Electrochemical storage behavior of NiCo₂O₄ nanoparticles anode with structural and morphological evolution in lithium-ion and sodium-ion batteries

NiCo₂O₄ nanoparticles (5-10 nm) were prepared by a simple sol-gel method and evaluated in the Li/Na-cell as an anode. The anode exhibited excellent lithium storage capacity (1050 and 860 mAh g⁻¹ at specific currents of 0.1 and 0.5 A g⁻¹, respectively) and outstanding cycling performance of over 200 cycles. However, it showed a moderate sodium storage capacity with poor cycle retention. A clear comparison of the structural stability of the electrode determined via the cross-sectional scanning electron microscopy (SEM) micrographs indicates swelling and extensive volume expansion in the Na cell. The investigations conducted using in situ X-ray diffraction (XRD) and ex situ X-ray absorption spectroscopy (XAS) reveal the limited reduction of Co and Ni oxidation states and a minimal degree of conversion during Na uptake. This study highlights the ability of NiCo₂O₄ nanoparticles to withstand high mechanical stress during the conversion reaction with Li, thus providing excellent performance. Conversely, the NiCo₂O₄ anode with Na could not be overcome massive volume expansion and irreversibility by reducing the size of particles in nano-dimension.