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.