Safety and modelling of aged Li-ion Batteries

The electrification and hybridization of ships with Li-ion batteries has gained momentum becoming an important new business area for several industries in Norway. The largest battery system for a ship currently built stores several MWh of electric energy. The consequences of a fire in such a system can be catastrophic. The degradation and ageing of Li-ion batteries will in many cases contribute to reduced thermal stability. This can potentially affect the safety performance of the batteries. This project relates to building in-depth knowledge for safety aspects of new and aged Li-ion batteries. The batteries are intended for use in maritime applications with a strong requirement for long cycle and calendar life. The knowledge of safety aspects on aged Li-ion cells is scarce. This project increases the understanding of the safety of large Li-ion battery cells aged at both freezing conditions and high temperatures. Advanced ageing tests of large Li-ion cells were performed, and complex battery data was collected at several specific ageing conditions. These conditions encompass various temperatures, currents, voltage ranges and state-of-charge. These data were used to diagnose the ageing characteristics through advanced diagnostic techniques. Based on the ageing data an empirical lifetime model has been developed, and a physics-based mathematical models was parameterized to increase the knowledge of the battery, battery lifetime and the temperature development within the batteries. The fire properties of both the same large Li-ion cells were investigated. Safety tests of the aged Li-ion showed that the safety of cells cycled at lower temperatures (5 °C) and high currents can be more unstable than cells aged and cycled at higher temperatures. Measurements of fire energy have been performed of Li-ion cells at various states-of-charge and state-of-health.

En rekke av resultatene fra dette prosjektet kan beskrives å være nye funn som har gitt ny kunnskap. Det er spesielt viktig å forstå når en Li-ion celle blir termisk ustabil, og det å kunne påvise dette vil være meget viktig. Resultatene kan også bidra til å velge om man kan gjenbruke Li-ion celler i en ny applikasjon eller om man bør resirkulere cellene i stedet. Hvis funnet om tidlig påvisning av en sikkerhetskritisk testbetingelse viser seg å være reproduserbar, så kan dette ha stor betydning for videre diagnostikk av Li-ion celler. Denne nye kunnskapen kan industripartnerne muligens implementere i sine batteristyringssystemer for å forbedre diagnostikken i disse. Det vil til slutt også være nyttig for resten av forskningsfeltet og samfunnet å få forbedret kunnskap om sikkerheten av store Li-ion celler. Det er også utviklet nye metoder for å analysere batteridata som øker kvaliteten av analysene betydelig. Dette har også gjort det mulig å analysere data fra tidligere prosjekter på nytt og gitt ny innsikt fra gamle data målt i tidligere avsluttede prosjekter. I framtidige prosjekter vil metodene utvikles kontinuerlig videre for å oppnå enda høyere kvalitet på data-analysene fra batteritesting.

The electrification and hybridization of ships with Li-ion batteries has gained momentum becoming an important new business area for several industries in Norway. There is a large potential of reduction in energy consumption and emissions of CO2, NOx and particulate matters through electrification. The largest battery system for a ship currently built stores several MWh of electric energy. The consequences of a fire in such a system can be catastrophic. The degradation and ageing of Li-ion batteries will in many cases contribute to reduced thermal stability. This can potentially affect the safety performance of the batteries. This project relates to building in-depth knowledge for safety aspects of new and aged Li-ion batteries. The batteries are intended for use in maritime applications with a strong requirement for long cycle and calendar life. The knowledge of safety aspects on aged Li-ion cells is scarce. This project will increase the understanding of the safety of large Li-ion battery cells aged at both freezing conditions and high temperatures. The fire properties of both cells and modules will be also investigated. Based on collected battery data, mathematical models will be developed to understand battery life and battery temperature.