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The rapid development of consumer electronics, electric vehicles, and smart meters demands high-performance energy storage devices. By now, supercapacitors are expected to become one of the most promising energy devices for future energy technology. In this work, NiO nanoparticles supported on activated carbon nanofibers (NiO/ACNFs) have been synthesized by atomic layer deposition technique, which is directly used as self-supporting binder-free electrodes for supercapacitors. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman results show that NiO nanoparticles (3.1 nm) are uniformly coated on ACNFs. The NiO/ACNFs-600 electrodes demonstrate a specific capacitance of 870 F·g−1 (1 A·g−1) and good rate capability (remain 67% at 10 A·g−1). The asymmetric supercapacitor devices with NiO/ACNFs-600//ACNFs electrodes yield a fairly high energy density of 39.85 Wh·kg−1 at 2000 W·kg−1 and excellent capacitance retention of 87% after 10,000 cycles. The excellent electrochemical capacitance performance for NiO/ACNFs is attributed to the high conductivity and large specific surface area of ACNFs, high capacity, small size, and even dispersion of NiO as well as the synergistic effect between them. These results demonstrate that NiO/ACNFs can serve as excellent electrode materials for high-performance asymmetric supercapacitors. [Display omitted] • NiO is dispersed evenly on lignin-derived ACNFs by ALD for the first time. • The oxygen-containing functional groups of ACNFs provide the active site for the anchoring of NiO. • Combined advantages of porous ACNFs and highly dispersed NiO nanoparticles. • NiO/ACNFs-600 electrode exhibits excellent specific capacitance of 870 F·g−1 (1 A·g−1). • NiO/ACNFs-600//ACNFs device yields outstanding energy density of 39.85 Wh·kg−1 at 2000 W·kg−1. [ABSTRACT FROM AUTHOR]