Efficacy of atomic layer deposition of AlO on composite LiNiMnCoO electrode for Li-ion batteries.

LiNiMnCoO (NMC811) is a popular cathode material for Li-ion batteries, yet degradation and side reactions at the cathode-electrolyte interface pose significant challenges to their long-term cycling stability. Coating LiNiMnCoO (NMC) with refractory materials has been widely used to improve the stability of the cathode-electrolyte interface, but mixed results have been reported for AlO coatings of the Ni-rich NMC811 materials. To elucidate the role and effect of the AlO coating, we have coated commercial-grade NMC811 electrodes with AlO by the atomic layer deposition (ALD) technique. Through a systematic investigation of the long-term cycling stability at different upper cutoff voltages, the stability against ambient storage, the rate capability, and the charger transfer kinetics, our results show no significant differences between the AlO-coated and the bare (uncoated) electrodes. This highlights the contentious role of AlO coating on Ni-rich NMC cathodes and calls into question the benefits of coating on commercial-grade electrodes.