Melt Diffusion Assisted Performance Enhancement of Organic Cathode Materials for Zinc-Ion Batteries

Aqueous zinc-ion batteries present safer and sustainable alternatives to lithium-ion batteries. Organic cathode materials have been extensively explored in place of inorganic oxide cathode materials due to the strong electrostatic interaction of Zn2+ with oxides. However, organic cathode materials generally exhibit solubility in the electrolyte with cycling leading to capacity decay. To address it, we proposed a melt-diffusion-based electrode engineering technique to infuse the organic molecule into the carbon pores, imparting better conductivity and capacity as the infused molecules strongly interact (through π–π interactions) with the graphitic carbon matrix. To demonstrate the efficiency of this process, 2,7-ditertbutylpyrene-4,5,9,10-tetraone (DTB-PTO) and 2,11-ditertbutylquinoxalino[2′,3′:9,10]phenanthro[4,5-abc]-phenazine (DTB-QPP) were explored. The electrode with melt-diffused DTB-PTO and DTB-QPP gave specific capacities of 110 and 120 mAh g–1, respectively, at a current density of 500 mA g–1, while the hand-mixed slurry only gave respective capacities of 95 and 45 mAh g–1. The difference in capacity between hand mixing and melt-diffusion is higher in the case of DTB-QPP due to its extended conjugation and planarity compared to DTB-PTO, leading to an effective π–π stack with carbon.