Advances in Lithium–Oxygen Batteries Based on Lithium Hydroxide Formation and Decomposition

Tracing the impact of CO2 on the electrochemical and charge-discharge behavior for Al-Mg alloy in KOH and LiOH electrolytes for battery applications

For the first time, it has been found that the electrochemical performance of the Al-Mg alloy as an anode in alkaline batteries has been markedly enhanced in the presence of CO2 and LiOH as an electrolyte. This work compares the electrochemical performance of an Al-Mg alloy used as an anode in Al-air batteries in KOH and LiOH solutions, both with and without CO2. Potentiodynamic polarization (Tafel), charging-discharging (galvanostatic) experiments, and electrochemical impedance spectroscopy (EIS) are used. X-ray diffraction spectroscopy (XRD) and a scanning electron microscope (SEM) outfitted with an energetic-dispersive X-ray spectroscope (EDX) were utilized for the investigation of the products on the corroded surface of the electrode. Findings revealed that the examined electrode's density of corrosion current (icorr.) density in pure LiOH is significantly lower than in pure KOH (1 M). Nevertheless, in the two CO2-containing solutions investigated, icorr. significantly decreased. The corrosion rate of the examined alloy in the two studied basic solutions with and without CO2 drops in the following order: KOH > LiOH > KOH + CO2 > LiOH + CO2. The obtained results from galvanostatic charge-discharge measurements showed excellent performance of the battery in both LiOH and KOH containing CO2. The electrochemical findings and the XRD, SEM, and EDX results illustrations are in good accordance.

Insights into the LiI Redox Mediation in Aprotic Li-O2 Batteries: Solvation Effects and Singlet Oxygen Evolution

Lithium-oxygen aprotic batteries (aLOBs) are highly promising next-generation secondary batteries due to their high theoretical energy density. However, the practical implementation of these batteries is hindered by parasitic reactions that negatively impact their reversibility and cycle life. One of the challenges lies in the oxidation of Li2O2, which requires large overpotentials if not catalyzed. To address this issue, redox mediators (RMs) have been proposed to reduce the oxygen evolution reaction (OER) overpotentials. In this study, we focus on a lithium iodide RM and investigate its role on the degradation chemistry and the release of singlet oxygen in aLOBs, in different solvent environments. Specifically, we compare the impact of a polar solvent, dimethyl sulfoxide (DMSO), and a low polarity solvent, tetraglyme (G4). We demonstrate a strong interplay between solvation, degradation, and redox mediation in OER by LiI in aLOBs. The results show that LiI in DMSO-based electrolytes leads to extensive degradation and to 1O2 release, affecting the cell performance, while in G4-based electrolytes, the release of 1O2 appears to be suppressed, resulting in better cyclability.

Unravelling the Complex LiOH-Based Cathode Chemistry in Lithium-Oxygen Batteries

The LiOH-based cathode chemistry has demonstrated potential for high-energy Li-O₂ batteries. However, the understanding of such complex chemistry remains incomplete. Herein, we use the combined experimental methods with ab initio calculations to study LiOH chemistry. We provide a unified reaction mechanism for LiOH formation during discharge via net 4 e^- oxygen reduction, in which Li₂ O₂ acts as intermediate in low water-content electrolyte but LiHO₂ as intermediate in high water-content electrolyte. Besides, LiOH decomposes via 1 e^- oxidation during charge, generating surface-reactive hydroxyl species that degrade organic electrolytes and generate protons. These protons lead to early removal of LiOH, followed by a new high-potential charge plateau (1 e^- water oxidation). At following cycles, these accumulated protons lead to a new high-potential discharge plateau, corresponding to water formation. Our findings shed light on understanding of 4 e^- cathode chemistries in metal-air batteries.