Polymer electrolytes based on alkali metal salts in poly(ethylene oxide) are important for possible use in rechargeable batteries for both electric vehicle and consumer electronics applications. We measure a complete set of transport properties for one particular binary salt solution: sodium trifluoromethanesulfonate in poly(ethylene oxide), over a wide range of salt concentrations (0.1 to 2.6M) at a particular temperature (85~ The transport properties measured include the conductivity, the salt diffusion coefficient, and the sodium ion transference number. The mean molar activity coefficient of the salt is also determined. The conductivity is measured using the standard ac impedance method. The salt diffusion coefficient is found by using the method of restricted diffusion. The conductivity and diffusion coefficients of NaCF3SO3 are similar in magnitude to those of LiCF3SO3 in poly(ethylene oxide). The transference number and thermodynamic factor are found by combining concentration cell data with the results of galvanostatic polarization experiments. This novel method of measuring the transference number is straightforward to perform experimentally and yet does not require that the solution be either dilute or ideal. A theoretical analysis of the experimental method based on concentrated-solution theory is given. Our study verifies that the transference numbers derived from the experiments retain fundamental significance in applications involving both steady and transient processes and in systems coupling the polymer electrolyte with electrodes of all types (stoichiometries). The relevant transference numbers can be determined independently of any knowledge of speciation of the polymer electrolyte. The transference numbers found here for the sodium ion are much lower than those reported for the lithium ion, especially in the concentrated solutions. The transference number of the sodium ion is negative in the more concentrated solutions and levels off at its maximum value of 0.31 in the dilute concentration range. The transference number results are interpreted in terms of complexation of the sodium ion with the anionic species. IntrocluctionThe study of solid polymer electrolytes for use in rechargeable batteries has been a popular research topic for over a decade. 1-~ Many different types of ionically conducting polymers have been developed, with the main consideration for their usefulness being the conductivity of the polymer/salt solution. These include conductive polymers that utilize an additional liquid-phase cosolvent, such as proton exchange membranes or gel electrolytes. Polymer/ electrolyte solutions are generally nonideal and concentrated, as demonstrated from activity coefficients, 4 studies of ion-pairing, 5"6 and the concentration dependence of measured transport properties] Therefore, in order to describe completely the transport processes in these materials, it is necessary to have n(n -1)/2 concentration-dependent transport properties, where n is the number of independent species in the solutio...

Electrochemical insertion of sodium ions into carbon using solid polymer electrolytes or organic liquid electrolytes is described. Cells with the configuration normalNa/Pfalse(EO)8NaCF3SO3/CPfalse(EOfalse)=normalpolyethylene oxide ) or Na/liquid electrolyte/C were galvanostatically discharged, charged, and cycled. The extent of insertion into C (i.e., x in Na+Cx− ) was found to be a strong function of the type and particle size of the carbon used, and the reversibility of the process was highly dependent upon the type of electrolyte used. The possibility of designing a sodium ion rocking chair cell is discussed, and a first‐generation example, using a petroleum coke anode, polymer electrolyte, and sodium cobalt bronze cathode is described.

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An effective, dense and well adherent coating was produced on 430SS that has the result of significantly reducing the oxidation rate of this alloy at elevated temperatures. The coating is essentially a Mn-Co-O spinel, applied in powder form, and compacted to improve its green density. A simplified model is presented that allows an assessment of the effects of the contact and scale geometries. For 850 o C, an ASR can be predicted of approximately 0.5Ωcm 2 , after 50,000hrs in air, taking into account a factor of 10 penalty for unfavorable contact geometries. The effect of the densified Mn-Co spinel coating is to reduce significantly Cr 2 O 3 sub-scale formation, lower the thermal expansion mismatch, and increase the electronic conductivity of the scale.The findings point to several potential remedies for achieving coatings on 430 SS that allow for metal interconnects with a service life of 50,000hrs or more. Considering contact geometries, such service life is unlikely to be possible above operating temperatures of about 700 o C, unless highly specialized alloys are used, with potential processing and cost penalties.

Table I. Comparison of measured and calculated (Eq. 5) diffusion coefficients.

“In situ toughened” silicon carbides, containing Al, B, and C additives, were prepared by hot pressing. Densification, phase transformations, and microstructural development were described. The microstructures, secondary phases, and grain boundaries were characterized using a range of analytical techniques including TEM, SEM, AES, and XRD. The modulus of rupture was determined from fourpoint bend tests, while the fracture toughness was derived either from bend tests of beam‐shaped samples with a controlled surface flaw, or from standard disk‐shaped compact‐tension specimens precracked in cyclic fatigue. The R‐curve behavior of an in situ toughened SiC was also examined. A steady‐state toughness over 9 MPa·m1/2 was recorded for the silicon carbide prepared with minimal additives under optimum processing conditions. This increase in fracture toughness, more than a factor of three compared to that of a commercial SiC, was achieved while maintaining a bend strength of 650 MPa. The mechanical properties were found to be related to a microstructure in which platelike grain development had been promoted and where crack bridging by intact grains was a principal source of toughening.

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