Sulfur-Doped Nickel–Cobalt Double Hydroxide Electrodes for High-Performance Asymmetric Supercapacitors

In this work, an effective strategy was proposed to improve the electrochemical performance of nickel–cobalt layered double hydroxide (NiCo-LDH) by controlling the sulfur doping. The prepared NiCo-LDH material with a 7.5% mol S dopant compared to LDH (NiCo-LDH-S7.5) possesses a unique nanosheet spherical structure, so it can expose more active sites and make better contact with the electrolyte. The synthesized NiCo-LDH-S7.5 has an outstanding specific capacitance of 2417.7 F g–1 at 1 A g–1. Meanwhile, the sulfur dopant significantly improves the electrical conductivity of the electrode material, enhancing the rate performance of the electrode. When the current density increases from 1 to 20 A g–1, the electrode retains a specific capacitance of 81.8%. In addition, we also manufactured an asymmetric supercapacitor using NiCo-LDH-S7.5 and activated carbon as positive and negative electrodes, respectively. Also, it exhibits an exceptionally high energy density of 73.54 Wh kg–1 at a power density of 375 W kg–1 and excellent cyclic stability (90.19% performance remained after 5000 cycles at 2 A g–1). The supercapacitor has been tested to power 88 LEDs (∼2 V) in series, indicating great potential for practical application.