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

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_0.921Co_0.069Al_0.01]O₂ (NCA) CAM microstructure, tuned by doping with Ti⁴⁺, Ta⁵⁺, and W⁶⁺, 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.