news

한어Русский языкEnglishFrançaisIndonesianSanskrit日本語DeutschPortuguêsΕλληνικάespañolItalianoSuomalainenLatina

IT Home reported on August 21 that Yanshan University issued a press release on August 19, stating that it was cooperating with the Institute of Physics of the Chinese Academy of Sciences.Important progress has been made in sodium-ion layered oxide positive electrode materials, and the relevant research results were published in the journal Science.

About the Team

Professor Huang Jianyu led the team of the National Key Laboratory of Metastable Materials Preparation Technology and Science of Yanshan University, and cooperated with the research teams of the Institute of Physics, Chinese Academy of Sciences and the Yangtze River Delta Physics Research Center to publish relevant results in the magazine Science. Yang Yang, a doctoral student at the Institute of Physics, Chinese Academy of Sciences, and Wang Zaifa, a doctoral graduate from Yanshan University, were the first authors of the paper.

Project Background

Layered oxide cathode materials, with their outstanding high capacity and scalable production characteristics, occupy 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 selection of transition metal elements - no need to rely on expensive cobalt and nickel, but more cost-effective iron and copper can be used as substitutes, sodium-ion layered oxide positive electrode materials have shown significant cost-effectiveness.

However, the air sensitivity of such materials has plagued the sodium-ion layered oxide cathode material research community for more than four decades, becoming a major obstacle that needs to be overcome in the process of commercialization.

Project Research Results

The research team pointed out that breaking the coupling between gases is a key external factor in achieving stable storage of materials.

Quantification of acidic and oxidative degradation and development and design principles for intrinsically air-stable sodium-ion layered oxide cathode materials Image provided by the project team

The team used the widely studied NaNi1/3Fe1/3Mn1/3O2 (NFM111) as a model material and expanded to its homologues. They combined advanced characterization methods such as in-situ ambient atmosphere transmission electron microscopy, isotope labeling, secondary ion mass spectrometry, neutron scattering, and synchrotron radiation X-ray absorption spectroscopy to find that water vapor, carbon dioxide, or oxygen alone do 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 key bridging role in the degradation process, carbon dioxide and oxygen can be linked to the material, initiating acidic and oxidative degradation, respectively.

• in,Acidic degradationIt will trigger a violent Na+/H+ exchange, forming sodium carbonate or sodium bicarbonate on the surface of the material, and will also trigger subsequent reactions such as crack extension growth, lattice distortion, dislocation generation, and surface transition metal ion reduction and reconstruction under strong acid conditions;

• Oxidative degradation, transition metal ions with lower redox potentials (closer to the Fermi level) in the bulk phase will be oxidized first, while releasing sodium ions to the surface to balance the charge. The oxidized transition metal ions (Ni3+) are usually unstable on the surface and are easily reduced, thus causing surface reconstruction.

At the same time, the research team also developedA standardized air stability test method based on titration gas chromatography, which is used to quantitatively evaluate the contribution of different reaction pathways and the air stability of different materials.

Based on the quantitative results of sodium loss after degradation of more than 30 materials and previous research results, the ionic potential and initial sodium content of each composition were comprehensively considered.The cation competition coefficient η is defined as, and found that:

• Acidic degradation dominates the deterioration reactions of most materials;

• The acid resistance of the material can be effectively improved by reducing the cation competition coefficient and increasing the particle size of the material;

• The main factor that can effectively improve the material's antioxidant capacity is by selecting a high-potential redox pair.

IT Home attaches the reference address