Electrochemical Formation of Four Al-Li Phases (β-AlLi, Al₂Li₃, AlLi_2−x, Al₄Li₉) at Intermediate Temperatures

Aluminum electrodes have been considered for use in lithium and lithium ion batteries for nearly four decades. Although the Al-Li equilibrium phase diagram contains multiple Al-Li phases, only β-AlLi forms during room temperature cycling. Al 2 Li 3 can be formed when electrochemically inserting Li at temperatures above 400°C, and Al 4 Li 9 is occasionally detected after extended room temperature cycling. Here, four equilibrium phases of Al-Li (β-AlLi, Al 2 Li 3 , AlLi 2−x , Al 4 Li 9 ) were produced by the electrochemical lithiation and delithiation of 1100-series aluminum foil at moderate to intermediate temperatures (30–150°C) using a carbonate-based electrolyte. Phase identification was performed using ex-situ X-ray diffraction and coulometry, after accounting for the consumption of lithium in electrolyte breakdown products. After overcoming an initial nucleation barrier, β-AlLi formed at all temperatures, Al 2 Li 3 and AlLi 2−x formed at temperatures above 60°C at moderate rates, and above 35°C at low rates, and Al 4 Li 9 formed at temperatures above 100°C. All expected phases were also encountered during delithiation. The effects of nucleation and diffusion on observed phases and capacities are also discussed.