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

Abstract

AbstractSmall‐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.