Detection of highly conductive pathways in LiMn2O4–carbon black composites for Li ion batteries by microcontact impedance spectroscopy

The arrangement of carbon black around active particles in LiMn2O4 composite cathodes is studied by using EDS analysis, scanning electron microscopy (SEM) and microelectrode impedance spectroscopy. It is shown that a uniform carbon black distribution around the active particles is reflected in a normal-like distribution of locally probed resistances around the active particles. If the carbon black is non-uniformly arranged (that is, it tends to form agglomerates within the composite), then a bi-modal distribution of local resistances is obtained. The normal-distribution case leads to considerably lower polarization of cathodes and, consequently, to higher cathode capacities at given current densities.