Ultra-long cycle life organic-sodium batteries enabled by thiophene-based porphyrin in-situ electropolymerization

• Thiophene functionalized porphyrin is proposed as new cathode for organic-sodium batteries. • In-situ polymerization strategy renders excellent cycling stability (11000 cycles). • High energy (508 Wh kg -1 ) and power density (18 KW kg -1 ) are achieved as well. • Nitrogen and Sulfur atoms are active sites for charge storage. Organic-sodium batteries have attracted extensive attention due to the abundance of sodium resource and the molecular tunability of organic materials. However, the dissolution of organic materials in electrolytes and low electronic conductivity limit its development. Here, a porphyrin complex of [5,15-di(thiophen-2-yl) porphinato] M(II) (MTP, M=Cu, Ni) is proposed as highly stable cathode material for organic-sodium batteries. Benefiting from the multiple electron transfer of metal porphyrin complex and in-situ polymerization of thiophene groups of porphyrin complex in initial cycles, the CuTP cathode delivers a reversible capacity of 203 mAh g -1 at 100 mA g -1 and long-term cycling stability up to 11000 cycles at a high current density of 5 A g -1 owing to the enhanced conjugated structure induced by in situ polymerization process. A specific energy density of 508 Wh kg -1 and a power density of 18 KW kg -1 are achieved for metal porphyrin-based cathode. The charge storage sites and in-situ polymerization mechanism of MTP cathode are systematically evaluated by both experimental and simulated studies. This study would provide a new strategy to address the dissolution issue of organic cathode and improve cycling stability of the organic-sodium batteries.