Bulk Modification of Porous TiNb2O7 Microsphere to Achieve Superior Lithium-Storage Properties at Low Temperature

TiNb 2 O 7 , as a promising alternative of Li 4 Ti 5 O 12 , exhibits giant potential as low-temperature anode due to its higher theoretical capacity and comparable structural stability. However, the sluggish electronic conductivity still remains a challenge. Herein, bulk modification of Cu + doping in porous TiNb 2 O 7 microsphere is proposed via a simple one-step solvothermal method with subsequent calcination treatment. The results show that the electronic conductivity is improved effectively due to the reduced band gap after doping, while enhanced lithium-ion diffusion is achieved benefiting from the increased interplanar spacing. Therefore, the optimal sample of Cu 0.06 Ti 0.94 Nb 2 O 7 exhibits a high reversible capacity of 244.4 mA h g −1 at 100 mA g −1 after 100 cycles, superior rate capability, and long-term cycling stability at 1000 mA g −1 at room temperature. Particularly, it can also display good performance in a wide temperature range from 25 to –30 °C, including a reversible capacity of 76.6 mA h g −1 at –20 °C after 200 cycles at 200 mA g −1 . Moreover, Cu 0.06 Ti 0.94 Nb 2 O 7 //LiFePO 4 full cell can deliver a high reversible capacity of 177.5 mA h g −1 at 100 mA g −1 . The excellent electrochemical properties at both ambient and low-temperatures demonstrate the great potential of Cu + -doped TiNb 2 O 7 in energy-storage applications.