Organic-Carbon Core-Shell Structure Promotes Cathode Performance for Na-Ion Batteries

The organic-carbon core-shell structure is constructed for the cathode material of [N,N'-bis(2-anthraquinone)]-perylene-3,4,9,10-tetracarboxydiimide (PTCDI-DAQ, 200 mAh g(-1)) through an interesting strategy called the surface self-carbonization. As expected, the organic-carbon core-shell structure (PTCDI-DAQ@C) can endow PTCDI-DAQ the outstanding cathode performance in Na-ion batteries. In half cells using 1 m NaPF6/DME, PTCDI-DAQ@C can maintain 173 mAh g(-1) for nearly one year, while PTCDI-DAQ quickly decreases from 203 to 121 mAh g(-1) only after 100 cycles. Meanwhile, the constructed Na-ion full cells with the Na-intercalated hard carbon anode can deliver the peak discharge capacity of 195 mAh g(cathode)(-1) and the high median voltage of 1.7 V in 0.9-3.2 V, corresponding to the peak energy densities of 332 Wh kg(cathode)(-1) and 184 Wh kg(total mass)(-1), respectively. Notably, the electrode materials only include the very cheap elements of C, H, O, N, and Na. Furthermore, the Na-ion full cells can also show the very impressive high-temperature (197 mAh g(cathode)(-1) at 50 degrees C) and subzero (185/90 mAh g(cathode)(-1) at -10/-40 degrees C) performances, respectively. To the best of the authors' knowledge, the comprehensive properties of the Na-ion full cells are the best results based on organic cathodes.