Researchers have found a new way to microscopically view battery electrodes while they are bathed in wet electrolytes, mimicking realistic conditions inside actual batteries.
The work showed that many aspects can be studied under dry conditions, which are much easier to use. However, wet conditions are needed to study the hard-to-find solid electrolyte interphase layer, a coating that accumulates on the electrode's surface and dramatically influences battery performance.
Materials scientist Chongmin Wang of the Department of Energy's Pacific Northwest National Laboratory, and colleagues used high-powered microscopes to watch how the ebbing and flowing of positively charged ions deform electrodes.
Squeezing into the electrode's pores makes the electrodes swell, and repeated use can wear them down.
Working with JCESR colleagues, Wang led development of a wet battery cell in a transmission electron microscope at EMSL, the DOE's Environmental Molecular Sciences Laboratory on the PNNL campus.
The team built a battery so small that several could fit on a dime. The battery had one silicon electrode and one lithium metal electrode, both contained in a bath of electrolyte.
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When the team charged the battery, they saw the silicon electrode swell, as expected. However, under dry conditions, the electrode is attached at one end to the lithium source - and swelling starts at just one end as the ions push their way in, creating a leading edge. In this study's liquid cell, lithium could enter the silicon anywhere along the electrode's length. The team watched as the electrode swelled all along its length at the same time, which is how it would happen inside a battery.
As far as the elusive solid electrolyte interphase layer goes, Wang said they couldn't see it in this initial experiment. In future experiments, they will try to reduce the thickness of the wet layer by at least half to increase the resolution, which might provide enough detail to observe the solid electrolyte interphase layer.
The results have been published in journal Nano Letters.