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 bla ck as the conductive additive to MnO2 cathodes in lithium cells, produ ced a more gently sloping discharge curve (desirable for applications requiring end-of-life indication). These filament composite cathode pl ates also occupied less volume (higher packing density) and were handl eable without the use of a binder, thus resulting in higher volumetric energy density than the carbon black counterpart. The Li/MnO2 dischar ge 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 a nd the carbon's electron transfer rate were enhanced by surface treatm ent of the carbon. For carbon filaments, solvent cleansing, followed b y either surfactant treatment or chopping plus drying, was effective; solvent cleansing also decreased the volume resistivity of both the ca rbon compact and the MnO2/filament compact. For carbon black, surfacta nt treatment was effective and resulted in increases in test cell disc harge capacity, open- and closed-circuit voltages (OCV and CCV), and c athode packing density. The volume electrical resistivity of the filam ent compact was lower than that of the carbon black compact, but the v olume resistivity of the composite cathode was higher using carbon fil aments instead of carbon black; the latter is due to the spreadability of carbon black between the MnO2 particles.