An obstacle to the clean energy revolution that researchers from all over the world are working to overcome is batteries. Batteries are at the core of society’s most important green advances, from electric vehicles to renewable grid-scale energy storage, but they need to pack more punch to make these technologies widely used and feasible.
Now, a team of researchers led by chemists at the Pacific Northwest National Laboratory (PNNL) and Brookhaven National Laboratory of the U.S. Department of Energy (DOE) has uncovered the intricate chemical mechanisms of the interphase, a battery component that is essential for increasing energy density. Their research was recently published in Nature Nanotechnology.
DOE’s Battery500 consortium zeroes-in on lithium metal anodes
Currently, a lot of electronics—including smartphones and even electric vehicles—use standard lithium-ion batteries. Lithium-ion batteries have grown in popularity due to their high efficiency and long lifespan, though they have limitations in more demanding applications such as long-distance electric car charging.
The Battery500 collaboration was created by researchers from many national laboratories and universities, supported by the DOE, to develop a better battery for electric vehicles. The consortium, led by PNNL, seeks to produce battery cells with an energy density of 500 watt-hours per kilogram, or more than double that of current-generation batteries. The group is concentrating on lithium-metal batteries to do this. These batteries use lithium metal anodes as opposed to the graphite anodes used in lithium-ion batteries.
Compared to graphite anodes, lithium metal anodes offer a significantly better energy density; however, there are drawbacks. Finding a method to maintain the anode during the battery’s charging and discharging is one of the largest issues scientists are now facing.
In search of such a technique, researchers from PNNL and Brookhaven Lab conducted a thorough investigation into the solid-electrolyte interphase of lithium metal batteries.As a battery charges and discharges, a chemical layer called the interphase is created between the anode and the electrolyte. The interphase, which is the key to stabilizing lithium-metal batteries, has been discovered by scientists, but it is a very delicate sample with complex chemistry, making it challenging to analyze and, consequently, impossible to fully comprehend.
“The cyclability of the entire battery is influenced by the interphase.” This mechanism is crucial but difficult to understand. Enyuan Hu, a chemist at Brookhaven, conducted the work. This small, delicate sample, which also possesses both crystalline and amorphous phases, can be harmed by a variety of methods.
Cryo-electron microscopy has been used in several research projects by the scientific community to better comprehend the interphase, although the picture is still far from being clear and comprehensive.
The development of a functional interphase requires a thorough understanding of the interphase, according to PNNL scientist Xia Cao, who co-led the study and oversaw the creation of the electrolyte. “Collaborations are greatly encouraged by the Battery 500 Consortium. “We have been working closely with Brookhaven Lab on a variety of research initiatives, particularly one that focuses on the interphase.”
The researchers used a unique instrument called the National Synchrotron Light Source II to delve deeper into the intricate and enigmatic chemistry of the interphase (NSLS-II).
NSLS-II shines light on interphase chemistry
Brookhaven Lab’s NSLS-II is a DOE Office of Science User Facility that produces ultrabright x-rays for examining the atomic structure of materials. For many years, Hu and coworkers have been using the cutting-edge capabilities of the X-ray Powder Diffraction (XPD) beamline at NSLS-II to achieve novel findings in battery chemistry. The team went back to XPD to collect their most accurate data on the interphase yet, building on their prior triumphs.
High-energy synchrotron x-rays have not yet been found to harm the interphase sample, according to Hu. “This is crucial since the samples’ extreme sensitivity to other types of radiation, such as low-energy x-rays, makes defining the interphase one of the most difficult tasks. “In order to capture the chemistries of both the crystalline and the amorphous phases in the lithium metal anode interphase, we used pair distribution function analysis and x-ray diffraction, two methods that require high intensity x-rays.”
The scientists disassembled the cell, scraped out a tiny quantity of interphase powder from the surface of the lithium metal, and used XPD’s high-energy x-rays to examine the sample to reveal its complex chemistry after cycling a lithium metal battery 50 times and collecting enough interphase sample.
Sanjit Ghose, head beamline scientist at XPD and a co-author of the study, claimed that “XPD is one of the few beamlines in the world that is capable of carrying out this research.” The beamline offered three benefits for this work: a small absorption cross section that causes less sample damage; combined techniques using x-ray diffraction to obtain phase information and pair distribution function to obtain real-space information; and a high-intensity beam for delivering high-quality data from a trace sample.
The team was able to create a full chemical map of the interphase components, including their origins, functions, interactions, and evolutionary histories, thanks to this special combination of cutting-edge x-ray techniques.
Sha Tan, a postdoc at Brookhaven who is the paper’s primary author, explained that “we concentrated on three main components of the interphase.” “The process through which lithium hydride is formed came first.” “Lithium hydride was previously found to occur in the interphase, and this time we have located the hydrogen source.”
The researchers determined that the likely contributor to lithium hydride is lithium hydroxide, which is naturally present in the lithium metal anode. Scientists will be able to design a better interphase with the maximum performance achievable by managing the composition of this molecule.
“We investigated lithium fluoride, which is critical for electrochemical performance, and discovered that it can be produced in significant quantities in low concentration electrolytes,” Tan said.
The formation of lithium fluoride was formerly thought to require the use of costly salts and high-concentration electrolytes. The research shows that less expensive, low-concentration electrolytes may be capable of delivering good performance in these battery systems.
“Third, we investigated the consumption of lithium hydroxide during battery cycling. “These are all really recent discoveries that are crucial for comprehending the interphase.”
Together, our results shed light on hitherto unnoticed interphase components, paving the way for more precise and controllable interphase design for lithium metal batteries.
The team will keep providing new studies to the Battery 500 collaboration in the future. Right now, Battery 500 is in its second phase, which will last through 2026.
The Office of Science at DOE, the Office of Energy Efficiency and Renewable Energy, and the Office of Vehicle Technologies all provided funding for this work. The Office of Science supports NSLS-II operations.
