Scientists decode chemistry inside a battery

Researchers have developed a new technique to study battery electrodes in action, an advance that can bring long-lasting, inexpensive rechargeable batteries closer to reality.
US researchers developed a way to microscopically view battery electrodes while they are bathed in wet electrolytes, mimicking realistic conditions inside actual batteries.
While life sciences researchers regularly use transmission electron microscopy to study wet environments, this time scientists have applied it successfully to rechargeable battery research.
The results are good news for scientists studying battery materials under dry conditions.
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.

"The liquid cell gave us global information about how the electrodes behave in a battery environment," said materials scientist Chongmin Wang from the US Department of Energy's Pacific Northwest National Laboratory.
"And it will help us find the solid electrolyte layer. It has been hard to directly visualise in sufficient detail," Wang said.
Wang 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.

But up to this point, the transmission electron microscopes have only been able to accommodate dry battery cells, which researchers refer to as open cells.
In a real battery, electrodes are bathed in liquid electrolytes that provide an environment ions can easily move through.
So, working with colleagues from Joint Centre for Energy Storage Research (JCESR), Wang developed a wet battery cell in a transmission electron microscope.
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.
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 the study's liquid cell, lithium could enter the silicon anywhere along the electrode's length. The electrode swelled all along its length at the same time.
"The electrode got fatter and fatter uniformly. This is how it would happen inside a battery," said Wang.
The study was reported in the journal Nano Letters.