Self‐Medicating Molten‐Salt Synthesis of Bulk‐Stabilized High‐Energy Cathodes for Li‐Ion Batteries

High‐energy lithium‐ion batteries necessitate stable Ni‐rich layered cathodes, yet critical challenges such as lattice distortion and surface structure collapse remain unresolved. While conventional high‐valence doping greatly alleviates surface degradations, it is ineffective in stabilizing bulk lattice due to dopant segregation. Here, we propose a slightly Li‐rich (SLR) lattice design by partially substituting transition‐metal (TM) ions with Li + ions in TM layers, reducing electrostatic repulsion against high‐valence dopants. Integrated theory‐experiment analyses reveal uniform bulk doping of Mo 6+ in SLR cathodes, realized via a self‐medicating and scalable molten‐salt synthesis route. An optimized high‐energy cathode (880 Wh kg −1 cathode ) achieves 89% retention after 1000 cycles in Ah‐scale pouch cells, sustains 10 C ultrafast charging/discharging for 300 cycles (3.8 min to 80% state‐of‐charge), and operates stably in all‐solid‐state batteries. Multimodal characterizations link uniform Mo 6+ doping to suppressed lattice strain and structural collapse. This work establishes a new paradigm for bulk lattice engineering of advanced battery cathodes.