Capacity Limitation and Ionic Transport Disruption in Li-Rich Cathodes under Practical High Active Material Fractions for Halide-Based Solid-State Batteries

Li-rich layered oxide (LLO) cathodes possess high theoretical capacity and voltage, but constructing cathodes with high active material fractions to achieve high energy density in all-solid-state batteries (ASSBs) remains challenging. In this work, it is demonstrated that the main limitation to electrochemical performance lies not in interfacial instability but in sluggish Li+ transport arising from intra- and interparticle voids. Intraparticle voids are found to hinder ion diffusion within polycrystalline LLO, while extensive interparticle voids are introduced in reduced-particle-size LLO due to particle aggregation under limited solid-state electrolyte content. In these aggregated domains, Li+ conduction is restricted to isolated LLO regions and the intrinsically low ionic conductivity of LLO further aggravates transport limitations. To address these issues, a composite cathode with a Li3InCl6 coating was designed to improve the interfacial contact and Li+ conduction pathways. The resulting ASSB delivers 245.2 mAh/g at 0.1 C, retains 80.9% capacity after 250 cycles at 0.3 C, and maintains 75.9 mAh/g at 5 C with only 27.5 wt % Li3InCl6. This work provides a practical cathode design strategy for realizing high-energy-density LLO-based halide ASSBs.