Batteries are everywhere these days: from your cell phone, laptop, through power tools all the way to electric vehicles and grid storage systems. At the moment, the most prominent type of a battery is the Li-ion battery, which has been first proposed in 1970s and commercially used in 1991. Scientists and engineers have worked hard over the decades to improve the amount of energy such a battery can hold, reduce its cost and make it possible to charge faster and provide more power. Incremental improvements were especially important on the cathode side, as that side is the bottleneck of most of the performance qualities as well as cost of a Li-ion battery. Remarkable progress has been made, and new generations of Li-ion batteries are constantly evolving. However, as the batteries are required to work harder and longer, degradation of their performance over time becomes an issue.
In my work, I study the processes behind the degradation of some novel cathode materials using a set of remarkable techniques within the field of electron microscopy. In these microscopes, electrons are accelerated inside of a vacuum, then they are shaped into a narrow beam using electromagnets called lenses (but they are not made of glass, in fact, they are just empty space with some copper wire around) and focused onto a sample. Then, we the electrons that bounce off or go through the sample are detected, as well as X-rays that are emitted by the sample because of the interactions with said electrons. By using electrons instead of light, these microscopes give us access to much higher resolutions, even down to resolving individual atoms. I am using these capabilities to investigate how does the Li-ion battery cathode material change during its operation, and which of these changes might be responsible for the decay of performance. The materials cracks, the arrangement of atoms changes on the surface, some atoms dissolve into the electrolyte and there are side reactions forming additional layers on the surfaces. These processes happen at very short length-scales of nanometres, but heavily influence the properties and behaviour of the whole battery. Therefore, by using electron microscopes we can examine the processes causing the degradation, understand them better and hopefully, propose solutions that would improve the performance and lifetime of Li-ion batteries in the future.
Jędrzej Morzy
NanoDTC Student, c2017