Prof. Kang Yong-mook at the Department of Materials Science and Engineering of Korea University and Dr. Wanli Yang at the Lawrence Berkeley National Lab in California discovered anion oxidation and reduction in LiNi1/3Co1/3Mn1/3O2 (NCM) for the first time in the world. The performance and stability of the NCM material, which is used as an anode material for lithium secondary batteries of electric vehicles, and the batteries themselves are expected to improve together based on the research outcome published in the international edition of the Angewandte Chemie journal.
The performance of lithium secondary batteries used in portable power supplies, electric vehicles, energy storage systems, and so on depends on the properties of the four key materials of cathode, anode, electrolyte and separation membrane. The performance of the anode material matters the most when it comes to charging capacity, which determines the duration of battery use.
Their joint research team employed resonant inelastic X-ray scattering (RIXS), one of the most reliable methods for observation of anion oxidation and reduction, and discovered that transition metals become free from oxidation and charging is conducted by electron desorption from oxygen once 70 percent of lithium ions are removed during NCM charging. The team also confirmed that the electron desorption has a certain level of reversibility and thus can contribute to reversible capacity improvement for NCM.
These days, observation of anion oxidation and reduction is revolving around Li-rich layered anode materials. This observation technique is known as a mechanism in which an electron movement is caused beyond the range of existing transition metal oxidation and reduction, the use of lithium ions is increased, and the capacity of lithium secondary batteries can be substantially increased as a result. According to proposed theories, however, the phenomenon occurs only in the event of asymmetry in the layered structure attributable to excess lithium, a structural defect, or the like.
“Our research has confirmed that making oxidation and reduction from anions or oxygen reversible is the most important part for an innovative enhancement of the capacity and energy density of NCM, which is one of the most typical commercial anode materials,” the professor explained. The research team is planning to maximize the utility of the material by further looking into the cause of anion oxidation and reduction in non-Li-rich layered anode materials and NCM.