NiCo2O4 spinel:: First report on a transition metal oxide for the negative electrode of sodium-ion batteries

This is the first time that a mixed transition metal oxide is used for the negative electrode of a sodium-ion battery. The NiCo2O4 spinel was prepared by thermal decomposition of oxalate precursors at 320 degreesC. The electrochemical reactions of this material with sodium lead to the complete reduction of the transition metals and the formation of Na2O. The new electrode material shows reversible capacities of ca. 300 mA h g(-1) in sodium-ion cells versus NaxCoO2.