Benchmarking Solid-State Batteries Containing Sulfide Separators: Effects of Electrode Composition and Stack Pressure

Abstract

Integrating sulfide separators into solid-state batteries (SSBs) containing high energy cathodes typically requires one or more materials and engineering solutions including: (i) applying interfacial coatings to mitigate electrolyte decomposition, (ii) applying high stack pressures to form robust solid-solid contacts, and (iii) using alloying anodes to avoid Li dendrite formation. Despite the promise of these approaches, a lack of standardized testing protocols makes it difficult to directly compare results among different studies. To address this problem, the present work benchmarks the performance of SSBs containing β-Li3PS4 (LPS) separators and composite cathodes. By systematically varying the anode/cathode composition and stack pressure, this work demonstrates that cathode design is a major bottleneck for solid-state cells cycled at low rates (<100 µA cm- 2). Operando stack pressure measurements show that, while mechanical confinement generally promotes higher active material utilization and cycling stability, this strategy alone does not address interfacial reactivity between LPS and high voltage cathodes. These results also demonstrate that stress evolution during cycling is dominated by volume changes at the Li metal anode. Finally, we show that FeS2 cathodes with moderate operating voltages (<3 V vs Li/Li+) exhibit superior cycling performance compared to high voltage cathodes by facilitating formation of stable cathode/electrolyte interfaces.