Seamlessly integrated high-energy wireless charging supercapacitor for on-body powering

The rapid growth of flexible and wearable electronics demands safe, mechanically compliant energy-storage systems compatible with wireless operation. Solid-state supercapacitors offer high power density and cycling stability, but their practical use is constrained by limited voltage windows, slow ion transport in polymer electrolytes, and integration challenges with contactless charging. Despite progress in mixed-ion and polymer-based electrolytes, achieving simultaneous voltage stability, flexibility, and device-level performance remains challenging. Here, we report a flexible solid-state supercapacitor based on highly reduced graphene (HrG) electrodes and a dual-cation polyvinyl alcohol-Rochelle salt (PVA-RS) gel electrolyte. The HrG electrodes provide enhanced electronic conductivity and accessible charge-storage sites, while the PVA-RS electrolyte enables cooperative Na⁺/K⁺ ion transport and a widened electrochemical stability window of up to 1.8 V. The resulting device delivers a specific capacitance of 138F g⁻¹, an energy density of 62.14 Wh kg⁻¹, and a power density of 22,500 W kg⁻¹, with 98% capacitance retention of over 10,000 cycles and stable performance under different mechanical deformation conditions. Further, in the practical utility of the HrG-SSS device, the wireless charging via resonant inductive coupling demonstrates the feasibility of contactless energy replenishment for wearable applications.