Surface substitution of polyanion to improve structure stability and electrochemical properties of lithium-rich layered cathode oxides

Abstract

Lithium-rich layered cathode oxides attract enormous attention due to their superior capacity, high voltage and environmentally friendliness. However, it is considerable that they suffer from serious capacity fade, voltage attenuation and phase transition deriving from inevitable oxygen evolution. In this work, polyanions are induced on the surface of the oxides via the method of surface substitution, considering synergy effects of bulk substitution and surface modification to stabilize crystal structure and promote electrochemical properties. The material doped with 5 wt% PO43− exhibits excellent specific capacity of 217.1 mAh g−1 with capacity retention of 88.43% and average discharge voltage drop of 0.4846 V after 200 cycles at 0.5 C significantly superior to the pristine material. And the discharge capacity of the material can reach 105.6 mAh g−1 at 10 C owing to enlarged interlayer spacing and improved ionic conductivity. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS) of the material before and after cycle verify that polyanions are beneficial to supply more active oxygen, restrain transition metal migration, reduce surface microstrain, and enhance electronic and ionic conductivities. All above indicate that it is effective for polyanions to promote lithium-rich cathode oxides to give full play to their electrochemical advantages.