Enhanced charge storage capacity and high rate capabilities of Ni2Co-layered double hydroxides/expanded-graphite composites as anodes for Li-ion batteries

Abstract

Layered double-hydroxides (LDHs) have been at the forefront of research due to their multi-faceted advantages towards lithium-ion batteries (LIBs). However, their low electronic conductivity, huge volume change during lithiation and delithiation process, and slow ion diffusion hamper their cycling stability as well as rate capabilities, limiting their usage for LIBs. To address the above-mentioned issues, expanded graphite (EG) has been used as a conductive additive using in situ methods, which helped in anchoring Ni₂Co-LDH on to the surface of EG. Using Ni₂Co-LDH/EG composites as anodes for LIBs showed enhanced charge-storage capacities of 1880 and 919 mA h g⁻¹ compared to 1028 and 92 mA h g⁻¹ for Ni₂Co-LDH at 0.05 A g⁻¹ and 1 A g⁻¹, respectively. Moreover, staircase potentio-electrochemical impedance spectroscopy (SPEIS) studies indicated that the charge-storage dynamics of Ni₂Co-LDH/EG composites could be attributed to the battery-like behaviour. Furthermore, to understand the significant enhancement in charge-storage capabilities of Ni₂Co-LDH/EG composites, density functional theory (DFT) calculations are carried out. The calculations suggest that the relatively large lithium interaction energy of Ni₂Co-LDH/EG and the PDOS overlapping of lithium and carbon in the valence band region gave rise to a stable Li-ion intercalation process.