Scientists at the Technische Universitaet Muenchen (TUM) have synthesized a novel framework structure consisting of boron and silicon, which could serve as a Lithium-ion battery electrode material. The new material is similar to the carbon atoms in diamond as the boron and silicon atoms in the novel lithium borosilicide (LiBSi2) are interconnected tetrahedrally.
The new material adds a new dimension as they form, making channels within the structure with many more sites where the lithium ions can locate. That suggests laptops could work longer and electric cars could drive farther with increases in the capacity of their lithium-ion batteries.
The electrode material has a decisive influence on a battery’s capacity. Today’s lithium ion negative electrode typically consists of graphite, whose layers can store lithium atoms. The scientists at (TUM) have developed a process to build a material made of boron and silicon that could enable systems with higher capacities.
Loading a lithium-ion battery produces lithium atoms that are taken up by the graphite layers of the negative electrode. However, the capacity of graphite is limited to one lithium atom per six carbon atoms. Silicon could take up to ten times more lithium. But unfortunately, its dimensions expand during this process – which leads to unsolved problems in battery applications.
But a 10-fold capacity increase potential is a powerful incentive.
Thomas Fässler, professor at the Institute of Inorganic Chemistry at TUM said, “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.”
In the high-pressure laboratory of the Department of Chemistry and Biochemistry at Arizona State University, the scientists brought the starting materials lithium boride and silicon to a reaction. At a pressure of 100,000 atmospheres and temperatures around 900 degrees Celsius, the desired lithium silicide formed.
“Intuition and extended experimental experience is necessary to find out the proper ratio of starting materials as well as the correct parameters,” added Fässler.
As a bonus, lithium borosilicide is stable to air and moisture and withstands temperatures up to 800° C (1472º F).
Next, Fässler and his graduate student Michael Zeilinger 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.
It will be interesting to see if a strong and hard alloy structure can remain stable, crack apart or stuff itself with a huge load of lithium ions over many cycles. Then comes the question of production costs and scaling. There is a long way to go.
Because the framework structure of the lithium borosilicide is unique, Fässler and Zeilinger had an opportunity a name to their new framework material. In honor of their university, they chose the name “tum.” We’ll be watching for it.
The research effort was widespread. Cooperation partners of the project were the Department of Physics at University of Augsburg and the Department of Materials and Environmental Chemistry at Stockholm University. 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.
One hopes this works with an incredible number of charge and discharge cycles made commercially at low cost. Lithium-ion technology is going to get competition and more advantages need to come soon. We consumers will be pleased with more and better choices.