Phosphorene as a promising anchoring material for lithium-sulfur batteries

(Nanowerk Spotlight) Lithium-sulfur (Li-S) batteries, which employ sulfur as cathode and metallic lithium as anode materials, have been extensively studied as promising alternatives to the widely used lithium-ion batteries because – theoretically – they can render 3-6 times higher energy density (2600 Wh kg -1 ).

In practice, though, it has proven challenging to approach that theoretical value. Specifically, the rapid capacity fading, low Coulombic efficiency, and irreversible loss of active materials have impeded large-scale commercial use of Li-S batteries.

Researchers now have shown that trapping lithium polysulfide (Li 2 S x ) species on (nanoscale) host materials is an effective way to overcome these challenges.

The team, led by Zhongfang Chen, a professor in the Department of Chemistry at the University of Puerto Rico, has reported their findings in Journal of Materials Chemistry A ("Phosphorene as a promising anchoring material for lithiumsulfur batteries: a computational study").

(a) The lowest-energy adsorption configurations of S 8 and Li 2 S x on the phosphorene surface, (b) the adsorption energies (Eads) and charge transfer (Q) from Li 2 S x to phosphorene at different lithiation stages. (© The Royal Society of Chemistry)

Phosphorene is a single atomic layer of black phosphorus that has recently garnered the attention of researchers due to its unique puckered structure, outstanding anisotropic physical and mechanism properties, and wide potential applications for the design of nanodevices.

"In our recent work, by means of density functional theory computations, we have explored the potential of phosphorene as a host material to anchor Li-S species," Chen tells Nanowerk. "According to our computations, all Li 2 S x species can moderately bind with phosphorene, exhibit ultrahigh diffusivity along the zigzag direction of phosphorene, and enhance the electrical conductivity of phosphorene."

The team's results indicate that the performance of Li-S species anchored on phosphorene is comparable to well-established host materials such as 2D metal sulfide materials.

"Our results showed that Li 2 S x species with long chains can be moderately adsorbed on the phosphorene surface with moderate binding strength, and their structures are well maintained, thus avoiding their dissolution into the electrolyte," explains Chen. "Due to the puckered structure, the diffusion of LiS x species with a longer chain length along the zigzag direction is highly favorable with a small energy barrier of 0.20 eV."

"Furthermore," he adds, "a certain amount of charge is transferred from Li 2 S x species to phosphorene, which accounts for the band gap reduction after the deposition of Li 2 S x species on phosphorene. Therefore, our theoretical results suggest that phosphorene is a highly promising anchoring material for high performance LiS batteries."

Chen's team will continue their efforts to develop low-dimensional nanostructures for stabilizing Li-S species, especially S 8 species.