Electrochemical Energy Reviews

Structural Design of Lithium-Sulfur Batteries: From Fundamental Research to Practical Application

Xiaofei Yang, Xia Li, Keegan Adair, Huamin Zhang, Xueliang Sun

2018, 1(3): 239-293. doi:10.1007/s41918-018-0010-3

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Lithium-sulfur (Li-S) batteries have been considered as one of the most promising energy storage devices that have the potential to deliver energy densities that supersede that of state-of-the-art lithium ion batteries. Due to their high theoretical energy density and cost-efectiveness, Li-S batteries have received great attention and have made great progress in the last few years. However, the insurmountable gap between fundamental research and practical application is still a major stumbling block that has hindered the commercialization of Li-S batteries. This review provides insight from an engineering point of view to discuss the reasonable structural design and parameters for the application of Li-S batteries. Firstly, a systematic analysis of various parameters (sulfur loading, electrolyte/sulfur (E/S) ratio, discharge capacity, discharge voltage, Li excess percentage, sulfur content, etc.) that infuence the gravimetric energy density, volumetric energy density and cost is investigated. Through comparing and analyzing the statistical information collected from recent Li-S publications to fnd the shortcomings of Li-S technology, we supply potential strategies aimed at addressing the major issues that are still needed to be overcome. Finally, potential future directions and prospects in the engineering of Li-S batteries are discussed.

Full-text：https://link.springer.com/article/10.1007/s41918-018-0010-3

Recent Advances in Sodium-Ion Battery Materials

Yongjin Fang, Lifen Xiao, Zhongxue Chen, Xinping Ai, Yuliang Cao, Hanxi Yang

2018, 1(3): 294-323. doi:10.1007/s41918-018-0008-x

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Grid-scale energy storage systems with low-cost and high-performance electrodes are needed to meet the requirements of sustainable energy systems. Due to the wide abundance and low cost of sodium resources and their similar electrochemistry to the established lithium-ion batteries, sodium-ion batteries (SIBs) have attracted considerable interest as ideal candidates for grid-scale energy storage systems. In the past decade, though tremendous eforts have been made to promote the development of SIBs, and signifcant advances have been achieved, further improvements are still required in terms of energy/power density and long cyclic stability for commercialization. In this review, the latest progress in electrode materials for SIBs, including a variety of promising cathodes and anodes, is briefy summarized. Besides, the sodium storage mechanisms, endeavors on electrochemical property enhancements, structural and compositional optimizations, challenges and perspectives of the electrode materials for SIBs are discussed. Though enormous challenges may lie ahead, we believe that through intensive research eforts, sodium-ion batteries with low operation cost and longevity will be commercialized for large-scale energy storage application in the near future.

Full-text：https://link.springer.com/article/10.1007/s41918-018-0008-x

Core-Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

Rongfang Wang, Hui Wang, Fan Luo, Shijun Liao

2018, 1(3): 324-387. doi:10.1007/s41918-018-0013-0

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Pt-based catalysts are the most efcient catalysts for low-temperature fuel cells. However, commercialization is impeded by prohibitively high costs and scarcity. One of the most efective strategies to reduce Pt loading is to deposit a monolayer or a few layers of Pt over other metal cores to form core-shell-structured electrocatalysts. In core-shell-structured electrocatalysts, the compositions of the core can be divided into fve classes:single-precious metallic cores represented by Pd, Ru, and Au; singlenon-precious metallic cores represented by Cu, Ni, Co, and Fe; alloy cores containing 3d, 4d or 5d metals; and carbide and nitride cores. Of these, researchers have found that carbide and nitride cores can yield tremendous advantages over alloy cores in terms of cost and promotional activities of Pt shells. In addition, desirable shells with reasonable thicknesses and compositions have been recognized to play a dominant role in electrocatalytic performances. And recently, researchers have also found that the catalytic activity of core-shell-structured catalysts is dependent on the binding energy of the adsorbents, which is determined by the d-band center of Pt. The shifting of this d-band center in turn is mainly afected by strain and electronic efects, which can be adjusted by adjusting core compositions and shell thicknesses of catalysts. In the development of these core-shell structures, optimal synthesis methods are of primary concern because they directly determine the practical application potential of the resulting electrocatalysts. And in this article, the principles behind core-shell-structured low-Pt electrocatalysts and the developmental progresses of various synthesis methods along with the traits of each type of core and its efects on Pt shell catalytic activities are discussed. In addition, perspectives on this type of catalyst are discussed and future research directions are proposed.

Full-text：https://link.springer.com/article/10.1007/s41918-018-0013-0

Toward Better Lithium-Sulfur Batteries: Functional Non-aqueous Liquid Electrolytes

Shizhao Xiong, Michael Regula, Donghai Wang, Jiangxuan Song

2018, 1(3): 388-402. doi:10.1007/s41918-018-0015-y

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Having been extensively studied in the past fve decades, lithium-sulfur (Li-S) batteries possess a high theoretical energy density (~2600 Wh kg^-1), ofering the potential to power advanced twenty-frst-century technologies such as electric vehicles and drones. However, a surprisingly complex engineering challenge remains in the application of these batteries:the identifcation of appropriate electrolytes that are compatible with both sulfur cathodes and lithium metal anodes. Non-aqueous liquid electrolytes, typically consisting of a lithium salt dissolved in an organic solvent, cannot themselves demonstrate efective electrochemical performances. Researchers have found that functional electrolytes ofer unique possibilities to engineer the surface chemistries of sulfur cathodes and lithium anodes to enable long-term cycling. In this article, recent progresses in the development of functional non-aqueous liquid electrolytes in Li-S batteries are reviewed, including novel co-solvent solutions, lithium salts, additives, redox mediators, and ionic liquids. Characterization techniques and interpretations are cited to elucidate the efects of these components on the kinetics of sulfur redox reactions, lithium passivation, and cell performance. The information presented and the studies highlighted in this review will provide guidance for future optimized electrolyte designs.

Full-text：https://link.springer.com/article/10.1007/s41918-018-0015-y

Multifunctionality of Carbon-based Frameworks in Lithium Sulfur Batteries

Tianyu Tang, Yanglong Hou

2018, 1(3): 403-432. doi:10.1007/s41918-018-0016-x

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Compared with conventional lithium ion batteries (LIBs), lithium sulfur (Li-S) batteries possess advantages such as higher theoretical energy densities and better cost efciencies, making them promising next-generation energy storage systems. However, the commercialization of Li-S batteries is impeded by several drawbacks, including low cycling stabilities, limited sulfur utilizations, existing shuttle efects of polysulfde intermediates, serious safety concerns, as well as inferior cycling performances of lithium metal anodes. To address these issues, researchers have achieved rapid developments for sulfur cathodes and increased their attention to lithium metal anodes to facilitate the widespread application of Li-S batteries. And among the substrate materials for electrodes in Li-S batteries being developed, carbon-based materials have been especially promising because of their multifunctionality, demonstrating great potential for application in advanced energy storage and conversion systems. In this review, recent advancements of carbon-based frameworks applied to Li-S batteries will be summarized and diverse utilization methods of these carbon-based materials for both sulfur cathodes and lithium metal anodes will be provided. Future research directions and the prospects of Li-S batteries with high performance and practicability will also be discussed.

Full-text：https://link.springer.com/article/10.1007/s41918-018-0016-x

In Situ and Surface-Enhanced Raman Spectroscopy Study of Electrode Materials in Solid Oxide Fuel Cells

Xiaxi Li, Kevin Blinn, Dongchang Chen, Meilin Liu

2018, 1(3): 433-459. doi:10.1007/s41918-018-0017-9

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Solid oxide fuel cells (SOFCs) represent next-generation energy sources with high energy conversion efciencies, low pollutant emissions, good fexibility with a wide variety of fuels, and excellent modularity suitable for distributed power generation. As an electrochemical energy conversion device, the SOFC's performance and reliability depend sensitively on the catalytic activity and stability of electrode materials. To date, however, the development of electrode materials and microstructures is still based largely on trial-and-error methods because of the inadequate understanding of electrode process mechanisms. Therefore, the identifcation of key descriptors/properties for electrode materials or functional heterogeneous interfaces, especially under in situ/operando conditions, may provide guidance for the design of optimal electrode materials and microstructures. Here, Raman spectroscopy is ideally suited for the probing and mapping of chemical species present on electrode surfaces under operating conditions. And to boost the sensitivity toward electrode surface species, the surfaceenhanced Raman spectroscopy (SERS) technique can be employed, in which thermally robust SERS probes (e.g., Ag@SiO₂ core-shell nanoparticles) are designed to make in situ/operando analysis possible. This review summarizes recent progresses in the investigation of SOFC electrode materials through Raman spectroscopic techniques, including topics of early stage carbon deposition (coking), coking-resistant anode modifcation, sulfur poisoning, and cathode degradation. In addition, future perspectives for utilizing the in situ/operando SERS for investigations of other electrochemical surfaces and interfaces are also discussed.

Full-text：https://link.springer.com/article/10.1007/s41918-018-0017-9

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