Unveiling the impact of Mg doping and in-situ Li reactive coating on the Ni-rich cathode material for LIBs

The LiNi0.91Co0.06Mn0.03O2 Ni-rich cathode material is modified with Mg doping and Li3PO4 coating through an efficient and single-step method. The samples are characterized by XPS, XRD, FESEM and FETEM. Cycling results demonstrate that, 1 mol% MgHPO4 modified NCM (MgP-1) exhibits 73.5% capacity retention while pristine sample shows only 50.6% at 4.3 V cycling. The presence of Mg2+ inside the crystal lattice provides pillaring effect during delithiation which screen O2− — O2− repulsion that inhibits the phase transition in the modified samples. These results are confirmed by cyclic voltammetry test. Besides that, transforming the surface residual lithium into lithium phosphate (Li3PO4) coating on the active material surface is facilitating the Li+ diffusion during cycling. In addition, this coating acted as a protective layer against hostile attack of electrolyte. The lower Rct of MgP-1 is due to the Li3PO4 coating which contributes to the highest discharge capacity at high current rate (160.8 mAh g−1 at 2C and 124.6 mAh g−1 3C) as compared to pristine (157.2 mAh g−1 at 2C and 107.2 mAh g−1 at 3C). These results confirm that Mg doping along with Li-ion conductor Li3PO4 coating is a promising technique to control the surface residual lithium and enhance the electrochemical performance of cathode electrode.