Resilient aligned carbon nanotube/graphene sandwiches for robust mechanical energy storage

The use of microscale flexible mechanical energy storage devices, instead of traditional electrochemical energy storage devices based on supercapacitors and Li-ion batteries, is highly considered for portable electronics, actuators, and meso-micro scale systems. The selection of resilient and robust building blocks is the first step for high energy-density mechanical energy storage system. Herein, alternative aligned carbon nanotubes (CNTs) and graphene were effectively sandwiched into freestanding sp² all-carbon hybrids, rendering the excellent loading transfer in the three-dimensional framework. The millimeter-scale aligned CNT/graphene sandwiches could be repeatedly compressed at high strains (ε>90%), with a highest energy absorption density of 237.1kJkg^-1, an ultrahigh power density of 10.4kWkg^-1, and a remarkable efficiency of 83% during steady operation, providing novel nanocomposites with outstanding mechanical energy storage performance comparable to electrochemical batteries and bridging nanoscopic structures to micro- and mesoscale applications.