| The current research has focused on the development of solid polymer electrolytes for rechargeable lithium batteries with liquid-like lithium ion conductivity, high transference number and the mechanical properties of a thermoplastic film by use of novel surface modified nanomaterials. Various grafting techniques were developed to maximize the attachment of polyethylene oxide (PEO) oligomers on fumed silica with a primary particle size of 7nm and a nominal surface area of 380 m2/g. The maximum amount of attachment of PEO chains on silica was ∼33-wt% (2 molecules/nm 2) obtained by weight loss using thermogravimetric analysis (TGA). Attachment of PEO oligomers resulted in complete suppression of crystallization and raised the glass transition temperature (Tg) by 35°C. Nanocomposite polymer electrolytes prepared by using PEO-grafted silica as filler in a PEO-salt (LiClO4) matrix showed improved ambient temperature conductivity compared to native fumed silica. In order to reduce the amount of inert silica and increase the fraction of PEO chains ends, much smaller (0.7nm diameter) silica cages, polyhedral oligosilsesquioxanes (POSS), were functionalized with PEO oligomers of various ethylene oxide (EO) repeat units (n = 2, 4, <8>, <12.5>) by a hydrosilylation reaction. The effect of the interface on the thermal transitions of PEO functionalized silsesquioxanes (Q8 M8PEO(n = 2,4,8,(2.5)) depends on the EO chain length: glass transition temperatures (Tgs) increase and the effect of the POSS surface on suppressing PEO crystallization decreases with chain length. A new class of electrolytes, POSS based electrolytes, were developed by mixing PEO functionalized POSS [Q8M8PEO(n = x) with (MnS = 3000–5000)], with LiClO4 with lithium ion conductivities of ∼10−4 S/cm at room temperature, comparable to conductivities of PEO liquids with M ns of 300–500. Strong self supporting transparent films could be made with as little as 10% methyl cellulose and 90% Q8M 8PEO(n = 8) with ambient temperature conductivities greater than 10−5 S/cm. POSS based single ion conductors (SICs) were developed by bifunctionalizing POSS surfaces with highly dissociative anions (lithium salts of allyloxy trifluorosulfonamide and allyloxy 1,1,2,2-tetrafluorethane sulfonic acid) and PEO oligomers to obtain anion/PEO-functionalized silsesquioxanes(Q 8M8-x-yHMxPEOM yanion) with conductivity of 5 × 10−6 and a transference number of 0.85. |
