The researchers from the N.S. Kurnakov RAS Institute of General and Inorganic Chemistry and Jewish University in Jerusalem created new composite material for anodes in sodium-ion batteries. It is based on the combination of nanoparticles of germanium sulfide and MXene, bidimensional titanium carbide. This solution opens the way to creating batteries capable of very quick recharging maintaining high capacity during thousands of operational cycles.
The drawbacks of modern batteries are to a great extent associated with limitations of anodic materials. These materials may be conventionally divided into three types. The first and the most common one – intercalation materials, such as graphite. They provide for stability and durability, but do not have high specific capacity. The second type is represented by conversion materials, e.g., oxides or sulfides of transition metals. They provide for accumulating more energy, but their operation results in complete rebuilding of their structure causing significant changes in volume and facilitation the deterioration of electrode. The third type – drift-woods, such as silicon or tin forming alloys with the ions of alkali metals. They provide for record-high capacity, but lead to colossal (up to 300%) increase in volume, hence, quick loss of productivity. Conversion and alloyed anodes also feature a pronounced voltage hysteresis – the difference between charge and discharge, which leads to losing up to one-fourth of the energy in the form of heat dissipation.
The researchers proposed a solution on the nano-level. They used MXene as the conducting and mechanically solid base, and they placed ultra-small particles of germanium sulfide on its surface. Such a design prevents adhesion and agglomeration of active particles during the charge-discharge cycling operation. MXene is a conductive matrix and an amortizing structure accepting mechanical strain, while as germanium sulfide provides for high capacity by combining the conversion-based and the alloy-based operation mechanisms.
The tests showed impressive results. The new anodic material was exclusively stable even under extremely high speed of charging. When the charge density was increased 30 times, the capacity loss made less than 15%. Under currents above 1 A/g, the GeSₓ/MXene composite significantly outperformed the analogues based on graphene oxide confirming the efficiency of MXene as conductive matrix.
Alexei Mikhailov, one of the authors of the research, a senior fellow of the Institute of General and Inorganic Chemistry, noted that the key success factor was the method of synthetizing using surfactants, which allowed for controlling the size of the particles and for preventing their agglomeration. The combination of high electrical conductivity of MXene and high capacity of germanium sulfide provided for a strong synergy effect making the new composite a very high-potential solution for the next generation of batteries.
Thus, the study of Russian and Israeli scientists became an important step in developing alternative technologies for energy accumulation, which may successfully compete in the future with lithium-ion batteries.
