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 °C. 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 Na x CoO2.

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New LiNi0.5Ti x Mn1.5 - x O4 (0.05 ≤ x ≤ 0.6) spinel oxide materials have been obtained. The cubic unit cell parameter increases with the substitution of manganese by titanium in the octahedrally coordinated 16d sites, as evidenced by X-ray and neutron diffraction studies. For Ti-free LiNi0.5Mn1.5O4 up to x = 0.10, a decrease in the line broadening of the X-ray diffraction profiles is observed. For x > 0.1, X-ray line broadening and a progressive loss of resolution in the FTIR spectral profiles are observed. The presence of small amounts of Ti (x = 0.05 and 0.1) yields a net improvement of the electrochemical performance, whereas a deterioration of the reversible capacity is observed for large Ti contents. The electrochemical oxidation mechanism involves the appearance of two or three cubic phases with different lattice parameters, as evidenced by ex situ XRD of electrodes prepared at different depths of the first charge.