A Binary Ionogel Electrolyte for the Realization of an All Solid-State Electrical Double-Layer Capacitor Performing...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Electrolytes

Background:

• Classical electrical double-layer capacitors (EDLCs) with organic electrolytes face safety issues due to leakage at high temperatures.
• Ionogels, ionic liquids confined in solid matrices, offer improved safety but struggle with low-temperature performance due to high ionic liquid melting points.
• Existing ionogels derived from single ionic liquids exhibit melting points that limit their operational temperature range.

Purpose of the Study:

• To develop a novel ionogel electrolyte for solid-state EDLCs with enhanced low-temperature performance and safety.
• To investigate the effect of a binary ionic liquid mixture on the ionogel's thermal and electrochemical properties.
• To demonstrate the feasibility of using these binary ionogels in EDLCs for operation in extreme environments.

Main Methods:

• Preparation of binary ionogel films by encapsulating a 70 wt% mixture of [EMIm][BF4] and [EMIm][FSI] into a PVdF-HFP polymer matrix under oxygen/moisture-free conditions.
• Characterization of the ionogel's ionic conductivity, thermal properties (glass transition, melting point), and flexibility.
• Fabrication and testing of laminate EDLCs using the binary ionogel separator and hierarchical micro-/mesoporous carbon electrodes.

Main Results:

• The binary ionogel films exhibit high flexibility and good ionic conductivity (5.8 mS/cm at 20°C).
• The crystallization of the confined binary ionic liquid is quenched, showing only a glass transition at -101°C, unlike parent ionogels.
• EDLCs with the binary ionogel separator operate up to 3.0V from -40°C to room temperature, exhibiting significantly higher specific energy at low temperatures compared to cells with liquid electrolytes.

Conclusions:

• The developed binary ionogel electrolyte effectively suppresses ionic liquid crystallization, enabling superior low-temperature ionic conductivity and EDLC performance.
• This approach provides a pathway for creating safe, flexible, solid-state energy storage devices capable of operating in extreme subambient temperature conditions.
• The binary ionogel concept addresses key limitations in current energy storage technologies for demanding applications.