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Project VALUABLE, led by HSSMI, has been instrumental in shedding light on second life opportunities for Li-ion batteries. As the project closed at the end of March, we are now sharing our findings in order to generate discussion amongst the public and, in particular, those who are looking to continue the research that VALUABLE began. In this blog series, we will be discussing a different battery-related topic each time – from testing and legislation to end of life, reuse, recycling and remanufacturing. This time, we get into testing and metrology.
Roughly 70% of a battery cell’s value can be attributed to the cost of materials. This presents a major challenge for cell manufacturers, who want to be resource efficient, avoid the significant financial impact that faulty parts and rejects can have on their business models, as well as minimise production waste and associated costs.
A major challenge currently seen in industry is the impact of detecting failures further down the manufacturing line from where they originally occurred. During cell assembly, typically only mechanical and electrical performance tests are conducted, and any changes in electrochemical performance are only detected at end-of-line testing, i.e. in the expensive formation and ageing processes (FA&T).
Moreover, some failures are either non-visible with the naked eye or occur over time within the cell and currently can only be detected using destructive testing techniques prior to FA&T. There is a need for non-destructive, in-line testing methods that can measure parameters related to cell performance, as well as mechanical or secondary performance indicators, such as electrode alignment, density and homogeneity. The development of non-destructive inline testing machines and procedures will enable manufacturers to employ a no-faults-forward principle, thereby reducing costs invested in failed parts, limiting unnecessary waste and optimising the number of FA&T (formation, ageing and testing) channels.
Within VALUABLE, project partners National Physical Laboratory (NPL) and University College London (UCL) led the work exploring testing and metrology. Their collaboration looked at various testing methodologies, including X-ray testing, optical imaging, as well as dimensional and acoustic testing methods.
In combination with acoustics and electrochemistry, dimensional metrology capabilities can rapidly map the macroscopic changes to a battery as a function of its State of Health (a metric expressing the fraction of full charge capacity remaining relative to its initial value). Additional applications of dimensional techniques include the in-line characterisation of electrode coating homogeneity on a pilot line as a function of rolling speed. These methods and techniques have the potential to allow a battery triage approach for second life opportunities and scale up for adoption in manufacturing lines.
Commercialisation of the acoustic testing method has been investigated in the Automotive Transformation Fund project AcouBat, which includes UCL, HSSMI, AMTE Power, and JW Froehlich. [Hyperlink] The acoustic test method provides a cheap, non-invasive and highly sensitive way to assess mechanical internal characteristics of completed cells and infer electrochemical performance. It can be used for a range of battery chemistries to determine whether cell damage is occurring under test conditions and aid in predicting cell failures. The inline acoustic method can detect faulty cells or poor electrode coatings before the cells are formed, stopping errors at source and preventing their progress down the production line.
The AcouBat project will test the acoustic method in a real-life setting – on AMTE Power’s production line. Alongside the physical validation, HSSMI will create a digital simulation, which will help analyse different scenarios and establish where the acoustic method brings the most benefit along a high volume production line.