Guest interviewer Erick Espinosa Villatoro, SLAC National Accelerator Laboratory / SSRL, and featuring Ellen Williams, Exum Instruments.
This interview has been edited for clarity and length.
Like many researchers, SLAC scientist Erick Espinosa Villatoro obsesses over how batteries degrade. Next-generation batteries–whether high-nickel cathodes, silicon-rich anodes, or lithium metal–often rise or fall on a deceptively simple question: what is actually happening inside the cell as it cycles?
We sat down with Erick to hear why understanding degradation mechanisms remains one of the biggest technical hurdles to commercialization–and how pairing synchrotron X-ray methods with laser ablation laser ionization time-of-flight mass spectrometry (LALI-TOF-MS) opens a new window into lithium distribution, SEI chemistry, and transition-metal migration.
Erick, welcome. To start, tell us about your work at SLAC and SSRL.
Erick Espinosa Villatoro: Thank you for inviting me–it’s a pleasure to be here. I’m a postdoctoral researcher at SLAC, and for over three years I’ve been working mainly at SSRL, the synchrotron at SLAC, and more recently with the SLAC Stanford Battery Center. My work is to understand different battery material chemistries–I’m not focused on just one material system–and to apply multiple techniques to uncover the challenges we’re seeing and the results we’re finding.
From your perspective, what are the biggest technical barriers keeping next-gen batteries from commercial viability?
Erick: There are many, but one of the biggest we think about is how easily materials degrade–and understanding why that degradation happens.
For cathodes, questions include why particles crack, why capacity is limited, and why materials don’t hold energy. On the anode side, you form interfacial layers during cycling–those can be stable or unstable, and they strongly impact performance.
Cost is also a major driver. You want to reduce reliance on materials that are difficult to obtain–like cobalt–and move toward more available options like silicon, nickel, manganese, or iron. But when you introduce new materials, you also introduce new degradation pathways. Understanding how these materials interact and degrade–both in the lab and as projects move toward commercial relevance–is essential.
What projects and chemistries are you focused on right now?
Erick: I’ve been working the longest on lithium nickel oxide–a high-nickel cathode material. We explore dopants, including small amounts of manganese, and also some cobalt and aluminum.
And because I’m in a national lab environment, I also work on multiple systems. Recently, I’ve been working with sodium batteries, silicon anodes, and lithium metal anodes. The most recent–and most exciting for me–are lithium nickel oxide, lithium metal, and silicon-based anodes.
How does SSRL support your work? What are you measuring with synchrotron X-ray tools?
Erick: SSRL lets us use many powerful techniques in a complementary way. For example:
- X-ray diffraction (XRD) to understand bulk crystallography
- Operando measurements while batteries are cycling to track phase changes
- Spectroscopy for local coordination information
- Transmission X-ray imaging to observe particle-level degradation–cracks, fissures
- Oxidation-state mapping during charge/discharge
- X-ray fluorescence (XRF) for electrode-scale elemental distributions (Ni, Co, Mn, etc.)
I try to connect information from particle scale up to electrode scale, so we can understand what’s happening across multiple levels–not just one view of the material.
X-rays are powerful, but also limited. What can’t you see–and why does that matter for batteries?
Erick: The big limitation is that with the hard X-rays most commonly used at SSRL, we can typically see transition metals well–titanium, vanadium, iron, copper, cobalt, manganese, nickel. But it’s much harder for lighter elements like phosphorus and sulfur, and for very light elements like sodium and especially lithium, it’s basically impossible with these approaches.
You can sometimes use soft X-rays to access lighter elements, but those experiments often require vacuum and specialized setups. That makes them more expensive and not always practical or reliable for routine battery investigations.
If you can’t directly measure lithium with X-rays, what critical information are you missing?
Erick: Lithium is central to lithium-ion batteries–so if you can’t see lithium, you miss a lot.
You miss questions like:
- How homogeneous is lithium distribution in cathodes and anodes?
- In lithium metal systems, where and how are dendrites forming?
- How does lithium plating occur and where does inactive lithium accumulate?
These are extremely difficult to answer with X-rays alone unless you take an indirect route. But lithium behavior is deeply tied to degradation mechanisms–not only in electrodes, but also in electrolytes and interfaces. Understanding lithium distribution and interaction with cathode/anode materials is critical.
So how do you get around those limitations?
Erick: There are indirect methods–XPS, other surface techniques, or looking at proxy signals like changes in carbon chemistry. But recently we’ve been using a technique developed by Exum Instruments: laser ablation laser ionization time-of-flight mass spectrometry, or LALI-TOF-MS.
This technique has been helping us see lithium directly, along with many other elements and compounds. It’s very sensitive and gives you a lot of information about electrodes and materials.
For readers new to it: how does LALI-TOF-MS work?
Erick: The system operates under vacuum, which is valuable for analyzing air-sensitive or moisture-sensitive samples while minimizing contamination.
The basic workflow is:
- The first laser ablates material from the sample surface (perpendicular to the sample).
- The second laser ionizes that ablated material (parallel geometry).
- The ions enter the time-of-flight mass spectrometer, which creates a full mass spectrum, from lithium to uranium, at each laser spot.
Ellen: It’s especially good for solid materials like electrodes, and even powders if you press them into a pellet. You can acquire a lot of information quickly–minutes or hours depending on mapping and depth profiling needs.
You can tune spatial resolution from 5 µm to 150 µm. That means you can do a fast, wide survey at lower resolution or go very detailed at high resolution. The data are collected spot-by-spot, so you can build chemical distribution maps of what’s present.
How is it complementary to synchrotron X-ray methods?
Erick: With X-rays you can get crystallographic structure and transition-metal information. With LALI-TOF-MS you can’t directly get crystallography, but you can get chemical distribution, including lithium-containing species. The two approaches fill in each other’s gaps.
What makes LALI-TOF-MS different from other mass spec approaches like ICP-MS?
Erick: One difference is the amount of material removed per layer, which enables depth profiling. You can remove thin layers–on the order of tens to hundreds of nanometers–and build depth information.
Also, because of the laser ablation process and the conditions during ionization, you can sometimes observe dimers or clusters–combinations like lithium with oxygen or carbon–that can be harder to capture with other approaches. That makes the data more information-rich than simply elemental composition.
You mentioned depth profiling and 3D reconstruction. What does that enable in real battery samples?
Erick: You can scan across millimeter-scale regions of a sample, not just tiny fields of view. That lets you compare chemical distribution at the edge vs. center of an electrode, or across other regions of interest.
And by ablating layer-by-layer, you can look beyond the surface and understand how lithium or sodium diffuses and distributes in depth. From that, you can build a kind of 3D representation of the chemical distribution.
Can you give a concrete example of how this changes battery R&D?
Erick: One of the hardest things is understanding the solid electrolyte interphase (SEI) on the anode side (and related interfacial layers). With X-rays and even techniques like SEM or XPS, it can be difficult to observe directly.
With LALI-TOF-MS, we can map the chemical distribution of SEI components directly–things like lithium oxides, lithium carbonates, lithium hydroxides, fluorine distribution, and even transition metal migration.
In our work, we use X-rays to measure transition-metal distributions, and LALI-TOF-MS to map SEI chemistry. We’re also looking at how transition metals migrate from cathode to anode and how that relates to SEI formation–because the migration is not homogeneous, it occurs in specific regions, and it changes with depth and cycling history.
That “where” aspect matters as much as “how much,” right?
Erick: Exactly. It’s not only quantification–it’s understanding where things are and how they move around the anode. Distribution is key.
One more practical point: how hard is sample prep?
Erick: It’s a post-mortem method–you cycle cells, disassemble them, and then use air-free transfer holders developed by Exum for air-sensitive materials. You can load electrodes in a glovebox, seal them, transfer into the instrument, and measure. For battery components that are not air sensitive, you can load them directly into the instrument after disassembly. We often run multiple samples–like 1 cycle, 50 cycles, 100 cycles–and compare them. You don’t need extensive preparation: open the cell, place the electrode in the holder, transfer, and measure. The instrument can accommodate any number of samples that fits within the 90-mm-by-90-mm sample holder.
What this means for Battery R&D
As battery R&D pushes toward higher-nickel cathodes, silicon-rich anodes, and beyond, analytical constraints increasingly become commercialization constraints. Erick’s perspective is a reminder that breakthroughs often come from new ways to better understand the mechanisms of existing chemistries rather than efforts to develop completely new ones.
By pairing synchrotron X-ray tools with localized, lithium-sensitive chemical mapping from LALI-TOF-MS, researchers can track degradation with a level of spatial and chemical specificity that’s hard to achieve otherwise–and convert “black box” failure modes into solvable engineering problems.
