Hot pressing a high loading FeS2 all-solid-state composite cathode improves initial cycle performance

Abstract

This study reports that hot pressing a high loading (9.375 mg cm⁻²; > 5 mAh cm⁻²) all-solid-state FeS₂ composite cathodes at 240 °C and 47 MPa improved initial cycle performance. At 25 °C, a cold-pressed cell delivered negligible capacity whereas a hot-pressed cell delivered 332 mAh g⁻¹ (2.34 mAh cm⁻²). At 60 °C, a cold-pressed cell delivered 666 mAh g⁻¹ (4.70 mAh cm⁻²) whereas a hot-pressed cell delivered 782 mAh g⁻¹ (5.52 mAh cm⁻²). Hot-pressed cathode composites had a 20% porosity whereas cold-pressed cathode composites had a 30% porosity. Increased initial discharge capacity was attributed to better solid–solid interfacial contact between sulfide solid-state electrolyte (SSE) particles and between SSE and FeS₂ active material particles. Cell failure occurred upon extended cycling due to the stresses generated by the expansion of lithiated FeS₂. FIBSEM cross-sectional imaging of post mortem cathode composites revealed horizontal cracking indicative of electrode delamination due to electrode expansion.