Discarding a long-standing pessimistic hypothesis to rescue next-generation lithium-ion battery technology

Discarding a long-standing pessimistic hypothesis to rescue next-generation lithium-ion battery technology

by Nicolas Posunko, Skolkovo Institute of Science and Technology

Study rescues next-generation lithium-ion battery technology by discarding long-standing pessimistic hypothesis
By analyzing the data from the European Synchrotron Radiation Facility (ESRF), the authors of the study have shown that the oxygen gas molecule (O₂), implicated in cathode degradation and observed in resonant inelastic X-ray scattering (RIXS) spectra, had actually formed as a result of X-ray exposure in the experiment. Credit: Liubov Savenkova

In a megascience-scale collaboration with French researchers from College de France and the University of Montpellier, Skoltech scientists have shown a much-publicized problem with next-generation lithium-ion batteries to have been induced by the very experiments that sought to investigate it. Published in Nature Materials, the team’s findings suggest that the issue of lithium-rich cathode material deterioration should be approached from a different angle, giving hope for more efficient lithium-ion batteries that would store some 30% more energy.

Efficient energy storage is critical for the transition to a low-carbon economy, whether in grid-scale applications, electric vehicles, or portable devices. Lithium-ion batteries remain the best-developed electrochemical storage technology and promise further improvements. In particular, next-generation batteries with so-called lithium-rich cathodes could store about one-third more energy than their state-of-the-art counterparts with cathodes made of lithium nickel manganese cobalt oxide, or NMC.

A key challenge hindering the commercialization of lithium-rich batteries is voltage fade and capacity drop. As the battery is repeatedly charged and discharged in the course of normal use, its cathode material undergoes degradation of unclear nature, causing gradual voltage and capacity loss. The problem is known to be associated with the reduction and oxidation of the  in NMC, but the precise nature of this redox process is not understood. This theoretical gap undermines the attempts to overcome voltage fade and bring next-generation batteries to the market.

A leading hypothesis has purported that over the lifetime of a battery, the oxygen atoms, originally incorporated into the crystal structure of the cathode, form the familiar O₂ molecules—like those in the air we breathe. In fact, several studies using advanced X-ray spectroscopy have detected the O₂ signature in lithium-rich cathode materials.

That form of oxygen is almost electrochemically inactive, degrading the battery’s performance. In a way, this hypothesis spelled disaster for next-generation batteries, because once formed, the O₂ molecules are so stable that this unwanted process would be very hard to reverse.

“Thankfully, our latest study relegates the molecular oxygen hypothesis to history,” said Assistant Professor Dmitry Aksyonov of Skoltech Energy, who co-authored the research.

“By examining the data from major X-ray scattering experiments, we have demonstrated that the O₂ molecules trapped in the cathode material and supposedly responsible for its worsening performance are likely the artifact of the experiment. Apparently, their formation was induced by the very X-rays used to discover them.”