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 H2O electrolysis on the surface of the charged electrode. This work provides an innovative strategy for the application of high-voltage aqueous SCs.