Lithium- and manganese-rich (LMR) oxide cathode materials are among the most attractive candidates for next-generation energy-storage materials owing to their anomalous capacity. However, severe Mn dissolution that occurs during long-term cycling, which leads to capacity loss, hinders their application prospects. In this study, nanoscale \(\textrm{AlPO}_{4}\) -coated \(\textrm{Li}_{1.2}\textrm{Ni}_{0.13}\textrm{Co}_{0.13}\textrm{Mn}_{0.54}\textrm{O}_{2}\) (LMR@APO) with significantly enhanced electrochemical performance is successfully synthesized using a simple and effective sol–gel method to mitigate Mn dissolution and suppress local structural distortion at high voltages. Because of the complex evolution of the structure and oxidation state of LMR materials during electrochemical cycling, observing and analyzing them using traditional single characterization methods may be difficult. Therefore, we combine various synchrotron-based characterization techniques to conduct a detailed analysis of the electronic and coordination structures of the cathode material from the surface to the bulk. Synchrotron-based hard and soft X-ray spectroscopies are integrated to investigate the differences in O and Mn evolution between the surfaces and bulk of the cathode. Advanced synchrotron-based transmission X-ray microscopy combined with X-ray near-edge absorption-structure technology is utilized to visualize the two-dimensional nanometer-scale reactivity of the LMR cathode. The \(\textrm{AlPO}_{4}\) -coating layer can stabilize the surface structure of the LMR material, effectively alleviating irreversible oxygen release on the surface and preventing the dissolution of \(\textrm{Mn}^{2+}\) at the interface caused by side reactions after a long cycle. Therefore, the spatial reaction uniformity of Mn is enhanced by the \(\textrm{AlPO}_{4}\) -coating layer, and rapid capacity decay caused by Mn deactivation is prevented. The \(\textrm{AlPO}_{4}\) -coating method is a facile modification strategy for high-performance LMR materials.
