INSITU DETERMINATION OF GRAVIMETRIC AND VOLUMETRIC CHARGE-DENSITIES OF BATTERY ELECTRODES - POLYANILINE IN AQUEOUS AND NONAQUEOUS ELECTROLYTES

Polyaniline (PANI) electrodes with redox capacities >1 C/cm2 were investigated by in situ electrogravimetry in aqueous electrolytes of pH values varying from <0 to 3 and in nonaqueous, propylene carbonate-based media. Film mass, volume, and bulk density were determined in situ as a function of electrode potential. For aqueous electrolytes, the gravimetric analysis supports a charge-transfer mechanism which depends on pH and involves the exchange of protons, electrolyte anions, and H2O. Protonation equilibria of reduced PANI were monitored gravimetrically in aqueous HCl, H2SO4, and HClO4. In nonaqueous electrolytes, however, the main charge-compensating process appears to be reversible insertion of anions. For LiClO4/propylene carbonate solutions, it was shown that up to 0.9 electrons can be transferred per aniline unit, resulting in experimental charge densities of 270 Ah/kg, based on dried reduced PANI. Upon immersion and cycling in nonaqueous electrolytes, the practically usable charge density was lowered to 160 Ah/kg due to sorption of solvent and incomplete oxidation. Based on in situ gravimetry, a detailed analysis of mass and volume requirements for electroactive material and electrolyte in rechargeable PANI batteries (e.g., Li/PANI) was derived.