Free Mesogen Assisted Assembly of the Star-shaped Liquid-crystalline Copolymer/Polyethylene Oxide Solid Electrolytes for Lithium Ion Batteries

Abstract

Solid composite polymer electrolytes based on polyethylene oxide (PEO)/LiClO4 with the star-shaped liquid-crystalline copolymer, 3-arm- poly {10-[(4-cyano-4′-biphenyl) oxy] decatyl methacrylate}-block-poly [methoxy -poly (ethylene glycol) methacrylate] (3PMALC-PPEGMA), and 4-cyano-4′-[(10-hydroxyalkyl) oxy] (10-BPCN) biphenyl are prepared. The star-shaped liquid-crystalline copolymer 3PMALC-PPEGMA is composed of a conductive block (PPEGMA block) and an orientation block (PMALC block). Incorporation of star-shaped liquid-crystalline copolymer into the system promotes the better miscibility of composites and suppresses the crystallinity of PEO to favor the chain mobility. At the same time, the strong assembly ability of star-shaped liquid-crystalline copolymer ensures the composite systems to develop an ordered morphology for efficient lithium transportation. It is worthy to note that such ordered assembly could be further strengthened by adding the appropriate amount of small molecular liquid crystals (10-BPCN) to repair the stacking defects of star copolymer. As a results, composite polymer electrolytes based on the ternary blend containing 70/25/5 (PEO/3PMALC-PPEGMA/10-BPCN) mass percent with lithium perchlorate (LiClO4) exhibit the best performance with the maximum value of 1.3×10−5 S/cm (25°C) after annealed from liquid crystal state, enhanced by more than two orders of magnitude than the pristine PEO/LiClO4 electrolytes. The high lithium ion transference number and wide electrochemical stability window also show the acceptable performance of this system. Therefore the better miscibility and reduced crystallinity as well as the efficient transport channel in the present system pave a potential way to develop solid state polymer electrolytes for Li-ion batteries.