Inside the Laboratory: The Weker Group at SLAC National Accelerator Laboratory, Part III

"Inside the Laboratory" is a joint series with LCGC and Spectroscopy, profiling analytical scientists and their research groups at universities all over the world. This series spotlights the current chromatographic and spectroscopic research their groups are conducting, and the importance of their research in analytical chemistry and specific industries. In this edition of “Inside the Laboratory,” Johanna Nelson Weker of SLAC National Accelerator Laboratory discusses her laboratory’s work in battery analysis (1,2).

In Part 2, Weker discusses nutrient recovery systems and how X-ray techniques can improve them. In Part 3, Weker discusses battery cell geometry configurations and how they inform battery design.

Will Wetzel: What insights have you gained by comparing different model electrode or cell geometry configurations, and how do they inform battery design or manufacturing improvements?

Johanna Nelson Weker: We haven't done a lot of comparisons between different cell geometries because we are limited by what X-rays can get through. In standard university settings, people often use coin cells. We don't like to use coin cells because with the stainless-steel casing of a coin cell, the X-rays don't go through very easily. You can punch a hole through the coin cell and then put a window on it, but it's changing the pressure that you've established when making the coin cell.

So, what we typically use is small-format pouch cells, which is the next step up from a coin cell. These are slightly more industrial relevant than the coin cells. So, if we are working with industry, we often have to take their large format cells and scale them down to our single-layer pouch cells. But if we're working with universities, we have to take their coin cells and scale them up to a pouch cell. So, we're sitting in the middle.

One thing about pouch cells that we often have to worry about is putting external pressure on the cells, because, unlike a coin cell, which has a spring in it and provides its own pressure, pouch cells are flexible, and most battery materials work better under a slight pressure. What we do is typically use aluminum plates with a window, and that window usually has a windowpane of either beryllium or glassy carbon, something that's X-ray transparent but structurally rigid. That provides a uniform pressure across the cell but allows our X-rays to get through. If we want to compare, for example, our scaled down version of an industrial relevant cell, what we will typically do is use our cell to watch things in situ, watch the chemistry or the crystal structure changes, as well as compare them to harvested cells from the company, so we can always compare what we're seeing in situ to something that we've harvested and looked at ex situ. And I think that's a really good way to make sure that what you're studying in situ is relevant to a slightly larger or different battery format. Otherwise, it's hard to make these manufacturing improvements, and it's hard for companies to take what we've learned and apply it to what they care about.

One other thing that we've been looking at is just how manufacturing is done, and this is more relevant in a solid-state battery. In a liquid battery, the manufacturing has been sort of perfected over the last 30 years. It's as cheap as it can get, and it's as good as it needs to be. In solid-state batteries, the quality of the manufacturing needs to be much better, because you have a lot of solid interfaces. For example, the lithium solid electrolyte interface needs to be uniform and essentially perfect, or you start forming voids as you strip the lithium from the lithium side and go through the electrolyte to the cathode side, where the lithium is forming voids.

Those voids typically are the starting point for lithium dendrites when you plate the lithium back on. Over time, as you're cycling the lithium back and forth, those voids can grow and they become essentially inactive spots, because unlike a liquid electrolyte, which will fill in voids and fill in spaces, the solid electrolyte cannot creep into those voids. And so, the manufacturing, the initial way you make a solid electrolyte battery, is really important for the long-term stability of that battery. We have been looking at different ways to make solid-state batteries, looking at them as they are made, and then after they've cycled as well.

This interview segment is part three of a four-part interview with Weker.

References

1. SLAC – National Accelerator Laboratory, About Us. Stanford.edu. Available at: https://www6.slac.stanford.edu/about/our-story (accessed 2025-04-25).
2. SLAC – Stanford Battery Center, Johanna Weker. SLAC.Stanford.edu. Available at: https://batterycenter.slac.stanford.edu/person/johanna-weker (accessed 2025-04-25).