Enhanced electrochemical performance with surface coating by reactive magnetron sputtering on lithium-rich layered oxide electrodes.

Electrode films fabricated with lithium-rich layered 0.3Li2MnO3-0.7LiNi5/21Co5/21Mn11/21O2 cathode materials have been successfully modified with ZnO coatings via a reactive magnetron sputtering (RMS) process for the first time. The morphology and chemical composition of coating films on the electrodes have been in deep investigated by transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) characterizations. The results clearly demonstrate that ZnO film coatings are ultrathin, dense, uniform, and fully covered on the electrodes. The RMS-2 min (deposition time) coated electrode exhibits much higher initial discharge capacity and coulombic efficiency with 316.0 mAh g(-1) and 89.1% than that of the pristine electrode with 283.4 mAh g(-1) and 81.7%. In addition, the discharge capacity also reaches 256.7 and 187.5 mAh g(-1) at 0.1 and 1.0 C-rate, as compared to that of 238.4 and 157.8 mAh g(-1) after 50 cycles. The improved electrochemical performances of RMS-coated electrodes are ascribed to the high-quality ZnO film coatings that reduce charge transfer resistance and effectively protect active material from electrolyte oxidation.