Use of a Porous Phenanthrenequinone Polymer-Based Cathode in Mg-Ion Batteries

Rechargeable magnesium-ion batteries (RMIBs) are a promising alternative to lithium-ion batteries for their better volumetric capacity, 3833 mA h cm–3. The bottleneck in the development of RMIBs is an ideal cathode with a matching electrolyte. In this paper, we suggest a highly porous organic material, phenanthrenequinone-based microporous conjugated polymer (PMCP), as an ideal cathode material for Mg-ion batteries. Density functional theory calculations confirm the stability of this porous material with strong affinities for Mg ions at C═O sites. A single monomer of PMCP can accommodate up to four Mg ions having a specific theoretical capacity of 157.05 mA h g–1 and a positive redox potential of 1.37 V. No geometrical distortion and a significant decrease in band gap with the adsorption of Mg ions reveal better cycling performance. Furthermore, the smaller energy barrier for Mg ion movement in the PMCP pores demonstrates a rapid charging/discharging phenomenon. The electrolytes (anthracene/diglyme and MgCl2) improve the electrochemical performance of PMCP by enhancing the cell voltage, i.e., 3.49 V for MgCl2 and 2.86 V for the anthracene–diglyme electrolyte. This theoretical study suggests that PMCP is an ideal cathode material for RMIBs and needs further theoretical and experimental studies for its technological applications.