Dramatic Effects of Fullerene Soot Additives on the Electrochemical Cycling Behavior of Graphite Anodes

Arc-generated fullerene soot dramatically reduces the capacity fade of SFG-15 graphite electrodes in extended lithium ion cycling. Composite electrodes made by the addition of as little as 10% by mass fullerene soot exhibit less than 1.5% reduction in unload capacity over 200 cycles at a rate of C/2, whereas electrodes without the additive lose 79% of their capacity under the same conditions. The addition of the soot decreases the first cycle Coulombic efficiency of the electrodes, from 83.4% for graphite electrodes to 52.9% with the addition of 10% soot. However, the Coulombic efficiency of the composite electrodes surpasses that of the graphite electrodes after a few cycles and remains higher for subsequent cycles. The soot is estimated to increase the first cycle Coulombic losses by ∼ 2000 mAh/g of soot. The soot makes only modest contributions to the capacity of the electrodes, ∼85 mAh/g for compositions with 30% or more graphite content by mass, significantly less (∼25 mAh/g) for composite electrodes with lower graphite content. However, the soot apparently prevents the irreversible loss of electrode capacity, allowing the capacity of the graphite active material to approach its theoretical limit for lithium storage (372 mAh/g) for low soot content compositions.