Design and Engineering of Advanced Cathode Hosts for Lithium-Sulfur Batteries

Abstract

[eng] Lithium-sulfur batteries (LSBs) are regarded as the most promising candidate to replace Lithium-ion batteries (LIBs) in next-generation energy storage systems. Compared with LIBs, LSBs are characterized by a sixfold higher theoretical energy density, and a potentially lower cost and environmental impact for commercialization. Despite these attractive advantages, the electrically insulating character of sulfur/Li2S and the shuttle effect of lithium polysulfides (LiPS) greatly limit the practical application of LSBs. Additionally, the serious volume changes (∼80%) and slow redox kinetics during the charging/discharging process also reduce the cycling life and power density. The rational design and engineering of the cathode host can effectively overcome the above challenges. In Chapter 1, I summarize the state of the art on advanced hosts for LSBs and detail the targeted requirements from three points of view: material, architecture, and heterogeneous interface. In Chapter 2, I detail my work on the design and engineering of u-NCSe nanostructures as efficient sulfur hosts to overcome the limitations of LSBs. u-NCSe provide a beneficial hollow structure to relieve volumetric expansion, a superior electrical conductivity to improve electron transfer, a high polarity to promote adsorption of LiPS, and outstanding electrocatalytic activity to accelerate LiPS conversion kinetics, which were confirmed by experiments and theoretical calculation. Owing to these excellent qualities as LSB cathode, S@u-NCSe electrodes delivered outstanding rate performance of 626 mAh g−1 at 5 C, and a very low capacity decay rate of only 0.016% per cycle during cycling. This work probed that transition metal selenides can be promising candidates as sulfur host, and was published in Advanced Functional Materials in 2019. In Chapter 3, I explain my work on the design and production of multifunctional Ag/VN@Co/NCNTs nanocomposite with multiple adsorption and catalytic sites within hierarchical nanoreactors as a robust sulfur host for LSB cathodes. In this hierarchical nanoreactor, heterostructured Ag/VN nanorods serve as a highly conductive backbone structure and provide internal adsorption and catalytic sites for LiPS conversion. Interconnected NCNTs in situ grown from the Ag/VN surface, greatly improve the overall specific surface area for sulfur dispersion and accommodate volume change in the reaction process. Owing to their high LiPS adsorption ability, outer Co nanoparticles at the top of the NCNTs catch escaped LiPS, thus effectively suppressing the shuttle effect and enhancing kinetics. Benefiting from the multiple adsorption and catalytic sites of the developed hierarchical nanoreactors, Ag/VN@Co/NCNTs@S cathodes display outstanding electrochemical performances, including a superior rate performance of 609.7 mAh g−1 at 4 C and good stability with a capacity decay of 0.018% per cycle after 2000 cycles at 2 C. This work demonstrated the great advantages of designing the host architecture, and it was published in ACS Nano in 2021. In Chapter 4, in view of the complexity and difficulty in the synthesis of superlattice materials, I detail a simple solution-based method to efficiently produce organic-inorganic PVP-WSe2 superlattices and demonstrate that the pyrolysis of the PVP compound enables to continuously adjust their interlayer space in the range from 10.4 Å to 21 Å, resulting in NG/WSe2 superlattices with superior electrical conductivities. Both experimental results and theoretical calculations further demonstrate that NG/WSe2 superlattices are excellent sulfur hosts for LSB, being able to effectively reduce the LiPS shuttle effect by dual-adsorption sites and accelerating the sluggish Li-S reaction kinetics. Consequently, S@NG/WSe2 electrodes delivered high sulfur usages, superior rate performance, and outstanding cycling stability. Overall, this work not only establishes a cost-effective strategy to produce artificial superlattices but also pioneers their application in the field of LSBs. This work has been published in Advanced Functional Materials in 2022.

[spa] Lithium-sulfur batteries (LSBs) are regarded as the most promising candidate to replace Lithium-ion batteries (LIBs) in next-generation energy storage systems. Compared with LIBs, LSBs are characterized by a sixfold higher theoretical energy density, and a potentially lower cost and environmental impact for commercialization. Despite these attractive advantages, the electrically insulating character of sulfur/Li2S and the shuttle effect of lithium polysulfides (LiPS) greatly limit the practical application of LSBs. Additionally, the serious volume changes (∼80%) and slow redox kinetics during the charging/discharging process also reduce the cycling life and power density. The rational design and engineering of the cathode host can effectively overcome the above challenges. In Chapter 1, I summarize the state of the art on advanced hosts for LSBs and detail the targeted requirements from three points of view: material, architecture, and heterogeneous interface. In Chapter 2, I detail my work on the design and engineering of u-NCSe nanostructures as efficient sulfur hosts to overcome the limitations of LSBs. u-NCSe provide a beneficial hollow structure to relieve volumetric expansion, a superior electrical conductivity to improve electron transfer, a high polarity to promote adsorption of LiPS, and outstanding electrocatalytic activity to accelerate LiPS conversion kinetics, which were confirmed by experiments and theoretical calculation. Owing to these excellent qualities as LSB cathode, S@u-NCSe electrodes delivered outstanding rate performance of 626 mAh g−1 at 5 C, and a very low capacity decay rate of only 0.016% per cycle during cycling. This work probed that transition metal selenides can be promising candidates as sulfur host, and was published in Advanced Functional Materials in 2019. In Chapter 3, I explain my work on the design and production of multifunctional Ag/VN@Co/NCNTs nanocomposite with multiple adsorption and catalytic sites within hierarchical nanoreactors as a robust sulfur host for LSB cathodes. In this hierarchical nanoreactor, heterostructured Ag/VN nanorods serve as a highly conductive backbone structure and provide internal adsorption and catalytic sites for LiPS conversion. Interconnected NCNTs in situ grown from the Ag/VN surface, greatly improve the overall specific surface area for sulfur dispersion and accommodate volume change in the reaction process. Owing to their high LiPS adsorption ability, outer Co nanoparticles at the top of the NCNTs catch escaped LiPS, thus effectively suppressing the shuttle effect and enhancing kinetics. Benefiting from the multiple adsorption and catalytic sites of the developed hierarchical nanoreactors, Ag/VN@Co/NCNTs@S cathodes display outstanding electrochemical performances, including a superior rate performance of 609.7 mAh g−1 at 4 C and good stability with a capacity decay of 0.018% per cycle after 2000 cycles at 2 C. This work demonstrated the great advantages of designing the host architecture, and it was published in ACS Nano in 2021. In Chapter 4, in view of the complexity and difficulty in the synthesis of superlattice materials, I detail a simple solution-based method to efficiently produce organic-inorganic PVP-WSe2 superlattices and demonstrate that the pyrolysis of the PVP compound enables to continuously adjust their interlayer space in the range from 10.4 Å to 21 Å, resulting in NG/WSe2 superlattices with superior electrical conductivities. Both experimental results and theoretical calculations further demonstrate that NG/WSe2 superlattices are excellent sulfur hosts for LSB, being able to effectively reduce the LiPS shuttle effect by dual-adsorption sites and accelerating the sluggish Li-S reaction kinetics. Consequently, S@NG/WSe2 electrodes delivered high sulfur usages, superior rate performance, and outstanding cycling stability. Overall, this work not only establishes a cost-effective strategy to produce artificial superlattices but also pioneers their application in the field of LSBs. This work has been published in Advanced Functional Materials in 2022.