Unveiling the synergistic effect of cobalt ion in nickel-cobalt layered double hydroxide for electrochemical energy storage: Experimental and computational approaches

As an important component of electrode materials, cobalt is crucial in electrochemical energy storage devices including Li ion battery and supercapacitor. It has been acknowledged that the addition of cobalt enables high-rate performance and significantly enhances the cycle stability. However, the electrochemical mechanism remains elusive due to the complexity of material microstructure and diversity of electrode processing. In this work, a series of nickel-cobalt layered double hydroxide (Ni-Co LDH) nanosheets with designed ratios of Ni/Co and controlled morphologies have been in-situ synthesized. In the light of experimental analyses and density functional theory calculations, the effect of cobalt in determining the crystal structure, morphology, ion diffusion, ion absorption ability of Ni-Co LDH nanosheets has been unambiguously demonstrated. Especially, both ratio and valence state of cobalt plays a significant role in the electrochemical performance. The Ni-Co LDH nanosheets with the ratio of Ni:Co = 3:1 shows the highest specific capacitance of 2875 F g − 1 (4.95 F cm−2) at a current density of 2 mA cm−2 and 88.3% capacity retention after 5000 cycles