Influence of Iron Sulfide Nanoparticle Sizes in Solid-State Batteries

Given the inherent performance limitations of intercalation-based lithium-ion batteries, solid-state conversion batteries are promising systems for future energy storage. A high specific capacity and natural abundancy make iron disulfide (FeS₂) a promising cathode active material. In this work, FeS₂ nanoparticles were prepared solvothermally. By adjusting the synthesis conditions, samples with average particle diameters between 8 and 31 nm were synthesized. The electrochemical performance was evaluated in solid-state cells with a Li‑argyrodite solid electrolyte. While the reduction of FeS₂ was found to be irreversible in the initial discharge, a stable cycling of the reduced species was observed subsequently. A positive effect of smaller particle dimensions on FeS₂ utilization was identified, which can be attributed to a higher interfacial contact area and shortened diffusion pathways inside the FeS₂ particles. These results highlight the general importance of morphological design to exploit the promising theoretical capacity of conversion electrodes in solid-state batteries.