The redox reactions occurring in the Li-S battery positive electrode conceal various and critical electrocatalytic processes, which strongly influence the performances of this electrochemical energy storage system. Here, we report the development of a single-dispersed molecular cluster catalyst composite comprising of a polyoxometalate framework ([Co4(PW9O34)2]10−) and multilayer reduced graphene oxide. Due to the interfacial charge transfer and exposure of unsaturated cobalt sites, the composite demonstrates efficient polysulfides adsorption and reduced activation energy for polysulfides conversion, thus serving as a bifunctional electrocatalyst. When tested in full Li-S coin cell configuration, the composite allows for a long-term Li-S battery cycling with a capacity fading of 0.015% per cycle after 1000 cycles at 2 C (i.e., 3.36 A g−1). An areal capacity of 4.55 mAh cm−2 is also achieved with a sulfur loading of 5.6 mg cm−2 and E/S ratio of 4.5 μL mg−1. Moreover, Li-S single-electrode pouch cells tested with the bifunctional electrocatalyst demonstrate a specific capacity of about 800 mAh g−1 at a sulfur loading of 3.6 mg cm−2 for 100 cycles at 0.2 C (i.e., 336 mA g−1) with E/S ratio of 5 μL mg−1.

The shuttle effect of dissolved polysulfides produced during the operation of lithium–sulfur batteries is the most serious and fundamental problem among many challenges. We propose a strategy via in situ formation of a functionalized molecule with a dual-terminal coupling function to bind the dissolved polysulfide intermediates, thus turning them back into solid-state organopolysulfide complexes by molecule binding, and then the polysulfides can be pinned on the cathode firmly. The dual-terminal coupling functional molecule binder (MB), which is formed in situ by reaction between quinhydrone (QH) and lithium, can not only bind polysulfides by reversible chemical coordination but also promote the conversion of polysulfides during cycling synchronously. In theory, with the dual-terminal coupling function, MB can bind polysulfide intermediates to copolymerize them, forming −[MB-Li2S n ]– that has faster reaction activity and redox conversion kinetics in comparison with simple Li2S n . With the MB, the Li–S battery exhibits a large initial capacity of 1347 mAh g–1 at 0.1 C. The remaining capacity of 963 mAh g–1 at 1 C shows no obvious decay for more than 400 cycles, and the retention of the first 300 cycles can reach 96.9%, in particular. This study delivers an alternative approach to resolving the shuttle effect and achieving excellent Li–S battery performance, with the potential significance going way beyond battery systems.

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