Combining Structural Modification and Electrolyte Regulation to Enable Long‐Term Cyclic Stability of MoO3‐x@TiO2 as Cathode for Aqueous Zn‐Ion Batteries

Abstract Orthorhombic MoO 3 ( α ‐MoO 3 ) with multivalent redox couple of Mo 6+ /Mo 4+ and layered structure is a promising cathode for rechargeable aqueous Zn‐ion batteries (AZIBs). However, pure α ‐MoO 3 suffers rapid capacity decay due to the serious dissolution and structural collapse. Meanwhile, the growth of byproduct and dendrite on the anode also lead to the deterioration of cyclic stability. This article establishes the mechanism of proton intercalation into MoO 3 and proposes a joint strategy combining structural modification with electrolyte regulation to enhance the cyclic stability of MoO 3 without sacrificing the capacity. In ZnSO 4 electrolyte with Al 2 (SO 4 ) 3 additive, TiO 2 coated oxygen‐deficient α ‐MoO 3 (MoO 3‐x @TiO 2 ) delivers a reversible capacity of 93.2 mA h g −1 at 30 A g −1 after 5000 cycles. The TiO 2 coating together with the oxygen deficiency avoids structural damage while facilitating proton diffusion. Besides, the additive of Al 2 (SO 4 ) 3 , acting as a pump, continuously supplements protons through dynamic hydrolysis, avoiding the formation of Zn 4 SO 4 (OH) 6 ·xH 2 O byproducts at both MoO 3‐x @TiO 2 and Zn anode. In addition, Al 2 (SO 4 ) 3 additive facilitates uniform deposition of Zn owing to the tip‐blocking effect of Al 3+ ion. The study demonstrates that the joint strategy is beneficial for both cathode and anode, which may shed some light on the development of AZIBs.