Crystal Facet Engineering of MXene-Derived TiN Nanoflakes as Efficient Bidirectional Electrocatalyst for Advanced Lithium-Sulfur Batteries.

The design of nanomaterials with grain orientation structure by crystal facet engineering is of great significance for boosting the catalytic ability and electrochemical properties, but the controllable synthesis is still a challenge. Here, TiN nanoflakes with exposed (001) facets are prepared using 2D Ti 3 C 2 MXene as the initial reactant and applied as a bidirectional electrocatalyst for the reduction and oxidation process in lithium-sulfur batteries (LSBs). The (001) facet-dominated TiN nanoflakes have a strong adsorption capacity for soluble lithium polysulfides (LiPSs). More importantly, theoretical calculations and experiment results confirm the (001) facet-dominated TiN nanoflakes catalyze the conversion of soluble LiPSs to Li 2 S 2 /Li 2 S to induce the Li 2 S uniform deposition in the discharge process and decrease the delithiation barrier of Li 2 S in the charge process. Therefore, the excellent electrochemical properties of LSBs are achieved, which demonstrates a high discharge capacity of 949 mAh g -1 at 1 C and maintains high capacity reversibility with a decay rate of 0.033% per cycle after 800 cycles.