Optimal Design of a Small-Molecule Crowding Electrolyte and Molecular Dynamics Simulation of an Electrode–Electrolyte Interface for Aqueous Supercapacitors with a Wide Operating Temperature Range

Designing a high-voltage aqueous electrolyte with a wide temperature range is essential to realize low-cost and high-safety supercapacitors (SCs). However, the theoretical decomposition voltage of water seriously limits the energy density and practical application. Herein, we propose a simple strategy to form small-molecule crowding electrolytes (SMCEs) by modulating the hydrogen bond network of water and ion interaction via ethylene glycol (EG). Therefore, the working voltage and specific capacitance of activated carbon-based SCs using SMCEs increase to 1.8 V and 165 F g –1, respectively. Significantly, molecular dynamics simulations reveal that the highly crowded environment induced by EG makes most of the water molecules be squeezed out of the electrode–electrolyte interfacial region, thereby inhibiting the H 2 O electrolysis on the surface of the charged electrode. This work provides an innovative strategy for the application of high-voltage aqueous SCs.