Cluster-type lithium polysulfides regulator for high performance lithium-sulfur batteries

1 The strategy of modifying lithium polysulfides with cluster-type regulator to improve the performance of Li-S batteries was proposed for the first time. 2 The macromolecular LiPyS clusters have low solubility and thus can be confined to the cathode side. 3 LiPyS clusters can combine with LiPSs through double Li···S bonds to inhibit the "shuttle effect". 4 LiPyS clusters accelerate LiPSs redox kinetics based on frontier molecular orbital energy regulation strategy. Lithium polysulfide intermediates suffer from serious "shuttle effect" and slow redox kinetics, resulting in limited rate performance, low discharge capacity and rapid capacity decay of lithium-sulfur (Li-S) batteries. Here, we propose a concept of cluster-type lithium polysulfides (LiPSs) regulator to address the above-mentioned problems. Dipyridyl disulfide (DpyDS) is introduced to be an electrolyte additive to form low solubility macromolecular lithium pyridine-2-thiolate (LiPyS) clusters in electrolyte by in-situ lithiation and Li bond network. The LiPyS monomer in the clusters form complexes (LiPyS-LiPSs) with LiPSs through bi-directional Li···S bonds, so as to restrict LiPSs to the clusters on the cathode side, preventing the parasitic reaction between LiPSs and Li metal. At the same time, LiPyS-LiPSs have higher HOMO energy levels and lower LUMO energy levels than that of single LiPSs. As a result, LiPSs can achieve an enhanced redox activity, and the Li-S battery regulated with DpyDS provides a capacity as high as 900 mA h g −1 at 2 C rate.