Self-Carbonation of Soluble Organic Cathodes for Highly Efficient Potassium-Ion Batteries

Small-molecule organic cathodes face dissolution problem in potassium-ion batteries (PIBs). For the first time, an interesting and effective strategy is unveiled to resolve this trouble 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 the amorphous carbon with the 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 behaviors 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% to 35% of NTCDI-DAQ during 30 cycles under the same conditions. In the full cells with KC8 anode, NTCDI-DAQ@C delivers a peak discharge capacity of 236 mAh g-1cathode and a high energy density of 255 Wh kg-1cathode in 0.1-2.8 V, maintaining 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 the best one among the soluble organic cathodes reported in PIBs.