Insight into faradaic mechanism of NiCo-CHH microspheres in high-performance Ni-Cu batteries

Preintercalation of ions/molecules into the crystal structure with further structural reconstruction can provide fundamental optimizations to improve the electrochemical performance of electrode materials. Herein, Co-doped nickel carbonate hydroxide hybridized (NiCo-CHH) microspheres are prepared by incorporating cobalt cations, carbonate ions and water molecules into the layered-structure of Ni(OH)2. The optimized NiCo-CHH electrode shows ultrahigh specific capacity, superior rate performance and excellent cycling stability. In situ Raman spectroscopy demonstrates that the preintercalation of Co cations, carbonate ions and crystal water molecules into the layered crystal structure of Ni(OH)2 can activate more active sites, improve the electronic conductivity, facilitate diffusion kinetics, and strengthen the crystal structural integrity of Ni(OH)2. Ex situ XRD, ex situ SEM and TEM images reveal the electrochemical reaction mechanism on the anode surface. These findings provide new insight into the faradaic mechanism generally applicable to aqueous rechargeable Ni-Cu batteries.