Didi Rinkel, research associate at the University of Cambridge is using NMR spectroscopy to investigate parasitic reactions at the positive electrode
Tell us about your research
I use NMR spectroscopy to investigate side reactions that happen between the electrodes and electrolyte solution inside lithium-ion batteries. Lithium ions move from the positive to the negative electrode through a liquid electrolyte during charging. One issue is that the liquid can react with the lithium ions and trap them in parasitic reactions, so they can’t reach the other side. This limits the capacity and reduces the lifetime of the battery. NMR spectroscopy can be used to precisely determine all the different reaction products that form through these unwanted reactions in the battery. I have been trying to characterise these products with an emphasis on the ones formed at the positive electrode. Knowing what products form helps us understand what the mechanism is for these parasitic reactions and how we can best prevent them.
How do you describe why your work is important to non-specialists?
My work focuses on understanding the complex puzzle of why lithium-ion batteries degrade and any insights we gain will hopefully contribute to making these batteries last longer. Lithium-ion batteries contain scarce essential raw materials (for example, lithium, cobalt and nickel) and can be quite expensive – they can make up over a third of the cost of an electric vehicle. Making batteries last longer will reduce cost of ownership of electric vehicles as well as the amount of precious resources that need to be mined and so will help the switch from combustion vehicles to electric vehicles. Understanding why lithium-ion batteries degrade and improving their lifetime are essential for the continued and more widespread use of these batteries.
How did you get into battery research?
My undergraduate degree was in Natural Sciences at the University of Cambridge, and I specialised in chemistry. I had a lecture course on NMR spectroscopy and absolutely loved it! So, for my masters project I wanted to do a project on NMR spectroscopy and fell into Professor Dame Clare Grey’s group, where I learned about battery research and its importance.
What is it about NMR spectroscopy that you love so much?
At the risk of being really nerdy, I find what we can do with it so beautiful and clever. NMR spectroscopy works by placing a sample in a magnetic field and exciting the nuclei by applying a radio wave. The nuclei are allowed to relax, and the “echo” – the energy emitted after the nuclei returns to base level – can be detected and provides information about a sample’s composition and molecular structure. There are many unique ways of applying and combining these relatively simple pulses, and they are all so clever! I’m glad I got interested in it because it allowed me to jump into the battery science field, which I had never considered pursuing.
What accomplishments are you most proud of?
The research that I have done brings me a lot of satisfaction. I feel like I have been able to contribute a small bit to understanding the positive electrode-electrolyte interactions, particularly in my recent paper on electrolyte oxidation pathways in lithium-ion batteries, published in the Journal of the American Chemical Society. I’m still surprised that we could use relatively routinely-used solution NMR experiments to almost fully tease out what decomposition products are formed. I hope some of our work can be used to help prevent battery degradation in working vehicles in the future.
I also think our work on dynamic nuclear polarisation (DNP) enhanced NMR spectroscopy applied to investigate the solid electrolyte interface (SEI) published in Nature Communications is very exciting. DNP is a technique that has become experimentally possible only recently (due to the development of high frequency microwave sources) and boosts the signal intensities in NMR spectra by using microwave irradiation. We developed a new DNP NMR methodology to probe “hidden” or “buried” interfaces, such as the interface between lithium metal and the SEI. Hopefully we can learn something about how the SEI affects lithium deposition and improve the safety issues that are associated with use of lithium metal in batteries.
What is a highlight of your career to date or the aspect that gives you greatest job satisfaction?
At risk of sounding a little narcissistic, it bring me a lot of joy when people tell me they have read and liked my work. I think it’s validating when other scientists appreciate your work, especially when it comes from people I look up to – every time it happens it makes my day! Another thing that I find very satisfying is the moment I understand what my data is telling me. I stare at many mysterious signals in NMR spectra and suddenly I figure out what decomposition species has formed and the whole puzzle of complex electrolyte-electrode reactions clicks together. It’s one of these ‘aha!’ moments that can keep me going for weeks.
What opportunities has being part of the Faraday Institution opened up for you?
The Faraday Institution has allowed me to connect and collaborate with other battery researchers. For example, I reached out to Dr Nuria Garcia-Araez at the University of Southampton to enquire about her expertise and experimental setup to precisely measure the internal pressure of a battery and determine which gases form. We embarked on a fantastic collaboration and produced a paper on two electrolyte decomposition pathways at nickel-rich cathode surfaces in lithium-ion batteries in the Royal Society of Chemistry’s Energy and Environmental Science journal. We kept in touch throughout the project and discussed our ideas often. The Faraday Institution was very valuable for allowing our groups to combine our different areas of expertise.
What are the biggest challenges you have had to overcome in your career and how have you gone about doing so?
In practice, science takes time and doesn’t always go the way you think (or hope!) it will go. During the first few years of my PhD, this was something I found particularly frustrating! A lot more work goes into research than meets the eye when you read a final paper. I learned to persevere even when things weren’t going as I wanted or expected them to. It’s a lesson that isn’t taught at university, as (undergraduate) practicals tend to be designed to teach students procedures rather than the realities of the research process. I’ve learned it’s best to keep trying and think of new and inventive ways to tackle a problem, even if it is risky, because that’s how we make new discoveries. Now, I thoroughly enjoy this “challenge” of doing science and I’m always excited to design new experiments and learn what the outcome is – I think it’s one of the best aspects of this job!
What are your career aspirations?
I always find this such a difficult question! I have thoroughly enjoyed doing research, and for now I would like to continue. I think NMR spectroscopy will always be part of what I do, but I’d like to learn other complementary techniques and expand my knowledge of other challenges in battery research and energy storage in general.
What advice would you have liked to have given your younger self starting out on your career?
During my PhD, I would tell myself to trust my instincts. If I thought something was worth pursuing, I should have just gone ahead and done the experiment I want to do. I’d also tell myself that doing research isn’t always easy, but when you find something cool, it is incredibly rewarding!
If people want to find out more about your research, where would you point them to?
My papers on electrolyte decomposition at LiCoO2 electrodes in the Journal of the American Chemical Society and at nickel-rich cathode surfaces in lithium-ion batteries in the journal Energy and Environmental Science, and my paper on NMR spectroscopy applied to observe the SEI-metal interface in Nature Communications.
There is also a University of Cambridge news article on our new DNP NMR methodology and my answer to the question “Why aren’t all batteries recyclable” on the Naked Scientists podcast. Of course, they are also welcome to email me if they want to have a chat, at email@example.com!
Connect with Didi on Twitter.
Published September 2022.
About the author: Cara Burke is the Faraday Institution’s Science Communications Intern in the summer of 2022. She has just completed her BSc Biological Sciences degree at Imperial College London and is pursuing a career in science communications.