New findings help develop smaller, lighter, cheaper car cr2032 button battery

According to foreign media reports, a team of researchers at the U.S. Department of Energy (DOE) Brookhaven National Laboratory has identified new details about the internal reaction mechanism of lithium metal anode cr2032 button battery. The results of this study are an important step towards developing smaller, lighter, and cheaper electric vehicle cr2032 button battery.

Battery researchers at Brookhaven National Laboratory (: Brookhaven National Laboratory)

Remaking lithium metal anodes

Traditional lithium-ion cr2032 button battery can be found in various electronic devices such as smartphones and electric vehicles. Although lithium-ion cr2032 button battery have made many technologies widely used, they still face challenges in powering electric vehicles for long distances.

In order to create cr2032 button battery that are more suitable for electric vehicles, several U.S. national laboratories led by the U.S. DOE Pacific Northwest National Laboratory (PNNL) and university researchers funded by DOE have formed an alliance called Battery500, with the goal of creating a battery cell with an energy density of 500Wh/kg, which is twice the energy density of today's most advanced cr2032 button battery. To this end, the alliance is focusing on cr2032 button battery made of lithium metal anodes.

Lithium metal cr2032 button battery use lithium metal as the anode, compared to lithium-ion cr2032 button battery, which mostly use graphite as the anode. "The lithium metal anode is one of the key factors in meeting the Battery500 energy density target, and the advantage is that it has twice the energy density of existing cr2032 button battery. First, the specific capacity of this anode is very high; second, it can achieve a higher voltage battery, and the combination of these two can achieve higher energy density."

Scientists have long recognized the advantages of lithium metal anodes; in fact, lithium metal anodes were the first anodes to be coupled to the cathode of a battery. But because this anode lacked "reversibility", that is, the ability to charge through a reversible electrochemical reaction, battery researchers eventually replaced lithium metal anodes with graphite anodes to create lithium-ion cr2032 button battery.

Now, after decades of progress, researchers are confident that they can achieve reversible lithium metal anodes to surpass the limits of lithium-ion cr2032 button battery. The key lies in the interface, that is, the layer of solid material that forms on the battery electrode during the electrochemical reaction.

"If we can fully understand this interface, it could provide important guidance for materials design and building reversible lithium metal anodes," said the researchers. "However, understanding this interface is a considerable challenge because it is a very thin layer of material, only a few nanometers thick, and is also sensitive to air and humidity, making it very tricky to handle the sample."

Visualizing the interface at NSLS-II

To address these challenges and "see" the chemistry and structure of the interface, the researchers used the National Synchrotron Light Source II (NSLS-II), a DOE Office of Science user facility at Brookhaven National Laboratory, to produce ultrabright X-rays to study the material properties of the interface at the atomic scale.

In addition to using the advanced capabilities of NSLS-II, the team needed to use a beamline (experimental station) that could probe all components of the interface, using high-energy (short-wavelength) X-rays to probe the crystalline phase as well as the amorphous phase. This beamline is the X-ray Powder Diffraction (XPD) beamline.

"The chemistry team used a multimodal approach with XPD, taking advantage of two different techniques available at the beamline, X-ray diffraction (XRD) and pair distribution function (PDF) analysis. XRD allows the study of crystalline phases, while PDF allows the study of amorphous phases," the researchers said.

The XRD and PDF analysis revealed something exciting: the presence of lithium hydride (LiH) at the interface. For decades, scientists have debated whether LiH exists at the interface, creating uncertainty about the fundamental reaction mechanisms that form the interface.

"LiH and lithium fluoride (LiF) have very similar crystal structures, and our claim to have found LiH was challenged by some who thought we had mistaken LiF for LiH," the researchers said.

Given the controversy surrounding the study and the technical challenges of distinguishing LiH from LiF, the team decided to provide multiple lines of evidence for the presence of LiH, including air exposure experiments.

"LiF is stable in air, but LiH is not," the researchers said. "If we expose the interface to humid air, if the amount of the compound decreases over time, that confirms that we are indeed seeing LiH, not LiF, which is indeed the case. Because it is difficult to distinguish LiH from LiF, and air exposure experiments have never been done before, it is very likely that LiH was mistaken for LiF in many reports in the literature, or that it was not observed due to the decomposition reaction of LiH in a humid environment."

The sample preparation work done at PNNL was critical to this study, and we also suspect that many people fail to identify LiH because their samples were exposed to humidity before the experiment. If the samples are not collected, sealed, and transported correctly, LiH may be missed."

In addition to confirming the presence of LiH, the team solved another long-standing mystery surrounding LiF. LiF has long been considered a favorable component of the interface, but no one has fully understood why. The team identified structural differences between LiF within the interface and the bulk of LiF itself, and found that the former can promote lithium ion transport between the anode and cathode.

The findings, which are being collaborated on by battery scientists at Brookhaven National Laboratory, other national laboratories and universities, will provide much-needed practical guidance for lithium metal anodes, pushing research on this promising material forward, the researchers said.

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