Optimizing LiNi0.8Co0.1Mn0.1O2 cathode material via modification by polyphosphoric acid on the surface

Abstract Nickel-rich layered oxide LiNi0.8Co0.1Mn0.1O2 (NCM) cathode material is widely noticed because of its high energy density and low cost. The widely explored NCM often shows inferior surface stability and tends to generate residual lithium carbonate (Li2CO3) on the surface, deteriorating the cyclic stability. The work attempts an efficient procedure by adopting polyphosphoric acid (PPA) to generate lithium phosphate (Li3PO4) as the surface coating layer, increasing the capacity retention ratio, which is 84.2% and 72.5% for the modified cathode material NCM@LP-3 (with the addition of 3% PPA) for 300 cycles and 500 cycles at 1 C. Electrochemical impedance spectra results show that the contact resistance and charge transfer resistance of NCM@LP-3 are significantly less than that of NCM after 500 cycles. SEM further demonstrates that microcracks of NCM@LP-3 are less severe than NCM. This work provides an effective method for surface modification.