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

Calciumion batteries (CIBs) are an appealing energy storage technology owing to the low redox potential of Ca2+/Ca and the abundant Ca reserves in the earth's crust. However, suitable cathode materials with high capacity and long lifespan are scarce. Herein, VO2(B)/reduced graphene oxide (rGO) heterojunction formed by interfacial V & horbar;O & horbar;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, VO2(B)/rGO heterojunction also shows an outstanding rate capability at 50 degrees C (127.1 mAh g(-1) at 1000 mA g(-1)). The remarkable electrochemical performance is attributed to the big tunnel structures of VO2(B) and the role of rGO in enhancing electronic conductivity. Density functional theory calculations reveal a feasible Ca2+ 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 VO2(B)/rGO holds great potential for building high-capacity and long-lifespan CIBs.