  The Weyl semimetal WTe$_{2}$ has shown several correlated electronic
behaviors, such as the quantum spin Hall effect, superconductivity,
ferroelectricity, and a possible exciton insulator state, all of which can be
tuned by various physical and chemical approaches. Here, we discover a new
electronic phase in WTe$_{2}$ induced by lithium intercalation. The new phase
exhibits an increasing resistivity with decreasing temperature and its carrier
density is almost two orders of magnitude lower than the carrier density of the
semi-metallic T$_{d}$ phase, probed by in situ Hall measurements as a function
of lithium intercalation. Our theoretical calculations predict the new
lithiated phase to be a charge density wave (CDW) phase with a bandgap of ~
0.14 eV, in good agreement with the in situ transport data. The new phase is
structurally distinct from the initial T$_{d}$ phase, characterized by
polarization angle-dependent Raman spectroscopy, and large lattice distortions
close to 6 % are predicted in the new phase. Thus, we report the first
experimental evidence of CDW in T$_{d}$-WTe$_{2}$, projecting WTe$_{2}$ as a
new playground for studying the interplay between CDW and superconductivity.
Our finding of a new gapped phase in a two-dimensional (2D) semi-metal also
demonstrates electrochemical intercalation as a powerful tuning knob for
modulating electron density and phase stability in 2D materials.
