Strategy to Increase Energy Density and Improve Stability of LiMPO4 (M=Co, Ni) Cathodes for All-Solid-State Li-Ion Batteries

• Applicant: Dr. Gennady Cherkashinin
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Synthesis and Properties of Functional Materials
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 447727465

The cathode material plays a key role in the energy density and life cycle of Lithium Ion Batteries (LIB). Its thermodynamic stability depends on the intrinsic voltage limit which is defined by the inherent oxidation limit of the anions within the relevant material. The extrinsic stability of the whole battery cell is additionally influenced by the redox potential of the electrolyte and by the chemical compatibility of the cathode/electrolyte interface. Power capability depends on the Li+ and/or electron transfer rates through the bulk cathode material and across the phase boundary cathode/electrolyte. Thus, to increase essentially the energy density and the power density, whilst maintaining a high battery stability, the following key issues have to be solved: a) chemical compatibility and thermodynamic stability of the battery cell operated at a high voltage charged state; b) high migration rate of Li+ ions through the phases and across the phase boundaries; c) high electronic conductivity in the electrode. The aim of our project is the preparation and investigation of novel 5V solid-state batteries. We focus on the LiMPO4 (M=Co, Ni) olivine-based material in which a high structural stability in the fully delithiated state is achieved via the material design with another polyphosphate phase of higher oxidation potential. The following scientific problems shall be addressed: a) what is the origin of unusually high electronic conductivity revealed for the designed cathode material? b) can the energy density of the battery be essentially increased via the involvement of the polyphosphate phase into the redox reaction? c) are the olivine-based materials chemically compatible with highly Li+ ion conductive solid electrolyte? d) is the cathode/electrolyte interface stable and Li+ ion conducting upon the charging/discharging of the battery cell? The film cathode materials and their interfaces will be prepared under UHV condition and their electronic and structural properties will be studied mostly by in situ and operando electron spectroscopy, HRTEM/STEM and XRD combined with the modelling of electronic and structural properties. With such a novel approach, we will address the intrinsic and extrinsic stability range of ion conductors and their interfaces by monitoring the evolution of the physicochemical properties during operation of the battery cell.

• DFG Programme: Research Grants
• International Connection: Italy
• Co-Investigator: Professor Dr. Lambert Alff
• Cooperation Partners: Dr. Matteo Cococcioni; Dr. Elena Magnano, Ph.D.