Researchers from ETH Zurich and Empa have succeeded for the first time to produce uniform antimony nanocrystals. Tested as components of laboratory batteries, these are able to store a large number of both lithium and sodium ions. These nanomaterials operate with high rate and may eventually be used as alternative anode materials in future high-energy-density batteries. The hunt is on – for new materials to be used in the next generation of batteries that may one day replace current lithium ion batteries. On the one hand, however, electric mobility and stationary electricity storage demand a greater number of more powerful batteries; and the high demand for lithium may eventually lead to a shortage of the raw material.
This is why conceptually identical technology based on sodium-ions will receive increasing attention in coming years. Contrary to lithium batteries, researched for more than 20 years, much less is known about materials that can efficiently store sodium ions. A team of researchers from ETH Zurich and Empa headed by Maksym Kovalenko may have come a step closer to identifying alternative battery materials: they have become the first to synthesize uniform antimony nanocrystals, the special properties of which make them prime candidates for an anode material for both lithium-ion and sodium-ion batteries. The results of the scientists’ study have just been published in Nano Letters.
For a long time, antimony has been regarded as a promising anode material for high-performance lithium-ion batteries as this metalloid exhibits a high charging capacity, by a factor of two higher than that of commonly used graphite. Initial studies revealed that antimony could be suitable for rechargeable lithium and sodium ion batteries because it is able to store both kinds of ions. Sodium is regarded as a possible low-cost alternative to lithium as it is much more naturally abundant and its reserves are more evenly distributed on Earth.
For antimony to achieve its high storage capability, however, it needs to be produced in a special form. The researchers managed to chemically synthesize uniform – so-called “monodisperse” – antimony nanocrystals that were between ten and twenty nanometers in size.
The full lithiation or sodiation of antimony leads to large volumetric changes. By using nanocrystals, these modulations of the volume can be reversible and fast, and do not lead to the immediate fracture of the material. An additional important advantage of nanocrystals (or nanoparticles) is that they can be intermixed with a conductive carbon filler in order to prevent the aggregation of the nanoparticles.
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