Hierarchical Structure Formation and Effect Mechanism of Ni/Mn Layered Double Hydroxides Microspheres with Large-Scale Production for Flexible Asymmetric Supercapacitors

In this study, Ni/Mn layered double hydroxides (LDHs) microspheres with three-dimensional flower-like hierarchical structure are fabricated by a large-scale and self-assembled chemical coprecipitation strategy (at 55 °C under normal pressure). In each integrated microsphere, the petals consist of ultrathin two-dimensional nanosheets. The self-assembly formation mechanism of this flower-like construction is systematically investigated according to the analysis results from the regulation of various reaction factors. The Ni/Mn LDHs microspheres show an optimal capacitance value as high as 1379 F·g^–1 at 1 A·g^–1. Sum frequency generation spectroscopy and charge storage behavior mechanism analysis further demonstrate that a favorable capacitive constitution is indeed dependent on the synergistic effect of active sites (different feed ratios) and surface area (different architectural features). Moreover, a novel flexible all-solid-state asymmetric supercapacitor is assembled by exploiting these microspheres and active carbon as positive and negative electrode materials respectively, which exhibits a superior capacitance value of 393 F·g^–1 (1 A·g^–1) and energy and power density of 131.17 Wh·kg^–1 and 1.45 KW·kg^–1 with favorable cyclic life (remains over 75.1% after 5000 cycles under 50 mV·s^–1), respectively. Overall, this work provides a significant prospect and deep understanding for the development of the next generation of flexible energy devices.