Race for potassium batteries hots up
Research aims to solve problems arising with potential lithium rival. Phil Dooley reports.
Battery technology based on potassium could be the key to storing energy from renewables, according to a team of scientists from Wollongong University in Australia.
Currently lithium ion batteries are widely used because of their high energy density, but, because lithium is a relatively rare element, mining costs make them expensive.
As an alternative, potassium, which is one of the Earth’s most abundant elements, could become the basis for a large-scale power storage, says Zaiping Guo, one of the authors of a review paper in the journal Science Advances.
“Potassium is a rechargeable with huge potential, and has theoretically cheaper performance compared with lithium,” she says.
The global market for lithium batteries was worth $25 billion in 2017, driven by technologies that require low-weight energy storage, such as electric cars and electronic devices.
Potassium batteries are unlikely to reach the same energy density, because it is a heavier atom than lithium. However, it may succeed as a stationary large-scale storage method, coupled to intermittent renewable energy sources.
“For a more sustainable society we need energy storage devices,” Guo says.
“Compared with other storage options, such as super-capacitors or fuel cells, batteries are the most mature and easy to apply.”
Even so, she estimates it will take 10 to 20 years before the potassium-based technology matures enough to close the gap on lithium.
One of the major obstacles in creating an efficient potassium battery is the sluggish movement of large potassium ions through a solid electrode.
Secondly, as the ions enter the electrode during the electrical reactions, their size causes the electrodes to swell, then shrink again as the reverse reaction occurs when the battery finishes charging and starts to discharge.
It’s a challenge to develop an electrode material that can survive such repeated size change, but the team points out that nanotechnology could provide answers.
Clusters of nanoparticles similar to bunches of grapes can withstand repeated size changes. Nanostructures with high surface areas could also remove the need for the potassium ions to penetrate far in to the electrode: various researchers have investigated structures with large surface areas.
The structures have names such as nanotubes, nanofibres and even nanoroses.
To complicate the situation, potassium is prone to other, less welcome reactions, which the nanomaterials can actually promote. However, careful choice of a material for the electrodes can help control these unwanted processes, for example by adding atoms of fluorine, oxygen, boron or sulfur to the carbon mix.
Unwanted reactions are also a problem in the electrolyte – the conductive solution that allows potassium ions to flow between the two electrodes. For example, the potassium can deposit into intricate tree-shaped crystals called dendrites, which can cause a short-circuit within the battery.
Guo points out that choice of solvent and use of additives can address these reactions. But it’s a balance, because the most effective solvents are organic, and therefore flammable. Alongside the tendency of potassium batteries to get hot, this is a safety issue that needs consideration.
The advent of powerful computer modeling will help solve such issues, say the authors. Although there a number of obstacles, they conclude that potassium battery technology is “emerging as a great candidate for large-scale energy storage”.