High‐Voltage Potassium Ion Micro‐Supercapacitors with Extraordinary Volumetric Energy Density for Wearable Pressure Sensor System

Abstract To cate for the rapid development of flexible, wearable and implantable microelectronics, the miniaturized and integrated energy storage devices with mechanically robust properties, high voltage, and highly compatible integration are in extreme demand. Here, potassium ion micro‐supercapacitors (KIMSCs) are rationally designed by applying MXene‐derived potassium titanate (KTO) nanorods anode and porous activated graphene (AG) cathode to power the sensitively integrated pressure sensing system. Benefiting from the advanced nanostructure of KTO nanorods, it offers a high potassium ion storage capacity of 145 mAh g −1 . Notably, the constructed KIMSCs exhibit a large operating voltage window of 3.8 V, outperforming the previously reported micro‐supercapacitors. Furthermore, an extraordinary volumetric energy density of 34.1 mWh cm −3 is achieved for KIMSCs with robust rate capability and remarkable capacitance retention, due to the dominated capacitive mechanism and tiny volume change of reversible intercalation/deintercalation of K cations in KTO and adsorption/desorption of bis(trifluoromethanesulfonyl) imide anions on AG. More importantly, a KIMSC compatibly integrated with a wireless pressure sensor on a flexible substrate can monitor body movement. Therefore, this work not only provides insight on designing high‐performance KIMSCs, but also presents a blueprint for KIMSCs powered flexible electronics.