Second Life Batteries: the reuse of lithium batteries from electric vehicles and the role of bidirectional power supplies
The life cycle of lithium batteries used in electric vehicles (EVs) is a central topic in the debate on environmental sustainability and the energy transition. As electric vehicles replace internal combustion ones, the question of what to do with batteries at end of life takes on strategic importance, not only for the Automotive industry but also for the Energy sector.
Once their primary cycle is exhausted, in fact, these batteries retain a residual capacity of 75-80%, offering the opportunity to be reused in less energy-intensive stationary applications.
The reintegration of these batteries, known as SLB – Second Life Batteries, however poses specific technical challenges.
Giovanni Andreazza, CONSYSTEM specialist, helps us explore the topic in more depth.
How to Optimize the Second Life of EV Batteries?
By 2030, the number of EVs on the road is expected to grow from 30 million in 2022 to 240 million. As a result, the number of lithium batteries reaching the end of their first life cycle will increase. Even though they have lost 20-30% of their initial capacity, these batteries still have significant energy storage potential and can find a second life in applications such as energy storage systems (ESS) and smart grid solutions.
SLBs therefore represent a valuable resource for stabilizing the grid and integrating renewable energy sources, also helping to build a circular economy.
Technical issues related to battery use and management
Second life batteries (SLBs) require specific assessment and reconditioning strategies. It is essential to classify batteries based on their State of Health (SoH), recondition them considering end-use requirements, and develop an accurate battery management system (BMS) to manage them at their best depending on the application. The main degradation mechanisms, such as SEI growth, lithiation and particle fracture, affect SLBs differently compared to new cells, presenting unique challenges in their assessment and in maintaining their efficiency over time.
More specifically, the use of Second Life Batteries presents some technical challenges that must be addressed to ensure their effectiveness and safety over time:
- State of Health (SoH) assessment: accurately determining the SoH of SLBs is crucial to predict their residual capacity and lifespan. This assessment is complicated by the variation in the initial usage conditions of the batteries, which may have undergone different charge and discharge cycles, temperatures and stresses.
- Safety and stability: SLBs may present increased risks of thermal and mechanical instability due to the degradation suffered during their first use. It is essential to ensure that battery management systems (BMS) are capable of detecting and mitigating such risks.
- Integration with existing infrastructure: integrating SLBs into energy storage systems or other applications requires compatibility with existing infrastructure and control systems, which are often designed for new batteries with different performance characteristics.
- Grid balancing: among the main needs, second life batteries often have to cope with peaks in energy demand or overloads that lead to instability and imbalances in the electrical grid.
Proposed solutions: Infypower’s bidirectional power supply modules
Distributed by CONSYSTEM, Infypower offers bidirectional converters that represent an innovative solution for the effective use of SLBs.
The BEG1K075G (22 KW) and LBG1K020G (35 KW liquid cooled) converters were specifically developed for applications that include the possibility of feeding energy back into the grid, integration into micro-grids, and EV charging systems with V2G/VPF functions, also using SLBs. Using high-frequency MOSFET/SiC technology, the modules guarantee excellent performance, high power density, great expandability and reliability.
Thanks to their liquid- or air-cooled design, they also offer high protection and silent operation, making them particularly well suited for use in grids and microgrids where second life batteries are employed. They also serve an important function as grid stabilizers.
Another interesting application also involves their use for simulations (for example, charge and discharge cycles) needed to test and verify how the battery reacts and must be controlled during a second life.
“Our converters – explains Giovanni Andreazza of Consystem – have a very important function. In an interconnected system, they allow the grid to be “rescued” whenever the grid is under too much stress. Bidirectional power supplies combined with SLB batteries can help regulate frequency and voltage through active and reactive power control. They help balance grid demand with a concept similar to V2G (vehicle to grid), acting through the temporary storage of energy“.
Technical Features:
- Bidirectional Functionality: the converters support power flows in both directions between the AC grid and the DC buses, essential for energy storage and V2G applications.
- Flexibility of use: designed to work with a wide range of voltages on both the source and load side, the power supplies are suitable for different battery configurations and grid standards and can be easily integrated into battery packs with different characteristics and states of health
- High efficiency: with a maximum efficiency of up to 97%, the converters minimize energy losses during the conversion process. In addition, the liquid- or air-cooled design ensures high protection and long-term reliability, reducing the risk of overheating and improving battery life.
- Reliability: the modules offer features such as smooth transition when the direction of power flow changes, essential for applications requiring high reliability and rapid response to changes in load or grid conditions.
- Enhanced safety: the ESTOP function, which can lower the output voltage to less than 60V within 300ms, and the internal insulation of the high-frequency transformer increase the safety of the operator and the installation.
- Off-grid support: the system is capable of operating in isolated mode, making it ideal for micro-grids and remote applications.
- Grid support solution: the converters act to balance and improve the quality of energy on the grid.
Designed for bidirectional applications in EV chargers with V2G/VPF function, use of retired batteries and micro-grids, these modules set new standards of safety, efficiency and reliability in battery reuse.
Article published in the magazine Fare Elettronica in April 2024