COPOLIBAT

This project aims at improving the performances of lithium and lithium ion batteries in terms of power and energy density, safety and battery design facility thanks to a new generation of solid state electrolytes based on self-organised block copolymers. Our project aims to by-pass the major drawback of the classical polymer electrolytes (mechanical strength and conductivity generally vary in opposite manner), by taking benefit of the self-organization of the block copolymers into ordered nanostructures with sizes in 10–100 nm range, which is determined by the molecular size of the blocks. Various organisations are achieved depending on both the interaction between blocks and their relative volume ratio. The micro-domains formed can be spheres, cylinders, bi-continuous (gyroid), perforated layers, and lamella. The interfaces between the micro-domains engender solid-like mechanical properties, even if each block component is well above its glass transition temperatures (Tg), while locally within each domain the polymer chain mobility remains high. When one block is a lithium salt solvating polymer, the block copolymer electrolytes formed behave mechanically like a solid but still possess high ionic conductivity. The originality of our project is to propose nano-textured BAB symmetric triblock copolymers as solid state electrolytes for lithium battery operation at room temperature. This block copolymer consists of two chemically dissimilar chains or ‘‘blocks’’: A block solvating the lithium salt brings a high ionic conductivity, while B block gives the mechanical properties as well as the thermal stability. The choice of blocks chemistry is very very wide, opening opportunities for the creation of new multi-functional materials. Our strategy is to play on the relative volume fraction of the A and B blocks and on their interaction in order to direct the self-organisation into hexagonal packed cylinders or gyroid micro-domains of the conducting block. In addition, the attachment of at least part of the anions to one block will guarantee that the Li+ concentration never goes to 0 during operation. The roadmap to a practical solution for a room-temperature operating solid state polymer electrolyte which we propose here, needs fundamental research steps in which we want to innovate, notably by studying the relationship between block copolymer self organisation and ionic charge transport mechanism or dendritic growth mitigation.