Electrification relies in part on the massive development of batteries that use electrode materials based on metals that are often rare and costly. A Franco-German team of scientists proposes a promising alternative to these materials: organic materials based on hydrogen, carbon, oxygen and nitrogen for the development of purely molecular batteries that are cheaper and more environmentally friendly. A study to be found in ACS Applied Polymer Materials.
Current lithium-ion batteries rely heavily on the use of critical, sometimes toxic metals, whose extraction and recycling pose environmental and geopolitical problems. For several years, scientists have therefore been exploring alternatives such as organic batteries, made from molecules rich in carbon, hydrogen and nitrogen.
These materials have several advantages: a less energy-intensive synthesis starting from widely abundant resources, better recyclability, and above all great freedom in chemical design. They even open the way to entirely metal-free molecular batteries of the "anion-ion" type. However, a major challenge remains: identifying materials for the negative electrode capable of operating at low potential while maintaining their stability over charge and discharge cycles.
German scientists from the University of Ulm and French scientists from the Institut des matériaux de Nantes Jean Rouxel (CNRS/Nantes Université) focused on a family of molecules called "super-electron donors." These compounds, very rich in electrons, can easily donate them during electrochemical reactions.
The team has incorporated for the first time one of these chemical motifs, based on bi(benzimidazole), into several polymers intended to serve as negative electrodes for this type of anion-ion battery. Two of these materials showed particularly interesting behavior: they operate around 2.1 V vs Li+/Li, a remarkably low value for this type of organic polymer.
While the tested polymers demonstrated an ability to store and release electrical energy reversibly, their performance decreases after several cycles. The team proposes a clue to explain this phenomenon: during electrochemical reactions, the reduced molecules could temporarily transform into "carbenes," highly reactive chemical species capable of progressively damaging the material.
These results will guide future research to design more stable and efficient organic materials based on super-electron donors.
Nevertheless, the studied polymers show that it is possible to obtain materials operating at low voltage without resorting to metals. They also highlight the crucial importance of chemical stability. Future work will now need to design molecular architectures capable of preserving the electronic properties of bi(benzimidazole) while preventing the formation of these reactive species. An essential step before considering truly durable and competitive organic batteries.
Editor: AVR.