Surface residual lithium compounds of Ni-rich cathodes are tremendous obstacles to electrochemical performance due to blocking ion/electron transfer and arousing surface instability. Herein, ultrathin and uniform Al2O3 coating via atomic layer deposition (ALD) coupled with the post-annealing process is reported to reduce residual lithium compounds on single-crystal LiNi0.6Mn0.2Co0.2O2 (NCM622). Surface composition characterizations indicate that LiOH is obviously reduced after Al2O3 growth on NCM622. Subsequent post-annealing treatment causes the consumption of Li2CO3 along with the diffusion of Al atoms into the surface layer of NCM622. The NCM622 modified by Al2O3 coating and post-annealing exhibits excellent cycling stability, the capacity retention of which reaches 92.2% after 300 cycles at 1 C, much higher than that of pristine NCM622 (34.8%). Reduced residual lithium compounds on NCM622 can greatly decrease the formation of LiF and the degree of Li+/Ni2+ cation mixing after discharge–charge cycling, which is the key to the improvement of cycling stability.

Surface modification for micro-nanoparticles at the atomic and close-to-atomic scale is of great importance to enhance their performance in various applications, including high-volume battery, persistent luminescence, etc. Fluidized bed atomic layer deposition (FB-ALD) is a promising atomic-scale manufacturing technology that offers ultrathin films on large amounts of particulate materials. Nevertheless, nanoparticles tend to agglomerate due to the strong cohesive forces, which is much unfavorable to the film conformality and also hinders their real applications. In this paper, the particle fluidization and coating process in an ultrasonic vibration-assisted FB-ALD reactor is numerically investigated from micro-scale to macro-scale through the multiscale computational fluid dynamics and discrete element method (CFD-DEM) modelling with experimental verification. Various vibration amplitudes and frequencies are investigated in terms of their effects on the fluid dynamics, distribution of particle velocity and concentration, as well as the size of agglomerates. Results show that the fluid turbulent kinetic energy, which is the key power source for the particles to obtain the kinetic energy for overcoming the interparticle agglomeration forces, can be strengthened obviously by the ultrasonic vibration. Besides, the application of ultrasonic vibration is found to reduce the mean agglomerate size in the fluidized bed. This is bound to facilitate the heat transfer and precursor diffusion in the entire FB-ALD reactor and the agglomerates, which can largely shorten the coating time and improve the film conformality as well as precursor utilization. The simulation results also agree well with our battery experimental results, verifying the validity of the multiscale CFD-DEM model. This work has provided momentous guidance to the mass manufacturing of atomic-scale particle coating from lab-scale to industrial applications.

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