Single Bipolar Polymer Electrode with MXene for Na/K‐Based Dual‐Ion Symmetric Batteries

Abstract An organic bipolar polymer electrode called poly[anthraquinone‐alt‐dihydrophenazine] (PAD) is in situ synthesized between the two‐electron n‐type unit of dibromoanthraquinone and two‐electron p‐type unit of dihydrophenazine on the layered MXene nanosheets, leading to the formation of the material composition called PAD@MX. PAD@MX shows almost the same redox mechanism and electrode performance in Na/K‐based batteries. In Na/K‐based half cells, PAD@MX can show the peak discharge capacities of 240/255 mAh g⁻¹ and peak energy densities of 511/597 Wh kg⁻¹, respectively, which are among the top results for cathodes in the world. Furthermore, the Na/K‐based dual‐ion symmetric batteries can be simultaneously constructed by using PAD@MX as the single electrode material. Both symmetric batteries fulfill the “ready‐to‐charge” property without any pre‐activation. Therein, PAD@MX delivers the reversible discharge capacities of 86/104 mAh g⁻¹_cathode and energy densities of 54/64 Wh kg⁻¹_{total mass}, stably running for 500 cycles. To the best of our knowledge, this is the first example of organic bipolar electrodes simultaneously applied to the Na/K‐based dual‐ion symmetric batteries in the world.