A bipolar-redox tetraalkynylporphyrin macrocycle positive electrode with 12-electrons-transfer for high-energy aluminum-organic batteries.

Abstract

Organic electrode materials with bipolar-redox activity are a promising candidate for high-energy aluminum-ion batteries (AIBs), but face the capacity ceiling due to limited active sites and low electron transfer number. To universally address this issue, seeking for a kind of multisite bipolar organic material to achieve multielectron transfer is a prerequisite but challenging. Herein, we develop a 12-electron transfer tetraalkynylporphyrin macrocycle positive electrode with two p-type amine (‒NH‒) motifs, two n-type imine (C = N) motifs and four n-type alkynyl (C ≡ C) motifs. The bipolar 18π-electron porphyrin macrocycle can alternately bind and release AlCl₄^- anions at ‒NH‒ sites and AlCl₂⁺ cations at C = N sites (oxidized from 18π to 16π or reduced from 18π to 20π), achieving four electrons transfer. Furthermore, each terminal C ≡ C site can also coordinate with two AlCl₂⁺ cations, thereby delivering eight electrons. The designed aluminum-organic battery achieves a high capacity of up to 347 mAh g^-1 (3-6 times that of conventional graphite positive electrode, 60-120 mAh g^-1) and a high specific energy of 312 Wh kg^-1 (up to 150% compared to cells with graphite as positive electrode) based on the mass of positive electrode materials.