A multifunctional binder capable of harvesting light, electronic transport, and photocharging a lithium-ion photobattery

Abstract

The polymer binder in a lithium-ion battery (LIB) plays no electrochemical role, and as such, it is a dead mass. By incorporating functionality into the binder, its role could be expanded to actively participate in the LIB operation. The binder could become photo- and electroactive by incorporating photoresponsive and electronically conductive constitutional components into its structure. Such multifunctional binder was possible by preparing an alternating copolymer consisting of a perylenediimide dye and ethylene oxide. The copolymer was processed to play the role of a conventional binder according to thermal and structural analyses. Microstructural analysis of the composite electrode, complemented with galvanostatic cycling, confirmed the copolymer was suitable for use in a LIB and that it was electronically conductive. Ultraviolet photoemission and fluorescence spectroscopies combined with electrochemistry confirmed the electronic levels of the copolymer were compatible for sustaining photoinduced electron transfer from LiFePO₄ (LFP) to the excited polymer. The capacity of the binder to harvest sunlight and generate a current by oxidizing LFP in the battery was confirmed by both photocurrent and open-circuit voltage (OCV) measurements during periodic 1-Sun illumination. Systematically analyzing the photoelectrode by FT-IR after illumination provided additional proof that the battery converts and stores electricity from harvested sunlight.