Looking for an alternative to pure silicon for use as high-capacity and stable Li-ion anodes, a team led by researchers at the Technische Universität München (TUM), with colleagues from Stockholm University, University of Augsburg and Arizona State University, have synthesized a novel framework structure consisting of boron and silicon.
A paper on their work is published in the journal Angewandte Chemie.
Similar to the carbon atoms in diamond, the boron and silicon atoms in the novel lithium borosilicide (LiBSi2) are interconnected tetrahedrally. Unlike diamond, they also form channels. Thomas Fässler, professor at the Institute of Inorganic Chemistry, TUM, and his graduate student Michael Zeilinger named the novel framework “tum” in honor of their university.
Open structures with channels offer in principle the possibility to store and release lithium atoms. This is an important requirement for the application as anode material for lithium-ion batteries.—Thomas Fässler
Using the facilities of the high-pressure laboratory of the Department of Chemistry and Biochemistry at Arizona State University, the scientists brought lithium boride and silicon to reaction. At a pressure of 100,000 atmospheres and temperatures around 900 °C, the desired lithium silicide formed.
The compound represents a new topology in the B-Si net (called tum), which hosts Li atoms in the channels. LiBSi2 is the first example where B and Si atoms form an ordered common framework structure with B engaged exclusively in heteronuclear B—Si contacts.—Zeilinger et al.
Lithium borosilicide is stable to air and moisture and withstands temperatures up to 800 °Celsius. Next, the researchers want to examine more closely how many lithium atoms the material can take up and whether it expands during charging. Because of its crystal structure the material is also expected to be very hard, which would make it attractive as a diamond substitute as well.
The work was funded by the TUM Graduate School, the German Chemical Industry Fund, the German Research Foundation, the Swedish Research Council and the National Science Foundation, USA.
Michael Zeilinger, Leo van Wüllen, Daryn Benson, Verina F. Kranak, Sumit Konar, Thomas F. Fässler, and Ulrich Häussermann (2013) LiBSi2: A Tetrahedral Semiconductor Framework from Boron and Silicon Atoms Bearing Lithium Atoms in the Channels, Angewandte Chemie International Edition 52, 5978-5982. doi: 10.1002/anie.201301540
Michael Zeilinger, Daryn Benson, Ulrich Häussermann, Thomas F. Fässler (2013) Single crystal growth and thermodynamic stability of Li17Si4, Chemistry of Materials 25, 1960–1967 doi: 10.1021/cm400612k