The photo is sourced from img.7dach.ru
The sodium-ion batteries and the lithium-ion ones have the same operation principle: they store energy by transferring alkali metal ions from the anode material (the electrode, in which electrons move away from it) to the material of the cathode (the electrode, in which electrons move towards it). At the same time, the anodes of sodium-ion batteries use solid carbon, which can be produced from any biomass, including nut shells and paper waste. For the first time, the experiment participants used Sosnovsky’s hogweed for this purpose, an aggressive weed, which according to Skoltech, is able to overgrow the entire European part of Russia by the middle of the century.
The researchers at Skoltech and Moscow State University have synthesised solid carbon by heating hogweed biomass to 1,300 degrees Celsius in an oxygen-free atmosphere (including pre-washing of raw materials with acids to remove the impurities) as well as by boiling in a closed reactor with water. One of the criteria, by which the obtained solid carbon was evaluated was the Coulomb efficiency: the higher it is, the less energy is spent in the anode operation on side processes that increase the battery wear. This factor reached 87% during the experiment; this is comparable to the efficiency of solid carbon obtained from other types of raw materials. At the same time, in terms of specific capacity (260 mAh/g), solid carbon from hogweed was inferior to the leading materials (300 mAh/g), but still remained competitive.
“To be more precise, we have considered separately the winter hogweed, which is easier to collect, and the more harmful summer hogweed, which blooms and smells. But we must say that it was the summer samples, from which the material with a higher Coulomb efficiency was produced, and this factor is the weak point of solid carbon anodes. So, this is what we focused on in our study. As for the specific capacity, we will probably be able to improve it in the future,” Skoltech quotes in its release Zoya Bobyleva, a co-author of the study, an engineer at the Department of Chemistry at Lomonosov Moscow State University.
The experiment results may be used for further cost reduction of sodium-ion batteries which will be particularly in demand in the power industry where compactness plays a less important role than in the automotive industry.
