Optimization of Block Copolymer Electrolytes for Lithium Metal Batteries

Safety is one of the most important criteria for electrochemical energy storage devices used in large scale applications such as wind or solar farms. In this context, solid polymer electrolytes based on nanostructured block copolymer electrolytes (BCEs) are promising because their properties can be finely tuned by adjusting simultaneously their block chemistries and polymer architectures. However, there is a need to rationalize the different properties of BCE that are optimal for battery applications. We produced by controlled radical polymerization a large number of BCEs based on either (1) linear poly(ethylene oxide) (PEO) or (2) comb PEO as the ionic conductor block, and polystyrene as the structural block. We varied the molecular weight of the PEO-based block, the composition, and the architecture (diblock vs triblock). We performed a systematic analysis of their thermodynamic, ionic transport, and mechanical properties. To verify the potential of BCEs as electrolytes, we evaluated their electrochemical stabilities. Laboratory scale batteries comprising the best BCEs and LiFePO4 as a positive active material were cycled at different rates and temperatures. This process allows the selection of the best architectures and compositions that had been successfully tested in battery prototypes and cycled for more than 600 cycles at high rates without any dendritic growth.