Phase Relationships in Positive Electrodes of High Temperature Li ‐ Al / LiCl ‐ KCl / FeS2 Cells

The phases present in FeS 2 electrodes operated in LiCl ‐ KCl eutectic electrolyte were determined by x‐ray diffraction and by metallographic examination. The phases were FeS 2 , KFeS 2 , Li 3 Fe 2 S 4 , Li 2.33 Fe 0.67 S 2 , Fe 1 − x S , Li 2 FeS 2 , LiK 6 Fe 24 S 26 Cl , Li 2 S , and Fe. The metallographic and crystallographic characteristics of these phases are presented. The sequence of Li‐Fe‐S phases in the FeS 2 electrode was in accord with the sequence predicted from the equilibrium Li‐Fe‐S phase diagram. Two of the Li‐Fe‐S phases found at room temperature ( Li 2.33 Fe 0.67 S 2 and Li 2 FeS 2 ) result from decomposition on cooling of a solid solution phase: Li 2 + x Fe 1 − x S 2 ( 0 ≤ x ≤ 0.33 ) .