Functionalized polysaccharides as Polymer binders in negative electrodes of Li-ion batteries – BIOLANT

Li-ion batteries are indispensable elements of our daily life, especially through our phones and laptops. To improve the capacities of these batteries, substitute part of the carbon graphite by silicon in the negative electrode is a promising way to improve their performance. The polymer binder is then, one of the essential constituents of this composite electrode. It helps to retain the capacity of the silicon by controlling the volume expansion during charge/discharge cycles. Various macromolecular parameters allow to obtain a stable electrode with good electrochemical performances. If the reference polymer remains carboxymethylcellulose, other polysaccharides have since been tested and showed very attractive binding properties. Unfortunately, these different studies did not lead to a sufficiently precise structure/property relationship to create the ideal polysaccharide for this application.
The objective of this project is to modify cellulose, in a very original way in the field of batteries, by simple chemical and enzymatic reactions: oxidation, esterification, amidation with lipophilic chains or cyclodextrins. The idea is to modulate their physico-chemical properties, hydrophilic/hydrophobic character in particular, and thus the interactions with the surface oxides of electrochemically active silicon. The contribution of enzymatic chemistry is relevant here with regard to the usual chemical reactions by being a much more specific, greener synthesis method, but also much less harmful to the macromolecular skeleton. One objective will thus be to determine the structural parameters conferring optimal binding properties to the polysaccharide. This will allow us to synthesize a cellulose based binder, not only bio-sourced by an innovative method but also inducing an excellent preservation of the cohesion of the silicon anode in the Li-ion battery.