Research Article Cite This: ACS Appl. Mater. Interfaces 2018, 10, 21254−21261
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Highly Conductive and Robust Three-Dimensional Host with Excellent Alkali Metal Infiltration Boosts Ultrastable Lithium and Sodium Metal Anodes Wan-Sheng Xiong,† Yu Xia,† Yun Jiang,† Yuyang Qi,† Weiwei Sun,‡ Dan He,† Yumin Liu,*,† and Xing-Zhong Zhao†,§
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†
Institute for Interdisciplinary Research (IIR), Key Laboratory of Optoelectronic Chemical Materials and Devices, Ministry of Education, Jianghan University, Wuhan 430056, China ‡ College of Aerospace Science and Engineering, National University of Defence Technology, Changsha 410073, China § School of Physics and Technology, Key Laboratory of Artificial Micro/Nano Structures, Ministry of Education, Wuhan University, Wuhan 430072, China S Supporting Information *
ABSTRACT: The direct utilization of metallic lithium and sodium as the anodes for rechargeable batteries would be highly advantageous, which has been considered as one of the most promising choices for next-generation high-energydensity storage devices. Although the induced safety concerns, inferior rate, and cycling performance severely hinder the commercialization of lithium metal batteries (LMBs) and sodium metal batteries (SMBs), the recent development of nanotechnology-based solutions really revives the lithium/ sodium metal anodes for high-energy batteries. In this work, an ultrastable carbon textile (CT)-based host with excellent infiltration for both metallic Li and Na has been designed and exhibits more flat voltage profiles, lower stripping/plating overpotential, and better cycling stability both in symmetric cell and full cell configurations, even in additive-free carbonate-based electrolyte compared with pure Li/Na electrodes. The highly conductive and mechanically robust three-dimensional CTs not only offer a stable scaffold against hyperactive lithium and sodium but also enable uniform nucleation and growth during stripping/plating process, which effectively suppress the dendrite growth and stabilize the electrode dimension. This facile strategy provides new insights into the design of stable hosts with prestored alkali metal to address the multifaceted issues in LMBs and SMBs simultaneously. KEYWORDS: carbon textiles, alkali metal infiltration, stable host, lithium metal anodes, sodium metal anodes
1. INTRODUCTION
anodes have been plagued for decades with the problems of dendritic Li formation, severe side reactions, and infinite relative volume change since the pioneering work by Whittingham in the 1970s.9−12 To overcome these formidable challenges of LMBs, increasing efforts have been devoted recently, such as electrolyte optimization for stabilizing Li anodes,13−18 artificial engineering of the anode−electrolyte interfaces,19−27 and employing the stable hosts for high-reactive metallic Li.28−32 On the other hand, concerning over potentially rising costs and the availability of global lithium resources, metallic sodium could be another ideal choice for anode material because of its low cost and high natural abundance. Owing to the high reactivity of alkali metal, sodium
To meet the ever-increasing demand of modern life to highenergy-density storage systems for electric vehicles, portable electronic devices, grid-scale energy storage, and other applications, the rechargeable batteries beyond the conventional “rocking-chair-based” lithium-ion or sodium-ion chemistry have attracted intensive research,1−6 which are of great scientific and technological importance. Li metal has been considered as one of the most promising anode materials attributed to its high theoretical capacity (3860 mA h g−1), lowest density (0.59 g cm−3), and most negative electrochemical potential (−3.040 V vs standard hydrogen electrode).7 Furthermore, the utilization of metallic Li as the anode remarkably promotes the energy density of lithium metal batteries (LMBs) with the employment of Li-free cathodes such as sulfur and oxygen, achieving high specific energy density of 2567 and 3505 W h kg−1, respectively.8 However, the Li metal © 2018 American Chemical Society
Received: March 2, 2018 Accepted: May 24, 2018 Published: May 24, 2018 21254
DOI: 10.1021/acsami.8b03572 ACS Appl. Mater. Interfaces 2018, 10, 21254−21261
Research Article
ACS Applied Materials & Interfaces
Figure 1. (a) Schematic illustration of the fabrication of Li/Na-infiltrated 3D SCTs. (b) Surface pictures of pure CTs and 3D SCTs before and after Li/Na infiltration. FE-SEM images of (c−e) Li-3D SCTs, (f−h) 3D SCTs, and (i−k) Na-3D SCTs.
scalable facile approach to afford lithiophilicity of the hosts. Furthermore, despite the differences in electrolyte composites and electrochemical kinetics for LMBs and SMBs, the development of stable hosts with prestored metallic Li/Na could be a universal strategy to facilitate the practical application of metallic Li/Na-based high-energy-density storage systems. Herein, we demonstrate a general strategy to construct a metallic Li- or Na-infiltrated three-dimensional (3D) scaffold via scalable oxide deposition that offers the primary infiltration for both Li and Na (Figure 1a). Carbon textiles (CTs) were employed as the host material for metallic Li or Na on account of the considerations including excellent stability, highly conductive bicontinuous networks, and robust flexibility. First, carbon-based hosts exhibit outstanding mechanical and chemical stabilization under the redox environment in rechargeable batteries, which is essential for the current collection toward electrochemical stripping and plating cycles. Second, the highly conductive carbon fiber-based 3D networks provide fast electron/ion transport pathway and achieve relatively large surface area for alkali metal deposition, reducing the effective current density and homogenizing the Li/Na ion flux. Furthermore, the CTs woven by carbon fibers with high flexibility (Figure S1a−c) are the ideal choice as unique supporting backbones for the infiltration of alkali metal. This robust scaffold affords the volume stability at the electrode
metal batteries (SMBs) and LMBs suffered from almost the same obstacles mentioned above. Nevertheless, in contrast to recent rapid development of LMBs, there are a handful of studies on room-temperature SMBs. Among all viable strategies, the employment of stable host materials, prestored metallic Li, is an effective approach to address these multifaceted issues. The introduction of stable hosts can minimize the infinite relative volume change during stripping/plating process, which is also a benefit to the solid electrolyte interphase (SEI) stability. In addition, the stable SEI avoids the danger of collapse during continuous cycling and the local formation of Li dendrite. More importantly, the designed and optimized stable hosts afford the opportunity to reduce the large polarization and strong electric field at the vicinity of the Li/Na metal anodes, which further suppress the dendrite growth.33 Recently, a layered composite of Li/reduced graphene oxide was fabricated, achieving a stable cycling performance, low polarization, and small electrode dimensional change.28 The Li-coated lithiophilic conductive scaffold or polymer matrix also exhibited good cyclability and minimal volume variation.29,31 Notably, excellent lithiophilicity is essential to the hosts for the infiltration of molten Li. In previous work, atomic layer deposition and chemical vapor deposition technology have been employed to obtain a thin and conformal lithiophilic layer.29,31 This process is complex and increases the cost. Thus, it is of great importance to develop a 21255
DOI: 10.1021/acsami.8b03572 ACS Appl. Mater. Interfaces 2018, 10, 21254−21261
Research Article
ACS Applied Materials & Interfaces
Li-3D SCT cells were cycled between 2.5 and 4.1 V under different current rates (x C = fully discharge within 1/x h) at room temperature.
level to stabilize the electrode dimension, which effectively avoids the danger of SEI collapse and the local formation of Li/ Na dendrites during continuous cycling. Notably, our highly conductive and robust 3D scaffold with the infiltration for both Li and Na achieved long-term reversibility of Li/Na metal anodes in additive-free carbonate-based liquid electrolytes, which provides new insights into the design of stable hosts with alkali metal infiltration for high-performance LMBs and SMBs.
3. RESULTS AND DISCUSSION Owing to the large surface tension of molten Li and Na on the carbon fibers, the pristine 3D CTs cannot be well-wetted by molten Li and Na as shown in Figure 1b. Thus, an ultrathin SnO2 layer was first coated on the carbon fiber surface via a scalable CBD approach, considering eco-efficiency, synthetic process, and scalability, to afford the infiltration for both Li and Na (Figure 1b). FE-SEM was employed to characterize the morphology of the obtained SnO2 nanocrystallines on the surfaces of the CTs. Figure 1f shows a well-established texture structure of the obtained 3D SCTs. The high-magnification SEM image (Figure 1g) reveals that the ultrathin SnO2 nanocrystallines were homogenously deposited on the surface of the carbon fibers. The cross-sectional SEM image further indicated the evident core−shell structure of 3D SCTs (Figure 1h). The crystalline phase of as-synthesized 3D SCTs before and after annealing was determined by XRD as shown in Figure S1e. All diffraction peaks observed at the XRD pattern can be indexed to the tetragonal SnO2 phase (JCPDS card no. 211250), excluding the peaks at ca. 25.7° and 43.6° associated with the (002) and the (101) planes of the CTs (JCPDS card no. 01-0640), respectively. HR-TEM analysis was carried out to further investigate the morphology and structure of the SnO2 nanocrystallines. Figure S2a indicates that the crystal size of the obtained ultrathin SnO2 nanocrystallines was less than 10 nm, and the neighboring lattice fringes with a distance of 3.36 Å can be corresponded to the (110) planes of the tetragonal SnO2 phase (Figure S2b), which confirmed the XRD results. Figure S1d demonstrates that the ultrathin SnO2 nanocrystallines can be homogenously deposited on the surface of CTs on a large scale via this facile CBD approach to afford the wetting property for molten Li and Na. After the contact of the 3D SCT pieces with molten Li, the molten Li could react with this ultrathin SnO2 layer and provide high driving force to infiltrate Li into the scaffold. The final obtained Li-3D SCTs with metallic luster still maintained the texture structure (Figure 1b). Figure 1c,d shows the SEM topview of the Li-3D SCTs. The molten Li was fully infused into the highly ordered 3D carbon fiber-based conductive scaffold, and the size of the SnO2 nanocrystallines turns larger owing to the spontaneous reaction between SnO2 and molten Li (Figure 1d, inset). Figure 1e shows the cross-sectional SEM images of Li-3D SCTs, which further indicates the full infiltration of molten Li into the carbon fiber-based matrix. Most impressively, this 3D SCTs also exhibited good wetting property for molten Na, which has not been reported in previous work. The full infiltration of molten Na into 3D SCTs needed more time than that of Li, and the Na-3D SCTs were more twinkling than Li-3D SCTs, as shown in Figure 1b. The surface of the obtained Na-3D SCTs was more uneven than that of Li-3D SCTs, as shown in Figure 1i,j, which could be attributed to the more reactivity of metallic Na than that of Li. Evident infiltration of molten Na into 3D SCTs was also observed from the cross-sectional SEM image (Figure 1k). To further indicate the existence of metallic Li in the 3D SCTs, XRD was employed to characterize the obtained Li-3D SCTs. The main diffraction peaks of the XRD spectra can be indexed to lithium (JCPDS 01-1131), as shown in Figure S3a. The other impurity peaks could be attributed to the formation of LixSn alloy. Owing to the hyperactivity of metallic Na in air,
2. EXPERIMENTAL SECTION 2.1. Scalable Oxide Deposition on 3D CTs. CTs (CeTech WOS1002, through-plane resistance
