For the first time researchers have used a transmission electron microscope - the One Angstrom Microscope (OÅM) at the Department of Energy's National Center for Electron Microscopy (NCEM) at Lawrence Berkeley National Laboratory - to image lithium atoms. Only atoms of hydrogen and helium are smaller and lighter than those of lithium, which under ordinary conditions is not a gas but a soft, white metal.
Yang Shao-Horn of the Department of Mechanical Engineering at the Massachusetts Institute of Technology and Michael O'Keefe of Berkeley Lab's Materials Sciences Division used the OÅM to simultaneously resolve columns of lithium, cobalt, and oxygen atoms in the compound lithium cobalt oxide (LiCoO2). They and their colleagues report their work in the July, 2003 issue of the journal Nature Materials, in a report currently accessible online.
LiCoO2 is commonly used in the positive electrodes of lithium rechargeable batteries, whose operation is based on reversible insertion and removal of lithium ions to and from their positive and negative electrodes. Widely used in laptop computers, digital cameras, and many other devices, lithium ion batteries store more energy for their weight, operate at a higher voltage, and hold a charge much longer than other rechargeable batteries.
To improve their performance will require understanding how the atoms in the electrode materials -- and the vacancies left by moving ions -- are arranged in 3-D on the atomic scale. The structure of LiCoO2 is known theoretically and has been confirmed with techniques like x-ray diffraction and neutron powder diffraction: layers of lithium atoms lie between slabs of cobalt and oxygen, which are arranged in octahedrons. But lithium ions have never been seen by these techniques, nor have they been seen in previous attempts to image LiCoO2 with electron microscopy.