COPOLIBAT2

Electrochemical energy storage is one of the major societal challenges of this century. The performances of classical lithium–ion technology based on liquid electrolyte have made great strides in the past two decades, but the intrinsic instability of the liquid electrolyte results in safety issues. Solid polymer electrolyte would be a perfect solution to these safety issues. However, as in liquids, the fraction of charge carried by lithium ions is small (1000) and with a very limited dendritic growth. We have developed (in previous COPOLIBAT project) a multifunctional single-ion block copolymer electrolyte (BCE) comprising polystyrene segments with grafted lithium trifluoromethanesulfonylimide (TFSILi) (PSTFSILi) and a poly(ethylene oxide) (PEO) central block. It overcomes most of the above limitations, with a lithium ion transport number close to unity, excellent mechanical properties and an electrochemical stability window spanning now 5 V vs. Li+/Li. A prototype of battery using this new polyelectrolyte outperforms conventional batteries based on polymer electrolyte, notably offering very good performances at 60°C , . The project proposed here aims at extending our effort on these very promising families of BCEs and at building pre-industrial batteries demonstrators. Two main aspects will be studied to address the objectives of the project: 1- Decrease of the operation temperature, improvement of power performances, and prevention of dendritic growth: ? We intend to modify the PEO central block to disturb its stereo-regularity in order to keep it amorphous till room temperature, enabling battery operation at 40°C. Also in this direction, the plasticization with small amount of plasticizers will be studied. ? We want to design and develop new anionic monomers which would improve ionic dissociation and therefore ionic conduction. Furthermore, we want to analyze the impact of the position of the anions in the backbone (i.e. on lateral blocks or in the PEO block) on the physico-chemical properties and notably on the ionic transport. ? These BCE prevent the formation of concentration gradients during battery operation, which is very beneficial for power performances on the one hand and, on the other hand, should prevent the lithium dendrite nucleation, one of the crucial features for the success of a LMP. The lithium/polymer interface will be particularly studied to analyze the nature of the lithium electrodeposits during the recharge and to calculate the faradic efficiency. 2- Building a pre-industrial LMP demonstrator to qualify the new BCE in real operation: ? We will first build LMP using LiFePO4 as model positive active material starting with the copolymers developed in the previous COPOLIBAT project. During this step, the industrial process of extrusion will be used to shape the BCE in thin film, and a composite electrode will be formulated and extruded. Finally, pre-industrial batteries will be assembled and tested. This will enable direct comparison with the actual standard of the industrial partner. ? As the project proceeds, new BCEs will be available and directly used to build batteries based on the know-how acquired in the previous step. ? At last, due to the grafting of the anions, the new BCEs seem stable up to 5V vs Li+/Li, therefore LMP batteries will be also assembled using active materials with higher potential (4-4.2V vs Li+/Li).