This article presents a novel single-ion polymer electrolyte based on polyanionic BAB triblock copolymers for lithium-metal batteries. The copolymers, composed of polystyrene segments and poly(styrene trifluoromethanesulphonylimide of lithium) (P(STFSLi)) and poly(ethylene oxide) (PEO), exhibit high ionic conductivity (1.3 × 10−5 S cm−1 at 60 °C), excellent mechanical properties, and an electrochemical stability window of up to 5 V versus Li+/Li. These properties overcome the limitations of traditional liquid electrolytes, such as safety issues and low power performances. The electrolyte was tested in lithium-metal batteries, showing superior power performances and cycling stability, particularly at 60 °C. The study highlights the potential of this new electrolyte for next-generation batteries, addressing key challenges in electric vehicle technology.This article presents a novel single-ion polymer electrolyte based on polyanionic BAB triblock copolymers for lithium-metal batteries. The copolymers, composed of polystyrene segments and poly(styrene trifluoromethanesulphonylimide of lithium) (P(STFSLi)) and poly(ethylene oxide) (PEO), exhibit high ionic conductivity (1.3 × 10−5 S cm−1 at 60 °C), excellent mechanical properties, and an electrochemical stability window of up to 5 V versus Li+/Li. These properties overcome the limitations of traditional liquid electrolytes, such as safety issues and low power performances. The electrolyte was tested in lithium-metal batteries, showing superior power performances and cycling stability, particularly at 60 °C. The study highlights the potential of this new electrolyte for next-generation batteries, addressing key challenges in electric vehicle technology.