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Resins containing dibenzo-18-crown-6 (phiDB18C6) as anchor groups have been prepared according to the procedure suggested by Blasius and the total capacity, CT, determined by micro analysis. The effective capacity, CE, of phiDB18C6 towards the alkali-metal salts using water as reaction media was obtained from saturation experiments. The electrolyte concentration dependence of the distribution ratio of 1:1 electrolytes between phiDB18C6 and water at 298K was studied and the results used to determine the concentration range at which a maximum separation factor between two ions could be achieved. The rational equilibrium constant, log K'ex, corrected for activity in the solution phase and the derived apparent free energy change, DeltaG'ex for the process taking place when phiDB18G6 is equilibrated with an aqueous or non-aqueous solutions (s) of the different M+A- electrolytes as represented by are calculated. The results obtained clearly reflect the influence of the anions on the extraction of cations by the resin containing the macrocyclic ligand. For aqueous solutions of electrolytes containing a common cation and different anions the selectivity found is in the order Pi→SCN→I→Br→C1-. An enhancement of selectivity by a factor of 1.55x104, 8.91x103, 2.09x103 and 1.55x103 is found for the picrate salts relative to the chloride, bromide, iodide and thiocyanate, respectively. The heats associated with the interaction of phiDB18C6 and 1:1 electrolytes in aqueous solutions were measured calorimetrically at 298K and the apparent enthalpy change evaluated. Combination of the free energy and enthalpy changes yield the corresponding entropy changes. The contribution of the enthalpy and entropy terms to the free energy suggests that the process of extraction of 1:1 electrolytes from the aqueous I s solution to the resin phase is enthalpically controlled. An interesting relationship is obtained when values for the effective capacity of the resin towards the different 1:1 electrolytes are plotted against the apparent enthalpies(DeltaH'ex) obtained for the different electrolytes in water. Distribution data for the 1:1 electrolytes and phiDB18C6 were obtained in solvents such as N,N-dimethylformamide (DMF), propylene carbonate (PC), acetonitrile, (AN), methanol (MeOH) and water (H2O), in an attempt to evaluate the reaction media effects on the extraction of 1:1 electrolytes by these resins. Distribution ratios decrease in the order AN→PC→MeOH→DMF→H2O. Interaction between organic molecules in aqueous solutions (urea, thiourea, and phenol) and phiDB18C6 were also studied. Effective capacity measurements as determined by saturation experiments at 298K using thiourea and phenol indicate that the 1:1 organic molecule crown ether ratio obtained for the former compound is altered to a 4:1 ratio in the case of phenol. A possible mechanism based on hydrogen bond formation in the resin phase is suggested.

Magister Scientiae - MSc / A new high temperature solid electrolyte composite was developed, with CsHSO4 and CsH2PO4 as the proton conducting material in composition with PTFE and SiO2 to enhance the solid electrolyte composites mechanical strength and conductivity. Conductivity measurements for CsHSO4 and CsH2PO4 and composites thereof, in temperature ranges 0 to 180 oC and 0 to 250 oC respectively, were carried out. The composites with different concentrations PTFE and silica were tested for stability in a enhanced conductivity. hydrogen atmosphere and different degrees of humidity. The CsHSO4 was seen to exhibit a super protonic phase change at temperatures between 132 – 140 C and CsH2PO4 around 230 C. The presence of the PTFE proved to be a stabilizing factor in the reduction of water re-adsorption once the membrane had been dried during thermal conductivity analysis. According to supporting data in the literature it has been found that composites including silica could be influenced by the hydrophilicity and specific surface area of the silica. In the composite system employed it was shown by impedance analysis the presence of two semi-circles in the Nyquist representation for the enhanced conductivity due the presence of silica. / South Africa

Bibliography: pages 103-106. / Beta-alumina solid electrolytes studied were subjected to charge and discharge cycles in a secondary, high energy density Na/beta-alumina/NaAlCl₄/FeCl₂ cell (known as the Zebra cell) at 250⁰ C. These electrolytes were studied by means of optical microscopy, as well as SEM and EDS analyses to est ablish possible failure modes. After cycling little discolouration, or impurity pickup was found to have occurred in the electrolyte. The forms of degradation of the beta-alumina electrolyte identified appeared to be a result of inherent flaws in the beta-alumina electrolyte tube, problems due to protracted storage of the tubes, or an apparent interfacial film on the cathode/electrolyte interface. A lead wetting agent was used in the cells to enhance the wetting of the beta-alumina electrolyte by the liquid Na. A study of the coating after cycling of the cell showed that the coating was adherent irrespective of the number of cycles completed. The coating did not appear to influence cracking of the electrolyte during cycling. Cracking of the beta-alumina electrolyte was found to have initiated from the Na/electrolyte interface. No evidence of crack initiation nor internal damage was found on the cathode/electrolyte interface. The cracks through the beta-alumina electrolyte wall were found to have sealed by the formation of a plug consisting largely of Na and Cl. On the basis of EDS analyses of the fracture surface of the sealed crack possible sealing mechanisms are proposed.

The polyelectrolyte titration method has been developed overthe years in order to determine the surface charge ofcellulosic fibers. The conditions have been varied depending onthe author. This work has been aimed at resolving theappropriate conditions for measuring the charge, such aselectrolyte concentration and molecular mass of thepolyelectrolyte. The charge ratio of variously treated pulpswas also investigated. The polyelectrolyte titration technique is based on a 1:1adsorption stoichiometry between fiber and polyelectrolytecharges. Adsorption of polydiallyldimethylammonium chloride(poly-DADMAC) was first performed at various electrolyteconcentrations and then with various molecular masses. ESCA(Electron Spectroscopy for Chemical Analysis) was used toindependently validate the polyelectrolyte titrationmethod. Results showed that stoichiometry prevailsat lowelectrolyte concentrations. Increasing the electrolyteconcentration screens the fiber charges, initially enhancingthe adsorption and causing a deviation from stoichiometry.Further increases in electrolyte concentration eventuallydecrease the adsorption. Deviation from stoichiometry occurredat higher electrolyte concentrations for higher charge densitypulps. ESCA-measurements showed that high and low molecularmass cationic polyelectrolyte adsorb to the same extent on thefiber surface, confirming stoichiometry. There was a goodagreement between the two techniques, hence, thepolyelectrolyte titration technique is a good method to measuresurface charges. Comparing the charge ratio between differentkind of pulps and treatments, it was found that mechanicalpulps have a higher surface charge than chemical pulps. Thecharge ratio of chemical pulps was, however, practicallyunchanged when comparing different types of wood and bleachingsequences. <b>KEYWORDS:</b>Adsorption, electrolyte, polyelectrolyte,polyelectrolyte titration, charge stoichiometry, charge ratio,diffuse electric double layer, Debye length, poly-DADMAC,cellulosic fibers, ESCA. / NR 20140805

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Ces travaux ont pour objet la synthèse et la caractérisation de nouveaux électrolytes polymères pour batterie lithium métal polymère (LMP). L’objectif principal de ces électrolytes est de combiner une conductivité ionique élevée jusqu’à basse température et une résistance efficace contre les dendrites de lithium. Pour y parvenir, trois catégories de copolymères à bloc ont été élaborés, ils permettent d’obtenir une synergie de propriétés à priori antagonistes au sein d’un même matériau. Premièrement, la rigidité du polystyrène (PS) a été combinée à la conductivité du polyoxyéthylène (POE) dopé avec un sel de lithium (LiTFSI). Le POE a été préalablement modifié pour en abaisser la température de fusion (Tf) initialement située à 60°C, ce qui permet d’atteindre de hautes conductivités (7.10-5 S.cm-1) à 40°C, associées à un module d’Young de 0,3 MPa. Cependant, les bonnes conductivités de ces matériaux ne sont assurées que par une petite fraction de Li+ (t+=0,15). Cela crée des gradients de concentration qui limitent les performances des batteries. Pour pallier cela, l’anion TFSI a été greffé sur le bloc PS (PSTFSI), augmentant le t+ à 1. Le bloc PSTFSI combiné à du POE modifié a permis des conductivités remarquables pour un électrolytes solide (10-6 S.cm-1 @ 40°C). Dans un second temps, l’ajout d’une chaine perfluorée entre le PS et l’anion a permis un gain supplémentaire de conductivité par rapport au PSTFSI (2.10-5 S.cm-1 @ 60°C), uniquement assurée par les Li+. Dans chacune des trois catégories d’électrolytes plusieurs compositions ont été synthétisées, nous permettant de suivre l’impact de cette composition sur les morphologies, les propriétés thermodynamique et mécanique ainsi que sur les propriétés de transport. Finalement, des batteries LMP de laboratoire ont été assemblées avec les meilleurs électrolytes. / This work deals with synthesis and characterization of new polymer electrolytes for lithium metal polymer (LMP) batteries. The main challenge of polymer electrolytes is to combine both high ionic conductivity at low temperature and good mechanical properties. To overcome these issues, block copolymers have been designed. Remarkable properties are reached thanks to the self-assembly of these triblock copolymers. Mechanical properties are given by stiff polystyrene (PS) domains whereas ionic mobility operates in an ionophilic phase, polyoxyethylene (POE) with a lithium salt (LiTFSI). By introducing chemical defects in the POE backbone, melting temperature of the copolymer has been considerably lowered leading to conductivities of about 7.10-5 S.cm-1 and a Young’s modulus of 0.3 MPa at 40°C. If interesting properties are obtained thanks to this strategy, the small fraction of conductivity insured by lithium ions (t+=0.15) remains an issue. The low t+ leads to large concentration gradients limiting the performances of the system. In a second approach, TFSI anions have been covalently tethered on the PS backbone, raising the t+ to 1. An important increase of Li+ conductivity was obtained by adding a perfluorinated spacer between PS and TFSI moieties, with an ionophilic phase based on PEO (2.10-5 S.cm-1 @ 60°C). The chemical modification of the PEO block leads to Li+ conductivities of 10-6 S.cm-1 at 40°C. The composition of these different copolymers have been varied and their structural, thermal, mechanical and transport properties have been studied. Finally the best electrolytes of each category have been assessed in a full cell configuration.

Non-aqueous rechargeable lithium-air (O₂) batteries are receiving intense interest because of their high theoretical specific energy, which are several times greater than that of lithium-ion batteries. To achieve it, the highly reversible formation/decomposition of Li₂O₂ is required to occur in the cathode during cycling. Due to the reactivity of reduced O₂ species, the aprotic electrolyte and carbon electrode substrate would be attacked and then decomposed. The organic carbonate decomposed on discharge, forming C₃H₆(OCO₂Li)₂, Li₂CO₃, HCO₂Li, CH₃CO₂Li, CO₂ and H₂O. Part of these by-products decomposed on the subsequent charge process and the rest remained and blocked the electrode surface. Finally, the cell cycling stopped because of the depletion of electrolyte and the passivation of the electrode surface. Possible mechanisms are proposed for reactions on discharge and charge. Some other types of aprotic solvents were investigated in the same way. Ethers, amides, sulfones, dimethyl sulfoxide (DMSO), etc reveal better stability than organic carbonates. Reversible formation/decomposition was observed together with minor side-reactions. Besides electrolytes, carbon substrate of electrode also slightly decomposed. Several other substrate materials were studied. If the carbon electrodes were replaced with the nanoporous gold electrodes, less side-reaction was observed in the cells, and the cell sustained 100 cycles without severe polarisation and capacity fading. The charge performance of a Li-O₂ cell remains a challenge. Great voltage polarisation even at modest rate was observed because of the difficulty of charge transfer between solid electrode surface and solid Li₂O₂. Redox mediators were used in a Li-O₂ cell, which transported the charge between electrode surface and solid Li₂O₂, acting as an electron-hole transfer agent. The oxidation of solid Li₂O₂ was facilitated and the cell with mediator demonstrated 100 charge/discharge cycles.

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