  We report first principle calculations of electronic and mechanical
properties of few-layer borophene with the inclusion of interlayer van der
Waals (vdW) interaction. The anisotropic metallic behaviors are preserved from
monolayer to few-layer structures. The energy splitting of bilayer borophene at
$\Gamma$ point near the Fermi level is about 1.7 eV, much larger than the
values (0.5--1 eV) of other layered semiconductors, indicating much stronger
vdW interactions in metallic layered borophene. In particular, the critical
strains are enhanced by increasing the number of layers, leading to much more
flexibility than that of monolayer structure. On the one hand, because of the
buckled atomic structures, the out-of-plane negative Poisson's ratios are
preserved as the layer-number increases. On the other hand, we find that the
in-plane negative Poisson's ratios disappear in layered borophene, which is
very different from puckered black phosphorus. The negative Poisson's ratio
will recover if we enlarge the interlayer distance to 6.3 $\mbox\AA$,
indicating that the physical origin behind the change of Poisson's ratios is
the strong interlayer vdW interactions in layered borophene.
