Porous Organic Cage as a Sulfur Host for Upgrading Capacity and Longevity of Li–S Batteries

Abstract

Suffering from the severe shuttle effect, constructing high-performance lithium–sulfur (Li–S) batteries with high capacity and prolonged cycling life remains a great challenge. Developing porous host materials for sulfur loading remains a tendency. Porous organic cages (POCs), as a kind of porous material, exhibit potential in energy storage and conversion because of their inherent cavities and plentiful active sites. Herein, two POC materials of CPOC-301 and HPOC-401 with large octahedral cavities and abundant N and O heteroatoms were explored as host materials for loading a high sulfur content of 84 wt % in Li–S batteries. The resulting CPOC-301-S and HPOC-401-S cathodes exhibit improved electrochemical performances with high specific capacity (1302 and 1109 mA h g–1 at 0.05 C, respectively) and excellent cycling reversibility and stability (a low average capacity fading rate of 0.015% for 2500 cycles at 5 C for CPOC-301-S). Moreover, the interconversion of keto-enamine in CPOC-301 could accelerate the redox kinetics. This work provides the blueprint for POC families applied as promising host materials for advanced Li–S batteries.

Progress of porous organic cages in photo/electrocatalytic energy conversion and storage applications

“…A similar type of work was further extended in 2023 by Yuan and co-workers, where an organic cathode composed of a high sulfur content (84 wt%) as guest molecules inside the host keto-enamine and acylhydrazone bond-linked organic cages CPOC-301-S and HPOC-401-S was developed for Li–S batteries, respectively. 46 The superior electrochemical performance, such as high specific capacity (range of 1302–1109 mA h g −1 at 0.05C), excellent cycling reversibility, and stability of the synthesized organic materials (Fig. 6b) revealed the good interconversion of keto-enamine in CPOC-301, which was responsible for the accelerated redox kinetics.…”

“…A similar type of work was further extended by the Yuan group in 2023, where two POC materials, namely, CPOC-301 and HPOC-401, with large octahedral cavities and abundant N and O heteroatoms active sites as host materials successfully encapsulated a high sulfur content (84 wt%) in Li–S batteries. 46 CPOC-301-S and HPOC-401-S were not only shown to be potential candidates to adsorb lithium polysulfide and inhibit the shuttle effect during the charge−discharge process but also promoted electron/charge transport in the reaction and catalyzed the redox kinetics of the sulfur species (Fig. 19c and d).…”

“…Recently, a keto-enamine bond-linked organic cage and its derivatives (resorcin[4]arene) were utilized as host cathodic materials with guest molecules in Li–S batteries. 45,46 The synergistic effects of large cavity (which can accommodate more guest molecules), good stability, and abundant N and O atoms of the resorcin[4]arene were mainly responsible for the high specific capacities and excellent cycling stability. These advantages make resorcin[4]arene-based POCs potential candidates for application in energy storage (rechargeable batteries).…”

“…35 Consequently, large-cavity, abundant O and N atom, resorcin[4]arene-based POCs with guest molecules have been successfully engineered with high specific capacities and excellent cycling stability toward energy storage applications. 45,46…”