Bimodal Composite Cathodes Advancing the Chemo-Mechanical Integrity and Kinetics for All-Solid-State Batteries

Abstract

All-solid-state batteries employing sulfide solid electrolytes promise high energy density and safety but suffer from poor cycling stability and rate performance due to fundamental shortcomings in composite electrode architectures. To address challenges, this study introduces bimodal composite cathodes formed by blending large polycrystalline and small single-crystalline cathode active materials (CAMs). This bimodal configuration optimizes particle packing and porosity, thereby reducing ionic tortuosity and enhancing Li+ transport. At an extreme CAM loading of 90 wt%, a bimodal composition with a 7:3 mass ratio of polycrystalline to single-crystalline CAM exhibited enhanced rate performance and 87.8% capacity retention after 200 cycles, outperforming unimodal composite cathodes. Distribution-of-relaxation-times analysis, operando X-ray diffraction, operando electrochemical pressiometry, and three-dimensional simulations revealed that the enhanced mechanical performance of densely packed electrode structures originates not from stress relaxation but from uniform stress dispersion. These findings establish a comprehensive framework for advancing the design and optimization of complex composite cathodes.