Life and Safety for Li-ion batteries in Maritime conditions (SafeLiLife)

In the project "Life and Safety for Li-ion batteries in Maritime conditions" (SafeLiLife), we have focused building in-depth knowledge on expected battery lifetime, ageing mechanisms and safety at different operating conditions. There has been a specific focus on condititions relevant for the maritime sector, e.g. ships and sub-sea installations. Lithium-ion batteries have evolved from small compact cells to larger cells with higher energy densities in a few years, enabling use in new applications. Specifically in applications with intermittent energy use, or applications where energy can be recovered (e.g. braking energy), hybridization with rechargeable batteries can reduce fuel consumption and hence reduce emissions of both CO2 and NOx. DNV GL has earlier shown that electrification of ships can give a return of investment (RoI) shorter than 5 years. For special niche applications; e.g. cranes, the RoI can be as low as 2 years. Within consumer electronics, the energy density of Li-ion batteries (weight and volume) is essential. In the transition to electric vehicles, safety and lifetime is as important as energy density. When using Li-ion batteries in boats, the battery systems are very large (MWh) and the safety demands extremely strict. The operating conditions can also be very demanding, handling very low temperatures in arctic conditions (-20 °C) or the high temperatures of an engine room (+50°C). In the SafeLiLife-project, we measured the cycle life of four different commercial Li-ion battery cells relevant for use in the maritime sector. We focused especially on battery life at different temperatures, different current rates and different state-of-charge for the battery cells. In general, temperature was the factor that affected cycle life most. Both high (45 °C) and low (5°C) temperatures reduced cycle life compared to 25 °C. We also observed a negative effect in increased current rate. The reasons for the reduced battery life differ at the different conditions, and this was studied by non-destructive methods. Entropy spectroscopy was tested as a new non-destructive method. This method can be used to both separate the different Li-ion battery chemistries and also give indications of the ageing mechanisms in the cell. The results were compared to changes in the batteries studied by post-mortem methods at end-of-life. The internal temperature of the Li-ion cell will normally increase while ageing at the same current rate. This can contribute to a faster reduction in battery life. This increase is caused by an increase in the internal resistance which normally occurs during ageing. In addition we studied how the thermal conductivity of the battery materials changed during ageing, and observed if this contributed to an additional increase in the internal temperature. It is well-known that Li-ion batteries have challenges with safety issues. The Li-ion cells cannot handle neither overcharge nor overdischarge. At temperatures above 60 °C, the batteries can initiate a self-heating mechanism which eventually can result in both gassing of electrolyte and fire/explosion. When charging at low temperatures, metallic lithium can be formed at one of the electrodes. This can eventually cause an internal short-circuit of the battery, which could again could cause a fire in the cell. In the SafeLiLife-project we tested the safety of all the different commercial cells and compared the safety properties for new and aged cells. For the aged cells we observed that the "thermal on-set temperature" could be reduced. This can contribute to more unstable safety aspects. This was especially distinct for cells cycled at low temperatures.

This project is a knowledge building project for life and safety for Li-ion batteries in maritime conditions. The main objective in this project is to build in-depth knowledge on how various Li-ion batteries chemistries decay both by storage and cycling. The decay (ageing) can have severe implications on the safety of the Li-ion battery and hence have large implications of a safe and durable operation of a marine operation as well. By building knowledge on how the Li-ion batteries are ageing, measures can be taken to optimize the batteries operational conditions to optimize life and hence also maximize the economic benefit of the battery system. By developing more sensitive measurements, relevant tests can be performed in much shorter time, speeding up development processes. The following topics will be covered to reach the main objective: -Apply innovative and advanced battery characterisation methods to enable prediction of Li-ion battery life and health for large-scale batteries applied in Nordic c onditions -Validate methods and tools for accelerated cycle life and reliability prediction -Perform accelerated battery cycle life predictions for several Li-ion battery chemistries at various temperatures. Especially with focus on Nordic sea-temperatur e conditions and operation in confined locations with poor ventilation -Validated methods for State of Health (SoH) predication based on the method of Entropy spectroscopy -Perform in-situ and ex-situ thermal characterisation (calorimetry and thermal cond uctivity measurements) on Li-ion batteries and battery materials -Build thermal Li-ion battery models for various load profiles -Monitor battery break-down characteristic -Simulate local short-circuit conditions -Analyse ageing mechanisms and physical pro perties through post-mortem analyses on aged Li-ion battery cells -Develop state of charge algorithms