Stabilizing the reversible capacity of SnO2/graphene composites by Cu nanoparticles.

Graphical abstract Highlights • SnO 2 /Cu/graphene composite is synthesized by a one-pot selective reduction method. • N 2 H 4 ·H 2 O deduces the selective reduction of Cu2+ to Cu and only hydrolysis of Sn2+. • Cu NPs promote charge transfer, compress volume stress and obstruct Sn aggregation. • Conversion reaction of Sn/Li 2 O to SnO 2 is highly reversible over 200 cycles. • SnO 2 /Cu/graphene composite demonstrates extraordinary long-term cycle stability. Abstract Low electronic conductivity and the tin coarsening caused irreversible capacity loss are the primary cause of poor cycle performances in SnO 2 materials. In this work, a ternary SnO 2 /Cu/graphene composite is synthesized by a one-pot selective reduction method to improve the cycle life of SnO 2 -based composite anode. During the liquid-phase synthesis process, the Cu2+ and Sn2+ cations are adsorbed uniformly on the surface of GO sheets under electrostatic attraction, which are then selective reduced by N 2 H 4 ·H 2 O because of its moderate reduction falling in between these two components (Eϴ (Cu 2+ /Cu) 0.34 V > Eϴ (Sn 2+ /Sn) −0.14 V). The electrochemical active SnO 2 and inactive Cu nanoparticles anchor tightly on the flexible conductive graphene sheets and locate in close proximity to each other. Cu nanoparticles can promote the charge transfer kinetics of insulating SnO 2 at the interfaces, compress the volume stress as lithium ions insertion/deinsertion, and obstruct the aggregation of metallic Sn and Li x Sn alloy, thus continuously promoting the reversibility of conversion reaction from Sn/Li 2 O to SnO 2. The as-prepared composite displays an excellent long-term cycling stability, delivering a reversible capacity of 890.6 mAh g−1 at 100 mAg−1 even after 200 cycles without any capacity decay. The excellent cyclic stability and facile liquid-phase synthesis method demonstrate the promising candidate of the Cu nanoparticles in stabilizing the reversible capacity of SnO 2 /graphene composite and its candidate in scalable application. [ABSTRACT FROM AUTHOR]