Nanophase ZnCo₂O₄ as a high performance anode material for Li-ion batteries

Abstract

ZnCo₂O₄ has been synthesized by the low-temperature and cost-effective urea combustion method. X-ray diffraction (XRD), HR-TEM and selected area electron diffraction (SAED) studies confirmed its formation in pure and nano-phase form with particle size ~15-20 nm. Galvanostatic cycling of nano-ZnCo₂O₄ in the voltage range 0.005-3.0 V versus Li at 60 mA g⁻¹ gave reversible capacities of 900 and 960 mA h g⁻¹, when cycled at 25°C and 55°C, respectively. These values correspond to ~8.3 and ~8.8 mol of recyclable Li per mole of ZnCo₂O₄. Almost stable cycling performance was exhibited in the range 5-60 cycles at 60 mA g⁻¹ and at 25°C with ~98 % coulombic efficiency. A similar cycling stability at 55°C, and good rate-capability both at 25 and 55°C were found. The average discharge- and charge-potentials were ~1.2 V and ~1.9 V, respectively. The ex-situ-XRD, -HRTEM, -SAED and galvanostatic cycling data are consistent with a reaction mechanism for Li-recyclability involving both de-alloying-alloying of Zn and displacement reactions, viz., LiZn↔Zn↔ZnO and Co↔CoO↔Co₃O₄. For the first time we have shown that both Zn- and Co-ions act as mutual beneficial matrices and reversible capacity contribution of Zn through both alloy formation and displacement reaction takes place to yield stable and high capacities. Thus, nano-ZnCo₂O₄ ranks among the best oxide materials with regard to Li-recyclability.