namely a high theoretical specific energy of ≈2500 W h kg −1 for Li-S battery. [1,2] What is more, sulfur is low cost, nontoxic, and natural abundant. Despite these considerable advantages, the development of sulfur cathode is still hindered by several obstacles. Foremost among these is the "shuttle effect." The lithium polysulfides with high solubility formed in both charge and discharge processes diffuse into the electrolyte and then react with lithium anodes, which causes low coulombic efficiency, rapid capacity decay, and severe self-discharge of the cells. The second is the relatively low utilization of the active materials resulting from the insulating nature of sulfur, Li 2 S 2 / Li 2 S discharge products. The third is the volumetric and structural change of sulfur during charging and discharging. [3,4] Various materials have been introduced as sulfur hosts in attempt to address the above mentioned issues, including the carbon materials, [1,[5][6][7][8][9] conductive polymers, [10,11] metal oxides, [12,13] etc. Very recently, the use of carbon nitride-based materials as sulfur hosts has been investigated in a number of articles. Pang and Nazar employed a nanoporous graphitic C 3 N 4 (g-C 3 N 4 ) with large surface area as a sulfur host.[14] The abundant nitrogen (N) atoms on the g-C 3 N 4 form Li-N chemical interaction with lithium polysulfides, [14][15][16] which retards the diffusion of lithium polysulfides into the electrolyte effectively. However, the g-C 3 N 4 has intrinsically poor electrical conductivity, thus the adsorbed polysulfides are difficult to be reduced directly on the g-C 3 N 4 surface especially at high current density, resulting in relatively low sulfur utilization. [13] Zhang and co-workers reported a simple method to synthesize graphene-like oxygenated carbon nitride material (OCN) and used it as a sulfur host. Compared with the poorly conductive g-C 3 N 4 host material, the improved capacity performance was obtained for OCN-900 composite. [17] So far, it has been proved utilization of carbon nitride-based materials as lithium polysulfides anchoring hosts is effective. Yet just as most other polar material with lithium polysulfides anchoring abilities, carbon nitride-based materials can only adsorb lithium polysulfides near their surfaces. When the surface area is too low and the sulfur content is higher than a certain value, the host materials are not able to provide sufficient interfaces to anchor all of the lithium polysulfides. [13] Therefore, rational design of the structure of carbon nitride-based materials become important.To suppress the shuttle effect and improve the sulfur utilization in lithiumsulfur battery, a novel hollow carbon nitride-based spheres material (HCN x ) has been synthesized via polymerization of ethylenediamine and carbon tetrachloride on silica spheres and used as a sulfur host. The rational designed structure of HCN x retards diffusion of lithium polysulfides by both chemisorption and physical confinement. The enhanced conductivity of HCN x improves the u...
