Lithium recycling behaviour of nano-phase-CuCo₂O₄ as anode for lithium-ion batteries

Abstract

Nano-CuCo₂O₄ is synthesized by the low-temperature (400 °C) and cost-effective urea combustion method. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) studies establish that the compound possesses a spinel structure and nano-particle morphology (particle size (10-20 nm)). A slight amount of CuO is found as an impurity. Galvanostatic cycling of CuCo₂O₄ at 60 mA g⁻¹ in the voltage range 0.005-3.0 V versus Li metal exhibits reversible cycling performance between 2 and 50 cycles with a small capacity fading of 2 mAh g⁻¹ per cycle. Good rate capability is also found in the range 0.04-0.94C. Typical discharge and charge capacity values at the 20th cycle are 755(±10) mAh g⁻¹ (~ 6.9 mol of Li per mole of CuCo₂O₄) and 745(±10) mAh g⁻¹ (~ 6.8 mol of Li), respectively at a current of 60 mA g⁻¹. The average discharge and charge potentials are ~ 1.2 and ~ 2.1 V, respectively. The underlying reaction mechanism is the redox reaction: Co ↔ CoO ↔ Co₃O₄ and Cu ↔ CuO aided by Li₂O, after initial reaction with Li. The galvanostatic cycling studies are complemented by cyclic voltammetry (CV), ex situ TEM and SAED. The Li-cycling behaviour of nano-CuCo₂O₄ compares well with that of iso-structural nano-Co₃O₄ as reported in the literature.