In a recently published report, “Lithium Metal Batteries 2025-2035: Technologies, Players, and Forecasts,” market analyst firm IDTechEx predicts that the lithium-sulfur market will exceed $1.3
billio by 2035. Lithium-sulfur batteries are batteries that use a lithium metal negative electrode and a sulfur positive electrode. These batteries have high energy density by weight, but their
volumetric energy density is limited due to the high sulfur content required for the positive electrode. Lithium-sulfur batteries also have the potential advantage of reduced cost due to abundant
sulfur reserves and improved safety due to the non-reactive nature of sulfur. Lithium-sulfur batteries have been developed on several continents and are expected to be in mass production by 2033.
Lithium-sulfur batteries have been heavily developed in the past. However, their inherent degradation mode - polysulfide shuttling - has led to limitations in their chemistry.
Polysulfides in the form of Li2Sx are generated in the positive electrode and shuttle into the electrolyte, effectively filtering out the active material. These polysulfides can also reach the negative
electrode and begin their own cycle of redox reactions, thereby lowering the effective redox potential of the battery.
The polysulfides also form an insoluble Li2S layer at the negative electrode, hindering ion transport. The overall effect of polysulfide shuttling is to significantly reduce the Coulombic efficiency of
the battery, severely affecting battery life.
The formation of lithium metal dendrites is also a problem, although its effects tend to be less severe than in polysulfide shuttle batteries. Lithium dendrites form at the anode and penetrate into
the electrolyte, where they undergo an irreversible reaction that results in the reduction of the battery's active material.
In addition, the sulfur cathode expands significantly during charging and discharging - as much as 80% during discharge. This puts considerable stress on the cathode structure and may reduce
the overall contact conductivity of the battery through crack formation and nucleation.
Polysulfide shuttling can be counteracted in a number of ways. Probably the most obvious method is to use a solid electrolyte, as this prevents polysulfide shuttling. However, since sulfur itself
is a poor conductor, this can lead to a significant decrease in conductivity at the electrolyte-positive interface. Alternative liquid electrolytes are a more attractive option.
Polysulfides are soluble in the liquid electrolytes currently used in graphite anode lithium ion batteries. However, there are some polysulfides that are insoluble in other solutions, such as cyclic
ethers, short chain ethers, and glycol ethers.
Alternatively, a diaphragm/spacer can be used to stop the polysulfide shuttle. The selected diaphragm must be selective, allowing lithium ions to pass, but not polysulfides.
The cathode swelling problem can be solved by alternative cathode structures, such as a lattice that is resistant to swelling or a stronger binder. Alternative materials can be developed in a single
material structure that does not contain a binder, thereby significantly increasing the rigidity of the collector. Sulfurized polyacrylonitrile (SPAN) is an example.
Lithium-sulfur batteries have a high specific energy but low energy density, making them particularly suitable for aerospace, defense and maritime applications, especially unmanned aerial vehicles
(UAVs). However, it is expected that this chemistry will also find applications in electric vehicles, particularly heavy-duty electric vehicles.IDTechEx predicts that global production of lithium-sulfur
batteries will exceed 14 GWh by 2035.
（The article is sourced from the internet）
