Every piece of technology that keeps our world running demands on-demand energy. To power electronic devices and illuminate buildings, energy must be stored and made available. The large diversity of devices that require on-demand energy has resulted in the development of several energy storage technologies.
To transform energy from one form to another, many energy storage systems combine chemical and electrical processes. As a result of this process, an interface is created, which is a point of action where two different materials meet and transform.
Scientists need to be able to control what happens at and around these interfaces in order to create more efficient and long-lasting energy storage systems. But it’s not going to be easy.
“Most research makes a complicated interface and then uses advanced characterization techniques to try to understand it,” said Grant Johnson, a chemist at Pacific Northwest National Laboratory (PNNL) who leads the Separation Science program. “In comparison, we don’t make the whole interface. We prepare each piece separately, which allows us to study the individual components and how they form.”
Their method is known as ion gentle landing. Scientists can use the approach to study how individual charged molecules, or ions, interact with an electrode surface and an electric potential at genuine energy storage interfaces.
It breaks down the complex interfaces found in real-world energy storage systems into distinct systems containing only one type of ion and the surface. The researchers can next look at the involvement of each molecule in the interface’s formation.
Most research makes a complicated interface and then uses advanced characterization techniques to try to understand it. In comparison, we don’t make the whole interface. We prepare each piece separately, which allows us to study the individual components and how they form.Grant Johnson
Softly landing ions for targeted studies in energy storage
Researchers can use ion soft landing to pick a single, specific type of ion based on charge and size. The ions are then gently released onto a conductive surface. This method creates a finely defined interface that is characterized by the responses of the chosen molecules and the surface material.
Researchers can then utilize other tools to analyze how the surface and the molecule interact once the interface has been prepared. This analysis exposes details about the chemical bonds that are disrupted and formed at the contact.
The most well-known energy storage devices are lithium-ion systems, which power many of our electronics. However, the PNNL research team is looking on even more efficient and potentially game-changing energy storage devices. Lithium-sulfur ions, lithium-based materials, and moving beyond lithium chemistry are among them.
The team begins with an electrolyte solution of molecules and soft lands selected ions, such as different lithium sulfides, on lithium metal with an oxygen-rich surface for this study. The negatively charged lithium-sulfur ions play a significant role in the operation of these new energy storage devices at interfaces, according to researchers.
They discovered that rather than lithium, the ions proceed through a series of processes focusing on sulfur reduction and oxidation chemistry. The discoveries shed light on the nature of sulfur-oxygen bonds and other reactive compounds used in energy storage devices.
The ion soft landing research explains why oxidized forms of sulfur exist at lithium-sulfur interactions at a molecular level. Researchers can break down the intricate interfaces in real devices by understanding how these essential ions convert into solid materials at a simulated interface.
“Each time we explore how an individual type of molecule reacts, we learn something new that builds collective knowledge about interface formation,” said Johnson.
Understanding the interfaces involved in energy storage
The Basic Energy Sciences Separation Science program at the Department of Energy (DOE) helped PNNL researchers enhance their ion soft landing capabilities. Venky Prabhakaran, a chemical engineer, employed ion soft landing to examine electrochemically active interfaces for separations as part of that initiative.
He was interested in seeing what the method could do in addition to separation systems. Ion soft landing entered the area of energy storage after a meeting with scientist Vijay Murugesan a few years ago. Murugesan is the director of a priority area for the DOE’s Joint Center for Energy Storage Research (JCESR).
“One day, I had a meeting with Vijay about something else and we started talking about our research,” said Prabhakaran. “We quickly realized that ion soft landing might be an important tool to help answer key questions in the JCESR focus area Vijay leads.”
The team’s forthcoming relocation to the Energy Sciences Center will streamline their operations and bring them closer together for more efficient collaboration and experimental studies.
“Currently, we have to go down several corridors to get from the ion soft landing lab to key characterization instruments,” said Murugesan.
While this may not appear to be a long-distance, it poses a challenge for their highly sensitive and reactive samples. The samples must be transported in a special “vacuum suitcase” by the researchers, even down the hall.
“In the Energy Sciences Center, our labs will be right next to each other,” said Prabhakaran. “We will have a connecting door.”
Because the distance between instruments is substantially shorter, there is less time for sample degradation or contamination. The team is enthused about a new breakthrough that includes selecting and depositing two types of ions, one positive and one negative, at the same time.
This method results in a more accurate representation of energy storage devices. The team was able to record the action at the interface by observing how the different ions interact with each other and with the surface.