Relevance of Covalent-Bond Connection on Electrochemical Performance of Nickel/Cobalt Doped Lignin-Based Carbon Materials

Supercapacitors have emerged as a popular area of research due to their exceptional attributes, including excellent cycling life, admirable power density, and rapid charge/discharge capabilities. However, the low energy density significantly restricts its range of applicable scenarios. Herein, the grafting copolymerization technique was employed to incorporate transition metals (nickel, cobalt) into the molecular chain of lignin, and lignin-based pseudocapacitor material (Ni/Co@LC) is obtained after thermal treatment. XRD, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive spectrometry results demonstrate a strong interaction between Ni/Co and carbon, with the transition metals encapsulated within a carbon shell. Hence, the Ni/Co@LC exhibits an approximately 69% increase in specific capacitance compared with those conventional pseudocapacitor materials which Ni/Co coated on the surface of carbon materials, and the equivalent series resistance is reduced by about 50%. Moreover, the assembled asymmetric supercapacitors of Ni/Co@LC//LC achieve an energy density of 52.89 W h kg–1 at a power density of 640 W kg–1 and maintain a capacitance retention rate of 99.28% after undergoing 10,000 charge–discharge cycles. This work presents a novel approach for designing pseudocapacitor electrode materials with low impedance and high cycling performance.