Nanophase ZnCo₂O₄ as a High Performance Anode Material for Li‐Ion Batteries

Abstract

Abstract ZnCo 2 O 4 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‐ZnCo 2 O 4 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 ZnCo 2 O 4 . 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 ↔ Co 3 O 4 . 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‐ZnCo 2 O 4 ranks among the best oxide materials with regard to Li‐recyclability.