Improvement in the electrochemical stability of Li[Ni0.5Co0.2Mn0.3]O2 as a lithium-ion battery cathode electrode with the surface coating of branched oligomer

Abstract

Although layered Li[Ni0.5Co0.2Mn0.3]O2 (LNCM 523) is one of the most promising cathode materials for lithium-ion batteries, large capacity losses during charging and discharging, due to poor surface stability, have limited its application. Surface modifications can be effective at improving the electrochemical performance of cathode materials. In this study, an oligomer polymer, named LIVING, was synthesized from bisphenol A diglycidyl ether diacrylate and barbituric acid and then used it as a coating material for LNCM 523 particles. Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, and electrochemical methods were employed to investigate the structure, surface properties, thermal stabilities, and electrochemical properties of the electrodes. Both coated (LIVING@LNCM 523) and uncoated (LNCM 523) electrodes were tested for their battery performance. A cathode material coated with 0.5 wt.% of LIVING (0.5% LIVING@LNCM 523) at a layer thickness of approximately 10 nm showed enhanced cycle stability, with over 80.7% of the capacity retained after 100 cycles at a rate of 0.2C; in comparison, the LNCM 523 electrode retained no more than 66.2% of its capacity under the same conditions. The coated electrode (0.5% LIVING@LNCM 523) also exhibited a better rate capability, retaining about 91% of its initial capacity after applying various current loads, whereas LNCM 523 retained only 79% after applying the same current loads under the same conditions. The improved electrochemical performance of the modified electrode is attributed to the chemical interactions between LNCM 523 and LIVING providing a uniform and stable oligomer layer on the LNCM 523 surface, thereby preventing the LNCM 523 surface from deeper electrolyte ion intercalation and suppressing the growth of interfacial resistance. The coating material (LIVING) appears to have great potential for improving the electrochemical performance of layered structure cathode materials, with promising applications in highly energy demanding lithium-ion batteries.