Interfacial Engineering Coupled Valence Tuning of MoO3 Cathode for High-Capacity and High-Rate Fiber-Shaped Zinc-Ion Batteries.

Aqueous Zn-ion batteries (ZIBs) have garnered the researchers' spotlight owing to its high safety, cost effectiveness, and high theoretical capacity of Zn anode. However, the availability of cathode materials for Zn ions storage is limited. With unique layered structure along the [010] direction, α-MoO3 holds great promise as a cathode material for ZIBs, but its intrinsically poor conductivity severely restricts the capacity and rate capability. To circumvent this issue, an efficient surface engineering strategy is proposed to significantly improve the electric conductivity, Zn ion diffusion rate, and cycling stability of the MoO3 cathode for ZIBs, thus drastically promoting its electrochemical properties. With the synergetic effect of Al2 O3 coating and phosphating process, the constructed Zn//P-MoO3- x @Al2 O3 battery delivers impressive capacity of 257.7 mAh g-1 at 1 A g-1 and superior rate capability (57% capacity retention at 20 A g-1 ), dramatically surpassing the pristine Zn//MoO3 battery (115.8 mAh g-1 ; 19.7%). More importantly, capitalized on polyvinyl alcohol gel electrolyte, an admirable capacity (19.2 mAh cm-3 ) as well as favorable energy density (14.4 mWh cm-3 ; 240 Wh kg-1 ) are both achieved by the fiber-shaped quasi-solid-state ZIB. This work may be a great motivation for further research on molybdenum or other layered structure materials for high-performance ZIBs.