Green solid electrolyte for electrochemical devices

The majority of all polymers are insulators which do not show any remarkable electro activity. In the past, researchers have found out how to obtain a conducting polymer by the introduction of salts, plasticizer and nanofillers. Uniform dispersion of plasticizer and fillers in salt-polymer matrices creates a class of novel materials exhibiting superior electrical and mechanical properties which are suitable to replace many existing materials such as those for engineering applications and in electrochemical devices.

Novel material which consists of starch is one of the most common renewable and biodegradable polymers deposited as granule in plants which can be found abundantly in our country. It is composed of repeating amylose and amylopectin.

In this research work, potato starch was chosen to be the polymer host because it has a better morphology in comparison to other starch. Physically, it appeared to be soft flexible film with high conductivity compared to corn starch. Furthermore, instead of just being a popular food item, potato starch is presently applied in the industrial field as coatings and sizing in paper, textiles and carpets as binders and adhesives, absorbents and encapsulates. The starch based film is reported to exhibit good mechanical properties. In addition, the dry thin film of starch could also be prepared easily.

Ammonium salt was chosen because it does not have a high tendency to break the starch. The thin clear films of potato starch were prepared by solution casting technique. A certain amount of potato starch (Sigma-Aldrich) was weighed and dissolved in 50ml of acetic acid (Systerm) in a 100mL beaker and left to be stirred for 20 minutes at a certain temperature. Once the cloudy solution turns clear and it is cooled to room temperature. The solution is then doped with various amounts of ammonium salts. Later, these dry thin films were characterized via Impedance Spectroscopy, Fourier Transform Infrared (FTIR), X-Ray Diffraction (XRD), and Scanning Electron Microscope (SEM).

Based on the impedance results, the conductivity of starch is low due to no mobile ions provided within the sample. The incorporation of salt increased the conductivity gradually. The higher the concentration of the ammonium salt, it actually attributed to increase in the density number of mobile ions. The number density of charge carriers' increased since the rate of ion dissociation has been greater than the rate of ion association. But if the salt concentration is too high, it could increase the influence of the ion pairs and higher ion aggregation, which can reduces the overall mobility and degree of freedom hence decreases the conductivity.

FTIR measurement was used to determine the interactions between salt and the polymer host. In the present work, FTIR spectroscopy was recorded using Spotlight 400 Perkin-Elmer spectrometer in the wavenumber range of 450-4000 cm_1. The FTIR spectra indicates that the complexation between starch and ammonium salt has occurred. Upon higher concentration of the salt, hydroxyl band shifted to higher wavenumber, this maybe due to the fact that either the excess salt did not dissociate or the ions recombine to form a neutral ion pair which decreases the number of ions. From the x-ray diffractogram, three crystalline peaks are observed thus indicates the pure starch film shows semi crystalline state due to the presence of both sharp and diffuse diffraction peaks. The fraction of amorphous phase and the charge carriers increase simultaneously with increasing ion concentration. The optimum composition of the green solid electrolyte has the potential to be used as solid electrolyte in electrical devices since it shows maximum conductivity of 10-3 and serve as an ionic conductor.