context: Recently, a high energy density (97.6 W h kg−1) along with impressive cycling steadiness (73% retention after 5000 cycles at 1 A g−1) was reported by Yang et al. for a lithium-ion capacitor fabricated by using PAN/hydrothermal-made V3O7·H2O nanowire derived CNFs/V2O3 hybrids as the anode and commercial activated carbon (AC) as the cathode. Additionally, the prepared CNFs/V2O3 nanocomposites with internal void spaces displayed a high capacity of 569.1 mA h g−1 at 0.1 A g−1 as well as unexpected rate capability (238.5 mA hg−1 at 10.0 A g−1) in half-cell tests. By electrospinning a PAN/VO(acac)2 precursor solution, followed by calcination, V–O–C nanocomposites with a specific surface area of 587.9 m2 g−1 were obtained. An atomic level dispersion of vanadium within the composite nanofibers enabled the resultant V–O–C nanocomposites to deliver a specific capacitance of 463 F g−1 at 1 A g−1 with good electronic conductivity and electrolyte penetration. Moreover, the electrochemical properties of V5+ are superior to those of V3+ and V4+ when vanadium oxide-embedded carbon fibers are applied in a supercapacitor. Bai et al. produced CNFs/V2O3, CNFs/VO2–V2O5 and CNFs/V2O5via electrospinning a PAN/VO(acac)2 precursor solution, followed by different calcination processes. The results showed that the electrochemical performance of CNFs/V2O5 is better than that of CNFs/V2O3 and CNFs/VO2–V2O5 when they were applied to SCs. In Tang's work, CNFs/VO/VOx web-like nanocomposites were obtained by electrospinning a polymer-based solution containing PAN, PVP, hybrid vanadium precursors (VO2, V2O5, and VO(acac)2) and DMF, followed by carbonization treatment. The formation of quasi-metallic VO (∼102 Ω−1 cm−1) in the CNF enhanced the rate of electron transfer in the web-like electrode. Besides, the well-developed pore structure and rich vanadium redox couples also promoted the rapid ion transfer rate. As a consequence, the SC equipped with symmetric CNFs/VO/VOx electrodes exhibited a specific capacitance of 325.7 F g−1 at 1 A g−1 with 92% retention at 4 A g−1 after 5000 cycles.
answer: activated carbon (AC)