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

TLDR

Li–S batteries promise high energy density but suffer from sluggish polysulfide redox kinetics that cause low sulfur utilization, polarization, shuttle, and limited cycle life. The authors aim to enhance polysulfide redox by incorporating sulfiphilic CoS2 into carbon/sulfur cathodes to create strong interactions with lithium polysulfides. CoS2 interfaces act as strong adsorption and activation sites for polar polysulfides, accelerating their redox reactions during cycling. The CoS2 strategy boosts energy efficiency by 10 %, delivers a high initial capacity of 1368 mAh g⁻¹, maintains a low decay rate of 0.034 % cycle⁻¹ over 2000 cycles, and suggests applicability to other high‑power systems.

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.