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 (P_AB6) (M_n = 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 P_AB6-1, P_AB6-2, and P_AB6-3). 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.