Site‐Preferential Trace Phosphorus Substitution Accelerates and Stabilizes the Activation of Lithium‐Rich Cathode Materials

Lithium‐rich manganese‐based layered oxides can access both transition‐metal and oxygen redox, but activation of the monoclinic Li 2 MnO 3 component is usually sluggish and structurally unstable. Uncontrolled activation promotes irreversible lattice distortion, oxygen‐related degradation, voltage decay, and capacity loss. Here we use trace phosphorus substitution to regulate the activation pathway of a Li‐rich Mn‐based cathode. Structural, spectroscopic, microscopic, and theoretical analyses show that P tends to incorporate at Li‐layer sites near Ni‐containing local environments. This site‐selective substitution modifies the Li‐slab structure and adjacent Ni─O/O electronic environment, enabling more effective activation of the Li‐rich monoclinic component with a self‐relaxing lattice response. As a result, the P‐substituted cathode reaches a peak discharge capacity of 273.1 mAh g −1 at the 50th cycle and still delivers 270.5 mAh g −1 after 300 cycles.