Li-rich layered oxide coated by nanoscale MoOx film with oxygen vacancies and lower oxidation state as a high-performance cathode material

摘要

Li-rich layered cathode material (Li1.2Ni0.13Co0.13Mn0.54O2) is subjected to severe irreversible oxygen evolution for the first cycle, barren rate performance, capacity fading and voltage decay despite the ultrahigh specific capacity over 250 mAh g(-1). In this paper, MoOx, was grown on the surface of lithium-rich material (LLO) via in situ hydrolysis deposition to ameliorate these problems. The surface of LLO was successfully coated with an amorphous MoOx modification layer, and a spine] phase was induced on the interlayer between the bulk material and the cladding layer, which was characterized by XRD, SEM, XPS and TEM. The Li1.2Ni0.13Co0.13Mn0.54O2 modified with 3 wt% MoOx exhibits the excellent electrochemical performance. The material performs higher capacity retention of 85.8% with 224.2 mAh g(-1) compared with the pristine one which retains 75.1% with 187.4 mAh g(-1) after 100 cycles at 0.5 C (1 C = 250 mA g(-1)) and exhibits high rate performance of 192.0 mAh at 5 C. These outstanding electrochemical properties are attributed to the presence of oxygen vacancies in the MoOx that can effectively accommodate the oxygen from the Li2MnO3 during the first cycle of activation and promote oxygen reversible redox process. The MoOx coating layer can also eliminate side reactions on the surface of the material and maintain the integrity of the oxygen array. Furthermore, the 3d orbitals of lower oxidation state Mo in MoOx extend and partially overlap to form wide t(2g) bands, combined with the spinal phase possessing fast Li+ diffusion channels, which can significantly reduce the Li+ diffusion energy barrier and improve its rate performance.