Repurposing of batteries from end-of-life electric vehicles in stationary storage systems

The recent attempts to reduce global carbon emissions have accelerated the development of electrified transportation systems. Electric vehicles, in this sense, support carbon-free initiatives when they are still on the roads, whereas their production and end-of-life phase need further investigations for environmental considerations. Batteries in electric vehicles are specifically the challenging components because of the material extraction for their production and the hazard they can potentially cause if not disposed of properly. However, circular life cycle thinking suggests exploiting the end-of-use battery stock with different strategies potentially by extending the battery lifetime via reusing or repurposing schemes. This thesis contains four peer-reviewed and published journal articles that address the projection of the upcoming volume of end-of-life battery units from disposed electric vehicles, estimating their state of health at the time of retirement in a hierarchical waste flow representation, the techno-economic evaluation of their second applications in the Irish electricity market, and evaluating the implication of cobalt-free electric vehicle batteries on the potential for lifetime extension through repurposing in electricity markets. Findings include:

• The growth of electric vehicles is mainly concerned with transportation regulations, technology advancement, and social acceptance. However, results show that government intervention is considerably more influential in their adoption than market availability. The expected volume of battery stockpile for different levels of regulations and market growth is estimated, showing that a substantial energy capacity within the retired batteries will be available. This signifies the likelihood of second-use market creation. Furthermore, the impact of the potential existence of second-use markets for electric vehicle batteries on their primary adoption has been examined and found to be directly proportional to the price gap between new and used batteries.

• A considerable repurposing potential has been found by categorizing the state of health of batteries coming to end-of-life. The hierarchical health representation of retired batteries is useful for refurbishment businesses to scale their investment based on the estimated secondary supply of batteries for high energy demanded applications for which the healthier batteries fit the best (above 85% or 90%), whereas the others (between 80 to 85%) can be used for less demanding applications such as back up storage. Similarly recycling operators will be able to scale appropriately while considering the export rate since repurposing does not always take place in the original market.

• The highest financial return is expected from retired batteries repurposed in reserve services in the Irish electricity market compared to energy trading applications. Although they are good candidates for less demanding applications in power systems, their huge upcoming flow to the end-of-life stream will exceed the demand for grid service applications; thus, the allocation of healthier ones is suggested for energy applications. The financial feasibility of their deployment in energy trading is shown to be sensitive to factors such as renewable penetration, battery price, and inflation, meaning that the future changes in energy structure and battery market should embrace the residual value within them.

• Comparing the financial feasibility of repurposing two different Lithium-ion battery types inspired by the market shift toward cobalt-free batteries, it has been found that Lithium Iron Phosphate batteries respond more frequently to price fluctuations in energy markets compared to Nickel Manganese Cobalt ones, resulting in improved financial returns. Although cobalt-based batteries have higher energy density and are easier to deploy in vehicles, the issue of cobalt in their supply chain and their lower cycle life comparatively, mitigate their advantage.