Variation of ionic conductivity in a plastic-crystalline mixture

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Ionically conducting plastic crystals (PCs) are promising for solid-state electrolytes in energy storage.
• Admixing larger molecules to succinonitrile enhances its ionic conductivity, highlighting the potential of binary mixtures.
• A broader understanding of charge transport mechanisms in PCs and the effects of mixing is needed.

Purpose of the Study:

• Investigate the phase behavior and ionic/dipolar dynamics of cyclohexanol and cyclooctanol mixtures with Li ions.
• Elucidate general mechanisms of ionic charge transport in plastic crystals.
• Determine the influence of mixing on conductivity and molecular dynamics.

Main Methods:

• Differential scanning calorimetry (DSC) to study phase transitions.
• Dielectric spectroscopy to analyze ionic and dipolar dynamics.
• Preparation of binary mixtures of cyclohexanol and cyclooctanol with 1 mol.% Li ions.

Main Results:

• All mixtures exhibited plastic-crystalline phases with orientational glass-transitions.
• Ionic conductivity is primarily governed by the "revolving-door" mechanism.
• A strong coupling between ionic translational and molecular reorientational dynamics was observed.
• Unlike succinonitrile mixtures, this coupling showed no significant variation with the mixing ratio.

Conclusions:

• Cyclohexanol and cyclooctanol mixtures form plastic crystals with tunable properties for solid-state electrolytes.
• The "revolving-door" mechanism is key to ionic transport, closely tied to molecular dynamics.
• The limited influence of mixing ratio on dynamics suggests a robust transport mechanism in these systems.