Nanoparticles, small but mighty

Crystal structure of insertion compound LiFePO4.

Figure 1: Crystal structure of insertion compound LiFePO4. Open framework facilitates intercalation and deintercalation of Li ions (green) [Fe blue, P purple, O orange]
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Nanoparticles, defined as being between 100 and 1 nanometers in size, stir excitement amongst researchers due to a wide variety of potential applications in biomedical, optical and electronic fields. With our current economy and environmental concerns, nanoparticles with uses in energy storage and energy efficient materials are particularly sought after.

The muon beamline at ISIS is being used to look at the lithium diffusion processes in components of lithium ion batteries to try and piece together the mechanisms for how the battery materials work at the atomic scale, with an aim to prepare better battery materials in the future.

Serena Corr and her group at the University of Kent are aiming to synthesise nanoparticles that could be used as a cathode component in a lithium ion battery which would be used in cameras, computers and mobile phones. Shrinking particles down to small sizes, such as those of nanoparticles, changes the properties of the material, with potential increases in efficiency being possible.

Insertion compounds which may be used as cathodes are typically in the form of layered sheet structures where lithium ions are positioned between the sheets, or tunnels where lithium ions sit within the channels. As the battery is discharged and charged, the lithium ions may move in and out of these structures (see Figure 1).

Reducing the size of the particle down to the nanoscale reduces the diffusion path length that the lithium has to travel and as the surface area is also increased, there is greater contact with the electrolyte as the lithium passes through.

At ISIS, Serena’s group have studied a range of nanoparticles in hope of demonstrating more efficient cycling of the battery. The particles were prepared using microwave synthesis which allows them to be highly crystalline.

Using the EMU instrument at ISIS, muons were employed as they are particularly susceptible to the changes in magnetic fields caused by lithium ions as they diffuse through the sample. Analysing the muon behaviour gives an idea of the diffusion processes happening in these materials, which are an integral part of the battery mechanism where questions remain.

Directly after EMU beam time, Serena’s team went across to Diamond to use the B18 beamline for x-ray absorption measurements of the cycling batteries, as combining several techniques gives a more intimate understanding of these cycling mechanisms.

There is a lot of scope for this on-going research, probed by questions such as can the behaviour of these materials be tailored through the size and shape of the nanoparticle used? And how does size and shape of the nanoparticles affect performance? Serena’s group intend to prepare a library of nanoparticles of different sizes and shapes and test the electrochemical performance of all of them to see which behaves the best and is the most efficient. Then there is the possibility to return to ISIS and Diamond to try and find out what is driving the efficiency – does the size and shape of the nanoparticles influence the battery mechanism?

As more and more is uncovered about these materials, it will aid with future research into the best materials for use in our every-day devices.

Emily Mobley

Serena Corr et al.

Research date: November 2012

Further Information

This research is on-going. For more information, please visit Serena Corr's research group, as part of Functional Nanomaterials at the University of Kent.

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