Subnano Al₂O₃ Coatings for Kinetics and Stability Optimization of LiNi_0.83Co_0.12Mn_0.05O₂ via O₃-Based Atomic Layer Deposition

The Ni-rich LiNi_xCo_yMn_1-x-yO₂ cathode (NCM, x ≥ 0.6) suffers rapid capacity decay due to serious surface degradations from the corrosion of the electrolyte. The processes of the H₂O- and O₃-based Al₂O₃ atomic layer deposition (ALD) on the single-crystal LiNi_0.83Co_0.12Mn_0.05O₂ (NCM83) are investigated by in situ measurements to understand the mechanism of their different impacts on the electrochemical performance of NCM83. C₂H₄ is found only produced during the trimethyl aluminum (TMA) chemisorption on NCM83 while not produced during TMA chemisorption on LiOH and Li₂CO₃ impurities or deposited Al₂O₃. As an indicator, the disappearance of C₂H₄ indicates that NCM83 is totally covered by four monolayers of Al₂O₃ via the H₂O-based ALD while seven monolayers of Al₂O₃ via the O₃-based ALD, which is owing to the O₃-based Al₂O₃ ALD undergoing a longer growth period from the nuclei to continuous coatings on NCM83 due to a lower nucleation and growth rate. At the same monolayers of Al₂O₃, the O₃-based ALD-coated NCM83 cathode shows better rate and cycling performance than the H₂O-based ALD-coated NCM83 cathode, which is attributed to higher Li⁺ diffusivity of NCM83 due to the more pristine surface of NCM83 exposed for the Li⁺ transfer and fewer surface and crystal degradations of NCM83 due to more robust coatings. The O₃-based ALD-coated NCM83 cathode with four monolayers of Al₂O₃ achieves the best balance of the rate and cycling performance, which almost retains the rate performance of the pristine NCM83 cathode and remarkably improves the cycling stability of pristine NCM83 cathodes from 42.1 to 91.2% after 300 cycles at 3.0-4.5 V and 1 C.