Phase transition behavior of a processed thermal battery.

Abstract

In order to fully understand the transition mechanism of a processed thermal battery, Micro X-ray Diffraction (μ-XRD) and Micro X-ray Fluorescence (μ-XRF) were employed to characterize various quench states. The transition of interest in this report is the formation of Li 7 Si 3 from Li 13 Si 4 (initial anode material). The unit cell conditions during Li 13 Si 4 transition to Li 7 Si 3 show a contraction of 0.04 and 0.02 Å (a and b-axis respectively), an expansion in the c-axis of 0.02 Å, and an overall reduction in the cell volume from 541.13 Å 3 to 539.21 Å 3 for the Li 13 Si 4 Orthorhombic (Pbam) component. The contraction in the a-b plane results from the loss of lithium atoms; the expansion in the c-axis direction is due to reorganization of the lithium and silicon within the unit cell. Transition processing also requires that an excess of 3⅔ moles lithium (within anode region) react with sulfur (within cathode region) to form Li 2 S. Micro-XRF confirms a definite migration of sulfur through the separator region during the transition. These results both explain peak shifts (in anode regions) and the formation of Li 2 S during transition states.