3D TiO₂@nitrogen-doped carbon/Fe₇S₈ composite derived from polypyrrole-encapsulated alkalized MXene as anode material for high-performance lithium-ion batteries

Nowadays, Ti₃C₂T_x MXene has been reported to afford an ideal platform for the growth of TiO₂ by oxidation. Unfortunately, the TiO₂ derived from Ti₃C₂T_x still possesses low lithium ion diffusion coefficient, poor electrical conductivity and relatively inferior capacity when used as anode of rechargeable lithium ion batteries (LIBs). In this work, three dimensional (3D) TiO₂@nitrogen-doped carbon (NC)/Fe₇S₈ composite was fabricated by a facile and simple hybrid strategy via in situ polymerization of pyrrole monomer with alkalized Ti₃C₂T_x and subsequent vulcanization at 700 °C. When evaluated as an anode material for LIBs, the TiO₂@NC/Fe₇S₈ demonstrates a high reversible capacity (516 mAh g⁻¹ after 100 cycles at 0.1 A g⁻¹), excellent rate capability (337 mAh g⁻¹ at 1 A g⁻¹) and robust long cycling stability (282 mAh g⁻¹ after 1000 cycles at 4 A g⁻¹). The excellent electrochemical performances are contributed by the unique architecture of TiO₂@NC/Fe₇S₈, where 3D urchin-like TiO₂ with good structural stability provides adequate space to increase the contact between electrode and electrolyte, shorten the lithium ion diffusion length and alleviate the volume change; nitrogen-doped carbon shell layer improves the electrical conductivity, facilitates the electron transport and prevents the aggregation for Fe₇S₈; Fe₇S₈ contributes high specific capacity during charge/discharge process. Importantly, the hybrid approach in this work enlightens the exploration on combing the MXene-derived oxides with other metal sulfides for promising applications in energy storage field.