Hierarchical Porous N-doped Carbon Encapsulated Fluorine-free Mxene with Tunable Coordination Chemistry by One-pot Etching Strategy for Lithium-Sulfur Batteries

摘要

Continuous and considerable exploration of two-dimensional transition metalcarbides and nitrides (MXenes)toward interlayer spacing expansion, surfacetermination modification and composition architecture construction hasaroused significant interest in energy storage fields. Nevertheless, theiremployment remains severely impeded by a fundamental lack ofcomprehension of the coordination chemistry of MXenes. Herein, hierarchicalporous N-doped carbon encapsulated fluorine-free Ti_3C_2T_x with tunablecoordination chemistry is fabricated by a novel one-pot etching strategy. TheTi coordinated with N manipulated by phase reconstruction is identified byhigh-angle annular dark-field scanning transmission electron microscopy andX-ray photoelectron spectroscopy. Moreover, hierarchical porousnitrogen-doped carbons (HPNC) are distinctly observed that result in amultifold increase in material surface area derived from a substantialincrement of micro- and mesoporosity. The structural synergistic effect of Ticoordinated with N, and HPNC heighten binding energy and reduce energybarriers that accelerate redox kinetics, and boosts physical immobilization oflithium polysulfides. The aforementioned MXenes modified separators endowlithium-sulfur batteries with a reversible capacity of 889.5 mA h g~(-1) withcapacity retention of 79.5% after 100 cycles at 0.5 A g~(-1). Overall, this workaffords a novel and universal etching strategy in terms of directly synthesizingfluoride-free MXene with tunable coordination chemistry toward exploring thecorrelation between structural and electrochemical properties.