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We have employed a variety of experimental methods, including DC and AC conductivity, scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), Fourier Transform Infrared (FTIR) spectroscopy, and pulsed field gradient nuclear magnetic resonance (NMR), to investigate the poly(ethylene oxide):LiI system. The effect of stretching the polymer electrolyte on its DC conductivity is dramatic, resulting in up to a 40-fold increase in the LiI P(EO) 7 composition. Structural ordering imposed by the stretching is observed in SEM and AFM images, and the cation solvation sheath (i.e., the helical PEO structure) is also affected by stretching in a manner believed to favor enhanced transport, according to the FTIR results. The NMR results demonstrate unambiguously that Li + diffusivity is anisotropic and enhanced along the stretch direction. Although the cation transport mechanism in polyether-salt polymer electrolytes is believed to rely heavily on polymer segmental mobility, this investigation suggests that other factors also contribute significantly. Such factors which can be augmented by stretching are modest changes in the cation solvation sheath and alignment of the helical structural units characteristic of PEO and its salt complexes.

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A composite anode material was prepared that contains nanosize (<100 nm) particles of tin alloy Sn65Sb18Cu17 and Sn62Sb21Cu17. The alloys were electroplated at high current densities (above iLfalse) from aqueous solutions, directly onto the copper current collector, and were coated by a polyvinylidene fluoride-graphite matrix at a ratio of alloy:graphite matrix 70:30 and 80:20 w/w, respectively. The processes involved in electrode production by this method are inexpensive, simple, and fast. Over 40 (100% depth of discharge) cycles were demonstrated, in half-cell, and over 30 were demonstrated with a LiCoO2 battery containing 1 M LiPF6 ethylene carbonate-diethyl carbonate electrolyte. The faradaic efficiency false(QnormalDe­normalins/QnormalInsfalse) is less than 100%. Lithium is fully deinserted from the host matrix only when the anode is cycled at low current densities. The kinetics of lithium insertion to and deinsertion from the composite anode material, slow gradually as the cycle number increases. X-ray diffraction patterns of the anode material show that the alloy becomes amorphous during cycling, while the graphite does not. X-ray photoelectron-spectroscopy measurements reveal that the solid electrolyte interphase consists of mainly LiF, small amounts of Li2O, and possibly, polymeric substances. The electrochemical behavior of the alloy changes with cycle number, while that of the graphite does not. The fall of the deinsertion capacity of the graphite from the first cycle to the 34th by more than 50% proves that the active material in the anode suffers from particle-to-particle break off. © 2002 The Electrochemical Society. All rights reserved.

In semicrystalline complexes of poly(ethylene oxide) (PEO) with different salts, such as lithium iodide, lithium trifluoromethanesulfonate (LiTF) and lithium trifluoromethanesulfonimide (LiTFSI), stretching induced longitudinal DC conductivity enhancement was observed, in spite of the formation of more ordered polymer electrolyte (PE) structure. It was found that the more amorphous the PE, the less its lengthwise conductivity is influenced by stretching. The results of our investigation suggest that ionic transport occurs preferentially along the PEO helical axis, at least in the crystalline phase, and that the rate‐determining step of the lithium ion conduction in LiI:P(EO)20, LiTF:­P(EO)20 polymer electrolytes below Tm is “interchain” hopping. Understanding ion transport processes is clearly a fertile field for research and development in the synthesis of new rigid polymers with ordered channels and composition appropriate for enhanced ionic conductivity. Copyright © 2003 John Wiley & Sons, Ltd.

The demand for a solid polymer electrolyte membrane for fuel-cell systems, capable of withstanding temperatures above 130°C , has prompted this study. A low-cost, highly conductive, nanoporous proton-conducting membrane, based on a polytetrafluoroethylene (PTFE) backbone has been developed. It comprises a nonconductive nano-size ceramic powder, PTFE matrix, and an aqueous acid. Impregnation of the ceramic powder into the PTFE matrix was carried out using sol-gel synthesis. The preparation procedures were studied and the membrane was characterized. This membrane demonstrated promising properties of high thermal stability (up to 300°C ), pressure-retention difference up to 2.2bars , room-temperature conductivity up to 0.11Scm−1 (10–15% (w/w) SinormalO2 , 3M normalH2SnormalO4 ), a hydrophilic/hydrophobic pore ratio of 1:1 and very high water flow at low pressure. A nonoptimized direct-methanol fuel cell with a 137μm thick membrane was assembled and tested. It produced 133mWcm−2 at 80°C , 0.05bars (g) dry air, 1.9 stoich (air), and 198mWcm−2 at 110°C , 2.2bars (g) dry air, 1.9 stoich (air).