Fiona M. Gray

Synthesis and characterization of ABA block copolymer-based polymer electrolytes

Abstract The synthesis and some of the properties of a novel ion-conducting polymer are described. The polymer, based on a styrene-butadiene-styrene ABA triblock copolymer has pendant, short-chain poly(ethylene oxide) (PEO) grafted onto the B block. The concentration of PEO in the polymer can be controlled by varying either the number of pendant groups per molecule or the molecular weight of the PEO chain. The polymers were combined with LiCF 3 SO 3 to form ion-conducting phases. The conductivities of films of these materials were found to be sensitive to preparation technique, and especially to casting solvent. The best conductivities, typically 10 −5 S cm −1 at ambient temperatures, were obtained using solvents that were likely to induce microphase separation (with concomitant improvement in the mechanical properties of the system). The temperature dependence of the conductivity suggested that the materials were essentially amorphous over the range studied.

Poly(ethylene oxide) - LiCF3SO3 - polystyrene electrolyte systems

Abstract Polymer electrolytes based on poly(ethylene oxide), polystyrene and LicF 3 SO 3 have been prepared. Thin films formed by a hot-pressing technique had superior conductivities to solvent cast systems. The inclusion of the polystyrene support polymer at concentrations up to 60% by volume, improve the physical strength of the electrolytes without seriously impairing the conductivity at temperatures above 60 °C.

Conductance and conducting species in amorphous polyether-lithium perchlorate systems at very low salt concentration

The molar conductance dependence on salt concentration has been obtained for LiClO4 complexes of an amorphous solid polyether [-(OCH2CH2)x-OCH2-]y and a low molecular weight polyether CH3(OCH2CH2)4OCH3. Measurements were made over the concentration range 0.1×10−3 to 1.2 mol dm−3. Both solid and liquid systems showed similar behaviour, with substantial ion-pairing and the formation of triple-ion clusters at low salt concentrations implied. At high salt concentrations, the more pronounced fall in conductivity in the solid medium has been interpreted as being due to differing effects of Tg and bulk viscosity on ion transport.

An anhydrous polymer electrolyte containing trivalent cations: Poly(ethylene oxide):La(ClO4)3

Abstract The polymer electrolyte PEO:La(ClO 4 ) 3 has been prepared and investigated. In addition to crystalline PEO, X-ray and DSC results indicate the existence of a crystalline complex between the salt and polymer. Transference number meaurements indicate that the lanthanum is immobile. The conductivities, though lower than poly(ethylene oxide) based electrolytes containing monovalent cations or Hg 2+ , are similar to those of other anhydrous divalent cation-based polymer electrolytes.

The mixed-salt effect in a polymer-based ionic conductor

The effect of the mixing of lithium triflate and sodium iodide at high and equal concentrations in a polymer-based (poly(ethylene oxide)) ionic conductor are investigated. A variety of characterisation techniques, namely conductivity, X-ray diffraction, DSC and NMR, are employed. The salient observations involve enhanced conductivities, reduced microviscosity, greatly enhanced mobility of those lithium ions observed by NMR and a recurring absence of NMR observability of a substantial fraction of the cations. The data are interpreted as indicating that the effects of mixing of the salts are to enhance greatly the volume of available amorphous phase. Another feature of the interpretation is the inhomogeneous distribution of the various cations and anions around the different phases present in the materials.

Dielectric studies of poly(ethylene oxide)-based polymer electrolytes using time-domain spectroscopy

High-frequency dielectric measurements in the range 100 MHz to 10 GHz have been performed on poly(ethylene oxide) (PEO) and its complex s with RbI and LiClO4 over a limited temperature and concentration range using time-domain spectroscopy. This technique is shown to be a viable and straight forward means of obtaining dielectric data on polymer electrolytes. Results were comparable to those reported in the literature for frequency-domain measurements. The effect of crystallinity on the high-frequency conductivity has been demonstrated as well as salt and concentration effects on the permittivity which may result from different ion-polymer interactions.

SECONDARY BATTERIES – LITHIUM RECHARGEABLE SYSTEMS | Lithium Polymer Batteries

Lithium ion polymer (LiPo or LiPoly) cells first appeared in consumer electronics in the mid-1990s. The technology for these devices evolved from previously established lithium ion (lithium ion) cells. The difference between the two lies in the electrolyte; in Li ion batteries it consists of a lithium salt dissolved in a low molecular weight solvent, whereas a LiPo electrolyte is a polymer gel network. Substitution of liquid electrolyte by a solid analog allows simplification of the cell structure, and many restrictions in terms of architecture and safety are eliminated. Three decades of R&D on solvent-free polyether-based electrolytes have seen many advances, but barriers still remain, restricting their commercial exploitation. Commercial viability was realized in polymer gel electrolytes, a compromise between the liquid and solvent-free systems. The all-solid-state LiPo concept translates into a battery that can be shaped to suit the device it will power, is lighter, and can undergo denser packaging than its liquid electrolyte counterpart. The battery energy density is potentially much greater than that achieved by competing cell chemistries, including the Li ion cell. With recent advances in LiPo cell technology, the commercial balance between the Li ion and LiPo systems is expected to shift in favor of the latter.