New hybrid carbon/sulfur cathode material enables high-energy, high-power Li-sulfur battery; “matching the level of engine-driven systems”
Researchers at Tsinghua University have combined two types of carbon materials to create a new composite sulfur cathode material for a high-energy and high-power lithium-sulfur battery. In a paper in the journal Advanced Functional Materials, they report the composite cathode (a hierarchical all-carbon nanostructure hybridized with small cyclo-S8 clusters) has a high specific capacity of 1121 mAh g−1 at 0.5 C; a favorable high-rate capability of 809 mAh g−1 at 10 C; a very low capacity decay of 0.12% per cycle; and cycling stability of 877 mAh g−1 after 150 cycles at 1 C.
As sulfur loading in the cathode increases from 50 wt% to 77 wt%, high capacities of 970, 914, and 613 mAh g−1 are available at current densities of 0.5, 1, and 5 C, respectively. Based on the total mass of packaged devices, gravimetric energy density of the cell consisting of the composite cathode and a lithium-metal anode (GSH@APC-S//Li) is expected to be 400 Wh kg−1 at a power density of 10 kW kg−1—“matching the level of engine-driven systems,” according to the team.
As often noted, the lithium-sulfur battery is one of the most promising candidates for next-generation energy storage because of its very high theoretical energy density of 2,600 Wh kg-1 (based on lithium-sulfur redox couple); wide operating temperature range benefiting from a unique multiple-electron-transfer chemistry; and the abundant reserves and environmental friendliness of sulfur.
However, well-known barriers to commercialization include the ultra-low electrical conductivity of sulfur and its lithiated products; huge volumetric changes during charge and discharge; and the shuttling mechanism of soluble intermediate polysulfides.
The new Tsinghua cathode material combines sp2-hybridized nanocarbon (e.g., carbon nanotubes (CNTs) and graphene) and nanostructured porous carbon. The former exhibits extraordinary mechanical strength and electrical conductivity but limited external accessible surface area and a small amount of pores, while the latter affords a huge surface area and abundant pore structures but very poor electrical conductance.
Combining the two creates a novel carbon nanoarchitecture with the advantages of each. The sp2 graphene/CNT interlinked networks give the composites good electrical conductivity and a robust framework, while the meso-/microporous carbon and the interlamellar compartment between the opposite graphene accommodate sulfur and the lithium polysulfides; provide accessibility for liquid electrolyte to the active material; and suppress the shuttle behavior due to the spacial confinement.
The team will present a paper on their work at the upcoming 17th International Meeting on Lithium Batteries in June in Como, Italy. Future work will explore the increase of sulfur loading, as well as the optimization of the structure of the cell.
Peng, H.-J., Huang, J.-Q., Zhao, M.-Q., Zhang, Q., Cheng, X.-B., Liu, X.-Y., Qian, W.-Z. and Wei, F. (2014), “Nanoarchitectured Graphene/CNT@Porous Carbon with Extraordinary Electrical Conductivity and Interconnected Micro/Mesopores for Lithium-Sulfur Batteries” Adv. Funct. Mater., 24: 2772–2781 doi: 10.1002/adfm.201303296
Peng, H.J. et al. (2014) “Hierarchical Nanostructured Carbon/Sulfur Hybrid Cathode for High-Performance Lithium-Sulfur Battery,” IMLB 17
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