SULFONATED POLYANILINE FILMS AS CATION INSERTION ELECTRODES FOR BATTERY APPLICATIONS .1. STRUCTURAL AND ELECTROCHEMICAL CHARACTERIZATION

Sulfonated polyaniline (SPAN) was synthesized by sulfonation of polyan iline (PANI) base with fuming sulfuric acid. Thin films were cast from polymer solutions in basic media. The polymer films were characterize d by X-ray photoelectron spectroscopy (XPS), Fourier transform infrare d (FTIR) spectroscopy, ultraviolet-visible-near-infrared spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry. XPS in com bination with FTIR showed that the preparation procedure led to ca. 47 % sulfonation of an otherwise unchanged polyaniline backbone. The NIR spectra of SPAN films showed a polaron band at higher energies than wi th polyaniline. This is in agreement with the lower conductivity of SP AN as compared with polyaniline. SEM micrographs of the SPAN films sho wed a compact globular morphology. Electrodes modified with thin SPAN films exhibited two redox steps, both in aqueous and in non-aqueous el ectrolytes. The specific charge stored in SPAN films was found to be c a. 37 A h kg(-1) in aqueous solution (only the first redox step) and c a. 68 A h kg(-1) in non-aqueous media (both redox steps). A practical SPAN-LI battery could have 50% more specific energy than a PANI-Li bat tery. The optical spectra of SPAN films exhibited bands at 310, 450 an d 750 nm, the intensities of which changed during the redox process. T he absorption coefficients of SPAN (emeraldine base state) solutions h ad Values of a = 410 at 313 nm and a = 239 at 563 nm. The suitability of SPAN for use as a cation-insertion material for battery and electro chromic applications is discussed.