Optimizing the p charge of S in p-block metal sulfides for sulfur reduction electrocatalysis

Understanding sulfur conversion chemistry is key to the development of sulfur-based high-energy-density batteries. However, unclear relationships between the electronic structure of the catalyst and its activity are the major problem. Here, we provide a direct correlation between the p electron gain of S in p-block metal sulfides and the apparent activation energies (Ea) for the sulfur reduction reaction (SRR), in particular, Li2Sn to Li2S conversion, which is the rate-determining step of the SRR. The maximum p charge occurs in bismuth sulfide and results in the lowest Ea and a high SRR rate in the cathode. Li–S batteries with the Bi2S3 catalyst work steadily at a high rate of 5.0C with a high-capacity retention of ~85% after 500 cycles. A high areal capacity of ~21.9 mAh cm−2 was obtained under a high sulfur loading of 17.6 mg cm−2 but a low electrolyte/sulfur ratio of 7.5 μl mg−1. Lithium–sulfur batteries are promising energy storage devices where catalysis can play an important role, but developing design principles for optimal performance remains a challenge. Now, a series of p-block metal sulfide cathodes are evaluated, revealing a direct correlation between the p electron gain of sulfur in the sulfide material and the apparent activation energy for the sulfur reduction reaction.