A spherical Sn–Fe3O4@graphite composite as a long-life and high-rate-capability anode for lithium ion batteries

Abstract

In order to further enhance the reversible capacity and cyclability for lithium storage of Sn-based alloy anode materials, a spherical-shaped Sn–Fe₃O₄@C ternary-phase composite consisting of nanosized tin (Sn), magnetite (Fe₃O₄), and graphite (C) was prepared via a two-step process using high-efficiency discharge plasma-assisted milling (P-milling). Ultrafine Sn nanoparticles were embedded and tightly contacted with nanosized Fe₃O₄, with graphite nanosheets coating the outside to form a multiscale spherical structure. The Sn–Fe₃O₄@C nanocomposite anodes demonstrate a stable and high capacity of 793 mA h g⁻¹ after 240 cycles between 0.01 and 3.0 V vs. Li/Li⁺ at 200 mA g⁻¹. Furthermore, a reversible capacity of ∼750 mA h g⁻¹ was obtained after 500 cycles, even when the current density increased to 2000 mA g⁻¹. The high capacity, good cycle performance, and superior high-rate capability characteristics were attributed to the unique nanostructure of the Sn–Fe₃O₄@C composites. The good dispersion of co-existing Sn and Fe₃O₄ nanoballs in a spherical carbon matrix resulted in an electrode with high structural stability and fast kinetics for Li ion and electron transfer, which contributed to high reversibility of alloying reactions in Sn and conversion reactions of Fe₃O₄. Furthermore, the spherical shape of the materials and simple preparation as compared to those of commercial anodes make the Sn–Fe₃O₄@C composites good candidates for practical applications.