Efficient Synergy of Sea Urchin-like Graded Structure Supercapacitor Electrodes by Modulating the Morphology of Layered Double Hydroxide Composites

Rational design of the multidimensional structure of self-supporting composite electrode materials is an effective way to maintain the structural stability of supercapacitors and the efficient energy storage performance of ion and electron transport. Here, layered double hydroxide (LDH) composite electrodes (CoMn LDH@CoNi LDH/NF, CM@CN LDH) with graded structure and unique sea urchin-like distribution are prepared on nickel foam (NF) by the solvothermal method. The synergistic effect of the dual-LDH leads to increased layer spacing and provides more electrochemically accessible surfaces together with short and effective ion transport paths, which helps to accommodate a large number of active sites to achieve a rapid Faraday oxidation–reduction reaction. The results show that the CM@CN LDH-S1 in the three-electrode system exhibits an excellent specific capacitance of 2381.3 F·g–1 at a current density of 1 A·g–1. The assembled asymmetric supercapacitor device has a high specific capacitance of 240.8 F·g–1 at 1 A·g–1, a high energy density of 75.3 Wh·kg–1, and an excellent cycling performance (85.2% initial retention after more than 5000 cycles at 5 A·g–1), indicating that the graded nanostructure dual-LDH material has excellent application potential.