Addressing the challenges of high-capacity electrodes for lithium batteries through coordination chemistry

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Due to their high theoretical capacities, low cost and low toxicity, silicon and sulfur are very promising active materials for lithium batteries. However, their commercial use is hampered by their insufficient cyclability. Despite its small proportion of the total electrode material (usually less than 10 wt.%), the binder plays a key role in the electrode performance since it ensures the cohesion of the electrode constituents (active material and conducting agent), as well as their adhesion to the current collector, both during the electrode preparation and under cycling conditions. Notably, in the case of Si and S electrodes, the binder should mitigate the very large electrode volume variation associated with the respective formation of LixSi and LixS without significant delamination, cracking and collapsing, which lead to the electronic wiring loss of the active mass, resulting in a large capacity fading with cycling.  In this research program, the opportunities offered by coordination chemistry to tackle these challenges will be evaluated. More precisely, the characteristics of the coordination bonds, notably their tunability and dynamic character, will be exploited to offer alternative paths for developing advanced binders likely to significantly improve the electrochemical performance of Si-based negative electrodes for Li-ion batteries and S-based positive electrodes for Li metal batteries. Considering the variety of coordination motifs available, there is clearly room for drastically modulating the properties of the binder and for enlarging the scope of accessible ecofriendly binders for advanced battery technologies. Especially, the ability of many functional groups present in polar binders to bind to metallic cations, in order to induce an ionic crosslinking of the binder polymer chains, will be studied. Such a coordination network is prone to deform, but also to recover its initial state easily, eventually inducing self-healing properties in the electrode. Additionally, cross-linked binders may assist in the formation of a more stable solid electrolyte interphase (SEI) layer at the surface of the Si active material or may favour the retention of the electrolyte-soluble polysulfide intermediates in the S cathode. In order to correlate the coordination state of the binder to the morphological, mechanical and electrochemical properties of the Si and S based battery electrodes, a significant part of the research program will be devoted to the development of a large panel of complementary in-situ/operando characterization methods. The proposed research program will strengthen Canada's expertise in the field of battery technologies and will provide a fertile ground for the training of highly qualified personnel urgently needed for developing green energy storage technologies in Canada.