Thiophene-functionalized porphyrin complexes as high performance electrodes for sodium ion batteries

Organic sodium-ion batteries (OSIBs) using eco-friendly organic materials as electrodes have recently received much attention. However, the practical applications of OSIBs are generally limited by the inherent disadvantages of organic electrodes, such as their low conductivity, poor stability, and high solubility in electrolytes. Herein, we presented 5, 10, 15, 20-tetrathienylporphinato M (II) (MTTP, M=2H, Ni) as new electrode materials in sodium-organic batteries. The incorporation of thiophene functionalized groups and nickel (Ⅱ) ion in the molecular design of porphyrins enabled stable and excellent electrochemical performance in sodium storage systems. Benefiting from multiple charge storage sites and bipolar characteristics, the NiTTP anode has a reversible capacity of 434 mAh g^-1 at a current density of 25 mA g^-1. An excellent long-term cycling stability and high average voltage were obtained when NiTTP was used as a cathode. In a symmetrical battery, where NiTTP was used as both cathode and anode materials, a high average voltage of 2.3 V and a practical energy density of 93 Wh kg^-1 was achieved. These results suggest that the thiophene-based porphyrin derivatives would be promising electrode materials for long-term organic sodium ion batteries for green and stable energy storage.