The role of carbon black in LiMn2O4-based composites as cathodes for rechargeable lithium batteries

LiMn2O4-based composites have been prepared by cold pressing physical mixtures of LiMn2O4, carbon black (CB), and polyvinylidenefluoride (PVDF). The PVDF content has been kept constant (ca. 14.5% by volume or 10% by weight). The LiMn2O4 and CB contents have been changed in an opposite way, i.e., from 59.6 vol % (or 90.6 wt %) to 19.2 vol % (or 19 wt %) for LiMn2O4, and from 0 vol % (or 0 wt %) to 32.2 vol % (or 38 wt %) for CB. The microstructure of the composites shows clusters formed of aggregated particles of either LiMn2O4 or CB. The electrical conductivity follows a percolating process in which the conductivity changes by five orders of magnitude, the percolation threshold being 3 vol % of CB. The first discharge capacity changes from 0 to 135 mAhg(-1) for increasing the CB content. The change in capacity also seems to follow a percolation process in which the sharp increase in capacity is observed for CB contents close to 3 vol %. The discharge capacity of the LiMn2O4-based composites is controlled by electronic transport within the composite, the electronic transport depending on the microstructure of the composite. (C) 2000 The Electrochemical Society. S0013-4651(00)06-068-7. All rights reserved.