Understanding the Role of Alumina (Al2O3), Pentalithium Aluminate (Li5AlO4), and Pentasodium Aluminate (Na5AlO4) Coatings on the Li and Mn‐Rich NCM Cathode Material 0.33Li2MnO3·0.67Li(Ni0.4Co0.2Mn0.4)O2 for Enhanced Electrochemical Performance

The active role of alumina, pentalithium aluminate (Li5AlO4, Li‐aluminate), and pentasodium aluminate (Na5AlO4, Na‐aluminate) as the surface protection coatings produced via atomic layer deposition on Li and Mn‐rich NCM cathode materials 0.33Li2MnO3·0.67LiNi0.4Co0.2Mn0.4O2 is discussed. A notable improvement in the electrochemical behavior of the coated cathodes has been found while tested in Li‐coin cells at 30 °C. Though all the coated cathodes demonstrate enhanced electrochemical cycling and rate performances, Na‐aluminate coated cathodes exhibit exemplary behavior. Prolonged cycling and rate capability testing demonstrate that after more than 400 cycles at 1 C rate, the uncoated cathode delivers only 63 mAh g−1, while those with alumina, Li‐aluminate, and Na‐aluminate coatings exhibit approximately two times higher specific capacities. The coated cathodes display steady average discharge potential and lower evolution of the voltage hysteresis during prolonged cycling compared to the uncoated cathode. Importantly, Na‐aluminate coated cathode shows a lowering in gases (O2, CO2, H2, etc.) evolution. Post‐cycling analysis of the electrodes demonstrates higher morphological integrity of the coated cathode materials and lower transition metals dissolution from them. The coatings mitigate undesirable side reactions between the electrodes and the electrolyte solution in the cells. Superior electrochemical performance is achieved through surface protection of Li and Mn‐rich (high energy NCM) cathode materials by alumina, Li‐aluminate, and Na‐aluminate coatings via the atomic layer deposition technique. Improved reversible anionic redox and suppressed lattice oxygen loss from the near‐surface region are achieved due to partial surface Mn‐reduction and some spinel‐like structure formation in the coated materials.