Designing Poly(ionic liquid)s as High-Performance LiFePO₄ Binders via Mechanistic Study and ML-Assisted...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Conventional lithium iron phosphate (LFP) cathodes using poly(vinylidene fluoride) (PVDF) binders face limitations in ionic conductivity, rate capability, and high-current cycling stability.
• PVDF binders also raise environmental concerns due to their high fluorine content.

Purpose of the Study:

• To develop novel poly(ionic liquid) (PIL) binders that enhance lithium-ion transport and improve the electrochemical performance of LFP cathodes.
• To investigate the anion-cluster-mediated Li+ hopping mechanism facilitated by PIL binders.
• To establish a molecular design framework for next-generation PIL binders using machine learning.

Main Methods:

• Synthesis of multifunctional poly(ionic liquid) binders.
• Electrochemical characterization including cyclic voltammetry and galvanostatic cycling at various rates.
• Nuclear magnetic resonance spectroscopy and molecular dynamics simulations to elucidate Li+ transport mechanisms.
• Integration of chemistry-informed machine learning with experimental validation.

Main Results:

• PIL binders accelerated Li+ transport by 140-200% and reduced fluorine content by 60%.
• Optimized LFP-PIL cathodes demonstrated high-rate performance (100 mAh·g-1 at 15C) and excellent cycling stability (95.5% capacity retention after 500 cycles at 5C).
• Anion aggregation in PILs was identified as key to promoting Li+ migration.

Conclusions:

• Poly(ionic liquid) binders offer a promising strategy for developing high-performance, sustainable lithium-ion battery cathodes.
• The anion-cluster-mediated Li+ hopping mechanism provides crucial mechanistic insight into enhanced battery performance.
• A generalizable design framework for advanced PIL binders was established, paving the way for future material development.