Post-Modification Approach for Self-Exfoliated Synthesis of Pyridinium Sulfobetaine Covalent Organic Frameworks for Enhanced Lithium-Ion Conductivity

Abstract

While covalent organic frameworks (COFs) have been extensively investigated in the field of organic electrolyte materials, there is potential for further enhancement of their room-temperature ionic conductivity. This study introduces a novel methodology to induce self-exfoliation in the parent COF during synthesis through a postmodification technique. This process yields covalent organic nanosheets that feature pyridinium sulfobetaine groups, referred to as PS-CON. Due to the strategic arrangement of pyridinium cations and sulfobetaine anions, the charge distribution in PS-CON varies substantially, leading to a significant enhancement in lithium-ion dissociation. The methodically organized one-dimensional pore channels, along with the linear structure of the pyridinium sulfobetaine groups, facilitate the lithium-ion transport. PS-CON demonstrated a remarkable ionic conductivity of 2.19 × 10 –4 S cm –1 and a low activation energy (0.26 eV) coupled with a broad electrochemical stabilization window (4.05 V). Furthermore, the symmetrical cell (Li|Li@PS-CON|Li) demonstrates stable Li plating/stripping for more than 1200 h, which highlights the vast potential of pyridinium-sulfobetaine based zwitterionic nanosheets as high-performance organic electrolytes.