Double‐Sheet Vanadium Oxide as a Cathode Material for Calcium‐Ion Batteries

Abstract Calcium‐ion batteries (CIBs) are theoretically considered one of the potential post‐lithium‐ion battery technologies. However, only a few host materials are known to intercalate Ca ions. Herein, we demonstrate the use of double‐sheet vanadium oxide V 2 O 5 ⋅ 0.63H 2 O as a high‐performance cathode material for CIBs. The vanadium oxide was synthesized via an electrochemical oxidation process on a graphite foil substrate. The material exhibited a high reversible capacity of 204 mAh g −1 at a 0.1 C rate in an aqueous electrolyte, with an average discharge voltage of 2.76 V vs. Ca/Ca 2+ , and a capacity retention of 86% after 350 cycles. The reaction mechanism can be described as a combination of diffusion‐controlled intercalation and surface‐limited pseudo‐capacitance reactions. This study provides a new type of Ca host material, motivating further development of new CIB cathode materials.