Improving performances of Lithium-Sulfur cells via regulating of VSe functional mediator with Doping-Defect engineering and Electrode-Separator integration strategy.

The sluggish redox kinetics and the severe shuttle effect of soluble lithium polysulfides (LiPSs) are the main key issues which would hinder the development of lithium-sulfur (Li-S) batteries. In this work, a nickel-doped vanadium selenide in-situ grows on reduced graphene oxide(rGO) to form a two-dimensional (2D) composite Ni-VSe/rGO by a simple solvothermal method. When it is used as a modified separator in Li-S batteries, the Ni-VSe/rGO material with the doped defect and super-thin layered structure can greatly adsorb LiPSs and catalyze the conversion reaction of LiPSs, resulting in effectively reducing LiPSs diffusion and suppressing the shuttle effect. More importantly, the cathode-separator bonding body is first developed as a new strategy of electrode-separator integration in Li-S batteries, which not only could decrease the LiPSs dissolution and improve the catalysis performance of the functional separator as the upper current-collector, but also is good for the high sulfur loading and the low electrolyte/sulfur (E/S) ratio for high energy density Li-S batteries. When the Ni-VSe/rGO-PP (polypropylene, Celgard 2400) modified separator is applied, the Li-S cell can retain 510.3 mA h g capacity after 1190 cycles at 0.5C. In the electrode-separator integrated system, the Li-S cell can still maintain 552.9 mA h g for 190 cycles at a sulfur loading 6.4 mg cm and 4.9 mA h cm for 100 cycles at a sulfur loading 7.0 mg cm. The experimental results indicate that both the doped defect engineering and the super-thin layered structure design might optimally be chosen to fabricate a new modified separator material, and especially, the electrode-separator integration strategy would open a practical way to promote the electrochemical behavior of Li-S batteries with high sulfur loading and low E/S ratio.