Progress and Prospect of Organic Electrocatalysts in Lithium−Sulfur Batteries

Abstract

Lithium−sulfur (Li−S) batteries featured by ultra-high energy density and cost-efficiency are considered the most promising candidate for the next-generation energy storage system. However, their pragmatic applications confront several non-negligible drawbacks that mainly originate from the reaction and transformation of sulfur intermediates. Grasping and catalyzing these sulfur species motivated the research topics in this field. In this regard, carbon dopants with metal/metal-free atoms together with transition–metal complex, as traditional lithium polysulfide (LiPS) propellers, exhibited significant electrochemical performance promotions. Nevertheless, only the surface atoms of these host-accelerators can possibly be used as active sites. In sharp contrast, organic materials with a tunable structure and composition can be dispersed as individual molecules on the surface of substrates that may be more efficient electrocatalysts. The well-defined molecular structures also contribute to elucidate the involved surface-binding mechanisms. Inspired by these perceptions, organic electrocatalysts have achieved a great progress in recent decades. This review focuses on the organic electrocatalysts used in each part of Li−S batteries and discusses the structure–activity relationship between the introduced organic molecules and LiPSs. Ultimately, the future developments and prospects of organic electrocatalysts in Li−S batteries are also discussed.

Self‐Assembled Macrocyclic Copper Complex Enables Homogeneous Catalysis for High‐Loading Lithium–Sulfur Batteries

“…In light of this, homogeneous catalysts capable of realizing solution-regulated reaction pathways exhibit unique advantages over heterogeneous catalysts in LiPSs conversion and Li 2 S deposition. [18,19] Most recently, inorganic additives (such as iodide and metallocene derivates) [20][21][22] and organic molecular (such as Schiff bases, conjugated quinones, and disulfide organics) [23][24][25][26] have been applied to realize the homogenous catalysis in Li-S batteries. Compared with the inorganic additives, organic molecules show the advantage of the stability of the working potential window.…”

Direct ink writing of metal‐based electrocatalysts for Li–S batteries with efficient polysulfide conversion

“…[ 18 ] Moreover, they also reduce the contact between long‐chain LiPSs and electrolytes during charge/discharge cycles. [ 19 ] To date, various catalytic materials, such as metal (Ni, Mo, and Co), [ 20 ] metal oxides (TiO 2 , Co 3 O 4 , and Fe 3 O 4 ), [ 21 ] metal sulfides (Co 9 S 8 , MoS 2 , and TiS 2 ), [ 22,23 ] metal nitrides (TiN and VN), [ 24 ] metal phosphides (CoP, Ni 2 P, and Cu 3 P), [ 25 ] and metal carbides (TiC, Mo 2 C, and Fe 3 C) have been studied as cathode host materials. [ 2 ] The published literature on Li–S battery electrocatalysts has also grown exponentially since 2012, with the trend shown in Figure 1A.…”

Sulfur Reduction Catalyst Design Inspired by Elemental Periodic Expansion Concept for Lithium–Sulfur Batteries

“…The resulting sluggish depletion of soluble LiPSs to Li 2 S 2 /Li 2 S precipitates, accompanied by the rapid generation of LiPSs (S 8 → LiPSs), leads to LiPS accumulation in the electrolyte. This causes large amounts of sulfur species to lose intimate contact with the electrode, which hinders electron/ion transport and potentially risks Li anode corrosion. , Accordingly, modulating sulfur reduction reactions (SRR), especially the conversion of LiPSs to Li 2 S, which accounts for more than 75% of the total capacity, to rapidly decrease the LiPS concentration in the electrolyte has received research attention. − Therefore, designing highly efficient SRR catalysts and developing SRR concepts are important for improving Li–S battery performance.…”