Rechargeable lithium ion batteries (LIBs) have penetrated ubiquitously into our daily lives from cell phones to laptops and recently, they are highly considered for powering electric vehicles (EVs) as well as for the storage and distribution of energy from sustainable sources, such as solar and wind energy. Nevertheless, the currently commercial LIBs still suffer from unsatisfied energy/power density, unavoidable performance degradation, short life time and various safety concerns. In order to investigate the underlying operating mechanisms of LIBs and find out which factor dominates the inevitable performance decay during cycling, a variety of investigation tools such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray tomography/radiography  have been employed. Unfortunately, a particular battery design (such as an open structure) and specialized electrolytes (such as ionic and Li₂O electrolyte) that don’t adequately simulate the real operating conditions of commercially available LIBs are adopted. This has, to some extent, prevented us from investigating the real operating mechanisms of LIBs and resultantly, the development of next-generation energy storage technologies has been slowed down.

In the present demonstration, we report the design and fabrication of two kinds of prototypes of LIBs for X-ray Tomography and Radiography and the resultant results have been analyzed and discussed. The motivation of this work is to visually observe the underlying operating process of LIBs by synchrotron and/or laboratory X-rays to identify failure mechanisms during cycling. To this end, we have designed and fabricated a tomography cell (tomo-cell) for three-dimensional investigation and a radiography cell (radio-cell) for two-dimensional investigation, as shown in Fig. 1.

Results of investigation of silicon (Si) based electrode coupled with Li during the first cycle are presented and discussed. The conclusion is that, apart from the big volume expansion/contraction of Si particles that leads to electrical disconnection from the current collector, the electrochemical deactivation of initially electrochemically active Si particles also contributes to the capacity decay. Furthermore, the electrochemically in-active Si particles that undergo no de/lithiation process can result in a decreased energy/power density.  

Fig. 1. Images of the proof-of-concept batteries: a) tomo-cell and b) radio-cell. c) Corresponding schematic representation of the tomo-cell. d)  Corresponding schematic representations of the radio-cell. e) Enlarged region of interest comprising from top to bottom: electrode (blue), separator (grey) and counter electrode (green). f) Schematic representation of the X-ray micro CT setup. From left to right: X-ray source (red), cone X-ray beam (yellow), sample representing either of the two cells (green) and rotation table (grey), detector (blue). The waves in c) and d) represent the direction of X-rays.