Improved electrochemical properties of Li(Ni0.6Mn0.2Co0.2)O2 by surface coating with Li1.3Al0.3Ti1.7(PO4)3

LiNi0.6Mn0.2Co0.2O2 (C622) is one of the Ni-rich layer-structured cathode materials with a high capacity, but it suffers from a poor cycling stability and rate capability. In this study, Li1.3Al0.3Ti1.7(PO4)(3) (LATP), a NASICON-type lithium-conductor, is coated on C622 by a sol-gel process to overcome the shortcomings of C622. We find that a 0.5 wt% coating of LATP on C622 significantly improves the cell performance including the discharge capacity, rate capability, and cycling stability. The pristine and LATP-coated samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). In addition, various electrochemical analyses such as cyclic-voltammetry (CV), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS) are conducted to determine the reason for the improvement of the cell performance. The cell performance of C622 is enhanced by a coating amount of less than 1.0 wt% and the overall performance degrades with the increase of the coating amount. The electrochemical analyses reveal that a high lithium-ion diffusion coefficient and a low interfacial resistance are the reasons for the improved cell performance; however, our study demonstrates that an excessive coating may degrade the cell performance, thereby acting as a barrier against the movement of lithium ions. (C) 2015 Elsevier B.V. All rights reserved.