An investigation into the capacity fading mechanism of Ni-Co hydroxide electrode materials

Nickel-cobalt layered double hydroxides (Ni-Co LDHs) are promising electrode materials for hybrid capacitors owing to their large specific capacity, numerous reactive sites, and fast ion exchange efficiency. However, poor cycling stability remains a persistent challenge for Ni-Co LDH materials. To address this, the capacity fading mechanisms of Ni-Co LDH were investigated through characterizations and kinetic analysis to gain insights for rational modification. Ni-Co LDH electrodes were prepared on conducting substrates via the solvothermal method, and control experiments were designed to examine the impact of the electrolytes on their cycling stability. The electrochemical performance of Ni-Co LDHs at different charge-discharge cycling stages was first analyzed. Meanwhile, their morphology, crystallinity, interlayer spacing, and composition changes were characterized. Results revealed that the alterations in the crystal structure, dissolved ions content, and interlayer distance of Ni-Co LDH mainly occurred before the plateau cycling stage and, thus, were not the predominant causes of capacity decay. Instead, electrolyte-induced morphological changes impaired ion diffusion kinetics, appearing fundamental to capacity decay. Insights of the work would supply crucial guidelines for structural design and stability enhancement of LDH-based electrode materials.