A new approach for End of Life Estimations in Electric Vehicle Batteries: Maximizing Battery Usage

Maite Etxandi

Corchero García, Cristina Canals Casals, Lluc

Energy Systems Analytics group (IREC)

The commitment to Electric Vehicles (EVs) requires careful management of their resource-intensive batteries to ensure that the transition does not have a high environmental impact. Technological advances and cost reductions have led to an increase in battery capacity and a substantial residual value expected from retired batteries, thus highlighting the importance of circular economy practices such as sharing and reuse. Decision-making throughout the battery life cycle requires an accurate estimate of the end of their useful life (EoL). Current methods use a universal criterion of 70–80% State of Health (SoH) to define EoL, but this criterion ignores the individual needs of each driver and the specific capacity of their vehicle's battery. The first part of the thesis assesses the validity of the universal EoL criterion. First, the performance of electric vehicles during driving is assessed to identify new criteria that determine functional EoL based on specific driving needs. Subsequently, EoL thresholds are determined for several realistic use cases using driving profiles derived from a proposed synthetic driving cycle model. The results indicate that performance limitations are influenced by factors such as battery capacity, charging frequency and driving times, highlighting the shortcomings of current EoL estimates. Considering these limitations, the second part of the thesis presents a new approach for EoL estimation using State of Function (SoF). This approach takes into account historical driving requirements to define customized EoL thresholds, and a data-driven algorithm to predict SoH under realistic use conditions, such as partial loads. Both aspects, EoL requirements and degradation, are integrated into the proposed definition of SoF, measuring the extent to which the battery is close to showing poor performance. The results of the thesis propose replacing the 70–80% SoH criterion with SoF to improve EoL estimates. This change not only represents a significant advance in the accuracy of battery life estimation, but also introduces a perspective more adapted to the reality of use of each driver, making decisions on maintenance, replacement or reuse of batteries more informed and efficient. Through this new methodology, it will be possible to better exploit the potential of batteries during their active life and respond to a critical need of the electric vehicle industry, which is the sustainable management of batteries throughout their entire life cycle. Furthermore, understanding functional EoL from a personalized perspective opens the door to new opportunities, such as the use of Vehicle to Grid (V2G) or the reuse of batteries in second-life applications. These alternatives not only maximize the use of batteries, but also reduce residual value, minimize environmental costs and contribute to the transition to a more sustainable mobility model.

IREC is actively exploring the exploitation of the technology with European project partners and specific industry partners in various areas. In each of the following points, connections will be made to the collaborations and links that have been developed throughout the thesis with different companies in the sector. These industrial relationships have helped to identify market needs and implementation opportunities, thus facilitating the transfer of knowledge acquired in research to real and marketable applications. • Integration in the automotive market (OEM): this technology could be implemented by electric vehicle manufacturers, offering them a competitive advantage by providing a unique functionality that increases user confidence and satisfaction. In this context, IREC has carried out a collaborative project with SEAT, where the useful life of the batteries was estimated under different operating conditions, including various driving and climate scenarios. This project was particularly relevant for studying battery warranties, allowing the identification of factors that can affect their performance and durability. The integration of the SoF would represent an important step in this collaboration, as manufacturers could offer drivers a clearer view of the operational status of the batteries, helping to better manage expectations regarding their useful life. In addition, this information would complement the previous studies carried out in the project with SEAT, improving the accuracy in estimating the durability of the batteries and reinforcing the warranties offered to customers. Thus, the SoF would contribute to consumer confidence and help manufacturers adjust their marketing and after-sales service strategies to improve the customer experience. Proposal for application of the results obtained Maite Etxandi Santolaya 5 • Collaboration with demand and charging managers: the evaluation of V2G through the SoF offers opportunities for collaboration with companies in the energy sector, creating new business models based on demand response and network stabilization services provided by electric vehicle users. IREC has established several collaborations with companies working in demand management, such as Bamboo Energy, a spin-off of IREC dedicated to offering demand management and aggregation services. This company can integrate the SoF to improve its estimates of the response capacity of electric vehicles in situations of high demand. In addition, IREC has worked with a variety of charger suppliers, including Wallbox, Enel X Way, EATON, among others, some of which have chargers that allow smart and bidirectional charging. A clear path to exploitation would be to use SoF in estimates to manage charging optimally and to manage demand and facilitate V2G, based on the data collected by the charger. In this regard, the communication protocols used will play a key role in ensuring that the information needed to estimate SoF is effectively transferred between the vehicle and the charging infrastructure. • Development of advisory services for second-hand electric vehicles: detailed information on the state of the batteries is essential for the second-hand electric vehicle business. In this context, IREC is starting an industrial project with BatteryCycle, which seeks to improve the knowledge about the state of the batteries for second-hand electric vehicle sellers. The first step of this project will focus on improving the SoH estimate that can be obtained. Once this objective is achieved, the next step would be the estimation of SoF, which will provide a clearer view on the capacity of the batteries to meet the needs of future owners. • Applications in other sectors: In the long term, SoF could be adapted for different types of batteries used in energy storage systems. In this regard, IREC is working on a project with Cellect, a company that provides management services for battery systems intended to provide services to the electricity grid. The initial objective of the project focuses on improving the estimation of SoH, which is essential to ensure optimal battery performance. However, Cellect has future plans to provide more detailed services, such as predictive maintenance, which requires a deeper understanding of SoF. Incorporating SoF in these systems could be key to improving battery management as they approach the end of their life.

Electric Vehicles (EVs); Resource-intensive Batteries; Environmental Impact; Circular Economy; Battery Sharing; Battery Reuse; Battery Life Cycle; End of Useful Life (EoL); State of Health (SoH); Universal EoL Criterion; Driving Performance; Functional EoL; Driving Needs; EoL Thresholds; Realistic Use Cases; Synthetic Driving Cycle Model; Performance Limitations; Battery Capacity; Charging Frequency; Driving Times; State of Function (SoF); Historical Driving Requirements; Customized EoL Thresholds; Data-driven Algorithm; SoH Prediction; Partial Loads; Degradation; Poor Performance; Maintenance Decisions; Replacement Decisions; Battery Reuse Decisions; Sustainable Battery Management; Vehicle to Grid (V2G); Second-Life Applications; Residual Value Reduction; Environmental Cost Minimization; Sustainable Mobility.