A series of PMMA ionomer containing the different ion contents or ionic moieties in the polymer backbone was synthesized by solution polymerization and was characterized by DSC and FT-IR spectroscopy. The ionic moieties studied were alkali metal methacrylate and maleate units, were chosen on the purpose of investigation on the arrangement effects of the ionic units on the electrical properties in the ionomer electrolytes. The ionomers were blended with the ethylene carbonate(EC) and salts, LiClO4 to form the ionomer electrolytes films. The addition of EC bring about the mobility of charge carriers and solvation of charge carriers. The ion conductivities of the ionomer electrolytes were measured as a function of ion contents of the ionomer and temperatures for each series of the ionomer with different ionic units. The ion conductivities of the methacrylate ionomer electrolytes showed strong dependency on the ion content of ionomers and maximum conductivity at 5 mol% ion content of the ionomer electrolyte. The maximum ion conductivity found at 5 mol% ionomer electrolyte was interpreted in terms of compatibility between EC and ionomer, and ion aggregates formed in the ionomer electrolytes. The ion aggregates formed in the ionomer electrolytes was supposed to reduce the mobility of the charge carrier as well as the charge carrier concentration. It was also possible to quantify the mobility and the charge carrier concentration with suitable design of in-situ FT-IR spectroscopy. For the methacrylate ionomer electrolytes with various ion contents of the ionomer, the peculiar ion aggregates was found at 7 mol% ionomer electrolytes causing the abrupt decrease in the ion conductivity.
A mechanism of the ion conduction in the ionomer electrolytes were also conducted by investigation of temperature dependency of ion conductivity. Some of the ionomer electrolytes showed VTF pattern which have been frequently reported in this filed, whereas the ionomer electrolytes containing the ion aggregates were found to follow neither VTF nor Arrhenius pattern. This was analyzed by the temperature dependence of the ionic force resulting in morphological change of the ionic aggregates in the ionomer electrolytes.
The other ionomer of which chemical structure contained maleate ionomer as a ionic units was studied as a function of the ion content of the ionomer and temperature. The ion conduction behavior of the maleate ionomer electrolytes was compared with that of the methacrylate ionomer electrolytes. The dependence of the ion conductivity on the ion content showed a similar manner to that of the methacrylate ionomer. The maximum ion conductivity was also found in the series of the maleate ionomer electrolytes at 8.5 mol% ion content of the ionomer, which is higher than in the case of the methacrylate ionomer electrolytes. The ion conductivities of the maleate ionomer electrolytes was shown to be higher than those of the methacrylate ionomer electrolytes. These differences were interpreted in terms of the arrangement effect of the ionic units which influences the aggregation behavior as well as the charge character which affects the interionic interaction between the ion sites of the ionomer and salts added. The charge carrier of the ionomer electrolytes was also found to be different in the two kinds of the ionomer electrolytes, which was proved by the comprehensive FT-IR investigation.
The interface and rechargeability of the maleate ionomer electrolytes were also studied. The repetition of the cyclic voltammetry showed the saturation of the amount of the energy charged and discharged at about $3^{rd}$ cycle. The interfacial resistance at the interface between the lithium metal and ionomer electrolytes was also monitored as a function of the ion content of the ionomer and temperatures. The interfacial resistance was improved by introducing the ion units into the polymer backbone. This is interpreted in terms of the compatibility between the ionomers and plasticizers. The ion aggregates in the ionomer electrolytes seemed to substantially reduce the interfacial resistance. The increase in the temperature led to the decrease in the interfacial resistance. This was thought to be driven by the change in the ion-dipole interaction through which the charge carriers were generated. The ATR studies for the lithium surface were also carried out after CV and dc polarization. From the ATR spectra, it was possible to suggest a model for description of the passivation layer and EC of the lithium surface. The electrochemical stability windows for the various ionomer electrolytes proved that all the ionomer electrolytes investigated were suitable one for the 4V battery applications.
