New electrodes and graphene will improve lithium-ion batteries

Electrodes made of new materials and carbon nanostructures will make it possible to create more powerful and durable batteries, and graphene nanowalls will protect them from destruction after many charge and discharge cycles. Employees of the D.V. Skobeltsyn together, Moscow State University named after M.V. Lomonosov, Dubna University and L.N. Gumilyov (Kazakhstan) used silicon and germanium in order to make ions more mobile. The results of the work were published in the Journal of Materials Chemistry A.

Lithium-ion batteries are the most commonly used type of energy storage in modern electronic devices. Such batteries consist of two electrodes: negative (anode) and positive (cathode). The space between them is filled with a porous separator saturated with an electrolyte ˗ dissolved lithium salt. The separator prevents short circuits between the electrodes and provides the necessary electrolyte reserve for high ionic conductivity. An electric current occurs when lithium ions move from the anode material through the electrolyte to the cathode material. In this case, the energy intensity is largely determined by the amount of lithium ions.

Scientists have developed and researched a new anode material that can significantly improve the energy efficiency of lithium-ion batteries, including those used in thin-film applications. “Today, a lot of attention is paid to the development of anode materials based on elements such as silicon (Si) and germanium (Ge). When interacting with lithium ions, these elements are capable of forming alloys, the theoretical energy capacity of which significantly exceeds the capacity of graphite ˗ the traditional anode material of modern lithium-ion batteries, ”said Viktor Krivchenko, co-author of the article, senior researcher at the Laboratory of Plasma Physics and Physical Foundations of Microtechnology, SINP MSU.

Of all the known anode materials, silicon has the highest theoretical lithium capacity, reaching 4200 mAh / g. This makes silicon the most promising battery material. In turn, the more expensive and less capacious germanium conducts electric current better: the transfer of lithium ions in it is several orders of magnitude more intense. Such features of germanium can significantly increase the power of lithium-ion batteries without significantly changing their volume.

The main problem of electrode materials is that their structure is destroyed in a cyclic process of charging and discharging, which leads to the failure of the lithium-ion battery. Scientists propose to solve this problem by switching to nanostructured materials and creating composite materials, where various carbon nanostructures can act as a stabilizing matrix.

“The main novelty of the presented work is that a matrix formed by plasma-chemically synthesized carbon structures with a very developed surface was used to realize anode materials with the required properties,” said Viktor Krivchenko. “Such structures are a dense array of graphene-like nanowalls oriented perpendicular to the surface of the metal substrate.”

In the course of their work, the scientists used the method of magnetron sputtering, which allowed them to uniformly cover the surface of nanowalls with a layer of silicon or germanium 10-50 nanometers thick. In this case, the final structure of the composite anode can consist of either one active material layer or alternating layers. As a result, it was shown that the obtained three-dimensional architecture allows one to achieve a high specific capacity and increases the stability of the specific characteristics of silicon and

germanium-based anodes.