Preparation And Electrochemical Study Of Graphene Based Composites For Lithium Ion Batteries

Li-ion batteries have been widely used as power sources for electricalvehicles, advanced electronic devices, medical equipments, etc. Currently,the main commercial anode materials are graphite materials. However,graphite materials have a low theoretical capacity, which can’t meet thedemand of electron devices’ development. On the other hand, somemetalloid/metal oxides exhibit a high specific capacity, but they sufferfrom rapid capacity fading because of large volume expansion occuringduring cycling process. Therefore, graphene materials have been used toprepare anode materials.In this paper, graphene-based composites have been synthesized.SnO2/graphene nanocomposites and Si@SiOx/graphene nanocompositeshave been characterized by XRD, TGA, Raman, SEM, TEM and XPS.Electrochemical performance including charge-discharge curves and rateperformance reveals that these graphene-based nanocomposites exhibit asignificantly improved lithium-storage capacity, good cycling stability andhigh rate capability. The main results of this paper lie in:1. SnO2nanorod/graphene nanocomposites have been synthesizedthrough a simple ultrasonic combined hydrothermal process. According toFESEM and TEM analysis, SnO2nanorods are directly grown and denselydistributed on graphene matrix in such a way that the structure of obtainednanocomposites is analogous to an array structure. The reversible capacityis kept as high as1107mA h g-1within100cycles at a current density of200mA g-1, retaining96.2%of the initial value. Furthermore, we havetried other methods to prepare nanocomposites. Sn with differentmorphologies has been prepared through a template method, and then been used to synthesis SnO2/graphene nanocomposites. The reversible capacitiesof SnO2nanoparticles/graphene nanocomposites are879mA h g-1within100cycles at a current density of200mA g-1, and400mA h g-1areretained within300cycles at a current density of1000mA g-1. The highperformance can be ascribed to the unique structure of SnO2/graphene andthe synergic effects of graphene and SnO2.2. Si@SiOx/graphene nanocomposites are synthesized bymechanically blending the mixture of expanded graphite with Sinanoparticles. The obtained materials show improved lithium-storagecapacity, high cycling stability and rate capability, e.g. the dischargecapacity is kept as high as1055mAh g-1within50cycles at a currentdensity of200mA g-1. The high performance of the obtainednanocomposites can be ascribed to graphene prepared through heat-treatand ball-milling methods, the decrease in the size of Si nanoparticles andSiOxlayer on Si surface.