In Situ Copolymerized Zwitterionic-Oligoether Gel Electrolytes: Balancing Li Transport versus Li-Mediated Cross-Links

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Gel polymer electrolytes (GPEs) offer improved safety and performance for lithium-ion batteries.
• A key challenge is achieving both high ionic conductivity and mechanical robustness simultaneously.

Purpose of the Study:

• To design and synthesize novel GPEs that balance ion transport and structural integrity.
• To investigate the effect of salt concentration and polymer composition on GPE properties.

Main Methods:

• In situ copolymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and poly-(ethylene glycol) methyl ether methacrylate (PEGMA).
• Systematic variation of salt concentration (EO/Li ratio) and MPC content.
• Electrochemical characterization (ionic conductivity, transference number) and mechanical testing.
• Raman spectroscopy to analyze ion-polymer interactions.

Main Results:

• GPEs exhibit a transition from transport-optimized to coordination-dominated regimes with increasing salt content.
• Maximum ionic conductivity of ~3.2 mS cm⁻¹ achieved at an EO/Li ratio of ~9.
• Apparent Li⁺ transference number increased up to ~0.42 at EO/Li ratios of ~3-2.5.
• MPC enhances mechanical strength and promotes salt dissociation by reducing Li-anion coordination.

Conclusions:

• A compositional regime was identified that optimizes Li⁺ transport and mechanical strength through Li⁺-mediated cross-linking.
• MPC plays a dual role in mechanical reinforcement and ion dissociation, crucial for robust and conductive GPEs.
• The findings emphasize balancing ion coordination and zwitterionic cross-linking for advanced lithium battery electrolytes.