Preparation and properties of new cross-linked polyurethane acrylate electrolytes for lithium batteries

A cross-linked polyurethane acrylate (PUA) is synthesized by end-capping a hexamethylene diisocyanate, hexamethylene diisocyanate/poly(ethylene glycol)-based prepolymer with hydroxy butyl methacrylate (HBMA). Significant interactions of lithium ions with the soft and hard segments of the host polymer are observed for the PUA complexed with lithium perchlorate (LiClO4) by means of differential scanning calorimetry (DSC), and Fourier transform infra-red (FT-IR) spectroscopy measurements. The DSC results indicate the formation of transient cross-links with the ether oxygen of the soft segment and mixing of soft and hard phases induced by the Li+ ions. The results of FT IR spectroscopy and thermogravimetric analysis measurements support the formation of different types of complexes by interaction of Li+ ions with different coordination sites of PUA. No detectable interactions are found between Li+ ions and groups in HBMA. In addition, PUA follows the Arrhenius relationship for ion transport. Predominant formation of contact ion-pairs of LiClO4 is observed through a.c. conductivity and DSC measurements. The lithium stripping-plating process is reversible and this implies better electrochemical stability over the working voltage range. Also, the PUA electrolyte shows better compatibility with lithium metal as inferred from impedance measurements and has a good cationic transference number that is suitable for the material to be used as a solid polymer electrolyte. Addition of HBMA into the PU matrix improves the tensile strength of the cross-linked PUA. Swelling measurements of PUA with plasticizer indicate better dimensional stability. A cell is constructed with PUA as the electrolyte and its performance is evaluated. (c) 2006 Elsevier B.V. All rights reserved.