NiSx@C Hollow

Subscriber access provided by UNIV OF DURHAM

Article

Ultra-thin nanosheets assembled hierarchical Co/ NiSx@C hollow spheres for reversible lithium storage Wanwan Wang, Peiyuan Zeng, Jianwen Li, Yueying Zhao, Mengna Chen, Jingwen Shao, and Zhen Fang ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00621 • Publication Date (Web): 09 Jul 2018 Downloaded from http://pubs.acs.org on July 12, 2018

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 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 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.

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 40 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 Nano Materials

Ultra-thin Nanosheets Assembled Hierarchical Co/NiSx@C Hollow Spheres for Reversible Lithium Storage Wanwan Wang,a,b Peiyuan Zeng, a,b Jianwen Li, a,b Yueying Zhao, a,b Mengna Chen, a,b Jingwen Shao, a,b Zhen Fang∗, a,b a

College of Chemistry and Materials Science, Anhui Normal University, Wuhu

241000, P. R. China. b

Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui

Normal University, Wuhu 241000, P. R. China. ∗

Corresponding author, Zhen Fang, Email: [email protected].

ABSTRACT Cobalt sulfides are good candidate anode materials for lithium ion storage for their high theoretical capacities. However, their electrochemical performance is restricted by their volume change during the cycles, leading to a sharp capacity fading in the subsequent process. To overcome these disadvantages, ultra-thin nanosheets assembled hierarchical cobalt sulfides@C hollow spheres are fabricated by a hydrothermal and subsequent carbon enwrapping strategy. The as-prepared hierarchical Co9S8@C hollow spheres deliver an enhanced electrochemical performance with both long-term cyclability and reversible specific capacities. 823 mA h g‒1 reversible capacity could be maintained after 200 cycles at a current density of 100 mA g‒1. More importantly, the present synthesis strategy shows good generality for the synthesis of nickel sulfide and Ni-Co bimetal sulfides hollow

ACS Paragon Plus Environment

ACS Applied Nano Materials 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

spheres with improved performance in anode materials of lithium-ion batteries.

KEYWORDS: Co/NiSx@C, hierarchical hollow spheres, ultrathin nanosheets, template method, lithium-ion batteries

1. INTRODUCTIONS Rechargeable lithium-ion batteries (LIBs) have aroused widespread concern and application in recent decades due to its high energy density, environment-friendly and long cycle lifespan1-3. Although LIBs have these superior advantages, it cannot match well with the higher energy density and rate performance demand in electric vehicle and grid energy storage.4-6 The developing of higher performance LIBs is still a challenge nowadays. Fortunately, many candidates with larger theoretical capacity than traditional carbonaceous anode materials exist. Among these potential materials, transition metal sulfides (TMS) are a fascinating one with characterization of high theoretical capacity, natural abundance and facile synthesis.7-14 Cobalt/Nickel sulfides are the potential anode materials since there high theoretical specific capacity (Co9S8: 544 mA h g‒1, CoS: 589 mA h g‒1, NiS: 590 mA h g-1).15-18 And for Ni-Co bi-metal sulfides, they can provide rich redox reaction sites than cobalt sulfides and nickel sulfides.

19-22

However, for TMS, there are two major disadvantages that limit its

practical applications. One is the large volume variation during the charge/discharge cycles, leading to the pulverization and thus fast capacity fading. Another is unsatisfied conductivity which lead to the low initial coulombic efficiency and poor cyclability.


Page 2 of 40

Page 3 of 40 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


Many efforts have been made to improve these drawbacks, including rational designed geometric shapes and morphologies, formation hollow interior structure, reducing the size, doping with other elements and hybrid with conductive carbon materials.2, 14 For examples, CoS2 nanobubble hollow prisms were synthesized by using ZIF-67 precursor. Thanks to its unique hollow structure, the CoS2 materials exhibit a remarkable electrochemical performance.23-25 N-doped carbon@CoS coaxial nanotubes as well as hollowed Co9S8 show high performance for the enhanced electrical conductivity and structure.26,

27

By hybridizing with carbon, the lithium

storage properties are also improved for NiS.20, 28-31 Ni-Co bimetal sulfides are also received intense interest for their improved electronic conductivity and multi-steps electrochemical process when used in LIBs. Recent studies illuminate that the undesirable performance of bimetal sulfides, which origin from high-volume change during cycling, could be improved by reducing its size to nanoscale and wrapped with carbon. The former results clearly indicate that the electrode performance of TMS is intimately related to their morphology and carbon coating. Therefore, studies on the optimization of the morphology as well as the carbon coated are the most importance for TMS.32-34

More recently, two-dimensional (2D) transition metal dichalcogenides nanosheets have attracted much interest in energy storage materials for its large surface areas and reduced ion transport distance that result in improved ion kinetics.35-40 However, the 2D nanosheets still suffered from aggregation in practice electrode which may reduce the active surface and increase the ion migration length.38, 41, 42 Therefore, porous 2D



Page 4 of 40

nanosheets are proposed by Yu and co-workers. With the help of the faster ion transportation feature of porous materials, the porous 2D nanosheets shows a hopeful perspective in advanced energy storage device.37,

43

2D nanosheets assembled

hierarchical hollow spheres are also proposed for they not only have considerable surface area, but also provide adequate flexible space for volume variation during cycling processes.44-46 However, present synthetic method for hollow spheres are often need a template removing process, which is cost and time-consuming. Therefore, developing an effective method for synthesis of 2D nanosheets assembled hierarchical hollow spheres is still a challenge. Herein, by using a synchronous strategy of formation of hollow spheres and template removing, ultra-thin nanosheets assembled hierarchical cobalt/nickel sulfides hollow spheres were synthesized by using SiO2 templates. Compare with the former reports that the silica templates removed by using hydrofluoric acid after the shell is formed, the templates removing step in present work takes place synchronously in the formation process of hollow spheres without using hydrofluoric acid. Our synthetical strategy is more time saving and environment-friendly. The obtained hierarchical hollow spheres exhibit remarkable electrochemical performance for the combination of the merits of 2D nanosheets and the hollow structures.

2. MATERIALS AND METHODS

2.1 Synthesis of SiO2 templates SiO2 templates were obtained by using a modified Stöber method.47 6 mL tetraethyl


Page 5 of 40 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


orthosilicate (TEOS) were dropped into 160 mL isopropanol and 40 mL deionized water (H2O). After stirring for 15 min, a transparent solution is formed and then 6 mL ammonium hydroxide (NH3·H2O) was added. After stirring about 10 min, the transparent solution gradually becomes milky white and continues stirring for another 24 h at room temperature. The white precipitate was collected by centrifugation after washed carefully and dried in a vacuum oven at 60 oC overnight.

2.2 Synthesis of hierarchical CoS hollow nanospheres

CoS hollow nanospheres were prepared firstly. 3 mmol CoSO4·6H2O was dissolved in 20 mL deionized water. Then, 8 mmol urea and 10 mmol thiourea were added to the above pink solution under stirring. Meanwhile, 0.120 g SiO2 spheres were added into 20 mL deionized water under ultrasonication for 0.5 h to obtain a homogenous solution. Subsequently, the two solutions were mixed under stirring and then transferred into a Teflon-lined stainless-steel autoclave. The autoclave reacted at 150 o

C for 24 h. After cooling down to room temperature, the CoS hollow nanospheres

which were washed with water and ethanol were collected by centrifugation, and dried at 60 oC overnight in a vacuum oven.

In order to prepare Co9S8@C hollow nanospheres, 0.1 g of the as-synthesized CoS was dispersed in 50 mL of water under ultrasonic at room temperature. 50 mg dopamine (DA) and 1.121 g HCl-tris were added into the suspension continues ultrasonic for another 10 min, 100 µL of concentrated hydrochloric acid was dropped into the suspension, followed by continuous stirring for 24 h. The product was



collected by centrifugation after washed several times with water and ethanol and dried in a vacuum oven at 60 oC. The obtained products were calcined at 500 oC for 2 h under N2 airflow with a heating rate of 2 oC min‒1. 2.4 Synthesis of hierarchical Ni3S2/Ni7S6@C hollow spheres The Ni3S2/Ni7S6@C hollow spheres were obtained by using the same method as former section, except 2 mmol NiSO4·6H2O were used to substitute CoSO4·6H2O. 2.5 Synthesis of hierarchical Ni/Co9S8@C hollow spheres For synthesis of Ni/Co9S8@C hollow spheres, the same method was also used except 3 mmol CoSO4·6H2O and 1 mmol NiSO4·6H2O were added. Material characterization and electrochemical measurements section are described in the supplementary material.

3. RESULTS AND DISCUSSION Scheme 1 depicted the formation process of the hierarchical Co9S8@C hollow spheres by using SiO2 templates. The SiO2 solid sphere templates possess smooth surface as well as a uniform diameter of 300 nm, which could be clearly revealed by SEM, TEM and XRD in Fig. S1. In the first step, CoS hollow spheres assembled by nanosheets were synthesized by a hydrothermal strategy. The hollow sphere inherited the sphere-like structure indicates that the template acted as a nucleate center during the reaction. In the second step, dopamine polymerized at the surface of the hollow sphere. The hierarchical Co9S8@C hollow spheres were gained by carbonization of


Page 6 of 40

Page 7 of 40 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


the dopamine in the last step.

In order to determine the function of templates and the formation mechanism of the hierarchical cobalt sulfide hollow spheres, TEM images analysis was carried out at different stages for the first step (Fig. S2). As shown in Fig. S2a, at the initial 0.5 h, no obvious hollow interior cavity could be found, the surface of the template became rough for the deposition of the CoS. In this stage, urea is hydrolyzed under the hydrothermal condition and NH3 released. NH3 will react with SiO2 slowly to form SiO44‒. Due to the existence of Co2+ in the solution, SiO44‒ will turn into Co2SiO4 at the template surface furtherly. The above-mentioned process had been approved by former reports.48 However, Co2SiO4 is not stable and react with S2‒ which come from the hydrolyzation of thiourea, then CoS is formed around the template. After 2 h reaction, a rattle-type structures appeared and the CoS nanosheets were formed around the template (Fig. S2b). As the reaction time went on (4‒12 h in Fig. S2c-e), the diameter of core gradually decreases for the SiO2 templates gradually dissolved in the alkaline solution.49 A well-defined hierarchical hollow spheres were formed after reacting for 24 h, (Fig. S2f). It should be pointed out the urea is important for removing the SiO2 template by the formation of SiO44‒. A controlled experiment was carried out in the absence of urea under the typical reaction (the TEM images in Fig. S3). The silica spheres were remained in the products indicating urea had taken part in the template removing reaction.

The products obtained in the first step were further identified by XRD. As show in Fig. 1a, the main peak of the products could be indexed into hexagonal phase CoS ACS Paragon Plus Environment


(JCPDS No.65-3418). Weak peaks of cubic phase Co4S3(JCPDS No. 30-0458) is also observed. The sharp and intensity peaks mean the high crystallinity of the as-synthesized products. To determine the morphologies and inner structures of CoS hollow spheres, FESEM and TEM analysis were carried out. Typical FESEM images and TEM images in Fig. 2a-b shows that the as-synthesized hierarchical CoS hollow spheres inherit the sphere morphology of SiO2 template with diameter of about 300 nm. It is noticed that the CoS nanosheets only exist on the surface of the hollow sphere from the inset image in Fig. 2a. More SEM and TEM images further confirmed the hierarchical and hollow interior structure (Fig. S4a and S4d). SEM and TEM images at different magnification also show the hollow spheres are composed of ultrathin nanosheets subunit. From a closer examination of an individual hollow spheres, it can be determined that the hierarchical shell of the sphere has a thickness of about 35 nm.

After carbonization, the CoS was converted into cubic phase Co9S8 (JCPDS NO.82-2273) (Fig. 1b). It is worth mentioning that the crystalline phase has changed after calcining. The conversion of CoS may root from the polymorphism of cobalt sulfide. As depicted by the phase diagram of Co-S in the diagram S-1, Co9S8 is a stable phase in present condition (500 oC). According to the SEM and TEM images in Fig. 2c and 2d, well-defined hierarchical Co9S8@C hollow spheres with the same diameter of CoS could be observed clearly. The Co9S8@C hollow sphere inherited the morphology and structure of the hierarchical CoS hollow spheres. HRTEM image in Fig. 3a and 3b shows that each nanosheet is composed of 1~6 layers with the


Page 8 of 40

Page 9 of 40 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


interlayer spacing of ~ 1.2 nm, which is larger than reported interlayer spacing of Co9S8.50, 51 It is suggested that the formation of larger interlayer spacing is due to the replacing of large SiO44- radical group with S2- when the intermediate product Co2SiO4 is converted to CoS. The extended layer spacing can decrease the ion migration resistance dramatically and can tolerate the volume change during charge/discharge cycles.52,

53

Moreover, the lattice spacing of the as-prepared

Co9S8@C hollow spheres is determined to be 0.574 nm, corresponding to the (111) facet (Fig. 3a). A series of diffraction rings in SAED pattern (Fig. 3b) suggest the polycrystalline nature of the cubic Co9S8 phase. Elemental mapping analysis was also carried out (Fig. 2e). Homogeneous distribution of Co, S, C and N on the hierarchical hollow spheres could be observed. Combine with XRD and HRTEM results, Co9S8@C hollow spheres had been prepared successfully. Raman spectroscopy was used to analyze the CoS and Co9S8@C hollow spheres. As showed in Fig. S5, four peaks locating at 183.6, 463, 504, 663 cm‒1appeared in both the bare CoS and Co9S8@C, which corresponded to the characteristic peak of cobalt sulfides.54 Compared with hierarchical CoS hollow spheres, the Raman spectrum of Co9S8@C in Fig. S5 exhibited two characteristic peaks located at 1358 and 1584 cm‒1, corresponding to the sp3-type disordered carbon (D band) and sp2-type graphitized carbon (G band), respectively.55 What’s more, compared with the commercial Co9S8, the A1g characteristic peak has a blue shift that drift from 666 cm-1 to 657 cm-1 for Co9S8@C hollow sphere. This obvious blue shift is mainly attributed to the expanded interlayer spacing of Co9S8@C which diminish van der Waals force of interlayer that



result in a stronger out-of plane vibration (in Fig. 4a).52 The carbon content of the as-prepared Co9S8@C composites was determined by TGA in air. As showed in Fig. 4b, a slight weight loss could be observed before 200 oC, which might assign to the removal of the absorbed moisture. From 200 oC to 550 oC, the weight loss could be assigned to the combustion of amorphous carbon. At the same time, a small quantity of metal Co formed for the reducing of Co9S8 with carbon. After 550 oC, the weight rising could be ascribed to the oxidation of Co to Co3O4.The XRD pattern of Co9S8@C hollow spheres after calcined in air shown in Fig. S6. The carbon content of the composites can be calculated as ~ 6.1 % according to the constant mass of Co element.

XPS was used to determine the composition and the valance of the as-prepared Co9S8@C hollow sphere. Five elements including Co, S, C, N and O could be observed in the XPS survey, the atomic ratio of Co to S is closed to 9 : 8 and in accordance with the XPS result (Fig. S7). In Fig. 5a, Co 2p3/2 and Co 2p1/2 of Co-S bond located at 780.6 eV and 796.8 eV, respectively. Other peaks centered at 782.0 eV, 787.1 eV and 803.4 eV are satellite peaks, alluded the presence of Co2+ and Co3+ in the composite.56, 57 The peaks located at 161.5eV (S 2p3/2) and 163.4 eV (S 2p1/2) can ascribe to the existence of S element (Fig. 5b). A major peak centered at 168.8 eV (S=O) results from oxygen adsorbed on the material surface or from the partial oxidation of the sample during the testing process.58 Fig. 5c shows the C1s spectra of the composite, peaks located at 284.6 eV, 285.3 eV, 286.4 eV and 288.3 eV ascribed to the functional group of C=N, C–O, C=O, and O–C=O groups, respectively.59 The


Page 10 of 40

Page 11 of 40 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-resolution XPS spectrum of N 1s in Fig. 5d can be divided into two peaks at 400.0 eV and 398.3 eV, corresponding to the pyrrolic and pyridinic nitrogen.

The N2 isothermal sorption/desorption measurement of CoS and Co9S8@C hierarchical hollow spheres was carried out (Fig. 6). The N2 sorption isotherm of the CoS and Co9S8@C could be classified as type-IV curves with H4 hysteresis loop. By calculation, the specific surface area of the two samples is about 138.22 m2 g‒1 and 208.51 m2 g‒1, respectively. According to the BJH method, the average pore radius of CoS and Co9S8@C composite are approximate 1.46 nm and 1.42 nm, which result from the layered surface. The hierarchical hollow spheres with large specific surface area and pore size could shorten the lithium-ions diffusion length, facilitate the diffusion of ions and provide more lithium-ion storage sites.

Fig. 7a shows the CV curves of fresh Co9S8 @C electrode at the initial three cycles. In the first cathodic sweep process, a weak peak at ~1.01 V can be assigned to the Li ions insertion reaction to form Li2S and metallic Co results from the following reaction: Co9S8 + 16 Li+ + 16 e− ↔ 9 Co + 8 Li2S. Strong cathodic peak at 0.545 V origin from the irreversible decomposition of electrolyte and the generation of the solid electrolyte interface (SEI).60 In the following cycles, the strong and broaden peak disappeared, indicating the SEI layer had been formed completely in the first cycle. The peak located at ~2.0 V corresponding to the metallic Co oxidized into Co9S8 in the anodic sweep process.61 The overlapped peaks after the first cycles indicated

that

the

material

has

a

good

reversibility.

The

galvanotactic

charge-discharge curves of the hierarchical Co9S8@C hollow spheres is showed in Fig. ACS Paragon Plus Environment


7b under a current density of 100 mA g‒1. 1263 mA h g‒1 of discharge capacity and 832 mA h g‒1 of charge capacity with the first Coulombic efficiency of 65.84 % is observed. The large initial capacity decay is mainly attributed to the decomposition of electrolyte and the formation SEI film as indicated by CV.62 In the following two cycles, the Coulombic efficiency increased to 92.5% and 93.19%, respectively. The increased coulombic efficiency and overlapped plots imply the high reversibility and capacity retention of the Co9S8@C composites. Rate capability is a significant parameter for lithium storage materials. In Fig. 7c, the rate performance of the CoS and the Co9S8@C hollow spheres are compared under different current densities. The two samples exhibited good reversibility during the whole rate test process. Of note, the capacity could recover to the initial level when the current density returned to 100 mA g‒1 after cycled in the high current density. This could be ascribed to the rational design of the hierarchical hollow structure. The ultrathin nanosheets and the porous shell nature facilitate the lithiation/delithiation process by diminish the lithium ions diffusion distance which result in an improved reaction kinetics.

Electrochemical impedance spectra (EIS) was analyzed to get further insight in the excellent electrochemical performance of the hierarchical Co9S8@C hollow spheres (Fig. 7d). A semicircle and a lope is gained in the high-to-medium frequency and the low frequency region, which corresponded to the charge transfer resistance (Rct) and lithium-ion diffusion, respectively. The impedance of the Co9S8@C exhibited lower resistance than that of the bare CoS before cycle, indicating that the N doped carbon ACS Paragon Plus Environment

Page 12 of 40

Page 13 of 40 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


layer could increase the conductivity of the material and lead to the fast lithiation/delithiation process. After 200 cycles, the Co9S8@C electrodes delivered lower resistance than fresh half-coin cells, which could be attributed to the electrodes activation and the formation of charge channels for lithiation/delithiation. For the CoS electrodes, the resistance was higher than fresh half-coin cells. It was due to the hollow sphere structure was destroyed and formed large particles after the fast lithiation/delithiation process without the confinement of carbon.

Typical cycling performance of hierarchical Co9S8@C and CoS hollow spheres are evaluated between 0.01 and 3.0 V at a current density of 100 mA g‒1. Both samples exhibit higher reversible capacities than theoretical values, this phenomenon have been observed widely for other anode materials.63, 64 The extra capacity mostly caused by the formation of SEI, the interfacial storage, the electrolyte decomposition and the insertion of lithium into conductive carbon black. In present work, we speculated that this might relate to the interfacial storage which was caused by unique ultra-thin nanosheets assembled hierarchical hollow structure. Another reason is the existed of N-doped carbon that is beneficial to the insertion of lithium. As showed in Fig. 7e, the hierarchical Co9S8@C hollow spheres exhibit better electrochemical performance than hierarchical CoS hollow spheres in terms of cyclability and reversible capacities. The Co9S8@C electrode exhibits a reversible capacity of 823 mA h g‒1 after 200 cycles, while the capacity of CoS electrode decreases rapidly after ~ 120 cycles. To determine the reasons for the different performance, TEM analysis was carried out to characterize the electrode after long-term cycling. Fig. S8a-b is the TEM images of



Co9S8@C electrode and CoS electrode after 200 cycles. It could be observed clearly that the CoS hollow spheres pulverized into pieces and then aggregated into bulk after cycling, which hindered the reversible reactions and weaken the cyclability. Different from CoS, hierarchical Co9S8@C hollow spheres kept the hollow structure during the whole test process.

The excellent performance of Co9S8@C hollow spheres could be assigned to following reasons. i) The hierarchical ultrathin nanosheets and the porous hollow structure shorten the ions diffusion distance. ii) The expanded interlayer spacing of Co9S8 can reduce the resistance during ions diffusion process. iii) Compared with CoS hollow spheres, the N doped carbon layer outside of the hierarchical Co9S8@C hollow spheres could enhance the conductivity and electrochemical activity of the composite, which will facilitate the transfer of electrons, and result in an improved the cycle stability of hierarchical Co9S8@C hollow spheres.65, 66 In order to investigate the electrochemical behavior of the hollower spheres furtherly, CV curves of the CoS and Co9S8@C hollow spheres was measured under scan rates of 0.1-5.0 mV s-1. As shown in Fig. 8, one pair of symmetry cathodic/anodic peaks were observed at all scan curves which indicate that the materials have good reversibility during the process of Li extraction/insertion reactions. The relationship between peak currents and Li-ion diffusion coefficient could be described by Randles–Sevcik equation, ip = 2.69×105ACLi1/2DLi1/2v1/2n3/2.67 The meaning of each symbol is as follows.


Page 14 of 40

Page 15 of 40 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


ip (Amperes), peak currents. A (cm2), electrode area. C (mol cm-3), shuttle concentration. D (cm2 s-1), Li-ion diffusion coefficient. v (V s-1), potential scan rate.

n, number of electrons involved in the redox process.

From the equation, a straight-line can be fitted from a plot of scan rate against the current. Normally the current obeys a power-law: i = a·vb,68 where a and b are appropriate values. When b = 0.5 or 1, the electrochemical reaction is controlled by ion diffusion or pseudocapacitance behavior, respectively.69As showed in Fig. 8, the calculated b-values are 0.5028, 0.6224, 0.6380 and 0.5469, respectively. All the calculated slope of the lines is close to 0.5 which indicating that the kinetics of hollow sphere cobalt sulfide was mainly controlled by ionic diffusion.70 The results indicating that the cobalt sulfide hollow sphere has a high Li-ion diffusion coefficient. Two main factors can explain the high Li-ion diffusion coefficient of the ultra-thin nanosheets assembled hierarchical hollow spheres. The hollow structure with high surface area provides a good contact with the electrolyte and more channels for Li-ion diffusion.71, 72

The ultra-thin nanosheets could shorten the Li-ions diffusion distance.73, 74

By using the same synthetic approach, nickel sulfide and Ni-Co bimetal sulfides hollow spheres also have been synthesized successfully. The characterizations of the



as-prepared nickel sulfide and Ni-Co bimetal sulfides hollow spheres are displayed in the Supporting Information. The SEM and TEM images of the nickel sulfide and the composites are showed in Fig. S9 a-d which indicated the uniform hollow spheres are obtained successfully. Fig. S10 a and 10c displayed the typical XRD pattern of the NiS and Ni3S2/Ni7S6@C hollow spheres that could be well indexed into standard card. The EDX results in Fig. S10 b and 10c confirm that the product has synthesized successfully. The as-synthesized nickel sulfides and the composites also delivered fascinating electrochemical properties, which could ascribe to the rational design of the structure. Fig. S11a and S11c displayed the first three cyclic voltammetry (CV) profiles of NiS and Ni3S2/Ni7S6@C hollow spheres at a scan rate of 0.1 mV s-1. From the CV profiles, the electrochemical processes of the two products are basically the same except the first cycle. For NiS, a broad cathodic peak located at ~0.80 V is observed, corresponding to the formation of SEI.75 Two small reduction peaks located at 1.57 and 1.23 V, which is owing to the conversion from NiS to Ni3S2 and Ni.76 For Ni3S2/Ni7S6@C, there is only one peak locate at 1.0 V. During the subsequent cycles, there are two cathodic peaks located at 1.66 and 1.35 V which are related to the electrochemical transformation process from NiS to Ni3S2 and Ni3S2 to Ni, respectively.77 To verify the superiority of carbon coated electrode, the long-term cycle stability of the samples was further evaluated. As shown in Fig. S12e, the capacity of NiS and Ni3S2/Ni7S6@C hollow spheres is 261 and 369 mA h g‒1 after 100 cycles at a current density of 100 mA g−1.Obviously, the performance of the Ni3S2/Ni7S6@C electrode is the better than NiS. However, for the Ni3S2/Ni7S6@C


Page 16 of 40

Page 17 of 40 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


material, the capacity is declined sharply in the first few cycles. It is mainly come from the multiphase transformation of nickel sulfide which illuminated by the CV curve. The multiphase transformation will consume electrolyte and form new SEI film, which result in a low coulombic efficiency at the first few cycles.

For Ni-Co bimetal sulfides, as illuminated by SEM and TEM image (Fig. S12), the morphological size of nickel cobalt sulfide and the composites is the same with the as-prepared cobalt sulfide. Therefore, the present synthetical strategy is a general method for synthesis of nickel/cobalt sulfide and its binary sulfide hollow spheres. The XRD patterns of the NiCo2S4 and Ni/Co9S8@C hollow spheres are shown in Fig. S13a and S13c. The peaks can be index as NiCo2S4 (JCPDS No.20–0782) and Co8S9@C (JCPDS No.19–0364), respectively. It is noticed that the phase has changed after carbonation procedure during the high-temperature. The existence of Ni elements could be detected by EDX in Fig. S13d, which infers that the Ni element was doped into the crystal lattice of Co9S8 (briefly as Ni/Co9S8@C). Fig. S14a and S14c displayed the initial three consecutive CV curves of the electrodes. Obviously, there is a significant difference between the first and subsequent cycle, indicating that different electrochemical processes have taken place in the electrode. And the electrochemical reversibility of the NiCo2S4 electrode gradually formed at the subsequent cycles. In the first cycle, the peak located at ~0.54 V can be assigned to the SEI layer formation. And the peak located at 1.15 V can be assigned to the formation of LixNiCo2S4 by the Li+ embedded into the NiCo2S4 lattice.78 Meanwhile, the first anodic scan shows a broad peak at 1.33 V and a sharp peak 2.08 V due to the



deintercalation of Li+ from LixNiCo2S4, which led to the formation of NiSx and CoSx.79 In subsequent cycles, the cathodic peaks shift to a higher potential, which corresponds to the Li+ embedding into NiSx and CoSx, respectively. The subsequent cycle curves are basically coincident together, indicating that the material has good cycle stability. As for Ni/Co9S8@C, the CV curves are same as that of above Co9S8@C. Galvanostatic charge-discharge test was performed to obtain further information on the electrochemical performance of the electrode. Fig. S14b and S14d shows the charge–discharge profiles of the NiCo2S4 and Ni/Co9S8@C electrode in the first three cycles at a current density of 100 mA g-1 in the range of 0.01-3.0 V. The initial Coulombic efficiency of NiCo2S4 and Ni/Co9S8@C is 63.7 % and 66.4%, respectively. The formed metallic nickel and cobalt cannot be completely converted to the corresponding original sulfide and the SEI layers formation is the main reason for the loss of irreversible capacity. This phenomenon is commonly observed in NiCo2S4 electrode materials. Fig. S14e compares the cycling stability of the NiCo2S4 and Ni/Co9S8@C electrode at a current density of 100 mA g-1. The discharge capacity of the NiCo2S4 and Ni/Co9S8@C electrode is 292 and 817 mA h g‒1 after 100 cycles. The Ni/Co9S8@C shows a superior stability that NiCo2S4, indicating the reversibility of the electrode also could be improved by hybridize with carbon. Compared with other previously reported metal sulfide hollow sphere electrodes materials (see Table S1), indicating the electrode materials prepared in this experiment have superior electrochemical properties which are attributed to the special hollow sphere structure,


Page 18 of 40

Page 19 of 40 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


ultra-thin nanosheets and nitrogen-doped carbon.

CONCLUSIONS

In summary, a series of ultra-thin nanosheets assembled hierarchical transition metal sulfides@C hollow spheres had been successfully synthesized via a hard-template method. The as-prepared composites deliver fascinating electrochemical performance in cycling stability, reversible capacities and rate capabilities. The rational design of the structure with ultrathin nanosheets and porous hollow structure facilitate the diffusion of ions and accommodate the volume variation. The N doped coating carbon layer restricts the volume change during cycling and provides more polar sites for Li+ storage. Specifically, the as-prepared hierarchical Co9S8@C hollow spheres exhibited a reversible discharge capacity of 823 mA h g‒1 after 200 cycles at a current density of 100 mA g‒1. For other two carbon-coated materials, nickel sulfide@C delivered an excellent specific capacity of 369 mA h g-1 after 100 cycles at a current density of 100 mA g-1. And the Ni-Co bimetal sulfides@C also exhibited excellent electrochemical performance with a reversible capacity of 817 mA h g‒1 in 100 cycles at 100mA g-1. The present synthesis strategy has universal applicability, and current work may provide new insights for electrode materials in lithium-ion batteries.

ASSOCIATED CONTENT

Supporting Information

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/xxxx. ACS Paragon Plus Environment


Detailed material characterization; experiment of electrochemical measurements; the SEM, TEM image and XRD of SiO2 templates; TEM images of the formation process of CoS hierarchical hollow spheres; TEM image of the products obtained in the absence of urea; SEM and TEM images of hierarchical CoS hollow spheres; Phase diagram of Co-S; Raman spectra of the hollow sphere Co9S8@C and CoS; XRD pattern of calcined Co9S8@C hollow spheres in air; XPS survey spectra of Co9S8@C; TEM images of CoS and Co9S8@C after cycles; SEM, TEM image, XRD and EDX of NiS, Ni3S2/Ni7S6@C, NiCo2S4, Ni/Co9S8@C hollow spheres; CV, charge/discharge profiles, and cycling performance of NiS, Ni3S2/Ni7S6@C, NiCo2S4, Ni/Co9S8@C hollow spheres.

AUTHOR INFORMATION

Corresponding Authors

E-mail: [email protected].

Tel & Fax: +86-0553-3869302

NOTES The authors declare no competing financial interest.

ACKNOWLEDGEMENTS

The present work financially supports from National Natural Science Foundation of China (NSFC 21671005), the Programs for Science and Technology Development of Anhui Province (1501021019), The Recruitment Program for Leading Talent Team of


Page 20 of 40

Page 21 of 40 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


Anhui Province and Anhui Provincial Natural Science Foundation for Distinguished Youth (1808085J27).

REFERENCES (1) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J. M. Nano-Sized Transition-Metal Oxides as Negative-Electrode Materials for Lithium-ion Batteries. Nature 2000, 407, 496−499. (2) Zhou, L.; Zhang, K.; Hu, Z.; Tao, Z.; Mai, L.; Kang, Y.-M.; Chou, S.-L.; Chen, J. Recent Developments on and Prospects for Electrode Materials with Hierarchical Structures for Lithium-Ion Batteries. Adv. Energy Mater. 2018, 8, 1701415. (3) Liang, X.; Hart, C.; Pang, Q.; Garsuch, A.; Weiss, T.; Nazar, L. F. A Highly Efficient Polysulfide Mediator for Lithium-Sulfur Batteries. Nature Commun. 2015, 6,5682. (4) Li, Y.; Li, Y.; Pei, A.; Yan, K.; Sun, Y.; Wu, C.-L.; Joubert, L.-M.; Chin, R.; Koh, A. L.; Yu, Y.; Perrino, J.; Butz, B.; Chu, S.; Cui, Y. Atomic Structure of Sensitive Battery Materials and Interfaces Revealed by Cryo-Electron Microscopy. Science 2017, 358, 506−510. (5) Sun, Y.; Hu, X.; Yu, J. C.; Li, Q.; Luo, W.; Yuan, L.; Zhang, W.; Huang, Y. Morphosynthesis of a Hierarchical MoO2 Nanoarchitecture as a Binder-Free Anode for Lithium-Ion Batteries. Energ. Environ. Sci. 2011, 4, 2870−2877. (6) Shyamsunder, A.; Beichel, W.; Klose, P.; Pang, Q.; Scherer, H.; Hoffmann, A.; Murphy, G. K.; Krossing, I.; Nazar, L. F. Inhibiting Polysulfide Shuttle in Lithium-Sulfur Batteries through Low-Ion-Pairing Salts and a Triflamide Solvent. Angew. Chem. Int. Ed. 2017, 56, 1−7. (7) Zhou, Y.; Yan, D.; Xu, H.; Feng, J.; Jiang, X.; Yue, J.; Yang, J.; Qian, Y. Hollow Nanospheres of Mesoporous Co9S8 as a High-Capacity and Long-Life Anode for



Advanced Lithium Ion Batteries. Nano Energy 2015, 12, 528−537. (8) Xiao, Y.; Hwang, J.-Y.; Belharouak, I.; Sun, Y.-K. Superior Li/Na-Storage Capability of a Carbon-Free Hierarchical CoSx Hollow Nanostructure. Nano Energy 2017, 32, 320−328. (9) Kaneti, Y. V.; Tang, J.; Salunkhe, R. R.; Jiang, X.; Yu, A.; Wu, K. C.; Yamauchi, Y. Nanoarchitectured Design

of

Porous Materials and Nanocomposites from

Metal-Organic Frameworks. Adv. Mater. 2017, 29, 1604898. (10) Guo, Q.; Ma, Y.; Chen, T.; Xia, Q.; Yang, M.; Xia, H.; Yu, Y. Cobalt Sulfide Quantum Dot Embedded N/S-Doped Carbon Nanosheets with Superior Reversibility and Rate Capability for Sodium-Ion Batteries. ACS Nano 2017, 11, 12658−12667. (11) Gu, C.; Guan, W.; Cui, Y.; Chen, Y.; Gao, L.; Huang, J. Preparation of Three-Dimensional Nanosheet-Based Molybdenum Disulfide Nanotubes as Anode Materials for Lithium Storage. J. Mater. Chem. A 2016, 4, 17000−17008. (12) Wu, R.; Wang, D. P.; Rui, X.; Liu, B.; Zhou, K.; Law, A. W. K.; Yan, Q.; Wei, J.; Chen, Z. In-Situ Formation of Hollow Hybrids Composed of Cobalt Sulfides Embedded within Porous Carbon Polyhedra/Carbon Nanotubes for High-Performance Lithium-Ion Batteries. Adv. Mater. 2015, 27, 3038−3044. (13) Wang, J.; Bai, F.; Chen, X.; Lu Y.; Yang, W. Intercalated Co(OH)2-Derived Flower-Like Hybrids Composed of Cobalt Sulfide Nanoparticles Partially Embedded in Nitrogen-Doped Carbon Nanosheets with Superior Lithium Storage. J. Mater. Chem. A 2017, 5, 3628−3637. (14) Sun, P.; Zhang, W.; Hu, X.; Yuan, L.; Huang, Y. Synthesis of Hierarchical MoS2 and Its Electrochemical Performance as an Anode Material for Lithium-Ion Batteries. J. Mater. Chem. A 2014, 2, 3498−3504. (15) Chen, T.; Ma, L. B.; Cheng, B. R.; Chen, R. P.; Hu, Y.; Zhu, G. Y.; Wang, Y. R.; Liang, J.; Tie, Z. X.; Liu, J.; Jin, Z. Metallic and Polar Co9S8 Inlaid Carbon Hollow


Page 22 of 40

Page 23 of 40 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


Nanopolyhedra as Efficient Polysulfide Mediator for Lithium−Sulfur Batteries. Nano Energy 2017, 38, 239−248. (16) Chen, T.; Zhang, Z. W.; Cheng, B. R.; Chen, R. P.; Hu, Y.; Ma, L. B.; Zhu, G. Y.; 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, 12710–12715. (17) Ma, L. B.; Zhang, W. J.; Wang, L.; Hu, Y.; Zhu, G. Y.; Wang, Y. R.; Chen, R. P.; Chen, T.; Tie, Z. X.; Liu, J.; Jin, Z. Strong Capillarity, Chemisorption, and Electrocatalytic Capability of Crisscrossed Nanostraws Enabled Flexible, High-Rate, and Long-Cycling Lithium–Sulfur Batteries. ACS Nano, 2018, 12, 4868–4876. (18) Chen, T.; Cheng, B. R.; Zhu, G. Y.; Chen, R. P.; Hu, Y.; Ma, L. B.; Lv, H. L.; Wang, Y. R.; Liang, J.; Tie, Z. X.; Jin, Z.; Liu, J. Highly Efficient Retention of Polysulfides in “Sea Urchin”-Like Carbon Nanotube/Nanopolyhedra Superstructures as Cathode Material for Ultralong-Life Lithium–Sulfur Batteries. Nano Lett., 2017, 17, 437–444. (19) Fang, G.; Zhou, J.; Cai, Y.; Liu, S.; Tan, X.; Pan, A.; Liang, S. Metal–Organic Framework-Templated Two Dimensional Hybrid Bimetallic Metal Oxides with Enhanced Lithium/Sodium Storage Capability. J. Mater. Chem. A 2017, 5, 13983−13993. (20) Liu, X.; Zou, F.; Liu, K.; Qiang, Z.; Taubert, C. J.; Ustriyana, P.; Vogt, B. D.; Zhu, Y.

A

Binary

Metal

Organic

Framework

Derived

Hierarchical

Hollow

Ni3S2/Co9S8/N-Doped Carbon Composite with Superior Sodium Storage Performance. J. Mater. Chem. A 2017, 5, 11781−11787. (21) Fang, G.; Wu, Z.; Jiang, Z.; Zhu, C.; Cao, X.; Lin, T.; Chen, Y.; Wang, C.; Pan, A.; Liang, S. Observation of Pseudocapacitive Effect and Fast Ion Diffusion in Bimetallic Sulfides as an Advanced Sodium‐Ion Battery Anode. Adv. Energy Mater. 2018, 8, 1703155



(22) Tang, X.; Huang, J.; Feng, Q.; Liu, K.; Luo, X.; Li, Z. Carbon Sphere@Co9S8 Yolk-Shell Structure with Good Morphology Stability for Improved Lithium Storage Performance. Nanotechnology 2017, 28, 375402. (23) Jin, R.; Zhou, J.; Guan, Y.; Liu, H.; Chen, G. Mesocrystal Co9S8 Hollow Sphere Anodes for High Performance Lithium Ion Batteries. J. Mater. Chem. A 2014, 2, 13241−13244. (24) Yu, L.; Yang, J. F.; Lou, X. W. Formation of CoS2 Nanobubble Hollow Prisms for Highly Reversible Lithium Storage. Angew. Chem. Int. Ed. 2016, 55, 13422−13426. (25) Liu, J.; Wu, C.; Xiao, D.; Kopold, P.; Gu, L.; Aken, P. A. v.; Maier, J.; Yu, Y. MOF-Derived Hollow Co9S8 Nanoparticles Embedded in Graphitic Carbon Nanocages with Superior Li-Ion Storage. Small 2016, 12, 2354−2364. (26) Chen, Y.; Li, X.; Park, K.; Zhou, L.; Huang, H.; Mai, Y. W.; Goodenough, J. B. Hollow Nanotubes of N-Doped Carbon on CoS. Angew. Chem. Int. Ed. 2016, 55, 15831−15834. (27) Zeng, P.; Li, J.; Ye, M.; Zhuo, K.; Fang, Z. In Situ Formation of Co9S8/N-C Hollow Nanospheres by Pyrolysis and Sulfurization of ZIF-67 for High-Performance Lithium-Ion Batteries. Chem. Eur. J. 2017, 23, 9517−9524. (28) Wang, X.; Liu, X.; Wang, G.; Zhou, Y.; Wang, H. General Formation of Three-Dimensional (3D) Interconnected MxSy (M=Ni, Zn, and Fe)-Graphene Nanosheets-Carbon Nanotubes Aerogels for Lithium-Ion Batteries with Excellent Rate Capability and Cycling Stability. J. Power Sources 2017, 342, 105−115. (29) Tan, Y.; Liang, M.; Lou, P.; Cui, Z.; Guo, X.; Sun, W.; Yu, X. In Situ Fabrication of CoS and NiS Nanomaterials Anchored on Reduced Graphene Oxide for Reversible Lithium Storage. ACS Appl. Mater. Inter. 2016, 8, 14488−14493. (30) Fan, H.; Yu, H.; Wu, X.; Zhang, Y.; Luo, Z.; Wang, H.; Guo, Y.; Madhavi, S.; Yan,


Page 24 of 40

Page 25 of 40 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


Q. Controllable Preparation of Square Nickel Chalcogenide (NiS and NiSe2) Nanoplates for Superior Li/Na Ion Storage Properties. ACS Appl. Mater. Inter. 2016, 8, 25261−25267. (31) Yu, X. Y.; Lou, X. W. Mixed Metal Sulfides for Electrochemical Energy Storage and Conversion. Adv. Energy Mater. 2018, 8, 1701592. (32) Yuan, D.; Huang, G.; Yin, D.; Wang, X.; Wang, C.; Wang, L. Metal-Organic Framework

Template

Synthesis

of

NiCo2S4@C

Encapsulated

in

Hollow

Nitrogen-Doped Carbon Cubes with Enhanced Electrochemical Performance for Lithium Storage. ACS Appl. Mater. Inter. 2017, 9, 18178−18186. (33) Yang, W.; Chen, L.; Yang, J.; Zhang, X.; Fang, C.; Chen, Z.; Huang, L.; Liu, J.; Zhou, Y.; Zou, Z. One-Step Growth of 3D CoNi2S4 Nanorods and Cross-Linked NiCo2S4 Nanosheet Arrays on Carbon Paper as Anodes for High-Performance Lithium Ion Batteries. Chem. Commun. 2016, 52, 5258−5261. (34) Wu, C.; Maier, J.; Yu, Y. Generalizable Synthesis of Metal-Sulfides/Carbon Hybrids with Multiscale, Hierarchically Ordered Structures as Advanced Electrodes for Lithium Storage. Adv. Mater. 2016, 28, 174−180. (35) Duan, X. D.; Wang, C.; Pan, A. L.; Yu, R. Q.; Duan, X. F. Two-Dimensional Transition Metal Dichalcogenides as Atomically Thin Semiconductors: Opportunities and Challenges. Chem. Soc. Rev. 2015, 44, 8859−8876. (36) Lhuillier, E.; Pedetti, S.; Ithurria, S.; Nadal, B.; Heuclin, H.; Dubertret, B. Two-Dimensional Colloidal Metal Chalcogenides Semiconductors: Synthesis, Spectroscopy, and Applications. Acc. Chem. Res. 2015, 48, 22−30. (37) Peng, L.; Xiong, P.; Ma, L.; Yuan, Y.; Zhu, Y.; Chen, D.; Luo, X.; Lu, J.; Amine, K.; Yu, G. Holey Two-Dimensional Transition Metal Oxide Nanosheets for Efficient Energy Storage. Nature Commun. 2017, 8, 15139. (38) Lv, R.; Robinson, J. A.; Schaak, R. E.; Sun, D.; Sun, Y. F.; Mallouk, T. E.;



Terrones, M. Transition Metal Dichalcogenides and Beyond: Synthesis, Properties, and Applications of Single- and Few-Layer Nanosheets. Acc. Chem. Res. 2015, 48, 56−64. (39) Rao, C. N. R.; Matte, H. S. S. R.; Maitra, U. Graphene Analogues of Inorganic Layered Materials. Angew Chem. Int. Ed. 2013, 52, 13162−13185. (40) Heine, T. Transition Metal Chalcogenides: Ultrathin Inorganic Materials with Tunable Electronic Properties. Acc. Chem. Res. 2015, 48, 65−72. (41) Peng, L.; Fang, Z.; Zhu, Y.; Yan, C.; Yu, G. Holey 2D Nanomaterials for Electrochemical Energy Storage. Adv. Energy Mater. 2017, 8, 15139. (42) Tan, C.; Lai, Z.; Zhang, H. Ultrathin Two-Dimensional Multinary Layered Metal Chalcogenide Nanomaterials. Adv. Mater. 2017, 29, 1701392. (43) Peng, L.; Fang, Z.; Li, J.; Wang, L.; Bruck, A. M.; Zhu, Y.; Zhang, Y.; Takeuchi, K. J.; Marschilok, A. C.; Stach, E. A.; Takeuchi, E. S.; Yu, G. Two-Dimensional Holey Nanoarchitectures Created by Confined Self-Assembly of Nanoparticles via Block Copolymers: From Synthesis to Energy Storage Property. ACS Nano 2018, 12, 820−828. (44) Liu, H.; Ma, F.-X.; Xu, C.-Y.; Yang, L.; Du, Y.; Wang, P.-P.; Yang, S.; Zhen, L. Sulfurizing-Induced Hollowing of Co9S8 Microplates with Nanosheet Units for Highly Efficient Water Oxidation. ACS Appl. Mater. Inter. 2017, 9, 11634−11641. (45) Han, L.; Dong, S. J.; Wang, E. K. Transition-Metal (Co, Ni, and Fe)-Based Electrocatalysts for the Water Oxidation Reaction. Adv. Mater. 2016, 28, 9266−9291. (46) Shang, P.; Zhang, J. A.; Tang, W. Y.; Xu, Q.; Guo, S. J. 2D Thin Nanoflakes Assembled on Mesoporous Carbon Nanorods for Enhancing Electrocatalysis and for Improving Asymmetric Supercapacitors. Adv. Funct. Mater. 2016, 26, 7766−7774. (47) Zhang, H. W.; Zhou, L.; Noonan, O.; Martin, D. J.; Whittaker, A. K.; Yu, C. Z. Tailoring the Void Size of Iron Oxide@Carbon Yolk-Shell Structure for Optimized


Page 26 of 40

Page 27 of 40 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


Lithium Storage. Adv. Funct. Mater. 2014, 24, 4337−4342. (48) Zhang, F.; An, Y. L.; Zhai, W.; Gao, X. P.; Feng, J. K.; Ci, L. J.; Xiong, S. L. Nanotubes within Transition Metal Silicate Hollow Spheres: Facile Preparation and Superior Lithium Storage Performances. Mater. Res. Bull. 2015, 70, 573−578. (49) Zheng, J.; Wu, B. H.; Jiang, Z. Y.; Kuang, Q.; Fang, X. L.; Xie, Z. X.; Huang, R. B.; Zheng, L. S. General and Facile Syntheses of Metal Silicate Porous Hollow Nanostructures. Chem. Asian J. 2010, 5, 1439−1444. (50) Wu, Z.; Zou, H.; Li, T.; Cheng, Z.; Liu, H.; Liu, Y.; Zhang, H.; Yang, B. Single-Unit-Cell Thick Co9S8 Nanosheets from Preassembled Co14 Nanoclusters. Chem. Commun. 2016, 53, 416−419. (51) Zhang, X. D.; Liu, Q, H.; Meng, L. J.; Wang H.; Bi, W. T.; Peng, Y. H.; Yao T.; Wei,

S. Q.; Xie,

Y.

In-Plane Coassembly Route

to Atomically Thick

Inorganic-Organic Hybrid Nanosheets. ACS Nano 2017, 7, 1682−1688. (52) Zhao, C.; Yu, C.; Zhang, M.; Sun, Q.; Li, S.; Norouzi Banis, M.; Han, X.; Dong, Q.; Yang, J.; Wang, G.; Sun, X.; Qiu, J. Enhanced Sodium Storage Capability Enabled by Super Wide-Interlayer-Spacing MoS2 Integrated on Carbon Fibers. Nano Energy 2017, 41, 66−74. (53) Wang, H. Y.; Jiang, H.; Hu, Y. J.; Li, N.; Zhao, X. J.; Li, C. Z. 2D MoS2/Polyaniline Heterostructures with Enlarged Interlayer Spacing for Superior Lithium and Sodium Storage. J. Mater. Chem. A 2017, 5, 5383−5389. (54) Xiao, Y.; Hwang, J. Y.; Belharouak, I.; Sun, Y. K. Superior Li/Na-Storage Capability of a Carbon-Free Hierarchical CoSx Hollow Nanostructure. Nano Energy 2017, 32, 320−328. (55) Huang, S. C.; Meng, Y. Y.; He, S. M.; Goswami, A.; Wu, Q. L.; Li, J. H.; Tong, S. F.; Asefa, T.; Wu, M. M. N-, O-, and S-Tridoped Carbon-Encapsulated Co9S8 Nanomaterials: Efficient Bifunctional Electrocatalysts for Overall Water Splitting. Adv.



Funct. Mater. 2017, 27, 1606585. (56) Dai, C.; Lim, J. M.; Wang, M.; Hu, L.; Chen, Y.; Chen, Z.; Chen, H.; Bao, S.-J.; Shen, B.; Li, Y.; Henkelman, G.; Xu, M. Honeycomb-Like Spherical Cathode Host Constructed from Hollow Metallic and Polar Co9S8 Tubules for Advanced Lithium– Sulfur Batteries. Adv. Funct. Mater. 2018, 28.1704443. (57) Cui, X.; Xie, Z.; Wang, Y. Novel CoS2 Embedded Carbon Nanocages by Direct Sulfurizing Metal-Organic Frameworks for Dye-Sensitized Solar Cells. Nanoscale 2016, 8, 11984−11992. (58) Wang, J. G.; Jin, D. D.; Zhou, R.; Shen, C.; Xie, K. Y.; Wei, B. Q. One-Step Synthesis of NiCo2S4 Ultrathin Nanosheets on Conductive Substrates as Advanced Electrodes for High-Efficient Energy Storage. J. Power Sources 2016, 306, 100−106. (59) Du, Y.; Zhu, X.; Zhou, X.; Hu, L.; Dai, Z.; Bao, J. Co3S4 Porous Nanosheets Embedded in Graphene Sheets as High-Performance Anode Materials for Lithium and Sodium Storage. J. Mater. Chem. A 2015, 3, 6787−6791. (60) Zhou, Y.; Yan, D.; Xu, H.; Liu, S.; Yang, J.; Qian, Y. Multiwalled Carbon Nanotube@a-C@Co9S8 Nanocomposites: a High-Capacity and Long-Life Anode Material for Advanced Lithium Ion Batteries. Nanoscale 2015, 7, 3520−3525. (61) Shi, W.; Zhu, J.; Rui, X.; Cao, X.; Chen, C.; Zhang, H.; Hng, H. H.; Yan, Q. Controlled Synthesis of Carbon-Coated Cobalt Sulfide Nanostructures in Oil Phase with Enhanced Li Storage Performances. ACS Appl. Mater. Interfaces 2012, 4, 2999−3006. (62) Wang, Q.; Zou, R.; Xia, W.; Ma, J.; Qiu, B.; Mahmood, A.; Zhao, R.; Yang, Y.; Xia, D.; Xu, Q. Facile Synthesis of Ultrasmall CoS2 Nanoparticles within Thin N-Doped Porous Carbon Shell for High Performance Lithium-Ion Batteries. Small 2015, 11, 2511−2517. (63) Zhou, Y.; Tian, J.; Xu, H.; Yang, J.; Qian, Y. VS4 Nanoparticles Rooted by a-C


Page 28 of 40

Page 29 of 40 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


Coated MWCNTs as an Advanced Anode Material in Lithium Ion Batteries. Energy Storage Mater. 2017, 6, 149−156. (64) Zhou, Y.; Yan, D.; Xu, H.; Feng, J.; Jiang, X.; Yue, J.; Yang, J.; Qian, Y. Hollow Nanospheres of Mesoporous Co9S8 as a High-Capacity and Long-Life Anode for Advanced Lithium Ion Batteries. Nano Energy 2015, 12, 528−537. (65) Guo, C.; Wang, L.; Zhu, Y.; Wang, D.; Yang, Q.; Qian, Y. Fe3O4 Nanoflakes in an N-Doped Carbon Matrix as High-Performance Anodes for Lithium Ion Batteries. Nanoscale 2015, 7, 10123−10129. (66) Song, J.; Gordin, M. L.; Xu, T.; Chen, S.; Yu, Z.; Sohn, H.; Lu, J.; Ren, Y.; Duan, Y.; Wang, D. Strong Lithium Polysulfide Chemisorption on Electroactive Sites of Nitrogen-Doped Carbon Composites for High-Performance Lithium-Sulfur Battery Cathodes. Angew Chem. Int. Ed. 2015, 54, 4325−4329. (67) Xu, X.; Liu, J.; Hu, R.; Liu, J.; Ouyang, L.; Zhu, M. Self-Supported CoP Nanorod Arrays Grafted on Stainless Steel as an Advanced Integrated Anode for Stable and Long-Life Lithium-Ion Batteries. Chem. Eur. J. 2017, 23, 5198−5204. (68) Wu, L. J.; Lang, J. W.; Wang, S. A.; Zhang, P.; Yan, X. B. Study of Ni-dopped MnCo2O4

Yolk-Shell

Submicron-spheres

with

Fast

Li+

Intercalation

Pseudocapacitance As An Anode for High-Performance Lithium Ion Batteries. Electrochim. Acta 2016, 203,128−135. (69) Qi, H.; Cao, L.; Li, J.; Huang, J.; Xu, Z.; Cheng, Y.; Kong, X.; Yanagisawa, K. High Pseudocapacitance in FeOOH/rGO Composites with Superior Performance for High Rate Anode in Li-Ion Battery. ACS Appl. Mater. Interfaces 2016, 8, 35253−35263. (70) Zhou, L. M.; Zhang, K.; Sheng, J. Z.; An, Q. Y.; Tao, Z. L.; Kang, Y. M.; Chen, J.; Mai, L. Q. Structural and Chemical Synergistic Effect of CoS Nanoparticles and Porous Carbon Nanorods for High-Performance Sodium Storage. Nano Energy 2017, 35, 281−289. ACS Paragon Plus Environment


(71) Zhang, W.; Chu, X.; Chen, C.; Xiang, J.; Liu, X.; Huang, Y.; Hu, X. Rational Synthesis of Carbon-Coated Hollow Ge Nanocrystals with Enhanced Lithium-Storage Properties. Nanoscale 2016, 8, 12215−12220. (72) Jian, G. Q.; Xu, Y. H.; Lai, L. C.; Wang, C. S.; Zachariah, M. R. Mn3O4 Hollow Spheres for Lithium-ion Batteries with High Rate and Capacity. J. Mater. Chem. A 2014, 2, 4627−4632. (73) Liu, J.; Gu, M.; Ouyang, L.; Wang, H.; Yang, L.; Zhu, M. Sandwich-Like SnS/Polypyrrole Ultrathin Nanosheets as High-Performance Anode Materials for Li-Ion Batteries. ACS Appl. Mater. Interfaces 2016, 8, 8502−8510. (74) Yu, X. Y.; Hu, H.; Wang, Y.; Chen, H.; Lou, X. W. Ultrathin MoS2 Nanosheets Supported on N-doped Carbon Nanoboxes with Enhanced Lithium Storage and Electrocatalytic Properties. Angew Chem. Int. Ed. 2015, 54, 7395−7398. (75) Zhang, Z. J.; Zhao, H. L.; Zeng, Z. P.; Gao, C. H.; Wang, J.; Xia, Q. Hierarchical Architectured NiS@SiO2 Nanoparticles Enveloped in Graphene Sheets as Anode Material for Lithium Ion Batteries. Electrochim. Acta 2015, 155, 85−92. (76) Han, D. D.; Xiao, N. R.; Liu, B.; Song, G. X.; Ding, J. One-Pot Synthesis of Core/Shell-Structured NiS@Onion-Like Carbon Nanocapsule as a High-Performance Anode Material for Lithium-Ion Batteries. Mater. Lett. 2017, 196, 119−122. (77) Jin, C.; Zhou, L.; Fu, L.; Zhu, J.; Li, D.; Yang, W. The Acceleration Intermediate Phase (NiS and Ni3S2) Evolution by Nanocrystallization in Li/NiS2 Thermal Batteries with High Specific Capacity. J. Power Sources 2017, 352, 83−89. (78) Wu, X.; Li, S.; Wang, B.; Liu, J.; Yu, M. NiCo2S4 Nanotube Arrays Grown on Flexible Nitrogen-Doped Carbon Foams as Three-Dimensional Binder-Free Integrated Anodes for High-Performance Lithium-Ion Batteries. Phys. Chem. Chem. Phys. 2016, 18, 4505−4512. (79) Wu, X.; Li, S.; Wang, B.; Liu, J.; Yu, M. In Situ Template Synthesis of Hollow


Page 30 of 40

Page 31 of 40 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


Nanospheres Assembled from NiCo2S4@C Ultrathin Nanosheets with High Electrochemical Activities for Lithium Storage and ORR Catalysis. Phys. Chem. Chem. Phys. 2017, 19,11554−11562.



Figure Captions

Scheme 1. Schematic illustration of the formation process of hierarchical Co9S8@C hollow spheres. Fig. 1. XRD pattern of the hydrothermal products and the carbonization products. (a) hexagonal phase CoS and (b) cubic phase Co9S8. Fig. 2. (a) SEM images (Inset image is the high magnification SEM of a broken CoS hollow sphere), (b) TEM image of hierarchical CoS hollow spheres, (c) SEM image and (d) TEM images of hierarchical Co9S8@C hollow spheres, (e) elemental mapping of hierarchical Co9S8@C hollow spheres. Fig. 3.

(a and b) TEM images of hierarchical Co9S8@C hollow spheres, (c) HRTEM

images of Co9S8@C, (d) SAED pattern of Co9S8@C. Fig. 4. (a) Raman spectra of the hollow sphere Co9S8@C and commercial Co9S8, (b) TGA curve of Co9S8@C. Fig. 5. High-resolution XPS elemental spectrum of (a) Co 2p, (b)S 2p, (c) C 1s and (d) N 1s, respectively.

Fig. 6. N2 sorption isotherm for the(a) CoS and (b) Co9S8@C hierarchical hollow spheres (Inset：the pore-size distribution curve). Fig. 7. (a) CV curves of hierarchical Co9S8@C hollow spheres at a scanning rate of 0.1 mV s‒1 in the voltage range of 0.01- 3.0 V. (b) Initial three galvanostatic charge/discharge curves of hierarchical Co9S8@C hollow spheres at a current density


Page 32 of 40

Page 33 of 40 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


of 100 mA g‒1. (c) Rate capability of hierarchical CoS hollow spheres and hierarchical Co9S8@C hollow spheres at different current densities (from 100 - 2000 mA g‒1). (d) EIS curves of the as-prepared electrodes. (e) Long-term cycling performances of hierarchical CoS hollow spheres and hierarchical Co9S8@C hollow spheres at a current density of 100 mA g‒1.

Fig. 8. (a and b) CVs and plots of peak oxidization and reduction currents with respect to scan rate of CoS hollow spheres, (c and d) CVs and plots of peak oxidization and reduction currents with respect to scan rate of Co9S8@C hollow spheres.



Figures

Scheme 1.

Fig.1


Page 34 of 40

Page 35 of 40 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


Fig. 2.



Fig. 3

Fig. 4


Page 36 of 40

Page 37 of 40 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


Fig. 5

Fig. 6



Fig. 7


Page 38 of 40

Page 39 of 40 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


Fig. 8



Table of Contents Graphic


Page 40 of 40

NiSx@C Hollow

Recommend Documents