Understanding the Lithium Ion Transport in Concentrated Block–Copolymer Electrolytes on a Microscopic Level

High Resolution Image Download MS PowerPoint Slide Block–copolymer electrolytes with lamellar microstructure show promising results regarding ion transport in experiments. Motivated by these observations, we study block–copolymers consisting of a polystyrene (PS) block and a poly(ethylene oxide) (PEO) block, which were assembled in a lamellar structure. The lamella was doped with various amounts of lithium-bis(trifluoromethane)sulfonimide (LiTFSI) until very high loadings, with ratios of EO monomers to cations up to 1:1, were reached. We present insights into the structure and ion transport from extensive Molecular Dynamics simulations. For high salt concentrations, most cations are not coordinated by PEO but rather by TFSI anions and THF. More specifically, LiTFSI partially separates from the PEO domain and forms a network-like structure in the middle of the lamella. This central salt-rich layer plays a decisive role in enabling remarkably good cationic mobilities as well as high transport numbers, in agreement with the experimental results.