Unlocking the Impact of Electrolytes on Charge Storage in High-Energy-Dense Supercapacitors

Safe electrolytes with a broad voltage window and high surface area, hierarchical porous activated carbon (HAC) electrodes are essential for developing high energy dense Electrochemical double-layer capacitors (EDLCs) and durable Aqueous Zinc-ion hybrid capacitors (AZHCs). Mindful of this, herein, the charge storage potency of HAC electrodes is unveiled in water-in-salt (WIS) 15m Lithium nitrate (LiNO₃: 2 V), ionic liquids, ILs 1-ethyl-3-methylimidazolium trifluoromethane sulfonate ([EMIM][OTf]:3 V) for EDLCs and quasi-solid state electrolytes Polyvinyl-Zinc trifluromethane sulfonate (PVA-(Zn(CF₃SO₃)₂: 1.6 V) for ZHCs. WIS electrolytes with locked free water molecules allow broad voltage and significant ion storage performance. The intrinsic broad voltage window, non-flammable nature of the ILs improve the energy density and power delivery of EDLCs. Additionally, the choice of polymer-based hydrogel is one of the facile strategies to develop stable, dendrite-free and durable ZHCs. Assembled coin cell devices show energy densities of 42, 77, and 78.8 Wh kg⁻¹ at 1 A g⁻¹ and power outputs of 12.8, 9.9, and 8 kW kg⁻¹ at 10 A g⁻¹ for WIS, IL-based EDLCs and AZHCs respectively. These devices demonstrate low self-discharge and long cycle life offering promising directions for next generation energy-dense EDLCs and durable ZHCs.