Advanced Single-Ion Conducting Block Copolymer Electrolyte for Safer and Less Costly Lithium–Metal Batteries

High-performance polymer electrolyte systems for lithium–metal batteries (LMBs) commonly contain a relatively high amount of fluorine to stabilize the electrode|electrolyte interfaces, particularly that with lithium metal. Herein, we report an advanced single-ion conducting polymer electrolyte that contains less fluorine in the backbone than previous systems, enabling a significant cost reduction, while still providing highly stable cycling of LMB cells containing LiNi0.6Co0.2Mn0.2O2 (NCM622) and LiNi0.8Co0.1Mn0.1O2 (NCM811) positive electrodes. Moreover, we show that the choice of the incorporated “molecular transporters”, i.e., small molecules with high mobility and a high dielectric constant to facilitate the Li+ transport, is essential for achieving high-performance LMB cells. In fact, the transition from pure ethylene carbonate to a mixture with propylene carbonate allows for an extended electrochemical stability toward oxidation and higher limiting current density, resulting in enhanced rate capability and cycling stability of Li∥NCM cells─and the possibility to cycle these cells also at ambient temperature.