Lithium-Ion Partial Molar Entropies in Liquid, Composite, and Solid-State Electrolytes.

Area of Science:

• Electrochemistry
• Materials Science
• Thermodynamics

Background:

• Electrolyte properties critically influence battery performance, affecting reaction kinetics, ion transport, and thermal management.
• Ion-solvent and ion-ion interactions in liquid electrolytes dictate electrochemical behavior and thermodynamics.
• Partial molar entropy of ion solvation quantifies changes in the solvation environment upon ion addition/removal.

Purpose of the Study:

• To measure partial molar entropies of lithium-ion solvation in solid-state electrolyte systems.
• To compare solvation entropy values between solid-state and liquid electrolytes.
• To develop a model for understanding the temperature coefficient in mixed electrolyte systems.

Main Methods:

• Potentiometric temperature coefficient measurements were employed to determine partial molar entropies.
• Experimental data from solid-state electrolytes (Li6PS5Cl, Li6.5La3Zr1.5T0.5O12) and a liquid electrolyte (1 M LiPF6 in EC:DEC) were analyzed.
• A one-dimensional analytical model was developed to analyze interface effects.

Main Results:

• Positive partial molar entropies of lithium-ion solvation were measured: 43.3 J mol⁻¹ K⁻¹ for Li6PS5Cl and 26.4 J mol⁻¹ K⁻¹ for Li6.5La3Zr1.5T0.5O12.
• The liquid electrolyte 1 M LiPF6 in EC:DEC exhibited a negative partial molar entropy of -76.0 J mol⁻¹ K⁻¹.
• The developed model elucidates the influence of multiple interfaces on the temperature coefficient.

Conclusions:

• Solid-state electrolytes demonstrate distinct lithium-ion solvation entropy characteristics compared to liquid electrolytes.
• The findings offer a unified framework for interpreting partial molar entropies of ion solvation across diverse electrochemical systems.
• This research contributes to understanding and designing advanced battery electrolytes.