Thermoreversible and Self-Protective Sol-Gel Transition Electrolytes for All-Printed Transferable Microsupercapacitors as Safer Micro-Energy Storage Devices

The safety issue caused by thermal runaway poses a huge threat toward the lifespan and application of high-density electrochemical energy storage devices, especially in the field of micro-energy, such as micro-supercapacitors (MSCs). The heat accumulation is difficult to be eliminated, considering the narrow space inside integrated electronic devices attached to the MSC group. Active thermal management is of paramount importance to ensure the normal operation of electronic devices. However, existing one-time thermal protection strategies cannot fully meet current requirements. Herein, we report a promising thermoreversible temperature-responsive electrolyte system, which can shut down the current flow before thermal runaway occurs, thanks to the sol-gel transition of Pluronic [poly(ethylene oxide)-block-poly(propylene oxide)-blockpoly(ethylene oxide)]-based graft copolymer solution. As the temperature rises to 80 degrees C, the self-protective electrolyte will change from the sol state to gel state. Meanwhile, the internal resistance increases and ionic conductivity decreases gradually as a result of the gelation of the sol electrolyte. The capacity of the energy storage device using the self-protective electrolyte is reduced by about 95%, and the ionic conductivity remains at only 1% at 80 degrees C compared with the initial value at room temperature, and it can be restored after cooling down. During 20 heating/cooling cycles, the electrochemical performance is substantially stable, demonstrating a potential approach to achieve repeatability and self-protection for micro-energy storage devices according to temperature changes. In addition, we integrated the as-prepared self-protective electrolyte into MSCs via three-dimensional printing technology to design an all-printed transferable micro-energy storage device with the dynamic reversible selfprotection behavior, and the thermo-switchable protection mechanism under series and parallel conditions were studied under appropriate temperature window (25-80 degrees C). The strategy disclosed herein is expected to provide new insights into the new-generation smart MSCs for their wide applications in diverse fields such as microelectronics and wearable devices.