Bulk Modification of Porous TiNb₂ O₇ Microsphere to Achieve Superior Lithium-Storage Properties at Low Temperature

TiNb₂ O₇ , as a promising alternative of Li₄ Ti₅ O₁₂ , 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 TiNb₂ O₇ 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 Nb₂ O₇ 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 Nb₂ O₇ //LiFePO₄ 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 TiNb₂ O₇ in energy-storage applications.