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

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 similar to 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 degrees C and 55 degrees C , respectively. These values correspond to similar to 8.3 and similar to 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 degrees C with similar to 98 % coulombic efficiency. A similar cycling stability at 55 degrees C, and good rate-capability both at 25 and 55 degrees C were found. The average discharge- and charge-potentials were similar to 1.2 V and similar to 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.