  Rational design of novel two-dimensional (2D) electrode materials with high
capacity is crucial for the further development of Li-ion and Na-ion batteries.
Herein, based on first-principles calculations, we systemically investigate Li
and Na storage behaviors in the recently discovered 2D topological nodal-loop
metal - the honeycomb borophene oxide (h-B2O). We show that h-B2O is an almost
ideal anode material. It has good conductivity before and after Li/Na
adsorption, fast ion diffusion with diffusion barrier less than 0.5 eV, low
open-circuit voltage (less than 1 V), and small lattice change (less than 6.2%)
during intercalation. Most remarkably, its theoretical storage capacity is
extremely high, reaching up to 2137 mAh/g for Li and 1425 mAh/g for Na. Its Li
storage capacity is more than six times higher than graphite (372 mAh/g), and
is actually the highest among all 2D materials discovered to date. Our results
strongly suggest that 2D h-B2O is an exceedingly promising anode material for
both Li- and Na-ion batteries with super high capacity.
