Pseudo-covalent triazine frameworks for superior Li-S batteries

Abstract

Rechargeable lithium-sulfur batteries are promising because of exceptional energy density and low cost. However, lithium-sulfur batteries suffer from severe polysulfide shuttle problems and sluggish conversion kinetics, which result in poor electrode reversibility and a limited lifespan. Herein, pseudo-covalent triazine frameworks integrated with conductive Ketjenblack have been desgined as sulfur hosts. The pseudo-covalent triazine frameworks, controllably synthesized via regulating on temperature and ratio between 1,4-dicyanobenzene precursor and ZnCl2, maintain highly porous triazine ring-lining skeleton with amorphous graphitic layers and abundant defects such as pyridine/pyrrole/quaternary-N atoms. Strong immobilization and fast catalytic conversion towards polysulfide are verified and theoretical explanations reveal these reaction sites are mostly occurring around triazine rings groups due to enhanced electron donating ability from N-atoms. Coin-type Li-S cells based on CTF@KB hosts exhibit outstanding rate performances (425.7 mAh/g at 10C) and lifespan (960.5 mAh/g mAh/g after 180 cycles), which are superior than previous reports. Pouch cells stress practicality of pseudo-covalent triazine frameworks (550.6 mAh/g after 60 cycles).