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

Continuous and considerable exploration of two-dimensional transition metal carbides and nitrides (MXenes)toward interlayer spacing expansion, surface termination modification and composition architecture construction has aroused significant interest in energy storage fields. Nevertheless, their employment remains severely impeded by a fundamental lack of comprehension of the coordination chemistry of MXenes. Herein, hierarchical porous N-doped carbon encapsulated fluorine-free Ti3C2Tx with tunable coordination chemistry is fabricated by a novel one-pot etching strategy. The Ti coordinated with N manipulated by phase reconstruction is identified by high-angle annular dark-field scanning transmission electron microscopy and X-ray photoelectron spectroscopy. Moreover, hierarchical porous nitrogen-doped carbons (HPNC) are distinctly observed that result in a multifold increase in material surface area derived from a substantial increment of micro- and mesoporosity. The structural synergistic effect of Ti coordinated with N, and HPNC heighten binding energy and reduce energy barriers that accelerate redox kinetics, and boosts physical immobilization of lithium polysulfides. The aforementioned MXenes modified separators endow lithium-sulfur batteries with a reversible capacity of 889.5 mA h g(-1) with capacity retention of 79.5% after 100 cycles at 0.5 A g(-1). Overall, this work affords a novel and universal etching strategy in terms of directly synthesizing fluoride-free MXene with tunable coordination chemistry toward exploring the correlation between structural and electrochemical properties.

Automated summary

A novel one-pot etching strategy is used to fabricate fluorine-free Ti3C2Tx nitrogen encapsulated hierarchical porous carbon with tunable coordination chemistry. Through phase reconstruction, Ti coordinated with N is identified. Hierarchical porous nitrogen-doped carbons (HPNC) significantly increase material surface area, enhancing redox kinetics and physical immobilization of lithium polysulfides. The modified MXene separator shows a reversible capacity of 889.5 mA h g(-1) with capacity retention of 79.5% after 100 cycles at 0.5 A g(-1). This work provides a novel etching strategy to explore the correlation between structural and electrochemical properties.