High electrochemical performance of in-situ carbon-coated vanadyl ethylene glycolate as cathode for aqueous zinc-ion batteries

Abstract

Organic-inorganic hybrid material of vanadyl ethylene glycolate (VEG) with formula VO(CH2O)2 has been studied as cathode material of zinc-ion aqueous batteries, and its structural information during the electrochemical process was evaluated for the first time using in-situ x-ray diffraction(XRD) technique. The VEG electrode exhibits good electrochemical performance. A high specific capacity of 364 mA h g−1 (at 100 mA g−1) is obtained, and the capacity can still remain 80% of the total capacity even after 100 cycles. The VEG electrode also exhibits good stability in large current density (74% and 65% specific capacity can be remained after 1000 cycles at current density of 2000 mA g−1 and after 2000 cycles at current density of 5000 mA g−1 respectively), and good rate capacity (157 mA h g−1 specific capacity at current density of 4000 mA g−1), which is much higher than the previous reported result. 96% of initial specific capacity can be retrieved with recuperating the current density to 100 mA g−1 after experienced various current density (including 4000 mA g−1) in 60 cycles. It is believed that the amorphous carbon layer formed during the PEG pyrolytic process is crucial to achieving high electronic conductivity of the VEG effectively and improving the electrochemical performance. In situ XRD pattern, the completely reversible appearance and disappearance of new phase even in the second cycle indicate that the electrode material possess an excellent reversibility of the Zn insertion/extraction.