Selection of Redox Mediators for Reactivating Dead Li in Lithium Metal Batteries

Li metal batteries have suffered from dendrite growth and its derived dead Li formation for a long time. A new lithium restoration method through the shuttling of redox mediators has been proposed recently. However, the side reaction of severe self-discharge often occurs when some redox mediators are used. Here, a selection principle of redox mediators for reactivating dead Li in lithium metal batteries is put forward, which is able to reactivate the dead Li effectively and reduce the self-discharge at the same time. Three redox mediators of ferrocene (Fc), 10-methylphenothiazine (MPT), and thianthrene (Th) with different redox potentials are tested in LiFePO4|Cu anode-free Li metal batteries to clarify the selection principle. Furthermore, 2,2,6,6-tetramethylpiperidinooxy (TEMPO), which is speculated to be a suitable one for reactivating dead Li in lithium metal batteries, is verified. This work provides a universal selection principle of redox mediators and may boost its practical application in Li metal batteries.