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.