Dual-Strategy Design Based on Polymer–Matrix Composite Cathode and Coated Separator for High-Performance Lithium–Iron Disulfide Batteries

Lithium–iron disulfide (Li-FeS2) batteries are plagued by the polysulfide shuttle effect and cathode structural degradation, which significantly hinder their practical application. This study proposes a dual-strategy design that combines a polyacrylonitrile–carbon nanotube (PAN-CNT) composite cathode and a polyvinylidene fluoride (PVDF)-conductive carbon-coated separator to synergistically address these bottlenecks. The PAN-CNT binder establishes chemical anchoring between polyacrylonitrile and FeS2, enhancing electronic conductivity and mitigating volume expansion. Specifically, the binder boosts the initial discharge capacity by 35% while alleviating the stress-induced pulverization associated with volume changes. Meanwhile, the PVDF-conductive carbon-coated separator enables effective polysulfide trapping via dipole–dipole interactions between PVDF’s polar C-F groups and Li2Sx species while maintaining unobstructed ion transport with an ionic conductivity of 1.23 × 10−3 S cm−1, achieving a Coulombic efficiency of 99.2%. The electrochemical results demonstrate that the dual-modified battery delivers a high initial discharge capacity of 650 mAh g−1 at 0.5 C, with a capacity retention rate of 61.5% after 120 cycles, significantly outperforming the control group’s 47.5% retention rate. Scanning electron microscopy and electrochemical impedance spectroscopy confirm that this synergistic design suppresses polysulfide migration and enhances interfacial stability, reducing the charge transfer resistance from 26 Ω to 11 Ω. By integrating polymer-based functional materials, this work presents a scalable and cost-effective approach for developing high-energy-density Li-FeS2 batteries, providing a practical pathway to overcome key challenges in their commercialization.