In order to develop high-capacity, long-life lithium ion batteries, the maximum possible amount of lithium must be stored in the electrode’s active material, which allows it to generate the highest possible number of electrons. To develop such a material, an accurate reading of the electron activity inside the battery is essential.

Existing analysis methods did not allow researchers to observe the movement of electrons. It was not possible to determine how the various electrodes’ active material—i.e. manganese (Mn), cobalt (Co), nickel (Ni), oxygen (O)—were emitting electrons and how many electrons were actually being emitted.

The newly-developed analysis method combines x-ray absorption spectroscopy that utilizes L-absorption edges and first principle calculations from Japan’s Earth Simulator supercomputer.

X-ray absorption spectroscopy analyzes the electronic state and local structure of materials by measuring the increased x-ray absorption energy (absorption edge) after irradiation with variant strength x-rays.

The absorption edge is the x-ray absorption value of energy (wavelength) that abruptly increases when the x-ray energy (wavelength) is changed. Each edge represents a different core–electron binding energy, and is named according to the principle quantum number of the electron that is excited: K for n=1, L for n=2, M for n=3, etc.

In a recent paper published in the ACS’ Journal of Physical Chemistry Letters, researchers from Europe and the US noted that new ultra-bright femtosecond X-ray pulses allow data collection before the onset of radiation damage, enabling studies under functional conditions that are useful for the study of, among other things, electron transfer processes.

They also noted that despite experimental difficulties, it is highly desirable to use L-edge spectroscopy for studying metal catalysts, as (i) it provides significantly higher resolution and (ii) the frontier orbitals are directly accessible under dipole selection rules. Direct probing of the 3d electronic structure at higher resolution gives greater chemical sensitivity to, e.g., oxidation states, symmetry, and covalency of the complex studied.

Furthermore … the experimental L-edge data can be complemented by theoretical calculations of the 3d electronic structure.

—Mitzner et al.

X-ray absorption spectroscopy had been used in the past to analyze batteries. However, the majority of this analysis was done using K-absorption edges that can only observe restrained electrons in the atom (electrons that are not involved in the charging and discharging due to the vicinity to the nucleus) and not the actual electrons involved in cell reaction.

(In December 2013, researchers at Berkeley Lab and its Advanced Light Source reported the development of a new soft X-ray spectroscopy technique that can measure the migration of ions and electrons in an integrated, operating battery electrode. In an open access paper in Nature Communications, they described distinct lithium-ion and electron dynamics in Li(Co_1/3Ni_1/3Mn_1/3)O₂ and LiFePO₄ cathodes in polymer electrolytes. (Earlier post.)

By applying x-ray absorption spectroscopy that utilizes L-absorption edges, electrons that were directly involved with the cell reaction can be observed, Nissan found. Accurate analysis of the amount of electron mobility is made possible by combining the observation results with first principle calculations from the Earth Simulator supercomputer.

Using this newly-developed analysis method, scientists can observe the exact phenomenon inside a battery cell, especially the behavior of active materials of electrodes, permitting further study of better-performing, longer-lasting electrode materials, Nissan said.

Nissan Arc has used the new analysis technique to investigate lithium-rich high-capacity electrode materials which are considered promising agents to increase energy density by 150%. The analysis revealed that at a high potential state, electrons originating from oxygen were active during charging. Meanwhile, electrons that originated from manganese were observed to be active during the discharge reaction. These findings were a big step forward toward the commercial development of lithium-rich electrode materials which can produce higher-capacity, long-lasting batteries, the company said.

Nissan was established in December 1990, with capital provided by Nissan Motor Co., Ltd. The main work areas are 1) commissioned analysis, research and investigation of organic and inorganic materials and their composites; 2) Commissioned training in analysis and analysis technology; and 3) research and development into analysis and analysis technology.

Resources

• Rolf Mitzner, Jens Rehanek, Jan Kern, Sheraz Gul, Johan Hattne, Taketo Taguchi, Roberto Alonso-Mori, Rosalie Tran, Christian Weniger, Henning Schröder, Wilson Quevedo, Hartawan Laksmono, Raymond G. Sierra, Guangye Han, Benedikt Lassalle-Kaiser, Sergey Koroidov, Katharina Kubicek, Simon Schreck, Kristjan Kunnus, Maria Brzhezinskaya, Alexander Firsov, Michael P. Minitti, Joshua J. Turner, Stefan Moeller, Nicholas K. Sauter, Michael J. Bogan, Dennis Nordlund, William F. Schlotter, Johannes Messinger, Andrew Borovik, Simone Techert, Frank M. F. de Groot, Alexander Föhlisch, Alexei Erko, Uwe Bergmann, Vittal K. Yachandra, Philippe Wernet, and Junko Yano (2013) “L-Edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X-ray Free-Electron Laser,” The Journal of Physical Chemistry Letters 4 (21), 3641-3647 doi: 10.1021/jz401837f

• J. E. Penner-Hahn (University of Michigan) X-ray Absorption Spectroscopy