Prediction of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi mathvariant="normal">L</mml:mi> <mml:msub> <mml:mi mathvariant="normal">i</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:mi mathvariant="normal">F</mml:mi> <mml:

Using a computational crystal structure search in the Li-Fe-B ternary system, we predict a stable phase of $\mathrm{L}{\mathrm{i}}_{3}\mathrm{F}{\mathrm{e}}_{8}{\mathrm{B}}_{8}$, featuring 1D channels that enable rapid Li-ion transport. Ab initio molecular dynamics simulations show that the Li-ion diffusion coefficient in $\mathrm{L}{\mathrm{i}}_{3}\mathrm{F}{\mathrm{e}}_{8}{\mathrm{B}}_{8}$ surpasses that of common electrode and conductive additive materials by several orders of magnitude. The high diffusion in $\mathrm{L}{\mathrm{i}}_{3}\mathrm{F}{\mathrm{e}}_{8}{\mathrm{B}}_{8}$ can be explained by the Frenkel--Kontorova model, which describes an incommensurate state between the Li diffusion chain and the periodic potential field caused by the FeB backbone structure. The favorable lithium-ion diffusivity and mechanical properties of $\mathrm{L}{\mathrm{i}}_{3}\mathrm{F}{\mathrm{e}}_{8}{\mathrm{B}}_{8}$ make it a promising conductive additive for battery materials. An external magnetic field can further manipulate the properties of this material due to its predicted itinerant ferromagnetism, which also offers a platform for exploring spin-dependent phenomena.