Additives in the polymer electrolytes

Besides the plasticizers, other additives can be explored to improve the characteristics of polymer or gel electrolytes. These materials can be incorporated for different purposes, such as the improvement of mechanical and thermal stability, enhancement of the charge transport, open circuit voltage, etc. 

An interesting approach consists of the addition of nanoscale inorganic fillers, to improve the mechanical, interfacial and conductivity properties of the (gel) polymer electrolytes. Since the pioneering work by Scrosati and co-workers, addition of T102 and other nanoparticles has been extensively employed to improve the ionic conductivity of polymer electrolytes. It is well known that the presence of such nanoparticles changes the conduction mechanisms assigned to the ions introduced in the polymer however, how these nanoparticles actually act is stiU unknown. These materials can also improve the mechanical properties of gel electrolytes and ionic liquid-based electrolytes. However, their effect on the mechanical stability can result in a loss in electrolyte penetration. 

Zhao and co-workers prepared an electrolyte based on PEO, poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP), SiO and conductive carbon nanoparticles. The conductivity mechanism was analyzed by AC impedance and DC voltage-current measurements. A change in the conduction mechanism was obtained by adding different amounts of carbon nanoparticles. Small amounts of carbon nanoparticles improved the ionic conductivity and a DSSC with 5 wt% of carbon nanoparticles in the electrolyte presented 77 = 4.3% compared with the original DSSC performance of 3.9%. When the content of nanoparticles was increased to 15 wt%, the efficiency decreased to 3.6%, as a consequence of a decrease in the ionic conductivity and an increase in interface recombination with the electrolyte, because of the electronic conductive path formed by the aggregated carbon nanoparticles. 

AI2O3 particles with different sizes were incorporated into electrolytes based on mixtures of ionic hquids, a PVDF derivative and polyacrylonitrile. It was observed that the added nanoparticles influenced the diffusion coefficient of I3 ions and also the charge transfer rate, and this effect depended on the AI2O3 particle size. The authors suggested that the imid-azolium cations might adsorb on the nanoparticle surface, and then the counter-anions 17I3 gather around them. 

These results showed that the addition of MMT clay to the plasticized polymer electrolyte led not only to an increase in the ionic conductivity, but also to the sohdification of the electrolyte, reflected as an improvement in the mechanical stability of the films. The solar cell devices containing the nanocomposite polymer electrolyte presented efficiencies of 1.6% and 3.2% at 100 and 10 mW cm , respectively. The FF values were very poor, only 40% under 100 mW cm , which was attributed to the low penetration of the composite electrolyte inside the pores of the T1O2 film.  

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