Studies on spinel cobaltites, MCo2O4 (M = Mn, Zn, Fe, Ni and Co) and their functional properties

Optimization of electrodes for charge storage with appropriate processing conditions places significant challenges in the developments for high performance charge storage devices. In this article, metal cobaltite spinels of formula MCo204 (where M = Mn, Zn, Fe, Ni and Co) are synthesized by oxalate decomposition method followed by calcination at three typical temperatures, viz. 350, 550, and 750 degrees C and examined their performance variation when used as anodes in lithium ion batteries. Phase and structure of the materials are studied by powder x-ray diffraction (XRD) technique. Single phase MnCo2O4,ZnCo2O4 and Co3O4 are obtained for all different temperatures 350 degrees C, 550 degrees C and 750 degrees C; whereas FeCo2O4 and NiCo2O4 contained their constituent binary phases even after repeated calcination. Morphologies of the materials are studied via scanning electron microscopy (SEM): needle-shaped particles of MnCo2O4 and ZnCo2O4, submicron sized particles of FeCo2O4 and agglomerated submicron particle of NiCo2O4 are observed. Galvanostatic cycling has been conducted in the voltage range 0.005-3.0 V vs. Li at a current density of 60 mA g(-1) up to 50 cycles to study their Li storage capabilities. Highest observed charge capacities are: MnCo2O4 - 365 mA h g(-1) (750 degrees C); ZnCo2O4 - 516 mA h g(-1) (550 degrees C); FeCo2O4 - 480 mA h g(-1) (550 degrees C); NiCo2O4 - 384 mA h g(-1) (750 degrees C); and Co3O4 - 675 mA h g(-1) (350 degrees C). The Co3O4 showed the highest reversible capacity of 675 mA h g(-1); the NiO present in NiCo2O4 acts as a buffer layer that results in improved cycling stability; the ZnCo2O4 with long needle-like shows good cycling stability.