Nissan develops world first analysis technique for better Li-Ion battery durability

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 is that the Japanese carmaker and its affiliate Nissan Arc Ltd have 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) — 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 the first principle calculation from Japan's Earth Simulator supercomputer.

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 says it has used the new analysis technique to investigate lithium-rich high-capacity electrode materials which are considered promising agents to increase energy density by 50 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.

Photograph: The Nissan Leaf EV’s lithium-ion battery pack.