A Small-Molecule Organic Cathode with Extended Conjugation toward Enhancing Na⁺ Migration Kinetics for Advanced Sodium-Ion Batteries

Organic cathode materials show excellent prospects for sodium-ion batteries (SIBs) owing to their high theoretical capacity. However, the high solubility and low electrical conductivity of organic compounds result in inferior cycle stability and rate performance. Herein, an extended conjugated organic small molecule is reported that combines electroactive quinone with piperazine by the structural designability of organic materials, 2,3,7,8-tetraamino-5,10-dihydrophenazine-1,4,6,9-tetraone (TDT). Through intermolecular condensation reaction, many redox-active groups C=O and extended conjugated structures are introduced without sacrificing the specific capacity, which ensures the high capacity of the electrode and enhances rate performance. The abundant NH2 groups can form intermolecular hydrogen bonds with the C=O groups to enhance the intermolecular interactions, resulting in lower solubility and higher stability. The TDT cathode delivers a high initial capacity of 293 mAh g(-1) at 500 mA g(-1) and maintains 90 mAh g(-1) at an extremely high current density of 70 A g(-1). The TDT || Na-intercalated hard carbon (Na-HC) full cells provide an average capacity of 210 mAh g(-1) during 100 cycles at 500 mA g(-1) and deliver a capacity of 120 mAh g(-1) at 8 A g(-1).