Achieving high efficiency and cyclability in inexpensive soluble lead flow batteries†

Here we report on the significant improvements made in the energy efficiency and cycle life of full-cell soluble lead flow batteries (SLFBs). We describe energy efficiency loss mechanisms, particularly in context to the deposition of PbO2 at the positive electrode. The morphology and crystal structure of deposits formed at the positive electrode, under galvanostatic and potentiostatic conditions, were characterized using both powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Rietveld refinements were performed to quantitatively determine the phase fraction of aand b-PbO2 formed. In addition, electrochemical impedance spectroscopy (EIS) was used to describe the chargetransfer reaction occurring at the positive electrode during conditions that promote the formation of various PbO2 morphologies. These features were used to evaluate and predict the long-term cycling stability of SLFBs as well as to diagnose potential problems arising during battery operation. We demonstrate that conditions optimized to preferentially deposit nanoscale PbO2 leads to long battery lifetimes, exceeding 2000 cycles at 79% energetic efficiency.