Water-in-Salt Ambipolar Redox Electrolyte Extraordinarily Boosting High Pseudocapacitive Performance of Micro-supercapacitors

Planar micro-supercapacitors (MSCs) are one key micropower source for microelectronics. However, the pseudocapacitive regulation strategies of extraordinarily multiplying capacitance and energy density of electric double-layer MSCs are underdeveloped. Herein, a versatile strategy for boosting the capacitance of graphene-based planar MSCs by highly concentrated water-in-salt ambipolar redox electrolyte (ZnI2 + ZnCl2) is proposed, which can serve as an ambipolar redox mediator to contribute remarkable pseudocapacitance for positive and negative electrodes simultaneously. The high volumetric capacity of 106 mAh cm–3, unprecedented energy density of 111 mWh cm–3 that outperfoms the reported graphene-based MSCs, and long-term cycling stability with 92.1% retention after 5300 cycles are acquired. The good performance results from the frustrated self-discharge by suppressing the formation and diffusion of polyiodide ions of I3– and I5–, as confirmed by in situ characterizations. Therefore, this work will open a new avenue of introducing ambipolar redox mediators into highly concentrated electrolytes for high-performance MSCs.