Promising VO2(B)/rGO Heterojunction Cathode for Building High‐Capacity and Long‐Lifespan Ca‐Ion Batteries

Abstract Calciumion batteries (CIBs) are an appealing energy storage technology owing to the low redox potential of Ca 2+ /Ca and the abundant Ca reserves in the earth's crust. However, suitable cathode materials with high capacity and long lifespan are scarce. Herein, VO 2 (B)/reduced graphene oxide (rGO) heterojunction formed by interfacial V─O─C bonds is constructed and first reported as a cathode material for CIBs, which exhibits an ultrahigh discharge capacity of 319.2 mAh g −1 and exceptional long lifespan (3000 cycles at 500 mA g −1 with capacity retention of 85%). In addition, VO 2 (B)/rGO heterojunction also shows an outstanding rate capability at 50 °C (127.1 mAh g −1 at 1000 mA g −1 ). The remarkable electrochemical performance is attributed to the big tunnel structures of VO 2 (B) and the role of rGO in enhancing electronic conductivity. Density functional theory calculations reveal a feasible Ca 2+ diffusion path at the interface. Furthermore, a reversible single‐phase insertion/extraction reaction is revealed by in situ X‐ray diffraction, ex situ Raman, and ex situ X‐ray photoelectron spectroscopy. This work demonstrates that VO 2 (B)/rGO holds great potential for building high‐capacity and long‐lifespan CIBs.