Relationships Between Carbon Black Cathode Material Characteristics and Lithium/Oxyhalide Cell Performance

Abstract

Nine carbon blacks with iodine surface areas ranging between 60 and 1222 m2/gm and with dibutyl phthalate absorption numbers ranging between 125 and 420 cm3/100 gm have been evaluated as lithium/oxyhalide cell cathode materials. Two criteria have been considered: their ability to serve as heterogeneous catalysts for the cathodic half‐cell reaction (a function of both internal surface area and specific activity), and their ability to accommodate the continuous deposition of solid discharge products with minimal internal resistance losses (a function of both the porosity and pore size distribution of the agglomerated carbon particle aggregates). For carbons with surface areas of at least 250 m2/gm, overvoltages for reduction are practically independent of carbon black surface area. Furthermore, cathode porosities and cell discharge capacities both correlate with the DBP absorptometer numbers characteristic of the high surface area carbon blacks themselves. If the activity of a low surface area carbon is augmented via a catalytic additive (e.g., supported platinum), overvoltages similar to those obtained with high surface area carbons and complete utilization of the cathode's internal pore volume are achieved. The use of cathode “pore formers” may also lead to improved performance characteristics, particularly at very high current densities where pore former particle diameters averaging about 200 μm yield optimal performance results. Of the commercially available carbon blacks examined, Ketjenblack EC and Black Pearls 2000 function best as cell cathode materials, greatly outperforming the standard carbon, Shawinigan acetylene black.