3D pomegranate-like TiN@graphene composites with electrochemical reaction chambers as sulfur hosts for ultralong-life lithium-sulfur batteries.

The low loading and poor cycling performance of sulfur cathodes are among the critical barriers restricting the practical application of lithium-sulfur (Li-S) batteries. The rational design of composites consisting of transition metals and conductive nanocarbon is considered an effective strategy to construct cathode materials for Li-S batteries with excellent cycling stability and rate capability. Herein, we propose a spray drying method to fabricate 3D pomegranate-like titanium nitride (TiN)@graphene composites as hosts for sulfur cathodes. The hollow spheres are coated with graphene layers to form a shell, serving as a highly efficient electrochemical reaction chamber and a reservoir for polysulfides. The TiN@graphene/S electrode exhibits an excellent capacity of 810 mA h g-1 after 200 cycles at 0.5C. The cathodes with high areal sulfur loadings of 2.8 and 3.6 mg cm-2 maintained remarkable capacities of 568 and 515 mA h g-1, respectively, after 500 cycles. The TiN hollow spheres not only accommodate the large volume expansion of sulfur but also improve the conversion of polysulfides during the discharge/charge process. The excellent electrical conductivity of the few-layered graphene shell facilitates electron transport and maintains structural stability. This work offers a strategy to combine inorganic compounds and nanocarbon as sulfur hosts to improve the electrochemical properties of Li-S batteries.