Scientists develop superfast-charging, high-capacity potassium batteries
Skoltech researchers in collaboration with scientists from the Institute for Problems of Chemical Physics of RAS and the Ural Federal University have shown that high-capacity, high-power batteries can be made from organic materials without lithium or other rare elements. In addition, they demonstrated the impressive stability of cathode materials and recorded high energy density in fast charge/discharge potassium-based batteries. The results of their studies were published in the Journal of Materials Chemistry A, the Journal of Physical Chemistry Letters and Chemical Communications.
Lithium-ion batteries are widely used for energy storage, particularly in portable electronics. The demand for batteries is surging due to the rapid advancement of electric vehicles with high requirements for lithium. For example, Volvo intends to increase the share of electric vehicles to 50 percent of its overall sales by 2025, and Daimler announced its plans to give up internal combustion engines altogether, shifting the emphasis to electric vehicles.
However, mass use of lithium-ion batteries exacerbates the acute shortage of resources needed for their production. Transition metals commonly used in cathodes, such as cobalt, nickel and manganese, are fairly rare, expensive and toxic. While the most of the less-common lithium is produced by a handful of countries, the global supply of lithium is too meager to replace all conventional automobiles with electric vehicles powered by lithium batteries. As estimated by the German Research Center for Energy Economics (FFE), the scarcity of lithium reserves may become a major issue in coming decades. Recently, scientists have suggested looking at alternatives such as sodium and potassium, which are similar to lithium in chemical properties.
Skoltech researchers led by Professor Pavel Troshin have made significant advances in the development of sodium and potassium batteries based on organic cathode materials. Their research findings were reported in three publications in top international scientific journals.
Their first paper presents a polymer that contains hexaazatriphenylene fragments. The new material proved to be equally suitable for lithium, sodium and potassium batteries that charge in 30 to 60 seconds while retaining their energy storage capacity after thousands of charge-discharge cycles. “Versatility is one of the key advantages of organic materials,” explains the first author of the paper and Skoltech Ph.D. student Roman Kapaev. “Their redox mechanisms are much less specific to the nature of the counter-ion, which makes it easier to find an alternative to lithium-ion batteries. With lithium prices going up, it makes sense to replace it with the cheaper sodium or potassium that will never run out. As for inorganic materials, things are a lot more complicated.”
The downside is that the hexaazatriphenylene-based polymer cathodes have a low operating potential (about 1.6 V volts with respect to K+/K potential), which results in decreased energy storage capacity. In their second paper, the scientists proposed another material, a dihydrophenazine-based polymer that does not have this drawback and ensures an increase in the battery’s average operating voltage up to 3.6 volts.
“Aromatic polymer amines can make excellent high-voltage organic cathodes for metal-ion batteries. In our study, we used poly-N-phenyl-5,10-dihydrophenazine in the potassium battery cathode for the first time. By thoroughly optimizing the electrolyte, we obtained specific energy of 593 Wh/kg, a record-high value for all the currently known K-ion battery cathodes,” explains the first author of the study and Skoltech Ph.D. student Philipp Obrezkov.
