Recently, glass batteries have smashed the news! Rechargeable batteries generally use a physical separator with liquid electrolyte, which makes the battery liable to develop dendrites, small sword-like structures made out of Lithium metal depositions which over time can pierce the separator and short-circuit the system. Solid electrolytes get around this problem and the basics are covered in this video.
All Draw Curiosity videos are fully subtitled in English and Spanish. The blog post builds on the concepts touched upon in the video.
I was very privileged to have a long interview with Helena Braga, the senior researcher involved in the project. I asked her plenty of questions about the technology behind these batteries, as well as what inspired her to pursue her career as a pioneer in battery science.
Inés Dawson: So, what are glass batteries?
Helena Braga: Before explaining what they are, we should start with how a battery works. A battery is composed of two electrodes, a positive and a negative, and as they discharge electrons flow from the negative to the positive. Ions go through the electrolyte that separates the two electrodes. It’s a bit like a sandwich!
The electrolyte forms the pathway for the ions. With liquid electrolyte you require a separator to prevent short circuits from happening, but with a glass you don’t need one because the solid itself separates it. The glass also enables the deposition of lithium to be homogeneous, whereas liquid electrolyte creates a nucleus, so the lithium nucleates in three dimensions, and lithium also grows forming swords which can penetrate the separator and produce a short circuit, and this is probably what you’ve heard about in devices such as cell phones and laptops and so on which have exploded. If you have a homogeneous growth of lithium, no dendrites are going to be formed, and so there will be no short circuits inside the cell. Glass has a wide electrochemical window, which means that it will work with all pairs of electrodes without oxidising, and will not promote internal reaction inside the cell that can lead to an explosion.
I.D.: When people hear ‘glass’, we think of something quite fragile. Are these cells susceptible to breaking if dropped? Could they pose a security threat in other ways?
H.B: The term glass may be confusing, because we are not referring to the glass of a window. It’s actually a powder that’s somewhere between a solid and a viscous liquid. This glass is applied to a matrix, very thin paper. In our case we use recyclable paper, forming a very flexible glass fibre which won’t shatter if dropped.
I.D.: How many people did it take to develop a glass battery?
H.B.: We’re not as large a team as you’d expect! In Portugal there were only two of us who began to work on the electrolyte. The other person was Verena Stockhausen, but at the time there wasn’t enough funding, so she had to leave for another project before the first paper was published. Jorge Amaral has always worked with me, and he’s still working in Portugal, and recently we had a new colleague, Joanna, and a PhD student. So that makes three of us in Portugal, and two working with Goodenough. He was a very important contribution, but he wasn’t in the lab as you may imagine. I love the lab though, I’m always following the experiments!
I.D.: When will we see these batteries in circulation?
H.B.: That doesn’t depend on us. We do the research, and we can create small cells with 9mg of lithium – these are very small coin cells, and are not the dimension of a cell for a car or a computer, those are developments that will depend on the industry. What we can say though, is that we think it is simple to scale it up, the metals aren’t hard to implement into the existing set ups.
I.D.: As someone who studies insect flight, and how this technology may influence future micro- and nano-air vehicles which will require very small cells, do you think it will be possible to make these batteries even smaller?
H.B.: What we make is quite small, but for something insect sized you’ll need something even smaller. Perhaps vapour deposition, or using very thin films of electrode and electrolyte layers for smaller batteries, but it shouldn’t be hard to implement. I love your area, and the way insects see fascinates me!
I.D.: Thank you very much! Scaling seems to depend very much on industry, how much does the process differ from that used in current batteries? I noticed you developed the glass batteries in a glovebox, would that make the set-up harder?
H.B.: There are actually already industries of coin cells which already use Lithium metal, Duracell and Energizer are two of them, so it’s possible to make. They don’t use a glovebox, as they have a means of extracting the first layer of oxide that forms, and they have dry rooms. Because lithium is much more sensitive to moisture as well as oxygen, it is more important to avoid moisture, and in this case a dry room is necessary. Here we use a glovebox, but the most important thing is to have a dry room. There are other ways of preparing the lithium, such as at very low temperatures, because it won’t oxidise as it might at room temperature.
I.D.: The articles in the news also claim that these glass batteries can endure more cycles and are more powerful than their traditional Lithium-ion counterparts, how is this so?
H.B.: Well, it’s more power in comparison to the same amount of lithium in industrial cells. We could prove that we have high power, but you always have to compare the power with the amount of lithium inside the cell, so it’s not an absolute but a relative value. This is mostly dependent on positive electrodes on the cathode side. We could make electrodes with a good interface, and lower resistance on the cathode side. We can go to a very high variance on the anode side. We have to work on the interface on the cathode side to improve that power, and the industry will need to do that as well.
I.D.: How easily disposable are these batteries?
H.B.: We aren’t only just working on lithium, but also on sodium cells which are totally disposable. Every single element that we use in the sodium cell you can have in sea water. With lithium cells you do have to recover and recycle the lithium metal inside the cell. It depends on your cathode too. If you have sulphur, that is common and not hazardous, whereas sulphur hydride is. I don’t know what the procedure is with other cathodes, such as manganese oxide.
Note from Inés: Please dispose of batteries in the appropriate battery recycling locations and never deposit them in landfill.
I.D.: And presumably these new batteries will offer backwards compatibility with other devices?
H.B.: I think so, I don’t see why not. The batteries we use are not just one cell, they are usually a lot of cells in series and in parallel, so when you roll a big sheet of cell in the jelly roll cell, it is like having a lot of batteries in parallel. You can increase the power and voltage of your cell by adding cells in parallel or in series. Of course, the resistance has to be small inside of your cells, but it’s an easy exercise that is used everywhere. Tesla cars have many, many batteries – thousands of them!
I.D.: Finally, I’d be really interested in hearing about what inspired you to research battery science in the first place!
H.B.: I actually started to work in science because I read a book! I read a book by Hubert Reeves, his first book which talked about the universe, the Big Bang and so on. And I fell in love with the concept of entropy!
When I was 16, I went to Paris and I stayed in a University, and I heard he was going to give a talk there. So I left him some questions about his book, on the entropy side, and he said to me: “I will reply to your questions in my next book”.
And then, he went to Portugal, to the University and he told me he would like me to attend. Unfortunately, he gave the conference in French, so when I went to welcome him to Portugal, he apologised for giving the conference in French, and gave me a copy of his new book. He knew my name, and I wondered whether all physicists were all as nice and humble as him.
So a mixture of loving the subject of entropy, and admiring scientists like him I decided to study physics, though I had some disappointments on the way because things aren’t so easy. After I started my physics degree, I discovered I loved the materials side – in particular, I had a very nice professor in material science who spoke about nanotechnology. So from there, due to my interest in materials, I started a PhD in engineering on the subject in materials. When you start going through that pathway, you don’t know where it’s going to take you. I love Antonio Machado, as he said: “Caminante, no hay camino, se hace el camino al andar”. It’s difficult, but you can do it!
 “Caminante, no hay camino, se hace el camino al andar” is a verse from “Caminante no hay camino”, a poem by Sevillian poet Antonio Machado. It can be translated as “Wanderer, there is no path, you make your path as you go”. The full version and its translation can be found well-recounted in this blog here: http://gwenglish.blogspot.co.uk/2014/04/poem-of-day-antonio-machados-caminante.html
It was an honour to speak and learn from such a charming and inspiring researcher, and a sign that science communication well done can certainly inspire bright and inquisitive minds to pursue science. Thank you again Helena!
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