Reinvestigation of Lithium Reaction Mechanisms in FeS[sub 2] Pyrite at Ambient Temperature

Lithiated samples with various lithium contents were examined by a combination of ex situ X-ray powder diffraction and ex situ scanning electron microscopy to provide experimental evidence for intermediate phases and insights to lithium reaction mechanisms of pyrite at ambient temperature. Natural and synthetic samples having distinctly different grain sizes were used in this study. Structural and morphological changes of these samples were compared under low and high current densities. Structural and morphological evidence revealed the presence of intermediate phases upon two-voltage-step lithium reduction of pyrite at ambient temperature. These intermediate phases were similar to some of those obtained from lithium reduction of near 400°C. Of significance was X-ray powder diffraction evidence of a layered solid solution phase upon the 1.7 V lithium reduction of at ambient temperature. A lithium reaction mechanism for two-voltage-step lithium reduction of pyrite was proposed and compared to those proposed in the literature. In addition, it was found that one-voltage-step lithium reaction of pyrite at 1.5 V or lower led to the formation of plate-like (plate thickness on the order of 20 nm) and Fe, which supported the reaction mechanism proposed by Fong et al. [ J. Electrochem. Soc. , 136 , 3206 (1989).] © 2002 The Electrochemical Society. All rights reserved.