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Flexible supercapacitors (FSCs) are promising energy suppliers for the emerging wearable devices. Because of the limited human body surface area, it is vital to prepare a flexible electrode with high areal performance. To address this challenge, we propose a facile hydrochloric acid (HCl) solvothermal strategy to fabricate high areal performance chlorine-doped reduced graphene oxide films (Cl-RGOFs). Owing to the electron-withdrawing effect induced by the doped Cl atoms and reducibility of HCl, the electrical conductivity of Cl-RGOF enhanced 2.5 times compared with the pristine-reduced graphene oxide film, which effectively decreased internal resistance, ensuring impressive capacitive performance. As a result, Cl-RGOF exhibits near-linear growth of specific areal capacitance with the increasing of mass loading to the commercial level. For flexible solid-state supercapacitors (FSSCs), Cl-RGOFs with 11 mg cm–2 mass loading present high areal capacitance of 2312 mF cm–2 and 78.7% capacitance retention from 1 to 20 mA cm–2. The FSSC shows a high areal energy density of 160.6 μW h cm–2 at the power density of 0.5 mW cm–2. Besides, the FSSC also shows stable capacitance at different bending angles or after 500-times bending, demonstrating high flexibility and practicality. This strategy provides a new path for the preparation of high areal performance FSC for wearable devices.

Pressure sensors have been widely expected to be applied in wearable electronics for monitoring daily motions or healthcare information. Specifically, portable plantar pressure detection, which could enrich the gait information in customer-level application and enhance the dynamic precision in medical-level inspection, is essential in the wearable electronic field and has been widely demonstrated in reports. However, recently reported pressure sensors barely fit the demand of high-resolution plantar pressure detection due to the limited operation range: the pressure in some position of planta could be over 300 kPa in the standing state, not to mention the pressure in walking and running states. To satisfy the critical demand of plantar pressure detection, herein, we introduced a frameless self-assembled spongelike structure graphene aerogel and further developed a high-performance pressure sensor. The aerogel freeze-dried from a glycerin-decorated alginate/graphene hydrogel presents a sponge structure and helped the as-present pressure sensor to achieve an extremely wide operation range of up to 1000 kPa with high sensitivity, low detection limit, high durability, and rapid response time. Based on the extraordinary performance of the pressure sensor, we designed a high confidence portable plantar pressure phase monitoring system. This system could provide impressive plantar pressure information for recognition of different testers and detecting different daily motion states and even warning for possible slipping.