Determining Battery Structure and Composition using SEM

Miniaturization is the secret to enhancing the specifications of new generation batteries. SEM is an unmatched technique for inspecting and analyzing nanoscale materials, enhancing production processes or detecting the reasons for failure. This article gives insights into how Phenom SEMs can be used to boost the performance of customers’ products.

The battery production cycle is a lengthy process that has many stages. Intermediate checks are required to check the quality of the production system, starting from the inspection of raw materials and the production of intermediate components, through to the checks on the final product, requiring the system used for the investigations to be highly versatile.

The insulating materials in batteries are generally non-conductive. Imaging with a SEM causes the electrons to be accumulated on the surface of such samples, which compromises the quality of the final picture and often hides important details.

Different solutions are available for perfectly imaging the structures of interest. Reducing the vacuum level in the imaging chamber can help to discharge the sample, thereby enhancing image quality instantly.

Moreover, interactions can be reduced by altering the value of the current applied, and surface damage can be prevented when handling very delicate samples.

If both of the previously-mentioned techniques do not work, a thin layer of gold can be coated on the surface, making it conductive and ready for high resolution imaging.

The Advantages of Electron Microscopy

• Integrated, non-destructive EDS analysis to measure chemical composition of the sample locally
• Access to nanoscale magnification
• 3D reconstruction of the surface to measure morphology
• Automated routines to collect data on pores, particles, and fibers - quickly and without wasting the operator’s time

With an electron microscope, one can observe:

• Size and orientation of pores and fibers in insulating membranes
• Size and granulometry of powders used as raw materials
• Presence of contaminants in the battery sublayers
• Three-dimensional structure of electrodes after production processes
• Response of materials to thermal or electrical solicitations

Figure 1a and 1b. SEM images of battery insulating membranes. Highly non-conductive samples require special treatment for imaging. Operating at a different vacuum level can reduce charging effects. Coating the sample with a thin gold layer will dramatically reduce the issue.

It is easy to image raw materials, such as powders, at very high magnification. Particles can then be measured, to assess the granulometry and shape distribution within the sample. With more sophisticated software analysis, these measurements can be automated, offering more accurate results and saving operators a considerable amount of time.

Figure 2a, 2b and 2c. Raw powders used in the production of cathodes. SEMs are ideal tools for investigating small particles in the range of micrometers or nanometers.

Figure 2d. Ion milled surface of a battery electrode. The data can be used to investigate the internal structure of the material.

The orientation and shape of the electrodes’ nanostructure is important to ensure that batteries are highly efficient and long lasting. Specifically, the secondary electrons detector (SED) can be employed to inspect the sample’s surface topography and morphology.

Using backscattered electron detector (BSD), the image will exhibit a different contrast for areas with different compositions. It is a powerful tool, coupled with the energy-dispersive detector (EDS), in the hunt for contamination and identifying which areas to analyze.

Figure 3a. The structure of an electrode imaged with a BSD detector. The bright particle close to the center has a different composition compared with the rest of the sample.

Figure 3b. Powders used in the production of anodes.

To check samples of interest from different points of view, they can also be tilted and rotated. Shape from shading and stereoscopic reconstructions can be used to produce three-dimensional models of the surface and assess its roughness and shape.

Inspecting behavior at varying temperatures, or while the sample is connected to a power supply, can also be done when using SEM. This type of testing will offer important information about the chemical and physical properties of the sample, when subjected to critical environments during its life cycle.

Figure 4a. An example of how EDS can be used to trace how the sample composition changes along a line. Spot analysis, line scan or area map can used to monitor the distribution of different phases in a specific region of the sample.

This information has been sourced, reviewed and adapted from materials provided by Phenom-World BV.

For more information on this source, please visit Phenom-World BV.