Finding the Perfect Match: Investigation of 1,2-Diketone-Based Materials for Use as Cathode Active Material in...

Motivated by the high capacity and energy enabled by the two-electron donation of earth-abundant magnesium, we developed a novel, generally applicable screening method to evaluate 1,2-diketone-based redox units as n-type cathode active materials (CAMs) for rechargeable magnesium batteries (RMBs). Preliminary DFT calculations (redox potentials, charge density mapping) and cyclic voltammetry in supporting and magnesium electrolyte solutions were used to screen exemplary diketone classes, eliminating unsuitable candidates and identifying phenanthrenequinone (PNQ) as the most promising redox unit for incorporation into a vinylic polymer. Non-conjugated PNQ-based vinylic polymers were successfully synthesized, characterized, and tested as CAMs at the coin-cell level. Non-optimized Mg-PNQ cells delivered a starting capacity of up to 77 mAh g^-1, two high-voltage discharge plateaus at 2.2 and 1.7 V vs. Mg^{2 +}/Mg, and capacity retentions of 65% after 50 cycles and 50% after 100 cycles, typical for Mg-quinone systems. A novel electrolyte, [Mg₂(Ohfip)₃][Al(Ohfip)₄] in DME, further improved performance to 91 mAh g^-1 with 72% retention after 50 cycles. These results demonstrate that the presented screening methodology efficiently identifies suitable CAM candidates within broad substance classes and is readily transferable to further materials.