Eutectoid Reaction Enabling In Situ Construction of Titanium Based Ternary Heterostructures for Boosted Lithium Polysulfide Conversion.

Typical shuttle effect of lithium polysulfides (LiPSs) and slow kinetics of redox reactions seriously hinder the potential application of lithium-sulfur batteries (LSBs). Herein, a titanium based ternary accordion heterostructure (i.e., TiC-TiN-TiO) is first fabricated through an acid-assisted eutectoid reaction of TiCN MXene obtained via efficiently gas-etching of TiAlCN MAX. The in situ crystal reconstruction not only creates functional sur/interface configuration but generates built-in electric field (BIEF) at the crystal interfaces, which induce interfacial charge redistribution and accelerate electronic/ionic conductions of the whole heterostructures. Besides, the well-defined functions of conductive TiC, adsorptive TiO, and catalytic TiN enable the efficient fixation and conversion of LiPSs. Accordingly, LSBs assembled with the TiC-TiN-TiO modified separators demonstrate a remarkable reversible capacity of 1185 mAh g at 0.5 C, and an outstanding capacity retention of 778 mAh g after 500 cycles with a decay rate of 0.078% per cycle. Moreover, excellent rate capability (838 mAh g at 5 C) and superior cycling stability with high sulfur loading (3.7 mg cm) and low electrolyte/sulfur ratio (6.0 µL mg) are also achieved. More significantly, the eutectoid reaction of solid solution MXenes it devised here provides an innovative avenue to design functional hierarchical heterostructures for high-performance LSBs and beyond.