Revisiting the Roles of Foreign Magnesium Dopants in Governing the Properties of Li-Rich Mn-Based Oxide Cathodes for Li-ion Batteries

Heteroatoms doping would validly stabilize the structure of Li-rich material and elevate electrochemical performance. For the synthesized Li-rich material, the conventional ex situ doping strategy can only incorporate heteroatoms in the outer particles, diminishing benefits for the internal structure of secondary particles. Recently, in situ doping has been employed to influence topological lithiation and achieve well-distribution in the bulk structure. However, the mechanisms of in/ex situ doping on elevating electrochemical performance for Li-rich material are ambiguous. Herein, by introducing magnesium (Mg 2+ ) ions on the precursor and synthesized Li-rich material, the in situ Mg doping (LRO-Mg1) and the ex situ Mg doping (LRO-Mg2) samples are successfully designed. Characterizations shows that Mg ion tend to incorporate into the Li-rich bulk structure for in situ doping, while they enrich in the surface for ex situ doping. Electrochemical measurement manifest that the in situ Mg doping Li-rich cathode exhibits more elevated high-rate performance, while the ex situ doping Li-rich cathode exhibits more elevated specific capacity, illuminating that enhances bulk structure of Li-rich cathode through in situ doping strategy is more effective than the surface modification (ex situ doping). Ex situ doping may be more effective for surface treatment, contributing to specific capacity improvement.