Ultrasonochemical-Assisted Synthesis of Defect-Rich Dual-Metal-Doped TiO ₂ Nanomaterial as a High-Performance Cathode for Aqueous Zinc-Ion Batteries

The development of advanced electrode materials for aqueous zinc-ion batteries (AZIBs) has gained considerable interest for large-scale energy storage applications. Despite their potential, AZIBs often suffer from low Coulombic efficiency (CE) and rapid capacity degradation, mainly due to cathode dissolution and irreversible side reactions occurring at both electrodes. This study reports the successful design of a defect-rich, dual-metal (Mg and La)-doped TiO₂ (D-ML-TiO₂) cathode for AZIBs. The D-ML-TiO₂ cathode demonstrates an impressive reversible capacity of 150 mAh g^-1 at a current density of 25 mA g^-1 over 100 cycles, along with exceptional rate capability (44 mAh g^-1 at 2.0 A g^-1). Furthermore, it exhibits remarkable long-term cyclic stability, maintaining 42 mAh g^-1 at 2.0 A g^-1 after 1000 cycles with nearly 100% CE. These findings highlight the pivotal role of defect-rich surface features in enhancing electrochemical performance, especially by improving the reversible capacity and cyclic stability. <i>Ex situ</i> characterizations confirmed a proton (H⁺)-assisted energy storage mechanism, involving coinsertion/extraction of Zn²⁺ and H⁺ ions on the D-ML-TiO₂ surface. This work highlights the potential of defect-rich TiO₂ as a high-performance cathode material for next-generation AZIBs.