Finding the Ideal Electrocatalyst Match for Sulfur Redox Reactions in Li-S Batteries

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Lithium−sulfur (Li-S) batteries have emerged as a promising energy storage technology driven by their potential to reach very high theoretical specific energy densities of up to 2600 Wh•kg −1 . This remarkably high energy density directly results from the reversible, multi-electron-transfer reactions between sulfur and lithium metal taking place during the charge and discharge cycles. However, the charge/discharge processes of Li-S batteries are invariably accompanied by changes in both the composition and the structure of the sulfur species in the cathode, all of which result in sluggish and incomplete sulfur transformation. It has been demonstrated that the application of electrocatalysts is an effective strategy to accelerate the sulfur reduction reaction (SRR). Recognizing this challenge, researchers worldwide have tried to develop efficient catalysts to accelerate the kinetics of the SRR and boost the overall performance of Li-S batteries. However, this goal necessitates an in-depth understanding of the intricate catalytic processes in the Li-S battery cathode. The effective characterization of the catalysts and a thorough investigation of the SRR process are essential steps to unraveling the underlying catalytic mechanism of sulfur reduction and to compare the performances of the different electrocatalysts.Nonetheless, this pursuit is hindered by the inherent complexity of the SRR process, which remains uniquely specific to the Li-S system under study. Throughout the SRR process, a multitude of intermediate products are created through catalytic conversions between liquid−solid and solid−solid phases. This complexity is markedly different from established heterogeneous catalytic processes, such as water-splitting reactions, where reactants, products, and reaction phases are relatively simple. Given these challenges, our response has been to design a series of catalysts with controlled structures to gain an in-depth understanding of the intricate reaction processes within Li-S catalysis.In this Account, we have undertaken a comprehensive analysis of the structure−function relationships governing the active sites of electrocatalysts in SRR. Our work thus encompasses three aspects�catalytic sites: their geometry and evolution during the reaction, catalytic mechanisms: a key factor that determines SRR kinetics, and catalytic materials: intelligent design toward optimized performance. Also presented in this Account is a brief discussion covering the broader domain of other electrocatalysts and sulfurbased electrochemical systems. Drawing upon the insights obtained from these works, we present future perspectives on potential opportunities and hurdles in the wider application of sulfur cathode electrocatalysts.

S@C composites constructed by a graded pore-making strategy for Mg–S batteries with outstanding rate performance

“…Because Mg anodes are not prone to metal dendrite growth 12–18 and have a high flash point that usually exceeds the initial runaway temperature of batteries, Mg–S batteries are safer alternatives for alkali metal (Li, Na, and K) batteries. 19–21 In addition to its safety benefits, magnesium has other advantages, 22 such as higher volumetric capacity (3833 mA h cm −3 for magnesium, 2062 mA h cm −3 for lithium, 1128 mA h cm −3 for sodium, and 591 mA h cm −3 for potassium batteries), 23 and air resistance. 24 Most importantly, the successful coupling of the divalent characteristics of Mg ions and the conversion mechanism of the sulfur cathode gives Mg–S batteries relatively high energy densities (1684 W h kg −1 for Mg–S batteries, 2600 W h kg −1 for Li–S batteries, 1274 W h kg −1 for Na–S batteries, and 914 W h kg −1 for K–S batteries).…”