Unconventional Hofmeister effect in stiff and tough electrolyte with strong spring-like hydrogen bonding for multifunctional composite structural hybrid supercapacitors working at -20 °C

Abstract

Applying Zn-ion-based multifunctional composite structural hybrid supercapacitors (CSHSs) at subzero temperature introduces significant constraints, primarily containing polymer electrolyte crystallization and structural deterioration under mechanical loading. The structural polymer electrolyte requires high ion conductivity and mechanical robustness, wherein stiffness and toughness are essential for transferring mechanical load between interlayers and preventing crack propagation. In this work, an unconventional Hofmeister effect of chaotropic ClO4− anions is observed in anti-freezing ethylene glycol (EG)-polymer, leading to simultaneous enhancements in the stiffness and toughness of the polymer composite. The formation of strong and long spring-like hydrogen bonding among ClO4−, EG, and the polymer matrix makes the material stiff and tough. Benefiting from the superior freeze resistance and mechanical strength, the fabricated CSHS demonstrates exceptional electrochemical stability, maintaining 88.9% of its initial specific capacity (60 mAh g−1) through 5000 cycles at 0.3 A g−1 even under cyclic three-point bending test (at a strain of 0.6%) at subzero temperatures. Furthermore, this investigation enhances the understanding of CSHS operation under both mechanical impact and subzero conditions, establishing design principles for CSHS applications.