Structural engineering of hydrated vanadium oxide cathode by K+ incorporation for high-capacity and long-cycling aqueous zinc ion batteries

Vanadium oxides are promising candidates for cathode materials in aqueous zinc-ion batteries (ZIBs) with low cost and high capacity yet requirements for long cycling necessitate the development of increasingly stable structure. This study reports a structural engineering method by incorporating K+ into hydrated vanadium pentoxide (V2O5·nH2O, VOH) to achieve unique hydrated vanadate (KV12O30-y·nH2O, KVOH). In contrast to previously reported works, K+ introduction leads to a new phase of KVOH with faster ion diffusion kinetics and better long-term cycling stability. This work establishes an understanding of the role of K+ incorporation in KVOH which goes beyond its conventional categorization as an agent for interlayer spacing adjustment, reflecting in maintaining structure flexibility for effective Zn2+ insertion/extraction even at high rates, improving materials conductivity by the electron hoping of V4+/V5+ and acting as a stabilizer to accommodate structural contraction/expansion with smaller voltage hysteresis and higher reversibility. KVOH displays a remarkable capacity of 436 mAh g−1 at 0.05 ​A ​g−1, maintains 227 mAh g−1 at 10 ​A ​g−1, which is better than VOH and the majority of reported monovalent and multivalent metal ions introduced in vanadates. KVOH exhibits excellent cycling stability with 92% capacity retention over 3000 cycles at 5 ​A ​g−1, high energy density (308 ​Wh kg−1) and power density (7502 ​W ​kg−1), as well as improved energy efficiency. These characteristics recommend KVOH cathodes for use in high-performance aqueous ZIBs.