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The unexpected key to extending EV battery life found in “oxygen release”

What if a battery could become more powerful as it ages? Much like wine developing a deeper flavor over time, researchers in Korea have uncovered the mechanism behind a battery material that can deliver greater usable capacity after repeated charging and discharging.

A research team led by Professor Jihyun Hong (Department of Battery Engineering at POSTECH) with Dr. Gukhyeon Lim and a team led by Professor Kyu-Young Park (Department of Battery Engineering & Materials Science and Engineering at POSTECH) with Ph.D. student Hojun Lee have identified the origins of performance degradation in manganese-based cathode materials, which are considered promising candidates for next-generation electric vehicle batteries. More importantly, the team proposed a new strategy for turning what has traditionally been regarded as a weakness of the material into a potential performance advantage. The study was published in Energy & Environmental Science, a leading international journal in the field of energy research. Recognizing its potential impact, the journal's editors selected the paper as a Hot Article, placing it among the top 10% of published articles.

The electric vehicle industry is actively searching for cost-effective next-generation battery materials capable of competing with inexpensive lithium iron phosphate (LFP) batteries manufactured in China. One of the most promising candidates is the lithium- and manganese-rich layered oxide (LMRO) cathode.

LMROs require less expensive nickel and cobalt while storing approximately 20% more energy than conventional nickel-based cathode materials, making them attractive for batteries that could potentially be both less expensive and capable of longer driving ranges.

However, LMROs have a critical drawback. Their capacity gradually decreases with repeated charging and discharging, while their operating voltage also declines. Previous studies attempting to identify the cause have reported different final structures inside the cathode, leaving the fundamental mechanism governing these structural changes unresolved.

The POSTECH team examined how the internal structure of the cathode evolved over hundreds of charge-discharge cycles. Initially, lithium and transition-metal atoms are neatly arranged in separate layers, resembling bricks stacked in an orderly wall. As charging continues, however, some of the oxygen atoms that stabilize this framework gradually escape from the material. This is similar to a well-organized drawer whose contents gradually become jumbled over time. 

As these oxygen atoms are removed, lithium and transition-metal atoms begin to migrate across their original layers and mix with one another. Eventually, the highly ordered layered structure transforms into a disordered rocksalt structure, in which the cations no longer follow their original long-range ordering. 

The researchers discovered that the amount of oxygen lost from the material acts as a key trigger determining how extensively the internal structure becomes disordered. They further demonstrated that oxygen loss can be controlled by how deeply the battery is charged—in other words, by how high the charging voltage is raised. Deeper charging led to greater oxygen loss, while the resulting oxygen vacancies progressively accumulated and drove structural rearrangement within the cathode. 

Improving battery energy density and cycle life by controlling oxygen-vacancy concentration(image above)

The most surprising finding came afterward. Oxygen loss would normally be regarded as a clear sign of battery degradation. However, as the cathode became disordered and transformed into a new structure, additional pathways through which lithium ions could move were created. As a result, the amount of usable capacity actually increased. By carefully controlling the degree of oxygen loss and the resulting structural evolution, the researchers demonstrated that the cathode retained 98.4% of its initial performance even after more than 200 charge-discharge cycles, showing remarkable long-term durability.

Structural disorder in battery materials has traditionally been regarded as an undesirable aging phenomenon that should be avoided. This study, however, demonstrates that when such structural evolution is precisely controlled, it can instead become a design tool for improving battery performance.

Professor Jihyun Hong said, “From an industrial perspective, our study shows that battery degradation can be delayed and battery lifetime extended simply by controlling parameters such as operating temperature and the surface environment.”. He added, “By regulating oxygen loss and thereby either promoting or suppressing structural disorder, it may become possible to design next-generation electric vehicle batteries optimized for different applications.”. Professor Kyu-Young Park, a co-corresponding author of the study, said, “By integrating precise materials characterization with computational materials science, we were able to address a problem that had remained unresolved for nearly two decades. The collaborative research environment within POSTECH's Department of Battery Engineering, which encourages interaction and cooperation among researchers through the Specialized Graduate School Program, played a decisive role in making this work possible.”

This research was supported by the Ministry of Trade, Industry and Energy through the Korea Planning & Evaluation Institute of Industrial Technology (KEIT) and the Korea Institute for Advancement of Technology (KIAT), the Ministry of Science and ICT through the National Research Foundation of Korea (NRF), and the Electronics and Telecommunications Research Institute (ETRI).

Researchers at the Pohang University of Science and Technology (POSTECH) in South Korea have discovered that controlling oxygen release in lithium- and manganese-rich oxide (LMRO) cathodes can turn structural wear into a performance advantage, allowing for the retention of 98.4% of capacity after more than 200 charge-discharge cycles.

Key research findings:

• Innovative material: The study focuses on lithium- and manganese-rich layered oxides (LMRO), which store approximately 20% more energy than traditional nickel-based cathodes while using less cobalt and nickel.

• Voltage control: The amount of oxygen released is directly dependent on the depth of charge (the level of the charging voltage).

• Structural reorganization: Rather than merely causing degradation, the controlled loss of oxygen and the formation of vacancies create new pathways for lithium-ion movement, increasing the material's usable capacity over time.

• Long-lasting performance: This method enables the battery to maintain 98.4% of its initial performance after more than 200 cycles of use.

POSTECH