On the trail of lithium dendrites: How destructive formations develop in batteries
During the operation of conventional battery storage, the tree-like lithium dendrites grow continuously and can pierce the electrically insulating separator layer between anode and cathode. The result: a short circuit and the end of life for the battery. © HZB/Ingo Manke, Dong et al.
While the deposited lithium stacks up as tiny balls at low electric currents, the deposits grow into tangled formations over time at high currents - the fractal dendrites. © HZB/Ingo Manke, Dong et al.
Tiny formations inside lithium batteries can severely limit the operating life of an energy storage device. A research team at the Helmholtz-Zentrum Berlin (HZB) has now investigated the process behind these formations in greater detail. Their results provide anchor points for the future development of longer-lasting and safer lithium batteries.
Dendrites can form inside lithium batteries. These small needles or trees resemble the branched extensions of our nerve cells, from which they get their name. Dendrites form when the ions of an alkali metal like lithium encounter tiny crystallisation nuclei as the ions migrate back and forth between the internal plus and minus poles of a battery during the charge/discharge cycles. These dendrites grow during each charge/discharge cycle and eventually short-circuit the battery, destroying it – and in some cases even causing an explosion. It is not yet clear how this danger can be averted, and how the service life of energy storage devices can be increased, because we do not yet fully understand how the dendrites develop and grow.
High-resolution insights in 3D
To unravel the mystery of this nucleation and growth of dendrites in lithium-ion batteries, a research team took a look deep inside a battery using two specialised methods at the HZB. “While conventional investigations with scanning or transmission electron microscopes generally provide a two-dimensional image, we use focussed ion-beam scanning electron microscopy to penetrate into the third dimension”, explains Kang Dong, a postdoc who works in Ingo Manke's research group involved with imaging methods at the HZB Institute for Applied Materials Research. “We also employed cryogenic transmission electron microscopy from Prof. Yan Lu's research group at the HZB. The low temperatures minimise the damage caused to our samples by the electron beam, and we obtain nearly realistic resolution in the nanometre range of the structure and chemistry of the lithium deposits.”
The researchers obtained high-resolution images of the internal lithium deposits accurate in every detail. “We discovered that the dendrites have extremely varied features that depend strongly on the local current densities”, explains Manke, who heads the research group. “At low current densities, they look like small spheres that clump together over time. At higher currents densities, they more closely resemble moss-like, fractal dendrites.” During their research, the team recorded images at different stages of the development of the lithium spheres and dendrites, which appear like whiskers. These three-dimensional images represent a milestone in understanding the mechanisms at work during deposition.
Anchor points for development of longer-lasting batteries
”We also found that the dendrites always commence at specific contamination points and/or structural inhomogeneities on the surface of the lithium anode”, Manke tells us about an additional discovery. ”The way the lithium reacts with the separator layer inside the battery has not yet been fully understood”, adds Kang Dong. They already suggest in the published paper the direction research could take: “We think that optimising the electrolytes and the engineering of the internal surfaces are important points for keeping the lithium deposits more spherical and amorphous. This could prevent the growth of the branched dendrites, helping improve the operating stability of the batteries.”
Publication: ACS Energy Letter
- The future of corals – what X-rays can tell usThis summer, it was all over the media. Driven by the climate crisis, the oceans have now also passed a critical point, the absorption of CO2 is making the oceans increasingly acidic. The shells of certain sea snails are already showing the first signs of damage. But also the skeleton structures of coral reefs are deteriorating in more acidic conditions. This is especially concerning given that corals are already suffering from marine heatwaves and pollution, which are leading to bleaching and finally to the death of entire reefs worldwide. But how exactly does ocean acidification affect reef structures?
Prof. Dr. Tali Mass, a marine biologist from the University of Haifa, Israel, is an expert on stony corals. Together with Prof. Dr. Paul Zaslansky, X-ray imaging expert from Charité Berlin, she investigated at BESSY II the skeleton formation in baby corals, raised under different pH conditions. Antonia Rötger spoke online with the two experts about the results of their recent study and the future of coral reefs.
- Susanne Nies appointed to EU advisory group on Green DealDr. Susanne Nies heads the Green Deal Ukraina project at HZB, which aims to support the development of a sustainable energy system in Ukraine. The energy expert has now also been appointed to the European Commission's scientific advisory group to comment on regulatory burdens in connection with the net-zero target (DG GROW).
- Long-term stability for perovskite solar cells: a big step forwardPerovskite solar cells are inexpensive to produce and generate a high amount of electric power per surface area. However, they are not yet stable enough, losing efficiency more rapidly than the silicon market standard. Now, an international team led by Prof. Dr. Antonio Abate has dramatically increased their stability by applying a novel coating to the interface between the surface of the perovskite and the top contact layer. This has even boosted efficiency to almost 27%, which represents the state-of-the-art. After 1,200 hours of continuous operation under standard illumination, no decrease in efficiency was observed. The study involved research teams from China, Italy, Switzerland and Germany and has been published in Nature Photonics.