Towards 99% Active Material Loading in LFP Cathodes Enabled by a Bifunctional PEDOT:PSS/PEG Binder with SWCNT

Abstract

Achieving ultra-high active material loading in lithium iron phosphate (LiFePO₄, LFP) cathodes is critical to improve the performance of LFP-based Li-ion batteries (LIBs). Conventional cathodes, however, typically comprise about 20% inactive binders and conductive additives, which significantly reduces the fraction of active material and limits the overall performance. In this study, we present a bifunctional binder composed of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and polyethylene glycol (PEG), further reinforced with single-walled carbon nanotubes (SWCNTs) to simultaneously provide strong adhesion, high thermal stability, and excellent electronic conductivity while minimizing inactive content. By optimizing the PEDOT:PSS/PEG ratio (1/0.3), LFP cathodes containing only 4% binder achieve 96% active material loading, delivering a high specific capacity of ~160 mAh g⁻¹ and excellent rate performance (~106 mAh g⁻¹ at 8 C). In particular, incorporating SWCNTs allow the binder content to be further reduced to 2 wt%, while sustaining robust cohesion (0.10 kN m⁻¹), and high conductivity (1.55 S cm⁻¹), resulting in excellent rate capability (~131 mAh g⁻¹ at 8 C) and stable cycling over 1000 cycles at 3 C. Remarkably, even electrodes containing 99% active material operate reliably when supported on a graphite-coated Al current collector, maintaining ~132 mAh g⁻¹ at 8 C and achieving a high areal capacity of ~3.5 mAh cm⁻². Furthermore, full-cell evaluations with graphite anodes confirm the practical applicability of this binder system, achieving ~125 mAh g⁻¹ at 8 C and long-term cycling stability even when operating at an elevated temperature of 60 °C. These results establish the PEDOT:PSS/PEG–SWCNT binder as a scalable and robust platform for fabricating ultra-high-loading, high-rate, and durable LFP cathodes for next-generation LIBs.