Design and understanding of dendritic mixed-metal hydroxide nanosheets@N-doped carbon nanotube array electrode for high-performance asymmetric supercapacitors

Design and fabrication of supercapacitors (SCs) with high energy density, fast discharge rate, and long cycle life is of great importance; however, the performances of SCs depend critically on advances in materials development. Here we report the development of a high-performance electrode material composed of hierarchical, porous interlaced ultrathin Zn and Ni co-substituted Co carbonate hydroxides (ZnNiCo-CHs) nanosheets branched on N-doped carbon nanotube arrays (C@ZnNiCo-CHs), which were grown directly on a nickel foam current collector. The mesoporous features and large open spaces of the interlaced ultrathin ZnNiCo-CHs nanosheets provide more active sites for redox reactions and facilitate fast mass transport; the self-standing N-doped carbon nanotube arrays offer large surface area, promote fast electron transport, and enhance structure stability, resulting in outstanding rate capability and long-term stability. Density functional theory calculations suggest that the ZnNiCo-CHs nanosheets have low deprotonation energy, greatly facilitating the rate of redox reactions. Further, an asymmetric SC constructed from a C@ZnNiCo-CHs positive electrode and an N-, S-codoped rGOs negative electrode demonstrates a high energy density of 70.9 W h kg⁻¹ at a power density of 966 W kg⁻¹ while maintaining a capacity retention of 91% even after 20,000 cycles at 20 A g⁻¹. The findings provide some important insight into rational design of transition metal compounds based materials for fast energy storage, which may be applicable to creating efficient and robust electrode materials for other energy-related devices.