Challenges of Nanoscale Characterisation of Litihum-Based Energy Materials

Abstract

The electric energy revolution is driven by battery technology. New chemistries and control systems enables the widespread use of portable electric devices, such as phones, computers, power tools and automobiles. The upward trend in battery performance relies on continuous research[1]. Scanning transmission electron microscopy (STEM) is a commonly used tool for nano-scale characterisation, as it allows for imaging as well as elemental and chemical analysis, when combined with energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS)[2], [3]. EELS is a particularly useful technique, as the near-edge structure of the ionization edges often give chemical bonding information. However, the high energy electron beam used in STEM can damage materials[4]. This is especially problematic in the field of battery research. Low-Z elements such as lithium, carbon and oxygen, are particularly susceptible to knock-on damage[4]. Since these elements are common in lithium-ion batteries, understanding how the beam affects materials is critical to the analysis of the materials. Commercially pure chemical compounds (LiF, LiCl, Li2CO3), acquired from MilliporeSigma, are exposed to the microscope beam, under condition favorable for EELS analysis of the Lithium K-edge. An EELS spectrometer is used to serially acquire energy loss spectra of the materials. These time-sensing series show how the near edge structure of lithium evolve as the material is damaged by the beam. In this work, the abherrent effects of the electron microscope on lithium samples is made evident.[1] J. B. Goodenough and K.-S. Park, “The Li-Ion Rechargeable Battery: A Perspective,” Journal of the American Chemical Society, vol. 135, no. 4, pp. 1167–1176, Jan. 2013.[2] D. B. Williams, Transmission electron microscopy: a textbook for materials science, 2nd ed. New York: Springer, 2008.[3] J. I. Goldstein et al., Scanning Electron Microscopy and X-Ray Microanalysis a Text for Biologists, Materials Scientists, and Geologists. Boston, MA: Springer US, 1992.[4] R. F. Egerton, “Mechanisms of radiation damage in beam-sensitive specimens, for TEM accelerating voltages between 10 and 300 kV,” Microsc. Res. Tech., vol. 75, no. 11, pp. 1550–1556, Nov. 2012. Figure 1