Ultralight and Binder-Free All-Solid-State Flexible Supercapacitors for Powering Wearable Strain Sensors

Flexible energy storage devices play a pivotal role in realizing the full potential of flexible electronics. This work presents high-performance, all-solid-state, flexible supercapacitors by employing an innovative multilevel porous graphite foam (MPG). MPGs exhibit superior properties, such as large specific surface area, high electric conductivity, low mass density, high loading efficiency of pseudocapacitive materials, and controlled corrugations for accommodating mechanical strains. When loaded with pseudocapacitive manganese oxide (Mn3O4), the MPG/Mn3O4 (MPGM) composites achieve a specific capacitance of 538 F g(-1) (1 mV s(-1)) and 260 F g(-1) (1 mV s(-1)) based on the mass of pure Mn3O4 and entire electrode composite, respectively. Both are among the best of Mn3O4-based supercapacitors. The MPGM is mechanically robust and can go through 1000 mechanical bending cycles with only 1.5% change in electric resistance. When integrated as all-solid-state symmetric supercapacitors, they offer a full cell specific capacitance as high as 53 F g(-1) based on the entire electrode and retain 80% of capacitance after 1000 continuous mechanical bending cycles. Furthermore, the all-solid-state flexible supercapacitors are incorporated with strain sensors into self-powered flexible devices for detection of both coarse and fine motions on human skins, i.e., those from finger bending and heart beating.