Nanoparticles in lithium-sulphur batteries detected with neutron experiment
The operando cell was developed at HZB and allows to analyse processes inside the battery during charging cycles with neutrons. © S. Risse/HZB
An HZB team has for the first time precisely analysed how nanoparticles of lithium sulphide and sulphur precipitate onto battery electrodes during the course of the charging cycle. The results can help increase the service life of lithium-sulphur batteries.
Lithium-sulphur batteries are regarded as one of the most promising candidates for the next generation of energy storage devices. They have a theoretical gravimetric energy density that is five times higher than that of the best lithium-ion batteries currently available. And they even work at sub-zero temperatures of down to -50 °C. In addition, sulphur is inexpensive and environmentally friendly.
Capacity loss
However, their capacity so far has fallen sharply with every charge-discharge cycle, so that such batteries are not yet long-lasting. The loss of capacity is caused by complicated reaction processes at the electrodes inside the battery cell. It is therefore particularly important to understand exactly how the charge (sulphur) and discharge (lithium sulphide) products precipitate and dissolve. While sulphur precipitates macroscopically and therefore lends itself to examination by imaging techniques or X-ray diffraction during cycling, lithium sulphide is difficult to detect due to its sub-10-nm particle size.
"Operando" observations with neutrons
Insight into this has now been provided for the first time by investigations with the BER II neutron source at the HZB. Dr. Sebastian Risse used a measuring cell he developed to illuminate lithium-sulphur batteries with neutrons during charging and discharging cycles (operando) and simultaneously performed additional measurements with impedance spectroscopy.
This enabled him and his team to analyse the dissolution and precipitation of lithium sulphide with extreme precision during ten discharge/charging cycles. Since neutrons interact strongly with deuterium (heavy hydrogen), the researchers used a deuterated electrolyte in the battery cell to make both the solid products (sulphur and lithium sulphide) visible.
Surprising insight
Their conclusion: “We observed that the lithium sulphide and sulphur precipitation does not take place inside the microporous carbon electrodes, but instead on the outer surface of the carbon fibres”, says Risse. These results provide a valuable guide for the development of better battery electrodes.
The study is published in ACS Nano, (2019): Operando Analysis of a Lithium/Sulfur Battery by Small Angle Neutron Scattering. Sebastian Risse, Eneli Härk, Ben Kent and Matthias Ballauff
DOI: http://dx.doi.org/10.1021/acsnano.9b03453
- The twisted nanotubes that tell a storyIn collaboration with scientists in Germany, EPFL researchers have demonstrated that the spiral geometry of tiny, twisted magnetic tubes can be leveraged to transmit data based on quasiparticles called magnons, rather than electrons.
- Bright prospects for tin perovskite solar cellsPerovskite solar cells are widely regarded as the next generation photovoltaic technology. However, they are not yet stable enough in the long term for widespread commercial use. One reason for this is migrating ions, which cause degradation of the semiconducting material over time. A team from HZB and the University of Potsdam has now investigated the ion density in four different, widely used perovskite compounds and discovered significant differences. Tin perovskite semiconductors produced with an alternative solvent had a particular low ion density — only one tenth that of lead perovskite semiconductors. This suggests that tin-based perovskites could be used to make solar cells that are not only really environmentally friendly but also very stable.
- Synchrotron radiation sources: toolboxes for quantum technologiesSynchrotron radiation sources generate highly brilliant light pulses, ranging from infrared to hard X-rays, which can be used to gain deep insights into complex materials. An international team has now published an overview on synchrotron methods for the further development of quantum materials and technologies in the journal Advanced Functional Materials: Using concrete examples, they show how these unique tools can help to unlock the potential of quantum technologies such as quantum computing, overcome production barriers and pave the way for future breakthroughs.