UCLA Researchers Develop Imaging Technique to Enhance Next-Gen Lithium-Metal Battery Lifespan

UCLA Imaging Tech May Extend Next-Gen Battery Lifespan
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Lithium-metal batteries have yet to enter the market, but they hold the promise of addressing common frustrations related to diminishing battery life. These batteries are akin to the widely used lithium-ion batteries but have the potential to store twice as much energy. However, a significant challenge to their widespread adoption has been their limited recharge cycles.

A new study from the California NanoSystems Institute at UCLA (CNSI) may accelerate advancements in this technology. Published in the journal *Science Advances*, the research introduced an innovative imaging technique that captures a lithium-metal battery while it charges, achieving a level of detail smaller than the wavelength of light. This method, known as electrified cryogenic electron microscopy (eCryoEM), provides insights that could enhance lithium-metal battery design. By fostering this progress within U.S. research, there is potential for the U.S. to gain a competitive edge in this emerging technology, which currently sees dominance from Chinese companies.

Yuzhang Li, an assistant professor of chemical and biomolecular engineering at the UCLA Samueli School of Engineering and a member of CNSI, shared insights about the motivation behind this research.

### What prompted this research?

China significantly controls the lithium-ion battery supply chain, producing nearly 80% of these batteries. Competing in this landscape poses challenges, especially as the U.S. shifts towards electric vehicles and large-scale energy storage solutions. Lithium metal presents an opportunity for the U.S. to surpass lithium-ion technology since it effectively doubles the energy density. However, the cycling stability of lithium metal currently falls short; while lithium-ion batteries can endure thousands of charge cycles, the best lithium-metal batteries only reach about 200 cycles.

### How does eCryoEM differ from previous techniques?

Traditional cryogenic electron microscopy (cryoEM) tools used in physical sciences are similar to those in biological applications. In the context of batteries, they typically focus on postmortem analysis, capturing electrochemical reactions only in their initial and final states, leaving a gap in understanding the reactions in real-time.

In contrast, the eCryoEM technique developed over the past four years allows researchers to place a battery in liquid nitrogen while it charges. This required engineering a very thin battery and rapidly freezing it to avoid side reactions. By capturing the battery at various time points, researchers can create a sequence similar to a flipbook animation, illustrating the growth of the corrosion layer over time. Understanding this process is crucial for developing improved batteries.

### What were the findings?

The research compared two different electrolyte chemistries: one high-performing and one low-performing. The high-performing electrolyte can withstand around 100 charge cycles, while the low-performing one only about 50. The prevailing theory has been that the difference in performance relates to the corrosion film, which allows lithium ions to pass through but blocks electrons, thereby preventing continuous reactions with lithium metal.

Using eCryoEM, researchers measured the thickness of the corrosion layer over time. Initially, the growth rate depended on how quickly lithium could react. Once the corrosion film became sufficiently thick, the rate of growth was limited by electron diffusion. Remarkably, during the diffusion-limited stage, the high-performing electrolyte’s corrosion film grew slower than the low-performing one, but only by about 10%. In the earlier, reaction-limited stage, a more substantial difference—threefold—was observed, which came as a surprise.

### What are the implications for lithium-metal battery design?

Current research often focuses on engineering the properties of the corrosion layer to limit diffusion. Yet, this study suggests that the primary factor is not the speed of electron movement through the layer but rather the reactivity of the electrolyte. The findings imply that engineers should concentrate on making the liquid electrolyte as inert as possible. While this concept is not new, the study quantifies the significant impact it could have and underscores its potential as a beneficial approach.

### Broader implications of eCryoEM

Electrified cryoEM could represent the next generation of cryoEM for materials science. My research group aims to fundamentally understand molecular-scale processes applicable to various technologies, including supercapacitors and carbon dioxide conversion to fuels. We are fortunate to have private foundation funding through a Packard Fellowship for this exploration.

What excites me most is the opportunity to contribute to the biology community. Similar to batteries and electronics, brain function relies on electrical activity. Our concept involves stimulating a brain cell at various voltages and freezing it in that dynamic state. Observing changes in the shape of proteins that regulate ion movement across cell membranes can enhance our understanding of their function. This could lead to insights into new therapies for disease models.

We are grateful for the support from the National Institutes of Health through a Director’s New Innovator Award, which enables this exploration. The UCLA biology faculty have been immensely supportive in this endeavor. Additionally, Matthew Mecklenburg, managing director of the CNSI’s Electron Imaging Center for Nanosystems, championed our new ideas during the development of the eCryoEM technique. The EICN facilities are world-class and foster exploratory research, highlighting the beauty of science and the importance of interdisciplinary collaboration in generating new fields and ideas.

### About the study

The study’s co-first authors are UCLA doctoral students Chongzhen Wang and Jung Tae Kim, with other co-authors including Xintong Yuan, Jin Koo Kim, Bo Liu, Min-ho Kim, and Dingyi Zhao, all from UCLA. The research received funding from the Department of Energy.