Powering Lithium–Sulfur Battery Performance by Propelling Polysulfide Redox at Sulfiphilic Hosts

Abstract

Lithium-sulfur (Li-S) battery system is endowed with tremendous energy density, resulting from the complex sulfur electrochemistry involving multielectron redox reactions and phase transformations. Originated from the slow redox kinetics of polysulfide intermediates, the flood of polysulfides in the batteries during cycling induced low sulfur utilization, severe polarization, low energy efficiency, deteriorated polysulfide shuttle, and short cycling life. Herein, sulfiphilic cobalt disulfide (CoS2) was incorporated into carbon/sulfur cathodes, introducing strong interaction between lithium polysulfides and CoS2 under working conditions. The interfaces between CoS2 and electrolyte served as strong adsorption and activation sites for polar polysulfides and therefore accelerated redox reactions of polysulfides. The high polysulfide reactivity not only guaranteed effective polarization mitigation and promoted energy efficiency by 10% but also promised high discharge capacity and stable cycling performance during 2000 cycles. A slow capacity decay rate of 0.034%/cycle at 2.0 C and a high initial capacity of 1368 mAh g(-1) at 0.5 C were achieved. Since the propelling redox reaction is not limited to Li-S system, we foresee the reported strategy herein can be applied in other high-power devices through the systems with controllable redox reactions.

Recent development of metal compound applications in lithium–sulphur batteries

“…35,40 B. Co x S y Cobalt sulphides commonly show unique metallic or half-metallic characteristics, which means they exhibit particularly high room temperature conductivity. 41,42,136 Therefore the cobalt sulphides could afford efficient electron pathways and high electrocatalytic activity for polysulfide redox reactions in aqueous solutions. 41 Simultaneously cobalt sulphides can significantly enhance the redox reactivity of lithium polysulphides due to their strong chemical affinity.…”

“…41,42,136 Therefore the cobalt sulphides could afford efficient electron pathways and high electrocatalytic activity for polysulfide redox reactions in aqueous solutions. 41 Simultaneously cobalt sulphides can significantly enhance the redox reactivity of lithium polysulphides due to their strong chemical affinity. 41,42 For example, Zhang's group selected a cost-effective, nonporous mineral and bulk CoS 2 as the additive to the carbon/sulfur composite cathodes.…”

“…41 Simultaneously cobalt sulphides can significantly enhance the redox reactivity of lithium polysulphides due to their strong chemical affinity. 41,42 For example, Zhang's group selected a cost-effective, nonporous mineral and bulk CoS 2 as the additive to the carbon/sulfur composite cathodes. 41 The adsorption experiment as shown in Fig.…”

“…41,42 For example, Zhang's group selected a cost-effective, nonporous mineral and bulk CoS 2 as the additive to the carbon/sulfur composite cathodes. 41 The adsorption experiment as shown in Fig. 6(a) and the First-principle calculations based on DFT as shown in Fig.…”

“…A large amount of work nowadays reports that these metal compounds have much stronger adsorption ability to polysulphides compared to carbon, doped carbon, and conductive polymers. 35,[40][41][42][43] What's more, compared to the carbon materials, the metal compounds' exposed surfaces and morphologies are easier to control by chemical and physical methods. 19 Thus a variety of nanostructured metal compounds were designed, such as hollow, 34 porous, 40 layered, 35 laminar-structured, 42 and so on, to effectively hold the polysulphides in Li-S batteries.…”