Ionic transport, plasticized systems

Another important feature of the system poly(ethylene oxide) copoly-mer/GBL is that the ionic conductivity of the electrolyte is still significantly dependent on the composition of the copolymer. It was known from previous works that, for pure polymer electrolytes (without plasticizer), although the crystallinity degree increased with the increase in EO unit content in the copolymer P(EO-EPI), the conductivity also increased due to having more sites available for cation coordination, once the EPI units do not contribute to ionic transport. The same trend was observed for electrolytes prepared with Nal and P(EO-EPI) even after addition of 50 wt% of GBL to the electrolyte, indicating that the oxygen atoms from the polymer chains are probably still contributing to ionic transport, even in the presence of plasticizer. ... 

Another research still adds information on the influence of mobihty on conductivity. Figure 10.31 shows that an increase in molecular weight of plasticizer decreases ionic conductivity and Figure 10.32 shows that an increase in the amount of plastieizer increases ionic conductivity. Increase in amount and decrease in molecular weight increase mobility of lithium ion which transports charges through the system. ... 

This behavior can be expected from systems in which entropic factors can be neglected. ABS/PMMA blend plasticized with a mixtme of ethylene and propylene carbonates is an example of system where entropic factors play a role. PMMA is plasticized in polymer electrolytes to increase ionic conductivity. Addition of a plasticizer in an amount sufficient to achieve required conductivity decreases the mechanical performance of the gel to the level that it needs to be reinforced. ABS is added as reinforcing polymer and sufficient mechanical properties are obtained. Two phases are obtained plasticizer-reach phase giving pathway for ion transportation and ABS-rich phase which acts as a matrix increasing mechanical performance. ABS is miscible with PMMA forming transparent blends if no plasticizer is added. Addition of the plasticizer results in phase separation (opaque materials) because of incompatibility between ABS and the plasticizer. This is an example of a system in which the plasticizer is not uniformly distributed among participating polymers but the plasticizer is found in the PMMA-rich phase. ... 

The major problems associated to the use of polymer electrolytes in DSSC arise from the low ionic diffusion in a more viscous medium, low penetration of the polymer inside the nanostructured T1O2 electrode, and an increase in the interfadal charge-transfer resistance between the electrodes and the electrolyte. In order to enhance the overall conversion efficiency and the transport properties, the nature/composition of the polymer systems must be improved. Further improvements in device performance are readily achievable through optimization of the ionic conductivity. In this context, the addition of inorganic nanofillers, ionic liquids, oligomers based on EO, plasticizers and other additives has become a common route to elaborate polymer (or gel) electrolytes with improved ionic conductivity properties. 

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