The harmful side reactions between the cathode materials and liquid electrolyte within the lithium secondary batteries will deteriorate the performance of the cathode materials and batteries. The Li2O–2B2O3 glass with high Li+ conductivity and stability can be coated on the surface of LiNi0.8Co0.2O2 powders by mixing LiNi0.8Co0.2O2, LiOH·H2O and H3BO3 and heating the mixture at 500°C for 10h. The structure of the surface-treated and base LiNi0.8Co0.2O2 powders was characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET. It is shown the Li2O–2B2O3 layer can prevent LiNi0.8Co0.2O2 from contacting directly with liquid electrolyte, and minimize the side reactions within the batteries. The surface-treated LiNi0.8Co0.2O2 cathode material has increased reversible capacity, decreased irreversible capacity, stabilized cycling performance, reduced self-discharge, especially the improved high temperature performance. The results indicated that the surface treatment should be an effective way to improve the comprehensive properties of the cathode materials for lithium secondary batteries.