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Degradation - Safety Analytics in Energy Storage
The lucrative characteristics of high energy and power density from lithium-ion batteries have also become drawbacks when they are not handled appropriately. The reactive and flammable materials present within the cell raise safety concerns which need to be addressed. Aging of the cell components occurs in a natural way due to continuous cycling. Constant intercalation/deintercalation of Li-ions into the active materials induces stresses that in the long-term cycling mechanically modify the electrodes in an irreversible way. Also, electrode/electrolyte side reactions diminish the Li-ion inventory reducing the cell capacity and lifetime. Along with cell aging, intentional/unintentional abuse tests can occur at the hands of the final user. Improper handling and operation may lead the Li-ion cell to failure and possibly going into thermal runaway. This condition represents a threat to safety not only for cell integrity but also for user safety. Failure event can occur not only in brand new cells but also in aged cells. Current degradation studies focus either on the long-term aging degradation mechanisms or on fresh new cells’ abuse test. And few of them focused on the combination of both of them.In this work, the degradation of Li-ion cells is investigated at different levels. First, at the electrode level, the effect of electrode processing and the intercalation properties of an anode and cathode materials is investigated. Then, at the cell level, abuse conditions such as external short, overcharge and overdischarge are studied in fresh and aged cells with different levels of degradation. Last but not least, the cells are assembled in a module configuration to investigate how a minor difference from one cell to another can affect the long-term performance. The aim is accomplished via a controlled lab test approach in order to get insights about the electrochemical, thermal and morphological changes that take place when the cell degrades.