Electrochemical and Thermal Behavior of Modified Li and Mn-Rich Cathode Materials in Battery Prototypes: Impact of Pentasodium Aluminate Coating and Comprehensive Understanding of Its Evolution upon Cycling through Solid-State Nuclear Magnetic Resonance Analysis

In continuation of the work on the stabilization of the electrochemical performance of Li and Mn-rich Li_xNi_yCo_zMn_wO₂ (HE-NCM, x > 1, w > 0.5, x + y + z + w = 2) cathode materials via atomic layer deposition (ALD) surface coatings, herein, the active role of aluminum oxides-based coatings, during prolonged cycling in battery prototypes with graphite anodes, is discussed. Notable progress in electrochemical cycling and rate performance of Na-aluminate-coated Li_1.142Mn_0.513Ni_0.230Co_0.115O₂ cathode material is established. These coated electrodes delivered a stable discharge capacity of 145 mAh g⁻¹ (66% retention), compared to only 118 mAh g⁻¹ (55% retention) for the uncoated sample at a 1.0 C rate after 400 cycles. Steady average discharge potential, lower voltage hysteresis, and stable energy density profiles are the noteworthy achievements for the coated material during cycling. Significant improvement in the coated material's thermal stability compared with the uncoated one has also been confirmed. The present study also enlightens about the Na-aluminate coating's orientation and distribution on HE-NCM material's surface. ²³Na and ²⁷Al solid-state nuclear magnetic resonance (NMR) studies reveal the Na-aluminate coating's crystalline constituent's disappearance upon cycling. The partial dissolution of Na₅AlO₄ coating, followed by forming a secondary disordered edge-site phase that remains even after long-term cycling, is disclosed.