Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
A Superior Sodium/Lithium-Ion Storage Material: Sea Sponge C/Sn2Fe@GO Weixi Yan,†,§ Qingnan Wu,‡,§ Ming Wen,*,† Shipei Chen,† Qingsheng Wu,† and Nicola Pinna∥ †
Shanghai Key Laboratory of Chemical Assessment and Sustainability, School of Chemical Science and Engineering, Tongji University, Shanghai 200092, China ‡ College of Plant Protection, Henan Agricultural University, Zhengzhou 450002, China ∥ Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, Berlin 12489, Germany
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ABSTRACT: A well-structured anode nanomaterial, which can ensure electron and ion transport and avoid excessive pulverization, is of crucial importance to achieve high capacity with superior cycling stability for both sodium- and lithium-ion batteries (SIBs and LIBs). For the purpose of a superior rate performance, this work here has designed and successfully synthesized a new Na+/Li+ storage nanomaterial of SCS/ Sn2Fe@GO through loading of a Sn2Fe nanoalloy on sea-sponge-like carbon spheres (SCSs), followed by a graphene oxide (GO) wrapping process. In such a designed composite, the SCS skeleton ensures electronic conductivity and shorts Na+ and Li+ diffusion pathways, while the Sn2Fe nanoalloy delivers a high capacity and prevents excessive pulverization. The GO shell around SCS/Sn2Fe greatly enhances the cyclability. Used as an anode, the SCS/Sn2Fe@GO nanocomposite enables a high capacity up to 660 mAh g−1 at 50 mA g−1, which is maintained without decay up to 800 cycles in SIBs, and up to 850 mAh g−1 at 500 mA g−1 after 3500 cycles in LIBs, proving its applicability in new-generation SIBs and LIBs. theoretical capacity (685 mAh g−1 vs Na/Na+ and 804 mAh g−1 vs Li/Li+) and the nontoxicity of Fe.18,19 However, the capacity cycling stability is still less than satisfactory because of the aggregation of NPs. We herein have proposed a new strategy to cope with the above drawback through the loading of Sn2Fe NPs onto a stable skeleton of sea-sponge-like carbon spheres (SCSs) and then wrappin with graphene oxide (GO). This strategy has three advantages that allow one to achieve the desired performance as an anode electrode material in both SIBs and LIBs. The first advantage is due to the nanostructure of the SCSs: this kind of stable porous carbon skeleton with an abundant interconnected pore network is beneficial to the penetration of the liquid electrolyte and the electronic conductivity; meanwhile, it offers a large specific surface area to load active Sn2Fe NPs and avoids agglomeration, and the remaining pore volumes can cope with volume expansion of the electroactive materials during charging. The second advantage is due to the composition of the nanoalloy: the introduction of inert Fe into Sn to form Sn2Fe NPs can lead to a reduced volume expansion and maintain a similar theoretical specific capacity at the same time, because SnFe NPs on SCSs can expose lots of active sites for the electrochemical reactions. The third advantage is brought about by the wrapped shell of
1. INTRODUCTION The development of new-generation materials for sodium/ lithium-ion batteries (SIBs and LIBs) has involved tremendous efforts in the past decade. Because SIBs are of low cost and environmentally benign, they are promising for energy storage in grid harvesting from renewable energy sources.1−5 On the other hand, LIBs have become the most important power source for portable electronic devices and electric vehicles.6−8 For their high capacity and excellent cycling stability, wellstructured nanocomposites play a crucial role in ensuring the transport of electrons and Na+/Li+ ions while avoiding excessive expansion and pulverization of the electrode materials.9,10 Recently, Sn-based nanoalloys have become a family of important anode materials with good rate capability and safe thermodynamic potentials for both SIBs and LIBs because Sn exhibits a relatively high capacity (993 mAh g−1/7313 mAh cm−3) compared to commercialized graphite (372 mAh g−1/ 883 mAh cm−3).11,12 In order to alleviate the mechanical pulverization caused by the volume change during Na+ or Li+ insertion and extraction processes, some efforts have been focused on the synthesis of SnM (M = Fe, Cu, Co, Ni, etc.) nanoparticles (NPs) to avert excessive pulverization by employing a conductive inert metal, which acts as a framework to disperse the active metallic Sn.13−17 In particular, Sn2Fe is the best composition among SnM NPs because of its high © XXXX American Chemical Society
Received: March 3, 2019
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DOI: 10.1021/acs.inorgchem.9b00621 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Scheme 1. Schematic of the Sodiation/Lithiation and Desodiation/Delithiation Processes in a SCS/Sn2Fe@GO Nanostruture from a Simplified Two-Dimensional Cross-Sectional View
at 120 °C for 12 h, which gave rise to the APS-modified SCS/Sn2Fe nanocomposites. After the products were washed with toluene and dried overnight under vacuum at 60 °C, an aqueous dispersion (30 mL at 3 mg mL−1) of the APS-modified SCS/Sn2Fe composites was added into 30 mL of a GO aqueous dispersion (0.3 mg mL−1) under mild magnetic stirring. The mixture was stirred at room temperature for 1 h. The SCS/Sn2Fe@GO composites were obtained after centrifugation, washing with water, and finally drying in air at 60 °C. 2.4. Product Characterization. The morphology was measured by transmission electron microscopy (TEM; JEOL, JEM-2100EX) and field-emission scanning electron microscopy (FE-SEM, JEOL, S4800). Elemental analysis was conducted by energy-dispersive spectrometry (EDS; Oxford, TN-5400). The composite was characterized by X-ray diffraction (XRD; Bruker, D8 Advance) with a Cu Kα X-ray radiation source (λ = 0.154056 nm). X-ray photoelectron spectroscopy (XPS; PerkinElmer, PHI-5000C ESCA) with Al Kα radiation (hν = 1486.6 eV) was performed to determine the surface elemental composition. High-resolution and survey spectra (0−1400 eV) were recorded with a RBD 147 interface (RBD Enterprises, USA). Binding energies used C 1s at 284.6 eV as a reference, and data analysis was performed using the XPS Peak41. The thermal behavior and composition were tested by thermal gravimetric analysis (TGA; Netzsch, STA409PC) and differential scanning calorimetry (DSC; Netzsch, STA409PC). The specific surface area was carried out by adsorption isothermicity of nitrogen (Micromeritics, ASAP2020) at −196 °C based on the Brunauer− Emmett−Teller (BET) equation. Fourier transform infrared spectroscopy (FT-IR) was carried on with a FT-IR spectrometer (Thermo, NEXUS). 2.5. Electrode Preparation and Electrochemical Analyses. The working electrode was fabricated by mixing the SCS/Sn2Fe@GO powders, poly(vinylidene difluoride), and acetylene black at a weight ratio of 80:10:10 in N-methylpyrrolidone to obtain a homogeneous slurry. The slurry was cast onto copper foil (9 um) and dried under a vacuum oven at 100 °C for 12 h. A typical mass loading of 1.5−2.0 mg cm−2 was used for anode preparations. CR2025-type coin cells were fabricated inside a glovebox (filled with Ar gas, O2, and H2O content of
