Fast, reversible lithium storage with a sulfur/long-chain-polysulfide redox couple

Abstract

The cathodic reactions in Li-S batteries can be divided into two steps. Firstly, elemental sulfur is transformed into long-chain polysulfides (S8 ↔ Li2S4), which are highly soluble in the electrolyte. Next, long-chain polysulfides undergo nucleation reaction and convert into solid-state Li2S2 and Li2S (Li2S4 ↔ Li2S) by slow processes. As a result, the second-step of the electrochemical reaction hinders the high-rate application of Li-S batteries. In this report, the kinetics of the sulfur/long-chain-polysulfide redox couple (theoretical capacity=419 mA h g(-1)) are experimentally demonstrated to be very fast in the Li-S system. A Li-S cell with a blended carbon interlayer retains excellent cycle stability and possesses a high percentage of active material utilization over 250 cycles at high C rates. The meso-/micropores in the interlayer are responsible for accommodating the shuttling polysulfides and offering sufficient electrolyte accessibility. Therefore, utilizing the sulfur/long-chain polysulfide redox couple with an efficient interlayer configuration in Li-S batteries may be a promising choice for high-power applications.