Effective polysulfide adsorption and catalysis by polyoxometalate contributing to high-performance Li–S batteries

Lithium sulfur (Li–S) batteries have been considered as a prospective energy storage system because of its high specific capacity of 1675 mAh/g and cheap raw material cost. Although there are still some difficulties including the migration of soluble lithium polysulfides (LiPSs) intermediates, low conductivity of sulfur, and severe volume change. Designing the stable and functional interlayer is an efficient method for enhancing the performance of Li–S batteries. This work demonstrates how Keggin polyoxometalate H3[PW12O40]∙xH2O (PW12) performs as a functional interlayer material to improve performance of Li–S batteries by applying its strong chemical anchoring and effective catalytic activity for LiPSs, as well as low redox potentials within the scope of the equilibrium potentials of the redox reactions of S. As a result, after 300 cycles at 0.5 C, the cells with PW12 interlayer demonstrate high capacity of 892.6 mAh/g, and even after 1000 cycles at 1 C, a low fading rate of only 0.048% per cycle can be obtained. More significantly, it can retain 500.3 mAh/g at 1 C after 100 cycles under sulfur loading of 4.6 mg cm−2 and E/S ratio of 5 μL/mg. Besides, we compare the different behavior characteristics of PW12, K6[P2W18O62]∙14H2O (Dawson, P2W18), and (NH4)6[P2Mo18O62]∙11H2O (Dawson, P2Mo18) as interlayer materials for Li–S batteries, a conclusion can be received that compared with Mo-containing polyoxometalates, W-containing polyoxometalates have lower redox potentials, which is beneficial for the reduction of sulfur. Our strategy provides a feasible solution for the reasonable design of polyoxometalate interlayers and offers new opportunities for high-capacity and long-life Li–S batteries.