Self-Supported FeCo2S4 Nanotube Arrays as Binder-Free Cathode

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Energy, Environmental, and Catalysis Applications

Self-Supported FeCo2S4 Nanotube Arrays as Binder-Free Cathode for Lithium-Sulfur Batteries Bingshu Guo, Sateesh Bandaru, Chunlong Dai, Hao Chen, Youquan Zhang, Qiuju Xu, Shu-Juan Bao, Mingyang Chen, and Maowen Xu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b16948 • Publication Date (Web): 27 Nov 2018 Downloaded from http://pubs.acs.org on November 27, 2018

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ACS Applied Materials & Interfaces

Self-Supported FeCo2S4 Nanotube Arrays as BinderFree Cathode for Lithium-Sulfur Batteries Bingshu Guo,†,‡,§ Sateesh Bandaru,†, # Chunlong Dai,‡,§ Hao Chen,‡,§ Youquan Zhang,‡,§ Qiuju Xu,‡,§ Shujuan Bao,‡,§ Mingyang Chen,*, # and Maowen Xu*,‡,§ ‡

Institute for Clean Energy & Advanced Materials, Faculty of Materials and Energy, Southwest

University, Chongqing 400715, PR China. §

Chongqing Key Laboratory for Advanced Materials and Technologies of Clean Energies,

Chongqing 400715, P.R. China # Beijing

Computational Science Research Center, Beijing 100193, China.

KEYWORDS: polar nanotube array, catalytic effect, chemical adsorption, binder-free, lithiumsulfur batteries

ABSTRACT: Inhibiting shuttle effect, buffering volume expansion and improving utilization of sulfur have been the three strategic points for developing a high-performance lithium-sulphur (LiS) battery. Driven by this background, a flexible sulfur host material composed of FeCo2S4 nanotube arrays grown on the surface of carbon cloth is designed for binder-free cathode of the

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Li-S battery through two-step hydrothermal methods. Among the rest, the interconnected carbon fiber skeleton of the composite electrode ensures the basic electrical conductivity, whereas the FeCo2S4 nanotube arrays not only boost the electron and electrolyte transfer but also inhibit the dissolution of polysulfide due to their strong chemical adsorption. Meanwhile, the hollow structures of those arrays can provide a large inner space to accommodate volume expansion of sulfur. More significantly, the developed composite electrode also reveals a catalytic action for accelerating the reaction kinetic of the Li-S battery. As a result, the FeCo2S4/CC@S electrode delivers a high discharge capacity of 1384 mA h g-1 at the current density of 0.1 C and simultaneously exhibits a stable Coulomb efficiency of about 98%.

1. INTRODUCTION In recent decades, the development of traditional rechargeable lithium-ion batteries (LIBs) relying on intercalation reactions has encountered some ineluctable hurdles, such as limited energy density, gradual depletion of lithium resources and the ever-rising costs.1,

2

It is considered

insufficient to satisfy the ever-growing demands of rapid developing electric vehicles, largescale energy storage devices and advanced portable electronics in the long term. Of all the potential candidates for next generation high-energy rechargeable batteries, such as metal-sulfur including Li, Na, K, Mg, and Al batteries, the lithium-sulfur (Li-S) batteries, employing naturally abundant sulfur as a cathode, have occupied overwhelming superiorities owning to its high theoretical capacity (1675 mA h g-1) and energy density (2600 Wh kg-1) alongside the low costs, nontoxicity and eco-friendliness.3 However, the practical application of the Li-S batteries is still being impeded by several intrinsic demerits, including: (1) the insulating nature of sulfur (5×10-30 S cm-1 at 25 ºC) and its lithiated products (Li2S/Li2S2) bring about low utilization of active species, and thus


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decrease the specific capacity of the cathode material; (2) the high solubility and notorious shuttle effect of intermediate polysulfides (Li2Sx, 2 ≤ x ≤ 8) in the electrolyte during circulation process lead to the loss of active species and eventually result in fast capacity fade and poor Coulombic efficiency; and (3) the huge volumetric expansion of sulfur (≈ 80%) upon lithiation always can cause the microstructural collapse of cathode materials, which in part accounts for the inferior cycle life of Li-S batteries and also raises safety concerns.4 To address aforementioned issues, extensive efforts and improvements have been put in during the past decades, including rational design of novel composite cathode materials, electrolytes, separators, anode protections and different cell structures, and so on.5 Among these approaches, encapsulating sulfur into nanometer-sized porous structure of the carbon matrix has already been proven effective, which usually can improve conductivity of cathode materials and increase utilization of the active material due to their superb electron pathways and 3D interconnected nature. 6, 7 But the "fly in the ointment" is that the above designs are impeded by the weak physical Van Der Waals adsorption between the conjugate nonpolar carbon substrates and polar Li2Sx. Instead of inhibiting the migration of polysulfide, this undesirable affinity impedes effective interfacial charge transfer and slows down the electrochemical reaction kinetics. 8 As a result, the prolonged cycling stability remains insufficient. Fortunately, studies in recent years has demonstrated that the some polar inorganic compounds, such as transitional-metal oxides (Fe2O3 and MnO2), 9, 10 sulfides (MoS2, WS2, CoS2),11-13 hydroxides (Co(OH)2, Ni(OH)2)14, 15 nitride (VN, Co4N, TiN)16-18 and carbides (Fe3C, Mo2C)

19, 20

with polar surfaces can be employed as sulfur

hosts to trap the polysulfide intermediates and thus enhance the cycling stability. Moreover, Nazar and Cui et al. successively proposed that some of these inorganic materials can accelerate the redox kinetics associated with polysulfide intermediates.21, 22 However, it cannot be denied that only if



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these inorganic materials have a hollow architecture, they would be able to provide a large enough cavity for both loading large amount of sulfur and accommodating its large volumetric expansion. Conseduquently, the shells of these hollow materials would be act as a dam during the electrochemical reaction to prevent a flooding of polysulfides once they are confined within the host. Therefore, benefit from these merits, a series of hollow host materials have been designed and synthesized. For instance, Co3S4 23 and Ni/Fe LDH 24 hollow polyhedrons, NiS@C-HS hollow spheres,

25

NiO-NiCo2O4 heterostructure@C hollow nanocages,

26

TiO@C hollow spheres,27

MnO2@Carbon Hollow Nanoboxes,28 Co9S829 and Co3S4 nanotubes 22 have been used as effective encapsulation materials to confine sulfur. In addition to the above improved strategies, the current collector is also a critical factor in enhancing the performance of Li-S batteries, which usually plays a role of transport of current. Compared with the traditional aluminum foil, direct growth of sulfur host onto the 3D current collector, such as carbon fiber cloth, and hollow carbon fiber foam,

34

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nickel foam,

31

carbon paper,

32

carbon nanotube foam33

is also a decent choice. On the one hand, the 3D cathodes can

avoid the uses of conductive additives and binders, which usually will become as “dead” sites and adverses to the exposure of active material, maximizing the specific capacity to the uttermost. On the other hand, different from the powder-like materials, the 3D integral structure generally has lower resistance due to the tight interface contact between current collector and sulfur hosts, so that it can improve the rate capability. Furthermore, the 3D skeleton has interlinked network architecture that could act as an unimpeded expressway for electron transfer during the whole process of charging and discharging. Therefore, the 3D current collector will perform perfectly well for developing binder-free and flexible sulfur-containing electrodes to accelerate the revolution of electronic fields, such as wearable electronic devices, and bionic technology.


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Based on the above considerations, we synthesis a binder-free and flexible 3D hierarchical structure sulfur hosts by directly growing hollow FeCo2S4 nanotube arrays onto the carbon cloth substrate. The fabrication procedure is illustrated in Scheme 1a. Firstly, the uniform precursor nanorods arrays (precursor/CC) are fabricated via typical hydrothermal reaction in the presence of a piece of pre-treated carbon cloth, Co2+ and Fe3+ at 120 ºC. Secondly, through subsequently sulfuration process, the nanorods are situ transformed into well-defined hollow nanotubes (FeCo2S4/CC) as per the Kirkendall diffusion effect. 35 Finally, sulfur is encapsulated into the FeCo2S4/CC hosts with the method of melting-diffusion to obtain FeCo2S4/CC@S composite. As shown in Scheme 1b, the composite reveals several remarkable merits when is served as cathode for Li-S batteries. Firstly, the FeCo2S4 nanotube arrays are not only able to afford a large inner space to load sulfur and accommodate its volumetric expansion, but also able to capture the intermediate polysuldes generating from the process of electrochemical reaction due to their natural polarity of metal sulfide. Moreover, the ternary transition metal sulfides have a preferable electrical conductivity compared with monometal sulfides, combined with 3D interconnected carbon fiber skeleton, the FeCo2S4/CC@S generates an unimpeded highway for both electrolyte ion and electron, thereby greatly enhancing the sulfur utilization and rate capability of Li-S batteries. More significantly, FeCo2S4 also can catalyze the electrochemical reaction kinetic of the cathode. Finally, it is worth mentioning that this electrode is highly flexible without adding any binders and conductive additives. Due to the above advantages, the FeCo2S4/CC@S electrode delivers a high discharge capacity of 1384 mA h g-1 at the current density of 0.1 C and continued remaining 658 mAh g-1 even increase to 2 C.



Scheme 1. (a) Schematic illustration of the synthesis process of FeCo2S4/CC@S composite and (b) illustrations of the superiority of the FeCo2S4/CC@S composite during cycling.

2. EXPERIMENTAL SECTION 2.1. Grown FeCo2S4 nanotube arrays on the surface of carbon cloth (FeCo2S4/CC). The uniform nanotube arrays are obtained via two step hydrothermal procedures and the CC used here is pre-treated (details are displayed in the supportting information). A brief description is shown as following: firstly, 1 mmol of Fe(NO3)2.9 H2O, 2 mmol of Co(NO3)2.6 H2O, 93 mg NH4F and 300 mg of urea were dissolved in 40 mL of deionized (DI) water to form a mixed solution. Then, a slice of carbon cloth (CC, 2 ×2 cm) was placed in it and stirred for 10 min. The mixture and CC were transferred into a 50 mL autoclave and reacted at 120 ºC for 24 h. After reaction finished and cooled down to room temperature, the composite was washed by DI water and ethanol several times and dried at 60 ºC. Secondly, the as-obtained precursor (Precursor/CC) was sulfureted by


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putting it into 40 mL Na2S.9H2O solution and hydrothermal at 120 ºC for 8 h. The final product was washed by DI water and ethanol for three times and marked as FeCo2S4/CC. 2.2. Synthesis of FeCo2S4/CC@S. To uniformly encapsulate sulfur into FeCo2S4/CC nanotube arrays, 100 mg of high purity sulfur powder was dissolve into 10 mL of CS2 solution. Then, the sulfur powder was pre-dispersed into the FeCo2S4/CC composite by over and over dropping and drying method (taking different volume of the mixture solution). Next, the FeCo2S4/CC composites with sulfur were placed in an autoclave and successively heated at 155 ºC for 12 h and then 200 ºC for 20 min to remove residual sulfur particles from its surface. For comparing, the CC@S was also be achieved by the same processes, in which the carbon cloth was not fully covered by FeCo2S4 nanotube arrays. 2.3. Physical characterization.The morphologies and structures were conducted by fieldemission scanning microscope (FESEM, JSM-7800F, Japan) and transmission electron microscopy (TEM, JEM-2100, Japan). The XRD patterns were collected by using powder X-ray diffraction (XRD, MAXima-X XRD-7000) with Cu Ka radiation (λ = 1.5406 Å). The contents of S in the prepared composite were estimated through Thermogravimetric analysis (TGA, Q50, USA) under an N2 atmosphere with the heating rate of 10 °C min-1. In addition, the X-ray photoelectron spectroscopy (XPS) were measured on a Thermo Scientific ESCALAB 250Xi electron spectrometer. 2.4 Li-S cell assembly and electrochemical measurements. For the asymmetric cells, FeCo2S4/CC@S or CC@S was directly employed as the cathode and incorporated into a CR2025 coin-type cells in an Ar-filled glovebox. Herein, the lithium foil was serve as the anode, Celgard 2400 was acted as the separator and 1 M Lithium bis(trifluoromethanesulfonyl) sulfonimide



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(LiTFSI) solution in a mixture of 1,3-dioxolane (DOL) and dimethoxymethane (DME) (1:1, v/v) with 0.1 M LiNO3 additive was used as electrolyte. The dosage of the electrolyte was 40 μl and to ensure it could fully penetrate, the cells were aged for several hours before each electrochemical test. Galvanostatic recharge properties and Cyclic voltammogram (CV) curves were performed on a Land Instruments testing system (Wuhan Kingnuo Electronic Co., China) and an Arbin instruments within a voltage window of 1.7-2.8 V at a scan rate of 0.1 mV s-1 (vs. Li/Li+), respectively. Electrochemical impedance spectroscopy (EIS) was conducted by Zahner electrochemical workstation at a open circuit potential between 100 kHz and 0.01 Hz. For the symmetric cells, they were assembled without the presence of elemental sulfur and lithium foil, FeCo2S4/CC or CC was used as working and counter eletrodes, meanwhile 40 μl of the electrolyte and 16 μl of Li2S6 were added (Li2S6 was prepared by dissolving sulfur powder and lithium sulfide at a molar ratio of 1:5 in corresponding electrolyte and stirred for 20 h at 50 ºC under an argon atmosphere and the concentration was 1 mg ml-1). After aging for several hours, CV curves were collected between the voltage ranging from -0.8-0.8 V at a scan rate of 50 mV s-1. The EIS test condition was the same as the asymmetric cells. 2.5. Computational methods. The adsorption behaviors of Li2Sx (x = 1, 2, 4, 6 and 8) on FeCo2S4/CC@S composite were modeled using a FeCo2S4 (001) slab model at the density functional theory (DFT) level with the Vienna Ab Initio Simulation Package.36,

37

The

stoichiometric slab was created with the optimized bulk FeCo2S4 unit cell that is analogous to the rhombohedral Fe3O4 primitive unit cell with the vacuum space set to 15 Å. In the slab model, the octahedral cation sites were occupied by Co atoms and the tetrahedral sites were occupied by Fe atoms. The geometry of the slab was relaxed until and the maximum force on the atom was below 10−4 eV/Å. The geometry optimization calculations were performed with the Perdew-Burke-


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Ernzerhof exchange-correlation functional revised for solids (PBEsol)38 and the projector augmented wave pseudopotential. The onsite Coulomb corrections of the Fe and Co 3d orbitals through spin polarized DFT+U based (i.e. PBEsol+U).39 The Ueff values for the Fe (Ueff = 3.5), and Co (Ueff = 0.5) were taken from the literature.40 The dispersion corrections were included in the energies by using Grimme’s empirical DFT-D2 method.41 The number of plane waves for the DFT calculations were controlled by a cut-off energy of 520 eV. 3. RESULTS AND DISCUSSION In order to grow FeCo2S4 more easily, the pristine CC is pre-treated through modified Hummers method to improve it hydrophilicity. The contact angle measurements are displayed in Figure S1. For untreated CC, the contact angle is about 133.0º indicating a completely hydrophobic feature. But for treated CC, the contact angle is nearly 0º. It is suggested that many functional groups are appeared on the surface of each carbon fiber and make the CC become absolutely hydrophilic, which is propitious to the accessibility of Co2+ and Fe3+ ions during the hydrothermal reaction process. Moreover, compared with pristine CC, the surface of carbon fibers become rougher after acid etching (Figure S2). To display the self-supporting advantage of each sample, the digital images of bare CC, precursor/CC and FeCo2S4/CC are displayed in Figure S3. FESEM and TEM characterizations are used to observe the morphological features of asprepared samples. As shown in the low magnification FESEM image of precursor/CC (Figure S4a), the individual nanorod uniformly but densely grows on the surface of each carbon fiber and make the carbon frameworks look like a few interlaced fluffy bottle brushes. Comparing with bare carbon cloth (Figure S2c and S2d), the diameters of the carbon fibers increase from ~ 9.0 µm to ~ 28.2 µm, thereby the cover’s thickness, namely the lengths of nanorods are about 9.6 µm.



Meanwhile, the cracks of 3D carbon fibers network remain unblocked. Seen from the magnifying FESEM image (Figure S4b) of the precursor/CC, it can be found that every nanorod is vertically aligned with a smooth surface as well as a cuspidal tip. The average diameter of the nanorod is about 150 ~ 240 nm (Figure S4c). Figure S4d displays the comparison XRD patterns of the blank carbon cloth and precursor/CC. Excepting for the characteristic diffraction peaks of carbon at 2θ = 26.3º and 2θ = 44.2º, the other diffraction peaks are well consistent with the literatures.42 After subsequent sulfuration, the nanoarrays are still homogeneously covered in a large area (Figure 1a), while the nanorods are converted into nanotubes (Figure 1b) due to ions the exchange reaction, which would fast deliver electrolyte and electrons during the charge and discharge process. The EDS elemental mappings of FeCo2S4/CC are displayed in Figure S5. Moreover, the TEM image (Figure 1c) further reveals the hollow structure of delaminated FeCo2S4 nanotube with a tube wall thickness of about 45 nm. The XRD pattern of FeCo2S4/CC is shown in Figure. 1g, all of the diffraction peaks perfectly index to FeCo2S4 other than that of carbon fibers. Herein, it should be expounded that although there is no standard PDF card for comparing, each peaks position of FeCo2S4/CC is well identical with lately reported by Meng et al.43 After steaming sulfur into FeCo2S4/CC composite, the surface morphology basically remains unchanged (Figure 1d and 1e), but the darker contrast of the inside and the shell indicates that sulfur is homogeneously encapsulated into the inner cavity of FeCo2S4 nanotubes (Figure 1f). Furthermore, the emergence of the weak signal peak of sulfur in the XRD pattern of the composite (Figure 1h) can be additional assurance of that fact. According to EDS mapping of FeCo2S4/CC@S, three different elements of S (red), Co (yellow) and Fe (green) are distributed evenly along with the whole nanotube (Figure 1i). Finally, based on the TGA analysis (Figure S6a), the mass ratio of sulfur in the composite is about 17.6 % (average sulfur mass loading ranged from 3.1 to 3.3 mg cm-2). As a result, the 3D


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carbon network contributes the fundamental conductive scaffolds, whereas the polar nanotubes supplies the reaction space and rendered the chemical anchoring sites, such an interconnected structure would be conducive to maximize the utilization of sulfur and the electrochemical performance of the Li-S batteries.

Figure 1. FESEM, TEM images of (a-c) FeCo2S4/CC and (d-f) FeCo2S4/CC@S, XRD patterns of (g) FeCo2S4/CC and (h) FeCo2S4/CC@S and (i) EDS elemental mappings of FeCo2S4/CC@S. To identify the detailed elemental compositions and bonding characteristics of the assynthesized samples, the X-ray photoelectron spectroscopy (XPS) characterization is performed and the full survey scans are presented in the Figure S6b. For FeCo2S4/CC, the characteristic peaks of Fe 2p (714.0 eV), Co 2p (779.7 eV) and S 2p (162.8 eV) can be obviously detected, indicating an adequate growth of FeCo2S4 on the CC.44 Moreover, the supererogatory C 1s (561.7 eV) and O



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1s (284.5 eV) peaks respectively derive from the carbon fibers and the oxygen-containing reactant of the composite or air from the hydrothermal reaction. By Gaussian fitting, the Co 2p can be split into six peaks as shown in Figure 2a. The peaks seat at near 781.3 and 797.5 eV can be ascribed to Co2+ species, while the peaks locate at about 778.8 and 793.9 are assigned to Co3+ species. Besides, two shakeup satellite peaks are detected at 785.9 and 802.8 eV.

45

Similarly, the XPS

spectrum of Fe 2p is exhibited in Figure 2b, the peaks of Fe 2p2/3 and Fe 2p1/2 at about 712.1 and 720.2 eV indicate the existence of Fe2+ species. Another peak at 715.3 eV confirms the presence of Fe3+ in the material.44, 46 The high resolution XPS spectrum of S 2p is presented at Figure 2c. The two prominent peaks at binding energy of 161.7 and 162.5 eV are attributed to S 2p3/2 and S 2p1/2 peaks, respectively, both coming from the S2− pairs. Moreover, the peak at 168.8 eV corresponds to a shakeup satellite.47 After encapsulating sulfur, the sulfur content is significantly increased (Figure S6b). In addition, seen from the high resolution XPS spectra of Co2p+Li2S6 (Figure 2a) and Fe2p+Li2S6 (Figure 2b), the peak positions of Co 2p3/2, Fe 2p2/3 and Fe 2p1/2 change on some level, indicating a strong interaction between Li2S6 molecules and Co and Fe atoms.48, 49 In addition, a visual contrast analysis of the bare CC and FeCo2S4/CC composite is carried out. The forearmed Li2S6 is dissolved in 1, 2-dimethoxyethane (DME) to form a luminous yellow solution, as shown in Figure 2d. In contrast, the colour of Li2S6 solution basically remains unchanged after soaking bare CC. But after adding FeCo2S4/CC, the solution becomes transparent and colourless, which further attests the adsorptive property of FeCo2S4/CC for polysulfide.


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Figure 2. High resolution XPS spectra of (a) Co2p and (b) Fe2p characteristic peaks recorded from FeCo2S4/CC and FeCo2S4/CC+Li2S6, respectively, (c) high resolution XPS spectrum of S2p split from FeCo2S4/CC and (d) polysulfide entrapment by bare CC and FeCo2S4/CC composite. To probe the catalytic effect of FeCo2S4/CC on the polysulfide reaction, two free-standing asymmetric cells are directly assembled by using FeCo2S4/CC@S and CC@S as cathode and lithium foil as anode. Figure 3a shows their compared CV curves within the voltage ranging from 1.7 to 2.8 V. For those two kinds electrodes, both appear two cathodic peaks and one anodic peak, of which the former two peaks derive from the reduction of S8 molecules to soluble long-chain polysulfides (Li2Sx, 4 ≤ x ≤ 8) and further formation of insoluble short-chain polysulfides (Li2S/Li2S2), respectively, while the later single peak originates from the reverse conversion of generation of short-chain Li2S2/Li2S to S8. 50 However, it should be noted that the peak shapes and positions in the CV curves for FeCo2S4/CC@S and bare CC@S are discrepant and the detailed parameters of peak voltages and onset voltages are supplied in the Figure S7. In terms of FeCo2S4/CC@S, the cathodic peak shifts to more positive potential direction, while the anodic peak moves to more negative potential region, which perfectly reveals a relatively faster electrochemical reaction.25,

51

Moreover, the galvanostatic charge and discharge curves are



Figure 3. (a) CV curves and (b) discharge-charge curves of the FeCo2S4/CC@S and bare CC@S asymmetric cells, (c) CV curves and (d) EIS spectra of the FeCo2S4/CC and CC@S symmetric cells. displayed in Figure 3b. It can be observed that the plateau gaps difference between charge/discharge curves, namely the polarization (ΔE) at a half capacity of FeCo2S4/CC@S (158 mV) is lower than that of CC@S (225 mV) at the same current density of 0.1 C. This is well consistent with the CV test results, suggesting that FeCo2S4 really can induced kinetic redox reaction of polysulfide conversion. Additionally, considering the influence of lithium foil in the above cells, two analogous symmetric cells composed of FeCo2S4/CC and CC with/without Li2S6 electrolyte are also constructed to further attest the catalytic action. The CV curves of the symmetric cells are performed between -0.8 and 0.8 V. As shown in Figure 3c, the FeCo2S4/CC cell with Li2S6 shows the highest a current response than that of other batteries. Similarly, the


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electrochemical impedance (EIS) plots in the Figure 3d exhibits that the FeCo2S4/CC symmetric cell has a decreased semicircle diameter, namely a lower charge transfer resistance as compared to the bare CC symmetric cell.52 In conjunction with the XPS analysis, the results obtain from the asymmetric and symmetric cells further confirm that the FeCo2S4/CC host material both possess polysulfide adsorption and catalytic conversion effect during the electrochemical reaction process. Figure 4a displays the compared rate capabilities of FeCo2S4/CC@S and bare CC@S electrodes. In contrast, the composite electrode delivers higher discharge capacities of 1384, 1166, 984, 851 and 658 mA h g-1 with increasing of the current density from 0.1, 0.2, 0.5, 1.0 C and 2.0 C than the bare CC@S, which only delivers 995 mA h g-1 at 0.1 C while 132 mA h g-1 at 2.0 C. Specifically, when the current density being abruptly switched back to 0.1 C, the capacity of FeCo2S4/CC@S electrode can recover to 1153 mA h g-1, suggesting a higher reversibility and superior rate performance. These extraordinary merits of the composite electrode probably profits from its high conductivity and special structure: on one hand, the uniform and compact nanotube arrays grow on the surface of each carbon fiber can provide the chemical adsorption sites for soluble polysulfide and further facilitate its conversion, which efficiently inhibits the shuttle effect; on the other hand, the conducive hollow FeCo2S4 nanotube arrays are not only beneficial to the full penetration of electrolyte, but also supply inner spaces to buffer the volume expansion of the sulfur. Figure 4b sets out the charge/discharge curves of FeCo2S4/CC@S with current density increase from 0.1 to 2 C. It well agrees with the peaks in its CV curves that each discharge curve shows two plateaus and the corresponding charge curve appears one plateau. Besides, Figure 4c shows the cycle performances of FeCo2S4/CC@S and CC@S with a different current density. The composites can deliver a discharging capacity of 969 mA h g-1 at 0.5 C in the initial cycle and



Figure 4. (a) Rate capabilities of FeCo2S4/CC@S and bare CC@S asymmetric cells, (b) charge/discharge curves of FeCo2S4/CC@S at different current densities, (c) cycling performances of FeCo2S4/CC@S and CC@S, (d) the separator of FeCo2S4/CC@S and CC@S after the 300th cycles and (e) FESEM image of FeCo2S4/CC@S after 300th cycling. remains 729 mA h g-1 after 300 cycles with per cycle only 0.08% capacity decay. After increasing the current density to 1.0 C, the initial discharge capacity of is reduced to 860.1 mA h g-1 with a capacity attenuation rate of 0.07% per cycle. Visually, a high Coulombic efficiency is achieved throughout the whole cycle (~ 98%). In comparison, the bare CC@S exhibits a rapid capacity decay from 770 to 325 mA h g-1 at 0.2 C (0.2% per cycle), which is apparently larger than that of


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FeCo2S4/CC@S arising from the fast dissolving and diffusing of polysulfides in the electrolyte. The superior cycling stability of the FeCo2S4/CC@S cathode can be attributed to the catalytic action of FeCo2S4 and its unique hollow structure that can physically block the outward diffusion pathways of LiPSs. Figure S8 shows the CV curves of FeCo2S4/CC@S asymmetric cell for the first three cycles. Figure 4d provids a visual proof. As can be observed, the separator from FeCo2S4/CC@S cell shows a clearly white colour, but the separator from CC@S presents light yellow. To inspect the morphology change, FESEM image of FeCo2S4/CC@S after cycling is characterized and presents in Figure 4e. It is revealed that the original array architecture still be preserved after 300th cycling. Compared with some reported binder-free electrodes for Li-S batteries, our FeCo2S4/CC@S electrode also displays some superior performances in both capacity and attenuation ratio and the detailed statistics are supplied in Table S1. Furthermore, the sulfur content of a cathode material is closely related to the electrochemical performance of the battery. For comparison, the electrochemical performance of FeCo2S4/CC@S composite with different sulfur loadings are tested. The results indicate that the composite exhibits an excellent rate performance under a low sulfur content (12.4 %), while the discharge capacity is only 1118 mAh g-1 at current density of 0.1 C (Fig. S6a, Fig. S9a and b). However, when the mass loading is increased to 23.5%, the discharge capacity as well increases to 1345 mAh g-1, but the rate performance begins fade (Fig. S6a, Fig. S9a and b). As shown in Fig. 8c, after 300 cycles at the same current density of 1.0 C, the capacity attenuation of the high load composite is more obvious. Thus, it can be seen that sulfur content of 17.6 % is the optimal proportion. To further understanding the internal resistance and charge-transfer processes of the composite electrode, the EIS of the FeCo2S4/CC@S cathode is also investigated before and after cycling. As shown in Figure S10, the Nyquist plot of the fresh cell is basically composed of



semicircle in the high frequency region and sloping line in the low frequency region, in which the semicircle diameters and horizontal axis intercepts are respectively equal to charge-transfer resistance and equivalent series resistance, while the inclined line corresponds to the semi-infinite Warburg diffusion process of Li+ in the electrode.7 After 300th cycling, there are two semicircles in the Nyquist plot. The semicircle in the high frequency region attributes to the interface chargetransfer process of the electrode caused by the irreversible deposition of Li2S2/Li2S layer. While the semicircle in the medium frequency region can be linked to the charge-transfer resistance occurring on the electrolyte-electrode interface, which is affected by the thickness of the Li2S2/Li2S passivating layer.53 It is obviously that the semicircle in the medium frequency region is very blurry, which further implies that the chain polysulfide deposits on the surface of the cathode is not very substantial during cycling due to the catalytic action of the FeCo2S4 nanotube arrays. 54 To explore the origins for excellent performances of the bind-free FeCo2S4/CC@S, DFT calculation on the adsorption of the Li2Sx (x ≤ 8) on the FeCo2S4 (001) are performed. The (001) surface (Figure 5a) is chosen based on the observation that the simulated XRD spectrum for the ultrathin polar-FeCo2S4 (001) film (Figure 5b) is in excellent agreement with the experimental XRD spectrum for FeCo2S4/CC@S (Figure 1h), which suggests that the surface of FeCo2S4/CC@S is dominated by FeCo2S4 (001) surface. The simulated XRD spectrum also suggests that the FeCo2S4 layer is ultrathin, as the simulated XRD spectrum of the bulk FeCo2S4 (Figure 1b) shows significantly different characteristics than the experimental spectrum. For example, in the simulated XRD spectrum of the bulk FeCo2S4, the (220) diagnostic peak (at 2θ ≈ 27º) is comparatively stronger and the (400) peak (at 2θ ≈39º) is much weaker than those peaks in both the experimental XRD spectrum of FeCo2S4/CC@S and the simulated XRD spectrum of the ultrathin FeCo2S4 (001) film.


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The free elements of S can form strong adsorption on the FeCo2S4 (001) surface. A single S atom can adsorb on a surface hollow site (h-site, Figure 1a) forming bonds with two surface S and a surface Fe with a binding energy of -3.87 eV (Figure S11). The adsorption of S at the bridge site between two surface S atoms and at the bridge site between two surface Co atoms are also very exothermic, for which the binding energies are -3.83 and -3.62 eV, respectively. When lithium polysulfides are formed from the free elements of S during the discharge stage, the lithium atoms can mainly occupy two typical surface sites, the 3-coordinate surface S site (S3c) or the h-site that is surrounded by 4 S atoms (Figure 5a). Since the distance between two adjacent S3c-sites and the distance between two adjacent h-sites are comparable to the Li-Li bond distance in the Li2Sx, Li2Sx can adsorb on either the double-S3c site (denoted as 2S3c-site, Figure 5a) or the double-hollow site (denoted as 2h-site, Figure 5a). The 2h-site is found to be more energetically favourable than the 2S3c-site for the adsorptions of all the Li2Sx -species (Figure 5c and Figure S11). When the free elements of S on the surface are reduced to form the lithium polysulfide intermediates during the discharge stage, the initial Li2S8 product forms strong 2h-adsorption and moderate 2S3cadsorption with binding energies of -5.21 eV and -1.99 eV respectively. It is noted that the high binding energy of the Li2S8 at 2h-site is due to the S82- chain of Li2S8 forming an additional strong bond with a surface Co atom. As the Li2Sx polysulfide chain becomes shorter during the discharge stage, the 2h-adsorption (Figure 5d) becomes less exothermic at x = 6 (binding energy = -3.94 eV) and the exothermicity monotonically increases as x decreases for 6 ≥x ≥ 1 (binding energy = -6.65 eV at x = 1), whereas the binding energy for the 2S-adsorption remains essentially the same. No S-Co bonds are found in the adsorption configuration of Li2Sx, x < 8. Such differences may be the origin for the two plateaus in the discharge curves of FeCo2S4/CC@S (Figure 5b). On the FeCo2S4



Figure 5. (a) Structure and binding sites on FeCo2S4 (001) surface, (b) simulated XRD spectra for the ultrathin FeCo2S4 (001) film and FeCo2S4 bulk crystal, (c) calculated binding energies of Li2Sx (x = 2-8) at the 2S3c-site and 2h-site of FeCo2S4 (001) surface, and (d) the charge density difference diagram for Li2S6@ FeCo2S4 (001). Different colours of the atoms indicate different elements: Fe in brown, Co in blue, S in yellow and Li in light green. (001), the h-sites are expected to be covered first by the Li2Sx, followed by the adsorption of L2Sx at the S3c-sites. The long-chain Li2Sx (4 ≤ x ≤ 8) forms strong chemical adsorption with the FeCo2S4 (001) at the 2h-sites, which is indicated by the calculated binding energies as well as the charge density difference diagrams (Figure 5b and Figure S11). The strong interactions between the polysulfide and FeCo2S4 (001) are likely to suppress the dissolution and diffusion of polysulfide, which in turn prevents the detrimental shuttle effect.


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4. CONCLUSIONS In summarize, a 3D carbon cloth self-supported polar FeCo2S4 nanotube arrays composite is designed and prepared for Li-S batteries. As a cathode material, it shows three main superiorities including of high electrical conductivity for maximizing utilization of sulfur, strong absorptive and catalytic properties for inhibiting shuttle effect and a hollow tubular structure for adjusting the volume expansion, all of which are likely to be conducive to enhancing its electrochemical performances. More importantly, unlike traditional powder materials, the flexible FeCo2S4/CC@S composite can be used directly to assemble Li-S batteries without adding any conductivity and binder agents, and thus saving a lot of fussy craft and reducing the manufacturing cost. Therefore, we believe that the Li-S batteries being applied to the field of wearable electronic devices is just around the corner. ASSOCIATED CONTENT Supporting Information Contact angle measurement of pristine CC and treated CC; FESEM images of pristine and treated CC; The digital images of pristine CC, precursor/CC and FeCo2S4/CC to show their selfsupporting advantage; FESEM, TEM images and XRD pattern of precursor/CC; EDS elemental mappings of FeCo2S4/C; TGA curve of FeCo2S4/CC@S and XPS full spectra of FeCo2S4/CC and FeCo2S4/CC@S; the comparison of peak voltages and onset voltages of FeCo2S4/CC@S and CC@S electrodes; CV curves of the FeCo2S4/CC@S composite electrode at a scan rate of 0.1 mV s-1; Rate capabilities and rate performance comparison and the cycling performances of FeCo2S4/CC@S with different sulfur content; EIS of the FeCo2S4/CC@S electrode before and after cycling; Optimized structures and charge density difference diagrams at the PBEsol+U level



for the adsorption of Li2Sx and S at different sites of FeCo2S4 (001) surface; The comparisons of binder-free electrodes for Li-S batteries. AUTHOR INFORMATION * E-mail: [email protected] (M. W. Xu); [email protected] (M. Y. Chen). Author Contributions † Bingshu Guo and Sateesh Bandaru contributed equally to this work. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work is financially supported by grants from the National Natural Science Foundation of China (No. 21773188, No.51802269), Program for Innovation Team Building at Institutions of Higher Education in Chongqing (CXTDX201601011), Graduate scientific research innovation project of Chongqing (CYB18092), MC acknowledges funding from Beijing Computational Science Research Center and National Natural Science Foundation of China (U1530401) and computational resources from the Beijing Computational Science Research Center. Furthermore, especially thanks to professor Limin Liu for his help in calculation aspects. REFERENCES (1) Choi, J. W.; Aurbach, D. Promise and Reality of Post-Lithium-ion Batteries with High Energy Densities. Nat. Rev. Mater. 2016, 1, 16013. (2) Chen, T.; Zhang, Z.; Cheng, B.; Chen, R.; Hu, Y.; Ma, L.; Zhu G.; Liu J.; Jin, Z. Self-Templated Formation of Interlaced Carbon Nanotubes Threaded Hollow Co3S4 Nanoboxes for High-Rate and Heat-Resistant Lithium-Sulfur Batteries. J. Am. Chem. Soc. 2017, 139, 127.


Page 22 of 30

Page 23 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(3) Lochala, J.; Liu, D.; Wu, B.; Robinson, C.; Xiao, J. Research Progress Toward the Practical Applications of Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces. 2017, 9, 24407-24421. (4) Wu, W.; Pu, J.; Wang, J.; Shen, Z.; Tang, H.; Deng, Z.; Tao X.; Pan F.; Zhang, H. Biomimetic Bipolar Microcapsules Derived from Staphylococcus Aureus for Enhanced Properties of LithiumSulfur Battery Cathodes. Adv. Energy Mater. 2018, 8, 1702373. (5) Wu, F.; Ye, S.; Huang, Q.; Zhao, T.; Qian, J.; Zhao, Y.; Li L.; Wei L.; Luo, R.; Huang, X.; Xing ,Y.; Chen, J. Sulfur Nanodots Stitched in 2D “Bubble-Like” Interconnected Carbon Fabric as Reversibility-Enhanced Cathodes for Lithium-Sulfur Batteries. Acs Nano. 2017, 11, 4694-4702. (6) Li, X.; Cheng, X.; Gao, M.; Ren, D.; Liu, Y.; Guo, Z.; Shang C.; Sun, L.; Pan, H. AmyloseDerived Macrohollow Core and Microporous Shell Carbon Spheres as Sulfur Host for Superior Lithium-Sulfur Battery Cathodes. ACS Appl. Mater. Interfaces. 2017, 9, 10717-10729. (7) Gueon, D.; Hwang, T.; Yang, B.; Cho, E.; Sohn, K.; Yang, K.; Moon, H. Spherical Macroporous Carbon Nanotube Particles with Ultrahigh Sulfur Loading for Lithium-Sulfur Battery Cathodes. ACS nano. 2018, 12, 226-233. (8) Zhang, J.; Hu, H.; Li, Z.; Lou, W. Double-Shelled Nanocages with Cobalt Hydroxide Inner Shell and Layered Double Hydroxides Outer Shell as High-Efficiency Polysulfide Mediator for Lithium-Sulfur Batteries. Angew. Chem. Int. Edit. 2016, 55, 3982-3986. (9) Zheng, C.; Niu, S.; Lv, W.; Zhou, G.; Li, J.; Fan, S.; Deng, Y.; Pan, Z.; Li, B.; Kang, F.; Yang, H. Propelling Polysulfides Transformation for High-rate and Long-life Lithium-Sulfur Batteries. Nano Energy. 2017, 33, 306-312. (10) Li, Y.; Ye, D.; Liu, W.; Shi, B.; Guo, R.; Zhao, H.; Pei, H.; Xu, J.; Xie, J. A MnO2/Graphene Oxide/Multi-Walled Carbon Nanotubes-Sulfur Composite with Dual-efficient Polysulfide Adsorption for Improving Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces. 2016, 8, 28566-



28573. (11) Hu, L.; Dai, C.; Lim, J. M.; Chen, Y.; Lian, X.; Wang, M.; Li Y.; Xiao P.; Henkelman G., Xu, M. A Highly Efficient Double-Hierarchical Sulfur Host for Advanced Lithium-Sulfur Batteries. Chem. Sci. 2018, 9, 666-675. (12) Lei, T.; Chen, W.; Huang, J.; Yan, C.; Sun, H.; Wang, C.; Zhang, L.; Li R.; Xiong, J. MultiFunctional Layered WS2 Nanosheets for Enhancing the Performance of Lithium-Sulfur Batteries. Adv. Energy Mater. 2017, 7, 1601843. (13) Yuan, Z.; Peng, H. J.; Hou, T. Z.; Huang, J. Q.; Chen, C. M.; Wang, D. W.; Cheng, X. B.; Wei, F.; Zhang, Q. Powering Lithium-Sulfur Battery Performance by Propelling Polysulfide Redox at Sulfiphilic Hosts. Nano Lett. 2016, 16, 519-527. (14) Niu, X. Q.; Wang, X. L.; Wang, D. H.; Li, Y.; Zhang, Y. J.; Zhang, Y. D.; Yang, T.; Yu, T.; Tu, J. P. Metal Hydroxide-A New Stabilizer for the Construction of Sulfur/Carbon Composites as High-Performance Cathode Materials for Lithium-Sulfur Batteries. J. Mater. Chem. A. 2015, 3 17106-17112; (15) Dai, C.; Hu, L.; Wang, M. Q.; Chen, Y.; Han, J.; Jiang, J.; Shen, B. L.; Niu, Y. B.; Bao, S. J.; Xu, M. Uniform α-Ni (OH)2 Hollow Spheres Constructed From Ultrathin Nanosheets as Efficient Polysulfide Mediator for Long-Term Lithium-Sulfur Batteries. Energy Storage Mater. 2017, 8, 202-208. (16) Sun, Z.; Zhang, J.; Yin, L.; Hu, G.; Fang, R.; Cheng, H. M.; Li, F. Conductive Porous Vanadium Nitride/Graphene Composite as Chemical Anchor of Polysulfides for Lithium-Sulfur Batteries. Nat. Commun. 2017, 8, 14627. (17) Deng, D.; Xue, F.; Jia, Y; Ye, J.; Bai, C.; Zheng, M.; Dong, Q.; Co4N Nanosheet Assembled Mesoporous Sphere as a Matrix for Ultrahigh Sulfur Content Lithium-Sulfur Batteries. ACS nano.


Page 24 of 30

Page 25 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2017, 11, 6031-6039. (18) Li, C.; Shi, J.; Zhu, L.; Zhao, Y.; Lu, J.; Xu, L. Titanium Nitride Hollow Nanospheres with Strong Lithium Polysulfide Chemisorption as Sulfur Hosts for Advanced Lithium-Sulfur Batteries. Nano Res. 2018, 11, 4302-4312. (19) Li, H.; Ma, S.; Cai, H.; Zhou, H.; Huang, Z.; Hou, Z.; Wu, J.; Yang, W.; Yi, H.; Fu, C.; Kuang, Y. Ultra-thin Fe3C Nanosheets Promote the Adsorption and Conversion of Polysulfides in Lithium-Sulfur Batteries. Energy Storage Mater. 2018, xxx, xxx-xxx. (20) Shang, C.; Cao, L.; Yang, M.; Wang, Z.; Li, M.; Zhou, G.; Wang, X.; Lu, Z. Freestanding Mo2C-Decorating N-Doped Carbon Nanofibers as 3D Current Collector for Ultra-Stable Li-S Batteries. Energy Storage Mater. 2018, xxx, xxx-xxx. (21) Peng, H. J.; Zhang, G.; Chen, X.; Zhang, Z. W.; Xu, W. T.; Huang, J. Q.; Zhang, Q. Enhanced Electrochemical Kinetics on Conductive Polar Mediators for Lithium-Sulfur Batteries. Angew. Chem. Int. Edit. 2016, 128, 13184-13189. (22) Pu, J.; Shen, Z.; Zheng, J.; Wu, W.; Zhu, C.; Zhou, Q.; Zhang, H.; Pan, F. Multifunctional Co3S4@Sulfur Nanotubes for Enhanced Lithium-Sulfur Battery Performance. Nano energy. 2017, 37, 7-14. (23) Xu, H.; Manthiram, A. Hollow Cobalt Sulfide Polyhedra-Enabled Long-Life, High ArealCapacity Lithium-Sulfur Batteries. Nano Energy. 2017, 33, 124-129. (24) Zhang, J.; Li, Z.; Chen, Y.; Gao, S.; Lou, X. W. Nickel-Iron Layered Double Hydroxide Hollow Polyhedrons as a Superior Sulfur Host for Lithium-Sulfur Batteries. Angew. Chem. Int. Ed. 2018, 57, 10944-10948. (25) Ye, C.; Zhang, L.; Guo, C.; Li, D.; Vasileff, A.; Wang, H.; Qiao, S. Z. A 3D Hybrid of Chemically Coupled Nickel Sulfide and Hollow Carbon Spheres for High Performance Lithium-



Sulfur Batteries. Adv. Funct. Mater. 2017, 27, 1702524. (26) Hu, L.; Dai, C.; Liu, H.; Li, Y.; Shen, B.; Chen, Y.; Bao, S.; Xu, M. Double-Shelled NiONiCo2O4 Heterostructure@Carbon Hollow Nanocages as an Efficient Sulfur Host for Advanced Lithium-Sulfur Batteries. Adv. Energy Mater. 2018, 1800709. (27) Li, Z.; Zhang, J.; Guan, B.; Wang, D.; Liu, L. M.; Lou, X. W. D. A Sulfur Host Based on Titanium Monoxide@Carbon Hollow Spheres for Advanced Lithium-Sulfur Batteries. Nat. Commun. 2016, 7, 13065. (28) Rehman, S.; Tang, T.; Ali, Z.; Huang, X.; Hou, Y. Integrated Design of MnO2@Carbon Hollow Nanoboxes to Synergistically Encapsulate Polysulfides for Empowering Lithium Sulfur Batteries. Small. 2017, 13, 1700087. (29) Dai, C.; Lim, J. M.; Wang, M.; Hu, L.; Chen, Y.; Chen, Z.; Chen, H.; Bao, S. J.; Shen, B. L.; Li, Y.; Henkelman, G.; Xu, M. W. Honeycomb-Like Spherical Cathode Host Constructed from Hollow Metallic and Polar Co9S8 Tubules for Advanced Lithium-Sulfur Batteries. Adv. Funct. Mater. 2018, 28, 1704443. (30) Wu, X. W.; Xie, H.; Deng, Q.; Wang, H. X.; Sheng, H.; Yin, Y. X.; Zhou W. X.; Li R. L.; Guo, Y. G. Three-Dimensional Carbon Nanotubes Forest/Carbon Cloth as an Efficient Electrode for Lithium-Polysulfide Batteries. ACS Appl. Mater. Interfaces. 2017, 9, 1553-1561. (31) Zhao, Q.; Hu, X.; Zhang, K.; Zhang, N.; Hu, Y.; Chen, J. Sulfur Nanodots Electrodeposited on Ni Foam as High-Performance Cathode for Li-S Batteries. Nano lett. 2015, 15, 721-726. (32) Kong, L. L.; Zhang, Z.; Zhang, Y. Z.; Liu, S.; Li, G. R.; Gao, X. P. Porous Carbon Paper as Interlayer to Stabilize the Lithium Anode for Lithium-Sulfur Battery. ACS Appl. Mater. Interfaces. 2016, 8, 31684-31694. (33) Ummethala, R.; Fritzsche, M.; Jaumann, T.; Balach, J.; Oswald, S.; Nowak, R.; Sobczak N.;


Page 26 of 30

Page 27 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Kaban I.; Rümmeli M. H.; Giebeler, L. Lightweight, Free-Standing 3D Interconnected Carbon Nanotube Foam as A Flexible Sulfur Host for High Performance Lithium-Sulfur Battery Cathodes. Energy Storage Mater. 2018, 206-215. (34) Fang, R.; Zhao, S.; Hou, P.; Cheng, M.; Wang, S.; Cheng, H. M.; Liu, C.; Li, F. 3D Interconnected Electrode Materials with Ultrahigh Areal Sulfur Loading for Li-S Batteries. Adv. Mater. 2016, 28, 3374-3382. (35) Xiao, J.; Wan, L.; Yang, S.; Xiao, F.; Wang, S. Design Hierarchical Electrodes with Highly Conductive NiCo2S4 Nanotube Arrays Grown on Carbon Fiber Paper for High-performance Pseudocapacitors. Nano Lett. 2014, 14, 831-838. (36) Perdew, J.; Zunger, A. Self-Interaction Correction to Density Functional Approximation for Many Electron Systems. Phys. Rev. B. 1981, 23, 5048. (37) Zhang, P.; Zheng, X.; Wu, S.; He, D. A Computer Simulation of Nucleation and Growth of Thin Films. Comput. Mater. Sci. 2004, 30, 331-336. (38) Perdew, J. P.; Ruzsinszky, A.; Csonka, G. I.; Vydrov, O. A.; Scuseria, G. E.; Constantin, L. A.; Zhou, X.; Burke, K. Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces. Phys. Rev. Lett. 2008, 100, 136406. (39) Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.; Sutton, A. P. Electronenergy-Loss Spectra and the Structural Stability of Nickel Oxide: An LSDA+ U study. Phys. Rev. B. 1998, 57, 1505. (40) Santos-Carballal, D.; Roldan, A.; Grau-Crespo, R.; de Leeuw, N. H. First-Principles Study of the Inversion Thermodynamics and Electronic Structure of FeM2X4 (thio) Spinels (M= Cr, Mn, Co, Ni; X= O, S). Phys. Rev. B. 2015, 91, 195106. (41) Grimme, S. Semiempirical GGA-type Density Functional Constructed with A Long-Range



Dispersion Correction. J. Comput. Chem. 2006, 27, 1787. (42) Zhu, J.; Tang, S.; Wu, J.; Shi, X.; Zhu, B.; Meng, X. Wearable High-Performance Supercapacitors Based on Silver-Sputtered Textiles with FeCo2S4-NiCo2S4 Composite NanotubeBuilt Multitripod Architectures as Advanced Flexible Electrodes. Adv. Energy Mater. 2017, 7, 1601234. (43) Tang, S.; Zhu, B.; Shi, X.; Wu, J.; Meng, X. General Controlled Sulfidation toward Achieving Novel Nanosheet-Built Porous Square-FeCo2S4-Tube Arrays for High-Performance Asymmetric All-Solid-State Pseudocapacitors. Adv. Energy Mater. 2017, 7, 1601985. (44) Deng, C.; Yang, L.; Yang, C.; Shen, P.; Zhao, L.; Wang, Z.; Wang, C. H.; Li, J. H. Qian, D. Spinel FeCo2S4 Nanoflower Arrays Grown on Ni Foam as Novel Binder-Free Electrodes for Long-Cycle-Life Supercapacitors. Appl. Surf. Sci. 2018, 428, 148-153. (45) Xu, Y.; Gao, X.; Chu, W.; Li, Q.; Li, T.; Liang, C.; Lin, Z. Ni-Co Sulfide Nanoboxes with Tunable Compositions for High-Performance Electrochemical Pseudocapacitors. J. Mater. Chem. A. 2016, 4, 10248-10253. (46) Zhu, B.; Tang, S.; Vongehr, S.; Xie, H.; Zhu, J.; Meng, X. FeCo2O4 Submicron-Tube Arrays Grown on Ni Foam as High Rate-Capability and Cycling-Stability Electrodes Allowing Superior Energy and Power Densities with Symmetric Supercapacitors. Chem. Commun. 2016, 52, 26242627. (47) Elshahawy, A. M.; Li, X.; Zhang, H.; Hu, Y.; Ho, K. H.; Guan, C.; Wang, J. Controllable MnCo2S4 Nanostructures for High Performance Hybrid Supercapacitors. J. Mater. Chem. A. 2017, 5, 7494-7506. (48) Wang, M.; Liang, Q.; Han, J.; Tao, Y.; Liu, D.; Zhang, C.; Lv, W.; Yang, Q. H. Catalyzing Polysulfide Conversion by gC3N4 in A Graphene Network for Long-Life Lithium-Sulfur Batteries.


Page 28 of 30

Page 29 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Nano Res. 2018, 11, 3480-3489. (49) Li, C.; Liu, X.; Zhu, L.; Huang, R.; Zhao, M.; Xu, L.; Qian, Y. Conductive and Polar Titanium Boride as a Sulfur Host for Advanced Lithium-Sulfur Batteries. Chem. Mater. 2018, 30, 69696977. (50) Ren, W.; Xu, L.; Zhu, L.; Wang, X.; Ma, X.; Wang, D. Cobalt-Doped Vanadium Nitride Yolk-Shell Nanospheres@Carbon with Physical and Chemical Synergistic Effects for Advanced Li-S Batteries. ACS Appl. Mater. Interfaces. 2018, 10, 11642-11651. (51) Li, L.; Hou, L.; Cheng, J.; Simmons, T. J.; Zhang, F.; Zhang, L. T.; Zhang, L.; Robert, J.; Koratkar, N. A Flexible Carbon/Sulfur-Cellulose Core-Shell Structure for Advanced LithiumSulfur Batteries. Energy Storage Mater. 2018. (52) Peng, H. J.; Zhang, G.; Chen, X.; Zhang, Z. W.; Xu, W. T.; Huang, J. Q.; Zhang, Q. Enhanced Electrochemical Kinetics on Conductive Polar Mediators for Lithium-Sulfur Batteries. Angew. Chem. Int. Ed. 2016, 42, 12990-12995. (53) Barchasz, C.; Leprêtre, J.; Alloin, F.; Patoux, S. New Insights into the Limiting Parameters of the Li/S Rechargeable Cell. J. Power Sources. 2012,199, 322-330. (54) Huangfu, Y.; Zheng, T.; Zhang, K.; She, X.; Xu, H.; Fang, Z.; Xie, K. Facile Fabrication of Permselective g-C3N4 Separator for Improved Lithium-Sulfur Batteries. Electrochim. Acta. 2018, 272, 60-67.



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Self-Supported FeCo2S4 Nanotube Arrays as Binder-Free Cathode

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