Ni‐Rich Cathodes for High‐Energy All‐Solid‐State Batteries Suppressing Phase‐Gradients

ABSTRACT All‐solid‐state batteries (ASSBs) based on Ni‐rich layered cathode active materials (CAMs) promise high energy density and enhanced safety; however, their electrochemical performance is inferior to that of conventional Li‐ion batteries. A key challenge is the inefficient Li‐ion diffusion within the CAM particles, which limits Li‐ion utilization. Here, we investigate how the Ni‐rich Li[Ni 0.921 Co 0.069 Al 0.01 ]O 2 (NCA) CAM microstructure, tuned by doping with Ti 4+ , Ta 5+ , and W 6+ , influences the electrochemical performance of ASSBs. It is revealed that the CAM microstructure plays a crucial role in governing the Li‐ion diffusion dynamics, suppressing microcrack formation, and mitigating phase‐gradient development within the secondary CAM particles, thereby strongly influencing the overall electrochemical performance. W‐doped NCA, which features the most radially aligned columnar primary particles, provides efficient and sustainable Li‐ion diffusion pathways, leading to superior capacity, rate capability, and cycling retention. Furthermore, transmission electron microscopy revealed that W doping suppresses the formation of a crystallographic phase gradient, which is indicative of surface‐to‐core electrochemical heterogeneity within secondary CAM particles in ASSBs. These insights provide essential design principles for the optimization of Ni‐rich CAMs for ASSBs.