Preparation And Lithium Storage Performance Of Graphene-Tin Based Composite Materials

Graphite has been considered as one of the excellent anode materials because of its high stability and long service life. However, it suffers from safety issues, low theoretical capacity and poor high rate lithium storage performance. Tin-based materials have been considered as promising substitutes for graphite owing to their good safety, high weight capacity and volume capacity, and low toxicity. Nevertheless, the application of tin-based materials has been limited due to the fast capacity fading, which arises from the large volume variation during the charge-discharge cycling. In this work, graphene has been utilized to prepare SnS-graphene composite material, with enhanced low rate lithium storage capability. The as-prepared SnS-graphene is treated hydrothermally to fabricate SnO2-graphene. And SnO2-graphene composites further enhance the cyclic performance and rate capability of tin-based materials. To increase the coulombic efficiency of tin-based materials, Sn-graphene composite material has been prepared, and the enhanced lithium storage mechanisms have been discussed.Graphene oxide was synthesized by a modified Hummers’ method, and graphene was obtained by reduction of graphene oxide. The as-prepared graphene is an excellent template for the preparation of graphene-tin based composite material owing to its open porous structure. SnS nanopartices and SnS nanorods were synthesized via a solvothermal method. SnS nanorods exhibited superior lithium storage properties to SnS nanoparticles. The SnS nanorods-graphene and SnS nanoparticles-graphene were prepared by a precipitation method followed by the solvothermal treatment. The effect of graphene content on lithium storage capability of SnS nanoparticles-graphene was also discussed. The results showed that the SnS nanoparticles-graphene with15wt.%graphene exhibited superior capacity and cycling performance at low rate. The composite material also showed superior lithium storage capability compared with bare SnS and pure graphene. The lithium storage mechanism of the as-prepared SnS nanoparticles-graphene was investigated through Brunauer-Emmett-Teller analysis, electrochemical impedance spectroscopy measurements and TEM analysis. Mechanism for interaction between SnS and electrolytes, SnS-GNS and electrolytes and mechanism of electron transfer within SnS and SnS-GNS were also proposed to explain the enhanced lithium storage capability of SnS-GNS.SnS-graphene composite material was prepared via a facile and economic homogeneous precipitation method. The lithium storage properties of the composites were also investigated. SnO2-graphene composites were prepared with the optimized SnS-graphene precursors. The as-prepared composites exhibited a reversible capacity of597mAh g-1after100cycles at a current density of500mA g-1. To further inhibit the expansion of SnO2on the surface of the composites, a facile low temperature hydrothermal method was developed to fabricate sulfur coated SnO2-graphene composites. The composite electrode exhibited superior lithium storage properties compared to bare SnO2, bare graphene, and SnO2-graphene. The reversible capacity of the composite material was815mAh g-1after200cycles at500mA g-1. Rate capability tests indicated that the composites exhibited excellent high current properties, and the reversible capacity was as high as580mAh g-1even at4000mA g-1. The lithium storage mechanism of sulfur coated SnO2-graphene was investigated by cyclic voltammetry and electrochemical impedance spectroscopy, and mechanism about the effect of graphene and sulfur on SnO2-based composite materials was also proposed.To further increase the coulombic efficiency of graphene-tin based composites, a low temperature precipitation method was devoted to preparing Sn-graphene composite material. The lithium storage performance was also investigated. The composites exhibited an initial coulombic efficiency of70.3%at500mA g-1, which was higher than that of graphene-tin sulfide and tin oxide. After60cycles, the reversible capacity was430mAh g-1. The three dimensional porous Sn-graphene composites were prepared through electrophoretic deposition method to improve the reversible capacity of Sn-graphene-based composites, and a reversible capacity of520mAh g-1was obtained after60cycles at500mA g-1. To further improve the reversible capacity of tin-graphene composites, a facile low temperature co-precipitation method was developed to fabricate Sn-Co-graphene composites. The Sn-Co-graphene composite material exhibited a reversible capacity of560mAh g-1after60cycles at500mA g-1and a good rate capability. Finally, the possible mechanism of higher coulombic efficiency of Sn-graphene compared with other graphene-tin-based materials was proposed. And the mechanism of the enhanced lithium storage performance of Sn-graphene compared with Sn was investigated by density functional theory.