Effect of mechanical milling on lithium-ion conductivity of LiAlH4

Abstract

The effect of mechanical milling on the lithium-ion conductivity of lithium alanate (LiAlH4) is investigated. Although pristine LiAlH4 is a poor ion conductor in its highly crystalline state, short-time mechanical milling for 0.1–2 h is shown to significantly improve the conductivity. Hand-milling treatment in an argon-filled glove box is also shown to improve the conductivity. The activation energy (Ea) for ion conduction of milled LiAlH4 is ~0.70 eV, which is attributed to Li-ion site vacancy-mediated conduction. However, the Ea of pristine LiAlH4 shows a large value of 0.84 eV. The 7Li, 6Li, 27Al nuclear magnetic resonance and infrared spectra suggest that surface Li hydroxide species would exhibit Li-ion conduction in pristine LiAlH4. Thus, the milling treatment can eliminate the effect of surface hydroxide species and increase the vacancy concentration at the Li-ion site of inner LiAlH4 grains, which results in the enhancement of the conductivity.