Omni-directionally flexible, high performance all-solid-state micro-supercapacitor array-based energy storage system for wearable electronics

All-solid-state micro-supercapacitors (MSCs) receive huge attention owing to their superior electrochemical performance providing sufficient energy densities and mechanically flexible for wearable devices and robotic applications. Here, we present omni-directionally flexible MSC array-based energy storage system, which enables the continuous operation of multi-functional wearable devices while electrochemical performances of MSC array are well sustained and predicted via machine learning. In detail, the assembling MnO₂ nanospheres electrode-based micro-supercapacitor array vertical stacking (SAVS) exhibits outstanding performance in an impressive energy density of 8.1 mWh cm⁻³ at the current density of 11 mA cm⁻² and a significant specific capacitance of 509.6F cm⁻³ (∼1348.9F g⁻¹) due to the high theoretical capacitance of MnO₂ and their chemisorption mechanism with Na⁺. Especially, the device shows extremely high stability through the cyclic test with 93.0 % capacitance retention after 50,000 cycles, and minor changes in bending test at 90° during 2,000 continuous cycles. A trained machine learning model based on experimental dataset further points out that the capacitance retentions of MSC array go beyond 95.3 % in all bending conditions. This work also presents the incorporation of SAVS with a gas sensor in a wearable device, emphasizing its potential use in real-world applications.