Regulation of ion-dipolar and dipolar-dipolar interactions in aqueous electrolytes for supercapacitors with ultra-high cycle stability and low-temperature tolerance

Abstract

Aqueous supercapacitors are promising for sustainable and high-power energy storage, while suffer from rapid performance degradation at subzero temperatures and limited cycling stability, primarily due to low ion mobility and electrolyte freezing. This study addresses these challenges through molecular-level regulation of ion-dipolar and dipolar-dipolar interactions by introducing methanol (MeOH) as a cosolvent into a water-in-salt electrolyte (21 mol kg-1 LiTFSI/H2O), forming a diluted hybrid electrolyte. Results reveal that MeOH disrupts the original Li+-TFSI− binding via competitive ion dipolar coordination while reconstructing the hydrogen-bond network through preferential MeOH–H2O interactions. This dual regulation reduces the desolvation energy barrier for Li+ migration, suppresses parasitic interfacial reactions, and creates a low-freezing-point eutectic microenvironment. The optimized electrolyte exhibits an ultrawide liquid-phase range (−60 to 25 °C) and achieves an ionic conductivity of 2.8 mS cm−1 at −40 °C. The carbon-based supercapacitors demonstrate unprecedented cyclic durability with 94.2 % capacitance retention after nearly100,000 cycles at 2 V and maintain 84.3 % of room-temperature capacitance at −40 °C, showing superior cryo performance. This work validates the strategy of ion-dipolar and dipolar-dipolar interactions regulation for cryogenic SCs, providing fundamental insights into aqueous electrolyte engineering for extreme-condition energy storage devices.