Combinatorial Study of Tin-Transition Metal Alloys as Negative Electrodes for Lithium-Ion Batteries

A survey of the structural and electrochemical properties of combinatorially sputter deposited Sn-transition metal alloys [Sn(1-x)M(x) (0 < x < 0.7; M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu)] is reported. Over 512 compositions have been studied. Sputtered libraries of Sn(1-x)M(x), with M = Mn, Fe, Ni, and Cu show no evidence of nanocrystalline or amorphous phases at any composition. By contrast, libraries of Sn(1-x)M(x) with M = Ti, V, Cr, and Co show composition ranges where the films are highly nanostructured or amorphous, suggesting that these elemental combinations are better glass formers. The transition metal contents of the amorphous or nanostructured phase regions are 0.37 < x < 0.40 and x > 0.48 to at least x = 0.65 for M = Ti, x > 0.39 to at least x = 0.60 for M = V, 0.47 < x < 0.73 for M = Cr, and 0.28 < x < 0.43 for M = Co. Electrochemical tests using a 64 channel Li/Sn(1-x)M(x) combinatorial electrochemical cell show that the specific capacity of the alloys drops with transition metal content, as expected. The Sn(1-x)Co(x) system shows an amorphous phase with the largest specific capacity, primarily because the amorphous phase is reached at the lowest transition metal content for Sn(1-x)Co(x). Capacity retention vs cycle number is generally best for those compositions that are amorphous or highly nanostructured. Arguments are presented to suggest that amorphous Sn(1-x)V(x) alloys are the best choice among Li/Sn(1-x)M(x), alloys. Comparison with literature results for samples prepared by mechanical alloying, elec-trodeposition, vacuum deposition, etc. is made.