Synergistically application of electronic structure engineering and microstructure engineering for development of cobalt-free high voltage cathodes for Na-ion batteries

• Applicant: Professor Dr. Ehrenfried Zschech
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 504885810

The market of Li-ion batteries is currently the most dynamically growing field of electrical energy storage. Since resources of lithium and cobalt are limited, Co-free and Li-free Na-ion batteries have been recognized as potential candidates for next-generation rechargeable batteries. The SynBat project presents a unique approach called “electronic and microstructure engineering” in the development of high voltage Na2M2(SO4)3 (M = Fe, Mn, Ni…) cathode material for Na-ion batteries. There are only a few literature reports on synthesis of Na2Fe2(SO4)3 suggesting that it is not possible to obtain this material without a large amount of impurities (17 wt.%). The Polish PI group proposed a green method of synthesis of Na2M2(SO4)3 with significantly reduced impurity level (3 wt.%), with a high Fe3+/Fe2+ redox potential of 3.7 V vs. Na+/Na. Such high potential combined with large capacity for sodium intercalation leads to a high theoretical energy density of 456 Wh kg-1. These features enable the design of Na-ion batteries that are competitive with Li-ion analogues. In order to achieve this goal, the intrinsic drawback of this material, i.e. a low electrical conductivity, that limits the current density generated by the cell, has to be overcome. Due to the decisive role of cathode material in Na-ion batteries we will focus on a comprehensive interdisciplinary research involving chemistry, physics and solid state electrochemistry as well as DFT computer modelling of Na2M2(SO4)3 (M=Fe, Mn, Ni…) system. We intend to optimize chemical composition, synthesis method, structural and transport properties as well as morphology of nanometric Na2M2(SO4)3/carbon composite cathode material and control the electrochemical processes. The disclosure of relationships between crystal and electronic structure, valence states, transport properties and reactivity in relation to sodium will provide an invaluable tool for the design of high efficiency of the sodium intercalation process and consequently a high battery performance and reliability. The materials’ morphology is a crucial factor in designing high-performance electrochemical systems. A tailored 3D microstructure development of the cathode requires a quantitative determination of 3D parameters such as permeability, tortuosity (interconnectivity of pores) and fluid-dynamic behavior, which are major parameters for batteries that have to be optimized. A newly developed, unique transmission X-ray microscope for a wide range of photon energies (deepXscan DXS 1) combined with a chamber for electrochemical processes will allow non-destructive high-resolution imaging of kinetic processes (operando) to allow correlate battery performance with microstructure of composite cathode materials. Such an approach to develop new materials for Na-ion batteries, based on “electronic and microstructure engineering”, will allow a breakthrough in battery research.

• DFG Programme: Research Grants
• International Connection: Poland
• Cooperation Partner: Professorin Dr. Janina Molenda