All Si₃ N₄ Nanowires Membrane Based High-Performance Flexible Solid-State Asymmetric Supercapacitor

Recently, much attention has been drawn in the development of flexible energy storage devices due to the increasing demands for flexible/portable electronic devices with high energy density, low weight, and good flexibility. Herein, vertically oriented graphene nanosheets (VGNs) are in situ fabricated on the surface of free-standing and flexible Si₃ N₄ nanowires (NWs) membrane by plasma-enhanced chemical vapor deposition (PECVD), which are directly used as flexible nanoscale conductive substrates. NiCo₂ O₄ hollow nanospheres (HSs) and FeOOH amorphous nanorods (NRs) are finally prepared on Si₃ N_4NWs @VGNs, which are served as the positive and negative electrodes, respectively. Profiting from the structural merits, the synthesized Si₃ N_4NWs @VGNs@NiCo₂ O_4HSs and Si₃ N_4NWs @VGNs@FeOOH_NRs membrane electrodes exhibit remarkable electrochemical performance. Using Si₃ N_4NWs membrane as the separator, the assembled all Si₃ N_4NWs membrane-based flexible solid-state asymmetric supercapacitor (ASC) with a wide operating potential window of 1.8 V yields the outstanding energy density of 96.3 Wh kg^-1 , excellent cycling performance (91.7% after 6000 cycles), and good mechanical flexibility. More importantly, this work provides a rational design strategy for the preparation of flexible electrode materials and broadens the applications of Si₃ N_4NWs in the field of energy storage.