Succeeded in Visualizing Incoming and Outgoing Motions of Lithium Ions at Positive Electrode by Electron Microscope

Dr. Akita Tomoki et al., AIST's researchers#1, succeeded in visualizing the incoming and outgoing motions of lithium ions at the positive electrode of the lithium ion battery by using the electron microscope.
The success will trigger the impetus of developing the lithium ion battery toward its performance enhancement.

No one has visualized the concentration distribution of lithium (Li).
The peak of the spectrum of the concentration distribution of Li is low in energy level to such an extent that it is difficult to distinguish from the peaks of the spectra of the background and other elements. This is the reason why the visualization is difficult.
The spectrum-imaging method using the STEM - EELS method#2 has been used for visualizing the concentration distributions of elements constituting a test piece.

The researchers found the fact "The second order derivative of the EELS spectrum is theoretically proportional to the concentration of an element of a test piece when the test piece is thin." A signal intensity analyzing method based on the second order derivative was developed anew. The signal intensities of lithium were quantitized by using the new analysis method to visualize the concentration distribution.

Further, the researchers elucidated a relationship between the nano structure of the positive electrode and the behavior of lithium ions by using the new visualizing technique.

For details of the results of this study, reference is made to "Electrochemical and Solid-State Letters" (IEEE transactions), electronic edition, issued on August 15, 2008, and the sources of this article referred to below.

[Sources: AIST's press release on August 18, 2008, List of AIST's major study results, and others]

#1: Akita Tomoki, chief researcher,
Research Institute for Ubiquitous Energy Devices, AIST (national institute of advanced industrial science and technology)
#2: STEM = scan transmission electron microscope
EELS = electron energy loss spectroscopy
Keywords: lithium ion battery, anode electrode, visualize, incoming and outgoing motions of lithium ions, concentration distribution of lithium, STEM - EELS