Enhanced Electrochemical Properties of Block Copolymer Electrolytes with Blended End-Functionalized Homopolymers
Jihoon Kim, Kyeong‐Jun Jeong, Kyoungwook Kim, Chang Yun Son, Moon Jeong Park
Abstract
Advanced polymer electrolytes for lithium-ion batteries were developed by introducing tailor-made end-functional groups. For poly(ethylene glycol) (PEG), the electrochemical stability was enhanced, and the lithium transference number was improved by controlling how terminal nitrile moieties were bound. Spectroscopic analyses and molecular dynamics simulations revealed that −C≡N···Li+···(EO)n interactions formed partially open Li+ coordination shells. Moreover, the EO and −CN moieties belonged to different chains, which facilitated the physical cross-linking of PEGs with dinitrile termini. Blending nitrile-functionalized PEGs with polystyrene-b-poly(ethylene oxide) (SEO) block copolymers produced nanostructured polymer electrolytes with enhanced mechanical stability and fast lithium relaxation dynamics. When the dinitrile termini were adjacent, PEG in the PEO domains of SEO predominantly agglomerated, assumed to form dry-brush-like blends that hampered ion transport. Conversely, wet-brush-like blends were favored when −CN groups were tethered at both the α- and ω-termini, resulting in synergistic improvements of the electrochemical and mechanical properties through effective interchain coordination interactions.