Tailoring the Voltage Gap of Organic Battery Materials Based on a Multi‐Electron Redox Chemistry

Abstract

Redox-active organics based on a multi-electron mechanism are of great interest in battery electrode materials as they are capable of delivering high capacity per molecular weight. However, most of such organics shows huge voltage gap that is inherited from their stepwise redox reactions occurring in the same conjugated redox moiety. This study focuses on the voltage tailoring of polymeric dihydrophenazine derivative, which shows high specific capacity as a cathode electrode material and decent cycling stability, but suffers huge voltage gap of ca. 0.8 V. We demonstrate a strategy to modify the voltage gap of dihydrophenazine derivatives through the incorporation of functional groups with different electron affinity near the redox moiety. The as-designed dihydrophenazine derivatives are further copolymerized to yield a polymeric material with significantly smoothened charge-discharge profiles and good capacity retention. We further demonstrate through theoretical calculation based on density-functional theory that the substitute site and types of functional groups are of great importance in voltage tailoring as well as structural stability of the dihydrophenazine derivatives.

Effective Design Strategy of Small Bipolar Molecules through Fused Conjugation toward 2.5 V Based Redox Flow Batteries

“…As is known, for n-type redox centers, a higher energy level of the lowest unoccupied molecular orbital (LUMO) indicates a weaker electron affinity and a lower redox potential. For p-type redox centers, a lower energy level of the highest occupied molecular orbital (HOMO) indicates a stronger electron affinity and a higher redox potential. , As is shown in Figure S4, the calculated HOMO energy level of QPT was significantly lower than those of PTZ-KT and BP-PT. It is notable that QPT showed a moderate LUMO energy level that was slightly lower than that of BP-PT, because the benzene ring of BP-PT has a high rotational degree of freedom, which can promote the conjugation integration with the ketone moiety, increasing the LUMO energy level.…”

p‐Type Redox‐Active Organic Electrode Materials for Next‐Generation Rechargeable Batteries

“…[154] In particular, synthesizing linear polymers of diaryl-PZ effectively suppressed the solubility, and thus the polymer cathodes delivered specific capacities of around 150 mAh g À1 with superior capacity retention (>90%) over a few hundred cycles. [66,67,153] However, the strong π-π interactions between the polymer chains narrowed the internal free volume, which adversely affected the rate performance by limiting the diffusion of bulky anions.…”

Polymer Electrode Materials for Lithium‐Ion Batteries

“…[201][202][203] In addition, the 1-/2-positions of phenazine and phenyl units are usually modified with different functionalities to adjust the redox voltage. The redox plateaus of -OMe substituted polymer decreased by 0.1-0.2 V and that of the -CN substituted polymer increased by 0.2 V. [204] Besides, the triphenylamine, [205] 2,4,6-triphenyl-1,3,5-triazine (Tz), 1,3,5-triphenylbenzene (Bz) [206] were utilized to replace the phenyl in p-DPPZ, forming highly-crosslinked structures. They showed remarkable cycle stability and high rate performance.…”