Folding the Energy Storage: Beyond the Limit of Areal Energy Density of Micro-Supercapacitors

摘要

Despite the ever-growing interest in micro-supercapacitors (MSCs) as apromising power source for microelectronics, their low areal energy densityhas plagued practical applications. Herein, accordion foldable MSCs (af-MSCs) are presented as a cell architectural strategy in contrast to traditionalmaterial-driven approaches. The constituent unit cells of an in-plane MSCarray are compactly stacked in a confined device footprint via accordionfolding. Decoupling the energy storage (MSC cells) and folding section (electricalinterconnection between the cells) in the MSC array, in combinationwith neutral plane-controlled flexible hydrophobic cellulose nanofiber (CNF)substrates, enables the realization of the af-MSCs. The af-MSCs achieve highareal integration density with a fill factor of 81.1% and on-demand (in-series/in-parallel) cell configurations owing to the microscale direct-ink–writing ofrheology-tuned MSC cell components on the CNF substrates. The af-MSCwith a miniaturized footprint (22.75 mm~2) achieves exceptional areal electrochemicalperformances (areal energy density of 89.2 μWh cm~(?2)), whichexceed those of previously reported in-plane MSCs.