Ester-Based Electrolyte Mixtures for Graphene Supercapacitors: A Molecular Dynamics Investigation

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Sustainable and high-performance electrolytes are crucial for advancing next-generation supercapacitors.
• Ionic liquids (ILs) offer tunable properties for energy storage applications.
• Graphene-based supercapacitors require optimized electrolytes for enhanced performance.

Purpose of the Study:

• To investigate the performance of graphene-based supercapacitors using hydrated ester-based ionic liquids.
• To analyze the structural and electrochemical properties of ILs with 1-butyl-3-methylimidazolium ([bmim]) cation and acetate ([ace]), benzoate ([bnz]), or propanoate ([prop]) anions.
• To provide guidelines for designing advanced IL electrolytes for sustainable supercapacitors.

Main Methods:

• Classical molecular dynamics simulations were employed to model graphene-based supercapacitors.
• Structural analyses focused on electric double layers (EDLs) and interfacial properties.
• Electrochemical performance was evaluated through electrostatic potential profiles, capacitance, and energy density calculations.

Main Results:

• Well-defined EDLs with moderate overscreening were observed.
• Potential drops (ΔΦ) varied from ~1.1 V to over 2.1 V, with [bmim][prop] showing the highest potential difference.
• Benzoate ([bnz])-containing mixtures exhibited the highest capacitances (up to 2.83 μF/cm²), while [bmim][prop] yielded the largest gravimetric (4.06 J/g) and volumetric (4.58 J/cm³) energy densities.
• At a fixed 2.5 V, [bnz]-containing electrolytes achieved superior energy densities (6.44 J/g gravimetric, 7.37 J/cm³ volumetric).

Conclusions:

• The benzoate ([bnz]) anion plays a critical role in tuning interfacial structure and enhancing energy storage in ester-based IL electrolytes.
• The choice of anion significantly impacts capacitance and energy density, offering a pathway for electrolyte optimization.
• These findings provide valuable insights for the rational design of high-performance, sustainable electrolytes for supercapacitors.