A bipolar organic molecule toward a universal pseudocapacitive cathode for stable dual ion charge storage

Organic molecules are promising electrode materials for green and sustainable rechargeable electrochemical energy storage due to their tunable theoretical capacity and environmental friendliness. However, the commercialization of organic electrode materials is impeded by high solubility in electrolytes and inherently low electronic conductivity. Herein, a series of bipolar organic molecules, [5,10,15,20-tetra(ethynyl)porphinato] M(II) (MTEPP, M= Cu, Zn, Mg, 2H), is proposed as new cathode for highly stable dual ion charge storage. The stacking property of the porphyrin molecules is significantly influenced by complex ions and the mixed valence state of cation (Cu+ and Cu2+) renders better charge storage performance in functionalized porphyrin cathode. Reversible capacity of 219 mAh g−1 is obtained for CuTEPP cathode based on a four-electrons transfer and it can be stably cycled up to 1000 times in lithium based organic batteries. Ex-situ spectroscopies as well as simulation studies evidence the multiple electron transfer and the charge storage sites. Highly reversible capability (> 160 mAh g−1) and stable cyclability (> 300 cycles) is also achieved as cathode in both sodium and potassium based organic cells. This study offers a new approach for developing ultrastable and universal organic cathode for electrochemical energy storage.