Small‐Molecular Crowding Electrolyte Enables High‐Voltage and High‐Rate Supercapacitors

Abstract

Aqueous energy storage devices attract increased attention due to their high safety, low cost, and easy maintenance. However, the low energy density caused by the narrow electrochemical stability window (ESW) of aqueous electrolytes severely restricts their widespread applications. Herein, a new type of “small‐molecule crowding” electrolyte of 95EG‐H2O (95 wt% ethylene glycol [EG]) is proposed for the first time. Significant enhancement of water molecular stability is accomplished through the engineering of a hydrogen bond network. The small‐molecular crowding agent (EG) not only expands the ESW to 3.2 V, but also endows the electrolyte with low viscosity. As a proof‐of‐concept device, the symmetry carbon‐based supercapacitor using the newly developed electrolyte exhibits a so far record‐high operating voltage of 2.8 V, a high energy density of 58.7 Wh kg−1 at a power density of 1.4 and 30.3 Wh kg−1 at a power density of 42 kW kg−1, and a durable lifespan exceeding 20 000 cycles at a current density of 5 A g−1.

Ultrahigh-voltage aqueous electrolyte for wide-temperature supercapacitors

“…3a-e 3f †). These results further indicated that a high voltage stability and high coulombic efficiency of AC-based SC with 1 M Na 2 SO 4 /H 2 O/EG electrolyte can be simultaneously obtained, which is a much better performance than that of other reported aqueous electrolytes 11,13,15,[18][19][20][21] (Table 1).…”

Broadening the Voltage Window of 3D-Printed MXene Micro-Supercapacitors with a Hybridized Electrolyte

“…Concurrently, the OH stretching of water at 3431 cm −1 shifted to a lower wavenumber of 3400 cm −1 (EG8), further substantiating the formation of hydrogen bonds between EG and water molecules. The interaction between EG and water molecules partially disrupts the hydrogen-bonding network among water molecules, attenuating their reactivity, which consequently diminishes the occurrence of hydrogen and oxygen evolution side reactions, thereby contributing to the enhanced stability of the electrolyte [ 47 ].…”

“…Molecules 2024, 29, 1393 6 of 14 occurrence of hydrogen and oxygen evolution side reactions, thereby contributing to the enhanced stability of the electrolyte [47].…”

A 2.6 V Flexible Supercapacitor Based on Al-MnO2-Na2SO4//AC-KOH with High Specific Energy

“…In a neutral electrolyte, the cell voltage could be up to 2.2 V . This value could be further enhanced to 2.6 V or higher by using the water-in-salt strategy, adding small molecules to the electrolyte, or other methods. − However, the electrochemical performance of electrode materials in neural electrolytes might be suppressed. For example, activated carbon (AC) in neutral electrolyte shows a specific capacitance only half of that in acid or alkaline electrolytes.…”