Cage and Microheterogeneity Dynamics Control Ionic Transport in Ionic Liquid-Based K-Ion Battery Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Ionic liquid electrolytes are promising for advanced battery technologies.
• Understanding ion dynamics and solvation structure is key to optimizing electrolyte performance.
• Potassium-ion batteries offer potential advantages over lithium-ion systems.

Purpose of the Study:

• To investigate the concentration and temperature dependence of electrolyte dynamics and microheterogeneity.
• To elucidate the solvation structure and interactions of ions within the electrolyte.
• To establish the relationship between ion-cage dynamics and transport properties for potassium-ion batteries.

Main Methods:

• Classical molecular dynamics simulations on the nanosecond scale.
• Analysis of structural and dynamic changes with varying concentration and temperature.
• Potential of Mean Force (PMF) calculations to determine ion-ion interaction energies.
• Arrhenius formulation to calculate activation energy for ionic transport.

Main Results:

• K+ coordination number changes from penta- to hexa-coordinated FSI- with increasing concentration.
• PMF calculations reveal stronger K+-FSI- interactions compared to PYR13+-FSI-.
• Increased temperature leads to higher conductivity and diffusivity, with an activation energy of 10.3 kJ mol-1.
• K+-FSI- ion-cage exhibits a longer lifetime than PYR13+-FSI- ion-cage.

Conclusions:

• The study establishes a direct correlation between ion-cage lifetime and transport properties in ionic liquid electrolytes.
• Stronger K+-FSI- interactions are critical for efficient potassium-ion transport.
• The findings provide valuable insights for designing high-performance electrolytes for potassium-ion batteries.