The body-centred cubic (bcc) structure is the most stable form for lithium metal at 298 K (25°C). Under normal conditions, all of the Group 1 (alakali metals) elements are based upon the bcc structure. The closest Li-Li separation is 304 pm implying a lithium metallic radius of 152 pm. This means that lithium is smaller than potassium. In the bcc lattice, every lithium atom is surrounded by eight other nearest neightbour lithium atoms organised into a cubic array. One way to visualize the bcc lattice is as two interlocked infinite cubic arrays of atoms.
M.R. Nadler and C.P. Kempfer, Anal. Chem., 1959, 31, 2109.