Application of NiCoP/NiCo2N designed by heterogeneous interface engineering in low-temperature flexible supercapacitors

In this work, a binder-free NiCoP/NiCo2N (NCPN) cathode grown in situ on carbon cloth (CC) was proposed by hydrothermal method and gas phase phosphonitridation treatment, and cypress sawdust derived porous carbon with B, S-doping is prepared as the anode. The binder-free NCPN/CC cathode realizes good wettability, high specific capacity (725 C·g−1 at 1 A·g−1), good rate performance 579 C·g−1 at 20 A·g−1) and a stable long cycle performance (80 % capacity retention after 10,000 cycles at 20 A·g−1). Besides, first-principles calculations proved that the NiCoP/NiCo2N heterojunction can rearrange the crystal structure and electronic field of the active substances, adjust their d-band center, and thus enhance their electrochemical activity. At the same time, due to atomic doping and reasonable pore structure design, B, S co-doped biomass carbon (CBS) also reveals higher graphitization degree, richer mesopores and micropores and higher electrochemical performance than commercial activated carbon (AC). Thanks to the excellent performance of positive and negative electrode materials, the assembled aqueous asymmetric supercapacitors (AASC) and hydrogel asymmetric supercapacitors (HASC) show excellently high capacity, good rate capability and high power density/energy density. Especially, the flexible HASC can maintain normal use at low temperatures and large bending angles, unfolding great application potential. The NCPN/CC//CBS hydrogel asymmetric supercapacitor (HASC) shows high power density/energy density and can maintain normal use at low temperature and bending, unfolding a good application potential. [Display omitted] •Application of d-Band center theory in supercapacitor energy storage.•Reasonable structure design to endure rapid electron and ion transmission.•Heterogeneous interface engineering to improve reaction kinetics and structural stability.•Flexible NCPN/CC//CBS HASC with good power/energy density, as well as low temperature and bending resistance.