Speaker
Dr
Marie-Liesse Doublet
(Institut Charles GERHARDT)
Description
Li-Ion batteries have become indispensable in the field of portable electronics and hybrid electric vehicles. If their high energy density is a major asset, their life and reliability are still inadequate to respond favorably to industry specifications to which they are subject. Understanding the degradation modes of the different elements of a Li-Ion battery is now one of the major objectives of the scientific community involved in this field. To achieve this, one possible strategy is to identify the indicators of failure in order to prevent degradation of our batteries and, hopefully, propose alternatives to this degradation. For the most part, the aging/degradation phenomena of a battery arise from the electrochemical reactivity at interfaces and from side reactions occurring between the different elements of the battery (electrode/electrode, electrode/electrolyte). These reactions occur, for example, when the redox mechanisms at the origin of the device performance are modified by a change in texture or morphology of the electrode during the charge/discharge. An essential step in the understanding and treatment of these phenomena is to define, in a systematic way the mechanical, electronic, chemical, electrical and ionic factors that are most relevant to describe the device as a whole. In other words, we need to understand how thermodynamics and kinetics are related in these systems. Understanding these parameters is a challenge for computational chemists, in particular at the atomistic level using first-principles methods. This presupposes to calculate, independently and without prejudging their impact on battery performance, a set of elementary reactions occurring in the bulk, at the surfaces and at the interfaces of the electrode, and to inject the as-obtained ab initio parameters in a model of higher scale to determine which of these elementary processes is dominant in the degradation mechanism. With these calculations, it is then possible to translate, at a macroscopic level, all the basic mechanisms occurring at the atomic scale, in order to identify factors causing degradation phenomena of Li-Ion batteries. The methodology we developed to investigate this first-step study towards multi-scale modeling will be presented for a set of Li-based materials, the so-called conversion materials. Our aim is to show how nano-sized effects crucially affect both the thermodynamics and the kinetics of the reactions and more specifically the electrochemical response of the battery.
