The application of transition metal oxides/hydroxides in energy storage has long been studied by researchers. In this paper, the core-shell CNFs@Ni(OH)2/NiO composite electrodes were prepared by calcining carbon nanofibers (CNFs) coated with Ni(OH)2 under an N2 atmosphere, in which NiO was generated by the thermal decomposition of Ni(OH)2. After low-temperature carbonization at 200 °C, 250 °C and 300 °C for 1 h, Ni(OH)2 or/and NiO existed on the surface of CNFs to form the core-shell composite CNFs@Ni(OH)2/NiO-X (X = 200, 250, 300), in which CNFs@Ni(OH)2/NiO-250 had the optimal electrochemical properties due to the coexistence of Ni(OH)2 and NiO. Its specific capacitance could reach 695 F g−1 at 1 A g−1, and it still had 74% capacitance retention and 88% coulomb efficiency after 2000 cycles at 5 A g−1. Additionally, the asymmetric supercapacitor (ASC) assembled from CNFs@Ni(OH)2/NiO-250 had excellent energy storage performance with a maximum power density of 4000 W kg−1 and a maximum functional capacity density of 16.56 Wh kg−1.

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Supercapacitors are considered as important energy conversion and storage devices, and one-dimensional carbon nanofibers derived from electrospinning have been widely applied for supercapacitor electrode materials. The integration of carbon and metal hydroxide materials has become particularly important in order to pursue their higher electrochemical properties. In this paper, a one-dimensional core-shell electrode with Ni(OH) 2 as shell and carbon nanofibers as core (Ni/CNFs@Ni-(OH) 2 ) was fabricated by electrospinning, high-temperature carbonization and hydrothermal synthesis. This electrode exhibited high energy storage performance (785 F g À 1 (1 A g À 1 )), good coulombic efficiency and cycling stability. Furthermore, the asymmetric supercapacitor (ASC) assembled with activated carbons as negative electrode and Ni/CNFs@Ni(OH) 2 as positive electrode demonstrated a good energy storage performance (62.5 F g À 1 (1.6 V)). Meanwhile, this ASC displayed a significant energy density of 22.2 Wh kg À 1 at 800 W kg À 1 and an outstanding rate capability, indicating that Ni/CNFs@Ni(OH) 2 had a high potential application value in supercapacitors.

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The combination of multiple electrode materials and their reasonable structural design are conducive to the preparation of composite electrodes with excellent performance. In this study, based on carbon nanofibers grown with Ni(OH)2 and NiO (CHO) prepared by electrospinning, hydrothermal growth, and low-temperature carbonization, five transition metal sulfides (MnS, CoS, FeS, CuS, and NiS) were hydrothermally grown on their surfaces, exhibiting that CHO/NiS had the optimal electrochemical properties. Subsequently, the effect of hydrothermal growth time on CHO/NiS revealed that the electrochemical performance of CHO/NiS-3h was optimal, with a specific capacitance of up to 1717 F g−1 (1 A g−1), due to its multistage core–shell structure. Moreover, the diffusion-controlled process of CHO/NiS-3h dominated its charge energy storage mechanism. Finally, the asymmetric supercapacitor assembled with CHO/NiS-3h as the positive electrode demonstrated an energy density of 27.76 Wh kg−1 at a maximum power density of 4000 W kg−1, and it still maintained a power density of 800 W kg−1 at a maximum energy density of 37.97 Wh kg−1, exhibiting the potential application of multistage core–shell composite materials in high-performance supercapacitors.