Unveiling the Electrochemical Reversibility of Multielectron Redox in s-Tetrazine Derivatives for Large-Capacity Electrode Materials

Abstract

1,2,4,5-tetrazine (s-tetrazine) is a promising redox center for organic electrode materials due to its low molecular weight and ability to undergo two-electron redox reactions. However, in practice, the irreversibility of the second-electron transfer has often limited the specific capacities of the s-tetrazine-based electrodes in metal-organic cells. Herein, electrochemically reversible two-electron-transfer processes from the s-tetrazine core are demonstrated by introducing electron-withdrawing pyridine rings at 3- and 6-positions. Comparative analysis of three s-tetrazine derivatives, 3,6-diphenyl-1,2,4,5-tetrazine (Ph-Tz), 3,6-di(4-pyridinyl)-1,2,4,5-tetrazine (4-Py-Tz), and 3,6-di(2-pyridinyl)-1,2,4,5-tetrazine (2-Py-Tz) reveals that both electron-withdrawing effect and Li-ion coordination play critical roles in redox reversibility. Among them, 2-Py-Tz exhibits the highest electron-transfer rate with Li+ diffusion coefficient attributed to the ortho-positioned pyridine nitrogen atoms, which strongly stabilize the dianion state through synergistic electron-withdrawing and Li-ion locking effects.