Laser-Irradiated B‑Doped Graphene Showing Enhanced Capacitance in a Fluorine-Free Water-in-Bisalt Electrolyte

Research progress on aqueous supercapacitors with carbon-based nanomaterials has surged significantly with the development of energy storage technology due to their low-cost synthesis methodology, environmental compatibility, and safety. Recently, water-in-salt (WIS) and water-in-bisalt (WIBS) electrolytes have gained substantial attention owing to their wide electrochemical stability window (ESW), surpassing that of conventional aqueous electrolytes (approximately 1.23 V). This study investigates the integration of laser-irradiated (LI) boron-doped graphene (BG) electrodes with a WIBS electrolyte (12 m NaNO₃ + 0.1 m KNO₃). Specifically, the utilization of a WIS environment with NaNO₃ and KNO₃ ions results in the formation of a thinner electric double layer (EDL), effectively enhancing capacitance while preserving the expansive ESW of 2 V. The observed improved specific capacitance using the WIBS electrolyte is 102.45 mF cm^–2 at a current density of 0.2 mA cm^–2. Remarkably, the performance of the symmetric full-cell supercapacitor exhibits exceptional cycling stability over 8000 cycles, maintaining nearly 100% Coulombic efficiency throughout the cycling, along with approximately 90% capacitance retention up to 6000 cycles and around 79% retention after 8000 cycles. Furthermore, the B-doped electrode immersed in the WIBS electrolyte attains a notable energy density of 56.916 mWh cm^–2 and a power density of 6 kW cm^–2. This investigation underscores the potential of LI-BG electrodes coupled with WIBS electrolytes in significantly elevating the energy density and overall performance in aqueous supercapacitor systems.