posted on 2022-06-08, 21:44authored byXi Zhang, Gaofeng Li, Junxiao Wang, Jun Chu, Feng Wang, Zijun Hu, Zhiping Song
Poly(o-phenylenediamine) (PoPDA) has been recognized
as a low-cost electroactive organic material and studied as a cathode
for aqueous zinc batteries or as an anode for nonaqueous lithium batteries.
However, there remains a lot of confusion about its synthesis, structure,
and electrochemical application. Especially, the previously studied
PoPDA samples were mostly synthesized at room temperature, which were
proved by us to be just a dimer, that is, 2,3-diaminophenazine (DAPZ).
By various characterization methods including elemental analysis and
mass spectrometry, we verified that the product synthesized at high
temperature, PoPDA-H, was a polymer based on DAPZ as the structural
repeat unit and with some imperfect substitutes (OH and NH3+CH3COO–). Based on the reversible
redox reaction of phenazine units and the stable polymer structure
within 1.3–3.8 V vs Li+/Li, PoPDA-H was more appropriate
to be applied as a cathode rather than as an anode for lithium batteries.
It achieved a high energy density of 490 Wh kg–1 (2.12 V × 231 mAh g–1) at 50 mA g–1 and a high cycling stability (79%@1000th cycle) at 500 mA g–1, both of which were comparable to previously reported
expensive pyrazine- and carbonyl-based polymers. This work clarifies
many misunderstandings of PoPDA, which is important to its further
development toward practical application in energy-storage devices.