Bi-ionic conducting polymer grafting conductive carbon black as binders enable fast charging/discharging and stable cycling of LiFePO4 cathodes

Lithium iron phosphate (LFP) cathodes face challenges in rate capability and cycling due to their low electronic/ionic conductivity, exacerbated by conventional polyvinylidene fluoride (PVDF) binders with insulating properties and weak adhesion. This work presents a water-soluble multifunctional binder prepared by the Bi-ionic conducting polymer grafting conductive acetylene black to address these bottlenecks. The 3D crosslinked structure facilitates the molecular entanglement, as well as the formation of unobstructed lithium-ion pathways (the ethylene oxide (EO) units and the lithiated ionomers), significantly enhancing the adhesion and Li⁺ ion diffusion of binder. Furthermore, the well dispersed acetylene black as the nodes in the crosslinking networks improves the conductivity of integrative LFP electrodes. As a result, the LFP cathode delivers a high capacity of 133.0 mA h g⁻¹ at 2C after 500 cycles with 89.9 % capacity retention. Even at 7C, the capacity of 110.6 mA h g⁻¹ can be obtained in LFP cathode, exhibiting outstanding rate performance. In addition, Li⁺ diffusion coefficient of 5.10 × 10⁻⁸ cm² s⁻¹ achieved in LFP with the modified binder is twice that of conventional PVDF-based electrodes. This work underscores the critical role of ion/electron-conductive binders in overcoming the trade-offs between conductivity, stability, and sustainability, providing a strategy for high-performance LFP cathodes in next-generation lithium-ion batteries.