In-Situ Construction of Iron Sulfide Nanoparticle Loaded Graphitic

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In-situ construction of iron sulfide nanoparticle loaded graphitic carbon capsules from waste biomass for sustainable lithium-ion storage Anupriya K. Haridas, Jinwoo Jeon, Jungwon Heo, Ying Liu, Rakesh Saroha, Jong Hoon Joo, Hyojun Ahn, Kwon-Koo Cho, and Jou-Hyeon Ahn ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b06346 • Publication Date (Web): 03 Mar 2019 Downloaded from http://pubs.acs.org on March 5, 2019

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ACS Sustainable Chemistry & Engineering

In-situ construction of iron sulfide nanoparticle loaded graphitic carbon capsules from waste biomass for sustainable lithium-ion storage Anupriya K. Haridas†, ‡, Jinwoo Jeon†, ‡, Jungwon Heo§, Ying Liu§, Rakesh Saroha†, Jong Hoon Joo∥, Hyo-Jun Ahn†, Kwon-Koo Cho†,*, and Jou-Hyeon Ahn†,§,* †Department

of Materials Engineering and Convergence Technology,

Gyeongsang National University, 501 Jinju-daero, Jinju 52828, Republic of Korea §Department

of Chemical Engineering,

Gyeongsang National University, 501 Jinju-daero, Jinju 52828, Republic of Korea ∥Department

of Advanced Materials Engineering,

Chungbuk National University, 1 Chungdae-ro, Cheongju 28644, Republic of Korea

*To

whom correspondence should be addressed:

Prof. Jou-Hyeon Ahn; [email protected]; Tel: +82-55-772-1784 (J.H. Ahn) Prof. Kwon-Koo Cho; [email protected]; Tel: +82-55-772-1668 (K.K. Cho) ‡These

authors contributed equally to the work.

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ACS Sustainable Chemistry & Engineering 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

ABSTRACT: Iron sulfide (FeS) has gained reasonable attention as potential electrode material for lithium-ion batteries owing to its high specific capacity. However, along with the intrinsically low conductivity of FeS, the generation of polysulfide intermediates and volume expansion encountered during the cycling process, deteriorates its electrochemical performance. A viable solution would be to design conductive carbon nano-architectures capable of effectively accommodating electrochemically active FeS to provide an appropriate conductive pathway which can accelerate ion/electron transport. With this objective, we report a facile, green strategy that facilitates the in-situ generation of FeS nanoparticles within graphitic carbon capsules (FeS@GCC) derived from waste biomass. Unlike the complex synthetic procedures reported before, the proposed eco-friendly strategy consists of simpler and fewer processing steps, thereby advocating the versatility of this method as a scalable and economic approach. The FeS@GCC composite is able to deliver superior discharge capacity of 505 mAh g-1 at 1 C-rate, even after 100 cycles of lithiation and delithiation. At 5 C-rate, a discharge capacity of 370 mAh g-1 is obtained for 500 cycles, substantiating the stable, high rate-cycling performance of this sustainable composite material. KEYWORDS: Iron sulfide, Waste biomass, Graphitic carbon, Lithium-ion batteries, Energy storage.


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INTRODUCTION The alarming rate at which fossil fuels and other non-renewable energy resources are being depleted has prompted researchers to focus their current efforts on energy storage and conversion devices that are eco-friendly and sustainable.1–5 In recent years, lithium-ion batteries have been widely used as a viable option for energy storage in portable electronic devices and electric vehicles, on account of their high energy density, light weight, and environmental friendliness.6 However, research on conventional cathodes based on transition metal oxides (such as LiCoO2 and LiMnO2) has reached a threshold, owing to the enormous amount of research and development during the past two decades.7–9 Moreover, existing commercialized transition metal oxide cathodes contain toxic elements such as cobalt, which can be detrimental to the environment. Thus, the exploration of new and sustainable electrochemically active materials with higher energy density to accommodate the demands of next-generation electronic devices is inevitable. Transition metal sulfides, which follow conversion redox chemistry, have been of profound research interest recently for reversible lithium storage owing to their ability to store more than one lithium ion per transition metal ion, as opposed to conventional intercalation cathodes.10–17 Among them, iron sulfide monochalcogenide with high theoretical capacity (609 mAh g-1) is an attractive candidate, considering its characteristic advantages such as its natural abundance, low cost, and environmental friendliness.17,18 Nevertheless, the unsatisfactory cycling performance of FeS-based electrodes at room temperature, which is attributable to inherent issues, such as the low degree of reversibility due to limited conductivity, volume expansion and pulverization upon cycling resulting in isolation from the current collector, and the formation of polysulfide intermediates along with the subsequent loss of active material, has been of paramount



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concern.19 Attempts to overcome these problems have included various approaches such as coating with transition metal oxides,20,22 encapsulation in porous as well as conductive carbon,23– 27

and graphene matrices,28–30 all of which have proven to be of worth, extending the cycle life

considerably. For instance, Xu et al. fabricated an interconnected porous FeS/C composite, consisting

of

FeS

nanoparticles

embedded

in

carbon

nanosheets

via

a

freeze-

drying/carbonization method using a NaCl template.31 Similarly, various research groups have reported ingenious ways to synthesize metal sulfide/carbon/graphene nano-architectures via rigorous procedures, utilizing sophisticated methods.32–36 However, these strategies involve several intricate steps in the fabrication process and are therefore time consuming. Apart from that, the utilization of toxic chemicals for their synthesis renders these procedures complex and non-viable for commercial application. In this paper we report the facile strategy we designed to synthesize nanostructured iron sulfide incorporated in graphitic carbon capsules (FeS@GCC) derived from the waste of raw biomass (sawdust) for green and sustainable lithium-ion batteries. Sawdust, which is a renewable, abundant, and ecofriendly resource, is an industrial/agricultural waste product that can be carbonized and utilized as a conductive carbon matrix. Our strategy involves the direct conversion of Fe3C-incorporated graphitic carbon obtained from the carbonization of iron precursor-impregnated sawdust to FeS nanoparticles incorporated in graphitic carbon. The graphitic carbon derived from biomass serves as an effective and scalable way to accommodate the volume changes of the material as well as to confine the polysulfide intermediates generated during the cycling process, apart from improving the conductivity and facilitating rapid electron transport in the composite. Investigation of the electrochemical performance against lithium


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reveals that the FeS@GCC electrode has superior discharge capacities of 505 mAh g-1 at 1 C after 100 cycles and 370 mAh g-1 at the high C-rate of 5 C even after 500 cycles.

EXPERIMENTAL SECTION Materials and methods. Iron nitrate nonahydrate (Fe(NO3)3∙9H2O, 98%, Sigma Aldrich), iron sulfide (FeS, 99.9%, Sigma Aldrich), sawdust (JRS Co. Ltd.), elemental sulfur (Sigma Aldrich), acetylene black (Alfa Aesar), PVdF (Poly(vinylidene fluoride), Sigma Aldrich), Nmethyl-2-pyrrolidone (NMP, 99.5%, Samchun Pure Chemical Co., Ltd.) were used as received without further purification. Synthesis of Fe3C@GCC composite. Fe(NO3)3∙9H2O (6 g) was dissolved in deionized water (40 mL). Sawdust (5 g) was added to the resultant solution, which was stirred thoroughly. The mixture was subjected to ultra-sonication (1 h) to obtain a homogeneous dispersion. The obtained sample was dried (80 °C, 24 h), after which the temperature was increased to 800 °C at a heating rate of 5 °C min-1 in nitrogen atmosphere and then maintained at this level (3 h) to allow the carbonization of sawdust. The obtained iron carbide-embedded graphitic carbon capsule composite (designated as Fe3C@GCC) was hand-ground using a mortar and pestle prior to further use. Synthesis of FeS@GCC composite. The synthesized Fe3C@GCC powder and elemental sulfur were uniformly mixed in a 1:3 weight ratio and subjected to heat treatment (600 °C, 6 h) after heating at a rate of 5 °C min-1 in nitrogen atmosphere to aid the formation of iron sulfideincorporated graphitic carbon capsules (referred to as FeS@GCC hereafter). Ball-milled commercial FeS powder was utilized as control electrode material in the present study.



Structural and electrochemical characterization. Field emission scanning electron microscopy (FE-SEM, Philips XL30S FEG) and transmission electron microscopy (TEM, TF30ST- 300 KV) were utilized to record the surface and internal morphologies of the Fe3C@GCC and FeS@GCC composites. The structure and phase purity of the composites were confirmed using X-ray diffractometry (XRD, D2 Phaser Bruker AXS). Thermogravimetric analysis (TGA, Q50 TA Instruments) was carried out from room temperature to 800 °C in air with a ramp rate of 10 °C min-1 to estimate the active material as well as carbon content in the final FeS@GCC composite. The specific surface area, pore volume and pore size of the synthesized composites were obtained by conducting Brunner-Emmet-Teller analysis (BET, ASAP 2010) via the Barrett-Joyner-Halenda (BJH) method. The electrodes were fabricated by mixing 80% FeS@GCC, 10% carbon black, and 10% poly(vinylidene fluoride) (PVDF) in N-methyl-2-pyrrolidone (NMP). The slurry was coated onto aluminum foil and was dried (60 °C, 12 h) to ensure that the residual solvent was completely eliminated. The casted slurry was then punched in the form of circular discs (diameter = 10 mm), which were directly employed as electrodes. Stainless steel Swagelok® cells were assembled in an argon-filled glove box using lithium foil (Cyprus Foote Mineral Co.), Celgard® 2400 and 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in dimethyl ether (DME) and 1,3-dioxolane (DOL) (v/v =1/1) as counter electrode, separator, and electrolyte, respectively. Cyclic voltammetry (CV) tests were conducted in the voltage range, 1-3 V at a scan rate of 0.05 mV s-1. Impedance spectra were recorded (ZIVE SP2, WonA Tech. Co.) in the frequency range 100 mHz to 2 MHz with an amplitude of 5 mV.


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RESULTS AND DISCUSSION The FeS@GCC composite was synthesized by a simple, scalable, and green strategy utilizing waste sawdust as the source of carbon. Figure 1 shows a schematic representation of the synthetic procedure employed in the work. To summarize, a certain amount of the iron precursor (Fe(NO3)3∙9H2O) was first dissolved in deionized water. The resultant solution was mixed with a certain amount of raw sawdust and the residual solvent was evaporated by drying the sample (80 °C, 24 h). Calcination of the sample at 800 °C for 3 h in nitrogen atmosphere resulted in the formation of the intermediate, Fe3C@GCC, by the simultaneous high-temperature catalytic graphitization-assisted carbonization of sawdust with the iron precursor.37 Further, subsequent heat treatment of the obtained Fe3C@GCC composite with elemental sulfur (1:3 wt/wt) at 600 °C in nitrogen atmosphere aided the conversion of Fe3C to FeS, resulting in the formation of iron sulfide nanoparticles embedded inside graphitic carbon capsules (FeS@GCC). The XRD patterns of the synthesized Fe3C@GCC and FeS@GCC composites are shown in Figure 2. High intensity, crystalline diffraction peaks were obtained, which coincided with those on the standard ICDD cards of Fe3C (ICDD 01-035 0772), graphitic carbon (ICDD 01-0714630), and Fe (ICDD 00-065-4889) as seen in Figure 2a, confirming the formation of the Fe3C@GCC composite after the initial heat treatment. The XRD pattern of the final FeS@GCC composite obtained after sulfurization of the Fe3C@GCC composite is shown in Figure 2b. The crystalline diffraction peaks of the composite were indexed to hexagonal FeS (ICDD 01-0896926). No impurity phases were detected in the sample. A sharp peak that corresponds to graphitic carbon (ICDD 01-071-4630) can be clearly observed at 26° in both composites. The FE-SEM images of the intermediate Fe3C@GCC composite display primary particles with sizes greater than 1 µm together with aggregated secondary particles of varying particle sizes, in the



100-500 nm range (Figure 2c and d). After the sulfurization process, no morphological variations were observed in the obtained FeS@GCC composite, compared to the FE-SEM images of the Fe3C@GCC composite (Figure 2e and f), which confirms retention of the carbon structure in the final composite even after the sulfurization process. The low- and high-resolution TEM images of the FeS@GCC composite, shown in Figure 3a and b, display FeS nanoparticles of 50-80 nm encapsulated within graphitic carbon capsules. The agglomerated iron precursor during the initial impregnation step leads to the formation of FeS particles without graphitic carbon encapsulation. However, the formation of such anomalous particles without graphitic encapsulation was minor in the final FeS@GCC composite. The observed internal morphology of the FeS@GCC composite is analogous to that of the Fe3C@GCC composite (Figure S1a, b, c). The graphitic carbon shell acts as a capsule that assists in controlling the growth of the FeS nanoparticles during the high-temperature heat treatment process, resulting in effective spatial confinement. FeS nanoparticles can be evidently seen (darker contrast region) entrapped within the graphitic carbon capsules (lighter contrast). Figure 3c, d, e, and f show the high-resolution TEM images of the FeS@GCC composite. The magnified image of the highlighted region in Figure 3c (shown in Figure 3d) confirms the lattice spacing corresponding to the (114) plane (0.207 nm) of hexagonal FeS. Similarly, the lattice spacing of the (002) plane of graphitic carbon is confirmed to be 0.34 nm from Figure 3f (magnified view of the region marked in Figure 3e). The EDS mapping results of the FeS@GCC composite are shown in Figure 3g, h, and i. The homogenous distribution of the elements iron and sulfur substantiates that FeS nanoparticles are confined successfully within the graphitic carbon capsules. The low- and high-resolution TEM images of the intermediate Fe3C@GCC composite prior to sulfurization are presented in Figure S1 for reference.


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The active material and carbon content in the FeS@GCC composite was estimated by conducting thermogravimetric analysis from room temperature to 800 °C in air atmosphere and the obtained result is shown in Figure 4a. An initial weight gain is observed for the composite from 200 °C to 350 °C, and after that significant weight loss is observed up to 630 °C. The initial weight gain can be associated with the partial oxidation of FeS leading to the formation of FeSO4 upon heat treatment in air and has been reported previously.38,39 The subsequent reduction in weight beyond 350 °C corresponds to the partial transformation of FeS into Fe2O3, which is stable in air. The weight loss observed above 405 °C can be attributed to the complete oxidation of FeSO4 to Fe2O3 along with the simultaneous oxidation of carbon present in the composite. Finally, a stable weight is observed beyond 630 °C, confirming the complete formation of Fe2O3.38,39 The XRD pattern of the final composite obtained after TGA analysis also confirms the formation of Fe2O3 (Figure S2) well in accordance with previous reports.17,28 Accordingly, the carbon content was estimated to be 45.5%, resulting in an FeS content of 54.5% in the synthesized composite. A detailed TGA calculation is presented in the Supplementary Information. The physical properties of the FeS@GCC composite were estimated by BET analysis. Figure 4b shows a type IV isotherm with a type H3 hysteresis loop, implying the existence of mesopores in the composite. Concurrently, the BET analysis of the Fe3C@GCC composite, recorded for comparison purposes (Figure S4), displays a similar isotherm. The surface area and pore volume of the FeS@GCC composite was determined to be 109.3 m2 g-1 and 0.22 cm3 g-1, respectively, which is lower than that of the Fe3C@GCC composite (Table S1, surface area: 204 m2 g-1; pore volume: 0.24 cm3 g-1). This observed reduction in surface area after sulfurization confirms the effective inclusion of FeS within the porous graphitic carbon capsules. The average pore diameter of the FeS@GCC composite was found to be 7.5 nm. The



pore size distribution curve confirmed the presence of mesopores (smaller than 5 nm) as well as macropores (smaller than 100 nm). Although the majority of the pores fall in the former category, a few are present in the latter. The Raman spectrum of the FeS@GCC composite is shown in Figure 4c. The characteristic Raman peaks of FeS that confirm the presence of asymmetric and symmetric stretching modes, can be clearly observed at 218, 283, and 400 cm1.40

Well-defined D and G bands can also be observed at 1336 and 1571 cm-1, respectively. The

dominant intensity of the G band compared to the D band is evident in the sample. Accordingly, the IG/ID ratio of the FeS@GCC composite was estimated to be 1.02, indicating the graphitic nature of the composite. Additionally, the G’ band (2D band) observed at 2695 cm-1 supports the presence of graphitic carbon in the composite.41 Generally depending on the voltage regime utilized, FeS-based electrodes have been employed as either anodes or cathodes in previous studies.17,23,29,30 However, here we stress their utility as powerful cathode materials, as we believe the comparatively low cell voltage could be compensated by the huge obtainable capacity, as well as the low polarization, highlighting their potential for use as a high-energy-density cathode for room-temperature rechargeable batteries. Accordingly, the electrochemical properties of the FeS@GCC composite were analyzed in detail by exploring the narrow voltage range of 1-3 V, as shown in Figure 5. Thus far, only limited research has explored the narrow voltage range in FeS electrodes.17,23,42,43 The cyclic voltammetry (CV) curves of FeS@GCC composite are presented in Figure 5a. In the first cycle, only a single reduction peak was observed at ~1.3 V, corresponding to the conversion reaction of FeS (FeS + 2Li+ + 2e−  Fe + Li2S).23 The oxidation peak obtained at ~1.8 V denotes the transformation of Fe to Li2-xFeS2.28 From the second cycle onwards, the reduction peaks are slightly shifted to a higher voltage (~1.4 V), associated with the structural

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changes induced by the initial conversion reaction in conversion-based electrodes.44 However, the subsequent oxidation peaks were still observed at ~1.8 V. The small reduction peak observed at 1.9 V from the second cycle onwards can be attributed to the conversion of Li2-xFeS2 to Li2FeS2.28,45 Figure 5b displays the charge-discharge profiles for the first three cycles at 0.2 Crate Well-defined, flat, and symmetric charge-discharge plateaus were obtained in accordance with the conversion chemistry, indicating the remarkable reversibility of the electrode. The first discharge plateau was observed at approximately 1.3 V, and from the second cycle onwards, the discharge plateau shifted to 1.4 V although the charge plateau remained at ~1.8 V, analogous to the observations from the CV curves. Interestingly, discharge capacity close to the theoretical capacity is obtained from the 2nd discharge cycle onward, which corresponds to the storage of almost two Li ions per transition metal atom Fe, according to the conversion reaction of FeS. The charge-discharge capacity of the FeS@GCC composite, obtained at a C-rate of 0.2, is shown in Figure 5c. After 100 cycles of lithiation and delithiation, the composite maintains a discharge capacity of 502.5 mAh g-1, much higher than that of ball-milled commercial FeS powder (385.2 mAh g-1). Furthermore, the rate capability of the FeS@GCC composite was investigated by switching the current density from 0.2 to 5 C-rate. Remarkably high discharge capacities of 565, 540, 517, 492, and 422 mAh g-1 were obtained at C-rates of 0.2, 0.5, 1, 2, and 5, respectively (Figure 5d). Switching the current density resulted in the observation of slight variations in the capacity during the initial cycles. However, when the C-rate was finally returned to 0.2, a high discharge capacity of 561 mAh g-1 was obtained, indicating good capacity retention. Notably, the capacity was stable and well-maintained, despite the C-rates being switched. However, the ball-milled commercial FeS powder displayed poor capacity retention, especially at high C-rates. The cycle performance of the FeS@GCC



composite at various C-rates is shown in Figure 6a. The FeS@GCC cathode delivers initial discharge capacities of 628, 549, 539, and 504 mAh g-1 and discharge capacities of 487, 505, 475, and 447 mAh g-1 even after 100 cycles at C-rates of 0.5, 1, 2, and 5, respectively. The capacity retention after 100 cycles was found to be 78%, 92%, 88%, and 88% at C-rates of 0.5, 1, 2, and 5 C, which confirms the stable performance of the composite even at high C-rates compared to lower C-rates. This could be the consequence of the effective electrolyte percolation pathways created within the mesoporous graphitic carbon capsules hosting the nanostructured FeS which ensure rapid ion transfer and is a commonly observed phenomenon in mesoporous materials.46,47 Additionally, the impedance spectra of the FeS@GCC electrode, which were recorded before and after cycling studies, were analyzed to understand the kinetics of the system. Figure 6b shows the impedance spectroscopy curve of the composite before and after cycling. The charge transfer resistance (Rct) was slightly reduced after the initial cycle compared to the fresh cell. This initial reduction in Rct can be attributed to the conversion reaction leading to the continuous formation of metallic iron nanoparticles upon discharge as reported in case of metal sulfide-based electrodes.48 However, the Rct decreased dramatically with cycling. This continuous reduction can arise from the gradual percolation of electrolyte into the porous FeS@GCC composite electrode as cycling proceeds. This explains the observed cycling stability of the composite. Furthermore, we investigated the long-term cycling performance of the FeS@GCC composite at a high C-rate of 5 C (Figure 6c). The FeS@GCC electrode was found to deliver 370 mAh g-1 even after 500 cycles at this C-rate, with 0.052 % capacity decay per cycle, which highlights the stable high rate cyclability of the composite. Post-cycling studies were performed to investigate the superior performance of the synthesized FeS@GCC composite. After the cycling process, the FeS@GCC and the ball-milled


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commercial FeS cells were carefully disassembled in a glovebox. The FESEM images of the ball-milled commercial FeS electrode and the FeS@GCC electrode were recorded to verify the structural integrity of the electrodes. Both the cycled electrodes consisted of the active material surrounded by conductive carbon and binder. However, it can be clearly seen that the ball-milled commercial FeS electrode (Figure 7a and b) consists of cracks formed due to the volume changes in the active material FeS, while the FeS@GCC electrode (Figure 7c and d) is maintained intact with good integrity even after the cycling process. The TEM images of the FeS@GCC electrode were also recorded to verify the internal structure of the composite after the cycling process (Figure 8a-c). The graphitic carbon encapsulation was found to be preserved intact without any damage as shown in Figure 8c. This observation can be related to the good cycle performance of the FeS@GCC composite. Thus, the FeS@GCC hybrid can effectively suppress the volume changes encountered during the cycling process, and maintain the structural integrity of the electrode due to the presence of graphitic carbon encapsulation. The commendable electrochemical properties of the FeS@GCC composite in terms of cycling stability and rate performance can be mainly attributed to the following aspects viz. 1) encapsulation of the FeS nanoparticles in graphitic carbon, which buffers the volume changes encountered during the cycling process, 2) improved ion/electron transport in the composite on account of the conductive carbon network, and 3) the presence of meso- and macropores in the composite which promote electrolyte percolation within the composite and at the same time ensure the effective confinement of polysulfide species generated during the cycling process. We believe that such initiatives employing waste biomass-derived mesoporous carbon matrices as conductive hosts for in-situ generation of metal sulfides would serve as an impetus for the development of high energy density energy storage systems via sustainable and green routes.



CONCLUSIONS The green and sustainable strategy that was employed enables the in-situ generation of FeS nanoparticles in graphitic carbon capsules (FeS@GCC) derived from waste biomass. FeS nanoparticles (50-80 nm) were synthesized successfully within the graphitic carbon capsules derived from waste biomass, sawdust, by the direct conversion of Fe3C incorporated graphitic carbon yielded from the carbonization process. The nanosized FeS particles embedded within the mesoporous, conductive graphitic carbon capsules promote rapid percolation of the electrolyte, boosting ion/electron transport in the composite. Moreover, the graphitic carbon matrix acts as a buffer that accommodates the volume changes, apart from confining the polysulfide species generated during the cycling process. As a result, the FeS@GCC composite exhibits a high discharge capacity of 505 mAh g-1 after 100 cycles at 1 C-rate and commendable rate performance at 5 C-rate, maintaining a capacity of 370 mAh g-1 even after 500 cycles in the narrow voltage range of 1-3 V.

ASSOCIATED CONTENT Supporting Information. The following files are available free of charge. TEM images of Fe3C@GCC composite; XRD pattern of FeS@GCC after TGA; BET analysis of Fe3C@GCC composite; Detailed TGA curve and estimation of FeS content in FeS@GCC composite; XRD pattern, Raman spectrum, FE-SEM and TEM images, and EDS mapping of the GCC obtained after etching the Fe3C@GCC composite. (PDF)


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AUTHOR INFORMATION Corresponding Author *(J.H.

Ahn) Email: [email protected]

*(K.K.

Cho) E-mail: [email protected]

Author Contributions ‡These

authors contributed equally.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NO. NRF 2017R1A4A1015711).

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TOC

Synopsis: A green and ecofriendly synthesis strategy for iron sulfide-based sustainable lithiumion storage is demonstrated.


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Figure Captions Figure 1. Schematic procedure for the synthesis of FeS@GCC composite. Figure 2. XRD patterns of a) Fe3C@GCC, b) FeS@GCC, and FE-SEM images of c-d) Fe3C@GCC, and e-f) FeS@GCC composites. Figure 3. a-b) TEM images, c-f) HRTEM images, and g-i) EDS mapping of FeS@GCC composite. Figure 4. a) TGA curve, b) BET isotherms, and c) Raman spectrum of FeS@GCC composite. Figure 5. a) CV curves and b) charge-discharge voltage profile of FeS@GCC composite, c) cycle performance, and d) rate capability test of FeS@GCC composite and the ball-milled commercial FeS electrodes. Figure 6. Electrochemical properties of FeS@GCC composite: a) cycling performance at various C-rates, b) electrochemical impedance spectroscopy studies before and after cycling at 1 C-rate, and c) cycling performance at 5 C-rate. Figure 7. FE-SEM images of electrodes after cycling: a-b) ball-milled commercial FeS electrode and c-d) FeS@GCC electrode. Figure 8. TEM images of the FeS@GCC electrode after cycling: a) low-magnification image and b-c) high-magnification images showing the maintenance of the graphitic carbon encapsulation even after the cycling process.



Figure 1. Schematic procedure for the synthesis of FeS@GCC composite.


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Figure 2. XRD patterns of a) Fe3C@GCC, b) FeS@GCC, and FE-SEM images of c-d) Fe3C@GCC, and e-f) FeS@GCC composites.



Figure 3. a-b) TEM images, c-f) HRTEM images, and g-i) EDS mapping of FeS@GCC composite.


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Figure 4. a) TGA curve, b) BET isotherms, and c) Raman spectrum of FeS@GCC composite.



Figure 5. a) CV curves and b) charge-discharge voltage profile of FeS@GCC composite, c) cycle performance, and d) rate capability test of FeS@GCC composite and the ball-milled commercial FeS electrodes.


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Figure 6. Electrochemical properties of FeS@GCC composite: a) cycling performance at various C-rates, b) electrochemical impedance spectroscopy studies before and after cycling at 1 C-rate, and c) cycling performance at 5 C-rate.



Figure 7. FE-SEM images of electrodes after cycling: a-b) ball-milled commercial FeS electrode and c-d) FeS@GCC electrode.


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Figure 8. TEM images of the FeS@GCC electrode after cycling: a) low-magnification image and b-c) high-magnification images showing the maintenance of the graphitic carbon encapsulation even after the cycling process.


In-Situ Construction of Iron Sulfide Nanoparticle Loaded Graphitic

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