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

Conventional LiFePO₄ (LFP) cathodes employing poly(vinylidene fluoride) (PVDF) as binder exhibit relatively stable cycling performance but suffer from poor ionic conductivity, limited rate capability, restricted cycling stability at high current densities, as well as environmental concerns about the high fluorine content of PVDF. Here, we introduce an anion-cluster-mediated Li⁺ hopping mechanism in a series of newly synthesized and multifunctional poly(ionic liquid) (PIL) binders that can enable high-rate performance with an accelerated Li⁺ transport by 140-200%, meanwhile reducing the fluorine content by 60%. The counteranion aggregation along the PIL backbones can attract and promote the Li⁺ migration based on comprehensive validation of nuclear magnetic resonance spectroscopy, cyclic voltammetry and molecular dynamics simulations. The optimized LFP-PIL cathodes deliver superior high-rate performance (a capacity of 100 mAh·g^-1 at 15C) and cycling stability (95.5% capacity retention after 500 cycles at 5C). Furthermore, by integrating the chemistry-informed machine learning with experimental validation, we establish a molecular structure design methodology for next-generation PIL binders. This work provides both mechanistic insight and a generalizable design framework for high-performance and sustainable lithium cathode materials.