Calendar Aging Research Is Critical to Future of Silicon-Based Batteries

In the face of climate change, state-of-the-art energy storage solutions are crucial to harnessing electricity production from clean energy sources, and National Renewable Energy Laboratory (NREL) researchers are investigating strategies to increase battery cell energy density while reducing production costs.

Silicon anodes offer a promising improvement over existing lithium-ion (Li-ion) battery capacities for electric vehicles and stationary storage. Replacing the graphite anode material typically used in Li-ion batteries with silicon anodes can pave the way for reducing the battery pack by 25% –30% and increasing the driving range by 30% –40%.

NREL researchers are at the forefront of silicon anode research using cutting-edge facilities to explore the basic science of organic electrolytes with silicon interfaces. However, new findings highlight the importance of continued studies of the lifespan of silicon-based cells. In a new Natural energy Perspective article, “Calendar Aging of Silicon Batteries”, emphasizes battery researchers from the US Department of Energy’s Vehicle Technology Office, Silicon Consortium Project, the importance of ongoing research into the calendar life of this anode material.

“New research shows that calendar aging of silicon anodes is a bigger problem than we originally thought,” said Max Schulze, a postdoctoral researcher at NREL and co-author of the perspective. “With this report, we hope to encourage researchers to consider the unique challenges these batteries face. Collaboration across laboratories and in industry to evaluate and solve this problem is now crucial to the success of silicon electrodes in batteries. ”

Researchers are investigating new uncertainties in battery chemistry

To understand battery life, researchers need to consider the effects of both battery consumption and time. New electrodes are typically evaluated by cycling the cells – evaluating the capacity degradation over a certain number of charge / discharge cycles – to determine the capacity loss during use. To determine the capacity loss over time, charged cells are simply allowed to sit unused with periodic measurements of their capacity.

These types of calendar aging trials are time consuming, so many calendar life studies extrapolate data from short-term tests to predict aging trends. Although this approach has worked for traditional graphite-based anodes, scientists face new uncertainties when changing electrode chemistry. As a result, relatively little is known about the time-dependent degradation of silicon-based batteries.

“Silicon does not form the same stable interface with the liquid electrolyte that gives graphite electrodes their longevity,” said Andrew Colclasure, NREL researcher and another co-author of the perspective. “Further research is essential to better understand how the different electrode chemistry affects battery life.”

Recent studies outlined in Natural energy Perspective suggests that adding silicon to the battery node may result in a higher susceptibility to calendar aging. Compared to graphite anodes alone, silicon-containing anodes are significantly more reactive. These cells are vulnerable to harmful chemical reactions, such as gas formation, electrolyte degradation, or dissolution of the silicon electrolyte interface, stressors that can lead to degradation over time, regardless of whether the battery is used. As such, comprehensive studies of calendar aging are crucial to understanding the long-term stability of silicon in batteries.

NREL-led consortium focuses on lifetime predictions

The Silicon Consortium Project led by NREL investigates strategies to learn more about calendar aging of silicon in batteries. Researchers developed new test protocols to evaluate the progress of silicon modifications, cell designs, electrolytes or additives faster and more efficiently. Current methods do not yet provide absolute calendar life forecasts; however, researchers can use this data to identify the most promising strategies for mitigating calendar aging in silicon electrodes. Ultimately, the Silicon Consortium Project aims to implement these strategies to develop and demonstrate long-life batteries with silicon anodes.

Learn more about NREL’s research into energy storage.

Article courtesy of NREL.

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