Thiophene-Based Bipolar-Type Covalent Organic Frameworks with Extended π-Conjugation as Superior Cathode for Lithium-Ion Batteries

Abstract

Covalent organic frameworks (COFs) have latterly emerged as a promising platform for devising electrode materials used to acquire high-performance lithium-ion batteries (LIBs). However, the preparation of COFs with fast redox kinetics, high-efficiency utilization of active sites, superior stability, and high conductivity remains a challenge. Herein, a thiophene-based bipolar-type COFs (denoted as TT-TPDA-COF) featuring extended conjugation, rich multiple redox-active sites (C─S, C─N, and C═N), and hierarchical micro-mesoporosity is synthesized. TT-TPDA-COF exhibits significantly increased density of redox-active sites and enhanced electrical conductivity compared with its corresponding counterpart (Np-TPDA-COF). Remarkably, when TT-TPDA-COF is used as LIBs cathode, it shows exceptional specific capacity up to 309 mA h g⁻¹ at 200 mA g⁻¹, significantly surpassing that of Np-TPDA-COF (195 mA h g⁻¹ at 200 mA g⁻¹), high energy density of 714 W h kg⁻¹, superb rate property (182 mA h g⁻¹ at 5000 mA g⁻¹), and impressive capacity preservation of 84.3% after 5000 cycles at 5000 mA g⁻¹. Additionally, the predictable application of TT-TPDA-COF for prototype batteries has been proved by the high-performance dual-ion full cells assembled by using TT-TPDA-COF as cathode. Furthermore, the dual-ion storage mechanism of TT-TPDA-COF is comprehensively revealed by in/-ex situ studies and theoretical calculations.