Microporous Carbon Nanofibers

Nov 16, 2015 - This chemical bonding can not only promote robust and intimate contact between selenium and carbonaceous nanofiber matrix but also alle...
0 downloads 7 Views 3MB Size
Download PDF
Article pubs.acs.org/JPCC

Strongly Bonded Selenium/Microporous Carbon Nanofibers Composite as a High-Performance Cathode for Lithium−Selenium Batteries Yunxia Liu, Ling Si, Yichen Du, Xiaosi Zhou,* Zhihui Dai,* and Jianchun Bao Jiangsu Key Laboratory of Biofunctional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, People’s Republic of China S Supporting Information *

ABSTRACT: Although lithium−selenium batteries have attracted significant attention for high-energy-density energy storage systems due to their high volumetric capacity, their implementation has been hampered by the dissolution of polyselenide intermediates into electrolyte. Herein, we report a novel selenium/microporous carbon nanofiber composite as a high-performance cathode for lithium−selenium batteries through binding selenium in microporous carbon nanofibers. Under vacuum and heat treatment, selenium particles are easily transformed into chainlike Sen molecules that chemically bond with the inner surfaces of microporous carbon nanofibers. This chemical bonding can not only promote robust and intimate contact between selenium and carbonaceous nanofiber matrix but also alleviate the active material dissolution during cycling. Moreover, selenium is homogeneously distributed in the micropores of the highly conductive carbonaceous nanofiber matrix, which is favorable for the fast diffusions of both lithium ions and electrons. As a result, a high reversible capacity of 581 mA h g−1 in the first cycle at 0.1 C and over 400 mA h g−1 after 2000 cycles at 1 C with excellent cyclability and high rate performance (over 420 mA h g−1 at 5 C, 3.39 A g−1) are achieved with the selenium/microporous carbon nanofibers composite as a cathode for lithium−selenium batteries, performing among the best of current selenium−carbon cathodes. This simple preparation method and strongly coupling hybrid nanostructure can be extended to other selenium-based alloy cathode materials for lithium−selenium batteries.

1. INTRODUCTION Rechargeable lithium−selenium (Li−Se) batteries have recently attracted considerable attention as potential energy storage devices for portable electronics and electric vehicles because of their high volumetric capacity (3253 mA h cm−3),1−6 which is comparable to that of lithium−sulfur batteries (3467 mA h cm−3).7−18 Moreover, their cathode material, elemental selenium, possesses a high electronic conductivity (1 × 10−3 S m−1). Despite these advantages, great challenges exist in cathode of Li−Se batteries that impede their practical applications. Such challenges mainly involve the dissolution of polyselenide intermediates, which results in great loss of the active material and rapid deterioration of cycling stability.19,20 In order to solve the aforementioned problem of Li−Se batteries, one effective strategy is to confine selenium and polyselenides into carbonaceous matrix and meanwhile increase the electrical conductivity of the whole electrode. In this respect, various carbons including mesoporous carbons,2,4,21−27 microporous carbons,28−32 and graphene33−36 have been studied to fabricate selenium−carbon composites and have shown enhanced battery performances. Especially, microporous carbon demonstrates high electrical conductivity, large surface area, good flexibility, and excellent chemical and thermal stabilities. This offers new options to design and prepare © XXXX American Chemical Society

selenium−microporous carbon composites with unique structures. For example, selenium impregnated into metal−organic framework (MOF)-derived microporous carbon sponges,30 selenium confined within porous carbon nanospheres,31 and selenium implanted in microporous carbon polyhedra32 have been obtained for high-capacity Li−Se batteries, whereas polyselenides are still gradually dissolved in the electrolyte during cycling, commonly leading to the loss of active material and remarkable capacity decay especially at high current densities. Very recently, chemically bonding active materials on carbon networks is becoming an effective method to harness the theoretical capacity of active materials to practical applications.37−40 However, how to tightly bind selenium in the empty space of porous carbons remains a big challenge. Herein, we demonstrate a novel selenium/microporous carbon nanofibers (Se/MCNF) composite nanostructured cathode for Li−Se batteries through a facile melt−diffusion process. The large surface area and flexibility of MCNF enable them to well accommodate the Se particles during heat treatment, improving the entire conductivity and increasing the Received: September 30, 2015 Revised: November 13, 2015

A

DOI: 10.1021/acs.jpcc.5b09553 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

Figure 1. Schematic illustration of the preparation process for the Se/MCNF composite.

2050 surface area−pore size analyzer. X-ray photoelectron spectroscopy (XPS) measurements were measured on an ESCALab250Xi electron spectrometer from VG Scientific using 300 W Al Kα radiation. C K-edge X-ray absorption near-edge structure (XANES) measurements were determined by using beamline 4B7B at the Beijing Synchrotron Radiation Facility (BSRF), and the resulting data were normalized to the incident photon flux I0 measured by using a fresh gold target. 2.3. Electrochemical Measurements. Electrochemical experiments were conducted using CR2032 coin cells. The working electrodes were made by mixing Se/MCNF, Super-P carbon black, and sodium alginate with a weight ratio of 80:10:10 in water using a mortar and pestle. The as-made slurry was pasted onto pure aluminum foil (99.0%, Goodfellow) and then dried in a vacuum oven at 40 °C overnight. The mass loading of active material was typically 1.0−1.2 mg cm−2. The electrolyte for all tests was 1 M LiPF6 in ethylene carbonate/ diethyl carbonate (1:1 v/v). Glass fiber (GF/D) from Whatman and pure lithium metal foil were utilized as separators and counter electrodes, respectively. The coin cells were assembled in an argon-filled glovebox (H2O, O2 < 0.1 ppm, MBraun, Germany). Galvanostatic charge−discharge measurements of the batteries were performed on a Land CT2001A multichannel battery testing system in the fixed voltage window between 1.0 and 3.0 V versus Li+/Li at room temperature. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were recorded on a PARSTAT 4000 electrochemical workstation. CV was determined at a scan rate of 0.1 mV s−1, and EIS was studied by applying a sine wave with an amplitude of 10.0 mV over the frequency range from 100 kHz to 100 mHz.

material’s tolerance for the large volume changes of Se during lithium insertion/extraction processes by serving as a robust conductive matrix. In addition, the as-formed chainlike Sen molecules can chemically bond with MCNF during the melt− diffusion process, facilitating intimate contact between them and also confining the polyselenide intermediates. Taking advantage of this unique hybrid nanostructure and strong chemical bonding between Se and MCNF, the as-prepared Se/ MCNF composite exhibits a high reversible capacity of 581 mA h g−1 in the first cycle at 0.1 C and over 400 mA h g−1 after 2000 cycles at 1 C with superior cyclability and high rate capability (over 420 mA h g−1 at 5 C, 3.39 A g−1). The low-cost starting materials of MCNF together with the industry standard melt−diffusion route make this cathode material promising for practical application in Li−Se batteries.

2. EXPERIMENTAL SECTION 2.1. Material Preparation. The carbon nanofibers were first synthesized via a modified tellurium nanowires-templated hydrothermal method using glucose as the carbon source.41,42 Then an appropriate amount of deionized water was added to the mixture of carbon nanofibers and KOH with a weight ratio of 1:4 and the mixture was stirred for 40 min. The resulting slurry was dried at 110 °C for 12 h, heated to 800 °C with a heating rate of 5 °C min−1, and maintained at that temperature for 2 h under an argon atmosphere. The obtained product was rinsed with 100 mL of 0.5 M HCl and subsequently washed with hot deionized water several times. Afterward, the final MCNF was collected and dried under vacuum at 90 °C for 2 days. Se infusion was carried out by grinding Se powder and the as-prepared MCNF for 1 h with a weight ratio of 1:1, followed by heating at 260 °C in a sealed glass tube under vacuum for 12 h. For comparison, the Se−MCNF mixture was prepared by the same procedures as for Se/MCNF except that heat treatment was not applied. 2.2. Materials Characterization. X-ray diffraction (XRD) patterns were recorded on a Rigaku D/max 2500/PC diffractometer using Cu Kα radiation. Raman spectra were collected on a Labram HR800 with a laser wavelength of 514.5 nm. Thermogravimetric analysis (TGA) was carried out using a NETZSCH STA 449 F3 under argon flow with a heating rate of 10 °C min−1 from room temperature to 700 °C. Scanning electron microscopy (SEM) characterization was conducted using a JEOL JSM-7600F scanning electron microscope operated at 10 kV. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) characterizations were taken on a JEOL JEM-2100F transmission electron microscope operated at 200 kV. Scanning transmission electron microscopy (STEM) measurement as well as elemental mapping analysis were obtained on the JEOL JEM-2100F transmission electron microscope equipped with a Thermo Fisher Scientific energydispersive X-ray spectrometer. Nitrogen adsorption and desorption isotherms at 77.3 K were acquired on an ASAP

3. RESULTS AND DISCUSSION The Se/MCNF composite was prepared by a facile melt− diffusion method as illustrated in Figure 1. Commercial Se powder and MCNF (5:5, weight ratio) were homogeneously mixed using a mortar and pestle, followed by heat treatment at 260 °C for 12 h in a sealed glass tube under vacuum, yielding a Se/MCNF composite material (see Experimental Section for details). It has been known that the hydroxyl and epoxide groups of carbon matrix are able to immobilize sulfur through chemical bonding.43 Therefore, it is believed that the oxygencontaining functional groups of glucose-derived MCNF can also strongly bind the congener of sulfur, selenium. The structures of the Se/MCNF composite, as well as those of the original MCNF and Se particles, were investigated by powder XRD and Raman spectroscopy. Strong diffraction peaks at 2θ of 23.5°, 29.7°, 43.6° in the XRD pattern of the Se particles correspond to (100), (101), (102) planes of hexagonal crystalline Se (JCPDS card no. 06-0362) (Figure 2a). In the XRD pattern of Se/MCNF, the native Se peaks disappeared, suggesting that the Se experienced phase transition in the melt−diffusion process. A broad diffraction peak implies its B

DOI: 10.1021/acs.jpcc.5b09553 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

Figure 2. (a) XRD patterns of Se, MCNF, and Se/MCNF composite. (b) Raman spectra of Se, MCNF, and Se/MCNF composite.

amorphous structure in the Se/MCNF composite. The structure of Se/MCNF composite is further reflected by the Raman spectra (Figure 2b). The spectrum of MCNF displays a broad D band (1349 cm−1) and weak G band (1587 cm−1). Compared to MCNF, both the D band and the G band in Se/ MCNF blue-shift to 1355 and 1601 cm−1, respectively, indicating that there may be a strong force between Se and MCNF. Moreover, the wave shift of the characteristic peak of Se from 242 to 260 cm−1 suggests the transformation from crystalline Se to chainlike Sen,2,4,21 which is consistent with the XRD results. The Se content in the Se/MCNF composite was determined by TGA to be around 50 wt % (Supporting Information, Figure S1). The morphology of the Se/MCNF composite was further investigated by SEM and TEM. The Se/MCNF composite is interconnected with diameters of around 170 nm, as shown in the SEM image (Figure 3a). Figure 3b shows the highmagnification SEM image of Se/MCNF. The as-formed composite has a smooth surface, and no nanoparticles can be observed on the surface, implying all Se is implanted inside the carbonaceous nanofibers. The TEM image of Se/MCNF demonstrates all of these hybrid nanofibers are solid and homogeneous in contrast, suggesting Se is uniformly infiltrated in the carbonaceous nanofiber matrix. The selected-area electron diffraction (SAED) pattern displays diffuse scattering (inset of Figure 3c), indicating that the synthesized composite is amorphous, which is further verified by the HRTEM image as illustrated in Figure 3d. Besides, the Brunauer−Emmett−Teller (BET) surface area decreases from 402.5 m2 g−1 in the Se− MCNF mixture (without heat treatment) to 66.2 m2 g−1 in the Se/MCNF composite upon heat treatment (Supporting Information, Figure S2). This suggests that Se is largely located in the micropores of the carbonaceous nanofiber matrix.37 To clearly demonstrate the structure of the Se/MCNF composite, STEM and corresponding elemental mapping were carried out, as displayed in Figure 3e−g. The carbon (red) and selenium (green) can be found all over the samples, suggesting carbon and selenium are uniformly distributed throughout the composite. The interaction between Se and MCNF was further studied by XPS and XANES. Generally, Se particles are coated with a thin layer of selenium-based oxides owing to surface oxidation when exposed to air. This is confirmed by the appearance of Se−O (58.7 eV) characteristic peak in the XPS spectrum of Se (Supporting Information, Figure S3). Remarkably, two new peaks centered at 56.7 and 55.8 eV appear in the XPS spectrum of the Se/MCNF composite while the peak intensity of Se−O decreases (Figure 4a). This probably indicates the formation of Se−O−C bonds during the melt−diffusion process.43 To further reveal the presence of Se−O−C bonding, XANES

Figure 3. (a) SEM image, (b) high-magnification SEM image, (c) TEM image and SAED pattern (inset), (d) HRTEM image, (e) STEM image, and (f and g) EDX elemental mapping images of the Se/ MCNF composite.

Figure 4. (a) High-resolution Se 3d XPS spectrum of the Se/MCNF composite. (b) C K-edge XANES spectra of the Se−MCNF mixture and Se/MCNF composite.

measurements were conducted (Figure 4b). Compared to the Se−MCNF mixture, the Se/MCNF composite shows an obvious decrease of C K-edge peak intensity at 288.7 eV, corresponding to carbon atoms in carbonaceous nanofibers bonded with oxygen. It could be reflective of the generation of Se−O−C bonding between the chainlike Sen and oxygencontaining functional groups of microporous carbon nanofibers, which brings about lower electron density at the O site and thereby impairs C−O bonds in the composite.44−46 This chemical bonding grants MCNF to couple strongly with the chainlike Sen molecules and, consequently, helps prevent the loss of Se and polyselenide intermediates during electrochemical cycling. The electrochemical performance of the Se/MCNF composite for Li−Se batteries was first studied by CV. As C

DOI: 10.1021/acs.jpcc.5b09553 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

Figure S4). In contrast to the Se/MCNF composite cathode, the Se−MCNF mixture delivers a lower reversible capacity (399 mA h g−1) and more rapid capacity fading (only 31 mA h g−1 after 100 cycles), as shown in Supporting Information Figure S5. We also evaluated the rate capability of the Se/MCNF composite cathode with C-rate from 0.1 to 5 C, as displayed in Figure 5d. As the current density increases stepwise from 0.1 to 0.2, 0.5, 1, and 2 C, specific capacities of 560, 546, 522, 495, and 463 mA h g−1 are achieved, respectively. Even at 5 C, the composite still shows a high reversible capacity of 423 mA h g−1. When the rate is finally returned to 0.1 C after 60 cycles of rate testing, the specific capacity of the Se/MCNF cathode can recover to 537 mA h g−1, close to 560 mA h g−1 from the initial 0.1 C test. This implies that the charge/discharge for the Se/ MCNF electrode was reversible even under high current density. The good rate capability can be attributed to the much decreased size of Se, enabling the lithium ions relatively short diffusion paths for lithiation and delithiation, and the significantly improved electrical conductivity compared to the bulk Se cathode due to the combination of highly conductive carbon nanofiber matrix. Furthermore, the Se/MCNF electrode exhibits outstanding sodium storage properties (Supporting Information, Figure S6). A high charge capacity of 553 mA h g−1 with initial charge capacity retention of 94.9% was achieved after 20 cycles at a current density of 0.1 A g−1 in the voltage range of 0.7−2.7 V for sodium−selenium batteries. Even under 1.2 A g−1, the Se/MCNF cathode still maintains a reversible capacity of 316 mA h g−1. To gain insight into the reason for the improved electrochemical performance of the Se/MCNF cathode, EIS and elemental mapping analyses were performed on the Se/MCNF composite electrodes, as shown in Figure 6. The impedance spectra were analyzed by fitting to an equivalent circuit (inset of Figure 6) consisting of an electrolyte resistance (Re) and a

shown in Figure 5a, there is only one peak at 1.73 V during the first cathodic scan, corresponding to lithium insertion and

Figure 5. (a) CV curves of the first five cycles of the Se/MCNF cathode. (b) Galvanostatic charge−discharge profiles of different cycles for the Se/MCNF cathode. (c) Cycling performance and Coulombic efficiency of the Se/MCNF cathode, where the first 10 cycles are at 0.1 C and the remaining 1990 cycles are at 1 C. (d) Rate performance of the Se/MCNF cathode. The specific capacity is calculated based on the mass of selenium.

formation of lithium selenide. A strong broad peak at 2.01 V during the first anodic scan and was also detected in subsequent scans. This peak could be ascribed to a stepwise lithium ion extraction from the fully charged Li2Se phase to form the Li2Sex intermediates. In contrast to the CV plot of our recently reported Se@MICP composite,32 the separation between the major anodic peak and cathodic peak decreased from 350 mV (for Se@MICP composite) to 180 mV (for Se/MCNF composite) at the same scanning rate of 0.1 mV s−1. This suggests that the introduction of highly conductive microporous carbon nanofibers in Se/MCNF can significantly lower the polarization of the Li−Se cells and improve the kinetics of the electrochemical reaction. The electrochemical performance of the as-obtained Se/ MCNF composite was further evaluated by galvanostatic charge−discharge measurements at 1 C (1 C = 678 mA g−1) between 1.0 and 3.0 V versus Li+/Li. The typical charge/ discharge voltage profiles of the Se/MCNF composite are demonstrated in Figure 5b. Except for the first discharge curve which is different from the others because of the activation process, the general discharge curves comprise a sloping region from 3.0 to 1.95 V followed by an inclined plateau from 1.95 to 1.51 V and another sloping region from 1.51 to 1.0 V. Correspondingly, the charge curves consist of a sloping region from 1.0 to 1.77 V and an inclined plateau from 1.77 to 2.10 V followed by a sloping region up to 3.0 V. These observations are in good agreement with the CV results in Figure 5a. The Se/MCNF composite cathode exhibits an initial Coulombic efficiency of 66.5% and a reversible capacity of 581 mA h g−1 at 0.1 C, corresponding to 86% Se utilization in comparison with the theoretical specific capacity of Se. A high capacity of 403 mA h g−1 is still retained even after 2000 cycles at 1 C, giving rise to 80% capacity retention relative to the 11th cycle capacity of 501 mA h g−1. Note that the capacity contributed by MCNF is negligible considering its much lower capacity (∼42 mA h g−1) as a lithium ion battery cathode (Supporting Information,

Figure 6. (a) Nyquist plots and equivalent circuit (inset) of the Se− MCNF mixture and Se/MCNF composite cathodes after 10 cycles. (b) STEM image and corresponding (c) carbon and (d) selenium elemental mappings of the Se/MCNF cathode after 70 cycles. D

DOI: 10.1021/acs.jpcc.5b09553 J. Phys. Chem. C XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry C

■

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant Nos. 51577094, 21503112, and 21475062), the Natural Science Foundation of Jiangsu Province of China (BK20140915), the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the Program of Jiangsu Collaborative Innovation Center of Biomedical Functional Materials. The authors thank Professor Gang Li for his kind help on the XRD test.

constant phase element (CPE) in parallel with an ohmic resistance (Rf+ct), representing impedance of lithium ion transport through surface film and charge transfer at the electrode/electrolyte interface, which is connected with a Warburg element (Zw) in series accounting for the lithium ion diffusion inside active material.47,48 Obviously, the Se/MCNF electrode shows a much lower combined resistance Rf+ct than does the Se−MCNF mixture electrode (29.3 vs 50.8 Ω), indicating well-preserved electrical contact in the Se/MCNF composite during cycling. The carbon (Figure 6c) and selenium (Figure 6d) are found to be homogeneously distributed in the composite material after 70 cycles (Supporting Information, Figure S7), suggesting that the two components of Se/MCNF composite are still strongly coupled during battery test. These indicate the capacity fading originating from the dissolution of polyselenide intermediates has been effectively inhibited during cycling. The preservation of the good conductive network also facilitates fast charge/discharge of Se, as confirmed by the excellent rate performance demonstrated in Figure 5d.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.5b09553. TGA curve of the Se/MCNF composite, nitrogen adsorption−desorption isotherms of the Se−MCNF mixture and Se/MCNF composite, high-resolution Se 3d XPS spectrum of selenium powder, cycling performance of the MCNF and Se−MCNF mixture electrodes, galvanostatic charge−discharge profiles, cycling performance, and Coulombic efficiency and rate capability of the Se/MCNF cathode in Na−Se batteries, TEM image of the cycled Se/MCNF electrode material (PDF)

■

REFERENCES

(1) Abouimrane, A.; Dambournet, D.; Chapman, K. W.; Chupas, P. J.; Weng, W.; Amine, K. A New Class of Lithium and Sodium Rechargeable Batteries Based on Selenium and Selenium−Sulfur as a Positive Electrode. J. Am. Chem. Soc. 2012, 134, 4505−4508. (2) Yang, C.-P.; Xin, S.; Yin, Y.-X.; Ye, H.; Zhang, J.; Guo, Y.-G. An Advanced Selenium−Carbon Cathode for Rechargeable Lithium− Selenium Batteries. Angew. Chem., Int. Ed. 2013, 52, 8363−8367. (3) Zeng, L.; Zeng, W.; Jiang, Y.; Wei, X.; Li, W.; Yang, C.; Zhu, Y.; Yu, Y. A Flexible Porous Carbon Nanofibers-Selenium Cathode with Superior Electrochemical Performance for Both Li-Se and Na-Se Batteries. Adv. Energy Mater. 2015, 5, 1401377. (4) Luo, C.; Xu, Y.; Zhu, Y.; Liu, Y.; Zheng, S.; Liu, Y.; Langrock, A.; Wang, C. Selenium@Mesoporous Carbon Composite with Superior Lithium and Sodium Storage Capacity. ACS Nano 2013, 7, 8003− 8010. (5) Li, Z.; Yuan, L.; Yi, Z.; Liu, Y.; Huang, Y. Confined Selenium within Porous Carbon Nanospheres as Cathode for Advanced Li−Se Batteries. Nano Energy 2014, 9, 229−236. (6) Cui, Y.; Abouimrane, A.; Lu, J.; Bolin, T.; Ren, Y.; Weng, W.; Sun, C.; Maroni, V. A.; Heald, S. M.; Amine, K. (De)Lithiation Mechanism of Li/SeSx (x = 0−7) Batteries Determined by in Situ Synchrotron X-ray Diffraction and X-ray Absorption Spectroscopy. J. Am. Chem. Soc. 2013, 135, 8047−8056. (7) Ji, X.; Lee, K. T.; Nazar, L. F. A Highly Ordered Nanostructured Carbon−Sulphur Cathode for Lithium−Sulphur Batteries. Nat. Mater. 2009, 8, 500−506. (8) Guo, J.; Xu, Y.; Wang, C. Sulfur-Impregnated Disordered Carbon Nanotubes Cathode for Lithium−Sulfur Batteries. Nano Lett. 2011, 11, 4288−4294. (9) Gao, J.; Lowe, M. A.; Kiya, Y.; Abruña, H. D. Effects of Liquid Electrolytes on the Charge−Discharge Performance of Rechargeable Lithium/Sulfur Batteries: Electrochemical and in-Situ X-ray Absorption Spectroscopic Studies. J. Phys. Chem. C 2011, 115, 25132−25137. (10) Fu, Y.; Manthiram, A. Orthorhombic Bipyramidal Sulfur Coated with Polypyrrole Nanolayers as a Cathode Material for Lithium−Sulfur Batteries. J. Phys. Chem. C 2012, 116, 8910−8915. (11) Xin, S.; Gu, L.; Zhao, N.-H.; Yin, Y.-X.; Zhou, L.-J.; Guo, Y.-G.; Wan, L.-J. Smaller Sulfur Molecules Promise Better Lithium−Sulfur Batteries. J. Am. Chem. Soc. 2012, 134, 18510−18513. (12) Zhang, C.; Wu, H. B.; Yuan, C.; Guo, Z.; Lou, X. W. Confining Sulfur in Double-Shelled Hollow Carbon Spheres for Lithium−Sulfur Batteries. Angew. Chem., Int. Ed. 2012, 51, 9592−9595. (13) Yin, Y.-X; Xin, S.; Guo, Y.-G.; Wan, L.-J. Li−S Batteries: Electrochemistry, Materials and Prospects. Angew. Chem., Int. Ed. 2013, 52, 13186−13200. (14) Yao, H.; Zheng, G.; Hsu, P.-C.; Kong, D.; Cha, J. J.; Li, W.; Seh, Z. W.; McDowell, M. T.; Yan, K.; Liang, Z.; Narasimhan, V. K.; Cui, Y. Improving Lithium−Sulphur Batteries through Spatial Control of Sulphur Species Deposition on a Hybrid Electrode Surface. Nat. Commun. 2014, 4, 3943. (15) Zhao, M.-Q.; Zhang, Q.; Huang, J.-Q.; Tian, G.-L.; Nie, J.-Q.; Peng, H.-J.; Wei, F. Unstacked Double-Layer Templated Graphene for High-Rate Lithium−Sulphur Batteries. Nat. Commun. 2014, 5, 3410. (16) Li, Z.; Jiang, Y.; Yuan, L.; Yi, Z.; Wu, C.; Liu, Y.; Strasser, P.; Huang, Y. A Highly Ordered Meso@Microporous Carbon-Supported

4. CONCLUSIONS In summary, we have successfully developed a selenium/ microporous carbon nanofibers hybrid nanostructured cathode for Li−Se batteries through binding selenium in microporous carbon nanofibers. The Se confined in glucose-derived carbon nanofiber matrix via chemical bonding can not only allow MCNF to behave as a conductive matrix to preserve electrical contact with Se during lithium insertion and extraction processes but also help prevent the dissolution of polyselenide intermediates. This significantly improves the electrochemical performance as compared to a Se−MCNF mixture cathode, showing an initial specific capacity of 581 mA h g−1 at 0.1 C and a capacity retention of 80% relative to the 11th cycle even after 2000 cycles at 1 C, with a high average Coulombic efficiency of >99% after the first cycle. Taking the simple yet effective approach as well as the strong coupling interaction into account, this promising Se/MCNF composite possesses a great potential for practical application in high-performance Li−Se batteries.

■

Article

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Telephone/Fax: +86-2585891027. *E-mail: [email protected]. Telephone/Fax: +86-2585891051. Notes

The authors declare no competing financial interest. E

DOI: 10.1021/acs.jpcc.5b09553 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

and Ultralong Life Lithium−Selenium Batteries. Chem. Commun. 2015, 51, 3667−3670. (36) Kundu, D.; Krumeich, F.; Nesper, R. Investigation of NanoFibrous Selenium and Its Polypyrrole and Graphene Composite as Cathode Material for Rechargeable Li-Batteries. J. Power Sources 2013, 236, 112−117. (37) Song, J.; Yu, Z.; Gordin, M. L.; Hu, S.; Yi, R.; Tang, D.; Walter, T.; Regula, M.; Choi, D.; Li, X.; Manivannan, A.; Wang, D. Chemically Bonded Phosphorus/Graphene Hybrid as a High Performance Anode for Sodium-Ion Batteries. Nano Lett. 2014, 14, 6329−6335. (38) Zhang, G.; Xia, B. Y.; Wang, X.; Lou, X. W. Strongly Coupled NiCo2O4-rGO Hybrid Nanosheets as a Methanol-Tolerant Electrocatalyst for the Oxygen Reduction Reaction. Adv. Mater. 2014, 26, 2408−2412. (39) Zhou, X.; Liu, X.; Xu, Y.; Liu, Y.; Dai, Z.; Bao, J. An SbOx/ Reduced Graphene Oxide Composite as a High-Rate Anode Material for Sodium-Ion Batteries. J. Phys. Chem. C 2014, 118, 23527−23534. (40) Wang, Z.; Dong, Y.; Li, H.; Zhao, Z.; Wu, H. B.; Hao, C.; Liu, S.; Qiu, J.; Lou, X. W. Enhancing Lithium−Sulphur Battery Performance by Strongly Binding the Discharge Products on AminoFunctionalized Reduced Graphene Oxide. Nat. Commun. 2014, 5, 5002. (41) Liang, H.-W.; Guan, Q.-F.; Chen, L.-F.; Zhu, Z.; Zhang, W.-J.; Yu, S.-H. Macroscopic-Scale Template Synthesis of Robust Carbonaceous Nanofiber Hydrogels and Aerogels and Their Applications. Angew. Chem., Int. Ed. 2012, 51, 5101−5105. (42) Zhang, G.; Wu, H. B.; Hoster, H. E.; Lou, X. W. Strongly Coupled Carbon Nanofiber−Metal Oxide Coaxial Nanocables with Enhanced Lithium Storage Properties. Energy Environ. Sci. 2014, 7, 302−305. (43) Li, B.; Li, S.; Liu, J.; Wang, B.; Yang, S. Vertically Aligned Sulfur−Graphene Nanowalls on Substrates for Ultrafast Lithium− Sulfur Batteries. Nano Lett. 2015, 15, 3073−3079. (44) Zhou, X.; Zhu, X.; Liu, X.; Xu, Y.; Liu, Y.; Dai, Z.; Bao, J. Ultralong Cycle Life Sodium-Ion Battery Anodes Using a GrapheneTemplated Carbon Hybrid. J. Phys. Chem. C 2014, 118, 22426−22431. (45) Zhou, X.; Wan, L.-J.; Guo, Y.-G. Binding SnO2 Nanocrystals in Nitrogen-Doped Graphene Sheets as Anode Materials for Lithium-Ion Batteries. Adv. Mater. 2013, 25, 2152−2157. (46) Liang, Y.; Li, Y.; Wang, H.; Zhou, J.; Wang, J.; Regier, T.; Dai, H. Co3O4 Nanocrystals on Graphene as a Synergistic Catalyst for Oxygen Reduction Reaction. Nat. Mater. 2011, 10, 780−786. (47) Tang, W.; Hou, Y. Y.; Wang, X. J.; Bai, Y.; Zhu, Y. S.; Sun, H.; Yue, Y. B.; Wu, Y. P.; Zhu, K.; Holze, R. A Hybrid of MnO2 Nanowires and MWCNTs as Cathode of Excellent Rate Capability for Supercapacitors. J. Power Sources 2012, 197, 330−333. (48) Liu, X.; Liu, F.; Sun, Q.; Ng, A. M. C.; Djurišić, A. B.; Xie, M.; Liao, C.; Shih, K.; Deng, Z. In Situ Synthesis of CuxO/SnOx@CNT and CuxO/SnOx@SnO2/CNT Nanocomposite Anodes for Lithium Ion Batteries by a Simple Chemical Treatment Process. ACS Appl. Mater. Interfaces 2014, 6, 13478−13486.

Sulfur@Smaller Sulfur Core−Shell Structured Cathode for Li−S Batteries. ACS Nano 2014, 8, 9295−9303. (17) Zhou, G.; Pei, S.; Li, L.; Wang, D.-W.; Wang, S.; Huang, K.; Yin, L.-C.; Li, F.; Cheng, H.-M. A Graphene−Pure-Sulfur Sandwich Structure for Ultrafast, Long-Life Lithium−Sulfur Batteries. Adv. Mater. 2014, 26, 625−631. (18) Zeng, L.; Pan, F.; Li, W.; Jiang, Y.; Zhong, X.; Yu, Y. FreeStanding Porous Carbon Nanofibers−Sulfur Composite for Flexible Li−S Battery Cathode. Nanoscale 2014, 6, 9579−9587. (19) Yang, C.-P.; Yin, Y.-X.; Guo, Y.-G. Elemental Selenium for Electrochemical Energy Storage. J. Phys. Chem. Lett. 2015, 6, 256−266. (20) Liu, L.; Hou, Y.; Wu, X.; Xiao, S.; Chang, Z.; Yang, Y.; Wu, Y. Nanoporous Selenium as a Cathode Material for Rechargeable Lithium−Selenium Batteries. Chem. Commun. 2013, 49, 11515− 11517. (21) Ye, H.; Yin, Y.-X.; Zhang, S.-F.; Guo, Y.-G. Advanced Se−C Nanocomposites: a Bifunctional Electrode Material for Both Li−Se and Li-ion Batteries. J. Mater. Chem. A 2014, 2, 13293−13298. (22) Liu, L.; Hou, Y.; Yang, Y.; Li, M.; Wang, X.; Wu, Y. A Se/C Composite as Cathode Material for Rechargeable Lithium Batteries with Good Electrochemical Performance. RSC Adv. 2014, 4, 9086− 9091. (23) Zhang, J.; Zhang, Z.; Li, Q.; Qu, Y.; Jiang, S. Selenium Encapsulated into Interconnected Polymer-Derived Porous Carbon Nanofiber Webs as Cathode Materials for Lithium-Selenium Batteries. J. Electrochem. Soc. 2014, 161, A2093−A2098. (24) Zeng, L.; Wei, X.; Wang, J.; Jiang, Y.; Li, W.; Yu, Y. Flexible One-Dimensional Carbon−Selenium Composite Nanofibers with Superior Electrochemical Performance for Li−Se/Na−Se Batteries. J. Power Sources 2015, 281, 461−469. (25) Zhang, Z.; Yang, X.; Guo, Z.; Qu, Y.; Li, J.; Lai, Y. Selenium/ Carbon-Rich Core−Shell Composites as Cathode Materials for Rechargeable Lithium−Selenium Batteries. J. Power Sources 2015, 279, 88−93. (26) Luo, C.; Wang, J.; Suo, L.; Mao, J.; Fan, X.; Wang, C. In Situ Formed Carbon Bonded and Encapsulated Selenium Composites for Li−Se and Na−Se Batteries. J. Mater. Chem. A 2015, 3, 555−561. (27) Zhang, J.; Fan, L.; Zhu, Y.; Xu, Y.; Liang, J.; Wei, D.; Qian, Y. Selenium/Interconnected Porous Hollow Carbon Bubbles Composites as the Cathodes of Li−Se Batteries with High Performance. Nanoscale 2014, 6, 12952−12957. (28) Lee, J. T.; Kim, H.; Oschatz, M.; Lee, D.-C.; Wu, F.; Lin, H.-T.; Zdyrko, B.; Cho, W. I.; Kaskel, S.; Yushin, G. Micro- and Mesoporous Carbide-Derived Carbon−Selenium Cathodes for High-Performance Lithium Selenium Batteries. Adv. Energy Mater. 2015, 5, 1400981. (29) Yi, Z.; Yuan, L.; Sun, D.; Li, Z.; Wu, C.; Yang, W.; Wen, Y.; Shan, B.; Huang, Y. High-Performance Lithium−Selenium Batteries Promoted by Heteroatom-Doped Microporous Carbon. J. Mater. Chem. A 2015, 3, 3059−3065. (30) Li, Z.; Yin, L. MOF-Derived, N-Doped, Hierarchically Porous Carbon Sponges as Immobilizers to Confine Selenium as Cathodes for Li−Se Batteries with Superior Storage Capacity and Perfect Cycling Stability. Nanoscale 2015, 7, 9597−9606. (31) Jiang, Y.; Ma, X.; Feng, J.; Xiong, S. Selenium in NitrogenDoped Microporous Carbon Spheres for High-Performance Lithium− Selenium Batteries. J. Mater. Chem. A 2015, 3, 4539−4546. (32) Liu, Y.; Si, L.; Zhou, X.; Liu, X.; Xu, Y.; Bao, J.; Dai, Z. A Selenium-Confined Microporous Carbon Cathode for Ultrastable Lithium−Selenium Batteries. J. Mater. Chem. A 2014, 2, 17735− 17739. (33) Han, K.; Liu, Z.; Shen, J.; Lin, Y.; Dai, F.; Ye, H. A FreeStanding and Ultralong-Life Lithium−Selenium Battery Cathode Enabled by 3D Mesoporous Carbon/Graphene Hierarchical Architecture. Adv. Funct. Mater. 2015, 25, 455−463. (34) Han, K.; Liu, Z.; Ye, H.; Dai, F. Flexible Self-Standing Graphene−Se@CNT Composite Film as a Binder-Free Cathode for Rechargeable Li−Se Batteries. J. Power Sources 2014, 263, 85−89. (35) Fang, R.; Zhou, G.; Pei, S.; Li, F.; Cheng, H.-M. Localized Polyselenides in a Graphene-Coated Polymer Separator for High Rate F

DOI: 10.1021/acs.jpcc.5b09553 J. Phys. Chem. C XXXX, XXX, XXX−XXX