Partial Desolvation Causes Lithium Structural Transport in Liquid and Gel Polymer Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Spectroscopy

Background:

• Optimizing lithium diffusion in gel polymer electrolytes (GPEs) requires a molecular understanding of ion transport.
• Current models may not fully capture ion dynamics in complex electrolyte systems.

Purpose of the Study:

• To investigate lithium solvation structures and desolvation dynamics in liquid electrolytes and GPEs.
• To identify key factors governing lithium ion transport and ionic conductivity.
• To develop a more accurate descriptor for ion transport in GPEs.

Main Methods:

• Utilized polarization-selective pump-probe and two-dimensional infrared (2D IR) spectroscopy.
• Quantified lithium solvation structures, coordination numbers, and residence times.
• Introduced and validated a new descriptor: structural step times (τss).

Main Results:

• Lithium ions preferentially coordinate with propylene carbonate (PC), with coordination decreasing as poly(propylene carbonate) (PPC) concentration increases.
• Li+-solvent residence times significantly increase with polymer content.
• Structural step times (τss) quantitatively predict ionic conductivity across liquid and gel electrolytes, outperforming simple residence times.

Conclusions:

• Lithium structural diffusion is driven by partial desolvation events, challenging the "ion hopping" model.
• Structural step times (τss) provide a more accurate metric for ion transport in GPEs.
• Findings are crucial for designing advanced electrolytes for batteries and other electrochemical devices.