Design and synthesis of FeS/graphite sandwich structure with enhanced lithium-storage performance for lithium-ion and solid-state lithium batteries.

As a conversion-type cathode material, FeS emerges as a promising candidate for the next generation of energy storage solutions, attributed to its cost-effectiveness, environment-friendliness and high theoretical capacity. However, several challenges hinder its practical application, including sluggish kinetics, insulating reaction products and significant volume fluctuation during cycling, which collectively compromise its rate capability and cycle stability. Herein, a well-designed sandwich structure of FeS embedded between graphite layers (FeS/C) is obtained using a chloride intercalation and sulfidation strategy. The layered graphite-FeS-graphite configuration boosts the active sites and adsorption capacity of Li, thereby guaranteeing a high reversible capacity. Furthermore, the graphitic carbon matrix serves a dual purpose: it enhances electronic conductivity and restrain the volume fluctuation of FeS during long cycling. This combination ensures robust electrochemical kinetics, structural integrity and long life. Consequently, the FeS/C composites exhibit exceptional lithium storage performance, achieving capacities of 506.2 mAh g at 0.5 A/g and 277.2 mAh g at 5.0 A/g. Additionally, the FeS/C composites show promising potential as cathodes for all solid-state lithium batteries, showcasing high specific capacities of 658.0 mAh g at 0.1 A/g for the second cycle and maintaining a cycle performance of 288.5 mAh g after 800 cycles at 0.5 A/g. These values surpass the second discharge specific capacity of 96.1 mAh g and cycle capacity of 25.3 mAh g observed for FeO/C composites. The discharge mechanism of FeS/C composites was further characterized through in-situ transmission electron microscope test. This work provides valuable insights for designing and synthesizing FeS, highlighting its potential for lithium ion storage and all solid-state lithium batteries.