Carbonates (bicarbonates)/reduced graphene oxide as anode materials for sodium-ion batteries

Abstract

Carbonates/bicarbonates (FeCO₃, CoCO₃ and Ni(HCO₃)₂) supported on reduced graphene oxide (rGO) are prepared by a simple method and examined as anode materials for sodium-ion batteries for the first time. Although carbonates in the composite are of the order of micrometers, they show fair electrochemical activities, particularly for FeCO₃/rGO. It delivers a capacity of 247 mA h g⁻¹ after 500 cycles at 500 mA g⁻¹, corresponding to a capacity retention of 87% relative to the capacity at the second cycle. It also shows a superior rate capability with a capacity of 176 mA h g⁻¹ at 2 A g⁻¹. Ex situ XPS spectra, HRTEM images and SAED patterns demonstrate that the sodium uptake/extraction in FeCO₃, CoCO₃ and Ni(HCO₃)₂ is via M⁰/M²⁺-engaged redox reaction.