(103b) Transient Interfacial Zinc Oxide Formation in Cycling Alkaline Batteries Detected Using Synchrotron X-Rays

Energy dispersive X-ray diffraction (EDXRD) using white beam synchrotron radiation allows electrochemical cells with centimeter scale dimensions to be rapidly mapped crystallographically in both time and space. Using this technique, X-rays with a wide range of energies penetrate the cell, and X-ray diffraction intensity is measured at a single angle from a localized gauge volume within the cell. We report in situ EDXRD data collected on cycling LR20 Zn-MnO2 batteries collected using the superconducting wiggler beamline X17B1 at the National Synchrotron Light Source (NSLS) located at Brookhaven National Lab.

As data collection time for an EDXRD diffraction contour was short compared to the length of a battery cycle, material changes were resolved as a function of cycling stage as well as spatial location. This allowed us to resolve highly localized crystallographic changes within the battery. This is important, as batteries are designed to maximize interfacial area by employing thick, porous electrodes, which can display nonhomogenous reaction conditions. Concentration and reaction distributions within the electrodes can cause conditions that lead to battery failure during long term cycling.

The data revealed transient zinc oxide layers that formed and dissolved at the anode-separator interface during cycling, as a function of battery discharge rate. Massive zinc oxide formation was found in some cycled Zn-MnO2, and is believed to be a failure mechanism. Lattice strain was also detected in the cathode MnO2, and this lattice strain was found to be a function of radial distance from the anode.

It is generally recognized that electrochemical storage on a large scale is desirable for a number of societal reasons including electrical load leveling, power regulation, electrical demand peak shaving, the smart grid, and for firming intermittent renewables-based generation such as solar and wind power. Powerful in situ techniques such as EDXRD can aid in classifying long term battery failure mechanisms, which can have a multitude of causes some of which are localized and occur within thick, sealed devices.