K⁺ Vacancies and Fluorine Substitution Synergistically Regulate KTiOPO₄ Anode for All-Climate and Long-Life...

Although Ti-based polyanion anode materials with robust structures exhibit advantages such as high reversibility and high Coulombic efficiency for alkali metal-ion storage; however, their practical application is restricted by drawbacks including limited storage sites, low capacity, and intrinsically poor electronic conductivity. Herein, we propose a strategy of fluorine substitution combined with carbon coating of KTiOPO₄ (KTPF/C), along with the introduction of K⁺ vacancies to activate additional potassium storage sites. The resulting KTPF/C material demonstrates a high capacity of 204.7 mAh g^-1, corresponding to the reversible storage of 1.27 K⁺ ions. The synergistic effect of K⁺ vacancies and fluorine substitution not only lowers the operating voltage but also results in a more disordered structure, thereby reducing the volume change during potassiation/depotassiation to 7.3%. This enables an ultralong cycle life exceeding 20,000 cycles with an extremely low capacity fade rate of 0.011‰ per cycle. Moreover, the cooperation of K⁺ vacancies and carbon coating facilitates the transport of K⁺ and electrons, allowing the material to maintain excellent rate performance of 125.1 mAh g^-1 at 5 A g^-1. Practical full-cell testing further confirms the material's outstanding cycling stability, high power density, and all-climate applicability over a wide temperature range from -40 to 60 °C.