Pristine Poly(3-hexylthiophene) as an On-Demand Conductive Binder and Redox Mediator for Carbon-Additive-Free, High-Volumetric-Energy-Density, LiFePO4 Cathodes without Calendaring.

Poly(3-hexylthiophene) (P3HT) is introduced as a multifunctional conductive binder and redox mediator to fundamentally improve the performance and volumetric energy density of carbon-free LiFePO4 (LFP) cathodes. Unlike conventional Super P (SP):PVDF systems, P3HT can be electrochemically doped within the LFP operating potential range, forming an internal percolating conductive network that precedes and facilitates the LFP redox reaction. Strong π-π interactions and P3HT-Fe coordination enable P3HT to uniformly coat LFP particles, yielding intimate interfacial contact, enhanced adhesion, and an ultrathin, stable cathode-electrolyte interphase. As a result, P3HT-based LFP cathodes exhibit significantly improved packing density (2.70 g cm-3), delivering volumetric energy densities up to 1402 Wh L- 1, far surpassing SP:PVDF-based counterparts (1.43 g cm-3; 738 Wh L-1). The P3HT-based LFP cathodes achieve long-term cycling stability and high-rate capability comparable to or better than SP:PVDF-based LFP electrodes. Density functional theory further reveals strong P3HT-LFP adsorption (-80 to -170 kJ mol- 1), substantial charge transfer, and narrowed bandgap at the P3HT-LFP interface, confirming enhanced electronic coupling. This work shows that P3HT as a highly efficient binder can integrate conductivity, redox mediation, and interfacial stabilization, offering a compelling strategy for constructing next-generation high-density, long-life LFP cathodes.