The existence form and synergistic effect of P in improving the structural stability and electrochemical performance of Li2Mn0.5Fe0.5SiO4/C cathode materials

Abstract

Nano-Li2Mn0.5Fe0.5SiO4/C cathode material is synthesized by a hydrothermal route and phosphorus substitution is applied to improve structural stability and electrochemical properties. At low substitution content, P element completely enters into the lattice, forms [PO4] tetrahedrons and partially replaces [SiO4] tetrahedrons, which is confirmed by X-ray diffraction and X-ray photoelectron spectroscope measurements. Phosphorus substitution helps to suppress the change of coordination number of Mn and stabilize the material structure to some extent, obtaining better electrochemical performance in the early cycle. With the increase of P content, parts of P element exist in Li3PO4 which distributes uniformly and co-exists with active substance. Electrochemical tests prove that existing Li3PO4 has positive impacts on cycle and rate performance, and the lithium ion diffusion coefficient increases by about 14 times than pristine sample. Under the synergistic effects of phosphate substation and proper Li3PO4, Li2Mn0.5Fe0.5SiO4/C shows enhanced electrochemical performances.