Monitoring the Electrochemical Energy Storage Processes of an Organic Full Rechargeable Battery via Operando Raman Spectroscopy: A Mechanistic Study

摘要

The green, sustainable, and versatile nature of using organic compounds that can be derived from biomass makes them extremely interesting materials for use in various rechargeable batteries. However, the overall electrochemical reaction mechanism of an organic full rechargeable battery has seldom been reported because of the lack of straightforward and accessible analytical techniques that capable of probing the rechargeable battery system in real time. Herein, we configured an organic full rechargeable battery composed of a porphyrin metal complex [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP) anode, a graphite cathode, and a 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide (PP14TFSI) ionic liquid electrolyte. Operando Raman spectroscopy was employed to simultaneously monitor the evolution of Raman bands from the anode, cathode, and electrolyte of the battery caused by electrochemical energy storage (EES) processes. It was found that during EES processes, the electronic structural changes of the CuDEPP anode mainly occurred at the porphyrin ring and ethynyl substituent rather than at the Cu(II) metal center and benzene substituent, followed by interactions with PP14(+) cations of the electrolyte. Also, complementary density functional theory (DFT) calculations on the anode redox reaction mechanism were performed and support the spectroscopic results. Meanwhile, during EES processes at the cathode, TFSI- anions intercalated into/deintercalated out of the graphite cathode, which resulted in the appearance and disappearance of a G' spectral band at 1610 cm(-1). Our findings suggest the conjugated porphyrin ring and ethynyl substituent of the organic anode have a beneficial redox effect that supports charge-discharge cycling and reveals the interactions between the electrodes and electrolytes for the better design of organic EES devices.