| In this work, electrolytes for secondary batteries and fuel cells were investigated. Ionic liquids (ILs), for use as battery electrolytes, were formed using quaternary ammonium salts (Quats) and aluminum chloride. The room temperature (RT) carbonate fuel cell was demonstrated by modifying a commercially available anion exchange membrane, utilizing positive quaternary ammonium fixed sites, to transport carbonate.; The charge density on the nitrogen and the symmetry of the Quat were demonstrated to be the dominant factors in determining the IL melting point (MP). Introduction of a benzyl ring both increases the size and disrupts the symmetry of the Quat, lowering the MP of the resulting ILs. The ILs formed from the asymmetric BenzylR'R2"NCl salts were found to have lower melting points (below room temperature) than ILs formed when R' was equal to R". The additional asymmetry is believed to make crystallization more difficult, significantly lowering the melting point and viscosity. For the ILs with moderate viscosity, upon neutralization with NaCl and addition of an additive (SOCl 2), sodium can be reversibly deposited. The coulombic efficiency of the plating/stripping process, defined as the oxidation current over the reduction current, was found to be comparable to other chloroaluminate ILs.; An additive is necessary to disrupt the strong coordination between Na +, or Li+, and AlCl4-, which makes the ions unavailable for reduction to the metal. Additives, such as HCl or SOCl2, are effective in disrupting the alkali-chloroaluminate complex freeing the ions for electroreduction to the metal. The bulk conductivity was observed to increase with SOCl2 content as the ions became available and sodium reduction/reoxidation was observed. The chlorinated compounds chloroform-D and carbon tetrachloride were demonstrated to have similar performance to SOCl2 though a large number of chlorinated compounds could be utilized. The electronegative chlorine atoms found in these solvents are oriented near the positive sodium cation, weakening its attraction to AlCl4.; Along with free sodium ions, sufficient reductive stability of the Quat is necessary to deposit sodium. The electrochemical stability is dependent on the ability of the substituent groups to form stable radicals. The benzyl substituted cation (salt IX) was less stable than the alkyl substituted cation (salt XV), due to the benzyl group being a better leaving group than the smaller butyl chain. The 9-carbon salt, XV, was demonstrated to form a RTIL with significantly lower viscosity than the benzyl substituted ILs. This is due to the much smaller size of XV than IX. Utilizing only carbon, nitrogen and hydrogen, 9 carbons appears to be the smallest number of atoms, with which a RTIL can be formed. As with the benzyl substituted ILs, upon the addition of SOCl2, sodium can be efficiently reduced and reoxidized.; Based on its placement, the introduction of a rigid ether group, compared to an alkyl group, can result in a lower molecular weight RTIL. The ionic conductivity increased upon neutralization of the ether substituted ILs. However, due to the stability of the quaternary ammonium cation, an additive is still necessary to form an SEI. SOCl2 was demonstrated to form a more stable SEI than CDCl3. The greater availability of sodium in the ether systems results in larger sodium reduction current densities.; The Quat-based RTILs formed have been shown to support the deposition of both lithium and sodium. When neutralized with both lithium and sodium, a mixed state is developed that results in the electrodeposition of Li-Na alloys at efficiencies similar to those measured with sodium. The Li-Na alloy appears to suppress dendrite formation and could potentially be used as a metal based anode in a rechargeable Li battery.; A technique that is becoming fairly common is the packaging of fuel cell and battery technology together. In this work, a novel room temperature carbonate fuel cell has be... |
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