This study presents a novel single-ion polymer electrolyte based on polyanionic BAB triblock copolymers for use in lithium-metal batteries. The electrolyte, composed of polystyrene segments and poly(ethylene oxide) (PEO), exhibits a lithium-ion transport number close to unity, excellent mechanical properties, and an electrochemical stability window of up to 5 V versus Li⁺/Li. The single-ion conductivity of 1.3 × 10⁻⁵ S cm⁻¹ at 60°C is significantly higher than that of state-of-the-art materials, and the electrolyte demonstrates outstanding power performance and cycling stability, particularly at elevated temperatures. The material's unique structure enables efficient lithium ion transport and minimizes concentration gradients, which are critical for preventing dendritic growth and enhancing battery performance. The electrolyte also shows improved electrochemical stability compared to traditional PEO-based electrolytes, allowing the use of high-potential cathode materials that are not safe in liquid electrolytes. Battery prototypes using this electrolyte outperform conventional polymer electrolyte batteries, with more than 80 cycles at 60°C and a discharged capacity retention of over 85% at various temperatures. The material's high thermal stability (up to 350°C) and safety profile make it a promising candidate for next-generation lithium-metal batteries. The study highlights the potential of single-ion polymer electrolytes in addressing the challenges of energy density, safety, and power performance in lithium-metal batteries.This study presents a novel single-ion polymer electrolyte based on polyanionic BAB triblock copolymers for use in lithium-metal batteries. The electrolyte, composed of polystyrene segments and poly(ethylene oxide) (PEO), exhibits a lithium-ion transport number close to unity, excellent mechanical properties, and an electrochemical stability window of up to 5 V versus Li⁺/Li. The single-ion conductivity of 1.3 × 10⁻⁵ S cm⁻¹ at 60°C is significantly higher than that of state-of-the-art materials, and the electrolyte demonstrates outstanding power performance and cycling stability, particularly at elevated temperatures. The material's unique structure enables efficient lithium ion transport and minimizes concentration gradients, which are critical for preventing dendritic growth and enhancing battery performance. The electrolyte also shows improved electrochemical stability compared to traditional PEO-based electrolytes, allowing the use of high-potential cathode materials that are not safe in liquid electrolytes. Battery prototypes using this electrolyte outperform conventional polymer electrolyte batteries, with more than 80 cycles at 60°C and a discharged capacity retention of over 85% at various temperatures. The material's high thermal stability (up to 350°C) and safety profile make it a promising candidate for next-generation lithium-metal batteries. The study highlights the potential of single-ion polymer electrolytes in addressing the challenges of energy density, safety, and power performance in lithium-metal batteries.