Improving charging processes in lithium-oxygen batteries by Spiro[fluorene-9,9′-xanthene]-based redox mediators/singlet oxygen scavengers: A photochemical and electrochemical study

Lithium-oxygen batteries hold great promise for high energy density applications, but their performance is often limited by high charge overpotentials and stability issues. This work evaluates two soluble spiro [fluorene-9,9′-xanthene] (SFX) derivatives as charge redox mediators and singlet oxygen scavengers to address these challenges. Electrochemical and photophysical analysis provided estimations of redox potentials and confirmed structural stability under typical operating conditions. Galvanostatic cycling tests showed reduced overpotentials during charging and improved surface passivation of cathode electrode, supported by EIS and SEM, respectively. The studied molecules exhibit excellent redox properties, high resistance to superoxide anions, and effective deactivation of singlet oxygen leading to enhanced battery cyclability (up to 135 cycles). These findings suggest that SFX molecules are efficient, stable, and sustainable redox mediators, representing a promising alternative to conventional mediators in lithium-oxygen batteries.