Pyroprotein-Derived Hard Carbon Fibers Exhibiting Exceptionally

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Article

Pyroprotein-derived hard carbon fibers exhibiting exceptionally high plateau capacities for sodium ion batteries Jaewon Choi, Min Eui Lee, Sungho Lee, Hyoung-Joon Jin, and Young Soo Yun ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b01734 • Publication Date (Web): 08 Jan 2019 Downloaded from http://pubs.acs.org on January 9, 2019

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 27 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 Energy Materials

Pyroprotein-Derived Hard Carbon Fibers Exhibiting Exceptionally High Plateau Capacities for Sodium Ion Batteries Jaewon Choi1,†, Min Eui Lee2,†, Sungho Lee1, Hyoung-Joon Jin2,* and Young Soo Yun3,*

1Institute

of Advanced Composite Materials, Korea Institute of Science and Technology (KIST),

Jeonbuk, 55324 (South Korea) 2Department

of Polymer Science and Engineering, Inha University, Incheon 22212 (South Korea)

3Department

of Chemical Engineering, Kangwon National University, Samcheok 25913 (South

Korea)

†These

authors contributed equally to this work.

*Corresponding

authors (E-mail: [email protected] and [email protected])

Keywords: Carbon fiber; Pyroprotein; Hard carbon; Anode; Sodium-ion batteries

ACS Paragon Plus Environment

1

ACS Applied Energy 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

Page 2 of 27

ABSTRACT In this study, low-density, hard carbon fibers incorporating multitudinous closed pores with fewnanometer-scale widths were prepared from waste silk fabric by a simple high-temperature heating process (2000 °C). The pyroprotein carbon fibers exhibited a significantly high single-plateau capacity of 300 mA h g-1 at ~0.1 V Na+/Na, a high initial Coulombic efficiency of ~91.9%, and stable cycling behaviors of more than 200 cycles when used as the anode of a sodium-ion battery. Characterization using in situ X-ray diffraction patterns and ex situ field emission transmission electron microscopy confirmed that the outstanding charge storage behaviors of the pyroprotein carbon fibers are based on sodium-metal nanoclustering in the closed pores. Moreover, full cells assembled with the pyroprotein carbon-fiber-based anode and a reported cathode demonstrated their practical electrochemical performances, including a specific energy of 262 Wh kg-1.


2

Page 3 of 27 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


INTRODUCTION The number of fields in which energy storage devices (ESDs) are applied continues to increase in modern society, with new-industrial-revolution technologies as well as advancements in mobile electronic devices and transportation equipment.1,2 Li-ion batteries (LIBs), one of the most widely used ESDs, are becoming more ubiquitous with the dramatic increase in demand, thus accelerating a demand for mass-scalable and inexpensive energy-storage devices.3,4 In this respect, Na-ion batteries (NIBs) using readily available sodium resources and a similar chemistry to LIBs have attracted considerable attention as a promising next-generation energy-storage devices.3,4 However, given that sodium ions are ~55% larger, ~330% heavier, and have a potential that is 0.33 eV (vs. metal) higher than lithium ions, they exhibit a relatively poor energy density.3-5 Moreover, a practical anode material for NIBs, comparable to graphite in LIBs, has yet to be isolated.6,7 These major hurdles must be overcome before NIBs can take the place of LIBs in the market. The first candidate material to be examined for a NIB anode was hard carbon, composed of disordered graphitic carbon components. This material offers a relatively high energy-storage performance, low production cost, and similar chemistry to the graphite anodes of LIBs.6-14 In a conventional carbonate-based electrolyte, a commercial hard carbon exhibits a high specific capacity of ~300 mA h g-1 consisting of a sloping-voltage section and low-voltage plateau in the galvanostatic discharge/charge profiles.8,9 Nevertheless, the plateau capacity is much smaller than that of the conventional graphite anodes in LIBs, leading to a low level of energy performance. Accordingly, with an increase in research interest in the plateau capacity, there has been discussion about the origin of the plateau capacity – whether it is caused by sodium-ion intercalation in a graphitic lattice or pore filling with closed pores. Some reports have claimed that sodium-ion intercalation rather than pore filling happens in the low-voltage section, because of the discrepancy between


3


Page 4 of 27

Brunauer–Emmett–Teller (BET) specific surface areas and plateau capacities.15-18 However, this opinion incurs an issue in that the kinetic diameter of nitrogen molecules corresponds to a few tenths of a nanometer (≈ 0.4 nm) at low temperatures, which is not sufficient to penetrate the disordered graphitic lattices, thus limiting the characterization of the closed pores inside the hard carbons.19 In addition, considering the highly complex graphitic structure that is composed of numerous graphitic segments, it would be difficult to accept that there is no change in the chemical potential (two-phase reaction) as a result of the sodium ion intercalation into the disordered graphitic structure of the hard carbon. In contrast, Yun et al. reported that sodium ions could be reduced to nanometal clusters in the closed pores of hard carbons at ~0.1 V vs. Na+/Na.20 A similar claim was made by Dahn and Stevens, who reported on the insertion of sodium into the nanopores of the hard carbon.8 This claim has been supported by several subsequent reports.21-23 In particular, Tarascon et al. found that a single low-voltage plateau is observed for carbon nanofibers that have been carbonized at more than 2000 °C.22 The study highlighted that the single plateau originates from nanopore filling, which differs from that of sodium metal plating. Recently, through a careful comparison of reports with conflicting conclusions, Saurel et al. concluded that the formation of metal nanoclusters is a more reasonable theory than sodium ion intercalation.24 Previous reports stressed that the microstructure of hard carbon is key to their sodium-ion storage performances. In addition, more advanced hard carbon active materials will be required to enable the application of NIBs. However, despite several mechanistic studies having been undertaken, very few studies have addressed high-plateau-capacity hard carbon materials. A pyroprotein is a type of carbon-based material prepared from protein precursors by a simple pyrolysis process.25,26 In a previous study, the carbonization mechanism of β-sheet-rich protein fibers and the tunable graphitic structures of pyroprotein-derived carbon fibers (PP-CFs)


4

Page 5 of 27 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


were investigated. In the case of silk fibroin, β-sheet crystals are arranged along the fiber axis, and are transformed into carbon basic structural units (BSUs) by simple heating at a low temperature of approximately 350 °C. By further high-temperature heating of the silk fibroin, significant volume shrinkage of the fibers occurs, resulting in highly disordered graphitic structures. Because the β-sheet-derived graphitic structures include a large number of closed pores in the internal fibrous structure, their sodium ion storage performances could be maximized by tuning the local carbon microstructure. In this study, woven PP-CFs with different graphitic structures were prepared from waste silk fabric (WSFs) by thermal treatment from 800 to 2800 °C. The growth of graphitic structures under the bulk fibrous structure of PP-CFs is significantly retarded, even when subjected to hightemperature heating to 2000 °C, which produces highly disordered graphitic structures with a large number of closed pores. The PP-CFs exhibited an exceptionally high plateau capacity of ~300 mA h g-1 within a practical current range as a result of sodium metal nanoclustering. In addition, a high initial Coulombic efficiency (CE) of ~91.9% and stable cycling behaviors over more than 200 cycles were achieved. In a full cell test with a polyanion cathode, PP-CF-based NIBs demonstrated their feasibility as a next-generation energy-storage device.


5


Page 6 of 27

EXPERIMENTAL Preparation of PP-CFs. WSFs were washed with water and ethanol several times and then dried in a convection oven at 80 °C. The purified WSFs were heated in a tubular furnace or graphite furnace under an Ar flow of 200 mL min-1 and held at the target temperature of 800, 1200, 1600, 2000, 2400, and 2800 °C for 2 h. A heating rate of 5 °C min-1 was applied without any stabilization process. The resulting products were stored in a vacuum oven with no further treatment.

Characterization. The morphologies of PP-CFs were observed using field emission scanning electron microscopy (FE-SEM, S-4300SE, Hitachi, Japan) and high-resolution field emission transmission electron microscopy (FE-TEM, JEM2100F, JEOL, Japan). The high-resolution SEM (HR-SEM) images were characterized using SEM (Helios NanoLab 650; Eindhoven, Netherlands). X-ray diffraction (XRD, Rigaku, DMAX 2500) analyses were conducted using a Cu Kα radiation generator (λ = 0.154 nm) at 40 kV and 100 mA with a 2θ range of 5–60°. The Raman spectra were measured using a continuous linearly polarized laser with a wavelength of 532 nm and a 1200 groove/mm grating. The spot diameter of the Raman laser was approximately 1 nm with a 100× objective lens. The chemical composition and depth profile were examined using X-ray photoelectron spectroscopy (XPS, PHI 5700 ESCA, Chanhassen, USA) with monochromatic Al Kα radiation. The bulk densities of the PP-CFs were measured in a density gradient column filled with benzene (Daejung Chemicals & Metals Co., Ltd., 99.5%, South Korea) and 1,1,2,2tetrabromoethane (Junsei Chemical Co., Ltd., 98%, Japan). The ex situ TEM sample was prepared using a CR2032 coin-type cell. The specific surface areas of the samples were analyzed using nitrogen adsorption and desorption isotherms that were obtained using a porosimetry analyzer (ASAP2020, Micromeritics, USA) at -196 °C.


6

Page 7 of 27 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


Ex situ TEM characterization: The copper-mesh TEM grid and working electrode including the active materials were assembled with an electrolyte in an argon-filled glove box. Na metal was used as a counter electrode and a glass microfiber filter (GF/F, Whatman) as a separator. The coin cell was discharged to 0.01 V and maintained at 0.01 V (vs. Na+/Na) until it reached thermodynamic equilibrium. After discharging, the coin cell was disassembled in an argon-filled glove box, and the TEM grid was removed from the cell. The TEM grid was shrouded in dimethyl carbonate (DMC) electrolyte to limit its exposure to air and then moved to the TEM machine. In this process, the TEM grid was exposed to the air for no more than 3–4 s.

Electrochemical characterization. The electrochemical properties of the PP-CFs and Na1.5VPO4.8F0.7 cathode were characterized using a Wonatech automatic battery cycler and CR2032-type coin cells. For the half-cell experiments, the coin cells were assembled in a glovebox filled with argon using the samples as the working electrode and metallic Na foil as the reference and counter electrodes. NaPF6 (1 M; Sigma-Aldrich, 98%) was dissolved in a solution of diethylene glycol dimethyl ether (DEGDME) and used as an electrolyte for the Na metal anode. A glass microfiber filter (GF/F, Whatman) was used as a separator. The working electrodes were prepared by cutting the PP-CFs into Ø0.5-inch disks. The average active material loading weight of the PP-CFs was ~4 mg. In addition, for the cathode, the working electrodes were prepared by mixing the active material (70 wt%) with conductive carbon (20 wt%) and polyvinylidene fluoride (10 wt%) in N-methyl-2-pyrrolidone. The resulting slurries were uniformly applied to the Al foil. The electrodes were dried at 120 °C for 2 h and then roll pressed. The average active material loading weight of Na1.5VPO4.8F0.7 was ~3 mg. For a full cell test, the total electrode weight was ~4 mg, with the weight ratio of the PP-CF-2000 anode to the Na1.5VPO4.8F0.7 cathode being


7


Page 8 of 27

approximately 30%. The anode and cathode were precycled over 10 cycles, and were then assembled as a full cell.

In situ XRD characterization. In situ XRD characterization was conducted using a coin-cell configuration similar to that used for the electrochemical measurements. The charge and discharge processes were carried out in CC–CV mode with a 0.2 C-rate over a voltage range of 0.01 to 2.7 V. In situ XRD patterns were measured in the same copper Kα1 system with a PANalytical Empyrean diffractometer like that used for powder XRD analysis. Scans were performed over a 2θ range of 14–32° using a special X-ray holder with a beryllium window that allowed X-ray penetration. The special X-ray holder was subjected to charge and discharge actions.


8

Page 9 of 27 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


RESULTS AND DISCUSSION The morphologies of the heat-treated WSFs were observed using photographic and FE-SEM images, as shown in Figure 1a-c and Figure S1. The woven shapes of the monolithic fabrics were found to be well maintained after high-temperature heating from 800 to 2800 °C, as shown in Figure 1a, b and S1. The PP-CF components also retained their fibrous morphologies, as shown in Figure 1c and S1. The PP-CFs have a diameter of ~10 μm and a high aspect ratio of >1000, while their microstructural transition behaviors were found to be significantly different from those of commercial hard carbon particles. The FE-TEM image of PP-CF-2000 reveals poor graphitic ordering despite high-temperature heating to 2000 °C (Figure 1d), while the commercial hard carbons exhibit distinctive graphitic lattices as the heat-treatment temperature (HTT) increases (Figure S2). The XRD data for the PP-CFs also support the FE-TEM observations, as shown in Figure 1e. The XRD pattern for PP-CFs-2000 exhibits a broad graphite (002) peak at 25°, which is not well-developed after heating to 2800 °C. In contrast, the Raman spectra of the PP-CFs exhibit a pronounced change with an increase in the HTT, with the spectra gradually becoming narrower and sharper with an increase in the HTT, as shown in Figure 1f. The Raman spectrum of PP-CFs-2000 exhibits clear, separate D and G bands with a D-to-G band intensity ratio (ID/IG) of 1.42, indicating the formation of defect-free poly-hexagonal carbon planes of approximately 5.2 nm.25,26 Also, further high-temperature heating to 2800 °C results in a dramatically decreased ID/IG value of ~0.43. These results suggest that the poly-hexagonal sp2 aromatic carbon units become much better developed with an increase in the HTT, whereas their three-dimensional stacking ordering is poor, even at an HTT of 2800 °C. The La and Lc values of the PP-CFs, derived from the results obtained from the deconvoluted Raman spectra shown in Figure S3, and the XRD patterns, respectively, are summarized in Table S1. In the bulk fibrous structure, realignment of


9


Page 10 of 27

the intertwined carbon components would require a huge amount of energy, resulting in a loosely stacked graphitic structure after the high-temperature heating process. Accordingly, a large number of closed pores could be formed in the internal structure of the PP-CFs. The approximate volumes of the closed pores of the PP-CFs were characterized through the measurement of the bulk density (Table S1). The PP-CF-800 has a bulk density of 1.601, which is slightly increased to 1.661 after heating to 1200 °C. This could be caused by the small amount of densification induced from the reduction of the heteroatoms (Table S1). However, a dramatic decrease to 1.427 was observed for PP-CF-1600, and the bulk density was further decreased to 1.400 for PP-CF-2000. The result of this is that, despite the graphitic structures being more developed, the bulk densities of the PP-CFs are decreased significantly, making it reasonable to speculate that PP-CF-2000 has a large number of closed pores. To obtain solid evidence for the closed pores of PP-CF-2000, a fractured surface of a single PP-CF-2000 sample was observed using HR-SEM (Figure 2). A large number of fewnanometer-scale pores were observed across the entire fractured surface. The pores have irregular shapes and are densely packed, suggesting that the internal part of the PP-CF-2000 is composed of multitudinous closed pores. In addition, the relative closed pore ratio was calculated using a previously reported method based on a ball-milling process.27 The internal structures of the PPCFs were depicted as a schematic image with experimental results for d-spacing, La, and Lc, calculated from the XRD and Raman data, as shown in Figure 3. The PP-CFs prepared at HTTs of < 1600 °C are composed of loosely stacked carbon components with a d-spacing of > 0.37 nm, which is an open, porous sodium-ion structure that can be inserted into the carbon structure. In addition, the PP-CFs have large numbers of heteroatoms on their surfaces (see Table S1). Hence, those samples heated to relatively low temperatures would be more receptive to sodium-ion chemisorption, relative to the pore filling in a sodiation process.28 In contrast, the PP-CF-2400 and


10

Page 11 of 27 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


PP-CF-2800 have a relatively well-developed graphitic structure with interlayer distances of < 0.35 nm, which obstructs the sodium-ion diffusion into their internal closed pores. It was reported that the well-developed graphitic structures exhibit not only poor chemisorption of sodium ions but also poor pore-filling by sodium-metal nanoclustering in a conventional carbonate-based electrolyte.8,20,29 Therefore, the more ordered graphitic structures of PP-CF-2400 and PP-CF-2800 could lead to a high polarization of sodium-ion diffusion, resulting in a lower plateau capacity despite the large number of closed pores. Although, with an ether-based electrolyte, more sodium ions can be stored in the graphitic structure as a result of cointercalation, the theoretical capacity of cointercalation with graphite is less than half that of hard carbon.30,31 Meanwhile, the microstructure of the PP-CF-2000 includes not only a well-developed sp2 hexagonal carbon structure but also many few-nanometer-sized closed pores in the space between the highly disordered carbon layers. This appears to offer an ideal structure for charge storage by pore filling. Therefore, it is expected that the PP-CF-2000 would exhibit a significantly long plateau capacity in the low-voltage section as a result of its pore-filling behavior. The electrochemical performances of PP-CFs were tested in an electrolyte of 1 M NaPF6 dissolved in DEGDME over a voltage window of between 0.01 and 2.70 V vs. Na+/Na. As was expected, the PP-CF-2000 exhibited an exceptionally high single plateau capacity of ca, 300 mA h g-1 at ~0.1 V, as shown in Figure 4a, which is a much higher value than those of other PP-CF samples (Figure S4). In addition, a high CE of the first cycle corresponding to 91.9% was observed, as shown in Figure 4a. The specific capacity of the PP-CF-2000 gradually decreased as the current rate increased, as shown in Figure 4b. Furthermore, when the current rate returned to its initial value, the early specific capacity was restored, indicating good capacity reversibility. In addition, stable cycling behaviors were maintained over 200 cycles, indicating an average Coulombic efficiency of ~100%, with the


11


Page 12 of 27

exception of the initial few cycles (Figure 4c). After 200 cycles, a specific capacity equal to 93% of the initial capacity was retained. To elucidate the charge storage mechanism for the outstanding sodium-ion storage behaviors of PP-CF-2000, in situ XRD characterization was conducted (Figure 4d). In the discharge process, the XRD patterns obtained with different states of charges (SOCs) exhibit the same graphite (002) peaks at 25.8° despite the low-voltage plateau that occurs. In addition, the XRD patterns in the charge process exhibit the same graphite (002) peaks with no change. These results suggest that the plateau capacity is not related to the intercalation reaction of the sodium ions into the disordered graphitic structure. Nevertheless, the XRD patterns exhibit no direct evidence for the pore-filling mechanism. Hence, ex situ FE-TEM measurements of the PP-CFs-2000 were done after full sodiation at 0.01 V vs. Na+/Na (Figure 5 and Figure S5-S7). The ex situ FE-TEM image exhibits several sodium-metal nanoclusters, spread over the entire area, with a particle size of ~1–3 nm [Figures S5 and S6]. Furthermore, the energy dispersive spectrometer (EDS) data show that sodium and carbon are the main components of the characterized samples, supporting the finding that the nanoclusters are of sodium metal (Figure S7). In the high-resolution ex situ FE-TEM image (Figure 5), the sodium (200) lattices (d200-spacing: ~0.215 nm) are well matched with the body-centered cubic (BCC) structure of sodium metal (JCPDS 22-0948). The sizes of the observed metal nanoclusters that could form in the closed pores are so small that they are difficult to detect using in situ XRD characterization. The ex situ XPS depth profile of the PP-CF-2000 after full sodiation also shows that the sodium-metal nanoclusters are formed in the overall internal area of the fibers (see Figure S8). The atomic ratio of the sodium was found to increase with the etching time and saturated after 1000 s, while the atomic ratio of the carbon was diagonally opposite that of sodium. Moreover, when the fully sodiated PP-CF-2000 was exposed to air for a very short time, sodium


12

Page 13 of 27 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


oxide formed over the entire area, indicating that the discharge products are a highly reactive material (Figure S9). Hence, the single low-voltage plateau of PP-CF-2000 is induced by sodium metal nanoclustering in the nanometer-scale closed pores, thus exhibiting an outstandingly good electrochemical performance. The feasibility of PP-CFs-2000 was further demonstrated by full cell tests with a reported polyanion cathode material, Na1.5VPO4.8F0.7.32 The Na1.5VPO4.8F0.7-based cathode exhibits a reversible capacity of 103 mA h g-1 and an average working voltage of 3.87 V at a current rate of 100 mA g-1, as shown in Figure 6a. Highly stable cycling behaviors were observed over 100 cycles (Figure S10). Full cells were assembled using a precycled anode and cathode with an anode/cathode weight ratio of 0.4. As shown in Figure 6b, the galvanostatic charge/discharge profiles of the PP-CF-2000//Na1.5VPO4.8F0.7 cell are similar to that of the cathode material, because the PP-CF-2000 exhibits a single plateau close to 0 V vs. Na+/Na. Considering the weight of both the anode and cathode, the reversible capacity of the PP-CF-2000//Na1.5VPO4.8F0.7 cell was ~70 mA h g-1 at 20 mA g-1. The average working voltage was determined to be 3.85 V. With an increase in the current rate, the specific capacities gradually decreased, while the working voltage was similar to the initial voltage values, indicating the good rate capabilities of the full cell, as shown in Figure 6b. The specific energy of the PP-CF-2000//Na1.5VPO4.8F0.7 cell reached ~262 Wh kg-1 at 39 W kg-1, which is a much higher value than those of other full cell systems using carbon-based anode materials, such as 3DFC,33 CF,34 PNA,35 and AC36, as shown in Figure 6c. In addition, the PP-CF-2000//Na1.5VPO4.8F0.7 cell revealed a highly stable cycling behavior during a continuous galvanostatic cycling process over 100 cycles, as shown in Figure 6d. After the cycling process over 100 cycles, a capacity retention of ~97% was achieved, demonstrating the practicality of NIBs based on PP-CF-2000//Na1.5VPO4.8F0.7.


13


Page 14 of 27

CONCLUSION In summary, PP-CFs were prepared from WSFs by simple heating to different HTTs from 800 to 2800 °C. Graphitic structures of the PP-CFs gradually developed with an increase in the HTTs, and their bulk densities were not consistent with the graphitic ordering due to the formation of closed pores. In particular, PP-CF-2000 had a large number of closed pores with a few nanometersized widths that were observed by HR-SEM imaging. PP-CF-2000 with multitudinous closed pores was found to exhibit an exceptionally high single-plateau capacity of ~300 mA h g-1. In situ XRD and ex situ FE-TEM results proved that the plateau capacity originates from the formation of few-nanometer-sized sodium-metal nanoclusters. The charge storage behaviors of the PP-CF2000 by nanoclustering were highly reversible and stable, exhibiting an electrochemical performance that would be ideal for the anode of a NIB. Furthermore, full-cell tests with a reported cathode material demonstrated the feasible performance of PP-CF-2000.


14

Page 15 of 27 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


AUTHOR INFORMATION Corresponding Author *H.

J. Jin (E-mail: [email protected])

*Y.

S. Yun (E-mail: [email protected])

ACKNOWLEDGMENTS This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF2017R1C1B1004167 and NRF-2018R1A4A1025169).

ASSOCIATED CONTENT Supporting Information. Additional information is included in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.


15


Page 16 of 27

REFERENCES [1] Larcher, D.; Tarascon, J.-M. Towards Greener and More Sustainable Batteries for Electrical Energy Storage. Nat. Chem. 2015, 7, 19–29. [2] Chu, S.; Cui, Y.; Liu, N. The Path Towards Sustainable Energy, Nat. Mater. 2017 16, 16–22. [3] Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba S. Research Development on Sodium-Ion Batteries, Chem. Rev. 2014, 114, 11636–11682. [4] Slater, M. D.; Kim, D.; Lee, E.; Johnson, C. S. Sodium-Ion Batteries, Adv. Funct. Mater. 2013, 23, 947–958. [5] Yun, Y. S.; Park, Y.-U.; Chang, S.-J.; Kim, B. H.; Choi, J.; Wang, J.; Zhang, D.; Braun, P.V.; Jin, H.-J.; Kang, K. Crumpled Graphene Paper for High Power Sodium Battery Anode, Carbon 2016, 99, 658–664. [6] Chayambuka, K.; Mulder, G.; Danilov, D. L.; Notten, P. H. L. Sodium-Ion Battery Materials and Electrochemical Properties Reviewed, Adv. Energy Mater. 2018, 8, 1800079. [7] Kim, H.; Kim, H.; Ding, Z.; Lee, M. H.; Lim, K.; Yoon, G.; Kang, K. Recent Progress in Electrode Materials for Sodium-Ion Batteries, Adv. Energy Mater. 2016, 6, 1600943. [8] Stevens, D. A.; Dahn, J. R. The Mechanisms of Lithium and Sodium Insertion in Carbon Materials, J. Electrochem. Soc. 2001, 148, A803–A811. [9] Komaba, S.; Murata, W.; Ishikawa, T.; Yabuuchi, N.; Ozeki, T.; Nakayama, T.; Ogata, A.; Gotoh, K.; Fujiwara, K. Electrochemical Na Insertion and Solid Electrolyte Interphase for HardCarbon Electrodes and Application to Na-Ion Batteries, Adv. Funct. Mater. 2011, 21, 3859–3867. [10] Li, Y.; Yuan, Y.; Bai, Y.; Liu, Y.; Wang, Z.; Li, L.; Wu, F.; Amine, K.; Wu, C.; L. Jun. Insights into the Na+ Storage Mechanism of Phosphorus-Functionalized Hard Carbon as Ultrahigh Capacity Anodes, Adv. Energy Mater. 2018, 8, 1702781.


16

Page 17 of 27 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


[11] Wu, F.; Liu, L.; Yuan, Y.; Li, Y.; Bai, Y.; Li, T.; Lu, J.; Wu, C. Expanding Interlayer Spacing of Hard Carbon by Natural K+ Doping to Boost Na-Ion Storage, ACS Appl. Mater. Interfaces 2018, 10, 27030–27038. [12] Bai, Y.; Wang, Z. Wu, C.; Xu, R.; Wu, F.; Liu, Y.; Li, H.; Li, Y.; Lu, J.; Amine, K. Hard Carbon Originated from Polyvinyl Chloride Nanofibers As High-Performance Anode Material for Na-Ion Battery, ACS Appl. Mater. Interfaces 2015, 7, 5598−5604. [13] Väli, R.; Jänes, A.; Thomberg, T.; Lust, E. D-Glucose Derived Nanospheric Hard Carbon Electrodes for Room-Temperature Sodium-Ion Batteries, J. Electrochem. Soc. 2016, 163, A1619– A1626. [14] Wang, K.; Jin, Y.; Sun, S.; Huang, Y.; Peng, J.; Luo, J.; Zhang, Q.; Qiu, Y.; Fang, C.; Han, J. Low-Cost and High-Performance Hard Carbon Anode Materials for Sodium-Ion Batteries, ACS Omega 2017, 2, 1687−1695. [15] Qiu, S.; Xiao, L.; Sushko, M. L.; Han, K. S.; Shao, Y.; Yan, M.; Liang, X.; Mai, L.; Feng, J.; Cao, Y.; Ai, X.; Yang, H.; Liu, J. Manipulating Adsorption–Insertion Mechanisms in Nanostructured Carbon Materials for High-Efficiency Sodium Ion Storage, Adv. Energy Mater. 2017, 7, 1700403. [16] Li, Z.; Bommier, C.; Chong, Z. S.; Jian, Z.; Surta, T. W.; Wang, X.; Xing, Z.; Neuefeind, J. C.; Stickle, W. F.; Dolgos, M.; Greaney, P. A.; Ji, X. Mechanism of Na-Ion Storage in Hard Carbon Anodes Revealed by Heteroatom Doping, Adv. Energy Mater. 2017, 7, 1602894. [17] Bommier, C.; Surta, T. W.; Dolgos, M.; Ji, X. New Mechanistic Insights on Na-Ion Storage in Nongraphitizable Carbon, Nano Lett. 2015, 15, 5888–5892.


17


Page 18 of 27

[18] Ghimbeu, C. M.; Górka, J.; Simone, V.; Simonin, L.; Martinet, S.; Vix-Guterl, G. Insights on the Na+ Ion Storage Mechanism in Hard Carbon: Discrimination Between the Porosity, Surface Functional Groups and Defects, Nano Energy 2018, 44, 327–335. [19] Kim, N. R.; Lee, S. M.; Kim, M. W.; Yoon, H. J.; Hong, W. G.; Kim, H. J.; Choi, H. J.; Jin, H.-J.; Yun, Y. S. Amphicharge-Storage Pyropolymers Containing Multitiered Nanopores, Adv. Energy Mater. 2017, 7, 1700629. [20] Yun, Y. S.; Park, K.-Y.; Lee, B.; Cho, S.Y.; Park, Y.-U.; Hong, S. J.; Kim, B. H.; Gwon, H.; Kim, H.; Lee, S.; Park, Y. W.; Jin, H.-J.; Kang, K. Sodium-Ion Storage in Pyroprotein-Based Carbon Nanoplates, Adv. Mater. 2015, 27, 6914–6921. [21] Li, Y.; Hu, Y.-S.; Titirici, M.-M.; Chen, L.; Huang, X. Hard Carbon Microtubes Made from Renewable Cotton as High-Performance Anode Material for Sodium-Ion Batteries, Adv. Energy Mater. 2016, 6, 1600659. [22] Zhang, B.; Ghimbeu, C. M.; Laberty, C.; Vix-Guterl, C.; Tarascon, J.-M. Correlation Between Microstructure and Na Storage Behavior in Hard Carbon, Adv. Energy Mater. 2016, 6, 1501588. [23] Bai, P.; He, Y.; Zou, X.; Zhao, X.; Xiong, P.; Xu, Y. Elucidation of the Sodium-Storage Mechanism in Hard Carbon, Adv. Energy Mater. 2018, 8 1703217. [24] Saurel, D.; Orayech, B.; Xiao, B.; Carriazo, D.; Li, X.; Rojo, T. From Charge Storage Mechanism to Performance: A Roadmap Toward High Specific Energy Sodium-Ion Batteries through Carbon Anode Optimization, Adv. Energy Mater. 2018, 8, 1703268. [25] Cho, S. Y.; Yun, Y. S.; Lee, S.; Jang, D.; Park, K.-Y.; Kim, J. K.; Kim, B. H.; Kang, K.; Kaplan, D. L.; Jin, H.-J. Carbonization of a Stable β-Sheet-Rich Silk Protein into a Pseudographitic Pyroprotein, Nat. Commun. 2015, 6, 7145.


18

Page 19 of 27 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


[26] Zhang, N.; Liu, Q.; Chen, W.; Wan, M.; Li, X.; Wang, L.; Xue, L. High capacity hard carbon derived from lotus stem as anode for sodium ion batteries, J. Power Sources 2018, 378, 331. [27] Cho, S. Y.; Yun, Y. S.; Jang, D.; Jeon, J. W.; Kim, B. H.; Lee, S.; Jin, H.-J. Ultra Strong Pyroprotein Fibres with Long-Range Ordering, Nat. Commun. 2017, 8, 74. [28] Yun, Y. S.; Kim, Y. H.; Song, M. Y.; Kim, N. R.; Ku, K.; An, J. S.; Kang, K.; Choi, H. J.; Jin, H.-J. Energy Storage Capabilities of Nitrogen-Enriched Pyropolymer Nanoparticles Fabricated Through Rapid Pyrolysis, J. Power Sources 2016, 331, 507–514. [29] Datta, D.; Li, J.; Shenoy, V. B. Defective Graphene as a High-Capacity Anode Material for Na- and Ca-Ion Batteries, ACS Appl. Mater. Interfaces 2014, 6, 1788–1795. [30] Jache, B.; Adelhelm, P. Use of Graphite as a Highly Reversible Electrode With Superior Cycle Life for Sodium-Ion Batteries by Making Use of Co-intercalation Phenomena, Angew. Chem. Int. Ed. 2014, 53, 10169–10173. [31] Kim, H.; Hong, J.; Yoon, G.; Kim, H.; Park, K.-Y.; Park, M.-S.; Yoon, W.-S.; Kang, K. Sodium Intercalation Chemistry in Graphite, Energy Environ. Sci. 2015, 8, 2963–2969. [32] Park, Y.-U.; Seo, D.-H.; Kwon, H.-S.; Kim, B.; Kim, J.; Kim, H.; Kim, I.; Yoo, H.-I.; Kang, K. A New High-Energy Cathode for a Na-Ion Battery with Ultrahigh Stability, J. Am. Chem. Soc. 2013, 135, 13870–13878. [33] Yang, B.; Chen, J.; Lei, S.; Guo, R.; Li, H.; Shi, S.; Yan, X. Spontaneous Growth of 3D Framework Carbon from Sodium Citrate for High Energy- and Power-Density and Long-Life Sodium-Ion Hybrid Capacitors, Adv. Energy Mater. 2018, 8, 1702409. [34] Liu, S.; Cai, Z.; Zhou, J.; Zhu, M.; Pan, A.; Liang, S. High-Performance Sodium-Ion Batteries and Flexible Sodium-Ion Capacitors Based on Sb2X3 (X=O, S)/Carbon Fiber Cloth, J. Mater. Chem. A 2017, 5, 9169–9176.


19


Page 20 of 27

[35] Choi, J.; Kim, N. R.; Lim, K.; Ku, K.; Yoon, H. J.; Kang, J. G.; Kang, K.; Braun, P. V.; Jin, H.-J.; Yun, Y. S. Tin Sulfide-Based Nanohybrid for High-Performance Anode of Sodium-Ion Batteries, Small 2017, 13, 1700767. [36] Chen, Z.; Augustyn, V.; Jia, X.; Xiao, Q.; Dunn, B.; Lu, Y. High-Performance Sodium-Ion Pseudocapacitors Based on Hierarchically Porous Nanowire Composites, ACS Nano 2012, 6, 4319–4327.


20

Page 21 of 27 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 1. (a) Photograph of pristine WSF (top) and PP-CF-2000 (bottom), and (b), (c) FE-SEM images (different magnifications) of woven PP-CF-2000. (d) High-resolution FE-TEM image of PP-CF-2000. (e) XRD patterns and (f) Raman spectra of PP-CFs prepared at different HTTs.


21


Page 22 of 27

Figure 2. FE-SEM images of the fractured surface of PP-CF-2000, characterized at different magnifications.


22

Page 23 of 27 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 3. Schematic image of the microstructures of PP-CFs prepared at different HTTs with their layer distances, Lc and La, values.


23


Page 24 of 27

Figure 4. Electrochemical properties of PP-CF-2000 over a voltage window of 0.01–2.70 V vs. Na+/Na. (a) Galvanostatic discharge/charge profiles at a current rate of 10 mA g-1, (b) rate capabilities from 10 to 1000 mA g-1, and (c) cycling behaviors over 200 cycles at 25 mA g-1. (d) In situ XRD patterns of structural evolution of PP-CF-2000 during electrochemical sodium-ion insertion/extraction process with a 2D color plot of the XRD peak intensities relative to the reaction time.


24

Page 25 of 27 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 5. Ex situ FE-TEM images characterized at different magnifications after full sodiation by discharging at 0.01 V vs. Na+/Na.


25


Page 26 of 27

Figure 6. Electrochemical performances of (a) Na1.5VPO4.8F0.7 cathode and (b) PP-CF2000//Na1.5VPO4.8F0.7 cells at current rates of 10, 20, 40, 70, and 100 mA g-1 over a voltage window of 2.5–4.3 V. (c) Ragone plots of different energy storage devices including PP-CF2000//Na1.5VPO4.8F0.7 cells. (d) Capacity retention of PP-CF-2000//Na1.5VPO4.8F0.7 cells over 100 cycles at a current rate of 40 mA g-1.


26

Page 27 of 27 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


Table of Contents

Low-density, hard carbon fibers including multitudinous closed pores with few-nanometer-scale widths were prepared from waste silk fabric by a simple high-temperature heating process (2000 °C). The pyroprotein carbon fibers exhibited a significantly high single plateau capacity of ~300 mA h g-1 at ~0.1 V Na+/Na, a high initial Coulombic efficiency of ~91.9%, and stable cycling behaviors of > 200 cycles when used as the anode in a sodium-ion battery.


27

Pyroprotein-Derived Hard Carbon Fibers Exhibiting Exceptionally

Recommend Documents