Electrochemical Investigation of (De-)Lithiation Behaviors of Al Anodes and the Solubility Range of β-Lial Phase at Room Temperature

Abstract

Alloy anodes have been extensively studied over past decades to replace the graphite of lithium-ion batteries (LIBs). Most efforts are made towards those anode materials with high specific capacities such as silicon and germanium. To minimize the negative impacts of the volume expansions during Li incorporation, protective coatings or specific micro- and nanostructures have been suggested, but a commercialization on a larger scale was impeded by such preparation costly procedures. Therefore, the optimal alloy anode candidate should balance the cost, capacity and manufacturing complexity rather than solely maximize the specific capacity. Aluminum, an underappreciated anode material, possesses intrinsic properties that fulfill the criteria mentioned above. The origin of the main capacity of aluminum anode is upon the formation of the β phase (LiAl; ca. 1Ah/g). However, the (de-)alloying processes of Al remain poorly understood, especially at room temperature under which LIBs usually operate.In this study, we investigate the (de-)lithiation that occurs within the solubility range of the β phase Although this Li solubility is highlighted by multiple versions of the Li-Al phase diagrams, the solubility range at low temperatures was not specified yet due to the experimental conditions of previous phase diagram studies (> 400 °C). Various electrochemical analytic tools and methods are used to shed light on the Li solubility within the β phase. The Li solubility range of the β phase is determined to be roughly 5 at% by a potentiostatic charge counting experiment at room temperature. Moreover, the cyclic voltammetry of partially lithiated Al foils shows that the β phase can be (de-)saturated without propagating the phase front towards the α phase. If galvanostatic charge and discharge is smartly controlled by taking into consideration of the solubility range, the cycling life of β-LiAl anode can be significantly improved. Not only does this piece of work provide fundamental data for the β-LiAl phase at room temperature that complements the existing phase diagrams, but also implies that aluminum foil holds great potential as an anode material for the next generation of lithium-based batteries.