Neutron imaging technology tracks aaa battery alkaline electrodes

　　By 2023, lithium-ion batteries are expected to have a market value of US$47 billion. Lithium-ion batteries have been widely used in many fields because they offer relatively high energy density (storage capacity), high operating voltage, long shelf life, and less "memory effect." However, factors such as safety, charge-discharge cycles, and expected service life continue to limit the efficiency of lithium-ion batteries in heavy-duty applications such as electric vehicles.

　　Recently, researchers at the University of Virginia School of Engineering are using neutron imaging technology at Oak Ridge National Laboratory (ORNL) to explore lithium-ion batteries and gain a deeper understanding of the electrochemical properties of battery materials and structures. Their research was published in the journal PowerSources. In the study, they focused on thin and thick sintered samples using two electroactive materials: lithium titanate and lithium cobalt oxide, tracking lithiation and delithiation in lithium-ion battery electrodes. process, or charging and discharging process.

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　　Understanding how lithium moves within battery electrodes is important for designing batteries that charge and discharge at faster rates. In some batteries this is the slowest process. This means that increasing the movement of lithium through the electrodes will allow the battery to charge much faster.

　　Gary Koenig, associate professor in the Department of Chemical Engineering at the University of Virginia School of Engineering, said: "When the electrode is relatively thick, the transport of lithium ions through the porous material and separator structure limits the charge and discharge rate. In order to develop new methods to improve To transport lithium ions through the electrolyte-filled porous voids in the electrode, we first need to be able to track ion transport and distribution in the battery during charge and discharge."

　　Koenig said other techniques, such as high-resolution X-ray diffraction, can provide detailed structural data during electrochemical processes, but this approach typically averages out relatively large volumes of material. Similarly, X-ray phase imaging can visualize salt concentrations in lithium battery electrolytes, but this technique requires special spectrochemical units and only accesses compositional information between electrode regions.

　　To obtain detailed information over a larger area, the researchers conducted their study using neutrons from the Cold Neutron Imaging Beamline at the Oak Ridge Laboratory's High Flux Isotope Reactor.

　　"Lithium has a large absorption coefficient for neutrons, which means that the neutrons passing through the material are highly sensitive to the lithium concentration," said Nie Ziyang, a graduate student in Konin's research group and lead author of the paper. "We showed that we can use Neutron radiography tracks in situ lithiation reactions in thin and thick metal oxide cathodes inside lithium batteries. Because of the high penetrability of neutrons, we do not need to customize the battery for analysis, and can span the electrodes and The entire active area of the electrolyte to track lithium."

　　Comparing the lithiation process in thick versus thin electrodes is necessary to help understand the impact of inhomogeneities (local changes in mechanical, structural, transport and kinetic properties) on battery life and performance. Local non-uniformity can also lead to uneven battery current, temperature, state of charge and aging. Generally speaking, as the thickness of the electrode increases, the adverse impact of non-uniformity on battery performance also increases. However, if the application of thicker anodes and cathodes in batteries does not affect other factors, it will be beneficial to increase energy storage capacity.

　　For initial experiments, the thickness of the thin lithium titanate electrode sample was 0.738 mm and the lithium cobalt oxide electrode was 0.463 mm, while the thickness of the thick lithium titanate and lithium cobalt oxide electrodes were: 0.886 mm and lithium cobalt oxide electrode respectively. 0.640mm.

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　　"Our current goal is to develop a model to help us understand how to change the structure of the electrode, such as changing the orientation or distribution of the material, to improve the ion transport properties," Koening said. "We performed this experiment on each sample at different time points. Imaging, we can construct a two-dimensional image of the lithium distribution. In the future, we plan to rotate our samples in a neutron beam, providing three-dimensional information that can show in more detail how inhomogeneities affect ion transport."

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