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 LiNi_0.6Co_0.2Mn_0.2O₂ (NCM₆₂₂) and LiNi_0.8Co_0.1Mn_0.1O₂ (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.