Synthesis and Characterizations of Na4MnCr(PO4)3/rGO as NASICON-Type Cathode Materials for Sodium-ion Batteries

NASICON-type Na4MnCr(PO4)3 (NMCP) wrapped with reduced graphene oxide (rGO) was synthesized via a simple sol-gel method as composite cathode material Na4MnCr(PO4)3/rGO (NMCP/rGO) for Na ion batteries. The surface morphology, crystal structure and pore size distribution of pristine NMCP and as-synthesized NMCP/rGO composite cathode are identified by X-ray diffraction (XRD), field emission-scanning electron microscopy (SEM), transmission electron microscope (TEM), the Brunauer-Emmett-Teller (BET) method and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of composition-optimized NMCP/rGO composite cathode presents stable capacity retention and rate capability. The capacity retention of as-synthesized NMCP/rGO composite is 63.8%, and average coulombic efficiency maintains over 98.7% for 200 cycles. The reversible capacity of as-synthesized NMCP/rGO composite cathode still retained 45 mAh/g and 38 mAh/g under a current density of 0.5 A/g and 1.0 A/g, respectively, which was better than that of pristine NMCP, with only 6 mAh/g and 4 mAh/g. The redox reactions of pristine NMCP and as-synthesized NMCP/rGO composite are studied via cyclic voltammetry. The improved electronic conductivity and structure stability of bare NMCP is attributed to the contribution of the rGO coating.