Lithium Diffusion in Copper

Copper is the conventional, broadly applied anode current collector in lithium-ion batteries, because Li does not form intermetallic alloys with Cu at room temperature. Fast diffusion and trapping of lithium in copper were, however, suggested in the past, and the involved diffusion mechanisms are still not clarified. By using three complementary methods, we determine grain boundary and lattice diffusion of lithium in copper. We show that indiffusion into copper is possible not only from metallic lithium deposits at the surface but also from a Li+-containing electrolyte. Lattice diffusion (D0 = 3.9 × 10-9 cm2/s; Ea = 0.68 eV) and grain boundary diffusion (D0 = 1.5 × 10-11 cm2/s; Ea = 0.36 eV) are found to be 13 orders of magnitude lower than previously published. Furthermore, for practical Li-ion battery considerations, lithium trapping in copper current collectors, which relies heavily on operating temperature and morphology, is discussed.