High-Performance Asymmetric Li-Ion Pseudocapacitors Based on Pyroprotein Nanowebs

Modern industrial technologies require high power and energy storage devices with long-term cycling stabilities; the electrochemical performances of these devices are mainly dependent on the active electrode materials and their energy storage mechanisms. In this study, nanoweb-structured pyroprotein nanofibers (NW-PNFs) were prepared from electrospun silk protein by pyrolysis. NW-PNFs have an open macroporous structure formed by entangled nanofibers and numerous micropores originating from the amorphous pseudographitic microstructure of the nanofibers. In addition, they possessed a large number of heteroatoms (10.3 at. % oxygen and 5.2 at. % nitrogen). These material properties led to superior Li-ion storage performances with high reversible capacity of about 1,050 mA h g⁻¹ at 0.5 A g⁻¹ and great cycling performance over 3,000 cycles. In particular, NW-PNFs exhibited high rate capability even at the specific current of 50 A g⁻¹, at which the high specific capacity of circa 400 mA h g⁻¹ was achieved. Furthermore, asymmetric Li-ion storage devices based on NW-PNFs showed feasible electrochemical performances with a maximum specific energy of 235.7 Wh kg⁻¹ at 188.6 W kg⁻¹ and maximum power of 21,220 W kg⁻¹ at 69.6 Wh kg⁻¹.