7.0 Testing

Most recycling centres use data stored within a battery’s BMS to understand information about the status of the battery. Different battery producers typically use different systems. Thus, discharging and dismantling often needs to be adapted to the different battery types. Additionally, there are several tests that need to be carried out on EOL batteries to determine their state-of-health (SOH) and remaining useful life (RUL), including physical, electrochemical and spectroscopic tests. To avoid high costs and potential safety hazards, tests should ideally be carried out without the need to disassemble to battery cell. However, disassembly is unavoidable in most cases as cells that fail the required performance and safety standards must be replaced. There are several risks associated with battery testing and dismantling, including thermal runaway (which could lead to fire), gas leaks and exposure to heavy metals.

Generally, the first stage of assessment is visual inspection to check for deformities and/or leakage from the battery. If there are any signs of damage on the initial inspection, the battery will be sent for recycling rather than re-use. Although visual inspection is a relatively easy process and can be done quickly, it is labour-intensive, requires highly trained personnel and is susceptible to human error.

This is part of the reason why advanced technology is being developed to automate certain steps in the process of determining the next steps for the EOL EV battery.

Hantanasirisakul, K. & Sawangphruk, M. (2023). Sustainable Reuse and Recycling of Spent Li-Ion batteries from Electric Vehicles: Chemical, Environmental and Economical Perspectives. Global Challenges, 7. Retrieved from: https://onlinelibrary.wiley.com/doi/full/10.1002/gch2.202200212

Evaluating the condition of individual modules and cells within a battery pack is difficult, and existing technologies face trade-offs between the high costs of detailed battery scanning and potential uncertainty presented by cheaper processes. The fact that existing technologies can also be slow at obtaining results is another factor that leads to compromise.

Titan Advanced Energy Solutions (2023). Titan Advanced Energy Solutions Wins the U.S. Department of Energy’s Lithium-Ion Battery Recycling Prize. Retrieved from: https://www.linkedin.com/pulse/titan-advanced-energy-solutions-wins-us-department-energys-lithium-ion-/

Semi-automation of the process is currently being researched, for example, by the battery recycling company Hydrovolt. In June 2023, the company were awarded funding to develop a discharge and dismantling technology for batteries. Currently, parts of the process are done manually, but with the development of this technology the aim is to automate and manage the electrical energy discharged from the batteries.

Mercon Capital Group (2023). Battery Recycling Company Hydrovolt Secures $1.43 Million from Enova. Retrieved from: https://mercomcapital.com/battery-recycling-company-hydrovolt-secures-enova/

In some instances, the reclaimed energy from discharging is used to power the technologies required to then process the batteries. This is typically small amounts of excess energy and is only reportedly used internally (i.e., there is no energy to be reintroduced into the grid).

Automating the inspection of EOL EV batteries requires a high level of robot cognition as well as a fully standardised inspection procedure. Progress on image-based, object-detection algorithms and robotic intelligence could see robotic testing and disassembly become the norm at re-use and recycling centres. However, this process is likely still a long way off due to the large number of variables and uncertainties.

Zhu J. et al. (2021). End-of-life or second-life options for retired electric vehicles batteries. Cell Reports Physical Science, 2. Retrieved from: https://www.sciencedirect.com/science/article/pii/S2666386421002484

The economy of scale is also important to consider here, as it could be costly to screen a series of batteries without changing the software and, to some extent, the hardware too often, compared with the risks (fire/explosion) associated with storing large volumes of batteries.

As this is an emerging technology, there are several studies being carried out to further the research in this area. One such example is the “gateway testing and dismantling” workstream being carried out by researchers at the Faraday institute as part of the ReLib project.

The aim of the ReLiB Faraday Institution project is to understand the conditions required to ensure the sustainable management of lithium-ion batteries when they reach the end of their useful life in electric vehicles.

Research is being carried out into modelling the process that would be required for a recycling facility to receive, assess and process EOL EV batteries for re-use or recycling at an industrial scale, safely and efficiently. Researchers are specifically looking at automating the process of testing, disassembling and sorting batteries using advanced robotics and machine learning techniques to compile a dataset of the components that make up a battery from different car manufacturers.

Imaging and machine visions Europe (2023) Recycling EV batteries: a pressing automation problem. Retrieved from: https://www.imveurope.com/feature/recycling-ev-batteries-pressing-automation-problem

They are working to develop accurate and fast assessment methods to understand the condition of the battery and thus either recommend it for re-use or warn the downstream materials processes that it may be dangerous.

ReLib (2023) Co-Investigators; Dr Simon Lambert – Work Stream 1 Lead. Retrieved from: https://relib1.relib.org.uk/team/dr-simon-lambert/

To determine the SOH of an EV battery, analysis of the current-voltage relationship and capacity fade is carried out. There are several different types of non-destructive inspection processes, including X-ray and acoustic testing, which are detailed further in this section. Non-destructive measurements with three-dimensional (3D) and four-dimensional (4D) X-rays allow the battery to be inspected without the need to dissemble any parts. Atomic magnetometers can measure the magnetic field within the battery cell and identify any flaws as well as determine the exact state-of-charge. The measurements create maps of the magnetic susceptibility of the cell that, when combined with increasing research and measurements of the cells’ charge, can determine the SOH of the battery. This technique could lead to diagnostic systems to access cells in research, quality control, during operation or during EOL assessment.

Schoenberger, R. (2020). Nondestructive testing technique for lithium-ion batteries. Available at https://www.evdesignandmanufacturing.com/article/nondestructive-testing-technique-for-lithium-ion-batteries/

This type of technology is still in the research phase but, if it can be scaled, it could be a more cost-efficient and safer method of inspecting EOL EV batteries in comparison to manual inspections.

Non-destructive acoustic testing is a well-established technology that is used to monitor corrosion and cracking in concrete and steel structures. This type of testing involves listening for flaws in metals and welds and has recently been applied to study the electrochemical processes occurring in batteries. This type of inspection process has the potential to create a low-cost and scalable stream of data to supplement current/voltage data. A piezoelectric sensor is used to measure small releases of energy, which are part of the acoustic emissions (AEs) from the battery. The measurements taken are then categorised in terms of properties such as amplitude, duration, rise time and frequency, and can be correlated with current/voltage data. This information can then be used to compare the acoustic patterns of different active materials, electrolytes and cell designs and can even be used to detect degradation mechanisms.

Zhu J. et al. (2021). End-of-life or second-life options for retired electric vehicles batteries. Cell Reports Physical Science, 2. Retrieved from: https://www.sciencedirect.com/science/article/pii/S2666386421002484