Ural Scientists Create a Model of a Highly Efficient and Safe Lithium-Ion Microbattery Cell

13:58, December 8, 2020

The capacity of the stored energy in the prototype microbattery cell is 10 times greater than that of similar devices

Employees of the Institute of High-Temperature Electrochemistry of the Ural Branch of the Russian Academy of Sciences (UB RAS) and the Ural Federal University have created a computer model of the electrochemical cell of a lithium-ion microbattery. The capacity of the stored energy in it is 10 times greater than that of similar devices. The exceptional properties of the cell are the result of using a two-layer silicene on a graphite substrate as an anode element, as well as a solid electrolyte. The scientists published an article with a comparative description of the development in the journal Materials Science and Engineering.

“The difference between our work is that we did not study free-standing, so-called“ naked ”silicene, to which most theoretical scientific works are devoted, but ultrathin substrates, separately from which silicene cannot be obtained at present. We used a variety of materials as a substrate for silicene, including silver, nickel, copper, and aluminum. It turned out that the most suitable option is a graphite substrate, since the bond between silicene and graphite is rather weak, so graphite does not have a strong effect on two-dimensional silicon, and it largely retains the properties of free-standing silicene,” says the head of the research group, chief researcher of the laboratories electrode processes of the Institute of High Temperatures Ural Branch of the Russian Academy of Sciences and materials and devices for environmentally friendly energy of the Ural Federal University Alexander Galashev.

Moreover, scientists have found that, in combination with a graphite substrate, silicene is prone to metallization. A small electronic conductivity appears in it, which makes the use of silicene in lithium-ion battery cells even more expedient. Another development advantage is its solid-state design.

In addition, the model uses a thin-film electrolyte. In this case, electrical conductivity plays a lesser role than in electrolytes made of dense materials with a thickness measured in microns and even millimeters.

The electrical conductivity of the developed cell turned out to be quite high, its theoretical capacity is 3500 mAh / g-1. Consequently, a ready-made battery consisting of several hundred such electrochemical cells will be charged much faster.

“This is a fundamentally important quality, especially for the use of batteries in the automotive industry. Lithium-ion batteries have proven to be more promising than hydrogen fuel cells. However, to date, charging them takes 3-5 hours at best. Thus, the task is to reduce the charging time as much as possible, down to several minutes,” comments Alexander Galashev.

It should be added that the created electrochemical cell is also characterized by small size and low cost.

At present, work is underway at the Chemical-Technological Institute of Ural Federal University to create and test an experimental sample of the developed electrochemical cell. The physical properties of silicene are still poorly studied in experiments, and this adds to the uniqueness of the joint project of IHTE and UrFU. The research was supported by a grant from the Russian Science Foundation (No. 16-13-00061, Fundamentals of the electrochemical synthesis of new electrode materials based on silicon).

About Silicen

The battery capacity depends on the electrode material (cathode and anode) and electrolyte. Complex oxides of transition metals (for example, cobalt, nickel, manganese, etc.) are used as materials for the cathode, and this technology pays off. The main problem is in finding materials for the negative electrode - anode. Traditionally used graphite and its carbon substitutes are characterized by a very small electrical capacity, i.e. the ability to hold charge while charging the battery: six carbon atoms hold only one lithium atom, which is responsible for charge transfer in the battery.

One atom of silicon, the most productive, widespread and cheapest alternative to graphite, holds more than four lithium atoms. Thus, the theoretical capacity of silicon is more than an order of magnitude higher than that of graphite. However, during cycling (charging and discharging the battery), silicon crystals wear out quickly: they change greatly in volume, lose their original structure, become amorphous and collapse. Cracks form in the anode and the battery fails. The destruction becomes less if silicon nanoparticles are used, but they have poor adhesion to the material that holds them (binder), including graphite or graphene.

Discovered in 2010, silicene (a two-dimensional silicon compound similar in structure and electronic properties to graphene) easily interacts with the environment, binding with oxygen. Like silicon, silicene has good electrical capacitance, but it changes its volume slightly during cycling. When used in electronics, it is important that silicene has no point or line defects that alter its electronic properties.