Investigation into Durable Polymers with Enhanced Toughness and Elasticity for Application in Flexible Li-Ion Batteries

Next-generation wearable devices compel the development of lithium-ion batteries (LIBs) that can afford mechanical flexibility while remaining safe and stable energy sources. In conventional battery designs the electrode coatings are susceptible to fracture and disintegration when exposed to cyclic flexure. This results in capacity loss, resistance increases, and severely limits their cycle life. Polyurethane (PU) has been investigated as a battery binder but without research into the variety of chemistries available, and how they affect performance. This research investigates three different PU chemistries, each composed of a different polyol backbone–polyester, polyether and polycaprolactone. These are compared with PVDF, the most commonly used rigid binder in industry. The combination of electrochemical and mechanical characterization identified the importance of PU binder chemistry, particularly when the binder’s interaction with the electrolyte was considered. Both the polyester and polycaprolactone PU chemistries swelled significantly when placed in an electrolyte, compromising their conductive networks and mechanical advantages. In contrast, polyether PU was found to be a suitable binder for flexible batteries as it has strong adhesion and retains its properties even after swelling in the electrolyte. These findings present a promising polymer choice to facilitate the development of advanced and durable electrodes for flexible energy storage systems.