SnS2 Nanocrystal Building

Subscriber access provided by Grand Valley State | University

Article

Promising Dual-doped Graphene Aerogel/SnS2 Nanocrystal Building High Performance Sodium Ion Batteries Linlin Fan, Xifei Li, Xiaosheng Song, Nana Hu, Dongbin Xiong, Alicia Koo, and Xueliang Sun ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b18195 • Publication Date (Web): 27 Dec 2017 Downloaded from http://pubs.acs.org on December 28, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 38 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

ACS Applied Materials & Interfaces

Promising Dual-doped Graphene Aerogel/SnS2 Nanocrystal Building High Performance Sodium Ion Batteries

Linlin Fana, Xifei Lia,b,*, Xiaosheng Songa, Nana Hub, Dongbin Xionga, Alicia Kooc, Xueliang Sunc,a,b a

Institute

of

Advanced

Electrochemical

Energy,

Xi’an

University

of

Technology, Xi’an 710048, China E-mail: [email protected] b

Tianjin International Joint Research Centre of Surface Technology for Energy

Storage Materials, College of Physics and Materials Science, Tianjin Normal University, Tianjin 300387, China c

Nanomaterials and Energy Lab, Department of Mechanical and Materials

Engineering, University of Western Ontario, London, Ontario, N6A 5B9, Canada

ABSTRACT In this study, we report the effort in designing layered SnS2 nanocrystals decorated on nitrogen and sulfur dual-doped graphene aerogels (SnS2@N,S-GA) as anode material of SIBs. The optimized mass loading of SnS2 along with the addition of nitrogen and sulfur on the surface of GAs result in enhanced electrochemical performance of SnS2@N,S-GA composite. In particular, the introduction of nitrogen and sulfur heteroatoms could provide more active sites and good accessibility for Na-ions. Moreover, the incorporation of the stable SnS2 crystal structure within the

1

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 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

anode results in the superior discharge capacity of 527 mAh g-1 under a current density of 20 mA g-1 upon 50 cycles. It maintains 340 mAh g-1 even the current density is increased to 800 mA g-1. Aiming to further systematically study mechanism of composite with improved SIB performance, we construct the corresponding models based on experimental data and conduct first-principles calculations. The calculated results indicate the sulfur atoms doped in GAs show a strong bridging effect with the SnS2 nanocrystals, contributing to build robust architecture for electrode. Simultaneously, heteroatom dual-doping of GAs shows the imperative function for improved electrical conductivity. Herein, first-principles calculations present a theoretical explanation for outstanding cycling properties of SnS2@N,S-GA composite.

KEYWORDS: SnS2; Dual-doping; Graphene aerogel; Cycling performance; Sodium ion batteries

INTRODUCTION Sustainable sodium ion batteries (SIBs) have attracted much attention in renewable energy and smart grid applications because of high sodium reserves, significantly lower cost, as well as the insertion chemistry resembling lithium-ion batteries (LIBs).1-3 It has been accepted that the Na-ion intercalation into electrode materials is similar to that of Li-ions. However, the radius of Na+ (1.06Å) is about 1.4 times larger than that of Li+ (0.76Å).4,5 As a result, SIBs face significant challenges of anisotropic volume expansion, resulting in active material pulverization and 2


Page 2 of 38

Page 3 of 38 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


insufficient contact with the current collector or conductive agent.6 Additionally, from the energy density perspective, a considerable drawback is that the redox potential of Na is higher than that of Li. Therefore, the exploration of appropriate host anode materials with fast ion-diffusion pathways and large-sized tunnel structures is a primary bottleneck for SIBs. Over the past decade, graphite has been considered as a state-of-the-art anode material for LIBs. Unfortunately, it is an ineffective host for Na-ions, showing the low theoretical capacity (< 35 mAh g-1) because of larger Na-ion radius.7,8 Currently, significant efforts have been geared towards developing suitable materials for high-capacity SIB applications. Notably, many previous reports have demonstrated that tin and tin-based compounds can alloy with sodium, and show good prospects as SIB anodes compared to carbon materials.9-11 For instance, SnSb@carbon nanocables anchored on graphene nanosheets were successfully designed,12 where simultaneous encapsulation of SnSb alloy and carbon coating better function to relieve the volume expansion/shrinkage. Another exceptionally high performing SIB anode was proposed to use crystalline SnO2 nanoparticles confined in mesoporous carbon, which achieved superior SIB performance.13 In our group, the significant effects of SnO2 crystallinity (including amorphous and crystalline) on electrochemical performance of SIBs were studied systemically for the first time.14 Our work showed that the amorphous SnO2 obtained enhanced cycling performance, and the Na-ion diffusion coefficient was almost two times as high as crystalline SnO2. These inspiring phenomena clearly reveal that tin-containing compounds reveal great potential for use in SIBs. 3



Unfortunately, tin-sodium alloys suffer from severe volume expansion (520 % from Sn to Na3.75Sn) during uptake or removal of sodium,15 which is even larger than that of the corresponding tin-lithium alloy, causing greater limitations for the realization of durable anodes.16 SnS2, as a layered hexagonal CdI2-type crystal structure, consists of tin atoms sandwiched between two layers of closely packed sulfur slabs, with adjacent sulfur layers connected via van der Waals forces.17-19 SnS2 can host Na-ions and has a greater tolerance for cycling-induced volume changes due to the large interlayer spacing of 0.59 nm. As a result, this layered structure enables the convenient insertion and extraction of Na-ions.20 However, the capacity fading is inevitably severe due to the low electrical conductivity of SnS2 and dissolution of sulfur into the electrolyte.21 Much efforts have been made so as to overcome this limitation. The ultrafine few-layered SnS2 anchored on few-layered reduced graphene oxide was proposed.22 Exfoliated-SnS2 restacked on graphene was designed by the hydrolysis of lithiated SnS2.23 Inconceivably, all of the above attempts show high capacity and ultra-long cycle life. Motivated by the aforementioned considerations, graphene has been regarded as an ideal matrix due to the large theoretical surface area, high electronic conductivity, and excellent mechanical properties.24 More impressively, heteroatom (nitrogen, sulfur, and boron) doping in graphene could highly enhance its electrical conductivity as well as the surface hydrophilicity to facilitate electrode-electrolyte interactions and charge transfer.25 For instance, 3D N-doped graphene foam can deliver charge/discharge capacities of 605.6/594.0 mAh g-1 from 0.02 V to 3.0 V after 150 4


Page 4 of 38

Page 5 of 38 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


cycles at 1 C in LIBs.26 Accordingly, great effort has been made to employ nitrogen doping in graphene to improve its properties as a matrix, such as in N-doped graphene/SnO2,27

N-doped

graphene/NiO,28

and

N-doped

graphene/MoS2

composites.29 However, studies on the function of sulfur doping in graphene-based composites are relatively limited. Remarkably, Wang et al. designed the nanocomposites with few-layered MoS2 and sulfur-doped graphene via facile solvothermal technique.30 The unique composite architecture derived from the “bridging effect” resulted in excellent electrochemical performance of the electrode. Based on the above discussion, it has been proposed that nitrogen and sulfur dual-doped graphene could carry more active sites and extrinsic defects, improving the electrochemical activity and conductivity simultaneously and contributing to energy storage.31 Accordingly, our group synthesized nitrogen and sulfur dual-doped porous graphene aerogels. The results suggest that synergic effect of dual-doping heteroatoms into the graphene lattice is beneficial to enhanced performance, which facilitates the fast transfer for electrons and ions.32 In the present study, we design layered SnS2 nanocrystals decorated on nitrogen and sulfur dual-doped graphene aerogels (SnS2@N,S-GA). When used as an anode material for SIBs, the SnS2 nanocrystals are able to tolerate the volume changes that occur upon cycling while N,S-GA with large specific surface area can offer mass active sites to accommodate Na-ions. More significantly, sulfur doping makes GAs more electron-rich which causes polarization between the surfaces of N,S-GA and SnS2, resulting in a strong electronic coupling between them (see Scheme 1). Hence, 5



Page 6 of 38

the bridging layer of SnS2 along with the sulfur atoms covalently bonded to the graphene aerogels guarantee the robust architecture of the anode materials. These results are also supported by density functional theory (DFT) calculations. In summary, the SnS2@N,S-GA composites with appropriate SnS2 loading show improved electronic and ionic conductivity and enhanced sodium storage ability in terms of excellent cycling stability and high reversible capacity. EXPERIMENTAL SECTION Synthesis of the SnS2@N,S-GA composites with different SnS2 contents Graphite oxide (GO) was produced by the oxidative treatment of natural graphite via a modified Hummers' method based on our previous reports.33,34 SnS2@N,S-GA composites were synthesized using a facile hydrothermal method. Briefly, 65 mg GO was dissolved in 45 mL deionized water with sonication for 20 min. Three known amounts of SnO2 sol were added to the suspension to control the SnS2 loading in the composites, followed by 30 min vigorous stirring to form a homogeneous solution. 3.25 g thiourea (Tianjin Jiangtian Chemical Technology Co., Ltd.) was then mixed with above solution via another 30 min vigorous stirring. The resultant hybrid was transferred to a 50 ml Teflon-lined autoclave and heated in an oven at 180 °C for 24 h. The black products were washed several times with ethanol (Tianjin Jiangtian Chemical Technology Co., Ltd.) and deionized water by centrifugation at 10000 rpm, and

subsequently

freeze-dried.

The

collected

samples

were

marked

as

SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III, respectively. The pristine graphene aerogels (GAs) were prepared via the same process without the addition of SnO2 sol and thiourea. N,S-GAs were produced via the same process without the addition of SnO2 sol. The synthesis process is further illustrated in 6


Page 7 of 38 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


Scheme S1. Physical characterization The structures of nanocomposite were carried out via X-ray diffraction (XRD, DX-2700) using a CuKα (λ ≈ 1.54 Å) radiation source. The surface morphology of SnS2 in the presence of N,S-GAs was collected via scanning electron microscopy (SEM, SU8010, Hitachi) and transmission electron microscopy (TEM, FEI Tecnai G2 F20). The equipped Energy Dispersive X-ray Spectrometer (EDS) was used to analyze

chemical

composition.

Thermogravimetric

analysis

(TGA,

Pyris

Diamond6000 TG/DTA, PerkinElmer Co, America) was conducted to verify SnS2 contents in composites. The elemental characteristics of composite materials were performed by X-ray photoelectron spectroscopy (XPS, VG ESCALAB MK II). Raman spectra were tested on the LabRAM HR800 system. Electrochemical performance The electrochemical characterization was performed using CR2032 coin cells. The working electrode was synthesized by mixing composite material (70 %), carbon black (20 %), and polyvinylidene fluoride (PVDF, 10 %) dispersed in 1-methyl-2-pyrrolidinone (NMP), then pasted on copper foil and followed by drying under vacuum at 80 °C for overnight. Then, the electrodes were punched into 12 mm disks in diameter, and the typical electrode loading was about 0.55 mg cm-2. Metallic sodium foil as the counter and reference electrodes. The electrolyte was 1M NaClO4 in a mixture of ethylene carbonate (EC) and propylene carbonate (PC) (2:1 by volume) with a 10 vol% addition of fluoroethylene carbonate (FEC). Afterward, test cells were assembled in an Ar-filled glove box (H2O, O2 < 0.1 ppm). The cells were galvanostatically charged and discharged by a multi-channel battery testing system (LANHE CT2001A) between 0.01 V and 3.0 V. Electrochemical impedance 7



spectroscopy (EIS) at an alternating voltage of 5 mV over the frequency range of 100 kHz to 0.01 Hz and cyclic voltammetry (CV) ranging from 0.01 to 3.0 V at a scan rate of 0.1 mV s-1 were recorded over an electrochemical workstation (Princeton Applied Research VersaSTAT4). All electrochemical characterizations were performed at room temperature.

RESULTS AND DISCUSSION XRD phase of three SnS2@N,S-GA samples is showed in Figure 1a, the pristine GAs exhibit two graphite-like diffraction peaks at (002) and (100), and the average layer number of GAs is 9 (see Figure S1). Meanwhile, the diffraction peaks that emerge in the three SnS2@N,S-GA samples show a similar crystalline structure, agreeing with those of standard XRD patterns of hexagonal SnS2 (JCPDS card No. 23-0677).35 Notably, SnS2 in SnS2@N,S-GA-III has greater crystallinity, indicated by the increased peak intensities compared to those of SnS2@N,S-GA-I and SnS2@N,S-GA-II.36 Furthermore, the broad diffraction peaks seen in the SnS2@N,S-GA-I and SnS2@N,S-GA-II patterns indicate the presence of smaller SnS2 nanocrystals. Thermogravimetric analysis (TGA) is conducted to determine the mass loading of SnS2 on the N,S-GA framework. TGA and DTG curves of SnS2@N,S-GA-II show three distinct regions of weight loss (see Figure S2). For initial weight loss (7.2 %) ranging from 25 °C to 250 °C, which is associated with the evaporation of physically adsorbed water.37 In the second region from 250 °C to 500 °C, weight loss (21.6 %) may be owing to the oxidation of SnS2 into SnO2.38 The third region of weight loss (40.3 %) between 500 °C and 800 °C is ascribed to the removal of N,S-GAs in the composite. Hence, the SnS2 mass percentage is approximately 53 % for SnS2@N,S-GA-II as seen in Figure 1b. Accordingly, the SnS2 mass percentages in 8


Page 8 of 38

Page 9 of 38 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


SnS2@N,S-GA-I and SnS2@N,S-GA-III are 41 % and 75 %, respectively. Further structural insights of as-prepared samples are explored via Raman spectroscopy (Figure S3). The D-band (~1336 cm-1) attributes to disorder and defects in the hexagonal graphitic layers,39 while the G-band (~1574 cm-1) corresponds to the first-order scattering of the E2g mode of sp2 carbon atoms.40 The calculated ID/IG ratios for SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III are 1.73, 1.71, and 1.64, respectively. Notably, compared with SnS2@N,S-GA-I and SnS2@N,S-GA-II, the SnS2@N,S-GA-III exhibits a decreased ID/IG ratio, implying an increase in the average size of the sp2 graphitic domains.41 XPS test is employed to further validate element states of as-prepared SnS2@N,S-GA composites. As shown in Figure 2a, one can see the existence of tin, carbon, oxygen, sulfur, and nitrogen from the survey spectra. Clearly, N 1s peak of SnS2@N,S-GA-III is comparatively weaker, suggesting a lower amount of doped nitrogen. Furthermore, Sn 3d3/2 and Sn 3d5/2 peaks are found in XPS analysis with an energy difference of 8.4 eV (Figure 2b), confirming the presence of tin (IV).42 It can be seen from Figure 2c that the S 2p spectra of SnS2@N,S-GA-II can be divided into two types of doublets. The first set of doublets consist of the peaks centered at 161.4 eV (S1) and 162.7 eV (S2) corresponding to binding energies of SnS2.43 The second set of doublets are the higher-energy peaks seen at 163.8 eV (S3) and 164.9 eV (S4) that are assigned to the formation of a C-S-C bridge, indicating that sulfur is possibly covalently bonded with carbon.44,45 It is calculated that the total amount of sulfur doped in SnS2@N,S-GA-II is 4.6 %. In comparison, SnS2@N,S-GA-III shows no obvious S3 and S4 peaks (Figure 2d) which illustrates that the amount of sulfur doped is insignificant. In Figures 2e and f, the high resolution N 1s peaks are able to de-convolute into three components: pyridinic-N (398.5 eV, N1), pyrrolic-N (400.1 eV, 9



Page 10 of 38

N2), and graphitic-N (401.3 eV, N3).46 Moreover, as estimated by XPS results, the nitrogen concentrations of SnS2@N,S-GA-II and SnS2@N,S-GA-III are 2.41 % and 1.88 %, respectively. Note that the N1 and N2 species are dominant in the composites, suggesting that nitrogen heteroatoms mainly reside at the edges or at the nanoholes of the GAs. The vacancy and electron deficiency caused by nitrogen doping can provide a feasible pathway for Na-ions, which is favorable for enhancing sodium transmission rates.47 Additionally, Figures 2g and h present the high resolution C 1s spectra fitted with three types of carbon including C=C (284.6 eV, C1), C=N (285.4 eV, C2), and C-N (286.6 eV, C3). These results further support that the oxygen atoms in GAs have been substituted by nitrogen atoms successfully. Meanwhile, the overwhelming percentage of graphitic carbon is indicative of the graphitized nature of the GAs in SnS2@N,S-GA. Overall, these analyses show that SnS2@N,S-GA composites have been successfully designed. The

morphologies

of

SnS2@N,S-GA-I,

SnS2@N,S-GA-II,

and

SnS2@N,S-GA-III are analyzed via SEM (see Figure 3). As observed, three samples exhibit a typical graphene aerogel network structure, and no obvious SnS2 nanocrystals are observed in SnS2@N,S-GA-I and SnS2@N,S-GA-II due to the small particle size. This contrasts with the SnS2@N,S-GA-III sample where SnS2 nanocrystals are observed to anchor onto the N,S-GAs because of the high mass loading and large SnS2 particle size. It is important to note that an excess of SnS2 particles can result in severe aggregation which may cause large volume changes upon cycling and loss of electrical contact with the N,S-GAs. In this regard, the samples are analyzed via TEM to exhibit distribution of SnS2 on N,S-GAs, summarized in Figure 4. It can be seen in Figures 4a and b that low SnS2 loading results in particles of approximately 5 nm 10


Page 11 of 38 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


decorating the N,S-GAs. As shown in Figures 4c and d, suitable loading of SnS2 nanocrystals in SnS2@N,S-GA-II show an average particle size of 5 nm which uniformly anchor onto N,S-GAs. Additionally, the fringes with lattice spacings of 0.32 nm and 0.28 nm agree well with (100) and (101) planes in hexagonal SnS2, respectively.48 Meanwhile, the diffraction rings of the selected area electron diffraction (SEAD) pattern (see insert of Figure 4c) can be indexed to (100), (101), and (102) crystal planes for SnS2. In comparison, TEM images of SnS2@N,S-GA-III (Figures 4e and f) indicate that the N,S-GAs are heavily embellished with 10 nm particles of SnS2 due to the high SnS2 loading of SnS2, and the aggregation of SnS2 nanocrystals occurs severely. Figure

S4

presents the

EDS spectrum of

SnS2@N,S-GA-II, which reveals the presence of tin, sulfur, carbon, and nitrogen in the composites. The elemental mapping (Figure S5) further illustrates the homogeneous distribution of SnS2 nanocrystals in N,S-GAs. To explore sodium storage mechanisms of the SnS2@N,S-GA composites, cyclic voltammetry is carried out on the SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III electrode materials in the voltage range of 0.01-3.0 V at 0.1 mV s-1, as shown in Figures 5a-c. In the first cathodic scan, the peaks at higher voltage (1.20 V, 1.62 V) can be associated with the formation of NaSnS2:23,49 SnS2 + Na+ + e- → NaSnS2

(1)

Note that the reduction peak at 1.20 V disappears at the second scan. It is assigned to the formation of irreversible solid electrolyte interface (SEI) film, which can be further confirmed by the cyclic voltammogram of pristine GAs (Figure S6). Subsequently, the cathodic peaks from 0.65 to 0.30 V attributed to synthesis for metallic tin and sodium sulfide as well as the alloying process between tin and Na-ions.50,51 These reactions can be described by Equations (2) and (3): 11



NaSnS2 + 3Na+ + 3e- → Sn +2Na2S

Page 12 of 38

(2)

Sn + xNa+ + xe- → NaxSn

(3)

Intriguingly, these peaks are shifted to a higher potential at subsequent scans, suggesting that there is a phase transformation during the first cycle.52 Furthermore, the corresponding oxidation peaks (0.25 V, 0.75 V, 1.20 V) may be attributed to the desodiation reaction of NaxSn.53 However, the three above-mentioned peaks are inconspicuous in SnS2@N,S-GA-I and SnS2@N,S-GA-II due to the imperfect crystallinity of SnS2, which can be confirmed by XRD results. Additionally, three higher voltage oxidation peaks (1.61 V, 1.84 V, 2.10 V) can be found in all CV curves. The peak at 1.61 V is attributed to Na-ion storage/release in GAs, anodic peak concentrated in 1.84 V assigns to deinsertion process for NaSnS2, and the peak at 2.10 V corresponds to the sodium extraction from NaSnS2 and oxidation of Sn to SnS2.23,54 It is worth mentioning that although the CV curves of the three SnS2@N,S-GA are incomplete anastomosis due to the complex systems, all key points of the reaction mechanism are consistent with previous reports. The charge-discharge tests are presented in Figures 5d-f. The initial discharge capacities of SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III are 1155.6, 1267.3, and 1567.5 mAh g-1, respectively. Meanwhile, the corresponding coulombic efficiencies are 35.4 %, 42.9 %, and 43.4 %, respectively. It can be observed that the high irreversible capacity arises for three samples. This phenomenon generally results from the solid electrolyte interphase (SEI) formation due to the decomposition of electrolyte.55,56 During the subsequent cycles, it can be noticed that the specific capacity of SnS2@N,S-GA-II decreases slower than that of both SnS2@N,S-GA-I and SnS2@N,S-GA-III, suggesting better cycling performance. The cycling performance of bare SnS2 (see supporting materials for detailed 12


Page 13 of 38 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


synthesis information, and Figure S7 for morphological and structural features), pristine GAs, N,S-GAs, SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III are compared at 50 mA g-1 ranging from 0.01 to 3.0 V from the second cycle (see Figure 6a). The pristine GAs exhibit very poor specific capacity. In contrast, N,S-GAs obtain improved discharge capacity (177 mAh g-1 in 100th cycle) because of introduction of nitrogen and sulfur heteroatoms, which can facilitate the electrode-electrolyte interactions and charge transfer efficiently. Additionally, the cyclability of bare SnS2 is significantly hampered due to the aggregation and pulverization issue.57 Fortunately, the SnS2@N,S-GA composites all perform improved cycling properties. This phenomenon may be associated with the synergic effect of SnS2 with N,S-GAs.58 Furthermore, the sodium storage capacity of composites highly interrelates with SnS2 content and heteroatom concentrations. SnS2@N,S-GA-I delivers the reversible capacity of 221.4 mAh g-1 up to 100 cycles, which is lower than that of SnS2@N,S-GA-II and SnS2@N,S-GA-III due to the low SnS2 loading and inability to exploit the high specific surface area of GAs. SnS2@N,S-GA-III exhibits better sodium storage performance than SnS2@N,S-GA-II in the first 53 cycles, while when the cycling numbers increase to 100 cycles, the discharge capacity rapidly declines to about 288.7 mAh g-1, showing poor cycling stability. Remarkably, the SnS2@N,S-GA-II achieves an excellent reversible capacity (360.5 mAh g-1 in the 100th cycle). Based on the above results, the increase of SnS2 content in the composites enhances the reversible capacity. Unfortunately, the discharge capacity of SnS2@N,S-GA-III rapidly fades, while the SnS2@N,S-GA-II shows better cycling stability, demonstrating that both suitable mass loading of SnS2 and the introduction of more nitrogenous and sulfurous groups to the surface of GAs facilitate capacity improvements. Meanwhile, the coulombic efficiency of 13



SnS2@N,S-GA-II anode is more than 95 % in the process of cycling. Moreover, the cycling performance of SnS2@N,S-GA-II anode under varying current densities is tested and compared in Figure 6b. Fortunately, discharge capacity remains 527 mAh g-1 after 50 cycles when the current density is 20 mA g-1. The excellent coulombic efficiency of approximately 100 % from the second cycle is obtained. When tested under increasing current densities, the SnS2@N,S-GA-II exhibits similar cycling performance, showing insertion/extraction of Na+ for composites have no effect on their cyclability, and the crystal structure remains relatively unchanged under the higher charge-discharge currents.59 Notably, the cycling performance is unstable due to the variable temperature in the testing environment. The rate capability of the SnS2@N,S-GA composite is further investigated, as presented in Figure 6c. In the case of SnS2@N,S-GA-I, a visible decrease of capacity is found with an increase in current density. For SnS2@N,S-GA-II and SnS2@N,S-GA-III, they deliver similar rate capacities when the electrodes are tested at low current densities (50, 100, and 200 mA g-1). Nevertheless, discharge capacities of SnS2@N,S-GA-III decline significantly compared to that of SnS2@N,S-GA-II at high current densities of 400 and 800 mA g-1. More strikingly, SnS2@N,S-GA-II maintains the capacity of 340 mAh g-1 at a high current density of 800 mA g-1. Meantime, it recovers to a great extent, to around 434.3 mAh g-1 at 50 mA g-1. This result is even better than the electrode cycling in Figure 6a, implying excellent stability at high rate currents. Additionally, the relative capacity retention values based on the capacities obtained at various current densities are shown in Figure 6d, which further demonstrates that SnS2@N,S-GA-II possesses superior rate capability in SIB performance. The cyclic voltammograms of the SnS2@N,S-GA-II and SnS2@N,S-GA-III 14


Page 14 of 38

Page 15 of 38 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


electrodes at varying scan rates are shown in Figures 7a and b, respectively. It can be observed that the anodic potential shifts to higher voltages when the scan rate increases from 0.1 to 0.8 mV s-1. This behavior is caused by the increased polarization at higher sweep rates attributed to the kinetic limitations of sodium diffusion through the active materials.60,61 The following is the Randles-Sevcik equation:62,63 Ip = 2.687 × 105 n3/2 A D1/2 v1/2 C0

(4)

In this equation, Ip represents peak current (A), v is the scan rate (V s-1), n is number of reaction electrons (n=1), D expresses Na+ diffusion coefficient (cm2 s-1), A indicates the electrode area (A=1.13 cm2), and C0 is concentration of Na-ions in solution (C0=1 mol cm-3). According to Equation (4), the peak current is in direct proportion to square root of the scan rate (Figure 7c). Sodium diffusion coefficients of SnS2@N,S-GA-II and SnS2@N,S-GA-III can be calculated from the slopes of these plots, and are thus determined to be 3.80×10-12 and 4.82×10-13 cm2 s-1, respectively. These kinetics results imply that sodium storage performance is primarily related to the heteroatom doping, which can generate more extrinsic defects and active sites to accelerate Na-ion diffusion. To further understand the electrode reaction kinetics for composites, EIS is carried out on the 100th cycle. As shown in Figure 7d, the Nyquist plots consist of the characteristic partially overlapped semicircles appearing at high and intermediate frequencies as well as a sloped line at low frequency.64,65 Figure 7e shows the equivalent circuit where Rs is ohmic electrolyte resistance, Rsei represents resistance of Na-ion migration through the SEI film, Rct is charge transfer resistance, CPEsei is passivation film capacitance, CPEct represents the double layer capacitance.66,67 It can be seen that SnS2@N,S-GA-II shows a much lower Rct resistance in comparison with SnS2@N,S-GA-I and SnS2@N,S-GA-III, confirming that the electrode reaction kinetics and electron conduction of SnS2@N,S-GA-II are 15



improved. This phenomenon is primarily attributed to the increased nitrogenous and sulfurous groups on the surface of the GAs which significantly enhance the electrochemical performance of SnS2@N,S-GA-II.68 Significantly, we carry out density functional theory (DFT) calculations to analyze the structural properties of the composite materials in order to better understand the improved cycling capability of SnS2@N,S-GA composites with optimized SnS2 mass loading. We design a (4 × 4) SnS2 monolayer on a (6 × 6) graphene matrix. After stabilization, the lattice of the SnS2 is evaluated to be 3.62, 3.62, and 5.85 Å at the x-, y-, and z- axes. The electronic structure of valence electrons can determine the electronic and physicochemical interaction between SnS2 and GA, exhibiting an important influence on the structural stability.30,69 The charge density changes of SnS2@N,S-GA and SnS2@GA are presented in Figures 8a and b to further understand the interaction derived from the shared electron clouds. Intriguingly, massive charge transfer occurs from N,S-GA to SnS2 in SnS2@N,S-GA compared to SnS2@GA, which negatively polarizes the interface between SnS2 and N,S-GA. Meanwhile, note that the sulfur atoms doped in the graphene aerogel show a strong bridging effect with SnS2. These results ensure robust composite architecture for SnS2@N,S-GA. Figures 8c and d illustrate the band structures of SnS2@N,S-GA and SnS2@GA which have different characteristics. Some conduction bands of SnS2@N,S-GA move downward towards the valence band, allowing a facile promotion of valence electrons across the band gap, resulting in enhanced electrical conductivity. In addition, there are broadened bands for SnS2@N,S-GA which leads to smaller electron effective mass, suggesting better electronic transport capacity under an external electric field. As seen in Figures 8e and f, the calculated electronic density of states (DOS) reveal that the total DOS peak of SnS2@N,S-GA is much 16


Page 16 of 38

Page 17 of 38 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


higher than that of SnS2@GA, indicating a larger density of free electrons. Furthermore, after nitrogen and sulfur dual-doping, the contribution of sulfur atoms for enlarging the total DOS peak becomes more remarkable, while the nitrogen atoms have no obvious effect due to the lower doped concentrations. Therefore, the heteroatom doping plays an imperative role in the improved electrical conductivity of SnS2@N,S-GA.

CONCLUSIONS In summary, an effective technique is developed for successful synthesis of SnS2@N,S-GA composites. As an anode material of SIBs, SnS2@N,S-GA-II with suitable mass loading of SnS2 and nitrogenous/sulfurous groups in GAs presents outstanding cycling performance. It achieves high discharge capacity (527 mAh g-1 upon 50 cycles) as well as superior rate capability (340 mAh g-1 at a current density of 800 mA g-1). Therefore, the introduced nitrogen and sulfur heteroatoms on the surface of GAs play an important role in SnS2@N,S-GA composites by providing more active sites and good accessibility for the Na-ions. In addition, the optimized mass loading of SnS2 results in the ideal synergic effect between SnS2 and N,S-GAs. More significantly, the first-principles calculation confirms that the sulfur atoms doping in the GA shows a strong bridging effect with SnS2, which can ensure robust composite architecture. Simultaneously, the heteroatom dual-doping of graphene plays an imperative role in the improved electrical conductivity of SnS2@N,S-GA. Altogether, this study may stimulate the search for improved anode materials for high energy SIBs.

ASSOCIATED CONTENT Supporting information 17



Illustration of the synthesis procedure of SnS2@N,S-GA composites, The cross-sectional HRTEM images of Pristine GAs, TGA and DTG curves of SnS2@N,S-GA-II, Raman spectra of SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III, EDS spectra of SnS2@N,S-GA-II, Typical SEM image of SnS2@N,S-GA-II, The corresponding elemental mapping images of Sn, C, O, S, and N, The cyclic voltammetry curve of pristine GAs at a scan rate of 0.1 mV s-1 in the voltage range of 0.01-3.0 V, Typical SEM images and XRD pattern of bare SnS2, Synthesis of bare SnS2.

ACKNOWLEDGEMENTS This research was supported by the National Natural Science Foundation of China (51572194 and 51672189), Academic Innovation Funding of Tianjin Normal University (52XC1404), and Training Plan of Leader Talent of University in Tianjin.

REFERENCES (1) Li, H.; Shen, F.; Luo, W.; Dai, J.; Han, X.; Chen, Y.; Yao, Y.; Zhu, H.; Fu, K.; Hitz, E.; Hu, L. Carbonized-leaf Membrane with Anisotropic Surfaces for Sodium-ion Battery. ACS Appl. Mater. Inter. 2016, 8 (3), 2204-2210. (2) Sun, J.; Shen, J.; Wang, T. Electrochemical Study of Na0.66Ni0.33Mn0.67−xMoxO2 as Cathode Material for Sodium-ion Battery. J Alloy Compd. 2017, 709, 481-486. (3) Jin, T.; Han, Q.; Wang, Y.; Jiao, L. 1D Nanomaterials: Design, Synthesis, and Applications in Sodium-Ion Batteries. Small 2017, 1703086. (4) Kang, H.; Liu, Y.; Cao, K.; Zhao, Y.; Jiao, L.; Wang, Y.; Yuan, H. Update on 18


Page 18 of 38

Page 19 of 38 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


Anode Materials for Na-ion Batteries. J. Mater. Chem. A 2015, 3, 17899-17913. (5) Bao, T.; Zhong, H.; Zheng, H.; Zhan, H.; Zhou, Y. One-pot Synthesis of FeF3/Graphene Composite for Sodium Secondary Batteries. Mater. Lett. 2015, 158, 21-24. (6) Wang, J. W.; Liu, X. H.; Mao, S. X.; Huang, J. Y. Microstructural Evolution of Tin Nanoparticles During in Situ Sodium Insertion and Extraction. Nano Lett. 2012, 12, 5897-5902. (7) Yang, F.; Zhang, Z.; Han, Y.; Du, K.; Lai, Y.; Li, J. TiO2/Carbon Hollow Spheres as Anode Materials for Advanced Sodium Ion Batteries. Electrochim. Acta 2015, 178, 871-876. (8) Metrot, A.; Guerard, D.; Billaud, D.; Herold, A. New Results about the Sodium-graphite System. Synthetic Metals. 1980, 1, 363-369. (9) Liu, Y.; Yang, Y.; Wang, X.; Dong, Y.; Tang, Y.; Yu, Z.; Zhao, Z.; Qiu, J. Flexible Paper-like Free-standing Electrodes by Anchoring Ultrafine SnS2 Nanocrystals on Graphene Nanoribbons for High-performance Sodium Ion Batteries. ACS Appl. Mater. Inter. 2017, 9, 15484-15491. (10) Ji, L.; Gu, M.; Shao, Y.; Li, X.; Engelhard, M. H.; Arey, B. W.; Wang, W.; Nie, Z.; Xiao, J.; Wang, C.; Zhang, J. G.; Liu, J. Controlling SEI Formation on SnSb-Porous Carbon Nanofibers for Improved Na Ion Storage. Adv. Mater. 2014, 26, 2901-2908. (11) Gu, M.; Kushima, A.; Shao, Y.; Zhang, J. G.; Liu, J.; Browning, N. D.; Li, J.; Wang, C. Probing the Failure Mechanism of SnO2 Nanowires for Sodium-ion 19



Batteries. Nano Lett. 2013, 13, 5203-5211. (12) Li, L.; Seng, K. H.; Li, D.; Xia, Y.; Liu, H. K.; Guo, Z. SnSb@Carbon Nanocable Anchored on Graphene Sheets for Sodium Ion Batteries. Nano Res. 2014, 7, 1466-1476. (13) Jahel, A.; Ghimbeu, C. M.; Darwiche, A.; Vidal, L.; Hajjar-Garreau, S.; Vix-Guterl, C.; Monconduit, L. Exceptionally Highly Performing Na-ion Battery Anode Using Crystalline SnO2 Nanoparticles Confined in Mesoporous Carbon. J. Mater. Chem. A 2015, 3, 11960-11969. (14) Fan, L.; Li, X.; Yan, B.; Feng, J.; Xiong, D.; Li, D.; Gu, L.; Wen, Y.; Lawes, S.; Sun, X. Controlled SnO2 Crystallinity Effectively Dominating Sodium Storage Performance. Adv. Energy Mater. 2016, 1502057. (15) Zhang, Y.; Xie, J.; Zhang, S.; Zhu, P.; Cao, G.; Zhao, X. Ultrafine Tin Oxide on Reduced Graphene Oxide as High-performance Anode for Sodium-ion Batteries. Electrochim. Acta 2015, 151, 8-15. (16) Ren, Y.; Wang, J.; Huang, X.; Ding, J. Three-dimensional SnS2 Flowers/Carbon Nanotubes Network: Extraordinary Rate Capacity for Sodium-ion Battery. Mater. Lett. 2017, 186, 57-61. (17) Liu, Y.; Li, Y.; Kang, H.; Jin, T.; Jiao, L. Design, Synthesis, and Energy-related Applications of Metal Sulfides. Mater. Horiz. 2016, 3, 402-421. (18) Wu, Q.; Jiao, L.; Du, J.; Yang, J.; Guo, L.; Liu, Y.; Wang, Y.; Yuan, H. One-pot Synthesis of Three-dimensional SnS2 Hierarchitectures as Anode Material for Lithium-ion Batteries. J. Power Sources 2013, 239, 89-93. 20


Page 20 of 38

Page 21 of 38 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


(19) Zhang, Q.; Li, R.; Zhang, M.; Zhang, B.; Gou, X. SnS2/Reduced Graphene Oxide Nanocomposites with Superior Lithium Storage Performance. Electrochim. Acta 2014, 115, 425-433. (20) Yin, L.; Chai, S.; Ma, J.; Huang, J.; Kong, X.; Bai, P.; Liu, Y. Effects of Binders on Electrochemical Properties of the SnS2 Nanostructured Anode of the Lithium-ion Batteries. J Alloy Compd. 2017, 698, 828-834. (21) Mei, L.; Xu, C.; Yang, T.; Ma, J.; Chen, L.; Li, Q.; Wang, T. Superior Electrochemical Performance of Ultrasmall SnS2 Nanocrystals Decorated on Flexible RGO in Lithium-ion Batteries. J. Mater. Chem. A 2013, 1, 8658-8664. (22) Zhang, Y.; Zhu, P.; Huang, L.; Xie, J.; Zhang, S.; Cao, G.; Zhao, X. Few-layered SnS2 on Few-layered Reduced Graphene Oxide as Na-ion Battery Anode with Ultralong Cycle Life and Superior Rate Capability. Adv. Funct. Mater. 2015, 25, 481-489. (23) Liu, Y.; Kang, H.; Jiao, L.; Chen, C.; Cao, K.; Wang, Y.; Yuan, H. Exfoliated-SnS(2) Restacked on Graphene as a High-capacity, High-rate, and Long-cycle Life Anode for Sodium Ion Batteries. Nanoscale 2015, 7, 1325-1332. (24) Ji, L.; Xin, H. L.; Kuykendall, T. R.; Wu, S. L.; Zheng, H.; Rao, M.; Cairns, E. J.; Battaglia,

V.;

Zhang,

Y.

G.

SnS(2)

Nanoparticle

Loaded

Graphene

Nanocomposites for Superior Energy Storage. Phys. Chem. Chem. Phys. 2012, 14, 6981-6986. (25) Paraknowitsch, J. P.; Thomas, A. Doping Carbons Beyond Nitrogen: An Overview of Advanced Heteroatom Doped Carbons with Boron, Sulphur and 21



Phosphorus for Energy Applications. Energ. Environ. Sci. 2013, 6, 2839-2855. (26) Xu, J.; Wang, M.; Wickramaratne, N. P.; Jaroniec, M.; Dou, S.; Dai, L. High-performance Sodium Ion Batteries Based on A 3D Anode from Nitrogen-doped Graphene Foams. Adv. Mater. 2015, 27, 2042-2048. (27) Li, Z. T.; Wu, G. L.; Deng, S. Z.; Wang, S. J.; Wang, Y. K.; Zhou, J. Y.; Liu, S. P.; Wu, W. T.; Wu, M. B. Combination of Uniform SnO2 Nanocrystals with Nitrogen Doped Graphene for High-performance Lithium-ion Batteries Anode. Chem. Eng. J. 2016, 283, 1435-1442. (28) Chen, C. N.; Ma, T.; Zhang, Q.; Fan, W.; Fu, X. W.; Wang, Z. B. Synthesis and Electrochemical Properties of Nitrogen-doped Graphene (NG)/Nickle Oxide (NiO) Nanocomposite for Supercapacitor. J. Nanosci. Nanotechno. 2015, 15, 9699-9704. (29) Xie, D.; Tang, W. J.; Xia, X. H.; Wang, D. H.; Zhou, D.; Shi, F.; Wang, X. L.; Gu, C. D.; Tu, J. P. Integrated 3D Porous C-MoS2/Nitrogen-doped Graphene Electrode for High Capacity and Prolonged Stability Lithium Storage. J. Power Sources 2015, 296, 392-399. (30) Wang, X.; Li, G.; Seo, M. H.; Hassan, F. M.; Hoque, M. A.; Chen, Z. Sulfur Atoms Bridging Few-layered MoS2 with S-doped Graphene Enable Highly Robust Anode for Lithium-ion Batteries. Adv. Energy Mater. 2015, 5, 1501106. (31) Zhou, Y.; Zeng, Y.; Xu, D.; Li, P.; Wang, H.; Li, X.; Li, Y.; Wang, Y. Nitrogen and Sulfur Dual-doped Graphene Sheets as Anode Materials with Superior Cycling Stability for Lithium-ion Batteries. Electrochim. Acta 2015, 184, 24-31. 22


Page 22 of 38

Page 23 of 38 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


(32) Shan, H.; Li, X.; Cui, Y.; Xiong, D.; Yan, B.; Li, D.; Lushington, A.; Sun, X. Sulfur/Nitrogen Dual-doped Porous Graphene Aerogels Enhancing Anode Performance of Lithium Ion Batteries. Electrochim. Acta 2016, 205, 188-197. (33) Li, X.; Hu, Y.; Liu, J.; Lushington, A.; Li, R.; Sun, X. Structurally Tailored Graphene Nanosheets as Lithium Ion Battery Anodes: An Insight to Yield Exceptionally High Lithium Storage Performance. Nanoscale 2013, 5, 12607-12615. (34) Hummers, W. S.; Offeman, R. E. Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80, 1339-1339. (35) Tu, F.; Xu, X.; Wang, P.; Si, L.; Zhou, X.; Bao, J. A Few-layer SnS2/Reduced Graphene Oxide Sandwich Hybrid for Efficient Sodium Storage. J. Phys. Chem. C 2017, 121, 3261-3269. (36) Liu, S.; Lu, X.; Xie, J.; Cao, G.; Zhu, T.; Zhao, X. Preferentialc-axis Orientation of Ultrathin SnS2 Nanoplates on Graphene as High-performance Anode for Li-ion Batteries. ACS Appl. Mater. Inter. 2013, 5, 1588-1595. (37) Huang, Z. X.; Wang, Y.; Wong, J. I.; Yang, H. Y. Free Standing SnS2 Nanosheets on 3D Graphene Foam: An Outstanding Hybrid Nanostructure Anode for Li-ion Batteries. 2D Mater. 2015, 2, 024010. (38) Li, J.; Wu, P.; Lou, F.; Zhang, P.; Tang, Y.; Zhou, Y.; Lu, T. Mesoporous Carbon Anchored with SnS2 Nanosheets as an Advanced Anode for Lithium-ion Batteries. Electrochim. Acta 2013, 111, 862-868. (39) Luo, B.; Fang, Y.; Wang, B.; Zhou, J.; Song, H.; Zhi, L. Two Dimensional 23



Page 24 of 38

Graphene-SnS2 Hybrids with Superior Rate Capability for Lithium Ion Storage. Energy Environ Sci. 2012, 5, 5226-5230. (40) Chen, Y.; Wang, J.; Liu, H.; Banis, M. N.; Li, R.; Sun, X.; Sham, T. K.; Ye, S.; Knights, S. Nitrogen Doping Effects on Carbon Nanotubes and the Origin of the Enhanced Electrocatalytic Activity of Supported Pt for Proton-exchange Membrane Fuel Cells. J. Phys. Chem. C 2011, 115, 3769-3776. (41) Liang, J.; Zhao, Y.; Guo, L.; Li, L. Flexible Free-standing Graphene/SnO(2) Nanocomposites Paper for Li-ion Battery. ACS Appl. Mater. Inter. 2012, 4, 5742-5748. (42) Deng, W.; Chen, X.; Liu, Z.; Hu, A.; Tang, Q.; Li, Z.; Xiong, Y. Three-dimensional Structure-based Tin Disulfide/Vertically Aligned Carbon Nanotube Arrays Composites as High-performance Anode Materials for Lithium Ion Batteries. J. Power Sources 2015, 277, 131-138. (43) Jiang, X.; Yang, X.; Zhu, Y.; Shen, J.; Fan, K.; Li, C. In Situ Assembly of Graphene Sheets-supported SnS2 Nanoplates into 3D Macroporous Aerogels for High-performance Lithium Ion Batteries. J. Power Sources 2013, 237, 178-186. (44) Zhang, S.; Yao, F.; Yang, L.; Zhang, F.; Xu, S. Sulfur-doped Mesoporous Carbon from

Surfactant-intercalated

Layered

Double

Hydroxide

Precursor

as

High-performance Anode Nanomaterials for Both Li-ion and Na-ion Batteries. Carbon 2015, 93, 143-150. (45) Yan, Y.; Yin, Y. X.; Xin. S.; Guo, Y. G.; Wan, L. J. Ionothermal Synthesis of Sulfur-doped Porous Carbons Hybridized with Graphene as Superior Anode 24


Page 25 of 38 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


Materials for Lithium-ion Batteries. Chem. Commun. 2012, 48, 10663-10665. (46) Qu, Y.; Zhang, Z.; Zhang, X.; Ren, G.; Lai, Y.; Liu, Y.; Li, J. Highly Ordered Nitrogen-rich

Mesoporous

Carbon

Derived

from

Biomass

Waste

for

High-performance Lithium-sulfur Batteries. Carbon 2015, 84, 399-408. (47) Yang, J.; Wang, S.; Ma, Z.; Du, Z.; Li, C.; Song, J.; Wang, G.; Shao, G. Novel Nitrogen-doped Hierarchically Porous Coralloid Carbon Materials as Host Matrixes for Lithium-sulfur Batteries. Electrochim. Acta 2015, 159, 8-15. (48) Kim, T. J.; Kim, C.; Son, D.; Choi, M.; Park, B. Novel SnS2-nanosheet Anodes for Lithium-ion Batteries. J. Power Sources 2007, 167, 529-535. (49) Wu, Y.; Nie, P.; Wu, L.; Dou, H.; Zhang, X. 2D MXene/SnS2 Composites as High-performance Anodes for Sodium Ion Batteries. Chem. Eng. J. 2018, 334, 932-938. (50) Wang, Y.; Zhou, J.; Wu, J.; Chen, F.; Li, P.; Han, N.; Huang, W.; Liu, Y.; Ye, H.; Zhao, F.; Li, Y. Engineering SnS2 Nanosheet Assemblies for Enhanced Electrochemical Lithium and Sodium Ion Storage. J. Mater. Chem. A 2017, 5, 25618-25624. (51) Thangavel, R.; Pandian, A. S.; Ramasamy, H. V.; Lee, Y. S. Rapidly Synthesized, Few-Layered Pseudocapacitive SnS2 Anode for High-Power Sodium Ion Batteries. ACS Appl. Mater. Interfaces 2017, 9, 40187-40196. (52) Prikhodchenko, P. V.; Yu, D. Y.; Batabyal, S. K.; Uvarov, V.; Gun, J.; Sladkevich, S.; Mikhaylov, A.; Medvedev, A.; Lev, O. Nanocrystalline Tin Disulfide Coating of Reduced Graphene Oxide Produced by the Peroxostannate 25



Deposition Route for Sodium Ion Battery Anodes. J. Mater. Chem. A 2014, 2, 8431-8437. (53) Zhou, P.; Wang, X.; Guan, W.; Zhang, D.; Fang, L.; Jiang, Y. SnS2 Nanowall Arrays toward High-performance Sodium Storage. ACS Appl. Mater. Inter. 2017, 9, 6979-6987. (54) Wang, J.; Luo, C.; Mao, J.; Zhu, Y.; Fan, X.; Gao, T.; Mignerey, A.; Wang, C. Solid-state Fabrication of SnS2/C Nanospheres for High-performance Sodium Ion Battery Anode. ACS Appl. Mater. Inter. 2015, 7, 11476-11481. (55) Zhu, W.; Yang, Y.; Ma, D.; Wang, H.; Zhang, Y.; Hu, H. Controlled Growth of Flower-like SnS2 Hierarchical Structures with Superior Performance for Lithium-ion Battery Applications. Ionics 2014, 21, 19-26. (56) Guan, D.; Ma, L.; Pan, D.; Li, J.; Gao, X.; Xie, Y.; Qiu, M.; Yuan, C. Atomic Layer Deposition of Alumina Coatings onto SnS2 for Lithium-ion Battery Applications. Electrochim. Acta 2017, 242, 117-124. (57) Zhai, C.; Du, N.; Zhang, H.; Yu, J.; Yang, D. Multiwalled Carbon Nanotubes Anchored with SnS2 Nanosheets as High-performance Anode Materials of Lithium-ion Batteries. ACS Appl. Mater. Inter. 2011, 3, 4067-4074. (58) Cui, C.; Xu, J.; Wang, L.; Guo, D.; Mao, M.; Ma, J.; Wang, T. Growth of NiCo2O4@MnMoO4 Nanocolumn Arrays with Superior Pseudocapacitor Properties. ACS Appl. Mater. Interfaces 2016, 8, 8568-8575. (59) Li, G.; Jiang, D.; Wang, H.; Lan, X.; Zhong, H.; Jiang, Y. Glucose-assisted Synthesis of Na3V2(PO4)3/C Composite as an Electrode Material for 26


Page 26 of 38

Page 27 of 38 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


High-performance Sodium-ion Batteries. J. Power Sources 2014, 265, 325-334. (60) Ruan, Y. L.; Wang, K.; Song, S. D.; Han, X.; Cheng, B. W. Graphene Modified Sodium Vanadium Fluorophosphate as a High Voltage Cathode Material for Sodium Ion Batteries. Electrochim. Acta 2015, 160, 330-336. (61) Serras, P.; Palomares, V.; Goñi, A.; Kubiak, P.; Rojo, T. Electrochemical Performance of Mixed Valence Na3V2O2x(PO4)2F3−2x/C as Cathode for Sodium-ion Batteries. J. Power Sources 2013, 241, 56-60. (62) Li, Y.; Yao, J.; Uchaker, E.; Zhang, M.; Tian, J.; Liu, X.; Cao, G. Sn-doped V2O5 Film with Enhanced Lithium-ion Storage Performance. J. Phys. Chem. C 2013, 117, 23507-23514. (63) Chen, J.; Yang, L.; Fang, S.; Hirano, S.; Tachibana, K. Synthesis of Hierarchical Mesoporous Nest-like Li4Ti5O12 for High-rate Lithium Ion Batteries. J. Power Sources 2012, 200, 59-66. (64) Yan, B.; Li, M.; Li, X.; Bai, Z.; Dong, L.; Li, D. Electrochemical Impedance Spectroscopy Illuminating Performance Evolution of Porous Core-Shell Structured Nickel/Nickel Oxide Anode Materials. Electrochim. Acta 2015, 164, 55-61. (65) Fan, L.; Li, X.; Cui, Y.; Xu, H.; Zhang, X.; Xiong, D.; Yan, B.; Wang, Y.; Li, D. Tin Oxide/Graphene Aerogel Nanocomposites Building Superior Rate Capability for Lithium Ion Batteries. Electrochim. Acta 2015, 176, 610-619. (66) Yin, L.; Chai, S.; Huang, J.; Kong, X.; Pan, L. Preparation of Hierarchical SnS2/SnO2 Anode with Enhanced Electrochemical Performances for Lithium-ion 27



Battery. Electrochim. Acta 2017, 238, 168-177. (67) Li, X.; Liu, J.; Banis, M. N.; Lushington, A.; Li, R.; Cai, M.; Sun, X. Atomic Layer Deposition of Solid-state Electrolyte Coated Cathode Materials with Superior High-voltage Cycling Behavior for Lithium Ion Battery Application. Energy Environ Sci. 2014, 7, 768-778. (68) Wu, K.; Wu, C. J.; Tseng, C. M.; Chang, J. K.; Lee, T. C. Structure-mediated Electrochemical Performance of SnS2 Anode for Li-ion Batteries. J. Taiwan Inst. Chem. E. 2016, 66, 292-300. (69) Li, H. L.; Yu, K.; Fu, H.; Guo, B. J.; Lei, X.; Zhu, Z. Q. MoS2/Graphene Hybrid Nanoflowers with Enhanced Electrochemical Performances as Anode for Lithium-ion Batteries. J. Phys. Chem. C 2015, 119, 7959-7968.

28


Page 28 of 38

Page 29 of 38 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


Scheme 1. Illustration of (a) the strong interaction between SnS2 and N,S-GA and (b) the weak interaction between SnS2 and GA.

29



(a)

105 (b)

SnS2 GAs

(002) (100)

Weight (%)

ii

SnS2@N,S-GA-II

40 50 60 2theta/ degree

70

(203)

(202) (113)

(110) (111) (103)

(102)

60 45

15 0

20

30

SnS2@N,S-GA-III

75

30 (200) (201)

iv

(101)

(100)

(001)

iii

10

SnS2@N,S-GA-I

90

i

Intensity (a.u.)

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

Page 30 of 38

80

0

200 400 600 800 Temperature (°C)

1000

Figure 1. (a) XRD patterns of (i) pristine GAs, (ii) SnS2@N,S-GA-I, (iii) SnS2@N,S-GA-II, and (iv) SnS2@N,S-GA-III; (b) TGA curves of SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III.

30


Page 31 of 38

Sn 3p3/2

O 1s

Sn 3d5/2 Sn 3d3/2

Sn 3p1/2

Intensity (a.u.)

C 1s N 1s

S 2p

(b)

Sn 3d

S 2s

Sn 4d

Intensity (a.u.)

(a)

SnS2@N,S-GA-II

SnS2@N,S-GA-III

SnS2@N,S-GA-II

SnS @N,S-GA-III 2

0

200

400

600

800

1000

1200

480

485

490 495 Binding Energy (ev)

Binding Energy (ev) A

(c)

(d)

S 2p

S1

S 2p

S1

Intensity (a.u.)

Intensity (a.u.)

S3

S4

SnS2@N,S-GA-II

S2

S3 S4

158 160 162 164 166 168 170 Binding Energy (ev)

(e)

N 1s N1

(f)

N 1s

690

N2

Intensity (a.u.)

950

SnS2@N,S-GA-III

158 160 162 164 166 168 170 Binding Energy (ev) 720

1000 Intensity (a.u.)

500

S2

900 N3

850 SnS2@N,S-GA-II

800

N1

N2

660 SnS2@N,S-GA-III

N3

630 600 570

750

392 394 396 398 400 402 404 406 408 Binding Energy (ev)

392 394 396 398 400 402 404 406 408 Binding Energy (ev)

(g)

(h)

C 1s

Intensity (a.u.)

C1

C2 C3

C1

C2 C3 SnS2@N,S-GA-III

SnS2@N,S-GA-II

280

C 1s

Intensity (a.u.)

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


282 284 286 288 290 Binding Energy (ev)

292

280

282 284 286 288 290 Binding Energy (ev)

292

Figure 2. XPS analysis of SnS2@N,S-GA-II and SnS2@N,S-GA-III: (a) the survey spectrum, (b) Sn 3d spectra; S 2p spectra: (c) SnS2@N,S-GA-II and (d) SnS2@N,S-GA-III; N 1s spectra: (e) SnS2@N,S-GA-II and (f) SnS2@N,S-GA-III; C 1s spectra: (g) SnS2@N,S-GA-II and (h) SnS2@N,S-GA-III. 31



Figure 3. Typical SEM images of (a, b) SnS2@N,S-GA-I, (c, d) SnS2@N,S-GA-II, and (e, f) SnS2@N,S-GA-III.

32


Page 32 of 38

Page 33 of 38 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


Figure 4. TEM and HRTEM images of (a, b) SnS2@N,S-GA-I, (c, d) SnS2@N,S-GA-II (the insert is selected-area diffraction (SAED) pattern), and (e, f) SnS2@N,S-GA-III.

33



(a)

1.61V 1.84V

3.0

2.10V

0.81V

-0.02 1.20V

-0.04 0.38V

-0.06

1st 2nd

-0.08

2.5

0.09

0.5 1.0 1.5 2.0 2.5 + Potential (V) vs Na /Na

1st 2nd

1.0

10th

0.5

100th

(b)

0

Potential vs. Na /Na

1.84V

2.10V

+

0.00 0.77V

-0.03

1.62V

-0.06

1st 2nd

-0.09

1.20V

0.5

1.0 1.5 2.0 2.5 + Potential (V) vs Na /Na

0.06


+

0.00 1.62V

-0.03 0.65V 1.20V

-0.06 1st 2nd

-0.09

5.

0.5

The

10th

0.5

100th

200 400 600 800 1000 1200 1400 Specific capacity /mAh g-1

(f)

2.5 2.0 1.5

1st

1.0

10th

2nd 100th

0.5

0

1.0 1.5 2.0 2.5 3.0 + Potential (V) vs Na /Na

cyclic

2nd

0.0

0.59V

0.0

1st

1.0

3.0 1.84V 2.10V

0.75V

0.25V

1.5

0

1.61V

0.03

2.0

3.0

1.20V

(c)

(e)

2.5

0.0

0.30V

0.0

200 400 600 800 1000 1200 1400 Specific capacity /mAh g-1

3.0

1.61V

0.03

Figure

1.5

3.0

0.06

-0.12

2.0

0.0 0.0

Current (mA)

(d)

+

Current (mA)

0.00


0.02

Current (mA)

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

Page 34 of 38

voltammetry

curves

250 500 750 1000 1250 1500 Specific capacity /mAh g-1

of

(a)

SnS2@N,S-GA-I,

(b)

SnS2@N,S-GA-II, and (c) SnS2@N,S-GA-III at a scan rate of 0.1 mV s-1 in the voltage range of 0.01-3.0 V; The discharge/charge profiles of (d) SnS2@N,S-GA-I, (e) SnS2@N,S-GA-II, and (f) SnS2@N,S-GA-III in the 1st, 2nd, 10th, and 100th cycles.

34


80

600

SnS2

SnS2@N,S-GA-I

GAs

SnS2@N,S-GA-II

N,S-GAs

SnS2@N,S-GA-III

70

450

60

300

50

150

40

0

30

700

20

40 60 80 Cycle number

100

(c)

-1

SnS2@N,S-GA-II SnS2@N,S-GA-III

600 500 400 300 50

200 100

100 200

50 mA g

90 20 mA g

1000

50 mA g

800

-1

400 800

-1

200 mA g

70

-1

60

-1

600

50

400

40

10

20 30 40 Cycle number

30

50

700 (d)

600 SnS2@N,S-GA-I SnS2@N,S-GA-II SnS2@N,S-GA-III

500 400 300 200 100

-10 0 10 20 30 40 50 60 70 80 90 Cycle number

80

-1

100 mA g

0

SnS2@N,S-GA-I

100

1200

Discharge capacity /mAh g

800

0

1400 (b)

Coulombic efficiency

750

Coulombic efficiency

90


100

(a)

900

-1

Discharge capacity /mAh g -1

1050


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


-1

Page 35 of 38

0

150 300 450 600 750 -1 Current Density /mA g

900

Figure 6. (a) Comparison of the cyclic performance of bare SnS2, pristine GAs, N,S-GAs, SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III at a current density of 50 mA g-1 from the second cycle; (b) Comparison of the cyclic performance of SnS2@N,S-GA-II at various current densities of 20, 50, 100, and 200 mA g-1; (c) Rate capability of SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III at current densities: 50, 100, 200, 400, 800, 50 mA g-1; (d) The capacity retention of SnS2@N,S-GA-I, SnS2@N,S-GA-II, and SnS2@N,S-GA-III at 50, 100, 200, 400, and 800 mA g-1.

35



Page 36 of 38

Figure 7. The CV curves in the potential range of 0.01-3.0 V at scanning rates of 0.1, 0.2, 0.4, 0.6, and 0.8 mV s-1 for (a) SnS2@N,S-GA-II and (b) SnS2@N,S-GA-III; (c) The corresponding relationship between Ip and v1/2; (d) The electrochemical impedance

spectroscopy

of

SnS2@N,S-GA-I,

SnS2@N,S-GA-II,

and

SnS2@N,S-GA-III in the 100th cycle; (e) The corresponding equivalent circuit used to simulate EIS curves.

36


Page 37 of 38 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


Figure 8. Charge density difference distributions for (a) SnS2@N,S-GA and (b) SnS2@GA (the inserts are the corresponding models); The band structures of (c) SnS2@N,S-GA and (d) SnS2@GA; Calculated electronic density of states (DOS) of (e) SnS2@N,S-GA and (f) SnS2@GA.

37



Table of Contents


Page 38 of 38

SnS2 Nanocrystal Building

Recommend Documents