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

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 M-0/M2+-engaged redox reaction.