Better engineering layered vanadium oxides for aqueous zinc-ion batteries: Going beyond widening the interlayer spacing

Aqueous zinc-ion batteries (ZIBs) are regarded as among the most promising candidates for large-scale grid energy storage, owing to their high safety, low costs, and environmental friendliness. Over the past decade, vanadium oxides, which are exemplified by V2O5, have been widely developed as a class of cathode materials for ZIBs, where the relatively high theoretical capacity and structural stability are among the main considerations. However, there are considerable challenges in the construction of vanadium-based ZIBs with high capacity, long lifespan, and excellent rate performance. Simple widenings of the interlayer spacing in the layered vanadium oxides by pre-intercalations appear to have reached their limitations in improving the energy density and other key performance parameters of ZIBs, although various metal ions (Na+, Ca2+, and Al3+) and even organic cations/groups have been explored. Herein, we discuss the advances made more recently, and also the challenges faced by the high-performance vanadium oxides (V2O5-based) cathodes, where there are several strategies to improve their electrochemical performance ranging from the new structural designs down to sub-nano-scopic/molecular/atomic levels, including cation pre-intercalation, structural water optimization, and defect engineering, to macroscopic structural modifications. The key principles for an optimal structural design of the V2O5-based cathode materials for high energy density and fast-charging aqueous ZIBs are examined, aiming at paving the way for developing energy storage designed for those large scales, high safety, and low-cost systems.