FeS ₂ microspheres wrapped by N-doped rGO from an Fe-based ionic liquid precursor for rechargeable lithium ion batteries

Earth-abundant pyrite (FeS ₂ ) is a promising anode material for lithium ion batteries (LIBs) because of its high theoretical specific capacity (894 mA h g ^-1 ). However, LIBs using pristine FeS ₂ usually suffer from volume expansion, dissolution of polysulfides, and low conductivity of Li ₂ S. Herein, FeS ₂ /N-doped reduced graphene oxide microspheres (FeS ₂ /N-rGO) are first synthesized from an Fe-based ionic liquid, [C ₁₂ MMim]FeCl ₄ (C ₁₂ MMim = 1-dodecyl-2,3-dimethylimidazolium), which can not only be used as the metal and nitrogen source but also as an assembly medium and surfactant. As the anode material for rechargeable LIBs, the as-obtained FeS ₂ /N-rGO composites display a specific capacity of 950 mA h g ^-1 after 140 cycles at a current density of 150 mA g ^-1 and deliver an average reversible discharge capacity of 973, 867, 778, and 671 mA h g ^-1 at 0.2, 0.5, 1.0, and 2.0 A g ^-1 , respectively. Even at high current density, the specific capacity can still reach 510 mA h g ^-1 . More importantly, after deep cycling, a high reversible capacity of 973 mA h g ^-1 can still be recovered when the current density reduced to 0.2 A g ^-1 . This excellent stability and outstanding rate performance are mainly attributed to the suppression of dissolution of polysulfide intermediates and volume expansion by the conductive N-doped rGO matrix.