Scientists in Russia led by the Skolkovo Institute of Technology in Moscow (Skoltech) have added another innovation to the already lengthy list of potential alternatives to lithium-ion batteries by demonstrating a potassium-ion battery they say combines the high storage capacity of a metal-ion device with the fast charging capability of a supercapacitor.
The researchers began by working with an organic polymer material containing fragments of hexaazatriphenylene. “Versatility is one of the key advantages of organic materials,” said 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 [the material] with … cheaper sodium or potassium that will never run out. As for inorganic materials, things are a lot more complicated.”
The group found the material suitable for lithium, sodium and potassium battery chemistries and said it allowed for fast charging batteries which retained their capacity over thousands of cycles. However, according to a paper published in the Journal of Materials Chemistry A, the cathodes have a low operating potential in comparison to potassium, resulting in limited energy storage capacity.
Second cathode attempt
As a result, the group moved on to another organic cathode material, this one based on the dihydrophenazine polymer. “Aromatic polymer amines can make excellent high-voltage organic cathodes for metal-ion batteries,” said Skoltech Ph.D. Philipp Obrezkov. “In our study, we used poly-N-phenyl-5,10-dihydrophenazine in the potassium battery cathode for the first time.”
That led the group to develop a battery – described in a second paper, published in The Journal of Physical Chemistry Letters – which achieved specific energy of 593 Wh/kg, a figure Obrezkov claims is a record high value for all known potassium-ion battery cathodes.
The group then combined the cathode with potassium-sodium alloy applied on carbon paper, as an anode. With that combination they were able to create a battery which again offered strong energy capacity performance, losing only 11% after 10,000 cycles. The device, described in a third paper, in Chemical Communications, also demonstrated power of almost 100,000 W/kg, which the group claims is a level typically only seen with supercapacitors.
“We showed that electroactive organic materials can pave the way for a new generation of electrochemical energy storage devices combining the advantages of metal-ion batteries and supercapacitors,” said group leader and Skoltech associate professor Pavel Troshin, “thus eliminating the need for costly transition metal compounds and lithium.”