Oxygen vacancies-modulated tungsten oxide anode for ultra-stable and fast aqueous aluminum-ion storage

Rechargeable aqueous aluminum-ion battery (RAAB) is a potential candidate for safe and cost-effective energy storage device. Although tungsten oxide is a promising intercalation anode material to accommodate various metallic charge carriers, its main bottlenecks of application are the low conductivity and sluggish redox kinetics. Herein, a novel W18O49 anode with rich oxygen vacancies (denoted as W18O49-Ov) has been proposed for RAABs. According to the theoretical calculations and experimental results, we found the important role of oxygen vacancies in modulating electronic state and bandgap as well as offering abundant active sites for Al3+ diffusion within the W18O49-Ov anode. Moreover, a 3D robust architecture of W18O49-Ov anode is effectively constructed with excellent structural stability. In-situ Raman investigation further reveals the electrochemical mechanism of W18O49-Ov anode with reversible phase transition about redox reaction between W5+/W6+ states upon Al3+ insertion-extraction. These properties endow the superior aqueous Al3+ storage (-251.3 mAh g-1), rapid chargedischarge response, and high electrochemical reversibility for W18O49-Ov anode. For real-life applications, a high-performance Al-metal free RAAB is assembled with a long-term cycle performance (-95.3 % capacity retention after 5000 cycles), and this is the best value in RAABs reported so far, further suggesting its great potential in energy-related electronic fields.