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Abstract The development of practical lithium–sulfur (Li–S) batteries with prolonged cycle life and high Coulombic efficiency is limited by both parasitic reactions from dissolved polysulfides and mossy lithium deposition. To address these challenges, here lithium trithiocarbonate (Li2CS3)‐coated lithium sulfide (Li2S) is employed as a dual‐function cathode material to improve the cycling performance of Li–S batteries. Interestingly, at the cathode, Li2CS3forms an oligomer‐structured layer on the surface to suppress polysulfide shuttle. The presence of Li2CS3alters the conventional sulfur reaction pathway, which is supported by material characterization and density functional theory calculation. At the anode, a stable in situ solid electrolyte interphase layer with a lower Li‐ion diffusion barrier is formed on the Li‐metal surface to engender enhanced lithium plating/stripping performance upon cycling. Consequently, the obtained anode‐free full cells with Li2CS3exhibit a superior capacity retention of 51% over 125 cycles, whereas conventional Li2S cells retain only 26%. This study demonstrates that Li2CS3inclusion is an efficient strategy for designing high‐energy‐density Li–S batteries with extended cycle life.
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A wet-processed, binder-free sulfur cathode integrated with a dual-functional separator for flexible Li–S batteries
Developing flexible, robust and lightweight sulfur cathodes by rationally designing their structures and configurations through a viable and scalable strategy is a critical enabler for fulfilling flexible lithium–sulfur (Li–S) batteries. However, besides the requirements for cathode flexibility, intrinsic limitations from the shuttling of lithium polysulfides and the growth of Li dendrites have restricted the widespread implementations of Li–S batteries. Here, we report a wet-processed strategy by dissolving and recrystallizing S in a suitable solvent to fabricate a flexible, binder-free S cathode. Integrating the resulting S cathode with a dual-functional separator has demonstrated to be able to suppress both the shuttle effect and growth of dendritic Li. The wet-processed strategy not only enables the fabrication of flexible and binder-free S-nanomat cathodes, but also facilitates the deposition of the cathodes on the separators. Meanwhile, a dual-functional separator is fabricated by vapor-phase polymerization of polypyrrole (PPy) coating on both surfaces of the commercial separator, which leads to the reduction of the shuttle effect and the suppression of the growth of dendritic Li simultaneously. As a result, by integrating the S-nanomat and the dual-functional separator, the cathode exhibits exceptional mechanical properties and electrochemical performance. Li–S pouch cells are further demonstrated to show stable cycling performance in the bending state, indicating the feasibility of the integrated S cathode for flexible Li–S batteries.
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- Award ID(s):
- 1929236
- PAR ID:
- 10191473
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 12
- Issue:
- 9
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 5483 to 5493
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Conventional lithium-ion batteries are unable to meet the increasing demands for high-energy storage systems, because of their limited theoretical capacity. 1 In recent years, intensive attention has been paid to enhancing battery energy storage capability to satisfy the increasing energy demand in modern society and reduce the average energy capacity cost. Among the candidates for next generation high energy storage systems, the lithium sulfur battery is especially attractive because of its high theoretical specific energy (around 2600 W h kg-1) and potential cost reduction. In addition, sulfur is a cost effective and environmentally friendly material due to its abundance and low-toxicity. 2 Despite all of these advantages, the practical application of lithium sulfur batteries to date has been hindered by a series of obstacles, including low active material loading, poor cycle life, and sluggish sulfur conversion kinetics. 3 Achieving high mass loading cathode in the traditional 2D planar thick electrode has been challenged. The high distorsion of the traditional planar thick electrodes for ion/electron transfer leads to the limited utilization of active materials and high resistance, which eventually results in restricted energy density and accelerated electrode failure. 4 Furthermore, of the electrolyte to pores in the cathode and utilization ratio of active materials. Catalysts such as MnO 2 and Co dopants were employed to accelerate the sulfur conversion reaction during the charge and discharge process. 5 However, catalysts based on transition metals suffer from poor electronic conductivity. Other catalysts such as transition metal dopants are also limited due to the increased process complexities. . In addition, the severe shuttle effects in Li-S batteries may lead to fast failures of the battery. Constructing a protection layer on the separator for limiting the transmission of soluble polysulfides is considered an effective way to eliminate the shuttle phenomenon. However, the soluble sulfides still can largely dissolve around the cathode side causing the sluggish reaction condition for sulfur conversion. 5 To mitigate the issues above, herein we demonstrate a novel sulfur electrode design strategy enabled by additive manufacturing and oxidative vapor deposition (oCVD). Specifically, the electrode is strategically designed into a hierarchal hollow structure via stereolithography technique to increase sulfur usage. The active material concentration loaded to the battery cathode is controlled precisely during 3D printing by adjusting the number of printed layers. Owing to its freedom in geometry and structure, the suggested design is expected to improve the Li ions and electron transport rate considerably, and hence, the battery power density. The printed cathode is sintered at 700 °C at N 2 atmosphere to achieve carbonization of the cathode during which intrinsic carbon defects (e.g., pentagon carbon) as catalytic defect sites are in-situ generated on the cathode. The intrinsic carbon defects equipped with adequate electronic conductivity. The sintered 3D cathode is then transferred to the oCVD chamber for depositing a thin PEDOT layer as a protection layer to restrict dissolutions of sulfur compounds in the cathode. Density functional theory calculation reveals the electronic state variance between the structures with and without defects, the structure with defects demonstrates the higher kinetic condition for sulfur conversion. To further identify the favorable reaction dynamic process, the in-situ XRD is used to characterize the transformation between soluble and insoluble polysulfides, which is the main barrier in the charge and discharge process of Li-S batteries. The results show the oCVD coated 3D printed sulfur cathode exhibits a much higher kinetic process for sulfur conversion, which benefits from the highly tailored hierarchal hollow structure and the defects engineering on the cathode. Further, the oCVD coated 3D printed sulfur cathode also demonstrates higher stability during long cycling enabled by the oCVD PEDOT protection layer, which is verified by an absorption energy calculation of polysulfides at PEDOT. Such modeling and analysis help to elucidate the fundamental mechanisms that govern cathode performance and degradation in Li-S batteries. The current study also provides design strategies for the sulfur cathode as well as selection approaches to novel battery systems. References: Bhargav, A., (2020). Lithium-Sulfur Batteries: Attaining the Critical Metrics. Joule 4 , 285-291. Chung, S.-H., (2018). Progress on the Critical Parameters for Lithium–Sulfur Batteries to be Practically Viable. Advanced Functional Materials 28 , 1801188. Peng, H.-J.,(2017). Review on High-Loading and High-Energy Lithium–Sulfur Batteries. Advanced Energy Materials 7 , 1700260. Chu, T., (2021). 3D printing‐enabled advanced electrode architecture design. Carbon Energy 3 , 424-439. Shi, Z., (2021). Defect Engineering for Expediting Li–S Chemistry: Strategies, Mechanisms, and Perspectives. Advanced Energy Materials 11 . Figure 1more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9NR10966H
