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

Abstract

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.