Reversible aluminum ion storage mechanism in Ti-deficient rutile titanium dioxide anode for aqueous aluminum-ion batteries

Abstract Aqueous aluminum-ion batteries (AIBs) are potential candidates for future large-scale energy storage devices owing to their advantages of high energy density, resource abundance, low cost, and environmental friendliness. However, the exploration of suitable electrode materials is one of the key challenges for the development of aqueous AIBs. To address this issue, a new Ti-deficient rutile titanium dioxide (Ti0.95□0.05O1.79Cl0.08(OH)0.13) was achieved via univalent ion doping and evaluated as an anode for aqueous AIBs. This material yields a reversible capacity of 143.1 mA h g−1 at 0.5 A g−1. Even at 3 A g−1, an initial reversible charge capacity of 78.3 mA h g−1 can be achieved and retains almost 82% after 110 cycles. The Al3+ ion storage mechanism has been intensively investigated by ex-situ XRD, XPS, SEM, TEM and Raman techniques, indicating that Al3+ ions can reversibly insert into Ti vacancies and lattice of the Ti0.95□0.05O1.79Cl0.08(OH)0.13 without phase change, leading to much enhanced capacity as compared to the commercial rutile TiO2. These results demonstrate that cationic defect engineering is an effective strategy to improve the electrochemical properties of electrode materials for aqueous AIBs.