In situ synthesis of SnO2–Fe2O3@polyaniline and their conversion to SnO2–Fe2O3@C composite as fully reversible anode material for lithium-ion batteries

• SnO2–Fe2O3@C nanocomposite is synthesized by a two-step approach.
• In situ polymerization of PANI prevents particle growth in the synthesis.
• Carbonization of PANI guarantees full carbon coating of SnO2–Fe2O3.
• SnO2–Fe2O3@C achieves fully reversible reaction and alloy reaction of SnO2.
• SnO2–Fe2O3@C shows superior electrochemical properties.

We report a two-step approach to synthesize SnO2–Fe2O3@C nanocomposite as a good candidate for high-performance lithium-ion batteries (LIBs) anodes. In this route, the SnO2–Fe2O3@polyaniline is first prepared with in situ polymerization in sol, followed by a carbonized transformation process. The growth of metal oxides particles is firstly suppressed by the polyaniline (PANI) on their outer surface in the in-situ polymerization route and secondly restricted by fully coating of carbon shell in thermal treatment, which forms by in situ carbonization of the polymer. Due to the unique structure and a so-called synergistic effect between SnO2 and Fe2O3, an excellent capacity over 1000 mAh g−1 is maintained after 380 cycles at current density of 400 mA g−1. The key insight is that the composite anode presented here achieves fully reversible Li insertion/extraction reaction and maintains high capacity for a long cycling life at high current density, and is realized as promising high-performance LIBs anode materials.