Adding an electrolyte additive enhanced the charging speed of lithium metal batteries and resulted in novel insights into battery chemistry.
Chemists from the U.S. Department of Energy’s Brookhaven National Laboratory, aiming to enhance electric vehicle batteries, have employed an electrolyte additive to improve the functionality of energy-dense lithium metal batteries. By adding a compound called cesium nitrate to the electrolyte that separates the battery’s anode and cathode, the research team has significantly improved the charging rate of lithium metal batteries while maintaining a long cycle life.
The team’s new work, recently published in Battery500 Consortium, a collaboration of several national labs and universities. The Consortium, which is led by DOE’s Pacific Northwest National Laboratory, is striving to make batteries with an energy density of 500 watt-hours per kilogram—more than double the energy density of today’s state-of-the-art batteries.
This energy density cannot be achieved in the lithium-ion batteries powering most of today’s battery-operated devices—including phones, television remotes, and even electric vehicles. So, scientists needed to turn to lithium metal batteries to pursue their goals. These batteries possess a lithium metal anode, rather than the graphite anode present in lithium-ion batteries.
“The lithium metal battery is attractive because it can give twice the energy density of a battery with a graphite anode,” explained Rahman. “But there are lots of challenges to tackle.”
Brookhaven’s most recent research addresses one of these challenges—striking a balance between the charging speed and the cycle life.
The electrolyte that typically enables fast battery charging is also likely to be reactive with the lithium metal anode. If these chemical reactions proceed uncontrollably, the electrolyte decomposes and reduces the battery’s cycle life. To prevent this from happening, Brookhaven chemists set out to engineer the interphase.
Previous studies had indicated that the lithium metal anode could be stabilized with a cesium additive. But to increase the charging rate while maintaining the battery cycle life, the anode and cathode need to be stabilized simultaneously. The Brookhaven scientists believed cesium nitrate could serve this purpose for lithium metal batteries. As they had hypothesized, the positive cesium ion accumulated on the negatively charged lithium metal anode side of the battery, while the negative nitrate ion accumulated on the positively charged cathode.
To better understand how the cesium nitrate additive influenced the electrolyte composition and battery performance, the chemists brought the new batteries to the National Synchrotron Light Source II (NSLS-II), a DOE Office of Science user facility at Brookhaven Lab.
A gaze into the interphase
NSLS-II is one of the most advanced x-ray light sources in the world, producing light beams that are 10 billion times brighter than the sun. Of the 29 beamlines currently operating at NSLS-II, Rahman and Hu took advantage of the capabilities of four beamlines for their most recent research.
“NSLS-II is really a great facility for conducting battery research,” said Hu. “There is a breadth of techniques available, which enables us to conduct complete studies of complex materials.”
Among the four beamlines used by the chemists was the X-ray Powder Diffraction (XPD) beamline, a high energy diffraction beamline with DOI: 10.1038/s41467-023-44282-z
This work was supported by DOE’s Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office and DOE’s Office of Science. Operations at NSLS-II and CFN are supported by the Office of Science.