Post surface treatment of LiNi0.6Co0.1Mn0.3O2 electrode with poly(4-vinylphenol) for lithium ion batteries

•Surface of NCM is modified by PVP coating•Spin coating is very facile for post electrode coating.•PVP coating is finely modified by controlling crosslinking.•Surface failure of NCM is highly relieved by PVP coating.•Post electrode coating with PVP is effective for long cyclability.

For high energy density and long cycle life of rechargeable lithium ion batteries, the positive electrode of LiNi0.6Co0.1Mn0.3O2 (NCM-613) is post-surface treated by poly(4-vinylphenol) (PVP) though a spin coating method. The additional PVP coating on the electrode is highly beneficial for improving the cycle life of the cell. It is also found that the PVP coating initially causes a polarization for lithium surface transportation but enhances the rate capability after long cycling by reducing the growth of polarization from the repeated sequences of charge and discharge. To adjust these conflicting behaviours, the coating condition of PVP should be optimized. By using a systematic analysis of X-ray diffraction and surface analyses of field emission scanning electron microscopy and X-ray photoelectron spectroscopy, it is concluded that the PVP surface coating on NCM-613 prevents crystal structure deterioration leading to irreversible structure changes from hexagonal to monoclinic at a high potential of 4.3 V vs. Li/Li+.