  Kondo systems are usually described by the interaction of strong correlation
induced local moment with the highly itinerant conduction electrons. Here, we
study the role of electron correlations among conduction electrons in the
electronic structure of a Kondo lattice compound, Ce$_2$CoSi$_3$, using high
resolution photoemission spectroscopy and {\it ab initio} band structure
calculations, where Co 3$d$ electrons contribute in the conduction band. High
energy resolution employed in the measurements helped to reveal signature of Ce
4$f$ states derived Kondo resonance feature at the Fermi level and dominance of
Co 3$d$ contributions at higher binding energies in the conduction band. The
line shape of the experimental Co 3$d$ band is found to be significantly
different from that obtained from the band structure calculations within the
local density approximations, LDA. Consideration of electron-electron Coulomb
repulsion, $U$ among Co 3$d$ electrons within the LDA+$U$ method leads to a
better representation of experimental results. Signature of electron
correlation induced satellite feature is also observed in the Co 2$p$ core
level spectrum. These results clearly demonstrate the importance of the
electron correlation among conduction electrons in deriving the microscopic
description of such Kondo systems.
