Enhanced electrochemical performance of dual-conductive layers coated Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode for Li-ion batteries at high cut-off voltage

The surface coating of dual-conductive layers is implemented to optimize the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 (NCM) under high cut-off voltage (4.5 V) by the integrated use of sol-gel method and in-situ chemical polymerization. The X-ray powder diffraction (XRD) and Rietveld refinements results indicate that the dual-conductive layers hardly affect the crystal structure of NCM. Field emission scanning electron microscopy (FESEM), Energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED), and field emission transmission electron microscopy (FETEM) results confirm that the dual-conductive layers with Li3VO4 and polypyrrole (PPy) are successfully coated on the spherical particle surface and inhibit the dissolution of transition metals from crystal structure. The Li3VO4-PPy coated NCM sample exhibits excellent cycling stability at 0.5 C (1 C = 180 mAh/g) under high cut-off voltage (4.5 V), with a retention rate of 93.7% compared to 73.6% for the pristine NCM after 100 cycles. Moreover, it also shows super cycling performance at large current (2 C) with a retention rate of 93.8%, whereas the pristine NCM is only 61.6% after 100 cycles.