Poly(N-vinylcarbazole) as an advanced organic cathode for potassium-ion-based dual-ion battery

Owing to the unique redox reaction and the relative low molar mass of the repeating unit, poly(N-vinylcarbazole) (PVK) was selected as an advanced organic cathode for potassium-ion-based dual-ion battery (PDIB) with the K foil anode and KPF6-based electrolyte. The operation mechanism of this PDIB is that PF6− anions are migrated from the electrolyte and incorporated into PVK cathode via the attraction to the positively charged N atom of carbazole ligand, and then are released into the electrolyte in the subsequent discharge process; simultaneously, K+ cations are reversibly stored/removed in/from the anode during charging/discharging. It shows a high median operation potential of 4.05 V vs. K+/K and can achieve a high specific capacity of 117 mAh g−1 at 20 mA g−1, which is close to its theoretical value of 138 mAh g−1. More impressively, even at the highest current density of 2000 mA g−1 for 500 cycles, a high average specific capacity of 61 mAh g−1 can still be obtained with capacity rentation of 55%.