Abstract:
Among the various electrochemical storage systems, lithium-ion batteries (LIBs) appear as a flagship technology able to power an increasing range of applications because of their high energy density values. Consequently, the world production of LIBs is expected to keep on growing. However, faced with a production of several billion a year one has also to consider their environmental burden from "cradle-to-grave" like other goods. A main brake in making "greener" batteries is probably related to the chemistry used itself, which is typically based on non-renewable redox-active inorganic components. In this context, a possible parallel research to inorganic-based batteries consists in developing organic electrode materials. Basically, organic materials are composed of quite naturally abundant chemical elements (C, H, N, O, in particular) giving them the true possibility of being prepared from renewable resources and eco-friendly processes coupled with a simplified recycling management. Nevertheless, in practice, the development of efficient organic electrodes is clearly in its early stages, and much remains to be done. One significant issue of organic electrode materials is their tendency to dissolve in common liquid electrolytes used in batteries, which automatically ruins the cyclability of a promising redox-active species. Another limitation lies in the difficulty in finding robust lithiated organic cathode materials capable of being reversibly delithiated (charged) at a high enough potential, similar to that of common inorganic insertion compounds.
In this context, pi-conjugated enolate/C=O-based structures appear as highly interesting since the redox system is most often reversible whereas the dissolution phenomenon can be suppressed thanks to chemical tricks. For the past few years, we have been revisiting selected organic structures and we created a reliable experimental database of model chemical structures. Robust organic electrode materials able to react at both high and low potentials vs. Li have been identified and synthesized. The challenge is now the fabrication of efficient all-organic Li-ion cells.
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