Branched CNT@SnO₂ nanorods@carbon hierarchical heterostructures for lithium ion batteries with high reversibility and rate capability

A novel hierarchical heterostructure consisting of carbon-coated SnO ₂ mesocrystalline nanorods radially aligned on carbon nanotubes (CNTs) was designed and fabricated by a two-step growth process. SnO₂ nanorods were first grown directly on CNTs through a facile solvothermal reaction, which were subsequently coated with a thin layer of carbon to form a branched CNT@SnO₂@carbon sandwich-type heterostructure. When used as an anode material in lithium ion batteries, the branched CNT@SnO₂@C heterostructures exhibited highly reversible lithium storage behavior and excellent rate capability. The reversible capacity of the CNT@SnO₂@C heterostructure reached 984 mA h g^-1 at a current density of 720 mA g^-1, and retained 590 mA h g^-1 at 3.6 A g^-1 and 420 mA h g^-1 at 7.2 A g^-1. This superior performance might be ascribed to the improved mechanical capability and high loading content of SnO₂ of the branched architecture, the good electrical conductivity of the CNT backbones and the carbon layer, and the high electrochemical reactivity of the 1D mesocrystalline SnO₂ nanorods.