Towards High-Capacity Recovery Aprotic Li-O2 Batteries

Abstract

Lithium-oxygen batteries (LOBs) have great potential as energy storage systems to accelerate the energy transition, due to their high theoretical energy density (up to 3505 Wh/kg), coupled to their low cost and environmental impact (transition metal free) [1]. The development of reversible Li-O2 batteries relies on the optimization of multiple interconnected factors, such as complex interactions affecting the activity of redox mediators (RM) [2-4]. Amongst these, the cycling protocols, electrolyte composition, and electrode structure are of crucial importance to achieve high capacity recovery, and thus reversibility [1, 5].Here, we study the interconnectivity of these factors, testing a range of electrode/electrolyte combinations using different cycling protocols to evaluate the capacity recovery, overpotentials, and lifetime of Li-O2 cells. Typically in the Li-O2 literature, constant current (CC) discharge-charge cycles are used to evaluate the performance of cells [1]. However, the slow OER kinetics, especially at the end of charge, make the use of CC protocols problematic, as increased overpotentials are required to meet the current demands (Figure top). Constant current – constant voltage (CCCV) protocols are more suitable to evaluate this technology, as they enable higher capacity recovery upon charging, while keeping the cells at potentials in which the parasitic reactions can be managed.Our results show significant increased capacity retention while keeping the charge limited to various upper cut-off potentials in cells without RM (Figure bottom). Cells with LiI as RM can recover 100% of the discharge capacity at relatively low potentials (3.5-3.7 V), providing longer cycle life than without RM or CC protocols. Furthermore, the influence of the structure in graphene-containing electrodes to the capacity recovery and lifetime is also explored with regards to the kinetics of the ORR and OER reactions.This study demonstrates how the interplay between cycling protocols, electrolyte composition and electrode structure affects the reversibility, and highlights the need for a comprehensive approach for developing reversible non-aqueous Li-O2 batteries. Gao, Z., et al., Recent Progress in Developing a LiOH-based Reversible Nonaqueous Lithium-Air Battery. Advanced Materials, 2023. 35: p. 2201384.Jónsson, E., et al., On the Solvation of Redox Mediators and Implications for their Reactivity in Li-Air Batteries. Journal of The Electrochemical Society, 2021. 168(3): p. 030529.Liu, T., et al., Understanding LiOH Formation in a Li-O2 Battery with LiI and H2O Additives. ACS Catalysis, 2018. 9: p. 66-77.Temprano, I., et al., Toward Reversible and Moisture-Tolerant Aprotic Lithium-Air Batteries. Joule, 2020. 4: p. 1-20.Liu, T., et al., Current Challenges and Routes Forward for Nonaqueous Lithium-Air Batteries. Chem Rev, 2020. 120(14): p. 6558-6625. Figure 1