DIFFUSION OF LITHIUM IONS IN PURE AND DOPED fcc LITHIUM SULFATE

摘要

The concentration dependence of the diffusion of lithium ions has been studied at 620 °C in fcc Li2SO4 doped with MgSO4 (up to 60 mole %) or whit LiCl (up to 18 mole %). The diffusion coefficient DLi decreascs when MgSO4 is added, which should be expected if the lithium ions occupy octahedral lattice positions, while cations in tetrahedral positions are to be considered as interstitials. From the increase of DLi when LiCl is added, the Gibbs free energy required to take a Li ion from an octahedral to an interstitial position is estimated to be 0.37 eV. Preliminary computer calculations of ion potentials tend to support these experimental results. From some previous experiments on isotope effect it is concluded that the so called ƊK-factor is close to unity for the migration of Li or Na ions in fcc Li2SO4, which means that diffusing cations do not share much energy with the anion lattice. From a comparison between sell-diffusion and conductivity data it is concluded that there is a certain contribution from ring mechanisms in addition to the dominating vacancy mechanism for the migration of Li ions.