Operando X-ray Diffraction on a LiCoO₂ Coin Cell Battery

Introduction

The ongoing search for the best way to store electrical energy has led to the development of many different hardware solutions. The designs typically differ in capac-ity, energy density, mechanical stability and ease of man-ufacturing. With their relatively low weight, cheap produc-tion costs and versatile sizes, pouch or prismatic cells have become the go-to solution for applications that re-quire large, high performance batteries such as electrical vehicles, cell phones or laptop computers. For certain applications, however, high performance and low weight aren’t as important as compact size, high mechanical stability and long lifetime. Here, coin cells or button cells are the cell of choice. They come in various sizes and are commonly used in everyday devices like wrist-watches, hearing aids or remote controls.
X-ray diffraction (XRD) can give insights into the struc-tural changes occurring within a battery during cycling and storage, making it a useful tool for quality control and R&D. Since the method is non-destructive, and the pene-tration depth of X-rays allows investigation of the internal components of a fully assembled cell, it is the perfect method for in situ or operando measurements. XRD measurements on batteries can be challenging because the active material, which is what usually exhibits struc-tural changes, is only one of many crystalline compo-nents, and it can easily be masked by stronger signals of the metal foils used as current collectors or the metal housing of the battery. The changes in the XRD pattern usually come in the form of slight peak shifts so can be easily overlooked. For these reasons, XRD measure-ments on batteries require instrumentation that can pro-vide data with a high resolution, high intensity and good signal-to-noise and peak-to-background ratio.