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Batteries’ ‘guts’ reveal details on why they fail

Advanced Li-Ion battery. (Reference image by the Argonne National Laboratory, Flickr.)

Engineers and chemists at the University of Illinois Urbana-Champaign are working together to combine a powerful new electron microscopy technique and data mining to visually pinpoint areas of chemical and physical alteration within rechargeable ion batteries.

In a paper published in the journal Nature Materials, the scientists explain that their efforts are the first to map out altered domains inside rechargeable ion batteries at the nanoscale – a 10-fold or more increase in resolution over current X-ray and optical methods.

According to the group, previous efforts to understand the working and failure mechanisms of battery materials have primarily focused on the chemical effect of recharging cycles, namely, the changes in the chemical composition of the battery electrodes.

But the new electron microscopy technique, called four-dimensional scanning transmission electron microscopy, allows the team to use a highly focused probe to collect images of the inner workings of batteries.

“During the operation of rechargeable ion batteries, ions diffuse in and out of the electrodes, causing mechanical strain and sometimes cracking failures,” Wenxiang Chen, first author of the study, said in a media statement. “Using the new electron microscopy method, we can capture the strain-caused nanoscale domains inside battery materials for the first time.”

Chen pointed out that these types of microstructural heterogeneity transformations have been widely studied in ceramics and metallurgy but have not been used in energy storage materials until this study.

He and his colleagues also believe that the 4D-STEM method is critical to map otherwise inaccessible variations of crystallinity and domain orientations inside the materials.

“The combined data mining and 4D-STEM data show a pattern of nucleation, growth and coalescence process inside the batteries as the strained nanoscale domains develop,” co-author Qian Chen said. “These patterns were further verified using X-ray diffraction data collected by materials science and engineering professor and study co-author Daniel Shoemaker.”

Qian Chen plans to further this research by creating movies of this process – something for which her lab is well known.

“The impact of this research can go beyond the multivalent ion battery system studied here,” said Paul Braun, a materials science and engineering professor, also co-author of the study.

“The concept, principles and the enabling characterization framework apply to electrodes in a variety of Li-ion and post-Li-ion batteries and other electrochemical systems including fuel cells, synaptic transistors and electrochromics.”