How transition metals destabilize high-energy-density Li-ion batteries

Lithium-ion battery cells. (Reference image by Argonne National Laboratory, Flickr).

Researchers from Tohoku University and the Japan Synchrotron Radiation Research Institute produced fresh insights about the release of oxygen in lithium-ion batteries, paving the way for more robust and safer high-energy-density batteries.

In a paper published in the journal Advanced Energy Materials, the team explains how critical it is to develop the next generation of batteries that store more energy in order to achieve the UN’s Sustainable Development Goals and realize carbon neutrality.

However, the higher the energy density, the higher the likelihood of thermal runaway, which is the overheating of batteries that can sometimes result in a battery exploding.

Oxygen release from battery materials can cause thermal runaway. (Image by Takashi Nakamura, courtesy of Tohoku University).

Even though scientists know that oxygen released from cathode active material is a trigger for thermal runaway, knowledge around this process has been limited so far. But following a series of experiments, the Japanese group was able to determine that it is the high-valent transition metals that destabilize lattice oxygen in oxide-based battery materials.

To reach this conclusion, they investigated the oxygen release behavior and relating structural changes of cathode material for lithium-ion batteries LiNi1/3Co1/3Mn1/3O2(NCM111).

NCM111 acted as a model oxide-based battery material through coulometric titration and X-ray diffractions.

They discovered NCM111 accepts 5 mol% of oxygen release without decomposing and that oxygen release induced structural disordering, the exchange of Li and Ni.

When oxygen is released, it reduces the transition metals, that is nickel, cobalt and manganese, in NCM111 thus lessening their ability to keep a balanced charge in the materials.

Using soft-Xray absorption spectroscopy at BL27SU SPring-8—a JASRI operated large-scale synchrotron radiation facility in Japan, they observed selective Ni3+ reduction in NCM111 at the beginning stage of oxygen release. After the Ni reduction finished, Co3+ decreased, while Mn4+ remained invariant during 5 mol% of oxygen release.

According to the group, the reduction behaviors strongly suggest that high valent NI (Ni3+) enhances oxygen release.

To test this hypothesis, the researchers prepared modified NCM111 containing more Ni3+ than the original NCM111. They discovered the NCM111 exhibited much severer oxygen release than expected.

Based on this, the team proposed that the high-valent transition metals destabilize lattice oxygen in oxide-based battery materials.

“Our findings will contribute to the transition further development of high energy density and robust next-generation batteries composed of metal oxides,” Takashi Nakamura, one of the co-authors is the paper, said in a media statement.

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