Conformal graphene encapsulation of tin oxide nanoparticle aggregates for improved performance in reversible Li⁺ storage

The performance of SnO₂ nanoparticle (NP) aggregates for reversible storage of Li⁺ was improved after conformal encapsulation of individual aggregates with graphene (i.e., encapsulation without changing the underlying morphology of SnO₂ aggregates). Conformal encapsulation was carried out by modifying the surface of SnO₂ NP aggregates with amine terminating groups to increase their binding affinity to graphene. The thickness of the graphene encapsulation could then be varied by the amount of graphene oxide (GO) solution used in the preparation. Electron microscopy confirmed the successful coating of graphene as a thin layer on the NP aggregate surface. This unique construction method resulted in SnO₂-graphene composites with a satisfying cycling performance. In particular a composite with only 5 wt% graphene could deliver, without the use of any carbon conductive additive, a charge (Li⁺ extraction) capacity of 700 mA h g ^-1 at the regular current density of 0.1 A g^-1 and 423 mA h g^-1 after a tenfold increase of the current density to 1 A g ^-1 in the 0.005-2 V voltage window. There was evidence to suggest that the composite performance was determined by Li⁺ diffusion across the basal plane of the graphene layers.