Superionicity in Ionic-Liquid-Based Electrolytes Induced by Positive Ion-Ion Correlations

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Ionic-liquid (IL) electrolytes face challenges in ion transport due to strong ion-ion correlations, limiting their use in energy storage.
• Lithium-ion (Li) transport is often hindered by movement within anionic clusters, requiring counteracting anion fluxes.

Purpose of the Study:

• To design organic cations that leverage ion-ion correlations in concentrated IL electrolytes for improved Li transport.
• To achieve beneficial ion transport phenomena, termed "superionic" behavior, in IL-based electrolytes.

Main Methods:

• Synthesis of organic cations with Li-coordinating ether chains.
• Characterization using 1H NMR and Raman spectroscopy.
• Transport and conductivity measurements.
• Molecular dynamics (MD) simulations to analyze ion dynamics and correlations.

Main Results:

• IL cations with sufficient ether oxygens induced Li coordination to organic cations.
• An inverse Haven ratio greater than 1 was observed, indicating "superionic" behavior.
• MD simulations confirmed enhanced Li-IL cation correlations and inverted Li-anion correlations, leading to positive Li+ mobilities.

Conclusions:

• A novel concept of coordinating cations effectively corrects detrimental Li drift directions in ILs.
• Strong ion correlations in concentrated electrolytes can be beneficially exploited for superionic transport.
• This approach offers a new strategy for designing advanced electrolytes for energy storage applications.