Solid State Batteries from Chitosan Based Biopolymers

Abstract

Chitosan is a biopolymer which can provide some ionic conductivity when dissolved in acetic acid. The conductivity is due to the presence of protons from the acetic acid solution. The conducting chitosan film was prepared by the solution cast technique. Several films were prepared and each film was complexed with different amounts of hydrated copper sulphate crystals. The undoped film is colourless and films with more than 1.5 g of hydrated copper sulphate crystals added to it contain whitish spots indicating the possibility of exceeding the solubility limit of the copper sulphate crystals into the chitosan matrix. The electrical conductivity at room temperature stops increasing after more than 2.0 g of copper sulphate crystals have been added to the chitosan-acetic acid solution. The copper doped film with the highest electrical conductivity of ≈ 7 μS/cm was used to fabricate some thin film solid state batteries using various anode materials and cathode intercalation compounds. In the (Zn + CuSO₄)/chitosan film/(PbO₂) battery, an open circuit voltage (OCV) of 1.668 V was obtained. From this OCV value, it can be deduced via the electromotive force method that the chitosan film is a mixed conductor. Internal resistance measurements and discharge characteristics of the batteries fabricated will be presented.