Porosity vs. Carbon Shell Number: Key Factor Actually Affecting the Performance of Multi-Shelled Hollow Carbon Nanospheres in Li-S Batteries

•The pores in the carbon shells of HCNs play a key role in the Li+ diffusion and Li2Sx confinement.•Simply increasing the shell number in HCNs can not effectively confine the leakage of Li2Sx from the S cathode.•Porous 1S-HCNs endow the S cathode with better cycling stability and rate capability than the oligoporous 2S-HCNs and 3S-HCNs do.•After 700 cycles, a capacity of 759 mAh g−1 with 63 % retention is achieved for the S@1S-HCNs cathode at 0.2C.