Lithium sulphur batteries to be billion-dollar industry

Lithium-sulphur batteries are batteries with lithium metal anodes and sulphur cathodes and feature a high gravimetric energy density, says IDTechEx technology analyst Daniel Parr.

He says lithium-sulphur has also been noted for potential cost reductions due to the abundance of sulphur, as well as enhanced safety due to its non-reactivity.

“Lithium-sulfur (sulphur) is already seeing development across multiple continents and is expected to achieve mass production by 2033,” Parr says.

IDTechEx predicts in its report Lithium Metal Batteries 2025-2035: Technology, Players and Forecasts that by 2035 the lithium-sulphur market will exceed US$1.3 billion.

While lithium-sulphur has seen development efforts in the past the chemistry has been limited as a result of an intrinsic degradation method known as “polysulfide shuttle”. Polysulphides of the form Li2Sx are produced in the cathode and shuttle into the electrolyte, effectively leaching active materials away, says Parr.

These polysulphides can also reach the anode and begin a cycle of their own redox reactions, which reduces the effective redox potential of the cell, he says.

 Polysulphides can also form an insoluble layer of Li2S at the anode, preventing ion transport.

”The overall effect of polysulfide shuttle is to significantly reduce the coulombic efficiency of the cell, severely impacting battery lifetime,” says Parr.

“Lithium metal dendrite formation is also an issue, though it tends to be less significant than polysulfide shuttle.

“Lithium dendrites form at the anode and leach into the electrolyte, irreversibly reacting such that the active material of the cell is reduced. In addition, during charging and discharging, the sulfur (sulphur) cathode experiences significant swelling – as much as 80% during discharging. This places considerable pressure on the architecture of the cathode and potentially reduces the contact conductivity of the cell overall through the formation and nucleation of cracks.”

Parr says polysulphide shuttle can be counteracted in several ways.

“The most obvious approach may be to use a solid electrolyte, as this prevents polysulfides from shuttling. However, this can lead to significantly reduced conductivity at the interface between electrolyte and cathode, as sulfur (sulphur) is already a poor conductor.

“Alternative liquid electrolytes are a more compelling option. Polysulfides are soluble in incumbent liquid electrolytes used in graphite-anode lithium-ion. However, there are other solutions in which polysulfides are not soluble, cyclic ethers, short-chain ethers and glycol ethers.”

Alternatively, a separator layer/membrane may be used to prevent polysulphide shuttle, says Parr, adding the chosen membrane must be selective, allowing lithium-ions to pass but not polysulphides.

He says three ways may be used.

“Charge repulsion: utilising the fact that polysulfides are negative and lithium ions are positive.

“Shielding: physically blocking ions from directly contacting active materials, preventing polysulfide leaching (using carbon nanotubes). As polysulfides are much larger than lithium ions, they can be selectively blocked.

“Adsorption: trapping polysulfides in the cathode using polysulfide-attracting materials. Micropores may be used for this method.”

Cathode expansion can be solved using alternative cathode structures, such as.expansion tolerant lattices or stronger binders, says Parr.

“Alternative materials may allow for the development of single-material structures without binders, which significantly enhances the rigidity of the current collector. An example is sulfurised polyacrylonitrile or SPAN.”

Lithium-sulphur has seen interest from major players, especially LG Chem, however they have since fallen quiet, Parr says.

“Now, the industry is dominated by start-ups on the cusp of commercialisation.”

These include Lyten which aims to commercialise for aviation and maritime applications by the end of 2025 and already has plans for a gigafactory, he says.

Theion is a German start-up developing sulphur cathodes formed from a pure sulphur wafer grown directly from molten sulphur.

“The technology remains in the development stage, however the company is exploiting a battery testing AI platform to significantly reduce time-to-market,” says Parr.

Li-S Energy is an Australian company working on lithium-sulphur which uses boron nitride nanotubes (BNNTs) to form its cathode structure, says Parr.

“This allows for enhanced strength and conductivity. Li-S recently completed construction of a 2MWh pouch-cell production facility.”

Parr reckons lithium-sulphur’s higher specific energy but lower energy density make it particularly suitable for applications in aviation, defence and maritime, especially unmanned aerial vehicles (UAVs) or drones with the chemistry also expected to see some deployment in EVs, especially heavy-duty ones.

IDTechEx predicts that by 2035 more than 14GWh will be produced globally.