Improving Na₂Ti₃O₇ Anode Performance in Sodium-Ion Batteries via a Al Doping

Na₂Ti₃O₇ (NTO), with low sodium insertion potential (~0.3 V vs. Na⁺/Na) and potential for high-energy-density batteries, is regarded as one of the most promising anode materials for sodium-ion batteries (SIBs). However, its practical application is hindered by poor electronic conductivity, sluggish Na⁺ (de)intercalation kinetics, and interfacial instability, leading to inferior cycling stability, low initial Coulombic efficiency, and poor rate capability. In this work, micron-sized rod-like NTO and Al-doped NTO (NTO-Al) samples were synthesized via a one-step high-temperature solid-state method. Al doping slightly reduced the size of NTO microrods while introducing oxygen vacancies and generating Ti³⁺, thereby enhancing electronic conductivity and reducing ionic diffusion resistance. H₂-TPR confirms that doping activates lattice oxygen and promotes its participation in the reaction. The optimized NTO-Al0.03 electrode delivered a significantly improved initial charge capacity of 147.4 mA h g^-1 at 0.5 C, surpassing pristine NTO (124.7 mA h g^-1). Moreover, it exhibited the best cycling stability (49.5% capacity retention after 100 cycles) and rate performance (36.3 mA h g^-1 at 2 C).