Design criteria for crystal structures of zero-strain cathode materials for lithium ion batteries

• Applicants: Dr. Joachim Rudolf Binder; Professor Dr. Christian Elsässer
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Synthesis and Properties of Functional Materials
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 424815519

Zero-Strain (ZS) electrode materials, in which the charging and discharging of crystal structures with lithium ions can take place without large volume changes, are very attractive for improving the service life of lithium ion batteries. While lithium titanate spinel, a ZS anode material, is already used in commercial battery cells despite its significantly lower energy density compared to graphite, the currently known ZS cathode materials are still exclusively of scientific interest. However, it is not yet possible to derive any obvious parallels in crystal structure from these compounds, from which ZS behaviour could be deduced and a targeted representation of novel ZS cathode materials would be possible. The present project proposal deals with this problem: Are there crystal structure-chemical design criteria for a targeted development of ZS cathode materials? What structural, chemical and mechanical properties make the occurrence of a ZS effect probable in a lithium ion-storing crystal system? The focus is on the mechanism of solid solution formation of the two known ZS materials K0.6FeF3 and LiCaFeF6. For both structure types, substitution of the cations can provide fundamental insights which structural changes favour the ZS effect and which are counterproductive. To this end, coordinated experimental material synthesis and characterisation at the IAM in Karlsruhe and theoretical material modelling and simulation at the FMF in Freiburg are planned, to elucidate stoichiometry structure ZS property relationships of potential ZS cathode materials. This project aims to identify and explain the essential prerequisites for the ZS behaviour of Li+ electrode materials in terms of their crystal structure chemistry, and ideally new ZS compounds can then be produced in a more targeted way on the basis of such design criteria.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Holger Geßwein