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Cross-nanoflower CoS 2 on rGO nanosheets has been synthesized by simply controlling the pre-reaction step during hydrothermal route. Three-dimensional CoS 2 cross-nanoflowers of 150–200 nm in diameter are formed in-situ through self-assembling with rGO nanosheets reduced from GO (shorten as CoS 2 –NF/rGO-NS). From XRD, SEM, XPS and TEM analysis, these CoS 2 nanoflowers are composed of single crystal nano-slices of 20–30 nm in thickness and evenly distributed in the networks of flexible/conductive rGO nanosheets. Owing to both capacitive-controlled and diffusion-controlled mechanisms existing in the discharging/charging processes, CoS 2 –NF/rGO-NS composites show excellent rate performance and cycling stability as anode materials. According to DFT calculations/simulations, the corresponding diffusion barrier (E bar) is derived to be 0.47 eV along ⟨100⟩ diffusion direction for CoS 2 cross-nanoflower, indicating an effective lithium ion diffusion channel. Their enhanced electrochemical properties are therefore attributed to synergistic effects of two components: highly active/stable nanoflower-like CoS 2 –NF structure and flexible/conductive reduced graphene nanosheets (rGO-NS). Image 1 • 150–200 nm CoS 2 cross-nanoflower in-situ self-assembled on rGO nanosheet. • CoS 2 nanoflower composited of 20–30 nm single crystal nanochips in thickness. • CoS 2 nanochips provide a good Li+ diffusion channel along ⟨100⟩ by DFT calculations. • Advanced performance owing to highly active CoS 2 and pseudocapacitive effect by rGO. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 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. [ABSTRACT FROM AUTHOR]