Lithium-ion batteries became the main energy storage device for portable applications thanks to their high capacity per unit volume and weight. However they still suffer from a high capacity loss for long service application, such as automotive. As an electrochemical device, this technology is based on ionic exchange between two hosts, a cathode, usually a metal oxide, and an anode, usually graphite. The insertion of lithium ions into their hosts imply also internal stress, volume expansion and phase transformation. Loss of capacity can be originated from loss of active materials due to cracks or loss of electrical or ionic contact. These phenomena are still not well known, notably at the micro-scale, to understand failure. The project 4a is be focussed on getting the fundamental mechanical properties of active materials. Project 4b is focussed on measuring the coupling of mechanical expansion of the crystals due to ion motion by means of Electrochemical Strain microscopy (ESM), an Atomic-Force Microscopy (AFM) based technique.
Work Package 4a: Nanomechanics of Li-ion battery materials.ESR10-Hugues-Yanis Amanieu. Host institution: Robert Bosch GmbH, Gerlingen, Germany. Secondments: University of Aveiro, Aveiro, Portugal.
Our project investigates the mechanical properties at the (sub)-microscale of active particles of lithium-ion batteries used in current technology (See 1 in figure). Its primary aim is to comprehend the mechanical stresses induced by lithiation/delithiation of the particles and the number of cycles in general.
Instrumented indentation technique (IIT) is our main instrument (See 2 in figure). By fine analysis of our indentations and our samples (see 3 in figure), we want to establish by statistical method elastic-modulii, resistances to plastic deformation (see 4 in figure). We also want to develop novel techniques in order to study such complex and heterogeneous materials. Measuring the fracture toughness at the sub-micron scale is also on our agenda. AFM-based techniques, such as contact-resonance (CR-AFM), will also play an important role in the mechanical measurements.
Results from our work and the work of the 4B-team, put together, will permit to make a correlation between mechanical properties and electrochemical activity.
The project will apply and improve the ESM-technique (see Figure) on commercial intercalation materials, comprising anodes and cathodes, as well as solid electrolytes of Li-Ion Batteries for automotive applications. The ESM-technique will be used and implemented in the EU for the first time. It should be extended from the state-of-the-art qualitative Li-diffusion maps to a quantitative measurement quality. A theoretical model will be developed to describe the Li-diffusion in the different space directions quantitatively leading to a better understanding of the capacity decrease caused by degradation of the active particles as a function of cell lifetime. This work will deliver an experimental method and a supporting theoretical model to answer present questions about nanoelectromechanical (degradation) processes in Li battery materials.
Work Package 4c: SPM technology advancement (Experienced Researcher)ER1
This project is intended to help ESRs (especially in Li-batteries and biomaterials areas) with instrumental and theoretical aspects of SPM methods used. It will greatly accelerate their work as various efforts will be put on the development of PFM and ESM methods (for example low- and high temperature image acquisition) which are indispensable to fast progress of the ESRs. It is the challenging problem of modifying the measurement technique of scanning probe microscopy to newly developing challenges posed by the ever improving material developments. The ER will closely collaborate with the industrial partners, particularly the SPM developers (NANOTEC) and with the industrial partner Bosch on another side to bridge the gap between instrumentation and nanoscale properties of emerging functional materials studied by the Consortium.