Sulfur element achieves rapid and stable migration of Li+ in oxide cathode materials

Abstract

Higher energy density can be obtained by increasing the charging cut-off voltage of Ni-rich materials to meet the range requirements of electric vehicles. However, Ni-rich layered cathode materials exhibit severe capacity degradation under high-voltage cycling, which is caused by various factors such as particle rupture, structural collapse, and interface damage during the electrochemical process. Here, we achieve synergistic optimization effect on LiNi0.9Co0.05Mn0.05O2 (NCM) cathode material by introducing sulfur element and combining common Al and Ti elements. The addition of sulfur element in the precursor mixed lithium reaction successfully achieves the modification of the internal oxygen layer and interface coating in the cathode material. The internal oxygen layer dynamically improves the stability of Li+ migration back into the cathode material during discharge through the modification of S22-, while the external sulfate modification thermodynamically suppresses the interface side reactions of the cathode material and improves the thermal stability of the cathode system. The electrochemical results show that the modified NCM material maintained a capacity retention rate of 91% after 300 cycles at a high cut-off voltage of 4.6V. After cycling, there are almost no microcracks generated inside the particles, and the structure remained intact. A simple and effective modification method is provided to promote the development of high specific energy layered cathode materials.