Enhancement of lithium-ion hopping on halogen-doped χ

Borophenes, which are two-dimensional boron counterparts made of the three synthetic polymorphs T, β12 and χ3, have been considered as potential anode materials in Li-ion batteries with extremely high capacities. However, Li hopping on β12 and χ3 borophenes is quite slow with high energy barriers (around 0.6 eV), thus preventing the application of these borophenes in the fast charging realm. Here, we have used halogen functionalization in an attempt to boost the sluggish Li-ion diffusion dynamics in the prototype χ3 borophene system. Halogens bind strongly to χ3 borophene with substantial electron transfer from the latter to the former, thereby leading to local electron deficiency in the χ3 borophene. The synergy of electron extraction from χ3 borophene and the electrostatic attraction between halogens and Li results in an enhanced affinity between χ3 borophene and Li as well as a reduction in the Li-ion hopping barrier. Iodine is the preferred dopant, for which most diffusion paths exhibit energy barriers typically smaller than 0.2 eV. Our results suggest that halogen incorporation could facilitate intercalation and de-intercalation of Li-ions in borophene-based anode materials.