Korean researchers from Pohang University of Science and Technology (POSTECH) have studied the degradation mechanism (the gradual deterioration of characteristics) of manganese-based cathode materials. Such materials are considered promising for next-generation electric vehicle batteries.
The work was led by Professor Chihyon Hong with Dr. Gukhyon Lim and Professor Kyu Yong Pak with doctoral student Hojun Li. The results were published in the journal Energy & Environmental Science.
The automotive industry is looking for inexpensive battery materials capable of competing with cheap lithium iron phosphate (LFP) batteries from China. One of the main contenders is lithium manganese layered oxide (LMRO). It requires less expensive nickel and cobalt and stores roughly 20% more energy than conventional nickel cathodes. However, LMRO has a serious drawback: after repeated charging and discharging, capacity gradually declines and operating voltage drops. Previous studies cited various causes, but there was no unified mechanism.
The team traced how the internal structure of the cathode changes over hundreds of cycles. Initially, lithium and transition metal atoms are arranged in an ordered, layered fashion. But during charging, some of the oxygen atoms that hold this structure together gradually leave the material. As a result, lithium and metals begin to mix, and the ordered layered structure turns into a disordered "rocksalt" structure, where the atoms no longer follow the previous order.
The key factor turned out to be the amount of lost oxygen. The scientists showed that these losses can be regulated by the depth of charge: the higher the charging voltage, the more oxygen leaves. The accumulation of such vacancies (empty sites) triggers the restructuring.
The most interesting finding came next. Oxygen loss is usually considered a sign of wear. But when the cathode became disordered, additional pathways for lithium ion movement appeared in it, and useful capacity grew. By controlling oxygen loss and structural changes, the researchers achieved a result in which, after more than 200 charge-discharge cycles, the cathode retained 98.4% of its initial capacity.
"From a practical point of view, our work shows that battery degradation can be slowed and service life extended simply by controlling parameters such as operating temperature and surface condition," Hong was quoted as saying by the POSTECH press service. He also noted that by regulating oxygen loss and inducing or suppressing structural disorder, it is possible to design batteries for different tasks.
Co-author Professor Pak added that combining precise materials analysis methods with computer modeling helped solve a problem that had remained unresolved for almost twenty years.
It is important to emphasize: this is a laboratory study of a mechanism, not a finished commercial product. It is not yet clear how the new strategy will perform in real batteries and in mass production.