterization reveal that this unique falling gradient N-doping from the core to the surface is more beneficial than the common rising gradient N-doping in enhancing the performance of TiO2 in lithium ion batteries. This new insight highlights the importance of crystallographic location and spatial distribution in N-doping, which will form the foundation of a new design principle for high-performance N-doped TiO2.