Advances in Li-Ion battery packs Technologies for Electrification of Transports

In the current global scenario, growing awareness of environmental health and the urgency to address climate change have prompted both policymakers and technologists to prioritize decarbonization and develop strategies to reduce pollutants and Green House Gas (GHG) emissions. Among others, the European Community, by signing the Green Deal [1], has made climate neutrality (the zero emissions condition) legally binding for all Member Countries within 2050 and has put an intermediate objective to reduce emissions by 55% within 2030. In this complex situation, part of the solution of this problem is already taking shape through the development and diffusion of electric vehicles. This mobility transformation is facing all the issues and all the technological challenges that concern the world of electrochemical energy storages, going from the single cells up to whole systems of battery packs. This is the context in which this Ph.D. study was born and developed. The main questions that gave life to this work are: What can be developed in order to realize fault tolerant battery packs, able to stop the diffusion of unexpected undesired thermal runaways? Are cells and battery packs actually charged and discharged at the very 100% of their potential capacity either integrators and final applications are technically accustomed to use too many margins? Is it really possible and widespread avoiding the decrease of the performance of a battery pack due to the worst cell among thousands that constitute it? Is it possible to isolate the worst cells in a battery pack and to let other cells working at their maximum performances? Is there any chance to regenerate single exhausted cells? Is there any chance to regenerate single exhausted/broken cells while they are inserted in working battery packs? Trying to find macro-categories where to gather the previous questions, it could be said that this study has developed around the concepts of • safety • cell capacity exploitation • regeneration that, again, are in line with the objective of the European Union to create a circular economy within 2050 [2]. afety, considering single electrochemical cells up to battery packs, is a matter of great interest and discussion at the moment, because the knowledge and procedures in front of the faults of these technologies still are inadequate: electric cars with batteries fire are just abandoned by users and firefighters can only wait for the fire to end or Airlines just banned some mobile phones on board [3], rather than finding something smarter. Similar behaviors are used in the cells manufacturing factories (these factories are divided in compartments that can be isolated in case of fire, but, also in this case,firemen just wait for the fire to end in the quarantined silo and just help that other silos do not get damaged). In addition to that, batteries safety improvement will contribute to give a future to electrification of airplanes as well [4]. In fact, there are already several projects in that direction made by Companies such as Heart Aerospace (Sweden), Zero Avia (UK), Textron eAviation (Slovenia, company that has already flown with Velis Electro, certified full electric airplane lithium-ion liquid cooled battery power supplied) and Vaeridion (Germany). The very proper EASA (European Airspace Safety Agency) has started investigating the feasibility of the use of this technology on larger scale of planes. The world of marine applications is also moving towards electrification [5] with an increasing demand of large scale batteries (GWh order of magnitude) with the double aim of having full electric ships and hybrid ships able to switch to full electric propulsion when getting close to harbors. This technical environment will also help the development of the electrification of docks, something that will truly cut the emissions of ships waiting for the departures inside the ports. Cell capacity exploitation was encountered in this study while trying to find strategies to use 100% of the storage capability of commercial cells. This experimental investigation had to be done in order to verify if the declared performances of cell manufacturer datasheet were true, which conditions had to be achieved in order to obtain them and, eventually, to find if the using constraints imposed by the cell manufacturer were too much. All this work had the aim to avoid the beginning of a chain of events due to which, if every integrator put its margins, then in the end only 80% of the battery capacity would have been available and used, with a deterioration of some battery Key Performance Index (KPI) like ‘unreasonable’ effective value of weight/energy ratio. Regeneration [6] took shape in this work while developing techniques and methods to regenerate aged or exhausted Li-Ion cells (bring back the cells to their ‘just manufactured’ conditions without disassembling). This activity had the objective of decreasing the need of changing complete battery packs, generating, as a consequence, less need of dismantling exhaust and dangerous materials and less dependence from cells suppliers. The aim of this study is providing a general overview of the recent technological developments that have characterized the global evolution of the electric storage systems in the last decades and a detailed experimental work on the safety, capacity exploitation and regeneration techiques about Li-ion cells and Li-Ion battery packs. This Ph.D. has come along also with the hope that this work will help, in its own small way, to make a step toward a future in which parked electric cars will be a storage for the peaks of Renewable Energy Sources (RES) availability and the answer to peaks of energy needs, by allowing the owners of the cars to buy or sell energy from the grid until a certain level of battery charge [7]. The importance of this work is also the attempt to create a cooperation line among the different technological areas of Electrical and Electrochemical Engineering in order to realize a common knowledge which will bring to better and more robust design and testing skills. Indeed, nowdays, it is not possible to develop a part of the powertrain of an electric vehicle without taking into consideration what is before and what is next its component: battery is linked to the battery charger and to the inverter, the inverter is linked to the battery and to the electric motor and everything must be designed for both flow direction of energy (for energy recovery while braking). The preset work is the outcome of the scientific research that I developed during the three years long Industrial Ph.D. program in collaboration with Phase Motion Control S.p.A. (PMC).