Rechargeable batteries that are powering our everyday electronics go through their lifetime with countless charge/discharge cycles, after a few years the capacity has dropped noticeably. But how about batteries that are working as a back-up power system for when connection to the AC mains is not possible, they might only perform a handful of cycles but does this mean they last forever? On behalf of Getinge AB, this bachelor thesis aims to explore the subject named as ‘calendar aging’. Focus of the project has been mainly the impact of charging capacity, State of charge, on battery life for calendar aging and secondly the impact of heat on battery. Elevated environmental temperature during calendar aging test would imply acceleration in battery aging. The study is made with partly literature study and partly experimental testing on batteries during relatively limited time, though the results could be benchmarked with likely studies by others. The test was to investigate 12 units of NMC Li-ion batteries charged to 3 different levels of State of charge, 90 %, 95 % and 100 %, where 2 from each State of charge level were in a controlled heated environment and the other 2 were at room temperature. The test was in progress for 8 weeks and every two weeks measurement and data logging were collected and, if required, the batteries were recharged to origin voltage level. All data was documented in  and analyzed in Excel.  The results acquired were not significant enough to draw any conclusions but did show some tendency as would be expected from the literature studied during the time of the project. Future work is recommended to continue the test in this project to acquire more useful results. Further improvements in testing equipment should also be considered.

Cette thèse se concentre sur la fiabilité des batteries lithium pour des applications véhicules à faible émission en CO2. Pour cela, des méthodologies de caractérisation électriques et thermiques, des protocoles et des tests de vieillissement de batteries lithium sous différents modes (cyclage actif, calendaire simple et cyclage/calendaire) ont été mis en œuvre.Une première partie de ces travaux de thèse s’attache à la modélisation et à l’estimation des états de charge et de santé de la batterie.La deuxième partie est consacrée à l’étude du vieillissement calendaire des batteries lithium utilisant la spectroscopie d’impédance comme méthode de caractérisation. Ensuite, une méthode originale pour l’évaluation de l’état santé de la batterie est proposée. Elle est basée sur l’exploitation de l’étape de charge à tension constante lors d’une recharge complète et est donc bien adaptée à une intégration au sein d’un système de gestion de batterie. L’approche introduite est validée sur des données réelles de vieillissement allant jusqu’à deux ans de test.Enfin, une étude du phénomène de régénération de la capacité suite à un vieillissement des batteries de type combiné cyclage/calendaire est menée. Cette dernière partie constitue une ouverture pour le développement de stratégies d’usage des batteries lithium en incluant leur comportement thermique. / In this thesis, we focus on the reliability of lithium batteries used for automotive applications. For this purpose, electric and thermal characterization methodologies as well as aging tests under several modes (calendar, power cycling, calendar/power cycling) are carried out.In a first part of the work, battery modeling and battery state estimation (state-of-charge and state-of-health) are considered.Then, based on periodic characterization from electrochemical impedance spectroscopy, calendar aging is investigated. Next, we proposed an original process for precise battery state-of-health determination that exploits a full recharge and mainly constant-voltage charge step which allows easily its integration within a battery management system. Our experimental results, up to two years real-life data, confirm effectiveness of our technique.Finally, we study the capacity recovery phenomenon occurring due to combined battery aging (calendar/power cycling). This final part is almost dedicated to introduce strategies for battery use presenting at the same time a thermal behavior study.