“The concept here is that you start with an aluminium foil, and the way to think about this is when we charge and discharge the battery, the lithium ions are actually moving into the aluminium foil and then moving out of the aluminium foil, and you want that to be as reversible as possible”, Prof. Matthew McDowell, Georgia Institute of Technology

A research team led by Prof. Matthew McDowell at Georgia Institute of Technology has recently introduced an aluminium foil that could revolutionize solid-state lithium battery cells, potentially extending the range of electric vehicles and advancing battery technology. Collaborating with aluminium producer Novelis, the researchers are scaling up battery sizes to understand how the foil behaves and exploring cost-effective materials for integration.

Matthew McDowell is an Associate Professor and Woodruff Faculty Fellow at Georgia Tech with appointments in the Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering. He received his Ph.D. from Stanford University in 2013 and was a postdoc at Caltech from 2013 until 2015. McDowell’s research focuses on developing and characterizing battery materials and systems, including solid-state batteries, Li-ion batteries at low temperatures, and novel anode materials. McDowell has received numerous awards, including the Presidential Early Career Award for Scientists and Engineers (PECASE), Sloan Fellowship, NSF CAREER Award, and Georgia Tech’s Outstanding Achievement in Early Career Research award.

In an interview with AL Circle, Prof. Matthew McDowell delves deeper into the research's implications, the challenges, and the exciting trajectory that lies ahead.

AL Circle: Could you explain the rationale behind choosing aluminium as the key component of your research?

Prof. Mathew McDowell: Our recent work focuses on using aluminium foils with particular microstructures for lithium-based batteries, and the reason why we're doing this is that it has been known for a long time that aluminium can react with lithium and be used as an active battery material. I can store lithium inside the battery, but aluminium has never worked very well for that because when it does store lithium in a battery, the aluminium itself expands and contracts repeatedly during charge and discharge and its performance degrades. So, if we could make it work, it would be beneficial because it can store a lot of lithium as there's a high capacity, but it's been a challenge in the past.

AL Circle: Could you provide insights into the design considerations that led to this phase distribution and its role in the observed improvements?

Prof. Mathew McDowell: The concept here is that you start with an aluminium foil, and the way to think about this is when we charge and discharge the battery, the lithium ions are actually moving into the aluminium foil and then moving out of the aluminium foil, and you want that to be as reversible as possible. So it turns out that if you use just pure aluminium, it works okay, but what ends up happening is the lithium tends to get trapped in the aluminium, and it's difficult to extract the lithium when you want to. So what we decided to do based on some prior literature was to make a multi-phase alloy with another material, kind of a small amount of another material distributed throughout the aluminium in a different phase, and it helps a number of things, but especially it helps with improving the reversibility and the extraction of lithium so that we can get high efficiency in terms of the charge and discharge.

AL Circle: The paper mentions that the Al-In alloy-based electrodes exhibit less extensive solid-electrolyte interphase (SEI) growth compared to those in non-aqueous electrolyte solutions. Could you delve into the underlying reasons for this difference and how it contributes to prolonged stability?

Prof. Mathew McDowell: An important aspect of this that I haven't mentioned yet is that these electrodes that we're using, the aluminium that we're using is within solid-state batteries, and solid-state batteries are a relatively new technology that's under current development, and they could be safer than conventional lithium-ion batteries. The difference between a solid-state battery and a lithium-ion battery is that lithium-ion batteries have a flammable liquid electrolyte that conducts the ions throughout the cell. So you replace that liquid with a solid material for a solid-state battery, and so this all relates to the aluminium because it turns out that when you create a solid-state battery with an aluminium-based electric material, that aluminium ends up being much more stable as well because the interfaces are more stable and the liquid causes problems when you use aluminium and a lithium-ion battery. So everything works together very well. I would say it's a little complicated but we found that the results were quite promising.

AL Circle: Your research introduces the concept of microstructure engineering for the negative electrode. Could you elaborate on the specific challenges and strategies in designing and achieving the desired microstructure to enhance capacity and rate behaviour?

Prof. Mathew McDowell: Yes, it's quite interesting, actually. There's been a little work on this in the past in different battery systems, but what our work shows is that starting with a dense metallic foil material, controlling the microstructure can enable you to tailor the performance of the material, and this is interesting because it kind of opens up the door towards microstructural engineering and metallurgy for improving battery performance which is something that hasn't been a major focus of the battery field in the past. So we hope that the promising results we reported will inspire others to also work in these directions, and we're excited about our future work in this area.

AL Circle: The impact of stack pressure on electrochemical behaviour is explored in your research. Could you provide insights into how different stack pressures influence the performance of alloy-based negative electrodes and the implications for practical battery applications?

Prof. Mathew McDowell: That's a great question. It's a very important variable, the stack pressure. This is basically the amount of force you're applying to the battery cell and is particularly important in these solid-state batteries compared to conventional lithium-ion batteries. So, we found that higher stack pressures made it easier to achieve good performance in general, but there was some variability when you changed the stack pressure, and it went to lower values. We're exploring much lower values of stack pressure now because, for commercial applications, minimizing stack pressure is quite important.

AL Circle: The findings of your study suggest potential cost and energy savings. Could you discuss the feasibility and challenges of implementing such a design in large-scale battery manufacturing processes?

Prof. Mathew McDowell: Our material in this published paper is now 95% aluminium and 5% indium metal. Idium metal turns out to be a very expensive material, so we're not focused on indium metal for eventual commercialization. That's one challenge, though. In general, the process that we demonstrated is quite scalable to very large foil processing sizes. The company that we're working with on this is a large aluminium manufacturer, Novelis incorporated, and they commonly make foils at extremely large scales, especially compared to what we're used to in academic research. The whole intent of this work was to use processing methods that could be scaled to very large sizes from the very beginning. Although we haven't demonstrated that yet, ideally, that will be available going forward.

AL Circle: As your research focuses on aluminium-based electrodes, how applicable do you believe the observed performance improvements would be to other alloy systems, and are there specific considerations for exploring different alloy materials in solid-state batteries?

Prof. Mathew McDowell: I'm very excited about the possibility of various metal alloys as anodes and solid-state batteries for a few fundamental reasons, the main one being that the interfaces of these materials tend to be more stable over many charge-discharge cycles than they are in lithium-ion batteries, and so I think there's good promise going forward for alloy materials in solid-state batteries which is good because this could enable higher energy density battery systems. There's a lot of folks working on these materials out in the field, and I hope that there'll be some good progress in the next few years.

AL Circle: Looking ahead, your study identifies several areas for future exploration, including optimizing alloy composition, understanding material evolution, and investigating the effects of other elemental additions. Could you provide a glimpse into your thoughts on the next steps in advancing the field of solid-state batteries through your research findings?

Prof. McDowell: We're currently investigating different material combinations of different microstructured alloys, and we're also scaling our cells to larger sizes for testing purposes. So that's kind of our next step. I think, more broadly, there are efforts in the field to develop high alloy concentration electrodes that could enable solid-state batteries with high energy density, and so things are moving forward. Still, the process for commercialization of battery technology is always a long and arduous path actually, so it takes many years. It takes quite a lot of effort to go from a laboratory demonstration to a medium-scale cell to a full-scale cell all the way to high-volume manufacturing. It's important to note that there needs to be some patience in these efforts because it takes a while, but we're excited and moving forward as best we can.