The ternary system lithium–silver–silicon has been analyzed in a domain close to the composition Li 2 AgSi. The new compound Li 13 Ag 5 Si 6 has been characterized by both powder and single crystal X-ray diffraction. It crystallizes in the R3¯m rhombohedral system with the hexagonal cell parameters a=4.3906(6), c=42.293(5)Å, Z=2. The pseudo-tetrahedral structure is made up of [SiAg], hexagon-based, corrugated layers that are cross-linked via Si–Ag, Si–Si or Ag–Ag connections. Lithium atoms not only fill the interlayer space but also partially (∼19%) substitute for silver within the layers. The band structure indicates an anisotropic metallic character. Li 13 Ag 5 Si 6 behaves fairly well as an anodic material for lithium-ion batteries, with a reversible specific capacity around 800mAhg −1 .