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

Abstract 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 LiFePO 4 |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.