Scientists from TU Delft have recently conducted research that has shed more light on how popular rechargeable Li-ion batteries work. The new insights gained into the exact behaviour of the lithium-ions in these batteries mean that they can now be made more efficient and will be faster to charge too. The researchers in question recently had an article about their research published in the journal Advanced Energy Materials.

Neutron Depth Profiling

Researcher Marnix Wagemaker from the Reactor Institute Delft (RID) at TU Delft focused his attention on rechargeable Li-ion batteries, which are very popular.

‘The problem that I always found myself coming up against was the difficulty of visualising lithium-ions properly on the basis of conventional techniques. As a result, relatively little was known about exactly what factors play a role when charging and discharging these batteries or how it might be possible to make this process faster and more efficient. We believe that we have now resolved this situation, having been the first researchers to apply Neutron Depth Profiling (NDP) to a normal battery with the object of identifying the ions and ion movements.’

Unique insights

‘In our research, we used neutrons supplied by the Delft research reactor. When a neutron is fired and then captured by a Li-ion, it splits into a tritium nucleus and a helium nucleus. We can then detect these two particles and use this to deduce how the Li-ions move in the battery.’

‘This information yields unique insights into how Li-ions move in a battery in realistic (charging) conditions. We were particularly interested in the internal resistance in the battery, which determines how slow and efficient charging and discharging are.’

Three factors

Wagemaker: ‘Depending on the charging speed, our research showed that various processes in the battery determine this internal resistance. It was also found that there are, in principle, three methods that can be used to positively affect internal resistance and thus make the battery more efficient. These three methods, which are quite easy to apply, involve changing the size of the electrode sample, changing the Li-ion conductivity of the electrode and the electronic conductivity of the electrode’.

Immediate improvement possible

This research is in fact the first to identify which characteristics are best for a battery when used for a certain purpose. For example, if you want to be able to charge a battery quickly in a certain application, you will need to build the battery differently than you would if charging speed is less important. Wagemaker believes that the new insights achieved can be applied almost immediately in practice. ‘You could actually say that battery producers now have a ready-made recipe for the improvement of their products. Even if an improvement of just several percent were achieved, this would still represent a huge efficiency gain globally.’

TU Delft

#Energy