  While classical percolation is well understood, percolation effects in
randomly packed or jammed structures are much less explored. Here we
investigate both experimentally and theoretically the electrical percolation in
a binary composite system of disordered spherocylinders, to identify the
relation between structural (percolation) and functional properties of
nanocomposites. Experimentally, we determine the percolation threshold $p_c$
and the conductivity critical exponent $t$ for composites of conducting
(CrO$_2$) and insulating (Cr$_2$O$_3$) rodlike nanoparticles that are nominally
geometrically identical, yielding $p_c=0.305 \pm 0.026$ and $t=2.52 \pm 0.03$
respectively. Simulations and modeling are implemented through a combination of
the mechanical contraction method and a variant of random walk (de Gennes ant)
approach, in which charge diffusion is correlated with the system conductivity
via the Nernst-Einstein relation. The percolation threshold and critical
exponents identified through finite size scaling are in good agreement with the
experimental values. Curiously, the calculated percolation threshold for
spherocylinders with an aspect ratio of 6.5, $p_c=0.312 \pm 0.002$, is very
close (within numerical errors) to the one found previously in two other
distinct systems of disordered jammed spheres and simple cubic lattice, an
intriguing and surprising result.
