Mn5O8/GO and MnO_2/GO Nanocomposites As Cathodes for Li-Ion Battery

摘要

In this study Manganese Dioxide (MnO_2) nanoparticles with the polymorph composition of ramsdellite (31 wt%) and akhtenskite (69 wt%) were synthesized and used to develop enhanced cathode nanocomposites for Lithium-ion batteries (LIBs). The MnO_2 nanoparticles were wrapped with graphene oxide (GO) and annealed under N_2 to reduce oxygen functionalities. The temperature of annealing and concentration of GO were investigated for optimized performance. The crystalline structure and electrochemical performance of the products were characterized by x-ray diffraction (XRD)/Rietveld refinement and electrochemical tests i.e. galvanostatic cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results suggest that the composites annealed at 225°C results in collapse of 1 × 2 channels to 1 × 1 channels, which is facilitated more with increasing the GO concentration. The GO/MnO_2 composite with 7 wt% GO annealed at 225°C showed the best specific capacity enhancement. By annealing the composites at 400°C, the core MnO_2 is converted to Mn_5O_8 with a layered structure, which has not been studied as a cathode for LIBs to the best of our knowledge and showed significantly enhanced capacity retention. Rietveld results suggest that Mn_3O_4 grows in the structure as the result of increasing GO wt% in composition at 400°C, which results in lower capacity.