Miktoarm PEG–PCL Star Copolymer (AB6) Blend Composite Solid Electrolyte for All-Solid-State Lithium Metal Battery

A series of AB6 type-7 miktoarm star copolymers consisting of poly(ethylene glycol) (PEG) as the A arm and poly(ε-caprolactone) (PCL) as the B arm are synthesized by controlled ring-opening polymerization of the ε-caprolactone monomer. The chemical structure is confirmed and characterized by nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopies. The synthesized PEG–PCL star copolymers (PAB6) (Mn = 8400, 16,820, and 32,480) with arms of different lengths are introduced into the poly(ethylene oxide)-based solid electrolyte system. Moreover, the electrochemical, mechanical, and thermochemical properties of composite solid polymer electrolytes are enhanced by adding three miktoarm PEG–PCL star copolymers (referred to as PAB6–1, PAB6–2, and PAB6–3). The unique low-molecular-weight miktoarm copolymers with a central etheroxy group and branched carboxyl groups interact with poly(ethylene oxide) segments and lithium ions, enhancing the segment mobility of the polymer and lithium-ion transfer. Therefore, all-solid-state lithium metal batteries by the serial miktoarm star copolymer composite electrolytes display a high capacity retention of 128.1 mAh g–1 after 390 cycles.