Sulfonated polyaniline films as cation insertion electrodes for battery applications. Part 1.—Structural and electrochemical characterization
Sulfonated polyaniline (SPAN) was synthesized by sulfonation of polyaniline (PANI) base with fuming sulfuric acid. Thin films were cast from polymer solutions in basic media. The polymer films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible–near-infrared spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry. XPS in combination 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 with polyaniline. This is in agreement with the lower conductivity of SPAN as compared with polyaniline. SEM micrographs of the SPAN films showed a compact globular morphology. Electrodes modified with thin SPAN films exhibited two redox steps, both in aqueous and in non-aqueous electrolytes. The specific charge stored in SPAN films was found to be ca. 37 A h kg–1 in aqueous solution (only the first redox step) and ca. 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 battery. The optical spectra of SPAN films exhibited bands at 310, 450 and 750 nm, the intensities of which changed during the redox process. The absorption coefficients of SPAN (emeraldine base state) solutions had 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 electrochromic applications is discussed.