Dissertations and Theses
Understanding and Controlling Failure Mechanisms of the Zinc Anode for Rechargeable Alkaline Batteries
Date of Award
zinc, anode, alkaline, rechargeable, batteries, failure mechanisms
In the coming years, the transformation of the electric grid will be in part enabled by safe, low-cost, and reliable large-scale rechargeable battery energy storage systems. Zinc (Zn) alkaline electrodes hold great importance and promise in the battery technology community as they satisfy the safety and cost requirements, yet their behavior in real world application is still poorly understood.
Two experimental studies were carried out, the first of which investigates failure mechanisms and material evolution during cycling of 27 zinc-manganese dioxide (Zn-MnO2) cells in 37 wt% potassium hydroxide (KOH) electrolyte wherein the percent utilization of the theoretical capacity of the Zn electroactive material is systematically varied between 1% and 16%. Cell fabrication is kept typical to the prevailing industrial cell design. Cycle life ranges from 2800 to 60, depending inversely on the Zn utilization. In all cases, the Zn material microstructure sheds the PTFE binder and forms ZnO rods, with longer rods formed by lower current per Zn mass. Irreversible side reactions such as the hydrogen evolution reaction (HER), short circuits, or gas crossover cause the Zn anode’s charging efficiency to average 92% but be as low as 86%, which in turn causes the baseload of metallic Zn to gradually disappear. Cell failure usually occurs after the baseload of metallic Zn is exhausted. The total lifetime discharge capacity remains in the range of 5-23 Ah/g Zn invariant of Zn utilization, which suggests the aforementioned processes of Zn microstructural evolution and side-reaction destruction of baseload metallic zinc both progress linearly with cumulative cell discharge capacity. Investigations of individual Zn failure mechanisms were performed in 22 purpose-built cells. It was found that tight packing of the cell microstructure can lead to poor mass transfer, causing supersaturation of soluble Zn, which in turn produces high overvoltage during discharge. Low charging current density yields poor coulombic efficiency due either to competitive HER reaction or ‘soft’ short circuits.
In the second experimental thrust, 72 zinc oxide (ZnO)-based negative electrodes were cycled in alkaline electrolyte paired against sintered nickel positive electrodes. The electrolyte concentration was varied: 10 wt% KOH, 20 wt% KOH, and 37 wt% KOH. A range of 15% to 30% Zn theoretical capacity utilization was studied. Electrode additives used in the investigation include calcium hydroxide (Ca(OH)2), bismuth oxide (Bi2O3), the surfactant cetyltrimethyl ammonium bromide (CTAB), and a synthetic layered silicate with trade name Laponite. Reduced KOH concentration extends cycle life due to reduced solubility of the zinc oxide formed during discharge and in turn increased anode mass retention. In 20 wt% KOH at 15% Zn utilization, the combination of ZnO with Ca(OH)2 and Bi2O3 achieved almost 1200 cycles and the longevity is attributed to the formation of calcium zincate, as shown with in situ X-ray diffraction (XRD). Additionally, a baseline ZnO electrode in 10 wt% KOH at 15% Zn utilization delivered a lifetime volumetric capacity of over 240 Ah/mL anode, surpassing the best reported values in the literature. Failure mechanisms of the ZnO-based electrodes were ascribed to the inability to charge the electrode and deleterious side reactions, namely HER, leading to an 88% average charging efficiency.
D'Ambrose, Michael J., "Understanding and Controlling Failure Mechanisms of the Zinc Anode for Rechargeable Alkaline Batteries" (2022). CUNY Academic Works.