  Trapping lithium with a big number in a simplified experimental setup has
difficulties and challenges today. In this paper, we experimentally demonstrate
the enhancement of \textsuperscript{6}Li trapping efficiency in a
three-dimensional magneto-optical trap (3D MOT) by using the multiple-sideband
cooling in a two-dimensional magneto-optical trap (2D MOT). To improve the
number of trapped atoms, we broaden the cooling light spectrum to 102 MHz
composed of seven frequency components and then trap atoms with a number of
$6.0\times10^8$ which is about 4 times compared to that in the single-frequency
cooling. The capture velocity and dependence of atomic number on the laser
detuning have been analyzed, where the experimental result has a good agreement
with the theoretical prediction based on a simple two-level model. We also
analyze the loss rate of alkali metals due to fine-structure exchanging
collisions and find that the multiple-sideband cooling is special valid for
lithium.
