Researchers at the Hong Kong University of Science and Technology have developed a high-capacity, long-life lithium-sulfur battery using a bi-functional cathode substrate for Li–S batteries made of well-distributed boron carbide nanoparticles decorated activated cotton fiber (B₄C-ACF).

Long-term cycling test results of Li–S battery with S/B₄C-ACF electrode at 1 C. Zhang et al.

… Li–S batteries have drawn much attention because of their extra-high theoretical energy density (2567 Wh kg^-1), cost-effectiveness and eco-friendliness. … However, before the commercialization of this technology, there are several challenging issues need to be addressed.

For example, the insulator nature of S₈ and the discharge product (Li₂S) lead to a low utilization of active materials and poor reaction kinetics. The shuttle effect resulting from soluble long-chain lithium polysulfides (LiPS_s) in organic electrolyte results in low coulombic efficiencies and severe capacity decay. Worse still, the relatively large volume expansion of sulfur after lithiation easily causes the continual volume variation in cathode during discharge/charge process and eventually pulverizes the whole cathode architecture.

… Herein, we fabricate a novel positive electrode substrate made of uniform B4C nanoparticles decorated activated cotton fibers (B₄C-ACF) for Li–S batteries by a catalyst-assisted fabrication method.

—Zhang et al.

The B₄C-ACF substrate exhibits an ultrahigh Brunauer-Emmett-Teller (BET) specific surface area of 224.51 m² g􏰀^-1 with plentiful mesopores. The B₄C nanoparticles serve as not only robust chemically anchoring sites to trap polysulfides, but also afford abundant active sites for efficient sulfur conversion reactions. The ACF network provides fast electron pathways for the conversion reactions and acts as the current collector.

In a paper in the Journal of Power Sources, the researchers report that their Li-S battery is able to to deliver an initial capacity of as high as 1415 mAh g⁻¹ at 0.1 C, and an extra-high reversible capacity of 928 mAh g⁻¹ at 3 C with an areal sulfur loading of 3.0 mg cm⁻².

The B₄C-ACF substrate enables the Li–S battery to stably cycle for 500 times with a retention capacity of as high as 988 mAh g^􏰀-1 at 0.5 C—four times higher than that of a battery with pure ACF substrate (192 mAh g􏰀^-1 after 500 cycles).

Furthermore, the B₄C-ACF substrate-based battery could be stably operated for 3,000 cycles with a high coulombic efficiency of 99.24% and a capacity decay rate of as low as 0.012% per cycle at 1 C. These results, said the researchers, demonstrate that the B₄C-ACF substrate holds great potential in realizing the mass production of advanced Li–S batteries.

Resources

• Ruihan Zhang, Cheng Chi, Maochun Wu, Ke Liu, Tianshou Zhao (2020) “A long-life Li–S battery enabled by a cathode made of well-distributed B4C nanoparticles decorated activated cotton fibers,” Journal of Power Sources, Volume 451, doi: 10.1016/j.jpowsour.2020.227751