(549h) Rechargeable Al-CO2 Battery Enabled By a Homogeneous Redox Mediator with Ultra-Low Overpotential

Metal-CO₂ batteries have emerged as a promising strategy to improve energy storage technology while capturing/concentrating carbon dioxide. The Al-CO₂ battery has been previously demonstrated as a primary battery to have an excellent discharge capacity when a small amount of oxygen is introduced. Herein we demonstrate an Al-CO₂ battery that uses a homogeneous iodine-based redox mediator to enable the reversible discharge and recharge of the battery with an ultra-low overpotential of 0.05 V. By replacing oxygen gas with aluminum iodide in the electrolyte of the previously primary-only configuration, the battery maintains a high discharge capacity and can be recharged for 12 cycles at 20 mA/g_carbon. Without any additive the battery shows a negligible discharge capacity of 0.03 mAh/gwhen discharged at 20 mA/g to 0.5 V, which is increased to 3,557 mAh/g when aluminum iodide is introduced. The capacity enhancement is present at a very low aluminum iodide concentration of 0.05 M and shows low concentration dependence, indicating that the enhancement is due to a catalytic mechanism. The aluminum iodide additive also reduces stripping/plating overpotentials by 40% across a range of current rates compared to an unmodified imidazolium-based ionic liquid electrolyte. As shown in Figure 1, SEM imaging of battery cathodes with and without aluminum iodide after discharge and charge show that the control battery without aluminum iodide does not form significant discharge product after discharge, and the discharge product remains after recharge. In contrast, the battery with added aluminum iodide shows significant discharge product formation after discharge, and that discharge product almost entirely degrades after recharge. ²⁷Al NMR spectra and TGA analysis of the discharge product confirm the discharge product to be aluminum oxalate. Our work has successfully demonstrated a proof-of-concept rechargeable Al-CO₂ battery that can be applied to cost-effective energy storage while capturing and concentrating carbon dioxide.