Subnano Al<sub>2</sub>O<sub>3</sub> Coatings for Kinetics and Stability Optimization of LiNi<sub>0.83</sub>Co<sub>0.12</sub>Mn<sub>0.05</sub>O<sub>2</sub> via O<sub>3</sub>-Based Atomic Layer Deposition
Jiawei Li, Jianhua Wu, Mingxuan Wang, Di Wen, Xiao Liu, Bin Shan, Rong Chen
Abstract
The Ni-rich LiNi x Co y Mn 1– x – y O 2 cathode (NCM, x ≥ 0.6) suffers rapid capacity decay due to serious surface degradations from the corrosion of the electrolyte. The processes of the H 2 O- and O 3 -based Al 2 O 3 atomic layer deposition (ALD) on the single-crystal LiNi 0.83 Co 0.12 Mn 0.05 O 2 (NCM83) are investigated by in situ measurements to understand the mechanism of their different impacts on the electrochemical performance of NCM83. C 2 H 4 is found only produced during the trimethyl aluminum (TMA) chemisorption on NCM83 while not produced during TMA chemisorption on LiOH and Li 2 CO 3 impurities or deposited Al 2 O 3 . As an indicator, the disappearance of C 2 H 4 indicates that NCM83 is totally covered by four monolayers of Al 2 O 3 via the H 2 O-based ALD while seven monolayers of Al 2 O 3 via the O 3 -based ALD, which is owing to the O 3 -based Al 2 O 3 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 Al 2 O 3, the O 3 -based ALD-coated NCM83 cathode shows better rate and cycling performance than the H 2 O-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 O 3 -based ALD-coated NCM83 cathode with four monolayers of Al 2 O 3 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.