Graphene wrapped SnCo nanoparticles for high-capacity lithium ion storage

Graphene nanosheets (GNS) wrapped SnCo alloy nanoparticles are prepared by a chemical reduction method on an ice water bath. SnCo nanoparticles are dispersed uniformly on GNS and their particle sizes are around 8-12 nm, which are substantially smaller than the pristine SnCo particles (similar to 80-180 nm) prepared in the absence of GNS. The GNS-SnCo composite is fabricated as an anode material for lithium ion batteries. It shows a distinguished higher-than-theoretical capacity of 1117 mAh g(-1) at 72 mA g(-1) which is larger than bare GNS (727 mAh g(-1)) or Sn-Co particles (599 mAh g-1). Moreover, the GNS-SnCo composite shows a good rate performance at a large current of 720 mA g(-1). A high capacity of 922 mAh g(-1) is retained with more stable cycle life than that at a small current. These improved cycling performances are attributed to the complimentary effect of three elements. The mechanical stability of Sn upon cycling is improved by the presence of robust and electrically conductive GNS and the alleviated function of inactive cobalt element. The agglomeration of GNS is also hindered by the spacing effect of SnCo nanoparticles among neighboring GNS materials. (C) 2012 Elsevier B.V. All rights reserved.