The team was able to show through neutron measurements made at the Institut Laue-Langevin in Grenoble, France, that lithium ions do not penetrate deeply into the silicon. During the charge cycle, a 20-nm anode layer develops containing an extremely high proportion of lithium. This means extremely thin layers of silicon would be sufficient to achieve the maximal load of lithium.
Lithium ions migrate through the electrolyte (yellow) into the layer of crystalline silicon (c-Si). During the charging cycle, a 20-nm layer (red) develops on the silicon electrode adsorbing extreme quantities of lithium atoms.
Lithium-ion batteries provide laptops, smart phones, and tablet computers with reliable energy. However, electric vehicles have not gotten as far along with conventional lithium-ion batteries. This is due to currently utilised electrode materials such as graphite only being able to stably adsorb a limited number of lithium ions, restricting the capacity of these batteries. Semiconductor materials like silicon are therefore receiving attention as alternative electrodes for lithium batteries. Bulk silicon is able to absorb enormous quantities of lithium. However, the migration of the lithium ions destroys the crystal structure of silicon. This can swell the volume by a factor of three, which leads to major mechanical stresses.
Observation during charging cycle
Now a team from the HZB Institute for Soft Matter and Functional Materials headed by Prof. Matthias Ballauff has directly observed for the first time a lithium-silicon half-cell during its charging and discharge cycles. "We were able to precisely track where the lithium ions adsorb in the silicon electrode using neutron reflectometry methods, and also how fast they were moving", comments Dr. Beatrix-Kamelia Seidlhofer, who carried out the experiments using the neutron source located at the Institute Laue-Langevin.
Lithium-rich layer of only 20 nanometer
She discovered two different zones during her investigations. Near the boundary to the electrolytes, a roughly 20-nm layer formed having extremely high lithium content: 25 lithium atoms were lodged among 10 silicon atoms. A second adjacent layer contained only one lithium atom for ten silicon atoms. Both layers together are less than 100 nm thick after the second charging cycle.
Theoretical maximum capacity
After discharge, about one lithium ion per silicon node in the electrode remained in the silicon boundary layer exposed to the electrolytes. Seidlhofer calculates from this that the theoretical maximum capacity of these types of silicon-lithium batteries lies at about 2300 mAh/g. This is more than six times the theoretical maximum attainable capacity for a lithium-ion battery constructed with graphite (372 mAh/g).
Less is more
These are substantial findings that could improve the design of silicon electrodes: very thin silicon films should be sufficient for adsorbing the maximum possible amount of lithium, which in turn would save on material and especially on energy consumed during manufacture - less is more!
Publication: Lithiation of Crystalline Silicon As Analyzed by Operando Neutron Reflectivity, ACS Nano. Beatrix-Kamelia Seidlhofer, Bujar Jerliu, Marcus Trapp, Erwin Hüger, Sebastian Risse, Robert Cubitt, Harald Schmidt, Roland Steitz, and Matthias Ballauff.
Dr. Beatrix-K. Seidlhofer | EurekAlert!
A big nano boost for solar cells
18.01.2017 | Kyoto University and Osaka Gas effort doubles current efficiencies
Multiregional brain on a chip
16.01.2017 | Harvard John A. Paulson School of Engineering and Applied Sciences
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences