Small-Molecule Organic Cathodes with Carbon Coating for Highly Efficient Potassium-ion Batteries

Small-molecule organic cathodes face dissolution in potassium-ion batteries (PIBs). For the first time, an interesting and effective strategy is unveiled to resolve this issue by designing a new soluble small-molecule organic compound namely [N,N'-bis(2-anthraquinone)]-1,4,5,8-naphthalenetetracarboxdiimide (NTCDI-DAQ, 237 mAh g^-1 ): Through the precise manipulation of carbonization temperature and time, the molecules on the surface of NTCDI-DAQ particles can be transformed into amorphous carbon with controllable thickness. This strategy called surface self-carbonization can form a carbon protective layer on organic cathodes and significantly increase their insolubility against liquid electrolytes without affecting the electrochemical behavior of bulk particles. As a result, the as-obtained NTCDI-DAQ@C sample displays significantly improved cathode performance in PIBs. In half cells, NTCDI-DAQ@C shows superior capacity stability of 84 % compared to 35 % of NTCDI-DAQ during 30 cycles under the same conditions. In full cells with a KC₈ anode, NTCDI-DAQ@C delivers a peak discharge capacity of 236 mAh g^-1 cathode and a high energy density of 255 Wh kg^-1 cathode in 0.1-2.8 V, with 40 % capacity retention during 3000 cycles at 1 A g^-1 . To the best of our knowledge, the integrated performance of NTCDI-DAQ@C is among the best of soluble organic cathodes reported in PIBs.