Conditioning of all solid state Lithium Ion Batteries with LiMPO4 (M=Co, Ni) thin film cathodes

• Applicant: Dr. Gennady Cherkashinin
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268156926

The cathode material plays a key role in the determination of energy density, safety 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 develop a stable high power and high density battery, the following key issues have to be solved: a) thermodynamic stability and chemical compatibility 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 and a blocking electrolyte interface. The specific role of these factors can hardly be clarified in classical battery structures due to the complexity of the set-up involving additives. The aim of our project is the preparation and investigation of novel high voltage solid state batteries. We focus on the olivine type structure material as LiMPO4 (M=Fe, Co, Ni) in which the voltage window is increased by substitution of Fe by Co (4.8 V) and Ni (> 5 V. The following scientific problems shall be addressed: a) Are LiCoPO4 and LiNiPO4 olivine-type cathode materials thermodynamically stable under delithiation and are they suitable for high voltage application up to a still unknown intrinsic voltage limit? b) Are LiCoPO4 and LiNiPO4 chemically compatible with typical electrolytes as fluoroethylene carbonate and is the olivine/electrolyte interface stable at voltage around 5 V? c) Are LiCoPO4 and LiNiPO4 chemically compatible with solid electrolytes (as e. g. LIPON)?The film cathode materials and their interfaces will be prepared under UHV condition and their electronic properties will be studied in situ mostly by using electron spectroscopy. With such a novel surface science approach applied at ion conductors we will address the intrinsic and extrinsic stability range of high voltage Olivines and investigate possible routes to avoid corrosive side reactions.

• DFG Programme: Research Grants
• Major Instrumentation: Laser
• Instrumentation Group: 5730 Spezielle Laser und -Stabilisierungsgeräte (Frequenz, Mode)
• Co-Investigator: Professor Dr. Wolfram Jaegermann