Thiophene functionalized porphyrin complexes as novel bipolar organic cathodes with high energy density and long cycle life

Abstract

The low intrinsic electrical conductivity, low specific capacity, and high solubility of organic electrode materials have significantly plagued its practical application in electrochemical energy storage systems. Herein, bipolar organic molecules combining porphyrin and thiophene functional groups, [5, 15-bis-(ethynyl)-10, 20-dithienylporphinato]M(II), (M= Cu, Zn, Co, and 2H) are proposed as new cathodes. Thiophene groups and nitrogen atoms act as active sites affording 8 electrons transfer during redox reaction which strongly interact with both cations (Li+) and anions (PF6−), enabling high charge storage capability and fast kinetic. When CuDETP is used in organic lithium batteries, it delivers a reversible capacity of 350 mAh g − 1 at 100 mA g − 1 and a high specific energy density of 773.6 Wh kg−1 (based on the cathode material). Meanwhile, extremely stable cyclability up to 9000 cycles is achieved owing to the self-polymerziation during initial charging process. This investigation has great enlightenment for the molecular design and application of organic electrodes in terms of both high energy densities and long cycling life.