Chaotropic-anion assisted water-in-salt electrolyte with pseudo-solid enables the stability of MS electrode and operation under -40∼60℃

Abstract

Electrolyte engineering is critical to stabilizing electrode materials as well as the electrolyte/electrode interface. Traditional aqueous electrolytes have superior dynamic and storage properties, but they face the problems of dissolution, low voltage and stability of manganese (Mn) electrode materials. Here, strongly Chaotropic-anion trifluoromethanesulfonate (OTF⁻) was introduced into a 32 m low-cost potassium acetate (KOAc) water-in-salt (WIS) electrolyte to achieve a high ionic conductivity of 18.43 mS cm⁻¹ in a highly concentrated pseudo-solid electrolyte. Simulation and experimental results show that OTF⁻ can not only reduce the cathodic corrosion and Mn dissolution of graphene oxide composite manganese silicate (FA@MS/MO/GO), improve the stability of the material, but also occupy the position of H₂O in the potassium ion (K⁺) solvated structure, increase the voltage window (3.27 V) and promote the desolvation of K⁺, thus improving the intercalated pseudocapacitance energy storage. Therefore, the asymmetric supercapacitors (ASC) composed of FA@MS/MO/GO and commercial UltraSorb-1 activated carbon (USAC) achieve an operating voltage of 2.5 V and provide an energy density of 58.3 Wh kg⁻¹ at 630 W kg⁻¹ and capacity retention of 91.8 %@2 A g⁻¹ after 10,000 long-lasting cycles. In addition, the ASC is able to function normally at wide temperature, excellent power density is obtained at -40℃ where the dynamics are blocked. It is worth noting that this electrolyte design strategy is generally suitable for improving the stability and intercalation performance of MS materials.