Subnano AlO Coatings for Kinetics and Stability Optimization of LiNiCoMnO via O-Based Atomic Layer Deposition.

The Ni-rich LiNiCoMnO cathode (NCM, ≥ 0.6) suffers rapid capacity decay due to serious surface degradations from the corrosion of the electrolyte. The processes of the HO- and O-based AlO atomic layer deposition (ALD) on the single-crystal LiNiCoMnO (NCM83) are investigated by measurements to understand the mechanism of their different impacts on the electrochemical performance of NCM83. CH is found only produced during the trimethyl aluminum (TMA) chemisorption on NCM83 while not produced during TMA chemisorption on LiOH and LiCO impurities or deposited AlO. As an indicator, the disappearance of CH indicates that NCM83 is totally covered by four monolayers of AlO via the HO-based ALD while seven monolayers of AlO via the O-based ALD, which is owing to the O-based AlO 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 AlO, the O-based ALD-coated NCM83 cathode shows better rate and cycling performance than the HO-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-based ALD-coated NCM83 cathode with four monolayers of AlO 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.