Extraordinary lithium ion storage capability achieved by SnO₂ nanocrystals with exposed {221} facets

Rational design of SnO2 nanomaterials with superior architectures and excellent electrochemical properties is highly desirable for lithium ion storage. Here, several SnO2 nanoparticles with different exposed crystal planes, such as {101}, {110} and {221} facets, are developed and further embedded into graphene/carbon nanotube (G/CNT) networks, achieving highly conductive carbon/SnO2 films (C/SnO2) with homogeneous dispersion of SnO2 nanoparticles. Three-dimensional (3D) G/CNT networks with highly porous structures and electronic contacts with imbedded SnO2 nanoparticles provide excellent pathways for transfer of electrons and ions and further buffer structural changes of SnO2 nanocrystals during lithium-ion insertion/extraction processes. Close contact between G/CNT matrix and embedded SnO2 nanoparticles ensures that all high-energy {221} facets of SnO2 are exploited during rapid electrochemical reactions. The high electrical conductivity of G/CNT networks can further prevent pulverization of nanostructured SnO2. As a result, C/SnO2 film with 90% content of octahedral SnO2 nanocrystals (C/SnO2-O (90%)) exhibits superior reversible specific capacity of 1008 mA h g-1 at 0.1 A g-1, excellent rate capability, low internal resistance and long-term cycling stability for 1000 cycles. These results further confirm that SnO2 nanocrystals with high-energy {221} facets can provide numerous active sites for lithium ion storage than other SnO2 nanomaterials.