Modulating metal-free Zn-bromine batteries with covalent organic framework anode

Recently, deploying a reversible Zn2+-host anode to fabricate metal-free aqueous Zn ion batteries (AZIBs) provides an effective solution to solve the hindrances of Zn metal anode. However, the unsatisfactory energy density (<100 Wh kg−1) of assembled metal-free AZIBs is limited by low operated voltage of device (0.8∼1 V) and insufficient capacity of anode (<150 mAh g−1). Herein, for the first time, we proposed a polyimide covalent organic framework (Tp-DANT-COF) with multiple redox centers (C=O) as metal-free anode. It is found that the highly order interlayer structure, robust covalent framework and extended π-conjugated domain play key roles to facilitate ion/electron transport, structural integrity and active centers accessibility. As results, the COF anode exhibits an excellent specific capacity of 235.7 mAh g−1 at 0.1 A g−1, superior rate performance of 179.1 mAh g−1 even at 10 A g−1 and cycling stability over 10,000 cycles. Besides, the dual cation charge storage mechanism and favorable co-accommodate configuration of Zn2+/H+ are revealed by various characterizations and theory calculation. Importantly, matched to bromine cathode (AC-KBr) with high redox potential, the fabricated Tp-DANT-COF//AC-KBr full device achieves high energy density of 110.9 Wh kg−1 with 1.2 V operating voltage, exceeding the most reported congenerical devices.