Sulfide‐Bridged Covalent Quinoxaline Frameworks for Lithium–Organosulfide Batteries

Abstract

The chelating ability of quinoxaline cores and the redox activity of organosulfide bridges in layered covalent organic frameworks (COFs) offer dual active sites for reversible lithium (Li)‐storage. The designed COFs combining these properties feature disulfide and polysulfide‐bridged networks showcasing an intriguing Li‐storage mechanism, which can be considered as a lithium–organosulfide (Li–OrS) battery. The experimental–computational elucidation of three quinoxaline COFs containing systematically enhanced sulfur atoms in sulfide bridging demonstrates fast kinetics during Li interactions with the quinoxaline core. Meanwhile, bilateral covalent bonding of sulfide bridges to the quinoxaline core enables a redox‐mediated reversible cleavage of the sulfursulfur bond and the formation of covalently anchored lithium–sulfide chains or clusters during Li‐interactions, accompanied by a marked reduction of Li–polysulfide (Li–PS) dissolution into the electrolyte, a frequent drawback of lithium–sulfur (Li–S) batteries. The electrochemical behavior of model compounds mimicking the sulfide linkages of the COFs and operando Raman studies on the framework structure unravels the reversibility of the profound Li‐ion–organosulfide interactions. Thus, integrating redox‐active organic‐framework materials with covalently anchored sulfides enables a stable Li–OrS battery mechanism which shows benefits over a typical Li–S battery.

Boosting sulfur‐based cathode performance via confined reactions in covalent organic frameworks with polarized sites

“…19 For example, Kaskel et al conducted one-dimensional (1D) channel COF with dual active sites designed for intriguing Li-storage in Lithiumorganosulfide batteries. 20 Chen et al assembled COF with conductive carbon nanotube for high performance in Li-S battery. 21 It should be mentioned that although COFs are with random direction on electrodes, their 1D channels facilitated rapid and uniform Li + transport across the host matrix, 22 and greatly enhanced rate performance and improved the ionic mobility of the pristine matrix in previous reports.…”

Covalent Organic Frameworks as Model Materials for Fundamental and Mechanistic Understanding of Organic Battery Design Principles

“…The mechanism was investigated by Haldar et al by combining a computational approach with in situ Raman studies on redoxactive COF-electrodes named DUT-185-S 2 and DUT-185-S n . 107 Meanwhile, a new class of covalently anchored sulfurized COFs has recently been explored to suppress the commonly observed polysulfide shuttle problem during charge−discharge in lithium−sulfur (Li−S) batteries. Strategic substitution of halo atoms in the halobenzenes of the COF-building unit or inversevulcanization at vinylene backbones of COFs at high temperatures enables this polysulfide linking to the framework's backbone.…”

“…Among the other sulfur linkages in COFs, the organosulfides are well-known for the electrochemically reversible breaking and reconnection of the S–S bond during metalation ( E reduction : 2.25–2.51 V vs Li/Li + ). The mechanism was investigated by Haldar et al by combining a computational approach with in situ Raman studies on redox-active COF-electrodes named DUT-185-S 2 and DUT-185-S n . Meanwhile, a new class of covalently anchored sulfurized COFs has recently been explored to suppress the commonly observed polysulfide shuttle problem during charge–discharge in lithium–sulfur (Li–S) batteries.…”

“…The computationally calculated binding energy E B ( x 1 , x 2 ) of any metal ion (M + ) to any organic functional group is correlated to the redox potential for the subsequent electron transfer, as derived by the equation of Lee et al Followed by this, Haldar et al also analyzed the mechanism of M + interaction to COF in a stepwise manner by evaluating the energy profile diagram for the system. In consideration of the typical metal-ion battery reaction mechanism, the binding energy was calculated using the following equation: ,, E normalB ( x 1 , x 2 ) = prefix− ( E total false( x 2 false) − E total false( x 1 false) − false( x 2 − x 1 false) E M false( x 2 − x 1 false) e ) Here, E total ( x 2 ) and E total ( x 1 ) are the total energies of the system at two adjacent low-energy concentrations x 2 and x 1 , e is the electronic charge, and E M is the energy per metal atom in its bulk structure. Since reduction potential reflects the electrochemical potential required for electron transfer in a chemical reaction, the metalation and demetalation reactions in COFs were shown by Singh et al using the following equation: ( n e − ) + ( n M + ) +…”

“…The computationally calculated binding energy E B (x 1 ,x 2 ) of any metal ion (M + ) to any organic functional group is correlated to the redox potential for the subsequent electron transfer, as derived by the equation of Lee et al 109 Followed by this, Haldar et al also analyzed the mechanism of M + interaction to COF in a stepwise manner by evaluating the energy profile diagram for the system. In consideration of the typical metal-ion battery reaction mechanism, the binding energy was calculated using the following equation: 107,110,111 = i k j j j j j y…”