Tuning Redox Behavior of Pyrene–Benzothiadiazole/TTF–Based Covalent Organic Framework Electrodes in Dual-Ion Batteries

Covalent organic frameworks (COFs) have emerged as promising electrode materials for secondary-ion batteries, where redox-active building blocks and linkages enable tunable redox properties, while ordered pores serve as nanochannels for fast ion transport. We report a novel highly crystalline 2D PyTTF-COF, synthesized by integrating n-type pyrene–benzothiadiazole (PyBT) and p-type tetrathiafulvalene (TTF) subunits via an n-type imine linkage, yielding a bipolar electrode capable of reversible 16 e⁻ dual cation–anion storage. Initially, the dual-ion, redox synergy was tested in a Li-ion half-cell, where PyTTF served as cathode, and 1 м LiPF₆ or LiTFSI electrolytes were employed to probe anion-dependent electrochemical behavior. Electrochemical evaluation in Li-ion half cells revealed a wide electrochemical window of 0.1−3.6 V vs. Li/Li⁺, with markedly enhanced charge-storage kinetics and ion diffusion with LiTFSI relative to LiPF₆ electrolytes. The PyTTF electrode delivered specific capacities of 286 mAh g⁻¹ (LiTFSI) and 184 mAh g⁻¹ (LiPF₆) at 0.3 A g⁻¹, highlighting the strong influence of anion identity. Systematic variation of LiTFSI salt concentration (1−3 м) revealed strong correlations between electrolyte composition, ion storage dynamics, and interfacial charge-transfer resistance. This study highlights, for the first time, the critical importance of tailoring both charge-carrier identity and electrolyte concentration to unlock the full potential of bipolar COF electrodes for dual-ion batteries.