Cu3(OH)2V2O7.2H2O@rGO with bimetallic redox activity as a novel cathode material for calcium-ion batteries

Owing to the abundance of calcium and low redox potential and high safety, calcium-ion batteries (CIBs) are considered a promising candidate for post lithium-ion batteries. However, the lack of high-performance cathode materials is one of the main obstacles to the development of CIBs. Herein, a monoclinic Cu-3(OH)(2)V2O7.2H(2)O coated with reduced graphene oxide (CVO@rGO) is prepared using a facile one-step coprecipitation strategy without a surfactant at room temperature and proposed as a novel cathode material for CIBs. CVO@rGO shows a high discharge capacity of 189.9 mA h g(-1), an excellent rate performance (55.4 mA h g(-1)@1000 mA g(-1)) and can be used for 1000 cycles with a capacity retention of 84.2%. In addition, the Ca2+ storage mechanism of CVO@rGO based on the conversion reaction is revealed using in situ X-ray diffraction and an ex situ transmission electron microscope, and the bimetallic redox activity of CVO@rGO is confirmed using the ex situ X-ray photoelectron spectra and a transmission electron microscope. This work provides a new direction for developing high-performance cathode materials with bimetallic redox activity for CIBs.