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Lithium-sulfur (Li-S) batteries are a highly promising next-generation high-energy battery due to their advantages such as high energy density (2600 Wh kg–1), abundant crustal reserves, low cost, and low toxicity. However, the insulating nature of the sulfur cathode and the dissolution of lithium polysulfides (LiPSs) in the electrolyte during the reaction process lead to irreversible capacity loss, known as the shuttle effect, which severely hinders the practical application of Li-S batteries. Therefore, designing functionalized separators to effectively suppress LiPSs shuttling, promote electron/ion transport, accelerate sulfur conversion, and ultimately improve sulfur utilization and cycling stability is particularly important.
Recently, Prof. Xiangting Dong from Changchun University of Science and Technology and Lecturer Bin Yue from Tonghua Normal University published their latest research, titled "Interlayer of Lithium-Ion-Sieving Spodumene Nanosheets Coupled with Co-Loaded CNFs Enables High-Performance Li-S Batteries", in the Q1 journal *Advanced Functional Materials*. The researchers proposed a novel strategy using a facile electrospinning technique to fabricate uniquely functionalized spodumene-cobalt heterostructure carbon nanofibers (Spd-Co-CNFs) as an interlayer to suppress the LiPSs shuttle effect and enhance the reaction kinetics of Li-S batteries. Spodumene (Spd) nanosheets, as a two-dimensional layered material, provide abundant Li+ channels that selectively facilitate Li+ transport while blocking larger LiPSs molecules, exhibiting excellent Li+ sieving functionality. The carbon nanofibers offer ample electron transport pathways, thereby reducing the internal resistance of the battery and improving sulfur utilization. Additionally, the cobalt-loaded carbon fiber surface effectively adsorbs LiPSs and catalyzes the conversion of long-chain LiPSs into short-chain Li2S2 and Li2S. Consequently, the dual strategy of suppressing the shuttle effect and enhancing redox reaction kinetics through the ingeniously designed interlayer significantly improves the performance of Li-S batteries.
Figure 1:Morphological and structural characteristics of Spd-Co-CNFs, Spd-CNFs, and Co-CNFs: (a-c) SEM images of the three materials; (d) size distribution of cobalt-loaded carbon nanofibers and spodumene nanosheets in Spd-Co-CNFs; (e) HAADF-SEM image of Spd-Co-CNFs and EDS elemental mapping of C, Co, Al, Si, and O; (f-h) TEM and HRTEM images of Spd-Co-CNFs.
After detailed characterization tests of the modified material, the successful construction of the Spd-Co heterostructure was confirmed.
Figure 2: (a-c) Symmetric cell test curves, (d-f) Li2S deposition test curves, (g-i) Li2S dissolution test curves, and (j-l) GITT test curves for batteries assembled with different modified separators.
Figure 3: (a) Cycling performance of Li-S batteries assembled with different separators at 0.2 C; (b-d) charge/discharge curves of Li-S batteries assembled with Spd-Co-CNFs/PP, Spd-CNFs/PP, and Co-CNFs/PP separators at 0.2 C; (e) in-situ EIS tests at different potentials during charge/discharge; (f) in-situ EIS spectra of Li-S batteries assembled with Spd-Co-CNFs/PP, Spd-CNFs/PP, and Co-CNFs/PP separators.
Figure 4:(a) Rate performance of Li-S batteries assembled with different separators; (b-d) charge/discharge curves of Li-S batteries assembled with Spd-Co-CNFs/PP, Spd-CNFs/PP, and Co-CNFs/PP separators at different current densities; (e) C2/C1 ratios of Li-S batteries assembled with different separators at various current densities; cycling performance of Li-S batteries assembled with different separators at (f) 1 C, (g) 2 C, and (h) 4 C current densities.
In electrochemical performance tests, the Spd-Co-CNFs material demonstrated superior catalytic effects on polysulfides. Moreover, Li-S batteries assembled with this modified separator exhibited excellent electrochemical performance.
Figure 5: DFT calculations of (a) differential charge density, (b) density of states, (c) adsorption energies for different polysulfides, (d) site analysis of Spd-Co adsorption for different polysulfides, and (e) Gibbs free energy changes for polysulfide conversion reactions on different catalysts.
Figure 6: (a) Lithium-ion diffusion pathways in spodumene, (b) comparison of lattice dimensions between spodumene and LiPSs molecules, (c) schematic of the mechanism by which Spd-Co-CNFs/PP suppresses the polysulfide shuttle effect.
To analyze the catalytic conversion effect of the Spd-Co heterostructure on polysulfides, DFT theoretical calculations were performed to determine the Gibbs free energy changes of polysulfide conversion reactions at different catalyst interfaces. The results showed that the Spd-Co heterostructure surface required the lowest energy barrier (0.99 eV) for polysulfide conversion reactions, effectively catalyzing the process. Furthermore, spodumene nanosheets, as a lithium-ion sieve, possess abundant lithium-ion diffusion pathways, allowing rapid lithium-ion transport while blocking polysulfide shuttling.
Paper link: [https://doi.org/10.1002/adfm.202502945](https://doi.org/10.1002/adfm.202502945)
