Significant Progress in Sodium-Ion Layered Oxide Cathode Materials Research by Yanshan University and Chinese Academy of Sciences

TapTechNews August 21st news, on August 19th, Yanshan University released a press release stating that it has collaborated with the Institute of Physics, Chinese Academy of Sciences, and made significant progress in sodium-ion layered oxide cathode materials, and the relevant research results were published in the journal Science.

Team Introduction

Professor Huang Jianyu led the team of the State Key Laboratory of Metastable Materials Preparation Technology and Science of Yanshan University, and cooperated with the research team of the Institute of Physics, Chinese Academy of Sciences and the Yangtze River Delta Physical Research Center. The relevant results were published in the journal Science, and Yang Yang, a doctoral student of the Institute of Physics, Chinese Academy of Sciences, and Wang Zaifa, a doctoral graduate of Yanshan University, are the first authors of the paper.

Project Background

Layered oxide cathode materials, with their excellent high capacity and scalable production characteristics, have occupied a pivotal position in the field of lithium-ion batteries and sodium-ion batteries.

Thanks to the wide availability of sodium resources and the high flexibility in the choice of transition metal elements - without relying on expensive cobalt and nickel, but using more cost-effective iron and copper as substitutes, sodium-ion layered oxide cathode materials have shown significant cost-effectiveness.

However, the air sensitivity of such materials has plagued the research community of sodium-ion layered oxide cathode materials for more than forty years and has become a major obstacle to be overcome in its commercialization process.

Project Research Results

The research team pointed out that breaking the coupling effect between gases is the key external factor to achieve stable storage of materials.

By using the widely studied NaNi1/3Fe1/3Mn1/3O2 (NFM111) as a model material and extending to its homologues, combined with the use of advanced characterization methods such as in-situ ambient atmosphere transmission electron microscopy, isotope labeling method, secondary ion mass spectrometry, neutron scattering, synchrotron radiation X-ray absorption spectroscopy, it was found that water vapor, carbon dioxide or oxygen alone would not cause significant degradation reactions, challenging the traditional view that these three gases (especially water vapor) alone can cause severe degradation reactions:

Water vapor plays a crucial bridging role in the degradation process, which can connect carbon dioxide and oxygen to the material, respectively causing acidic degradation and oxidative degradation.

In which, in the acidic degradation, it will trigger a violent Na+/H+ exchange, forming sodium carbonate or sodium bicarbonate on the surface, and will also trigger crack growth, lattice distortion, dislocation generation and subsequent reactions such as surface transition metal ion reduction and reconstruction under strong acidic conditions;

In the oxidative degradation, the transition metal ions with a lower oxide redox potential (closer to the Fermi level) in the bulk phase will be preferentially oxidized, and at the same time release sodium ions to the surface to balance the charge. The oxidized transition metal ions (Ni3+) are usually unstable on the surface and easily reduced, thus triggering surface reconstruction.

At the same time, the research team also developed a standardized air stability test method based on titrat ion gas chromatography technology to quantitatively evaluate the contribution of different reaction paths and the air stability of different materials.

According to the quantitative results of sodium loss amounts after the degradation of more than 30 kinds of materials and previous research results, combined with the ionic potential and initial sodium content of each component, the cation competition coefficient η was defined, and it was found that:

Acidic degradation dominates the degradation reaction of most materials;

By reducing the cation competition coefficient and increasing the particle size of the material, the acid resistance of the material can be effectively improved;

By choosing a redox pair with a high potential, the antioxidant capacity of the material can be effectively improved as the main factor.

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