Tailoring the Fueling Capability of Halide Solid Catholyte through Composition. Correlation with the Underlying Redox Mechanism

Halide-based solid electrolytes have gained renewed interest for all-solid-state batteries (ASSBs). In this study, using synchrotron X-ray and neutron diffraction, MAS 7Li NMR, and operando (online) mechanical cell pressure and online electrochemical mass spectrometry gas measurements, we investigate the relationship between xLiCl–ZrCl4 (LZC) catholyte composition, structure, and the resulting electrochemical performance of LFP-based electrodes. It is shown that tuning the catholyte composition significantly improves the performance of these blend electrodes. In addition, we demonstrate that the sacrificial capacity of LZC can be enhanced by a factor of 28 across the composition range, offering significant industrial potential for full cells. Overall experiments reveal that the oxidative redox mechanism of LZC correlates with self-induced mechanical cell pressure changes during cycling, which can be further correlated to the proven Cl2 gas evolution. This research advances our understanding of halide SEs and provides practical insights for developing next-generation ASSBs.