Spotlighting Composite Cathode Heterogeneity: Challenges and Strategies for All-Solid-State Batteries

While sulfide-based all-solid-state batteries (ASSBs) have drawn significant attention due to their inherent safety and potential for high-energy-density cell designs, their performance is often hindered by various heterogeneities within the cathode. Unlike conventional lithium-ion batteries (LIBs) with liquid electrolytes, ASSB cathodes rely on solid–solid interfaces between cathode active material (CAM) particles and solid electrolytes (SEs), leading to challenges that previously have not been dealt with. This review examines cathode heterogeneities across multiple length scales─interface, particle, and electrode─focusing on how they are formed and lead to performance degradation. Additionally, we discuss various approaches that have been developed to mitigate these issues such as modifying fabrication methods, adjusting particle sizes, and inventing electrode structure designs. By addressing these challenges and strategies, we aim to facilitate further advancements in ASSB technology, paving the way for scalability and commercialization.