Marnix Wagemaker

During the EIRES Energizing Day on Friday June 23^rd, renowned speakers from within and outside of TU/e presented the latest in energy-related research. Marnix Wagemaker, Professor and head of the section Storage of Electrochemical Energy at TU Delft, introduced the audience into the balancing act of finding new materials for better performing batteries, that are safer and more environmentally friendly.

Marnix Wagemaker received his PhD in Physics from TU Delft, where he has been a full professor and head of the section Storage of Electrochemical Energy Since May 2017. His research is aimed at the development of next generation battery materials.

Whether it is your smartphone, tablet, laptop or electric car: ever more devices are powered by rechargeable batteries. ‘When the lithium-ion battery was invented, we seemed to be about done, since it could be used for all purposes. But the steep growth in the use of these types of batteries is nowhere near sustainable, if only because of the limited amount of lithium the Earth can provide,’ says Marnix Wagemaker. ‘In addition to that, future batteries need to store more energy, charge faster, have a longer lifespan, and be less flammable than preceding generations.’

Three main parts
In his research, Wagemaker works on ‘the active parts of a battery’: the electrodes and the electrolyte. A lithium-ion battery consists of three main parts: an anode, currently made from graphite, a cathode, consisting of a metal oxide, and a liquid electrolyte that allows the charged lithium ions to go from one electrode to the other. The materials the electrodes are made of contain voids where lithium atoms can be stored. The lithium is strongly bound to the metal oxide, whereas in the graphite, the lithium atoms are only loosely bound. This difference results in a chemical potential: the voltage of the battery.

During discharge, lithium atoms in the anode will each give up an electron and travel through the electrolyte to the cathode. When charging, the opposite happens. ‘In our research, we try to optimize several characteristics: we want to improve the energy density, speed up the charging process, increase the lifespan, and minimize the use of critical materials. In addition to that, safety is an issue, since the liquid electrolyte is highly flammable. So we also try to replace that by solid alternatives.’

Swelling silicon
What’s inconvenient though, is that just about every improvement made on one aspect tends to introduce problems with something else, Wagemaker says. ‘For example, to increase the amount of energy that can be stored per kilogram of material, you would want to increase the amount of lithium that can be stashed inside an electrode. In graphite, you can store 1 lithium atom per 6 carbon atoms. When you would trade the graphite for another material like silicon, that storage capacity becomes ten times higher. Why don’t we see any batteries based on silicon then? Because that material comes with its own downside: the more lithium the silicon absorbs, the bigger it gets, until eventually it quite literally breaks. So, in this case, as the energy density grows, the lifespan of the battery decreases.’

To study what happens inside the batteries during charging and discharging, Wagemaker makes use of a multitude of operando techniques, ranging from NMR and X-ray to synchrotron based imaging. ‘That way we can see on an atomic level what happens if we start filling our electrodes with lithium. Do the lithium atoms nicely disperse over the entire surface, or do they cluster somewhere? And how does their behavior influence the battery’s performance and lifespan?’

Bigger picture
Even though with these techniques Wagemaker can see the smallest of scales, he never looses sight of the bigger picture. ‘For me, the biggest challenge in battery research is not about expanding the driving range of an electric vehicle. It is about the availability of materials and the CO₂ footprint of battery technology as a whole. Imagine I come up with some ideal material, but it has a huge carbon footprint due to its production process. That is not a sustainable solution, so it will never be used in practice.’ To make sure that in the development of new batteries, all relevant questions are addressed, Wagemaker launched the e4BatteryDelft initiative, which brings together all TU Delft researchers on battery technology.

When asked to gaze into his crystal ball and predict the future of battery technology, Wagemaker is clear: ‘There is no silver bullet, the ideal solution simply does not exist. So, we have to find the next best compromise. And I am pretty sure that we will end up with a set of different batteries for different applications. The batteries that will power cargo trucks with a limited radius will not be the same as the home battery that stores the excess electricity from the solar panels on your roof. When in the end, my work will turn out to have contributed to new batteries based on non-critical materials with a low carbon footprint and a long lifespan, that can be used to store excess solar and wind energy, I’ll be more than happy.’