Identifying problematic phase transformations in Pb foil anodes for sodium-ion batteries

Abstract

Group IVA elements have aroused attention in sodium-ion batteries (SIBs) due to their Na-storage capability. Among them, Pb is less explored perhaps due to its perceived risks, but its long-standing success in Pb-acid batteries should not be neglected. Together with the well-established recycling procedures, the merits of Pb warrant further investigations as a practical SIB anode. In this work, four intermetallic phases are detected during electrochemical sodiation of Pb, which yields a capacity of ∼460 mAh·g−1 (∼1167 mAh·cm−3) upon the formation of Na15Pb4. When pursuing full capacities, the electrode stops functioning after only 3–4 cycles largely due to electrode physical damage. The reversibility of each phase transformation pair is then assessed to explore the origins of capacity fading. The NaPb/Na9Pb4 transformation shows the worst stability, consistent with the observed structural damage (e.g., cracks and voids). Through bypassing the problematic phase transformations using a partial cycling protocol, the stability of Pb foil anodes is improved, giving 20 cycles with 85% capacity retention. Considering other factors are unoptimized, it is suggested that the Pb-based anodes should not be fully eliminated from the future roadmap of SIBs, as the prospective merits can create value to ensure the management of such materials of concern.