Nissan develops world first analysis technique for better lithium ion battery durability

YOKOHAMA, Japan – Can the battery performance of electric vehicles be improved by observing electrons? Nissan sought an answer to this question through an advanced research project in partnership with universities in Japan. The result: Nissan Motor Company and its affiliate Nissan Arc Ltd. today announced the development of the world's first analysis method that enables direct observation of electron activity in the cathode material of lithium ion batteries during charging and discharging.

Applying this analysis technique to future research and design of battery materials could enable Nissan researchers to develop high-capacity and high-durability batteries that may extend the driving distance of zero emission EVs and improve their durability.

Nissan Arc Ltd., a 100-percent subsidiary of Nissan Motor Company, developed the analysis method in a joint R&D effort with Tokyo University, Kyoto University and Osaka Prefecture University. The newly developed technique provides an accurate depiction of how electrons are emitted from certain elements that constitute the cathode material of lithium ion batteries when charging and discharging.

Takao Asami, Nissan senior vice president and president of Nissan Arc Ltd., said: "Creating this analysis technique was a major step toward the further development of high-capacity, next-generation lithium ion batteries. It will play an important part in our future R&D aimed at extending the driving range of future zero emission vehicles."

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) — was emitting electrons and how many electrons were actually being emitted.

The newly developed analysis method combines x-ray absorption spectroscopy¹ that utilizes L-absorption edges² and the first principle calculation³ from Japan's Earth Simulator supercomputer⁴.

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. By applying x-ray absorption spectroscopy that utilizes L-absorption edges, electrons that were directly involved with the cell reaction can be observed. 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.

For years scientists have wanted to understand the origin of electrons during charging and discharging, and this newly-developed analysis method finally makes it possible. 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 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 percent. 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.

*1 X-ray absorption spectroscopy: An analysis method of electronic state and local structure of materials obtained by measuring the increase x-ray absorption energy (absorption edge) after irradiating variant strength x-rays.

*2 Absorption edge: The x-ray absorption value of energy (wavelength) that abruptly increases when the x-ray energy (wavelength) is changed. It is referred to as the K-absorption edge or L-absorption edge depending on the electron orbit.

*3 First Principle Calculation: A calculation method of electronic states without the use of experimental values.

*4 Earth Simulator: A supercomputer owned by the Japan Marine Science and Technology Center (JAMSTEC) originally developed to evaluate global environments.

About Nissan Motor Co.
Nissan Motor Co., Ltd., Japan's second-largest automotive company, is headquartered in Yokohama, Japan, and is part of the Renault-Nissan Alliance. Operating with approximately 236,000 employees globally, Nissan sold more than 4.9 million vehicles and generated revenue of 9.6 trillion yen (USD 116.16 billion) in fiscal 2012. Nissan delivers a comprehensive range of over 60 models under the Nissan and Infiniti brands. In 2010, Nissan introduced the Nissan LEAF, and continues to lead in zero-emission mobility. The LEAF, the first mass-market, pure-electric vehicle launched globally, is now the best-selling EV in history.

About NISSAN ARC, LTD.
NISSAN ARC, LTD. was established in December 1990, with capital provided by Nissan Motor Co., Ltd. The capital is 400 million yen and the number of employees is 90 persons. 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. NISSAN ARC is determined to meet the challenges of the coming era by continually improving our technology through innovative R&D, and also intend to further enhance our range of quality services.

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