(Invited) Searching for High Potential Organic Cathode Materials for High Energy Green and Sustainable Batteries

Abstract

Thanks to the use of abundant chemical elements, organic chemistry provides great opportunities for discovering innovative electrode materials, which could be prepared (i) from renewable resources (biomass) and (ii) via eco-efficient processes, making the concept of greener and sustainable batteries possible [1]. We are putting a lot of efforts on greener and sustainable organic non-aqueous and aqueous batteries at the IMN. In this communication, we report on novel crystallized organic positive electrode materials for the non-aqueous application of organic batteries. However the synthesis of high-voltage lithiated materials is rather challenging, so very few examples of all-organic Li-ion cells currently exist. Compounds of the Mn+ 2/n-p-DHT (with Mn+ = Li+, Mg2+, Ca2+ and Ba2+) family were studied to better understand the effect of substitution chemistry on the redox properties of the Li-diphenolate cycle of p-DHT. This innovative chemical approach makes it possible to tune the redox potential of lithiated organic electrode materials, by playing on the nature and the ionic potential of a spectator cation in the host structure. Indeed, by adjusting the attractor/donor electron effects in the organic redox-active backbone, it is possible to modify the redox potential of the molecule by inductive effect. We show that substituting magnesium (2,5-dilithium-oxy)-terephthalate for lithium (2,5-dilithium-oxy)-terephthalate enables an outstanding voltage gain of 800 mV, leading to a high operating voltage of 3.4V vs. Li+/Li [2]. This Mg(Li2)-p-DHT compound is the first lithiated organic positive electrode material with an operating potential as high as that of LiFePO4. Based on this finding, full organic Li-ion cells with an output voltage of 2.5V and long cycle life have been achieved, thus making a big step forward the design of high energy green and sustainable organic batteries.