Researchers develop MRI-based non-invasive method to visualize electrode surfaces and electrolytes in Li-ion batteries

13 February 2012

Researchers at Cambridge University, Stony Brook University, and New York University have developed a non-invasive methodology, based on magnetic resonance imaging (MRI), to visualize and to characterize the changes that occur on battery electrodes and in the electrolytes of Li-ion batteries. Their technique, which is described in the journal Nature Materials, creates the possibility of improving battery performance and safety by serving as a diagnostic of its internal workings.

Although in its current application, the methodology focuses on lithium-metal batteries and the observation of electrode microstructure build-up as a result of charging, the methods developed will be “highly valuable” in the quest for enhanced battery performance and in the evaluation of other electrochemical devices, the researchers suggest.

The increasing demands on batteries and other electrochemical devices have spurred research into the development of new electrode materials that could lead to better performance and lower cost (increased capacity, stability and cycle life, and safety). These developments have, in turn, given rise to a vigorous search for the development of robust and reliable diagnostic tools to monitor and analyse battery performance, where possible, in situ. Yet, a proven, convenient and non-invasive technology, with an ability to image in three dimensions the chemical changes that occur inside a full battery as it cycles, has yet to emerge.

Here we demonstrate techniques based on magnetic resonance imaging, which enable a completely non-invasive visualization and characterization of the changes that occur on battery electrodes and in the electrolyte.

—Chandrashekar et al.

MRI has been extremely successful in the medical field for visualizing disorders and assessing the body’s response to therapy. However, MRI is not typically used in the presence of a lot of metal, a primary component in many batteries. This is because conducting surfaces effectively block the radio frequency fields that are used in MRI to see beneath surfaces or inside the human body.

The researchers turned this limitation into a virtue. Because radio frequency fields do not penetrate metals, one can actually perform very sensitive measurements on the surfaces of the conductors. In the case of the popular lithium-ion batteries, for example, the team was able to directly visualize the build-up of lithium metal deposits on the electrodes after charging the battery. Such deposits can also detach from the surface, eventually leading to overheating, battery failure, and in some cases to fire or explosion.

Visualizing small changes on the surface of the batteries’ electrodes allows, in principle, for the testing of many different battery designs and materials under normal operating conditions.

The work is the result of a collaboration between Clare Grey, associate director of the Northeastern Center for Chemical Energy Storage and a professor at Cambridge and Stony Brook universities, and Alexej Jerschow, a professor in the Department of Chemistry at New York University who heads a multi-disciplinary MRI research laboratory.

New electrode and electrolyte materials are constantly being developed, and this non-invasive MRI technology could provide insights into the microscopic processes inside batteries, which hold the key to eventually making batteries lighter, safer, and more versatile. Both electrolyte and electrode surfaces can be visualized with this technique, thus providing a comprehensive picture of the batteries’ performance-limiting processes.

—Alexej Jerschow

MRI is exciting because we are able to identify where the chemical species inside the battery are located without having to take the battery apart, a procedure which to some degree defeats the purpose. The work clearly shows how we can use the method to identify where lithium deposits form on metal electrodes. The resolution is not yet where we want it to be and we would like to extend the method to much larger batteries, but the information that we were able to get from these measurements is unprecedented.

—Clare Grey

The research team also envisions that the method could lead to the study of irregularities and cracks on conducting surfaces in the materials sciences field.

The research was supported by grants from the US Department of Energy and the National Science Foundation.

Resources

• S. Chandrashekar, Nicole M. Trease, Hee Jung Chang, Lin-Shu Du, Clare P. Grey & Alexej Jerschow (2012) ⁷Li MRI of Li batteries reveals location of microstructural lithium. Nature Materials doi: 10.1038/nmat3246