Amino acid based ionic liquids for revitalization of sulfated lead anodes

Abstract

Lead acid batteries (LABs) are currently recycled using hazardous, polluting, and energy intensive procedures. Here we report a novel LAB recycling strategy with hydrophilic amino acid-based ionic liquids (ILs) to dissolve the water-insoluble PbSO4 crystals formed during deleterious hard sulfation at the anodes and then electrodeposit metallic Pb on a new surface. We identified two ILs, [Ch][Ser] and [Ch][Thr] ILs that show dramatic solubility towards PbSO4 at room temperature. [Ch][Ser] IL was successfully used in refurbishing hard sulfated anodes that had lost 99 % of their original capacity into a fresh Pb surface. More than 75 % of the capacity was renewed after a complete treatment on a half-cell. Electrodeposition of Pb from the Pb-[Ch][Ser] complex produced a uniform Pb microstructure. A remarkable 99 % of the IL-dissolved Pb2+ ions was electrodeposited. Furthermore, we solved the first crystal structure of the compound formed between Pb2+ and the amino acid-based IL. Based on 1H Nuclear Magnetic Resonance (NMR) spectrum of PbSO4 dissolved in the [Ch][Ser] IL and single crystal X-ray diffraction (XRD) studies, we discovered that the Pb2+ was coordinated with two [Ser] molecules and displayed a hemidirected five-coordinate geometry. ILs that can selectively dissolve PbSO4 thus hold promise for an environment-friendly alternative recycling paradigm for the LAB industry.