Enhancing Anionic Redox Reversibility and Structural Stability of Li-Rich Mn-Based Cathodes via Tuning Band Structure by Sn Doping.

Abstract

Li-rich Mn-based cathodes (LRMs) demonstrate exceptionally high specific capacity due to the anionic redox reaction. However, the irreversibility of anionic redox leads to lattice oxygen release; meanwhile, Mn-ion migration causes structural phase transitions and dissolution, resulting in severe capacity decay and voltage drop. Herein, we propose Sn doping at Mn sites to modulate the relative positions and overlap of energy bands, thereby enabling anionic redox reversibility and enhancing the structural stability. Compared with non-doped LRM, the Sn-doped LRM downshifts the energy of the O 2p non-bonding orbital and enhances its overlap with the (TM-O) antibonding orbital, preventing excessive oxygen oxidation and improving the reversibility of anionic redox. Meanwhile, it reduces the content of Mn³⁺ and alleviates the distortion of MnO₆ octahedra, resulting in the improved structural stability. Therefore, the Sn-doped LRM exhibits outstanding cycling stability and high-rate capability at high voltages. This work offers insights into improving the reversibility of the anionic redox reaction and structural stability of LRMs through energy band engineering.