Facile preparation of a Na2MnSiO4/C/graphene composite as a high performance cathode for sodium ion batteries

A new class of Na2MnSiO4/carbon/graphene (Na2MnSiO4/C/G) composite is successfully prepared and investigated for use as a cathode material for Na ion batteries. X-ray diffraction confirms that formation of a monoclinic structure with Pn space group. Morphological characterization shows that Na2MnSiO4 nanoparticles, about 30-40 nm in size with high density, are homogeneously anchored on the whole surface of the crumpled micrometer size graphene nanosheets. The sodium insertion extraction process of Na2MnSiO4 is similar to that of Li2MnSiO4 as a cathode in Li ion batteries. Compared with the Na2MnSiO4/C composite, the Na2MnSiO4/C/G composite shows much better electrochemical performance, including excellent rate performance and capacity retention. At the rate of 0.1C (1C = 139 mA h g(-1)), the discharge capacity of the initial cycle is 182.4 mA h g (1), corresponding to 1.31 Na+ insertion per Na2MnSiO4 molecule. Even at high rates of 1C, 2C and 5C, the composite exhibits discharge capacities of 106.9, 80.3 and 60.7 mA h g(-1,) respectively. The enhanced electrochemical performance arises from the conductive graphene nanosheets, which facilitate the electronic conductivity of the composite, improve the contact area for the electrode/electrolyte interface and decrease the particles sizes of Na2MnSiO4, as well as can reduce the diffusion length of Na+ ions.