Molecule Engineering of Dual-Electron-Withdrawing Groups for Rechargeable Aluminum Batteries

A rechargeable aluminum battery is expected to be the next-generation energy storage system due to abundant resources and good safety. Inorganic positive electrodes face the bottleneck to develop high-energy-density Al batteries. Organic molecules with active groups provide a promising opportunity to solve the restrictive problems. In this work, novel dual-electron-withdrawing group organic molecules are proposed as positive electrode materials of Al batteries. Molecule engineering of electron-withdrawing carbonyl groups is developed by introducing heterogeneous electron-withdrawing chloride groups and regulating the benzene ring. It is confirmed that the molecular polarity, orbital energy level, and reaction activity of carbonyl organic molecules can be effectively regulated by molecule engineering. By introducing electron-withdrawing chloride groups and decreasing the benzene ring number, discharge voltage and conductivity of organic molecules are obviously enlarged. However, the solubility in the ionic liquid electrolyte increases, which leads to poor cycling stability. The theoretical capacity depends on the weight ratio of carbonyl groups and organic molecules. 2,3-Dichloro-1,4-naphthalenedione (2Cl-NQ) with dual-electron-withdrawing carbonyl and chloride groups delivers an initial specific capacity of 150 mA h g-1. Particularly, the stable discharge voltage and energy density of 2Cl-NQ are up to1.5 V and 159 W h kg-1, respectively. Electron-withdrawing carbonyl groups as active sites contribute to the capacity by coordinating with positively charged AlCl2+. The charge/discharge mechanism is independent of the molecule structure and heterogeneous chloride groups. This work provides a clear insight to understand the design principle of organic positive electrodes. A novel dual-electron-withdrawing group organic molecule with high energy density for Al batteries is obtained.

Automated summary

In this work, novel dual-electron-withdrawing group organic molecules are proposed as positive electrode materials of Al batteries. By introducing electron-withdrawing chloride groups and decreasing the benzene ring number, discharge voltage and conductivity of organic molecules are effectively enhanced. However, the solubility in the ionic liquid electrolyte increases, leading to poor cycling stability. The charge/discharge mechanism is independent of the molecule structure and heterogeneous chloride groups. The obtained 2Cl-NQ exhibits high energy density and stable discharge voltage.