Abstract
To promote low emission electrochemical energy storage systems, a possible alternative consists in partially moving away from inorganic-based to organic-based redox-active electrode materials. Indeed, organic molecules present the advantage to be easily synthesized from abundant raw materials coupled with the real possibility of being derived from renewable resources (biomass). To that extent, the topic is focused on the identification and the development of redox-active organic materials able of being charged at high potentials and being discharged at low potentials for positive and negative electrode applications, with the aim of developing an "all-organic" Li-ion battery able to deliver a working voltage of at least 2 V. A molecular engineering approach has been applied to tune the electrochemical performances in particular the redox potential. Firstly, electron-withdrawing substituents (sulfonates) have been incorporated on lithiated enolate-based backbones offering lithium reservoir organic materials stable to oxygen, particularly the Li4-p-DHBDS (3,25 V vs. Li+/Li). Secondly, electron-donating substituents with inductive effect (+I) such as methyle and alkyne, and others with mesomeric effect (+M) such as amine, methoxide and bromine have been incorporated on carboxylate structures (terephthalate). It was found that substituents with inductive donating effect (+I) are quite interesting to lower the redox potential as observed with Li2-DMT (0,72 V vs. Li+/Li ; i.e, -110 mV in comparison with the lithium terephthalate). The work concluded with a preliminary test of an "all-organic-rocking-chair" battery operating at an average working voltage close to 2,5 V