Unveiling the electrochemical threshold properties of novel aluminum‑copper bimetallic foils anodes for high reversibility li-ion batteries

Abstract

High-reversibility aluminum‑copper bimetallic anodes have been characterized to determine the threshold specific capacity necessary to ensure a highly reversible process when used as anodes in Li-ion batteries. By controlling the intercalation step, the formation of a β-AlLi surface layer on the aluminum side is promoted. This layer effectively mitigates the stress generated during the expansion and contraction associated to the charging/discharging process. The threshold specific capacity was assessed by applying four different charging steps, corresponding to 5 %, 10 %, 20 %, and 50 % of the experimental specific capacity of aluminum, over 100 galvanostatic charge/discharge cycles. Additionally, the effects of different current densities (0.5 and 1 mA/cm2) and two aluminum qualities (1XXX and 3XXX) on the reversibility of the reactions and capacity loss were analyzed. The results indicated that charging steps corresponding to a specific capacity of 200 mA.h.g−1 were identified as the threshold capacity for achieving reversible anode behavior. Although this property is the most critical factor, the threshold point also depends on various factors such as the aluminum alloy used for the bimetallic anodes and the current density applied. The use of the 3XXX alloy, which is underexplored in the literature for this application, has shown to improve electrochemical (EC) behavior, in some cases doubling the number of cycles in which the anode exhibits reversible EC behavior. Conversely, higher current densities lead to rapid volume changes, and the resulting stress cannot be relieved, thereby affecting the anode's service life.