  Layered two-dimensional materials like graphene are highly appealing for
lithium battery applications owing to their high surface-volume ratios.
However, a critical issue that limits their practical applications is the
confined motion of lithium atoms within their van der Waal's gaps, which is the
leading cause for battery failure due to severe clustering and phase
separation. Here we demonstrate that antimonene, an exfoliatable 2D material
with a high structural stability, exhibits a highly mobile cross-sheet motion
owing to its unique structural features. The advent of the vertically permeable
channels opens a new pathway of lithium besides the normal motion along the
basal plane, rendering a 2+1 dimensional kinetics. Specifically, our
first-principles calculations combined with the discrete geometry analysis
revealed that the energy barrier for a lithium atom to diffuse across the
antimonene sheet is as low as 0.36 eV, which can be further reduced to 0.18 eV
under a tensile strain of 4%. These ultralow diffusion barriers across the
sheet can open a new dimension for controlling the motion of lithium atoms,
leading to a new paradigm for high-performance lithium batteries or inorganic
solid-state lithium-ion conductors.
