Protic ethers as highly efficient hydrogen-bond regulators for aqueous eutectic electrolytes

Abstract

Aqueous eutectic electrolytes are emerging as the cost-effective and environmentally benign alternatives governing the next-generation electrochemical energy storage (EES) devices. For example, Li-based eutectic (ALE) electrolyte benefits from the strong hydrogen bond (H-bond) interaction with dimethyl sulfoxide (DMSO)–H₂O eutectic mixtures, exhibiting non-flammability and high electrochemical stability compared to conventional aqueous electrolytes. However, the highly concentrated feature raises obstacles to sluggish ions transfer and low-temperature performance, limiting the practical application of ALE electrolytes. Herein, a novel approach regarding organic solvent regulation has been proposed to deal with concentration-related electrochemical-stability issues. For instance, the protic ether of 1,2-dimethoxyethane (DME) in the ALE electrolyte (ALE–DME_6.6) can efficiently occupy the primary solvating shell of Li⁺ and increase H-bond intensity between DME–H₂O and DMSO–H₂O, which ultimately delivers high capacitance of 66.2 F g⁻¹ at 0.5 A g⁻¹ and ∼80% capacitance retention after 20 000 cycles at room temperature. In addition, enhanced low-temperature operation in supercapacitors (SCs) displays high ionic conductivity of 0.62 mS cm⁻¹ and high capacitance retention of 80% (8000 cycles) at −20 °C. The DME regulator in eutectic electrolytes offers appealing prospects and guidance for the advanced design of eutectic electrolytes for diverse EES applications.