Beyond Metal‐Air Chemistry: Coupling n‐/p‐Type Organic Redox Chemistry Toward Sustainable Sub‐Zero‐Temperature All‐Polymer Seawater Batteries

Abstract Developing high‐efficiency durable rechargeable seawater battery (RSB) that directly harnesses natural seawater for sustainable energy storage is an attractive yet challenging task. Rather than use traditional metal‐air chemistry, for the first time it proposes a coupled n‐type/p‐type redox chemistry to establish a new all‐polymer RSB (APRSB) with high energy efficiency and long cycle lifespan even at subzero temperature. The strategy involves rational design of n‐type redox polyimide (NDIP) and p‐type redox radical polymer (RRP). By using flexible triamine linker to crosslink naphthalenetetracarboxylic dianhydride (NTCDA) molecules to tune aggregate structures, the newly‐produced NDIP attains consistent high storage capacity for multiple cations (Na ⁺ /K ⁺ /Mg ²⁺ /Ca ²⁺ ), enabling seawater‐adaptable low‐potential anodes with fast redox kinetics and large specific capacity along with long lifespan over 10 000 cycles—superior to most previous electrodes in seawater. By exerting inherent advantages of radicals, RRP is explored as seawater‐suitable well‐matched high‐potential cathodes, integrating facile redox property and superior adaptability with SO ₄ ²⁻ and even the corrosive Cl ⁻ . Thus, paring NDIP and RRP yields APRSB with high output voltage, large energy efficiency (81%), and 83.2% capacity retention after 800 cycles even at −4 °C—outperforming most previous room‐temperature seawater batteries. Detailed studies reveal facilitated organic redox kinetics in seawater resistive against low temperature.