Carbon filaments and carbon black as a conductive additive to the manganese dioxide cathode of a lithium electrolytic cell

Carbon filaments, when surface treated and used in stead of carbon black as the conductive additive to MnO₂ cathodes in lithium cells, produced a more gently sloping discharge curve (desirable for applications requiring end-of-life indication). These filament composite cathode plates also occupied less volume (higher packing density) and were handleable without the use of a binder, thus resulting in higher volumetric energy density than the carbon black counterpart. The Li/MnO₂ discharge capacity increased with the cathode's electrolyte absorptivity and rate of electrolyte absorption, as opposed to the cathode's electrical conductivity, whether carbon filaments or carbon black was used. The cathode's electrolyte absorption characteristics and packing density and the carbon's electron transfer rate were enhanced by surface treatment of the carbon. For carbon filaments, solvent cleansing, followed by either surfactant treatment or chopping plus drying, was effective; solvent cleansing also decreased the volume resistivity of both the carbon compact and the MnO₂/filament compact. For carbon black, surfactant treatment was effective and resulted in increases in test cell discharge capacity, open- and closed-circuit voltages (OCV and CCV), and cathode packing density. The volume electrical resistivity of the filament compact was lower than that of the carbon black compact, but the volume resistivity of the composite cathode was higher using carbon filaments instead of carbon black; the latter is due to the spreadability of carbon black between the MnO₂ particles.