Advanced lithium ion batteries with high capacity density, high rate capability and excellent durability are crucial for next-generation energy storage systems. Due to the much high theoretical capacity (4200 mAh/g), silicon is regarded as an excellent replacement candidate for the recently widely used graphite anode for next lithium-ion batteries^[1]. The abundance and relatively low working potential further provide wide and bright application prospects. However, the major obstacles for silicon are the microstructure degradation and volume expansion (~300 %) during the repetitive lithium insertion and extraction during cycling, which seriously influence the capacity performance and lifetime.^{[1, 2]}

Understanding the degradation phenomena in electrochemical systems is crucial to solve the problems facing silicon batteries. Fortunately, in situ and operando radiography techniques provide unique tools allowing analysis and description of the internal morphology and structure changes of electrodes during cycling non-destructively and noninvasively.^{[3, 4]}

Herein, the dynamic microstructure evolution of silicon particles during the first dis/charge processes are illustrated by operando synchrotron X-ray imaging. We present details on the process of lithiation/delithiation, fracturing/recovery and the volume expansion/shrinkage of the electrode. The diameter/volume variations of silicon particles with different sizes differ during de/lithiation. Furthermore we demonstrate a delay in the reaction of the particles behavior after switching current. In addition, inactive particles and gas evolution within the electrode have also been observed during operation, which shows the superior advantages of synchrotron X-ray imaging for battery degradation studies.

Figure 1 shows the a) schematic representation of the synchrotron X-ray imaging setup; and b) sketch of a customized cell for operando synchrotron X-ray imaging, with components from left to right are upper housing (claret-red), sealing ring (yellow), copper ring (orange), lithium plate (blue), separator (light grey), Si/carbon/binder composite (green), titanium foil (dark grey, current collector), copper ring (orange), bottom housing (claret-red).

References

[1] X. Su, Q. Wu, J. Li et al., Silicon-Based Nanomaterials for Lithium-Ion Batteries: A Review. Advanced Energy Materials, 2014, 4, 1300882.

[2] F. Sun, H. Markötter, K. Dong et al., Investigation of failure mechanisms in silicon based half cells during the first cycle by micro X-ray tomography and radiography. Journal of Power Sources, 2016, 321, 174-184.

[3] M. Ebner, F. Marone, M. Stampanoni, V. Wood, Visualization and quantification of electrochemical and mechanical degradation in Li ion batteries. Science, 2013, 342, 716-720.

[4] K. J. Harry, D. T. Hallinan, D. Y. Parkinson, A. A. MacDowell, N. P. Balsara, Detection of subsurface structures underneath dendrites formed on cycled lithium metal electrodes. Nat Mater, 2014, 13, 69-73.