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

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⁺/Mg²⁺/Ca²⁺), 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 SO₄ ^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.