The design principles of 'disordered rock salt materials', which are attracting attention as next-generation electric vehicle battery materials, have been newly presented, providing momentum to the development of materials that will lower the price of electric vehicles.

An international joint research team led by Professor Dong-Hwa Seo of the Department of Energy and Chemical Engineering at UNIST (President Yong-Hoon Lee) has discovered for the first time that the principle of ‘lithium excess composition,’ which was considered a design principle for high-performance disordered rock salt electrodes, does not apply to certain disordered rock salt materials.

It was known that lithium-excess composition, which designs the lithium ratio to be 35% or more higher than that of expensive transition metals, increases electrode performance but at the same time reduces the lifespan of the battery, but the research team discovered a material that overturns this principle.

The results of this study, in which Professor Jinhyeok Lee of the Department of Materials Science and Engineering at McGill University in Canada and Professor Ju Li of MIT in the United States participated, were published on May 6 in Advanced Energy Materials, an international academic journal in the field of energy materials.

cobalt, cathode materials containing large amounts of expensive rare metals such as nickel account for more than 20% of the cost of electric vehicle battery (lithium-ion battery) cells. For this reason, they have a structure similar to the atomic arrangement of disordered rock-salt salt crystals (rock salt, NaCl), which contain large amounts of inexpensive and abundant manganese and iron. The cations, transition metals and lithium, are arranged randomly (disorderedly), giving them the name disordered rock-salt material.

This material is attracting attention as a new cathode material. Compared to commercially available materials, its capacity is 30-50% greater, making it suitable not only for electric vehicles but also as a large-capacity battery material for storing power generated by renewable energy sources.

On the other hand, the short lifespan of disordered rock salt cathodes has been a stumbling block to their commercialization. Previous research has shown that to maximize high-capacity performance, these cathodes must be designed with a higher lithium content than conventional cathodes. However, high lithium content in the material can lead to unstable oxygen leaking out of the electrode, which reduces battery life.

According to the joint research team's research, certain metal-based disordered rock salt materials, such as manganese and vanadium, can maintain the performance of high-capacity electrodes even with reduced lithium content, and the lifespan is more than twice that of existing ones. On the other hand, in the case of nickel or cobalt metal-based disordered rock salt materials, the higher the lithium content, the better the electrode performance, as per the existing theory.

The research team discovered this fact, which runs counter to existing theories, through experiments using two types of manganese-based disordered rock salt materials with different lithium contents and quantum mechanical modeling techniques based on density functional theory.

Professor Jinhyeok Lee, the first author and co-corresponding author, explained, “A new disordered rock salt material that can maintain high performance while reducing lithium content has been discovered, opening the way to replacing expensive battery cathode materials with cheaper disordered rock salt materials.”

Professor Seo Dong-hwa said, “With the increase in renewable energy generation as well as electric vehicles, there is a growing interest in inexpensive, high-capacity battery materials,” adding, “If disordered rock salt materials are commercialized, they will be able to meet this demand.”

This research was conducted with the support of the National Research Foundation of Korea's Basic Science and Engineering Research Project and the Overseas Excellent Research Institute Attraction Project, and with the support of the supercomputer of the Korea Institute of Science and Technology Information.