The selection of the electrolyte in Mg batteries introduces one key distinction compared to Li-based system -the possibility of presence of different ionic species in discharged polymer. In the chlorinated electrolyte, the coordination of reduced carbonyls was predominantly done with MgCl + ionic complexes, rather than Mg 2+ ions, in agreement with prior reports and confirmed by energy dispersive X-ray spectroscopy (EDX) (Table ). Conversely, in the non-chlorinated electrolyte, a large fraction of Mg 2+ was present, although ion pairs still partially participate in coordination as evidenced by the increased presence of fluorine in the discharge cathode. This shows that COF performance is governed by the choice of salt/solvent combination, with the effect of electrolyte being more pronounced in Mg batteries than in their lithium counterparts. This raises the challenge of designing COFs that would perform better when coupled with multivalent charge carriers. One of the strategies could be to design COFs with active units in which the position of carbonyl groups is tuned to help accommodate divalent cations. Changing the active unit from an anthraquinone-based one to a smaller unit such as benzoquinone could lead to higher potentials and ultimately higher energy densities, as has already been demonstrated in the case of COF cathodes in Li-based batteries. Potential improvements in COFs for Mg batteries could lead to readily available cathodes for other divalent batteries suffering from similar issues, such as Ca-based ones.