Design and synthesis of novel pomegranate-like TiN@MXene microspheres as efficient sulfur hosts for advanced lithium sulfur batteries.

Lithium-sulfur (Li-S) batteries have the characteristics of low cost, environmental protection, and high theoretical energy density, and have broad application prospects in the new generation of electronic products. However, there are some problems that seriously hinder the Li-S batteries from going from the laboratory to the factory, such as poor stability caused by the large volume expansion of sulfur during charging and discharging, sluggish kinetics of the electrochemical reaction resulting from the low conductivity of the active materials, and loss of active materials arising from the dissolution and diffusion of the intermediate product lithium polysulfides (LiPSs). In this paper, the two-dimensional layered material MXene and TiN are firstly combined by spray drying method to prepare pomegranate-like TiN@MXene microspheres with both adsorption capacity and catalytic effect on LiPSs conversion. The interconnected skeleton composed of MXene not only solves the problem of easy stacking of MXene sheets but also ensures the uniform distribution of sulfur. Without affecting the excellent characteristics of MXene itself, the overall conductivity of the composite electrode material is improved. The TiN hollow nanospheres are coated with MXene layers to form a shell, catalyzing the adsorption of LiPSs and accelerating the transformation of high-order LiPSs to LiS/LiS. As a result, the TiN@MXene cathode delivers a high initial discharge capacity of 1436 mA h g at 0.1C, excellent rate performance of 636 mA h g up to 3C, and an ultralong lifespan over 1000 cycles with a small capacity decay of 0.048% per cycle at the current density of 1.0C.