Principle of progressively and strongly immobilizing polysulfides on polyoxovanadate clusters for excellent Li–S batteries application

Sulfur-fixing materials have important effects on lithium-sulfur batteries application, but the principles and processes are not very clear yet. For the first time, we proposed the excellent performance of (NH4)6V10O28 (NVO) clusters as sulfur-fixing materials and found that they have a unique two-step progressive sulfur-fixing mechanism. Firstly, the Li of lithium polysulfides (LiPSs) would attract the O of NVO cluster, which could widen the angle of O–V–O and expose the V atom inside the cluster. Secondly, the S of LiPSs can adsorb the V of NVO. The above progressive double interaction (Li–O and S–V) between NVO and LiPSs shows super strong binding energy (−423.41 to −627.19 kJ mol−1), which is 1.6 times higher than that of Li–O interactions only. It is also confirmed via both experimental test and DFT simulation. As a result, the Li–S batteries with NVO addition can deliver a reversible capacity of as high as 685 mAh g−1 at 1C. Even at a high sulfur loading of 6 mg cm−2, batteries showed a low decay rate of about 0.1% per cycle within 200 cycles at 0.1C.