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

Abstract

Nowadays, Ti3C2Tx MXene has been reported to afford an ideal platform for the growth of TiO2 by oxidation. Unfortunately, the TiO2 derived from Ti3C2Tx 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 Ti3C2Tx 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.