Effects of PVP-assisted Co3O4 coating on the electrochemical and storage properties of LiNi0.6Co0.2Mn0.2O2 at high cut-off voltage

A uniform Co3O4 layer is coated on nickel-rich cathode material LiNi0.6Co0.2Mn0.2O2 via a facile polyvinyl pyrrolidone (PVP)-assisted wet coating process. The 1 wt.% Co3O4-coated LiNi0.6Co0.2Mn0.2O2 shows improved electrochemical performance, especially the cycling stability, at high cut-off voltage of 4.6 V. Its highly continuous and compact coating layer is confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The improved performance can be attributed to Co3O4 coating layer which acts as HF scavenger and protects LiNi0.6Co0.2Mn0.2O2 core from electrolyte attack. Cyclic voltammetry (CV) results indicate that the coated sample exhibits lower polarization and higher reversibility of electrode reaction. The storage property of LiNi0.6Co0.2Mn0.2O2 is also ameliorated by Co3O4 coating. After storing in air for three months, the initial discharge capacities of pristine and 1 wt.% Co3O4-coated LiNi0.6Co0.2Mn0.2O2 decrease from 206.4 mAh g−1 and 209.5 mAh g−1 at 0.1C (18 mA g−1) to 177.8 mAh g−1 and 198.6 mAh g−1, respectively. Electrochemical impedance spectroscopy (EIS) results reveal that the charge transfer resistance of coated sample after storage is much smaller than that of stored pristine sample. The improved storage property also benefits from Co3O4 coating layer which can prevent the formation of electrochemical inactive Li2CO3/LiOH impurities.