Strongly anisotropic thermal conductivity in planar hexagonal borophene oxide sheet

The flat hexagonal borophene oxide (B2O) has the highest Li storage capacity among existing two-dimensional materials. Thermal conductivity is an important parameter for the safety of Li-ion batteries. We investigate the lattice thermal conductivity of B2O by solving phonon Boltzmann transport equation combined with the first-principles calculations. We found that the relaxation time approximation remarkably underestimate the thermal conductivity (kappa) of monolayer B2O, revealing phonon hydrodynamics characteristic. The kappa of B2O from the exact solution of Boltzmann transport equation is 53 Wm(-1) K-1 and 130 Wm(-1) K-1 along armchair-direction and zigzag-direction at 300 K, respectively. B2O exhibits strong thermal transport anisotropy due to anisotropic phonon group velocity, obviously larger than that of other borophene allotropes. At room temperature, the phonon mean free path of B2O is about 231 nm and 49 nm along armchair-direction and zigzag-direction, respectively. The highly anisotropic thermal conductivity of B2O offers new possibilities for its applications in thermal management. (C) 2020 Elsevier B.V. All rights reserved.