A team of engineers from Monash University have developed a new lithium-sulphur battery design with a nanoporous polymer-coated lithium foil anode, which has reduced the amount of lithium required in a single battery.
Manufacturers’ Monthly spoke to PhD candidate and lead researcher Declan McNamara to find out more about the significance of their new battery design and the potential applications of the technology.
Connventional lithium-ion batteries, typically found in electric vehicles, smart phones, and some house-hold appliances, require materials such as lithium, nickel, manganese, and cobalt. All these materials can only be extracted through mining, while pivotal, can still be damaging to the environment.
As consumers move towards more sustainable modes of transportation and greater use of batteries generally, the demand for these critical minerals will continue to increase.
McNamara said that manufacturers should be open to adopting technologies that contain less lithium.
“The amount that we have, versus the amount that we can access in the near future is limited,” he detailed.
“Reducing lithium is definitely a good prospect as it will be cheaper and there are societal and environmental impacts from using it.”
Not only does their lithium-sulphur battery design require less lithium to manufacture compared to other lithium-sulphur batteries, but it also does not require any nickel, manganese, or cobalt.
The design process
The team initially conceptualised the battery design while working on an entirely different scientific project.
“Our group does a lot of work in a bunch of different areas, but the thing that links them all together is porous materials and separations,” McNamara said.
The idea occurred to the team while using polymer that had been used previously in gas separation membranes.
“We thought, gases are functionally fluid – in our battery, we’ve also got a fluid. We understood the properties of this polymer quite well and we thought that it could work inside of a battery,” McNamara explained.
“In terms of processing, we had this idea that we wanted to make a solution that would be scalable.”
The polymer coating on lithium significantly improved the number of times their battery design could be cycled.
“The polymer contains tiny holes less than a nanometre in size – one billionth of a metre – which allow lithium ions to move freely while blocking other chemicals that would attack the lithium,” McNamara said.
“The coating also acts as a scaffold for lithium, and helps it charge and discharge repeatedly.”
“Utilising the huge amount of energy stored in metallic lithium is a challenge, but when done correctly it can make some incredible energy storage devices that are easier to make. This coating is a step towards highly efficient, easily manufactured Lithium Sulphur batteries,” McNamara continued.
According to the 2023 Western Australia battery and critical minerals profile, Lithium mines from around the globe produced around 130,000 tonnes of material in 2022, with Australia producing almost half of that at 55,000 tonnes.
Compared to 2010’s 28,100 tonnes, there has been a significant increase of lithium production in the past decade.
The team from Monash University is determined to provide a more sustainable alternative to the current lithium-ion battery.
“The first and probably most important thing for me is environmental sustainability,” said McNamara.
“The main benefit of lithium sulphur batteries is that there is no need for traditional battery materials. In current batteries, lithium-ion batteries that we use day-to-day, the cathode is comprised of nickel, manganese, and cobalt in varying concentrations.”
“Those three elements are not fantastic, acquiring them is a problematic process at the best of times.
“The processing of nickel has substantial environmental impacts, and then the processing of the ore, the leaching is awful for the environment, for cobalt, the same is true,” McNamara continued.
Cobalt production alone is expected to produce up-to three million tonnes of carbon dioxide emissions annually by 2030.
The team from Monash University are also determined to address the ethical dilemma of sourcing cobalt.
“Most of the cobalt that’s used is sourced from the Democratic Republic of the Congo,” McNamara said.
“There are some serious ethical concerns about the way the cobalt obtained.”
According to the Cobalt Institute, 70 per cent of the world’s cobalt is produced in the Democratic Republic of the Congo.
Twenty per cent of that cobalt is sourced from artisanal miners or small-scale mining operations.
These, sometimes informal, operations are commonly associated with low levels of safety measures, healthcare, or environmental protection.
Unlike, conventional batteries, the cathode in Monash’s new design requires only carbon and sulphur to be manufactured – which McNamara says are also environmentally benign, materials.
“Using sulphur, which is ubiquitous, so it’s in the Earth’s crust, all over the world means that we won’t be as reliant on these critical minerals,” McNamara continued.
Alternative sources of lithium
Typical methods of lithium mining involve either extracting minerals such as spodumene, lepidolite, petalite, amblygonite, and eucryptite from the earth, or brine reservoirs.
“The majority of lithium that has been sourced at the moment comes from brines in countries such as Chile and Argentina,” McNamara said.
“Currently lithium supply is split between Australia with hard rock, and South America with brines” McNamara said.
“It’s quite a long process, what will happen is there’ll be water that has a very high salt concentration and it’s placed into enormous baths hundreds of metres, sometimes kilometres long, and left out in the sun to evaporate.”
“The water evaporates, the other metals first form crystals, and then finally we’re left with the lithium in a crystal form – this process can take up to two years, depending on the size of the reservoir,” McNamara explained.
This method often comes at the cost of the local populations water security, where communities near lithium mines will often face water scarcity.
Each tonne of lithium requires around two million litres of water to be evaporated.
The San Cristóbal Mine in Bolivia, uses around 50,000 litres of water per day.
The process of converting lithium crystals to battery grade chemicals is also very carbon intensive.
Apart from processing spodumene, the team is also considering sourcing lithium from the sea, as well as from brackish waters or brines using membranes instead of chemical processes.
While these alternative sources are financially viable and environmentally sustainable relative to conventional methods, there are still significant time constraints with processing.
This is a challenge that the team will address later in the future.
“Getting it out quick enough might be a problem, but it’s an active area of research,” said McNamara.
Throughout the design process, the Monash team encountered several challenges, which was always expected but still required a great deal of work to rectify.
“There were a bunch of variables that we needed to kind of dial in,” McNamara said.
One of the primary challenges was coating the lithium with the correct amount of polymer, which in-turn effected how the battery would cycle.
“If the layer was too thick, then the cells would become too resistive.”
When the cell becomes too resistive, the batteries efficiency declines.
“Getting the right concentration was pretty difficult, because if it was too low, then you
would also get a phenomenon called shrinkage.” McNamara said.
“Shrinkage is where you have a polymer that is dissolved into a solvent in a solution. When it dries out, as a total fraction of the initial mixture, the higher the proportion of the solvent, the more total mass is lost, causing the polymer to shrink.”
With all batteries containing nickel, cobalt or manganese, there is always a risk of thermal runaway – where the internal temperature of batteries will rise, risking the possibility of fires or explosions.
“Once they start heating up above a certain temperature they enter a feedback loop,” McNamara said.
Current research suggests that lithium sulphur batteries have improved safety.
“Research suggests that overcharging or over discharging will brick the battery,” continued McNamara.
“The battery will not be happy about it, and it probably won’t work very well, but it likely won’t cause a catastrophic failure in the same way that a lithium-ion battery will. This is another area we are actively investigating.”