Study of the Reaction of Lithium with Isostructural A[sub 2]B and Various Al[sub x]B Alloys

Abstract

The electrochemical alloying reaction of Li with isostructural A2B and Al-based alloys has been investigated. The binary A2B alloys we selected (Sb2Ti, Sb2V, Sn2Co, Sn2Mn, Sn2Fe, Al2Cu, and Ge2Fe) are isostructural (Al2Cu type) and comprise an active element (A) that alloys with lithium, and an inactive one (B) that does not. These compounds were prepared by mechanical alloy- ing and have small grain size (10-20 nm). With the exception of Al2Cu, we observed a full reaction of A with lithium (A2B ⫹ 2xLi r B ⫹ 2LixA, where the theoretical values of x are 1 for Al, 3 for Sb, and 4.4 for Si, Ge, and Sn). Extremely slow electro- chemical cycling at 55⬚C and potentiostatic tests at lithium potential proved the total inactivity of the Al2Cu vs. lithium. However, thermodynamic considerations predict that the reaction of Al2Cu with Li should occur and that the formation of LiAl should be observed. Other Al-transition metal intermetallics were studied and were also found to be inert toward Li, suggesting that the Al- transition metal bond has unique features.