Chemical diffusion in intermediate phases in the lithium-tin system

The compositional variation of the chemical diffusion coefficient in the six intermediate phases LiSn, Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2, and Li22Sn5 of the lithium-tin system at 415°C has been measured. Among these intermediate phases, the phase Li13Sn5 has the highest chemical diffusion coefficient, varying with composition from 5.01 × 10−5 to 7.59 × 10−4 cm2/sec at that temperature. Combining this information with coulometric titration curves (emf versus composition), the self-diffusion coefficient of lithium has also been determined in the various intermetallic phases as a function of composition under the assumption that the tin atoms do not move appreciably compared with the lithium atoms. The lithium self-diffusion coefficient in the phase LiSn is lower than those in the more lithium-rich phases by one order of magnitude. This result is discussed in terms of the difference between the crystal structures of LiSn and the other lithium-rich phases in the lithium-tin system.