Batteries with silicon anodes: Neutron experiments show how formation of surface structures reduces amp-hour capacity
Neutrons (red arrows) detect the presence of Lithium ions which have migrated into the silicon anode. © HZB
In theory, silicon anodes could store ten times more lithium ions than graphite anodes, which have been used in commercial lithium batteries for many years. However, the amp-hour capacity of silicon anodes so far has been declining sharply with each additional charge-discharge cycle. Now an HZB team at BER II of the HZB in Berlin and the Institut Laue-Langevin in Grenoble has utilised neutron experiments to establish what happens at the surface of the silicon anode during charging and what processes reduce this capacity.
”With the neutron experiments and other measurements, we were able to observe how an inhibition or “blocking” layer forms on the silicon surface during charging that hinders the penetration of lithium ions”, explains HZB physicist Dr. Sebastian Risse. This 30-60 nanometre layer consists of organic molecules from the electrolyte liquid and inorganic components. When charging, the layer partially dissolves again so that the lithium ions can penetrate the silicon anode. However, energy is needed to dissolve the layer, which is then no longer available for storing. The physicists used the same electrolyte fluid in the experiment that is used in commercial lithium batteries.
Several cycles observed
After preliminary investigations with HZB’s BER II neutron source, the experiments at the Institut Laue-Langevin (ILL) in Grenoble provided a precise insight into the processes. ”Cold neutrons at very high flux are available at the ILL reactor. We were able to use them to non-destructively observe the silicon anode during several charge cycles”, explains Risse. Using a measuring cell developed at the HZB, physicists were able to examine the silicon anodes with neutrons during the charge-discharge cycles (in operando) and also record a number of other measurement values such as electrical resistance using impedance spectroscopy.
Efficiencies of 94 %
As soon as this inhibition layer is dissolved, the efficiency of the charge-discharge cycles increases to 94 per cent (94 % of the stored charge can be delivered again). This value is higher than that of lead-acid batteries (90 %), but slightly lower than that of batteries employing more highly developed lithium-ion technology, which deliver up to 99.9 %.
Outlook: Preventing the blocking layer
”We now want to investigate whether it is possible to prevent the formation of this inhibition or “blocking” layer by applying a very thin protective layer of metal oxide so that the capacity of silicon anodes decreases less over the course of many charge-discharge cycles”, says Risse.
The study was published in „Energy Storage Materials“: "Surface structure inhibited lithiation of crystalline silicon probed with operando neutron reflectivity". Arne Ronneburg, Marcus Trapp, Robert Cubitt, Luca Silvi, Sébastien Cap, Matthias Ballauff, Sebastian Risse.
- Ultrafast demagnetisation - Thinner iron, stronger effectThe thinner an iron film, the more easily it can be demagnetised by a laser pulse. Researchers at the University of Duisburg-Essen, working with Helmholtz-Zentrum Berlin and other partners, have discovered why: the key lies in the magnetic order at the material's interfaces. In the long term, these findings could contribute to the development of new technologies for magnetic data storage. The results have been published in the scientific journal Advanced Science.
- Blind spot for the arrangement of atomsArtificial intelligence is increasingly being used to predict the properties of new materials. A research team from Jena and the United States now shows in a study published in the journal Nature Computational Science that when language models are used for this purpose, they reliably identify which types of atoms a material contains. However, they make insufficient use of information about how those atoms are arranged in space. Neither larger models nor additional training data resolve this weakness. For material properties that depend strongly on structure, AI models specifically designed to process spatial relationships are therefore the more reliable choice. (DOI: 10.1038/s43588-026-01045-2)
- Patterns of polar vortices in lead-free superlattices on siliconA team at HZB has, for the first time, reported polar vortices in (BaTiO3/SrTiO3)10 superlattices on silicon. These results expand the range of materials and substrates on which polar topological textures can occur and open up new options for incorporating complex ferroelectric states into silicon-based technologies.