Two-dimensional metal–organic polymers as cathode hybrid materials for high-performance Al-batteries

Abstract

Organic materials represent a promising alternative to critical raw materials for energy storage applications due to their sustainable production combined with tunable structures and functionalities. Unfortunately, the biggest limitation of organic materials is their high solubility in aqueous electrolytes, which results in a poor cycling stability. Metal–organic polymers (MOPs) have emerged as versatile organic materials, which exhibit enhanced chemical stability as well as redox activity depending on the employed building units. Here, by mastering a coordination chemistry approach, two novel MOPs were synthesized via a coordination process between tetraminobenzoquinone (TABQ) and a metal ion (i.e., zinc or copper) and were explored as cathode materials for aluminum-ion batteries. The resulting Zn-TABQ MOP exhibited superior electrochemical performance compared to other common cathode materials in Al-batteries. Specifically, Zn-TABQ revealed a specific capacity of 198 mA h g⁻¹ at 0.05 A g⁻¹, combined with high-capacity retention (92%) after 5000 cycles at a scan rate of 1 A g⁻¹ and an outstanding energy density of 247 W h kg⁻¹. We demonstrated via ex situ characterization that the electrochemically active carbonyl (CO) units of Zn-TABQ coordinate with AlCl₂⁺ and EMIM⁺ ions, thereby governing the mechanism of ion storage and release by taking advantage of the nature of the reversible interaction.