- Email: [email protected]
Dopamine derived nitrogen-doped carbon sheets as anode materials for high-performance sodium ion batteries
Accepted Manuscript Dopamine derived nitrogen-doped carbon sheets as anode materials for highperformance sodium ion batteries Fuhua Yang, Zhian Zhang, Ke Du, Xingxing Zhao, Wei Chen, Yanqing Lai, Jie Li PII: DOI: Reference:
S0008-6223(15)00340-1 http://dx.doi.org/10.1016/j.carbon.2015.04.049 CARBON 9867
To appear in:
Carbon
Received Date: Accepted Date:
17 January 2015 20 April 2015
Please cite this article as: Yang, F., Zhang, Z., Du, K., Zhao, X., Chen, W., Lai, Y., Li, J., Dopamine derived nitrogendoped carbon sheets as anode materials for high-performance sodium ion batteries, Carbon (2015), doi: http:// dx.doi.org/10.1016/j.carbon.2015.04.049
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dopamine derived nitrogen-doped carbon sheets as anode materials for high-performance sodium ion batteries Fuhua Yang, Zhian Zhang*, Ke Du, Xingxing Zhao, Wei Chen, Yanqing Lai, and Jie Li
School of Metallurgy and Environment, Central South University, Changsha Hunan 410083, China
Corresponding author: Zhian Zhang Institute: School of Metallurgy and Environment, Central South University. Address: No.932, Lushan Road, Changsha city, Hunan Province, 410083 China Tel: +86 731 88830649; Fax: +86 731 88830649 E-mail: [email protected]
*
Corresponding author: Tel: +86 731 88830649; Fax: +86 731 88830649.
E-mail address: [email protected] (Z. Zhang).
1
Dopamine derived nitrogen-doped carbon sheets as anode materials for high-performance sodium ion batteries
Fuhua Yang, Zhian Zhang*, Ke Du, Xingxing Zhao, Wei Chen, Yanqing Lai, and Jie Li School of Metallurgy and Environment, Central South University, Changsha Hunan 410083, China
Abstract
Designed as an anode material for sodium ion batteries , nitrogen-doped carbon sheets (NCSs) were successfully synthesized using graphene and dopamine as template and carbon precursor, respectively. The NCSs demonstrate high reversible capacity and excellent rate performance, delivering a high reversible capacity of 382 mAh g-1 at 50 mA g-1 after 55 cycles. Even up to 10 A g-1, a rate capacity of 75 mAh g-1 can be obtained. Furthermore, NCSs also have remarkable cycling stability with specific capacity of 165 mAh g-1 after 600 cycles (under 200 mA g-1 ). The excellent performance of NCSs can be ascribed to the nitrogen-doped two-dimension sheet structure.
*
Corresponding author: Tel: +86 731 88830649; Fax: +86 731 88830649.
E-mail address: [email protected] (Z. Zhang).
2
1. Introduction
Lithium ion batteries(LIBs) have been widely used as the power source for electric vehicles and mobile devices.[1-4] Considering their relatively high cost and limited terrestrial reserves of lithium, large-scale commercial applications of LIBs would be extremely difficult.[5, 6] There is an urgent need to explore alternative energy storage technologies for large-scale energy storage. Sodium ion batteries (SIBs) have been regarded as an attractive alternative to LIBs owing to the similar physical/chemical properties of sodium with lithium and the abundant supply of sodium, which make SIBs cheaper.[6, 7] However, it’s still a challenge to find appropriate host materials with large interstitial space to guarantees sodium ion accommodation, since sodium ion is 55% larger than lithium ion in radius.[8, 9] Therefore, investigating suitable electrode materials is crucial for the development of SIBs. Although many efforts have been made in the field of cathode materials for SIBs, researches on the anode material are still at a very early stage.[10, 11] Recent years, Na-storage anode materials, such as Sn,[12, 13] Ge,[14, 15] Sb,[16-18] and P[19-22] have been explored as anode candidates for SIBs, but the application of these materials is hampered because of the large volumetric expansion during sodiation and the intrinsic low conductivity. Carbonaceous materials have been attracted tremendous attention since the first report of hard carbon as anode for SIBs[23], on account of the versatile preparation methods and large interlayer space for Na+ insertion[24]. To enhance the electrochemical performance of carbonaceous anodes, 3
many strategies have been proposed.[25-30] Among them, fabricating structures (such as fibers, hollow spheres and hollow wires) seems to be an effective way.[24, 27, 31-34] For example, Huang et al.[27] fabricated carbon fibers using a template method, which presented a specific capacity of ~130 mA h g-1 after 200 cycles at 200 mA g-1 and excellent rate performance. Maier et al.[31] showed that hollow carbon spheres can retain a capacity of ~160 mA h g-1 after 100 cycles at 100 mA g-1. Hollow carbon wires[24] were also prepared and delivered a high capacity of 251 mA h g-1 over 400 cycles under 50 mA g-1, even at a current rate of 125 mA g-1, a specific capacity of 149 mA h g-1 was observed. Despite progresses have been made in the carbonaceous anode materials, more efforts still need to be made to promote the commercial application of SIBs. Two-dimension carbon structures have been regarded as a potential structure for energy storage devices. With the unique properties of two-dimension structure, when used as the anode for SIBs, carbon sheets (CSs) will adequately contact with the electrolyte, facilitate good transport of electrons/sodium ion, and facile strain relaxation during the charge-discharge process.[35-37] Graphene have been used as template to fabricate CSs because of its stable chemical property and remarkable conductivity, which is conducive to the electrochemical performance of the CSs electrode. Meanwhile, introduction of nitrogen is also an effective strategy to enhance the carbon electrodes’ performance for SIBs.[39-41] To synthesis nitrogen-doped carbon materials, calcination of nitrogen rich carbon precursor is the most common and facile method. Zhang et al.[34] prepared graphene-templated nitrogen-doped CSs
4
by coating graphene with polypyrrole. But this procedure is tedious and the electrochemical performance of the CSs anode is unsatisfactory. According to the previous studies, dopamine can self-polymerize at alkaline pH values under oxygen atmosphere. Polydopamine have the following advantages when used as carbon precursors: (1) the strong and convenient coating capability; (2) the conformal nature of polydopamine coating; (3) uniform nitrogen source will retain in the final carbon product.[38] Polydopamine should be a promising carbon precursor for the fabrication of CSs. However, to the best of our knowledge, dopamine derived CSs for SIBs have not been reported yet. Herein, we report a nitrogen-doped carbon sheets (NCSs), which is fabricated by pyrolyzation of polydopamine-graphene oxide (GO) sheets precursors, as SIBs anode materials. The NCSs present high reversible capacity of 382 mA h g-1 at a constant current of 50 mA g-1 after 55 charge-discharge processes, outstanding cycling stability with capacity of ~165 mAh g-1 (under a high current density of 200mA g-1) after 600 cycles without any decay, and the rate performance of the NCSs is impressive (212, 168, 129, 113, 97, 84 and 75 mA h g-1 at 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g-1, respectively). The excellent electrochemical performances of the NCSs anode can be ascribed to the two-dimension sheet structure and nitrogen doping property.
2. Experimental 2.1 Preparation of nitrogen-doped carbon sheets (NCSs)
The
starting
materials
dopamine
5
hydrochloride
and
tris(hydroxymethyl)aminomethane (TRIS) were purchased from aladdin. All these chemicals were analytical reagent grade. Graphene oxide (GO) was synthesized using a modified Hummers method. The NCSs were synthesized by pyrolysis of polydopamine modified graphene oxide (GO) sheet precursors, which were prepared by a template method. Typically, 0.2 g GO was dispersed in 200 mL of deionized water to form a homogeneous GO suspension. Then, 1.5 g dopamine hydrochloride was added to the suspension under magnetic stirring. After that, the pH value of dispersion was adjusted to 8.5 by adding TRIS solution, and the solution kept stirring for 24 h. Centrifugation was carried out to collected the polymer/GO composite, then the solid product was washed with deionized water and ethyl alcohol for three times. The as-prepared polymer/GO sheets formed after freeze-drying process. After heat treatment of the as-prepared polymer/GO sheets at 800 oC for 2 h with a heating rate of 4 oC min-1, the NCSs were finally obtained. For comparison, nitrogen-free carbon sheets (CSs) were prepared by heat treatment of GO at 800 oC for 2 h.
2.2 Material characterization
Scanning electron microscopy (SEM, Nova
SEM 230) and transmission
electron microscopy (TEM, Tecnai G2 20ST) were applied to investigate the material morphology. The structure of the NCSs was characterized using X-ray diffraction (XRD, Rigaku3014). Nitrogen adsorption/desorption measurements were carried out on a Quantachrome instrument (Quabrasorb SI-3MP). Surface functional groups and bonding characterization were conducted using X-ray photoelectron spectroscopy
6
(XPS, Thermo Fisher ESCALAB250xi). The fitting errors of XPS test results are within ±1%. The Raman measurements were carried out on a Jobin-Yvon LabRAM HR-800 spectrometer.
2.3. Electrochemical measurements
To conduct electrochemical measurements of the NCSs electrode, a CR-2032 type coin cell was fabricated. Sodium pellet and whatman glass fiber membrane were served as counter electrode and separator, respectively. A mixed slurry of NCSs, Super P and carboxymethyl cellulose (CMC) (8:1:1, in wt. %) in deionized water was spread onto a copper foil. The coating copper foil was first dried in air, then transferred into a oven at 80 oC for 12 h. The assembly of the tested cells were carried out in a glove box under argon atmosphere. The electrolyte used in this work composition of 1 M NaClO4 (Sigma-Aldrich) in a solvent mixture of ethylene carbonate and propylene carbonate (with a volume ratio of 1:1). Galvanostatic charge/discharge test were conducted using a battery test system. Cyclic voltammetry (CV) measurements were carried out at a scan rate of 0.2 mV s-1 between 0.01 and 2.5 V on a electrochemical measurement system. Those electrochemical tests were carried out under a constant temperature of 25 oC.
3. Results and discussion 3.1 Synthesis and characterization
As presented in Fig. 1, the nitrogen-doped carbon sheets (NCSs) synthesis
7
procedure can be divided into four parts: dispersion, polymerization, collection and calcination. Graphene oxide (GO) was dispersed homogeneously in deionized water after ultrasonic treatment for 2 h. GO served as template in this work, while dopamine used as carbon precursor. When the solution pH value was adjusted to 8.5, dopamine occurred self-polymerization and coated onto the surface of GO sheets uniformly. Centrifugation and freeze-drying processes were carried out to collect the solid product. The carbonization procedure was conducted at 800 oC for 2 h. Through the dopamine coating and carbonization procedures, 2D structure obtained and nitrogen configurations forming.
Fig. 1 Schematic of the NCSs fabricate procedures
The morphology characterization of NCSs were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). As exhibited in Fig. 2(a), (b) and (c), no free particle observed, the targeted products maintain the two-dimensional structure of graphene and the surface of the NCSs is obviously smooth. All those phenomenon indicate the homogeneous and continuous coating of polydopamine on GO surface owning to the strong coating capability of the polydopamine and the conformal nature of polydopamine coating.[42] Notablely, the NCSs display a thin thickness, which would result fast transport of electron/sodium 8
ions because the maximum electron/sodium ion diffusion distance is half of the thickness.[43] To reveal the microstructure of the NCSs, high resolution transmission electron microscopy (HRTEM) image is given in Fig. 2(d). This image displays a turbostatic structure, suggesting amorphous structure of NCSs. Fig. 2(e)~(g) show the Annular dark-field TEM images of NCSs and the corresponding elemental mapping of carbon and nitrogen. These figures reveal the presence and homogeneous distribution of nitrogen.
Fig. 2 (a), (b) SEM images, (c) TEM image and (d) HRTEM image of NCSs. (e) Annular dark-field TEM image, and corresponding (f) carbon and (g) nitrogen elemental mapping.
9
Fig. 3(a) presents the X-ray diffraction (XRD) pattern of NCSs. In this XRD pattern, two broad peaks are observed at around 23 and 43o, which can be indexed to (002) and (100), respectively. The relatively weak peak at 43o can be ascribed to the low crystalline structure. This XRD pattern indicates an amorphous structure of the NCSs. Based on the XRD result, the interlayer spacing (d002) of NCSs is calculated to be 0.38 nm. It is well know that the application of graphite for SIBs is hindered because of the limited interlayer spacing (0.34 nm), large interlayer spacing makes NCSs to be a suitable host material for SIBs to store sodium ion. Fig. 3(b) displays the Raman spectrum of the NCSs, which presents two peaks at 1354 and 1585 cm-1, ascribed to D-band (for the sp3 configuration) and G-band (for graphitic configuration), respectively. The value of ID/IG is commonly used to characterize the graphitization of carbon materials. The ID/IG value of NCSs is calculated to be 0.93, suggesting a highly disordered structure of the NCSs, which is agreed with the HRTEM micrographs of NCSs (Fig. 2(d)).
Fig. 3 (a) XRD pattern and (b) Raman spectrum of the NCSs.
X-ray photoelectron spectroscopy (XPS) was also conducted to investigate the
10
functional groups of the material. As shown in Fig. 4(a), the XPS spectrum of the NCSs display three peaks at 284.59, 532.36 and 400.8 eV, corresponding to C 1s, O 1s and N 1s, respectively, further confirm the existence of nitrogen, and the atomic percentage of N in the NCSs is about 5.54 at%. The XPS spectrum of the C 1s (inset of Fig. 1(a)) can be divided into three peaks. The main peak at 284.8 eV corresponds to the graphite-like sp2 C, indicating most of the C atoms in the NCSs are arranged in a conjugated honeycomb lattice. The small peaks at 285.7 and 287.5 eV reflect different bonding structure of the C-N bonds,corresponding to the N-sp2 C and N-sp3 C bonds, respectively. The N 1s peak can be deconvoluted into three peaks, centered at 398.3, 400.7 and 403.1 eV, respectively, which are ascribed to three nitrogen configurations, namely, pyridinic(N-6), pyrrolic(N-5) and quaternary (N-Q) nitrogen, respectively. According to the XPS result, it can be concluded that the nitrogen atom of the dopamine are well retained during the polymerization and calcination processes. The introduction of nitrogen atoms enhance the performance of NCSs electrode, not only because of the enhanced electric conductivity, but also the pseudo-capacitance.[27, 39] Role of Nitrogen in enhancing the performance can be presented as the following: Firstly, The nitrogen-doping in the carbon matrix can improve the electric conductivity of carbon;[44-46] Secondly, N-doping can generate extrinsic defects, and hence enhance the reactivity and capacity;[47] Thirdly, After nitrogen doping, a pseudo-capacitance can be generated due to the interaction between the electrolyte and the N species on the surface.[48, 49]
11
Fig. 4 (a) The total XPS spectrum of NCSs; inset is the XPS C 1s of HCNF@NPC. (b) The XPS N 1s spectra of the NCSs.
To further characterize the surface and the porous structures of the N-NCSs, N2 absorption-desorption measurement was also carried out. Fig. 5(a) shows a typical type IV isotherm with a hysteresis loop within a relative pressure P/P0 range of 0.4~1, suggesting
the
characteristic
mesoporous
structure.
The
specific
Brunauer-Emmett-Teller (BET) surface area of NCSs is 76 m2 g-1. As shown in the Fig. 5(b), the pore size of the NCSs is mainly distribute between 2~5 nm, further verify the mesoporous structure of the NCSs. These small pores probably are formed during the calcination process due to the physical activation of the carbon framework.[50]
Fig. 5 Porosity characterization of NCSs: (a) N2 sorption isotherms and (b) pore size distribution.
12
3.2 Electrochemical performance of the NCSs anode
To analyze the electrochemical properties of the NCSs anode, cyclic voltammetry (CV) tests and galvanostatic charge/discharge measurements were performed. Fig. 6(a) displays the CV curves of the NCSs anode between 0.01 and 2.5 V for the first 5 cycles. For the cathodic processes, three peaks locate at 0.75, 0.4 and 0.01 V are observed during the first cycle. The peaks at 0.75 and 0.4 V can be indexed to the decomposition of the electrolyte and formation of solid electrolyte interface (SEI) film,[24, 41] and these two peaks disappear in the following cycles, indicating the irreversibility of the reaction. The low coulombic efficiency of the first cycle can be mainly ascribed to the SEI forming and the electrolyte decomposition. While the sharp peak central at 0.01 V can be assigned to Na+ insertion into the carbonaceous materials. In the subsequent cycles, this peak still exists, suggesting the insertion of the Na+ is reversible. For the anodic processes, Na+ extraction occurs over a broad potential range (0~0.8 V). Notably, the oxidation broad peak intensities of the second and third cycles are stronger than that of the first cycle, this can be explained by the adsorption with charge transfer on both side of the graphene layers and the reaction between N group on the surface and the Na+, similar phenomenon have been reported.[25, 61] Coinciding with the previous researches, the Na+ insertion/extraction of the NCSs anode occur below 1.2 V. Furthermore, according to the CV results, after the first cycle, the subsequent CV curves overlap with each other, indicating outstanding reversibility of the NCSs.
13
Fig. 6 (a) Typical CV curves of the NCSs electrode at a potential sweep rate of 0.2 mV s-1 and (b) Charge–discharge profiles at a current density of 50 mA g-1
Fig. 6(b) shows the 1st, 2nd and 3rd charge-discharge profiles of the NCSs materials within 0.01~2.5 V, at 50 mA g-1. The initial discharge and charge capacities are 2900 and 765 mAh g-1, respectively, giving a coulombic efficiency of 26.4%. The large irreversible capacity loss is commonly caused by the electrolyte decomposition and SEI layer forming. For the Na+ insert into the disordered carbon reaction mechanisms, two main reaction models have been proposed:[52-54] (i) Na+ insertion occurs between the carbon layers corresponding to the slope region of the voltage profile; (ii) Na+ accommodates into the micropores of carbon, which is ascribed to the plateau region of the voltage profile. In the case of the NCSs electrode, as presented in Fig. 6(b), the 2nd and 3rd cycles discharge curves display a sloping property, and no obvious plateau at the low voltage region, indicating that Na+ manly insert between the carbon layers. The cycle and rate performances of the NCSs electrode were also tested. As illustrated in Fig. 7(a), the NCSs present a reversible capacity of 382 mAh g-1 after 55 cycles at 50 mA g-1. To verify the improvement of electrochemical performances of nitrogen doping, nitrogen-free carbon sheets (CSs) was prepared by heat treatment of
14
GO at 800 oC for 2 h, and tested as anode materials for sodium ion batteries. As showed in Fig. 7(a), the as-prepared CSs deliver a capacity of 54 mAh g-1, at 50 mA g-1 after 55 cycles, which is much lower than that of NCSs. The reversible capacity of the NCSs is excellent, and only a few studies have showed higher capacity at the same current density.[55] Although the initial coulombic efficiency is low, it increases to ~94% after several cycles. The small irreversible capacity during each cycle can be explained by the incomplete stabilization of the SEI during the charge-discharge processes.[31] A long cycle test was conducted at a current density of 200 mA g-1 (Fig. 7(c)). After ~60 cycles, the specific capacity stay around 165 mAh g-1, and a high coulombic efficiency (approaches 100%) is obtained. Even after 600 cycles, the specific capacity still remains at ~165 mAh g-1 without any decay. Those experiment results suggest impressive reversibility and cycling stability of the NCSs. In addition, the NCSs also present good rate performance (Fig. 7(b)). When tested at different current densities, the NCSs show high reversible capacities, namely, 212, 168, 129, 113, 97 and 84 mA h g-1 at 0.1, 0.2, 0.5, 1, 2 and 5 A g-1, respectively. Even at an extremely high current density of 10 A g-1, a high capacity of 75 mAh g-1 is still obtained. When the current density return to 0.1 A g-1 after 70 cycles, the specific capacity can be recovered up to ~190 mAh g-1. It is notable that the rate performance of the NCSs is comparable or even better than those previous studies.[27, 34, 39, 56]
15
Fig. 7 (a) Cycle performance of NCSs and CSs at current density 50 mA g-1, (b) rate performance at different current density and (c)long cycle performance at 200 mA g-1 of the NCSs electrode.
The excellent electrochemical performances of this NCSs anode for SIBs can be explained by several reasons: (1) the large interlayer spacing (0.38 nm) of the NCSs, which guarantees Na+ accommodation; (2) the two-dimensional structure material can adequately contact with the electrolyte and offer shortened paths for electrode/Na+ transport. Furthermore, facile strain relaxation during the charge-discharge process is important; (3) the introduction of nitrogen atoms can enhance the electric conductivity and capacity of the carbonaceous anodes; (4) the existence of graphene provide high electronic conductivity. 16
In order to further identify the structure change of the NCSs, SEM measurement was performed. Cells were disassembled and the working electrodes were washed with propylene carbonate to remove the residual NaClO4. Fig. 8(a) show the SEM images of NCSs before cycled, which is the same with Fig. 2(a)(b), suggesting that the electrode preparing process didn’t damage the morphology of the NCSs. Fig. 8(b) is the SEM image of NCSs after 55 cycles. Compare Fig. 8(b) with Fig. 8(a), it is obvious that morphology barely change, although the cycled electrode is covered with a dense and rough layer (SEI layer). The similar morphology indicates perfect structural stability during the sodium insertion/extraction processes.
Fig. 8 SEM images of the NCSs electrode (a) before and (b) after 55 cycles under current density 50 mA g-1.
4. Conclusion
Nitrogen-doped carbon sheets (NCSs) have been successfully prepared by calcination of polymer/graphene oxide sheets. When used as the anode materials for SIBs, The NCSs present excellent electrochemical performance: high reversible
17
capacity of 382 mA h g-1 (at a constant current of 50 mA g-1 after 55 charge-discharge processes); outstanding cycling stability (~165 mAh g-1 under a high current density 200 mA g-1 after 600 cycles without any decay); and remarkable rate performance (212, 168, 129, 113, 97, 84 and 75 mA h g-1 at 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g-1, respectively). The high electrochemical performance of NCSs can be ascribed to the two-dimension sheet structure and nitrogen doping property.
References
[1] Tarascon JM, Armand M. Issues and challenges facing rechargeable lithium batteries. Nature 2001; 414(6861):359-67. [2] Manthiram A. Materials challenges and opportunities of lithium ion batteries. J Phys Chem Lett 2011; 2(3):176-184. [3] Cui G, Gu L, Zhi L, Kaskhedikar N, van Aken PA, Müllen K, et al. A germanium-carbon composite material for lithium batteries. Adv Mater 2008; 20(16):3079-83. [4] Whittingham MS. Lithium batteries and cathode materials. Chem Rev 2004; 104(10):4271-302. [5] Slater MD, Kim D, Lee E, Johnson CS. Sodium-ion batteries. Adv Funct Mater 2013; 23(8):947-58. [6] Kim SW, Seo DH, Ma X, Ceder G, Kang K. Electrode materials for rechargeable sodium-ion batteries: potential alternatives to current lithium-ion batteries. Adv Energy Mater 2012; 2(7):710-21.
18
[7] Yabuuchi N, Kajiyama M, Iwatate J, Nishikawa H, Hitomi S, Okuyama R, et al. P2-type Nax[Fe1/2Mn1/2]O2 made from earth-abundant elements for rechargeable Na batteries. Nat Mater 2012; 11(6):512-7. [8] Stevens DA, Dahn JR. The mechanisms of lithium and sodium insertion in carbon materials. J Electrochem Soc 2001; 148(8):A803-11. [9] Wang L, Lu Y, Liu J, Xu M, Cheng J, Zhang D, et al. A superior low-cost cathode for a Na-ion battery. Angew Chem 2013; 52(7):1964-7. [10] Kim Y, Ha KH, Oh SM, Lee KT. High-capacity anode materials for sodium-ion batteries. Chemistry 2014; 20(38):11980-92. [11] Dahbi M, Yabuuchi N, Kubota K, Tokiwa K, Komaba S. Negative electrodes for Na-ion batteries. Phys chem chem phys 2014; 16:15007-28. [12] Liu Y, Zhang N, Jiao L, Tao Z, Chen J. Ultrasmall Sn particles Embedded in Carbon as High-Performance Anode for Sodium-Ion Batteries. Adv Funct Mater 2014; 25(2):214-20. [13] Xu Y, Zhu Y, Liu Y, Wang C. Electrochemical performance of porous carbon/tin composite anodes for sodium-ion and lithium-ion batteries. Adv Energy Mater 2013; 3(1):128-33. [14] Baggetto L, Keum JK, Browning JF, Veith GM. Electrochem Commun 2013; 34:41-44. [15] Abel PR, Lin YM, de Souza T, Chou CY, Gupta A, Goodenough JB, et al. columnar germanium thin films as a high-rate sodium-ion battery anode material. J Phys Chem C 2013; 117(37):18885-90.
19
[16] Wu L, Hu X, Qian J, Pei F, Wu F, Mao R, et al. Sb-C fibers with long cycle life as an anode material for high-performance sodium-ion batteries. Energy Environ Sci 2014; 7(1): 323-8. [17] Zhu Y, Han X, Xu Y, Liu Y, Zheng S, Xu K, et al. Electrospun Sb/C fibers for a stable and fast sodium-ion battery anode. ACS Nano 2013; 7(7):6378-86. [18] Zhou XL, Zhong YR, Yang M, Hu M, Wei JP, Zhou Z. Sb particles decorated N-rich carbon sheets as anode materials for sodium ion batteries with superior rate capability and long cycling stability. Chem Commun 2014; 50(85):12888-91. [19] Song J, Yu Z, Gordin ML, Hu S, Yi R, Tang D, et al. Chemically bonded phosphorus/graphene hybrid as a high performance anode for sodium-ion batteries. Nano lett 2014; 14(11):6329-35. [20] Li WJ, Chou SL, Wang JZ, Liu HK, Dou SX. Simply mixed commercial red phosphorus and carbon tube composite with exceptionally reversible sodium-ion storage. Nano lett 2013; 13(11):5480-4. [21] Qian J, Wu X, Cao Y, Ai X, Yang H. High capacity and rate capability of amorphous phosphorus for sodium ion batteries. Angew Chem 2013; 125(17):4633-6. [22] Kim Y, Park Y, Choi A, Choi NS, Kim J, Lee J, et al. An amorphous red phosphorus/carbon composite as a promising anode material for sodium ion batteries. Adv Mater 2013; 25(22):3045-9. [23] Doeff MM, Ma Y, Visco SJ, De Jonghe LC. Electrochemical insertion of sodium into carbon. J Electrochem Soc 1993; 140(2):L169-70.
20
[24] Cao Y, Xiao L, Sushko ML, Wang W, Schwenzer B, Xiao J, et al. Sodium ion insertion in hollow carbon wires for battery applications. Nano lett 2012; 12(7):3783-7. [25] Wenzel S, Hara T, Janek J, Adelhelm P. Room-temperature sodium-ion batteries: Improving the rate capability of carbon anode materials by templating strategies. Energy Environ Sci 2011; 4(9):3342-5. [26] Lotfabad EM, Ding J, Cui K, Kohandehghan A, Kalisvaart WP, Hazelton M, et al. High-density sodium and lithium ion battery anodes from banana peels. ACS Nano 2014; 8(7):7115-29. [27] Wang Z, Qie L, Yuan L, Zhang W, Hu X, Huang Y. Functionalized N-doped interconnected carbon fibers as an anode material for sodium-ion storage with excellent performance. Carbon 2013; 55:328-34. [28] Wen Y, He K, Zhu Y, Han F, Xu Y, Matsuda I, et al. Expanded graphite as superior anode for sodium-ion batteries. Nat Commun 2014; 5. [29] Li W, Zeng L, Yang Z, Gu L, Wang J, Liu X, et al. Free-standing and binder-free sodium-ion electrodes with ultralong cycle life and high rate performance based on porous carbon fibers. Nanoscale 2014; 6(2):693-8. [30] Luo W, SchardtJ, Bommier C, Wang B, Razink J, Simonsen J, et al. Carbon fibers derived from cellulose fibers as a long-life anode material for rechargeable sodium-ion batteries. J Mater Chem A 2013; 1(36):10662-6. [31] Tang K, Fu L, White RJ, Yu L, Titirici MM, Antonietti M, et al. Hollow carbon spheres with superior rate capability for sodium-based batteries. Adv Energy
21
Mater 2012; 2(7):873-7. [32] Chen T, Liu Y, Pan L, Lu T, Yao Y, Sun Z, et al. Electrospun carbon fibers as anode materials for sodium ion batteries with excellent cycle performance. J Mater Chem A 2014; 2(12):4117-21. [33] Li Y, Xu S, Wu X, Yu J, Wang Y, Hu YS, et al. Amorphous monodispersed hard carbon micro-spherules derived from biomass as a high performance negative electrode material for sodium-ion batteries. J Mater Chem A 2015; 3(1):71-7. [34] Wang HG, Wu Z, Meng FL, Ma DL, Huang XL, Wang LM, et al. Nitrogen-doped porous carbon sheets as low-cost, high-performance anode material for sodium-ion batteries. ChemSusChem 2013; 6(1):56-60. [35] Huang X, Qi X, Boey F, Zhang H. Graphene-based composites. Chem Soc rev 2012; 41(2):666-86. [36] Liu J, Liu XW. Two-dimensional architectures for lithium storage. Adv Mater 2012; 24(30):4097-111. [37] Zhou X, Zhu X, Liu X, Xu Y, Liu Y, Dai Z, et al. Ultralong cycle life sodium-ion battery anodes using a graphene-templated carbon hybrid. J Phys Chem C 2014; 118(39):22426-31. [38] Liu Y, Ai K, Lu L. Polydopamine and its derivative materials: Synthesis and promising applications in energy, environmental, and biomedical fields. Chem Rev 2014; 114(9):5057-115. [39] Fu L, Tang K, Song K, van Aken PA, Yu Y, Maier J. Nitrogen doped porous carbon fibres as anode materials for sodium ion batteries with excellent rate
22
performance. Nanoscale 2014; 6(3) 1384-9. [40]
Wang H, Zhang C, Liu Z, Wang L, Han P, Xu H, et al. Nitrogen-doped
graphene sheets with excellent lithium storage properties. J Mater Chem 2011; 21(14) 5430-4. [41] Shin WH, Jeong HM, Kim BG, Kang JK, Choi JW. Nitrogen-doped multiwall carbon tubes for lithium storage with extremely high capacity. Nano lett. 2012; 12(5):2283-2288. [42] Liu R, Mahurin SM, Li C, Unocic RR, Idrobo JC, Gao H, et al. Dopamine as a carbon source: The controlled synthesis of hollow carbon spheres and yolk-structured carbon composites. Angew Chem Int Ed 2011; 50(30):6799-802. [43] Ding J, Wang H, Li Z, Kohandehghan A, Cui K, Xu Z, et al. Carbon nanosheet frameworks derived from peat moss as high performance sodium ion battery anodes. ACS 2013; 7(7):11004-15. [44] Wang H, Zhang C, Liu Z, Wang L, Han P, Xu H, et al. Nitrogen-doped graphene nanosheets with excellent lithium storage properties. J. Mater. Chem. 2011, 21(14): 5430-4. [45] Slavko M, Gordana, Miroslava T, Jaroslav S. Conducting carbonized polyaniline nanotubes. Nanotechnology 2009; 20(24): 245601-10. [46] Qie L, Chen WM, Wang ZH, Shao QG, Li X, Yuan LX, et al. Nitrogen-doped porous carbon nanofiber webs as anodes for lithium ion batteries with a super high capacity and rate capability. Adv. Mater. 2012; 24(15):2047-50. [47] Shin WH, Jeong HM, Kim BG, Kang JK, Choi JW. Nitrogen-doped multiwall
23
carbon nanotubes for lithium storage with extremely high capacity. Nano lett, 2012, 12(5): 2283-2288. [48] Song Z, Xu T, Gordin ML, Jiang YB, Bae IT, Xiao Q, et al. Polymer-graphene nanocomposites as ultrafast-charge and discharge cathodes for rechargeable lithium batteries. NanoLett 2012;12(5):2205–11 [49] Hulicova-Jurcakova D, Seredych M, Lu GQ, Bandosz TJ. Combined effect of nitrogen- and oxygen-containing functional groups of microporous activated carbon on its electrochemical performance in supercapacitors. Adv Funct. Mater 2009;19(3):438–47. [50] Yu L, Brun N, Sakaushi K, Eckert J, Titirici MM. Hydrothermal casting: Synthesis of hierarchically porous carbon monoliths and their application in lithium-sulfur batteries. Carbon 2013; 61:245-253. [51] C. C. Li, X. M. Yin, L. B. Chen, Q. H. Li and T. H. Wang, J. Phys. Chem. C, 2009, 113, 13438-42. [52] Sato K, Noguchi M, Demachi A, Oki N, Endo M. A mechanism of lithium storage in disordered carbons. Science 1994; 264(5158):556-8. [53] Mabuchi A, Tokumitsu K, Fujimoto H, Kasuh T. Charge-discharge characteristics of the mesocarbon miocrobeads heat-treated at different temperatures. J Electrochem Soc 1995; 142(4):1041-6. [54] Stevens DA, Dahn JR. An in situ small-angle X-ray scattering study of sodium insertion into a porous carbon anode material within an operating electrochemical cell. J Electrochem Soc 2000; 147(12):4428-31.
24
[55] Yan Y, Yin YX, Guo YG, Wan LJ. A sandwich-like hierarchically porous carbon/graphene composite as a high-performance anode material for sodium-ion batteries. Adv Energy Mater 2014; 4(8):1301584. [56] Hong JL, Qie L, Zeng R, Yi ZQ, Zhang W, Wang D.et al. Biomass derived hard carbon used as a high performance anode material for sodium ion batteries. J Mater Chem A 2014; 2:12733-8.
25
S0008-6223(15)00340-1 http://dx.doi.org/10.1016/j.carbon.2015.04.049 CARBON 9867
To appear in:
Carbon
Received Date: Accepted Date:
17 January 2015 20 April 2015
Please cite this article as: Yang, F., Zhang, Z., Du, K., Zhao, X., Chen, W., Lai, Y., Li, J., Dopamine derived nitrogendoped carbon sheets as anode materials for high-performance sodium ion batteries, Carbon (2015), doi: http:// dx.doi.org/10.1016/j.carbon.2015.04.049
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dopamine derived nitrogen-doped carbon sheets as anode materials for high-performance sodium ion batteries Fuhua Yang, Zhian Zhang*, Ke Du, Xingxing Zhao, Wei Chen, Yanqing Lai, and Jie Li
School of Metallurgy and Environment, Central South University, Changsha Hunan 410083, China
Corresponding author: Zhian Zhang Institute: School of Metallurgy and Environment, Central South University. Address: No.932, Lushan Road, Changsha city, Hunan Province, 410083 China Tel: +86 731 88830649; Fax: +86 731 88830649 E-mail: [email protected]
*
Corresponding author: Tel: +86 731 88830649; Fax: +86 731 88830649.
E-mail address: [email protected] (Z. Zhang).
1
Dopamine derived nitrogen-doped carbon sheets as anode materials for high-performance sodium ion batteries
Fuhua Yang, Zhian Zhang*, Ke Du, Xingxing Zhao, Wei Chen, Yanqing Lai, and Jie Li School of Metallurgy and Environment, Central South University, Changsha Hunan 410083, China
Abstract
Designed as an anode material for sodium ion batteries , nitrogen-doped carbon sheets (NCSs) were successfully synthesized using graphene and dopamine as template and carbon precursor, respectively. The NCSs demonstrate high reversible capacity and excellent rate performance, delivering a high reversible capacity of 382 mAh g-1 at 50 mA g-1 after 55 cycles. Even up to 10 A g-1, a rate capacity of 75 mAh g-1 can be obtained. Furthermore, NCSs also have remarkable cycling stability with specific capacity of 165 mAh g-1 after 600 cycles (under 200 mA g-1 ). The excellent performance of NCSs can be ascribed to the nitrogen-doped two-dimension sheet structure.
*
Corresponding author: Tel: +86 731 88830649; Fax: +86 731 88830649.
E-mail address: [email protected] (Z. Zhang).
2
1. Introduction
Lithium ion batteries(LIBs) have been widely used as the power source for electric vehicles and mobile devices.[1-4] Considering their relatively high cost and limited terrestrial reserves of lithium, large-scale commercial applications of LIBs would be extremely difficult.[5, 6] There is an urgent need to explore alternative energy storage technologies for large-scale energy storage. Sodium ion batteries (SIBs) have been regarded as an attractive alternative to LIBs owing to the similar physical/chemical properties of sodium with lithium and the abundant supply of sodium, which make SIBs cheaper.[6, 7] However, it’s still a challenge to find appropriate host materials with large interstitial space to guarantees sodium ion accommodation, since sodium ion is 55% larger than lithium ion in radius.[8, 9] Therefore, investigating suitable electrode materials is crucial for the development of SIBs. Although many efforts have been made in the field of cathode materials for SIBs, researches on the anode material are still at a very early stage.[10, 11] Recent years, Na-storage anode materials, such as Sn,[12, 13] Ge,[14, 15] Sb,[16-18] and P[19-22] have been explored as anode candidates for SIBs, but the application of these materials is hampered because of the large volumetric expansion during sodiation and the intrinsic low conductivity. Carbonaceous materials have been attracted tremendous attention since the first report of hard carbon as anode for SIBs[23], on account of the versatile preparation methods and large interlayer space for Na+ insertion[24]. To enhance the electrochemical performance of carbonaceous anodes, 3
many strategies have been proposed.[25-30] Among them, fabricating structures (such as fibers, hollow spheres and hollow wires) seems to be an effective way.[24, 27, 31-34] For example, Huang et al.[27] fabricated carbon fibers using a template method, which presented a specific capacity of ~130 mA h g-1 after 200 cycles at 200 mA g-1 and excellent rate performance. Maier et al.[31] showed that hollow carbon spheres can retain a capacity of ~160 mA h g-1 after 100 cycles at 100 mA g-1. Hollow carbon wires[24] were also prepared and delivered a high capacity of 251 mA h g-1 over 400 cycles under 50 mA g-1, even at a current rate of 125 mA g-1, a specific capacity of 149 mA h g-1 was observed. Despite progresses have been made in the carbonaceous anode materials, more efforts still need to be made to promote the commercial application of SIBs. Two-dimension carbon structures have been regarded as a potential structure for energy storage devices. With the unique properties of two-dimension structure, when used as the anode for SIBs, carbon sheets (CSs) will adequately contact with the electrolyte, facilitate good transport of electrons/sodium ion, and facile strain relaxation during the charge-discharge process.[35-37] Graphene have been used as template to fabricate CSs because of its stable chemical property and remarkable conductivity, which is conducive to the electrochemical performance of the CSs electrode. Meanwhile, introduction of nitrogen is also an effective strategy to enhance the carbon electrodes’ performance for SIBs.[39-41] To synthesis nitrogen-doped carbon materials, calcination of nitrogen rich carbon precursor is the most common and facile method. Zhang et al.[34] prepared graphene-templated nitrogen-doped CSs
4
by coating graphene with polypyrrole. But this procedure is tedious and the electrochemical performance of the CSs anode is unsatisfactory. According to the previous studies, dopamine can self-polymerize at alkaline pH values under oxygen atmosphere. Polydopamine have the following advantages when used as carbon precursors: (1) the strong and convenient coating capability; (2) the conformal nature of polydopamine coating; (3) uniform nitrogen source will retain in the final carbon product.[38] Polydopamine should be a promising carbon precursor for the fabrication of CSs. However, to the best of our knowledge, dopamine derived CSs for SIBs have not been reported yet. Herein, we report a nitrogen-doped carbon sheets (NCSs), which is fabricated by pyrolyzation of polydopamine-graphene oxide (GO) sheets precursors, as SIBs anode materials. The NCSs present high reversible capacity of 382 mA h g-1 at a constant current of 50 mA g-1 after 55 charge-discharge processes, outstanding cycling stability with capacity of ~165 mAh g-1 (under a high current density of 200mA g-1) after 600 cycles without any decay, and the rate performance of the NCSs is impressive (212, 168, 129, 113, 97, 84 and 75 mA h g-1 at 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g-1, respectively). The excellent electrochemical performances of the NCSs anode can be ascribed to the two-dimension sheet structure and nitrogen doping property.
2. Experimental 2.1 Preparation of nitrogen-doped carbon sheets (NCSs)
The
starting
materials
dopamine
5
hydrochloride
and
tris(hydroxymethyl)aminomethane (TRIS) were purchased from aladdin. All these chemicals were analytical reagent grade. Graphene oxide (GO) was synthesized using a modified Hummers method. The NCSs were synthesized by pyrolysis of polydopamine modified graphene oxide (GO) sheet precursors, which were prepared by a template method. Typically, 0.2 g GO was dispersed in 200 mL of deionized water to form a homogeneous GO suspension. Then, 1.5 g dopamine hydrochloride was added to the suspension under magnetic stirring. After that, the pH value of dispersion was adjusted to 8.5 by adding TRIS solution, and the solution kept stirring for 24 h. Centrifugation was carried out to collected the polymer/GO composite, then the solid product was washed with deionized water and ethyl alcohol for three times. The as-prepared polymer/GO sheets formed after freeze-drying process. After heat treatment of the as-prepared polymer/GO sheets at 800 oC for 2 h with a heating rate of 4 oC min-1, the NCSs were finally obtained. For comparison, nitrogen-free carbon sheets (CSs) were prepared by heat treatment of GO at 800 oC for 2 h.
2.2 Material characterization
Scanning electron microscopy (SEM, Nova
SEM 230) and transmission
electron microscopy (TEM, Tecnai G2 20ST) were applied to investigate the material morphology. The structure of the NCSs was characterized using X-ray diffraction (XRD, Rigaku3014). Nitrogen adsorption/desorption measurements were carried out on a Quantachrome instrument (Quabrasorb SI-3MP). Surface functional groups and bonding characterization were conducted using X-ray photoelectron spectroscopy
6
(XPS, Thermo Fisher ESCALAB250xi). The fitting errors of XPS test results are within ±1%. The Raman measurements were carried out on a Jobin-Yvon LabRAM HR-800 spectrometer.
2.3. Electrochemical measurements
To conduct electrochemical measurements of the NCSs electrode, a CR-2032 type coin cell was fabricated. Sodium pellet and whatman glass fiber membrane were served as counter electrode and separator, respectively. A mixed slurry of NCSs, Super P and carboxymethyl cellulose (CMC) (8:1:1, in wt. %) in deionized water was spread onto a copper foil. The coating copper foil was first dried in air, then transferred into a oven at 80 oC for 12 h. The assembly of the tested cells were carried out in a glove box under argon atmosphere. The electrolyte used in this work composition of 1 M NaClO4 (Sigma-Aldrich) in a solvent mixture of ethylene carbonate and propylene carbonate (with a volume ratio of 1:1). Galvanostatic charge/discharge test were conducted using a battery test system. Cyclic voltammetry (CV) measurements were carried out at a scan rate of 0.2 mV s-1 between 0.01 and 2.5 V on a electrochemical measurement system. Those electrochemical tests were carried out under a constant temperature of 25 oC.
3. Results and discussion 3.1 Synthesis and characterization
As presented in Fig. 1, the nitrogen-doped carbon sheets (NCSs) synthesis
7
procedure can be divided into four parts: dispersion, polymerization, collection and calcination. Graphene oxide (GO) was dispersed homogeneously in deionized water after ultrasonic treatment for 2 h. GO served as template in this work, while dopamine used as carbon precursor. When the solution pH value was adjusted to 8.5, dopamine occurred self-polymerization and coated onto the surface of GO sheets uniformly. Centrifugation and freeze-drying processes were carried out to collect the solid product. The carbonization procedure was conducted at 800 oC for 2 h. Through the dopamine coating and carbonization procedures, 2D structure obtained and nitrogen configurations forming.
Fig. 1 Schematic of the NCSs fabricate procedures
The morphology characterization of NCSs were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). As exhibited in Fig. 2(a), (b) and (c), no free particle observed, the targeted products maintain the two-dimensional structure of graphene and the surface of the NCSs is obviously smooth. All those phenomenon indicate the homogeneous and continuous coating of polydopamine on GO surface owning to the strong coating capability of the polydopamine and the conformal nature of polydopamine coating.[42] Notablely, the NCSs display a thin thickness, which would result fast transport of electron/sodium 8
ions because the maximum electron/sodium ion diffusion distance is half of the thickness.[43] To reveal the microstructure of the NCSs, high resolution transmission electron microscopy (HRTEM) image is given in Fig. 2(d). This image displays a turbostatic structure, suggesting amorphous structure of NCSs. Fig. 2(e)~(g) show the Annular dark-field TEM images of NCSs and the corresponding elemental mapping of carbon and nitrogen. These figures reveal the presence and homogeneous distribution of nitrogen.
Fig. 2 (a), (b) SEM images, (c) TEM image and (d) HRTEM image of NCSs. (e) Annular dark-field TEM image, and corresponding (f) carbon and (g) nitrogen elemental mapping.
9
Fig. 3(a) presents the X-ray diffraction (XRD) pattern of NCSs. In this XRD pattern, two broad peaks are observed at around 23 and 43o, which can be indexed to (002) and (100), respectively. The relatively weak peak at 43o can be ascribed to the low crystalline structure. This XRD pattern indicates an amorphous structure of the NCSs. Based on the XRD result, the interlayer spacing (d002) of NCSs is calculated to be 0.38 nm. It is well know that the application of graphite for SIBs is hindered because of the limited interlayer spacing (0.34 nm), large interlayer spacing makes NCSs to be a suitable host material for SIBs to store sodium ion. Fig. 3(b) displays the Raman spectrum of the NCSs, which presents two peaks at 1354 and 1585 cm-1, ascribed to D-band (for the sp3 configuration) and G-band (for graphitic configuration), respectively. The value of ID/IG is commonly used to characterize the graphitization of carbon materials. The ID/IG value of NCSs is calculated to be 0.93, suggesting a highly disordered structure of the NCSs, which is agreed with the HRTEM micrographs of NCSs (Fig. 2(d)).
Fig. 3 (a) XRD pattern and (b) Raman spectrum of the NCSs.
X-ray photoelectron spectroscopy (XPS) was also conducted to investigate the
10
functional groups of the material. As shown in Fig. 4(a), the XPS spectrum of the NCSs display three peaks at 284.59, 532.36 and 400.8 eV, corresponding to C 1s, O 1s and N 1s, respectively, further confirm the existence of nitrogen, and the atomic percentage of N in the NCSs is about 5.54 at%. The XPS spectrum of the C 1s (inset of Fig. 1(a)) can be divided into three peaks. The main peak at 284.8 eV corresponds to the graphite-like sp2 C, indicating most of the C atoms in the NCSs are arranged in a conjugated honeycomb lattice. The small peaks at 285.7 and 287.5 eV reflect different bonding structure of the C-N bonds,corresponding to the N-sp2 C and N-sp3 C bonds, respectively. The N 1s peak can be deconvoluted into three peaks, centered at 398.3, 400.7 and 403.1 eV, respectively, which are ascribed to three nitrogen configurations, namely, pyridinic(N-6), pyrrolic(N-5) and quaternary (N-Q) nitrogen, respectively. According to the XPS result, it can be concluded that the nitrogen atom of the dopamine are well retained during the polymerization and calcination processes. The introduction of nitrogen atoms enhance the performance of NCSs electrode, not only because of the enhanced electric conductivity, but also the pseudo-capacitance.[27, 39] Role of Nitrogen in enhancing the performance can be presented as the following: Firstly, The nitrogen-doping in the carbon matrix can improve the electric conductivity of carbon;[44-46] Secondly, N-doping can generate extrinsic defects, and hence enhance the reactivity and capacity;[47] Thirdly, After nitrogen doping, a pseudo-capacitance can be generated due to the interaction between the electrolyte and the N species on the surface.[48, 49]
11
Fig. 4 (a) The total XPS spectrum of NCSs; inset is the XPS C 1s of HCNF@NPC. (b) The XPS N 1s spectra of the NCSs.
To further characterize the surface and the porous structures of the N-NCSs, N2 absorption-desorption measurement was also carried out. Fig. 5(a) shows a typical type IV isotherm with a hysteresis loop within a relative pressure P/P0 range of 0.4~1, suggesting
the
characteristic
mesoporous
structure.
The
specific
Brunauer-Emmett-Teller (BET) surface area of NCSs is 76 m2 g-1. As shown in the Fig. 5(b), the pore size of the NCSs is mainly distribute between 2~5 nm, further verify the mesoporous structure of the NCSs. These small pores probably are formed during the calcination process due to the physical activation of the carbon framework.[50]
Fig. 5 Porosity characterization of NCSs: (a) N2 sorption isotherms and (b) pore size distribution.
12
3.2 Electrochemical performance of the NCSs anode
To analyze the electrochemical properties of the NCSs anode, cyclic voltammetry (CV) tests and galvanostatic charge/discharge measurements were performed. Fig. 6(a) displays the CV curves of the NCSs anode between 0.01 and 2.5 V for the first 5 cycles. For the cathodic processes, three peaks locate at 0.75, 0.4 and 0.01 V are observed during the first cycle. The peaks at 0.75 and 0.4 V can be indexed to the decomposition of the electrolyte and formation of solid electrolyte interface (SEI) film,[24, 41] and these two peaks disappear in the following cycles, indicating the irreversibility of the reaction. The low coulombic efficiency of the first cycle can be mainly ascribed to the SEI forming and the electrolyte decomposition. While the sharp peak central at 0.01 V can be assigned to Na+ insertion into the carbonaceous materials. In the subsequent cycles, this peak still exists, suggesting the insertion of the Na+ is reversible. For the anodic processes, Na+ extraction occurs over a broad potential range (0~0.8 V). Notably, the oxidation broad peak intensities of the second and third cycles are stronger than that of the first cycle, this can be explained by the adsorption with charge transfer on both side of the graphene layers and the reaction between N group on the surface and the Na+, similar phenomenon have been reported.[25, 61] Coinciding with the previous researches, the Na+ insertion/extraction of the NCSs anode occur below 1.2 V. Furthermore, according to the CV results, after the first cycle, the subsequent CV curves overlap with each other, indicating outstanding reversibility of the NCSs.
13
Fig. 6 (a) Typical CV curves of the NCSs electrode at a potential sweep rate of 0.2 mV s-1 and (b) Charge–discharge profiles at a current density of 50 mA g-1
Fig. 6(b) shows the 1st, 2nd and 3rd charge-discharge profiles of the NCSs materials within 0.01~2.5 V, at 50 mA g-1. The initial discharge and charge capacities are 2900 and 765 mAh g-1, respectively, giving a coulombic efficiency of 26.4%. The large irreversible capacity loss is commonly caused by the electrolyte decomposition and SEI layer forming. For the Na+ insert into the disordered carbon reaction mechanisms, two main reaction models have been proposed:[52-54] (i) Na+ insertion occurs between the carbon layers corresponding to the slope region of the voltage profile; (ii) Na+ accommodates into the micropores of carbon, which is ascribed to the plateau region of the voltage profile. In the case of the NCSs electrode, as presented in Fig. 6(b), the 2nd and 3rd cycles discharge curves display a sloping property, and no obvious plateau at the low voltage region, indicating that Na+ manly insert between the carbon layers. The cycle and rate performances of the NCSs electrode were also tested. As illustrated in Fig. 7(a), the NCSs present a reversible capacity of 382 mAh g-1 after 55 cycles at 50 mA g-1. To verify the improvement of electrochemical performances of nitrogen doping, nitrogen-free carbon sheets (CSs) was prepared by heat treatment of
14
GO at 800 oC for 2 h, and tested as anode materials for sodium ion batteries. As showed in Fig. 7(a), the as-prepared CSs deliver a capacity of 54 mAh g-1, at 50 mA g-1 after 55 cycles, which is much lower than that of NCSs. The reversible capacity of the NCSs is excellent, and only a few studies have showed higher capacity at the same current density.[55] Although the initial coulombic efficiency is low, it increases to ~94% after several cycles. The small irreversible capacity during each cycle can be explained by the incomplete stabilization of the SEI during the charge-discharge processes.[31] A long cycle test was conducted at a current density of 200 mA g-1 (Fig. 7(c)). After ~60 cycles, the specific capacity stay around 165 mAh g-1, and a high coulombic efficiency (approaches 100%) is obtained. Even after 600 cycles, the specific capacity still remains at ~165 mAh g-1 without any decay. Those experiment results suggest impressive reversibility and cycling stability of the NCSs. In addition, the NCSs also present good rate performance (Fig. 7(b)). When tested at different current densities, the NCSs show high reversible capacities, namely, 212, 168, 129, 113, 97 and 84 mA h g-1 at 0.1, 0.2, 0.5, 1, 2 and 5 A g-1, respectively. Even at an extremely high current density of 10 A g-1, a high capacity of 75 mAh g-1 is still obtained. When the current density return to 0.1 A g-1 after 70 cycles, the specific capacity can be recovered up to ~190 mAh g-1. It is notable that the rate performance of the NCSs is comparable or even better than those previous studies.[27, 34, 39, 56]
15
Fig. 7 (a) Cycle performance of NCSs and CSs at current density 50 mA g-1, (b) rate performance at different current density and (c)long cycle performance at 200 mA g-1 of the NCSs electrode.
The excellent electrochemical performances of this NCSs anode for SIBs can be explained by several reasons: (1) the large interlayer spacing (0.38 nm) of the NCSs, which guarantees Na+ accommodation; (2) the two-dimensional structure material can adequately contact with the electrolyte and offer shortened paths for electrode/Na+ transport. Furthermore, facile strain relaxation during the charge-discharge process is important; (3) the introduction of nitrogen atoms can enhance the electric conductivity and capacity of the carbonaceous anodes; (4) the existence of graphene provide high electronic conductivity. 16
In order to further identify the structure change of the NCSs, SEM measurement was performed. Cells were disassembled and the working electrodes were washed with propylene carbonate to remove the residual NaClO4. Fig. 8(a) show the SEM images of NCSs before cycled, which is the same with Fig. 2(a)(b), suggesting that the electrode preparing process didn’t damage the morphology of the NCSs. Fig. 8(b) is the SEM image of NCSs after 55 cycles. Compare Fig. 8(b) with Fig. 8(a), it is obvious that morphology barely change, although the cycled electrode is covered with a dense and rough layer (SEI layer). The similar morphology indicates perfect structural stability during the sodium insertion/extraction processes.
Fig. 8 SEM images of the NCSs electrode (a) before and (b) after 55 cycles under current density 50 mA g-1.
4. Conclusion
Nitrogen-doped carbon sheets (NCSs) have been successfully prepared by calcination of polymer/graphene oxide sheets. When used as the anode materials for SIBs, The NCSs present excellent electrochemical performance: high reversible
17
capacity of 382 mA h g-1 (at a constant current of 50 mA g-1 after 55 charge-discharge processes); outstanding cycling stability (~165 mAh g-1 under a high current density 200 mA g-1 after 600 cycles without any decay); and remarkable rate performance (212, 168, 129, 113, 97, 84 and 75 mA h g-1 at 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g-1, respectively). The high electrochemical performance of NCSs can be ascribed to the two-dimension sheet structure and nitrogen doping property.
References
[1] Tarascon JM, Armand M. Issues and challenges facing rechargeable lithium batteries. Nature 2001; 414(6861):359-67. [2] Manthiram A. Materials challenges and opportunities of lithium ion batteries. J Phys Chem Lett 2011; 2(3):176-184. [3] Cui G, Gu L, Zhi L, Kaskhedikar N, van Aken PA, Müllen K, et al. A germanium-carbon composite material for lithium batteries. Adv Mater 2008; 20(16):3079-83. [4] Whittingham MS. Lithium batteries and cathode materials. Chem Rev 2004; 104(10):4271-302. [5] Slater MD, Kim D, Lee E, Johnson CS. Sodium-ion batteries. Adv Funct Mater 2013; 23(8):947-58. [6] Kim SW, Seo DH, Ma X, Ceder G, Kang K. Electrode materials for rechargeable sodium-ion batteries: potential alternatives to current lithium-ion batteries. Adv Energy Mater 2012; 2(7):710-21.
18
[7] Yabuuchi N, Kajiyama M, Iwatate J, Nishikawa H, Hitomi S, Okuyama R, et al. P2-type Nax[Fe1/2Mn1/2]O2 made from earth-abundant elements for rechargeable Na batteries. Nat Mater 2012; 11(6):512-7. [8] Stevens DA, Dahn JR. The mechanisms of lithium and sodium insertion in carbon materials. J Electrochem Soc 2001; 148(8):A803-11. [9] Wang L, Lu Y, Liu J, Xu M, Cheng J, Zhang D, et al. A superior low-cost cathode for a Na-ion battery. Angew Chem 2013; 52(7):1964-7. [10] Kim Y, Ha KH, Oh SM, Lee KT. High-capacity anode materials for sodium-ion batteries. Chemistry 2014; 20(38):11980-92. [11] Dahbi M, Yabuuchi N, Kubota K, Tokiwa K, Komaba S. Negative electrodes for Na-ion batteries. Phys chem chem phys 2014; 16:15007-28. [12] Liu Y, Zhang N, Jiao L, Tao Z, Chen J. Ultrasmall Sn particles Embedded in Carbon as High-Performance Anode for Sodium-Ion Batteries. Adv Funct Mater 2014; 25(2):214-20. [13] Xu Y, Zhu Y, Liu Y, Wang C. Electrochemical performance of porous carbon/tin composite anodes for sodium-ion and lithium-ion batteries. Adv Energy Mater 2013; 3(1):128-33. [14] Baggetto L, Keum JK, Browning JF, Veith GM. Electrochem Commun 2013; 34:41-44. [15] Abel PR, Lin YM, de Souza T, Chou CY, Gupta A, Goodenough JB, et al. columnar germanium thin films as a high-rate sodium-ion battery anode material. J Phys Chem C 2013; 117(37):18885-90.
19
[16] Wu L, Hu X, Qian J, Pei F, Wu F, Mao R, et al. Sb-C fibers with long cycle life as an anode material for high-performance sodium-ion batteries. Energy Environ Sci 2014; 7(1): 323-8. [17] Zhu Y, Han X, Xu Y, Liu Y, Zheng S, Xu K, et al. Electrospun Sb/C fibers for a stable and fast sodium-ion battery anode. ACS Nano 2013; 7(7):6378-86. [18] Zhou XL, Zhong YR, Yang M, Hu M, Wei JP, Zhou Z. Sb particles decorated N-rich carbon sheets as anode materials for sodium ion batteries with superior rate capability and long cycling stability. Chem Commun 2014; 50(85):12888-91. [19] Song J, Yu Z, Gordin ML, Hu S, Yi R, Tang D, et al. Chemically bonded phosphorus/graphene hybrid as a high performance anode for sodium-ion batteries. Nano lett 2014; 14(11):6329-35. [20] Li WJ, Chou SL, Wang JZ, Liu HK, Dou SX. Simply mixed commercial red phosphorus and carbon tube composite with exceptionally reversible sodium-ion storage. Nano lett 2013; 13(11):5480-4. [21] Qian J, Wu X, Cao Y, Ai X, Yang H. High capacity and rate capability of amorphous phosphorus for sodium ion batteries. Angew Chem 2013; 125(17):4633-6. [22] Kim Y, Park Y, Choi A, Choi NS, Kim J, Lee J, et al. An amorphous red phosphorus/carbon composite as a promising anode material for sodium ion batteries. Adv Mater 2013; 25(22):3045-9. [23] Doeff MM, Ma Y, Visco SJ, De Jonghe LC. Electrochemical insertion of sodium into carbon. J Electrochem Soc 1993; 140(2):L169-70.
20
[24] Cao Y, Xiao L, Sushko ML, Wang W, Schwenzer B, Xiao J, et al. Sodium ion insertion in hollow carbon wires for battery applications. Nano lett 2012; 12(7):3783-7. [25] Wenzel S, Hara T, Janek J, Adelhelm P. Room-temperature sodium-ion batteries: Improving the rate capability of carbon anode materials by templating strategies. Energy Environ Sci 2011; 4(9):3342-5. [26] Lotfabad EM, Ding J, Cui K, Kohandehghan A, Kalisvaart WP, Hazelton M, et al. High-density sodium and lithium ion battery anodes from banana peels. ACS Nano 2014; 8(7):7115-29. [27] Wang Z, Qie L, Yuan L, Zhang W, Hu X, Huang Y. Functionalized N-doped interconnected carbon fibers as an anode material for sodium-ion storage with excellent performance. Carbon 2013; 55:328-34. [28] Wen Y, He K, Zhu Y, Han F, Xu Y, Matsuda I, et al. Expanded graphite as superior anode for sodium-ion batteries. Nat Commun 2014; 5. [29] Li W, Zeng L, Yang Z, Gu L, Wang J, Liu X, et al. Free-standing and binder-free sodium-ion electrodes with ultralong cycle life and high rate performance based on porous carbon fibers. Nanoscale 2014; 6(2):693-8. [30] Luo W, SchardtJ, Bommier C, Wang B, Razink J, Simonsen J, et al. Carbon fibers derived from cellulose fibers as a long-life anode material for rechargeable sodium-ion batteries. J Mater Chem A 2013; 1(36):10662-6. [31] Tang K, Fu L, White RJ, Yu L, Titirici MM, Antonietti M, et al. Hollow carbon spheres with superior rate capability for sodium-based batteries. Adv Energy
21
Mater 2012; 2(7):873-7. [32] Chen T, Liu Y, Pan L, Lu T, Yao Y, Sun Z, et al. Electrospun carbon fibers as anode materials for sodium ion batteries with excellent cycle performance. J Mater Chem A 2014; 2(12):4117-21. [33] Li Y, Xu S, Wu X, Yu J, Wang Y, Hu YS, et al. Amorphous monodispersed hard carbon micro-spherules derived from biomass as a high performance negative electrode material for sodium-ion batteries. J Mater Chem A 2015; 3(1):71-7. [34] Wang HG, Wu Z, Meng FL, Ma DL, Huang XL, Wang LM, et al. Nitrogen-doped porous carbon sheets as low-cost, high-performance anode material for sodium-ion batteries. ChemSusChem 2013; 6(1):56-60. [35] Huang X, Qi X, Boey F, Zhang H. Graphene-based composites. Chem Soc rev 2012; 41(2):666-86. [36] Liu J, Liu XW. Two-dimensional architectures for lithium storage. Adv Mater 2012; 24(30):4097-111. [37] Zhou X, Zhu X, Liu X, Xu Y, Liu Y, Dai Z, et al. Ultralong cycle life sodium-ion battery anodes using a graphene-templated carbon hybrid. J Phys Chem C 2014; 118(39):22426-31. [38] Liu Y, Ai K, Lu L. Polydopamine and its derivative materials: Synthesis and promising applications in energy, environmental, and biomedical fields. Chem Rev 2014; 114(9):5057-115. [39] Fu L, Tang K, Song K, van Aken PA, Yu Y, Maier J. Nitrogen doped porous carbon fibres as anode materials for sodium ion batteries with excellent rate
22
performance. Nanoscale 2014; 6(3) 1384-9. [40]
Wang H, Zhang C, Liu Z, Wang L, Han P, Xu H, et al. Nitrogen-doped
graphene sheets with excellent lithium storage properties. J Mater Chem 2011; 21(14) 5430-4. [41] Shin WH, Jeong HM, Kim BG, Kang JK, Choi JW. Nitrogen-doped multiwall carbon tubes for lithium storage with extremely high capacity. Nano lett. 2012; 12(5):2283-2288. [42] Liu R, Mahurin SM, Li C, Unocic RR, Idrobo JC, Gao H, et al. Dopamine as a carbon source: The controlled synthesis of hollow carbon spheres and yolk-structured carbon composites. Angew Chem Int Ed 2011; 50(30):6799-802. [43] Ding J, Wang H, Li Z, Kohandehghan A, Cui K, Xu Z, et al. Carbon nanosheet frameworks derived from peat moss as high performance sodium ion battery anodes. ACS 2013; 7(7):11004-15. [44] Wang H, Zhang C, Liu Z, Wang L, Han P, Xu H, et al. Nitrogen-doped graphene nanosheets with excellent lithium storage properties. J. Mater. Chem. 2011, 21(14): 5430-4. [45] Slavko M, Gordana, Miroslava T, Jaroslav S. Conducting carbonized polyaniline nanotubes. Nanotechnology 2009; 20(24): 245601-10. [46] Qie L, Chen WM, Wang ZH, Shao QG, Li X, Yuan LX, et al. Nitrogen-doped porous carbon nanofiber webs as anodes for lithium ion batteries with a super high capacity and rate capability. Adv. Mater. 2012; 24(15):2047-50. [47] Shin WH, Jeong HM, Kim BG, Kang JK, Choi JW. Nitrogen-doped multiwall
23
carbon nanotubes for lithium storage with extremely high capacity. Nano lett, 2012, 12(5): 2283-2288. [48] Song Z, Xu T, Gordin ML, Jiang YB, Bae IT, Xiao Q, et al. Polymer-graphene nanocomposites as ultrafast-charge and discharge cathodes for rechargeable lithium batteries. NanoLett 2012;12(5):2205–11 [49] Hulicova-Jurcakova D, Seredych M, Lu GQ, Bandosz TJ. Combined effect of nitrogen- and oxygen-containing functional groups of microporous activated carbon on its electrochemical performance in supercapacitors. Adv Funct. Mater 2009;19(3):438–47. [50] Yu L, Brun N, Sakaushi K, Eckert J, Titirici MM. Hydrothermal casting: Synthesis of hierarchically porous carbon monoliths and their application in lithium-sulfur batteries. Carbon 2013; 61:245-253. [51] C. C. Li, X. M. Yin, L. B. Chen, Q. H. Li and T. H. Wang, J. Phys. Chem. C, 2009, 113, 13438-42. [52] Sato K, Noguchi M, Demachi A, Oki N, Endo M. A mechanism of lithium storage in disordered carbons. Science 1994; 264(5158):556-8. [53] Mabuchi A, Tokumitsu K, Fujimoto H, Kasuh T. Charge-discharge characteristics of the mesocarbon miocrobeads heat-treated at different temperatures. J Electrochem Soc 1995; 142(4):1041-6. [54] Stevens DA, Dahn JR. An in situ small-angle X-ray scattering study of sodium insertion into a porous carbon anode material within an operating electrochemical cell. J Electrochem Soc 2000; 147(12):4428-31.
24
[55] Yan Y, Yin YX, Guo YG, Wan LJ. A sandwich-like hierarchically porous carbon/graphene composite as a high-performance anode material for sodium-ion batteries. Adv Energy Mater 2014; 4(8):1301584. [56] Hong JL, Qie L, Zeng R, Yi ZQ, Zhang W, Wang D.et al. Biomass derived hard carbon used as a high performance anode material for sodium ion batteries. J Mater Chem A 2014; 2:12733-8.
25