  Mapping lithium evolution for evolved stars will provide restrictions and
constraints on the fundamental stellar interior physical processes, which
further shed light on our understanding of the theory of stellar structure and
evolution. Based on a sample of 1,848 giants with known evolutionary phases and
lithium abundances from the LAMOST-\kepler{} and LAMOST-\emph{K}2 fields, we
construct mass-radius diagrams to characterize the evolutionary features of
lithium. The stars at red giant branch (RGB) phase show natural depletion along
with their stellar evolution, particularly, there is no obvious crowd stars
with anomalously high Li abundances near the bump. Most of the low-mass stars
reaching their zero-age sequence of core-helium-burning (ZAHeB) have Li
abundances around $\sim1.0$\,dex, which show an increase of Li abundance by
$\sim0.6$\,dex compared to the stars above the bump of RGB. This suggests the
helium flash can be responsible for moderate Li production. While for super
Li-rich stars, some special mechanisms should be considered during helium
flash. Other scenarios, such as merger, could also be interpretations given the
Li-rich stars can be found at anytime during the steady state phase of core
He-burning. During the core He-burning (HeB) phase, there is no indication of
obvious lithium depletion.
