Synergistic Catalysis on Dual‐Atom Sites for High‐Performance Lithium–Sulfur Batteries

Abstract

The booming development of electric vehicles and mobile electronic devices has placed increasing demands on high-energy-density secondary batteries. [1] Li-S batteries afford a theoretical energy density of 2600 Wh kg À1 and are promising candidates as next-generation high-energy-density energy storage devices. [2] Typical Li-S batteries employ a sulfur cathode, a Li metal anode, and ether-based electrolyte. Multiphase and multielectron sulfur redox reactions take place at the sulfur cathode during charge and discharge. [3] Specifically, during the discharge process, solid sulfur is first reduced to lithium polysulfides (LiPSs) through solid-liquid conversion, then LiPSs undergo liquid-liquid reduction reactions in the electrolyte, and eventually liquid-solid conversion occurs to form Li 2 S 2 /Li 2 S precipitates from LiPS reduction. [4] The cathode sulfur redox reactions provide a high specific capacity of 1672 mAh g À1 that greatly exceeds the intercalation cathodes of Li-ion batteries and promises a high energy density of Li-S batteries. However, the sluggish kinetics of sulfur redox reactions leads to low utilization of active materials and severe polarization, which consequently result in low discharge capacity and poor rate performance of Li-S batteries and severely limit the practical implementation of Li-S batteries. [5] Therefore, facilitating the sulfur redox kinetics is essential for the construction of highperformance Li-S batteries.Introducing electrocatalysts is regarded as a promising solution to promote the sluggish sulfur redox kinetics. [6] Previous works have established that electrocatalysts such as metal oxides, [7] nitrides, [8] sulfides, [9] and carbides [10] can accelerate the sulfur redox kinetics and improve the performance of Li-S batteries. Among the various electrocatalysts, single-atom catalysts (SACs) are able to make efficient use of almost every transition metal atom as active site and the unsaturated coordinated transition metal atoms are more likely to interact with the active species over traditional catalyst particles. [11] As a result, Cobased, [12] Fe-based, [13] Ni-based, [14] and Mn-based [15] SACs have been massively reported as electrocatalysts for Li-S batteries to accelerate the sulfur redox kinetics. For example, Du et al. reported that atomic Co embedded in nitrogen-doped graphene could trigger the surface-mediated reaction and reduce the activation energy for the conversion from Li 2 S 4 to Li 2 S 2 /Li 2 S. [16] Ye et al. reported Fe-N and Co-N co-doped SACs that could catalyze the conversion reactions for both long-chain and short-chain LiPSs.

Atomically Dispersed Fe–N4 and Ni–N4 Independent Sites Enable Bidirectional Sulfur Redox Electrocatalysis

“…Apart from the LiPSs shuttling suppression, the reaction rate for the charging process is highly determined by the oxidation of insulating Li 2 S. An insufficient catalytic effect will cause surface passivation and lower the sulfur utilization. , Progress has been achieved in enhancing the catalytic activity (especially for sulfur reduction) by regulating the coordinated ligands or controlling the distance of the SAC sites. − Nevertheless, achieving a fast bidirectional sulfur conversion process by using a single metal atom catalyst is challenging. Recently, constructing dual-atom catalysts (DACs) also has been reported as an effective strategy to propel the kinetics of oxygen reduction reaction and polysulfides conversion by tailoring the electronic structure of metal centers. , Compared with coordination engineering of the SACs and electron structure modulation of the DACs, the appropriate selection of independent dual single atoms to separate sulfur oxidation and reduction could offer a viable approach toward a high catalytic effect, which has not been reported.…”

“…Recently, constructing dual-atom catalysts (DACs) also has been reported as an effective strategy to propel the kinetics of oxygen reduction reaction and polysulfides conversion by tailoring the electronic structure of metal centers. 26,27 Compared with coordination engineering of the SACs and electron structure modulation of the DACs, the appropriate selection of independent dual single atoms to separate sulfur oxidation and reduction could offer a viable approach toward a high catalytic effect, which has not been reported.…”

In Situ Trapping Strategy Enables a High-Loading Ni Single-Atom Catalyst as a Separator Modifier for a High-Performance Li–S Battery

“…31 Following this work, researchers developed various types of single atoms with superior catalysis activities on the lithiation/delithiation reactions of the LiPSs, such as Co single atoms on nitrogen-doped graphene 32 and Fe−Co single dual atoms on nitrogen-doped carbon. 33 In addition, the electronic environments of the single atoms can be controlled by changing the coordination status. For example, Chen et al 34 reported a novel Fe-SAC with oversaturated Fe−N 5 coordination structure that serves as a bifunctional site for anchoring and activating LiPSs, thus facilitating the conversion of both the solid sulfur and soluble sulfides.…”

“…Zhang et al proposed that Ni single atoms can act as LiPS traps by forming strong chemical bonds and exchange charge with LiPSs to enhance the conversion kinetics . Following this work, researchers developed various types of single atoms with superior catalysis activities on the lithiation/delithiation reactions of the LiPSs, such as Co single atoms on nitrogen-doped graphene and Fe–Co single dual atoms on nitrogen-doped carbon . In addition, the electronic environments of the single atoms can be controlled by changing the coordination status.…”

Efficient immobilization and bidirectional catalysis of polysulfide conversion by FeCoP quantum dots for lithium–sulfur batteries

“…Recently, some studies have investigated the oxidation and reduction processes on composite sulfur cathodes such as Fe-Co-NC, 27 TiO 2 -Ni 3 S 2 , 28 TiN-TiO 2 , 7 etc. Intentionally, these catalysts with heterojunctions synergistically suppressed the shuttling effect and improved the kinetics of LSBs.…”