Surface Pinning of Mn by Oxidation State Control for the Synthesis of Cobalt‐Free, Ni‐Rich, Core/Shell Structured Cathode Materials

Abstract Motivated by the increasing cost, environmental concerns, and limited availability of Co, researchers are actively seeking alternative cathode materials for lithium‐ion batteries. A promising strategy involves structure‐modified materials, such as a NiMn core/shell system. This design leverages the high energy density of a Ni‐rich core while employing an Mn‐rich shell to enhance interfacial stability by suppressing unwanted reactions with the electrolyte. This approach offers improved cycling stability and reduced reliance on Co. However, the interdiffusion of Mn ions between the core and shell remains a significant challenge during synthesis. This work presents a facile approach to address the issue of Mn interdiffusion in core/shell cathode materials. The study demonstrates that partial oxidation of the precursor during the drying stage effectively enhances the Mn oxidation state. This strategy successfully suppresses Mn interdiffusion during subsequent calcination, leading to the preservation of the core/shell architecture in the final cathode material. This optimized structure mitigates interfacial reactions, enhances chemomechanical properties, and reduces crosstalk, a major contributor to rollover failure. This work presents a novel approach for synthesizing high‐performance core/shell cathode materials for next‐generation lithium‐ion batteries.