Sulfur-Mediated Charge Delocalization Enables High-Voltage p-Type Polymer Cathodes for Ultralow-Temperature Potassium Dual-Ion Full Cells.

Abstract

High-voltage organic cathodes based on nitrogen-rich aromatic systems have been widely explored for sustainable potassium dual-ion batteries, yet their practical application remains hindered by insufficient redox potential, poor structural stability, and sluggish kinetics under extreme conditions. Here, we establish sulfur-mediated charge delocalization as a design strategy to overcome these fundamental limitations. By strategically incorporating electron-delocalizing sulfur atoms into the phenazine framework, we achieve extended π-conjugation and efficient delocalization of charges and electrons, thereby enhancing electronic conductivity and elevating the redox potential. Specifically, we develop a sulfur-substituted p-type conjugated polymer, poly[10-methyl-3-(phenazin-5(10H)-yl)-10H-phenothiazine] (P(PhTz)), as a model system to realize this concept. P(PhTz) exhibits an average discharge potential of 3.70 V (vs. K⁺/K), a specific capacity of 176 mAh g^-1, and rate capability up to 20C, outperforming its nitrogen-only analogue poly[5-phenyl-5,10-dihydrophenazine] (PPZ). When paired with a hard carbon anode, the full cell delivers a high specific capacity of 162 mAh g^-1 at a 3.55 V average discharge voltage, with stable cycling over 1300 cycles. Crucially, the full cell operates efficiently at -40°C, retaining 87% capacity retention after 850 cycles and achieving an energy density of 434 Wh kg^-1, which represents the highest reported energy density for potassium-ion full cells under low-temperature conditions.