Solvent Dynamics in Gel Polymer Electrolytes for Lithium-Sulfur Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium-sulfur (Li-S) batteries offer high theoretical energy density but are limited by sluggish sulfur redox reaction kinetics and the polysulfide shuttle effect.
• Polycaprolactone (PCL)-based gel polymer electrolytes (GPEs) are explored to mitigate these issues, yet the impact of solvent properties remains understudied.

Purpose of the Study:

• To systematically investigate the influence of solvent properties (dielectric constant, donor/acceptor numbers) on PCL-based GPEs for Li-S batteries.
• To correlate solvent properties with GPE physical characteristics, Li+ transport, solvation, and polysulfide confinement.

Main Methods:

• Comparison of three PCL-based GPEs using dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and tetraethylene glycol dimethyl ether (TEGDME).
• Characterization of GPEs' physical properties, ionic conductivity, Li+ transference number, and electrochemical performance (specific capacity, Coulombic efficiency).
• Utilized operando Raman and UV-vis spectroscopy to confirm polysulfide confinement by PCL.

Main Results:

• The DME-based GPE, featuring an intermediate donor number, showed lowest crystallinity (2.31%), highest ionic conductivity (7.49 mS/cm), and a high Li+ transference number (0.77).
• This DME-based GPE achieved a specific capacity of 795 mAh/g sulfur and 97.5% average Coulombic efficiency over 120 cycles at C/5.
• Operando spectroscopy confirmed PCL's effectiveness in confining polysulfides, reducing the shuttle effect.

Conclusions:

• GPEs with moderate donor numbers and balanced dielectric constants significantly enhance Li-S battery stability, cycle life, and rate performance.
• Optimizing solvent properties in PCL-based GPEs is crucial for advancing practical Li-S battery technology.
• This study provides critical insights for designing advanced electrolyte systems for next-generation energy storage.