Self-doping of Ti3+into Na2Ti3O7 increases both ion and electron conductivity as a high-performance anode material for sodium-ion batteries

As a safe, low-voltage anode material, in recent years, Na2Ti3O7 has become regarded as a highly alternative negative material for high energy room-temperature sodium ion batteries. However, its poor ion and electron conductivity produces very poor electrochemical performance of Na2Ti3O7, therefore greatly limiting its practical application in future scalable utilization. We report here a self-doping of Ti3+ into the Na2Ti3O7 electrode material, through a very simple post heat-treatment process, that is, annealing the Na2Ti3O7 precursor at an argon atmosphere containing 5% H2. By XPS characterization, it is confirmed that Ti3+ is successfully doped into Na2Ti3O7. Benefiting from this self-doped Ti3+ with larger ionic radius and better electronic conductivity, the obtained Na2Ti3O7 demonstrates improved electron conductivity and ion diffusion properties. Combined with a carbon coating, this self-doped Na2Ti3O7 electrode material exhibits superior electrochemical performance to that of non-doped electrode, e.g., this Na2Ti3O7 sample could delivers a specific capacity of 187.8 and 51.9 mAh g−1 from 0.1C to 10C at various rate of discharge, respectively. When recycled back to 0.1C, it can still reach 153 mAh g−1. Compared with numerous reported nanoscale means, we believe this approach is practical and productive, and may extend to other ti-based electrode materials.