CoS2 enhanced SnO2@rGO heterostructure quantum dots for advanced lithium-ion battery anode

The dual transition metals CoS 2 –SnO 2 @ reduced graphene oxide heterostructure quantum dots (shorten as CoS 2 –SnO 2 @rGO QDs) is intentionally synthesized by hydrothermal method. The compositions, grain sizes and contents of the synthesized CoS 2 –SnO 2 @rGO QDs are identified and calculated from XRD pattern. The layered structures and crystal sizes (<10 nm) of CoS 2 –SnO 2 heterostructure quantum dots are confirmed by TEM high-resolution image. Moreover, the CoS 2 –SnO 2 @rGO QDs deliver higher specific capacity of 940.4, 781.9, 673.8, 506.6 and 303.1 mAh g −1 at 0.2, 0.5, 1.0, 2.0 and 4.0 A g −1 , respectively, and remained 521.4 mAh g −1 (300 cycles) with 98.9% Coulomb efficiency under 1.0 A g −1 cycling. The DFT (density functional theory) calculation results suggest that the Li ions should diffuse through two possible paths with relatively lower E bar values of 0.519 and 0.566 eV in CoS 2 –SnO 2 @rGO QDs. Combining with XRD, XPS, TEM and DFT calculation, we therefore assign the excellent electrochemical performances of CoS 2 –SnO 2 @rGO QDs to its highly active CoS 2 –SnO 2 interfaces for electrode reactivity enhancement, to the characteristic heterointerfaces for “extra” Li + ions storage/release, and to super conductive/layered rGO network for better ionic/electronic transport. The successful synthesis of CoS 2 –SnO 2 @rGO QDs may provide a strategy for dual/multi-transition metal heterojunction to enhance lithium-ion battery electrode materials. • Grains of SnO 2 and CoS 2 in SnO 2 –CoS 2 @rGO QDs are ∼3.5 and ∼11.9 nm, respectively. • SnO 2 –CoS 2 @rGO QDs remains ∼521.4 mAh/g under 1.0 A/g after 300 cycles. • E bar of SnO 2 –CoS 2 heterointerface for Li are 0.519 and 0.566 eV by DFT calculation.