Synthesis and characterization of cathode materials for lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries have attracted considerable interest as next-generation high-density energy storage devices. However, their practical applications are limited due to rapid capacity fading when cycling cells with high mass loading levels. The combination of lithium and sulfur as the active materials in these batteries offers several advantages over traditional lithium-ion batteries. One of the key benefits of Li-S batteries is their high energy density, which allows them to store more energy per unit mass compared to other battery technologies. This makes them particularly attractive for electric vehicles and portable electronic devices where maximizing energy storage capacity is crucial. Another advantage of Li-S batteries is their low cost. Sulfur is an abundant and inexpensive element, making it a cost-effective choice for large-scale battery production. Additionally, the absence of expensive transition metals in Li-S batteries further contributes to their affordability. Furthermore, Li-S batteries exhibit improved safety characteristics compared to conventional lithium-ion batteries. The use of sulfur as the cathode material reduces the risk of thermal runaway reactions, which can lead to battery fires or explosions. This enhanced safety profile makes Li-S batteries a promising option for applications that prioritize safety, such as aerospace devices. One major issue is the shuttle effect, where polysulfide intermediates formed during the discharge process migrate between the cathode and anode, resulting in capacity loss and reduced cycle life. Researchers are actively working on developing strategies to mitigate this effect and improve the overall performance of Li-S batteries.<br /> <br /> This work provides a detailed study of composites of sulfur/ferroelectric nanoparticles/holey graphene (S/FNPs/hG) cathodes were fabricated for high-mass-loading S cathodes. The solvent-free and binder-free procedure is enabled using holey graphene as a unique dry-pressable electrode for Li-S batteries. The unique structure of the holey graphene framework ensures fast electron and ion transport within the electrode and affords enough space to mitigate the electrode's volume expansion. Moreover, ferroelectric polarization due to FNPs within S/hG composites induces an internal electric field, which effectively reduces the undesired shuttling effect. With these advantages, the S/FNPs/hG composite cathodes exhibit sustainable and ultrahigh specific capacity up to 1409 mAh/gs for the S/ BTO/hG cathode. A capacity retention value of 90% was obtained for the S/BNTFN/hG battery up to cycle 18. The high mass loading of sulfur ranging from 5.72 to 7.01 mgs/cm² allows maximum high areal capacity up to &sim;10 mAh/cm² for the S/BTO/hG battery and superior rate capability at 0.2 and 0.5 mA/cm². These results suggest sustainable and high-yielding Li-S batteries can be obtained for potential commercial applications.<br /> <br /> In additional, this work is the impact of the incorporation of ferroelectric nanoparticles (FNPs), such as BaTiO3 (BTO), BiFeO₃ (BFO), Bi₄NdTi₃Fe_0.7Ni_0.3O₁₅ (BNTFN), and Bi₄NdTi₃Fe_0.5Co_0.5O₁₅ (BNTFC), as well as the mass loading of sulfur to fabricated solvent-free sulfur/holey graphene-carbon black/polyvinylidene fluoride (S/FNPs/CBhG/PVDF) composite electrodes to achieve high areal capacity for Li-S batteries. The dry-press method was adopted to fabricate composite cathodes. The hG, a conductive and lightweight scaffold derived from graphene, served as a matrix to host sulfur and FNPs for the fabrication of solvent-free composites. Raman spectra confirmed the dominant hG framework for all the composites, with strong D, G, and 2D bands. The surface morphology of the fabricated cathode system showed a homogeneous distribution of FNPs throughout the composites, confirmed by the EDAX spectra. The observed Li+ ion diffusion coefficient for the composite cathode started at 2.17&times;10^&minus;16 cm²/s (S₂₅(CBhG)₆₅PVDF₁₀) and reached up to the highest value (4.15&times;10^&minus;15 cm²/s) for S₂₅BNTFC₅(CBhG)₆₀PVDF₁₀. The best discharge capacity values for the S₂₅(CBhG)₆₅PVDF₁₀ and S₂₅BNTFC₅(CBhG)₆₀PVDF₁₀ composites started at 1123 mAh/gs and 1509 mAh/gs and dropped to 612 mAh/gs and 572 mAh/gs, respectively, after 100 cycles; similar behavior was exhibited by the other composites that were among the best. These are better values than those previously reported in the literature. The incorporation of ferroelectric nanoparticles in the cathodes of Li-S batteries reduced the rapid formation of polysulfides due to their internal electric fields. The areal capacity for the S₂₅(CBhG)₆₅PVDF₁₀ composites was 4.84 mAh/cm² with a mass loading of 4.31 mgs/cm², while that for the S₂₅BNTFC₅(CBhG)₆₀PVDF₁₀ composites was 6.74 mAh/cm² with a mass loading of 4.46 mgs/cm². It was confirmed that effective FNPs incorporation within the S cathode improves the cycling response and stability of cathodes, enabling the high performance of Li-S batteries.