Nanoscale-Resolved STXM Reveals Shell π-Type Superexchange for Enhancing High-Voltage Stability in Surface Al-Doped LMR Cathodes

Lithium- and manganese-rich layered oxides (LMR) are promising high-capacity cathodes for next-generation lithium-ion batteries, yet their practical use is hindered by severe surface degradation and irreversible oxygen release under high-voltage operation. These surface instabilities not only accelerate voltage decay but also limit the structural integrity and cycle life. Here, we employ synchrotron-based scanning transmission X-ray microscopy (STXM), complemented by X-ray absorption fine structure (XAFS), to directly visualize shell–core-specific (surface-bulk) electronic reconstruction in LMR cathodes and establish its correlation with local atomic structures. We show that surface Al incorporation generates a controlled density of oxygen vacancies in the shell, which weakens 3d transition metal (TM)–O covalency while activating Ni t 2g –O 2p–Mn t 2g π-type superexchange (SE) interactions. This orbital reconfiguration stabilizes Ni in a high-spin Ni 4+ configuration even at 4.6 V, allowing Ni t 2g orbitals to buffer oxygen oxidation charges and thereby mitigate excessive oxygen anionic redox (OAR). As a result, irreversible O 2 evolution and lattice collapse are noticeably suppressed, while XAFS analysis confirms shortened Ni–O bonds and reduced coordination loss in Al-modified LMR. Importantly, the Mn valence and 3d configuration remain unchanged, highlighting the fact that the stabilization is dominantly Ni–O driven. These findings demonstrate how nanoscale orbital engineering at the particle shell can suppress the level of OAR driven surface degradation, offering a practical pathway to improve the cycling durability and high-voltage stability of advanced LMR cathodes.