Promising Electrodes for Long-lasting Lithium-sulfur Batteries
Researchers explore different material combinations for long-lasting, high-performance lithium-sulfur batteries.
To reduce global carbon emissions, scientists are trying to develop alternative battery technologies that are safer, more sustainable, and energy-dense than lithium-ion batteries. Lithium-sulphur (Li-S) batteries, which are lighter, cheaper, and can store more energy than lithium-ion models, maybe the promising power cells for electric vehicles, energy grids, and electronic gadgets if scientists can increase the number of charging cycles they undergo before failing.
Lithium-ion batteries. Image used courtesy of Pixabay
The main attraction of Li-S batteries is that they can store more energy than lithium-ion technology, which means they can discharge longer on a single charge. These batteries use sulfur instead of cobalt, exhibiting very high specific energies on the order of 550 Wh/kg, while li-ion batteries offer around 150 to 260 Wh/kg.
Moreover, the atomic weight of sulfur is less than cobalt, resulting in lightweight cells. These batteries could also overcome some of the chemical limitations of Li-ion batteries. Besides, cobalt is also vulnerable to a fragile supply chain. On the other hand, sulfur is a cheap raw material readily available as a by-product of the oil industry.
Despite these advantages, Li-S batteries suffer from a major hold-up. They must be recharged more times before they fail. In other words, they have a short lifespan. One of the dominant reasons for this drawback is that Sulphur needs loading on a conducting host made of materials poorly coated by electrodes, which impedes the diffusion of lithium ions in the batteries and reduces the overall capacity and performance.
Researchers at the University of Cambridge and the Faraday Institution have recently developed a high-performance Li-S battery with nanosheets of lithiated metallic 1T phase molybdenum disulfide (LixMoS2). Their recent paper published in Nature Energy outlines this new material and how it leads to superior energy densities.
In simple terms, sulfur cathodes have low conductivity and therefore require an extra mass of conductive agent to be applied to take advantage of the active mass to the capacity. Zhuangnan Li, a Faraday Institution research fellow and one of the researchers who carried out the study, suggests that the key point of their design is to use the minimum amount of electrolyte while not disturbing the battery's normal operation. He points out that sulfur material must possess high electrical conductivity, density, wettability, and polarity for adsorption and catalytic activity.
Newly developed high-performance lithium-sulfur battery. Image used courtesy of the University of Cambridge
Metallic 1T Phase Molybdenum Disulphide Nanosheets as Electrode Materials
Previous studies by researchers at the University of Cambridge have shown that nanosheets made of MoS2, which contain a high concentration of the metallic 1T phase, can intercalate hydrogen, lithium, and other ions with extraordinary efficiency. Besides high conductivity, it is also shown that this material demonstrates high volumetric energy, power density values, coulombic efficiencies, and stability over thousands of cycles.
Researchers found that 1T phase MoS2 nanosheets improved the adsorption of lithium polysulfides, enhanced lithium-ion transport, accelerated electrochemical reaction kinetics, and superior electrocatalytic activity for polysulfide conversion. These benefits helped them to achieve an energy density of 441 Wh/kg and 735 Wh/l, with capacity retention of 85.2% after 200 cycles.
Researchers believe their design of Li-S cathodes will provide new insights for creating next-generation energy storage devices. They now plan to translate this development into commercially feasible battery technology.