Researchers have developed a new way to analyze rechargeable batteries by studying them while they are bathed in wet electrolytes, Laboratory Equipment reported.
The technique involves mimicking conditions inside actual batteries. It successfully applies transmission electron microscopy, a technique a life sciences researchers regularly use to study wet environments, to rechargeable battery research.
Although it is easier to study many aspects of battery materials under dry conditions, scientists believe wet conditions are needed to study the hard-to-find solid electrolyte interphase layer, a coating that collects on the surface of the electrode and influences battery performance.
"The liquid cell gave us global information about how the electrodes behave in a battery environment," Chongmin Wang, materials scientist at the Department of Energy's Pacific Northwest National Laboratory, said in a statement. "And it will help us find the solid electrolyte layer. It has been hard to directly visualize in sufficient detail."
Before developing a new way to study rechargeable batteries, transmission electron microscopy technique has only been able to accommodate dry battery cells. This was an issue because the electrodes in real batteries are bathed in liquid electrolytes which provide an environment ions can easily move through.
To remedy this, Wang and her team built a battery, "small enough to fit several on a dime," that had one silicon electrode and one lithium metal electrode that were both contained in a bath of electrolyte.
When charged, as expected, the silicon electrode enlarged all along its length at the same time, Laboratory Equipment reported. Under dry conditions, this would not have happened, the electrode would have been attached at one end to the lithium source - and swelling starts at just one end as the ions push their way in, according to Laboratory Equipment.
"The electrode got fatter and fatter uniformly. This is how it would happen inside a battery," Wang said.
Researchers also found that the total amount the electrode swelled was about the same whether the researchers set up a dry or wet battery cell. That suggests researchers can use either condition to study certain aspects of battery materials.
"We have been studying battery materials with the dry, open cell for the last five years," Wang said. "We are glad to discover that the open cell provides accurate information with respect to how electrodes behave chemically. It is much easier to do, so we will continue to use them."
Wang said she could not see the solid electrolyte interphase layer in the initial experiments, but said she thinks that has to do with the thickness of the wet layer. In future experiments, she said she will reduce the thickness of the wet layer by at lease half to increase resolution.
"The layer is perceived to have peculiar properties and to influence the charging and discharging performance of the battery," she said. "However, researchers don't have a concise understanding or knowledge of how it forms, its structure, or its chemistry. Also, how it changes with repeated charging and discharging remains unclear. It's very mysterious stuff. We expect the liquid cell will help us to uncover this mystery layer."
