A High Performing Zn-ion Battery Cathode Enabled by in-situ Transformation of V2O5 Atomic Layers.

Developing high capacity and stable cathodes is a key to successful commercialization of aqueous Zn-ion batteries (ZIBs). Pure layered V 2 O 5 has a high theoretical capacity (585 mAh/g), but it suffers severe capacity decay. Pre-inserting cations into V 2 O 5 can substantially stabilize the performance, but at an expense of lowered capacity. Here we show that an atomic layer deposition derived V 2 O 5 can be an excellent ZIB cathode with high capacity and exceptional cycle stability at once. We report for the first time a rapid in-situ on-site transformation of V 2 O 5 atomic layers into Zn 3 V 2 O 7 (OH) 2 ⋅2H 2 O (ZVO) nanoflake clusters, also a known Zn-ion and proton intercalatable material. The extraordinary electrochemical performance arises from the unique attributes of the ALD-V 2 O 5 : high concentration of reactive sites, strong bonding to the conductive substrate, nanosized thickness and binder-free composition, all of which facilitate ionic transport and promote the best utilization of the active material. We also provide new insights into the V 2 O 5 -dissolution mechanisms for different Zn-salt aqueous electrolytes and their implications to the cycle stability. Our work offers an appealing engineering solution to develop high-capacity and stable cathodes for commercial ZIBs and contributes to the fundamental understanding of ionic storage mechanisms in rechargeable aqueous batteries.