- Email: [email protected]
Rose-like N-doped Porous Carbon for Advanced Sodium Storage
Electrochimica Acta 240 (2017) 24–30
Contents lists available at ScienceDirect
Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta
Rose-like N-doped Porous Carbon for Advanced Sodium Storage Ganggang Zhao, Guoqiang Zou, Xiaoqing Qiu, Sijie Li, Tianxiao Guo, Hongshuai Hou* , Xiaobo Ji College of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, China
A R T I C L E I N F O
Article history: Received 20 March 2017 Received in revised form 5 April 2017 Accepted 9 April 2017 Available online 14 April 2017 Keyword: electrochemistry N-doped carbon materials sodium-ion battery
A B S T R A C T
Carbon materials have been widely applied in the energy storage devices, however, the preparation of suitable carbon materials for sodium-ion batteries (SIBs) is still a challenge. In this paper, N-doped porous carbon material (NDPCs) with rose-like structure has been successfully prapared through pyrolysis of the as-prepared polyimides in-situ. The NDPCs shows rose-like structure derived from 2D nanosheets, an expanded interlayer distance of 0.387 nm, a high specific surface area of 215.7 m2 g1 and the electrochemical performances for Na-ion batteries are systematically investigated. A high reversible specific capacity of 240 mAh g1 at a current density of 100 mA g1 is attained and a specific capacity of 224 mAh g1 is remained even after 100 cycles. Remarkably, even at a high current density of 3.2 A g1, the reversible specific capacity of 104 mAh g1 can be observed. This excellent performance of NDPCs electrode may be ascribed to its superior structure, since the micropore/mesopore might efficiently shorten the diffusion distance of Na-ion and the enlarged interlayer spacing of 0.38 nm is significant for Na-ion insertion/extraction. Significantly, the approach to prepare carbon materials from PI may be generalized to other polymers. © 2017 Elsevier Ltd. All rights reserved.
1. Introduction Ever-increasing energy issues have still become a worldwide challenge, developing clean, renewable energy sources and energy storage devices are extremely urgent [1–3]. Thus, lithium-ion batteries (LIBs) have captured attention of world because of its high specific capacity and long lifetime in the past decades. Excitedly, tremendous progress on the research of LIBs has been achieved, which notably contributed to the rapid development of portable electronic devices and electronic vehicles [4–6]. However, the overall global concerns on reserves and cost of lithium resources increase with the expanding application of LIBs. Therefore, extensive efforts have been devoted to exploit alternatives of LIBs, and the focus was transferred to SIBs on account of the similar electrochemical principles with LIBs and abundant mineral of sodium [7–9]. Since the sodium ionic radius is larger than lithium’s counterpart, most of the electrode materials utilized in LIBs commonly displayed poor performances in SIBs [10,11]. Consequently, a great deal of explorations have been carried out to optimize the existed materials and explore novel anode materials
* Corresponding author. Tel.:+ +86 731 88879616; fax: +86 731 88879616. E-mail address: [email protected] (H. Hou). http://dx.doi.org/10.1016/j.electacta.2017.04.057 0013-4686/© 2017 Elsevier Ltd. All rights reserved.
for SIBs, so far series of achievements have been made on alloys, transition metal oxides, and carbon materials [12–16]. Because of their low-cost, high electric conductivity and abundant resources, carbon materials are considered to be the most promising electrode materials. For industrial application in SIBs, a string of carbon materials from different precursors, such as polymers, biomass carbons, and mineral carbons, have been prepared, and several of modifications, such as enlarging the interlayer spacing of graphite, heteroatom doping (for instance, N, S and P) have been made [17–22]. Hollow carbon nanowires were attained by the pyrolyzation of polyaniline nanowire and the insertion reaction of Na-ion was investigated. Excellent Na-ion insertion properties and a reversible capacity of 251 mAh g1 at a current of 50 mA g1 were delivered, which could be ascribed to the short diffusion distance in the hollow carbon nanowires [10]. Additionally, porous structure was also demonstrated as an effective approach to enhance electrochemical performances by the result that porous nitrogen doped carbon spheres showed a reversible capacity of 206 mAh g1 after 600 cycles at 0.2 A g1, which is much higher than the 96 mAh g1 of nonporous material [23]. PI, which can be obtained through the reaction of diamines and dianhydrides, are widely employed in membrane and filtration resulted from their stable thermal performance and high strength [24–26]. Recently, electrochemically active sites were detected in aromatic imide groups of polyimides and they have been applied in
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
the energy storage devices such as LIBs and supercapacitors [27– 29]. However, the way to prepare carbon materials from polyimides precursor has been rarely explored. For two-dimension (2D) carbon materials, 2D porous carbon nanosheets have been regarded as a potential anode material on account of their pore volume and higher specific surface area, which can supply more active sites for insertion/extraction reaction of Li/Na-ion and enable a good contact with electrolyte [11,30]. For instance, nitrogen doped porous carbon nanosheets were obtained by activating polypyrrole-functionalized graphene sheets with KOH. Benefited from the porous nanostructure, the electrodes exhibited excellent performance and a reversible capacity of 349.7 mAh g1 was achieved at a current density of 50 mA g1 even after 260 cycles [11]. Herein, N-doped porous carbon material with rose-like structure was prepared from the pyrolysis of PI and electrochemical performances were evaluated. Attributed to the heteroatom doping and superior structure, the NDPCs electrodes revealed outstanding cyclic stability and a high reversible specific capacity of 240 mAh g1 at the current density of 100 mA g1. Impressively, even at the current density of 3.2 A g1, a remarkable reversible capacity of 100.4 mAh g1 was remained. 2. Experimental section
was painted on copper foil and dried at 80 C under vacuum overnight as the anode. Na metal slice was used as reference electrode, the polypropylene film (Celgard 2400) as separator and an electrolyte solution of 1 M NaClO4 in propylene carbonate (PC) with a 5% (volume) fluoroethylene carbonate (FEC) additive. The CV measurements were conducted on Multi Autolab M204 electrochemical station in the voltage range of 0.01–3 V (vs. Na+/ Na). Galvanostatic cycling and rate tests were performed on an Arbin battery cycler in the voltage range of 0.01–3 V (vs. Na+/Na) at room temperature. 3. Results and discussion 3.1. Structure and compositions characterization XRD pattern of NDPCs is shown in Fig. 1a and two broad peaks concentrated at 23.5 and 44.0 were exposed, corresponding to the (002) and (101) diffraction peaks of graphitic structure. In addition, from the 2u = 23.5 of the (002) diffraction peak, the interlayer spacing of graphitic layer is calculated to be 0.38 nm utilized Bragg Equation, which is larger than the theoretical calculation result of the minimum interspace of 0.37 nm [10]. Furthermore, the low intensity of the two peaks illustrates the existence of disordered graphitic structure. Besides, the graphitic structure of PNDCs is
2.1. Synthesis of polyimide (PI) In a typical procedure, 1.84 g benzidine was dissolved into 60 mL of dimethylformamide (DMF) under magnetic stirring. After that, 3.22 g 5, 50 -carbonylbis (isobenzofuran-1, 3-dione) (BTDA) was added and continued stirring for 12 h at ambient temperature to acquire PAA solution. Then the PAA solution was shifted into an 80 ml Teflon-inner autoclave to undergo polymerization at 180 C for 10 h. After cooling to room temperature, the compound was collected by filtering and washed repeatedly with ethanol and subsequently was dried under vacuum at 90 C for 12 h, lastly the light yellow PI was obtained.
2.2. Preparation of the N-doped porous carbon (PNDCs) The PI was treated at 350 C for 1 h to further imidization in a horizontal furnace and kept at 900 C for another 2 h to carbonize under constant argon flow with a rate of 5 C/min. Afterwards the PNDCs were prepared.
2.3. Material characterization The structures and compositions were studied on XRD (Rigaku D/max 2550 VB+ 18 kW, Cu Ka radiation), XPS (K-Alpha 1063) and Raman (Jobin–Yvon Lab RAM HR-800). The Brunauer–Emmett– Teller (BET, BELSORP-MINI II) specific surface area was measured from the N2 adsorption/desorption isotherm recorded at 77 K. The morphologies were examined by Field-emission scanning electron microscopy (FESEM) (FEI Quanta 200) and Transmission electron microscopy (TEM) (JEM-2100F).
2.4. Electrochemical measurements The electrochemical performances were tested through cointype 2016 cells which were assembled in an argon filled glove box. The as-prepared PNDCs were mixed with carboxymethyl cellulose (CMC) binder and super C additive in a weight ratio of 70:15:15 to form homogenous slurry. Subsequently the homogenous slurry
25
Fig. 1. (a) XRD pattern and (b) Raman spectra of PDNCs.
26
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
further confirmed by Raman spectroscopy, as shown in Fig. 1b. Two broad peaks at 1347.7 and 1592.8 cm1 are clearly observed, which are related to the disordered D-band and graphitic G-band in the PNDCs [31]. The intensity ratio of the D-band to G-band is approximately 1.00, displaying the disordered graphitic structure of PNDCs, which is in good accordance with the results of XRD pattern. The BET specific surface area and the pore width distribution curves were determined by N2 adsorption-desorption isotherms of PNDCs. As exhibited in Fig. 2a, the isotherm can be classified to typical type IV isotherm with an obvious hysteresis loop, indicating the existence of microspores and mesopores. The rapid loop at low relative pressure implies the existence of microspores and the smooth loop displays the presence of mesopores. This result fits well with the pore width distribution curve of PNDCs presented in Fig. 2b. The pore sizes of PNDCs principally are centered at 1.2 nm and 4.1 nm and the total pore volume is 0.139 cm3 g1 obtained by DFT (density functional theory) method. Benefited from the abundant pore structure, the BET specific surface area of PNDCs reaches up to 215.7 m2 g1. Such resultants are constructive for Naion insertion/extraction since the porous structure can efficiently decrease the transport distance of Na-ion in electrodes and afford extra interspace for volume dilation during the charge and discharge [32]. To further identify the elements composition and content in PNDCs, XPS carried out was shown in Fig. 3a. There are three peaks in the survey spectra of PNDCs, specifying the existence of C, O and N types and the relative content percentage of C, O and N is 94.41%, 3.23% and 2.36% respectively. In order to detect the nature of N
Fig. 2. (a) N2 adsorption-desorption isotherm and (b) pore width distribution curve of PNDCs using DFT method.
species, the high resolution N1s can be fitted to four peaks: 403.2 eV, 401.1 eV, 399.6 eV and 398.4 eV, which are assigned to pyridinic N+- O, graphitic N, pyrrolic N and pyridinic N groups respectively [33]. Obviously, the four types of nitrogen were converted from the nitrogen atoms with pentagonal ring of PI during the carbonization treatment. 3.2. Morphology characterization The morphologies of as-prepared PI and PDNCs were observed by SEM and TEM images. As shown in Fig. 4(a–c), the PI mainly contains 3D rose-like structures with diameters about 2 mm which were derived from 2D nanosheets. Additionally, some 2D nanosheets failed to assemble into 3D structures still retained. The SEM images of NDPCs are presented in Fig. 4(d–f), displaying that the 3D structures of PI were maintained successfully after pyrolysis. Moreover, compared with PI, more homogeneous 3D rose-like structures and few 2D nanosheets were detected; suggesting that the PI assembled into 3D structure possesses superior stability in comparison with PI nanosheets which disintegrated largely during pyrolysis. TEM images further depict the morphologies and
Fig. 3. XPS spectra of the PNDCs: survey (a)and N1s (b).
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
27
Fig. 4. SEM images of the PI (a, b, c) and PNDCs (d, e, f). TEM images of the PNDCs (g, h, i, g).
structures of NDPCs. As shown in Fig. 4(g–j), highly graphitic structure was observed in the products and the interlayer spacing is 0.387 nm, agreeing well with the Raman spectra and the calculation based on the XRD of NDPCs. 3.3. Electrochemical performances The electrochemical performances of the as-prepared NDPCs as anode material for SIBs were investigated by the tests of a series of coin-type cells. Na-ion insertion/extraction behaviors in NDPCs were explored by CV and the typical CV curves at a scanning rate of 0.1 mV s1 from 0.01–3.00 V (vs Na+/Na) was shown in Fig. 5a. In the first negative sweep, two irreversible broad peak were observed at around 0.90 and 0.38 V, which can be attributed to the decomposition of the electrolyte, the reactions between sodium ion and surface functional groups,the formation of solid electrolyte interface (SEI) film and some other irreversible reactions [34–36]. In the following negative sweeps, two obvious peaks could be detected. The broad one between 0.8 and 0.5 V was mainly resulted from the charge transfer on the surface of small graphitic clusters and the sharp one around 0.01 V corresponding to the Na-ion insertion in the interlayer of the graphitic microcrystalline [10,37]. In the positive processes, one sharp peak at 0.2 V and another broad peak from 0.6 to 1.0 V corresponded to
the negative processes respectively. Additionally, the good overlap of CV curves after first cycle manifests excellent reversibility and cycle performance of the NDPCs electrode for Na-ion insertion/ extraction reaction. In order to further explore the nature of the electrochemistry process in the NDPCs/Na cell, kinetics analysis was conducted based on the CV curves at a variety of scan rates. As shown in Fig. 5b and c, CV curves at various scan rates from 0.1–50 mV s1 display similar shapes and the intensity of the oxidation and reduction peaks increases progressively with the increase of scan rate. Meanwhile the reduction potential is positive shift with the increase of scan rate. According to the correlation of the current (i) and the scan rate (v): i = avb
(1)
the b-value can indicate the dominant control process of the reaction. Accordingly, the b-value of 0.5 indicates a diffusioncontrol process while the b-value of 1 implies a capacitive process [38–40]. To determinate the value of b, the plot of log (v)-log (i) was carried out and the slope represents the b-value. As shown in Fig. 5d, the b-value of 0.54 can be reckoned according to the plot, which reveals a diffusion-control process, which is in good agreement with the CV curves and demonstrates the interlayer spacing of NDPCs is large enough for Na-ion insertion/extraction,
28
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
Fig. 5. Electrochemical characterization and performance of the NDCs as anode materials for SIBs. (a) CV curves of the PNDCs electrode in a range of 0.01–3.00 V (vs Na+/Na) as a scan rate of 0.10 mV s1. (b) CV curves at various scan rates, from 0.1-1.0 mV s1 in a range of 0.01–3.00 V. (c) CV curves at various scan rates of 2–50 mV s1 in a range of 0.01– 3.00 V. (d) Peak current as a function of root square of scan rate, V1/2 in the respective catholic processes.
consisting with the calculated value based on XRD and the measured value in TEM. Besides, this result can also match with the XPS date of NDPCs, since the tiny amounts of N content cannot enhance the pseudo capacitive significantly [36,41]. Fig. 6a displays the galvanostatic charge/discharge profiles of PNDCs electrodes at a current density of 100 mA g1. The initial capacity of discharge and charge are 350 mAh g1 and 150 mAh g1 respectively and the first coulombic efficiency is 42.8%. The vulgaris first coulumbic efficiency can be attributed to the larger specific surface area of NDPCs, which intensifies the formation of SEI film, the decomposition of electrolyte and some irreversible reactions among the functional groups [42–44]. In the first discharge curve, flat plateaus appear at around 0.9 and 0.4 V apart which can be attributed to the formation of SEI films and irreversible reactions. In the subsequent curves, two broad plateaus were observed close to 0.6 V and 0 V, corresponding to the charge transfer on the surface of small graphitic clusters and Na-ion insertion/extraction reaction in the interlayer of graphitic microcrystalline of NDPCs, agreeing well with the CV results. The cycling performance and coulombic efficiency of NDPCs electrode obtained at a current density of 100 mA g1 for 100 cycles is shown in Fig. 6b. The NDPCs electrode exhibits high specific capacity and good cycling performance. Even after 100 cycles, the remained reversible specific capacity can reach 224 mAh g1. Interestingly, the specific charge capacity increases gradually over
initial cycles, which can be ascribed to the activation progress [45]. In addition, the coulombic efficiency of the NDPCs electrode reached up to 97% after 6 cycles and remained beyond 98% after 15 cycles. The excellent cycling stability may be benefited from the porous structure of NDPCs, which can buffer the change in volume of NDPCs electrode. As an indispensable feature to evaluate electrochemical performances of electrode materials, the rate performance was tested at several current densities of 50, 100, 200, 400, 800, 1600 and 3200 mA g1. As depicted in Fig. 6c, the reversible specific capacities are 253.8, 239.4, 211.4, 175.8, 148.5, 126.7 and 104.1 mAh g1 respectively and the stable specific capacity can still recovery to 247.9 mAh g1 when the current density returns to 50 mA g1 which indicates the outstanding rate performance of NDPCs electrode. The porous rose-like structure play a crucial role in enhancing the electrochemical performance, since micropores/mesopores can supply active sites for insertion/ extraction reaction of Na-ion and enable a good contact with electrolyte and the high specific surface area gives rise to sufficient electrolyte/electrode interface to absorb Na-ion. 4. Conclusion NDPCs were prepared through carbonization of the as-prepared rose-like PI in-situ and the electrochemical performances of NDPCs electrode for SIBs were investigated in detailed. Benefited from the
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
29
Acknowledgment This work was financially supported by the National Postdoctoral Program for Innovative Talents (BX00192), National Natural Science Foundation of China (51622406, 21673298 and 21473258), Innovation Mover Program of Central South University (2016CX020, 2017CX004) and the Fundamental Research Funds for the Central Universities of Central South University (2016zzts022). References
Fig. 6. (a) Galvanostatic charge/discharge profiles of PNDCs electrodes at current density of 100 mA g1. (b) Cycle performance of PNDCs electrodes at current density of 100 mA g1. (c) Rate performance of PNDCs electrodes at various current densities (The cell was pre-cycled at 100 mA g1 for 10 cycles before the cycle performance).
special structure of NDPCs, the reversibility specific capacity of the NDPCs electrode is 224 mAh g1 after 100 cycles at the current density of 100 mA g1 and could persist 104.1 mAh g1 even at high current density of 3.2 A g1. The high specific capacity and good cycling performance of NDPCs electrode suggest that the nitrogendoped carbon materials derived from PI are promising anode alternative for SIBs. In addition, this work also introduces a new insight for the utilization of PI.
[1] X.X. Ning, Y. Wang, W. Qian, L.K. Ping, Advanced materials 24 (75) (2012) 76– 81. [2] B. Kang, G. Ceder, Nature 458 (2009) 190–193. [3] Y. Zhu, X. Ji, C. Pan, Q. Sun, W. Song, L. Fang, Q. Chen, C.E. Banks, Energy & Environmental Science 6 (2013) 3665–3675. [4] J. Liu, P. Kopold, P.A. van Aken, J. Maier, Y. Yu, Angewandte Chemie 54 (2015) 9632–9636. [5] C.K. Chan, H. Peng, G. Liu, K. Mcilwrath, X.F. Zhang, R.A. Huggins, Y. Cui, Nature Nanotechnology 3 (2008) 31–35. [6] Y. Yang, B. Qiao, X. Yang, L. Fang, C. Pan, W. Song, H. Hou, X. Ji, Advanced Functional Materials 24 (2014) 4349–4356. [7] S.W. Kim, D.H. Seo, X. Ma, G. Ceder, K. Kang, Advanced Energy Materials 2 (2012) 710–721. [8] D. Kundu, E. Talaie, V. Duffort, L.F. Nazar, Angewandte Chemie International Edition 54 (2015) 3431–3448. [9] Y. Zhang, C. Wang, H. Hou, G. Zou, X. Ji, Advanced Energy Materials (2016) 1600173. [10] Y. Cao, L. Xiao, M.L. Sushko, W. Wang, B. Schwenzer, J. Xiao, Z. Nie, L.V. Saraf, Z. Yang, J. Liu, Nano letters 12 (2012) 3783–3787. [11] H.G. Wang, Z. Wu, F.L. Meng, D.L. Ma, X.L. Huang, L.M. Wang, X.B. Zhang, ChemSusChem 6 (2013) 56–60. [12] Y. Zhang, C.W. Foster, C.E. Banks, L. Shao, H. Hou, G. Zou, J. Chen, Z. Huang, X. Ji, Advanced materials 28 (2016) 9391–9399. [13] J. Xu, M. Wang, N.P. Wickramaratne, M. Jaroniec, S. Dou, L. Dai, Advanced materials 27 (2015) 2042–2048. [14] B. Qu, C. Ma, G. Ji, C. Xu, J. Xu, Y.S. Meng, T. Wang, J.Y. Lee, Advanced materials 26 (2014) 3854–3859. [15] Y. Zhang, C.W. Foster, C.E. Banks, L. Shao, H. Hou, G. Zou, J. Chen, Z. Huang, X. Ji, Advanced materials 28 (2016) 9233–9233. [16] H. Hou, X. Qiu, W. Wei, Y. Zhang, X. Ji, Advanced Energy Materials (2017) 1602898. [17] T. Sun, Z.J. Li, H.G. Wang, D. Bao, F.L. Meng, X.B. Zhang, Angewandte Chemie International Edition 55 (2016) 10662–10666. [18] J. Ding, H. Wang, Z. Li, A. Kohandehghan, K. Cui, Z. Xu, B. Zahiri, X. Tan, E.M. Lotfabad, B.C. Olsen, Acs Nano 7 (2013) 11004–11015. [19] H. Hou, C.E. Banks, M. Jing, Y. Zhang, X. Ji, Advanced materials 27 (2015) 7861– 7866. [20] Y. Li, L. Mu, Y.S. Hu, H. Li, L. Chen, X. Huang, Energy Storage Materials 2 (2015) 139–145. [21] H. Hou, L. Shao, Y. Zhang, G. Zou, J. Chen, X. Ji, Advanced science 4 (2016) 1600243. [22] M. Wang, Y. Yang, Z. Yang, L. Gu, Q. Chen, Y. Yu, Advanced science (2017) 1600468. [23] D. Li, H. Chen, G. Liu, M. Wei, L.-x. Ding, S. Wang, H. Wang, Carbon 94 (2015) 888–894. [24] M. Ghosh, Polyimides: fundamentals and applications, CRC Press, 1996. [25] K. Vanherck, G. Koeckelberghs, I.F.J. Vankelecom, Progress in Polymer Science 38 (2013) 874–896. [26] P. Heikkilä, A. Taipale, M. Lehtimäki, A. Harlin, Polymer Engineering & Science 48 (2008) 1168–1176. [27] X. Han, C. Chang, L. Yuan, T. Sun, J. Sun, Advanced materials 19 (2007) 1616– 1621. [28] Z. Xu, X. Zhuang, C. Yang, J. Cao, Z. Yao, Y. Tang, J. Jiang, D. Wu, X. Feng, Advanced materials 28 (2016) 1981–1987. [29] Z. Song, H. Zhan, Y. Zhou, Angewandte Chemie 49 (2010) 8444–8448. [30] J. Hou, C. Cao, F. Idrees, X. Ma, Acs Nano 9 (2015) 2556. [31] G. Zou, X. Jia, Z. Huang, S. Li, H. Liao, H. Hou, L. Huang, X. Ji, Electrochimica Acta 196 (2016) 413–421. [32] Y. You, X.L. Wu, Y.X. Yin, Y.G. Guo, Energy & Environmental Science 7 (2014) 1643–1647. [33] Z. Wang, Y. Li, X.J. Lv, Rsc Advances 4 (2014) 62673–62677. [34] J.R. Dahn, T. Zheng, Y. Liu, J.S. Xue, Science 270 (1995) 590–593. [35] R. Alca’Ntara, P. Lavela, G.F. Ortiz, J.L. Tirado, Electrochemical & Solid State Letters 8 (2005) A222–A225. [36] L. Fu, K. Tang, K. Song, P.A. van Aken, Y. Yu, J. Maier, Nanoscale 6 (2014) 1384– 1389. [37] I. Mochida, C.H. Ku, Y. Korai, Carbon 39 (2001) 399–410. [38] C. Chen, Y. Wen, X. Hu, X. Ji, M. Yan, L. Mai, P. Hu, B. Shan, Y. Huang, Nature Communications 6 (2015) 6929. [39] S. Li, J. Qiu, C. Lai, M. Ling, H. Zhao, S. Zhang, Nano Energy 12 (2015) 224–230.
30
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
[40] H. Lindström, S. Södergren, A. Solbrand, H. Rensmo, J. Hjelm, A. Anders Hagfeldt, S.E. Lindquist, Journal of Physical Chemistry B 101 (1997) 7717– 7722. [41] F. Su, C.K. Poh, J.S. Chen, G. Xu, D. Wang, Q. Li, J. Lin, X.W. Lou, Energy & Environmental Science 4 (2011) 717–724. [42] Z. Wang, L. Qie, L. Yuan, W. Zhang, X. Hu, Y. Huang, Carbon 55 (2013) 328– 334.
[43] S. Komaba, W. Murata, T. Ishikawa, N. Yabuuchi, T. Ozeki, T. Nakayama, A. Ogata, K. Gotoh, K. Fujiwara, Advanced Functional Materials 21 (2011) 3859– 3867. [44] A. Ponrouch, E. Marchante, M. Courty, J.M. Tarascon, M.R. Palacín, Energy & Environmental Science 5 (2012) 8572–8583. [45] L. Qie, W.M. Chen, Z.H. Wang, Q.G. Shao, X. Li, L.X. Yuan, X.L. Hu, W.X. Zhang, Y. H. Huang, Advanced materials 24 (2012) 2047–2050.
Contents lists available at ScienceDirect
Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta
Rose-like N-doped Porous Carbon for Advanced Sodium Storage Ganggang Zhao, Guoqiang Zou, Xiaoqing Qiu, Sijie Li, Tianxiao Guo, Hongshuai Hou* , Xiaobo Ji College of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, China
A R T I C L E I N F O
Article history: Received 20 March 2017 Received in revised form 5 April 2017 Accepted 9 April 2017 Available online 14 April 2017 Keyword: electrochemistry N-doped carbon materials sodium-ion battery
A B S T R A C T
Carbon materials have been widely applied in the energy storage devices, however, the preparation of suitable carbon materials for sodium-ion batteries (SIBs) is still a challenge. In this paper, N-doped porous carbon material (NDPCs) with rose-like structure has been successfully prapared through pyrolysis of the as-prepared polyimides in-situ. The NDPCs shows rose-like structure derived from 2D nanosheets, an expanded interlayer distance of 0.387 nm, a high specific surface area of 215.7 m2 g1 and the electrochemical performances for Na-ion batteries are systematically investigated. A high reversible specific capacity of 240 mAh g1 at a current density of 100 mA g1 is attained and a specific capacity of 224 mAh g1 is remained even after 100 cycles. Remarkably, even at a high current density of 3.2 A g1, the reversible specific capacity of 104 mAh g1 can be observed. This excellent performance of NDPCs electrode may be ascribed to its superior structure, since the micropore/mesopore might efficiently shorten the diffusion distance of Na-ion and the enlarged interlayer spacing of 0.38 nm is significant for Na-ion insertion/extraction. Significantly, the approach to prepare carbon materials from PI may be generalized to other polymers. © 2017 Elsevier Ltd. All rights reserved.
1. Introduction Ever-increasing energy issues have still become a worldwide challenge, developing clean, renewable energy sources and energy storage devices are extremely urgent [1–3]. Thus, lithium-ion batteries (LIBs) have captured attention of world because of its high specific capacity and long lifetime in the past decades. Excitedly, tremendous progress on the research of LIBs has been achieved, which notably contributed to the rapid development of portable electronic devices and electronic vehicles [4–6]. However, the overall global concerns on reserves and cost of lithium resources increase with the expanding application of LIBs. Therefore, extensive efforts have been devoted to exploit alternatives of LIBs, and the focus was transferred to SIBs on account of the similar electrochemical principles with LIBs and abundant mineral of sodium [7–9]. Since the sodium ionic radius is larger than lithium’s counterpart, most of the electrode materials utilized in LIBs commonly displayed poor performances in SIBs [10,11]. Consequently, a great deal of explorations have been carried out to optimize the existed materials and explore novel anode materials
* Corresponding author. Tel.:+ +86 731 88879616; fax: +86 731 88879616. E-mail address: [email protected] (H. Hou). http://dx.doi.org/10.1016/j.electacta.2017.04.057 0013-4686/© 2017 Elsevier Ltd. All rights reserved.
for SIBs, so far series of achievements have been made on alloys, transition metal oxides, and carbon materials [12–16]. Because of their low-cost, high electric conductivity and abundant resources, carbon materials are considered to be the most promising electrode materials. For industrial application in SIBs, a string of carbon materials from different precursors, such as polymers, biomass carbons, and mineral carbons, have been prepared, and several of modifications, such as enlarging the interlayer spacing of graphite, heteroatom doping (for instance, N, S and P) have been made [17–22]. Hollow carbon nanowires were attained by the pyrolyzation of polyaniline nanowire and the insertion reaction of Na-ion was investigated. Excellent Na-ion insertion properties and a reversible capacity of 251 mAh g1 at a current of 50 mA g1 were delivered, which could be ascribed to the short diffusion distance in the hollow carbon nanowires [10]. Additionally, porous structure was also demonstrated as an effective approach to enhance electrochemical performances by the result that porous nitrogen doped carbon spheres showed a reversible capacity of 206 mAh g1 after 600 cycles at 0.2 A g1, which is much higher than the 96 mAh g1 of nonporous material [23]. PI, which can be obtained through the reaction of diamines and dianhydrides, are widely employed in membrane and filtration resulted from their stable thermal performance and high strength [24–26]. Recently, electrochemically active sites were detected in aromatic imide groups of polyimides and they have been applied in
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
the energy storage devices such as LIBs and supercapacitors [27– 29]. However, the way to prepare carbon materials from polyimides precursor has been rarely explored. For two-dimension (2D) carbon materials, 2D porous carbon nanosheets have been regarded as a potential anode material on account of their pore volume and higher specific surface area, which can supply more active sites for insertion/extraction reaction of Li/Na-ion and enable a good contact with electrolyte [11,30]. For instance, nitrogen doped porous carbon nanosheets were obtained by activating polypyrrole-functionalized graphene sheets with KOH. Benefited from the porous nanostructure, the electrodes exhibited excellent performance and a reversible capacity of 349.7 mAh g1 was achieved at a current density of 50 mA g1 even after 260 cycles [11]. Herein, N-doped porous carbon material with rose-like structure was prepared from the pyrolysis of PI and electrochemical performances were evaluated. Attributed to the heteroatom doping and superior structure, the NDPCs electrodes revealed outstanding cyclic stability and a high reversible specific capacity of 240 mAh g1 at the current density of 100 mA g1. Impressively, even at the current density of 3.2 A g1, a remarkable reversible capacity of 100.4 mAh g1 was remained. 2. Experimental section
was painted on copper foil and dried at 80 C under vacuum overnight as the anode. Na metal slice was used as reference electrode, the polypropylene film (Celgard 2400) as separator and an electrolyte solution of 1 M NaClO4 in propylene carbonate (PC) with a 5% (volume) fluoroethylene carbonate (FEC) additive. The CV measurements were conducted on Multi Autolab M204 electrochemical station in the voltage range of 0.01–3 V (vs. Na+/ Na). Galvanostatic cycling and rate tests were performed on an Arbin battery cycler in the voltage range of 0.01–3 V (vs. Na+/Na) at room temperature. 3. Results and discussion 3.1. Structure and compositions characterization XRD pattern of NDPCs is shown in Fig. 1a and two broad peaks concentrated at 23.5 and 44.0 were exposed, corresponding to the (002) and (101) diffraction peaks of graphitic structure. In addition, from the 2u = 23.5 of the (002) diffraction peak, the interlayer spacing of graphitic layer is calculated to be 0.38 nm utilized Bragg Equation, which is larger than the theoretical calculation result of the minimum interspace of 0.37 nm [10]. Furthermore, the low intensity of the two peaks illustrates the existence of disordered graphitic structure. Besides, the graphitic structure of PNDCs is
2.1. Synthesis of polyimide (PI) In a typical procedure, 1.84 g benzidine was dissolved into 60 mL of dimethylformamide (DMF) under magnetic stirring. After that, 3.22 g 5, 50 -carbonylbis (isobenzofuran-1, 3-dione) (BTDA) was added and continued stirring for 12 h at ambient temperature to acquire PAA solution. Then the PAA solution was shifted into an 80 ml Teflon-inner autoclave to undergo polymerization at 180 C for 10 h. After cooling to room temperature, the compound was collected by filtering and washed repeatedly with ethanol and subsequently was dried under vacuum at 90 C for 12 h, lastly the light yellow PI was obtained.
2.2. Preparation of the N-doped porous carbon (PNDCs) The PI was treated at 350 C for 1 h to further imidization in a horizontal furnace and kept at 900 C for another 2 h to carbonize under constant argon flow with a rate of 5 C/min. Afterwards the PNDCs were prepared.
2.3. Material characterization The structures and compositions were studied on XRD (Rigaku D/max 2550 VB+ 18 kW, Cu Ka radiation), XPS (K-Alpha 1063) and Raman (Jobin–Yvon Lab RAM HR-800). The Brunauer–Emmett– Teller (BET, BELSORP-MINI II) specific surface area was measured from the N2 adsorption/desorption isotherm recorded at 77 K. The morphologies were examined by Field-emission scanning electron microscopy (FESEM) (FEI Quanta 200) and Transmission electron microscopy (TEM) (JEM-2100F).
2.4. Electrochemical measurements The electrochemical performances were tested through cointype 2016 cells which were assembled in an argon filled glove box. The as-prepared PNDCs were mixed with carboxymethyl cellulose (CMC) binder and super C additive in a weight ratio of 70:15:15 to form homogenous slurry. Subsequently the homogenous slurry
25
Fig. 1. (a) XRD pattern and (b) Raman spectra of PDNCs.
26
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
further confirmed by Raman spectroscopy, as shown in Fig. 1b. Two broad peaks at 1347.7 and 1592.8 cm1 are clearly observed, which are related to the disordered D-band and graphitic G-band in the PNDCs [31]. The intensity ratio of the D-band to G-band is approximately 1.00, displaying the disordered graphitic structure of PNDCs, which is in good accordance with the results of XRD pattern. The BET specific surface area and the pore width distribution curves were determined by N2 adsorption-desorption isotherms of PNDCs. As exhibited in Fig. 2a, the isotherm can be classified to typical type IV isotherm with an obvious hysteresis loop, indicating the existence of microspores and mesopores. The rapid loop at low relative pressure implies the existence of microspores and the smooth loop displays the presence of mesopores. This result fits well with the pore width distribution curve of PNDCs presented in Fig. 2b. The pore sizes of PNDCs principally are centered at 1.2 nm and 4.1 nm and the total pore volume is 0.139 cm3 g1 obtained by DFT (density functional theory) method. Benefited from the abundant pore structure, the BET specific surface area of PNDCs reaches up to 215.7 m2 g1. Such resultants are constructive for Naion insertion/extraction since the porous structure can efficiently decrease the transport distance of Na-ion in electrodes and afford extra interspace for volume dilation during the charge and discharge [32]. To further identify the elements composition and content in PNDCs, XPS carried out was shown in Fig. 3a. There are three peaks in the survey spectra of PNDCs, specifying the existence of C, O and N types and the relative content percentage of C, O and N is 94.41%, 3.23% and 2.36% respectively. In order to detect the nature of N
Fig. 2. (a) N2 adsorption-desorption isotherm and (b) pore width distribution curve of PNDCs using DFT method.
species, the high resolution N1s can be fitted to four peaks: 403.2 eV, 401.1 eV, 399.6 eV and 398.4 eV, which are assigned to pyridinic N+- O, graphitic N, pyrrolic N and pyridinic N groups respectively [33]. Obviously, the four types of nitrogen were converted from the nitrogen atoms with pentagonal ring of PI during the carbonization treatment. 3.2. Morphology characterization The morphologies of as-prepared PI and PDNCs were observed by SEM and TEM images. As shown in Fig. 4(a–c), the PI mainly contains 3D rose-like structures with diameters about 2 mm which were derived from 2D nanosheets. Additionally, some 2D nanosheets failed to assemble into 3D structures still retained. The SEM images of NDPCs are presented in Fig. 4(d–f), displaying that the 3D structures of PI were maintained successfully after pyrolysis. Moreover, compared with PI, more homogeneous 3D rose-like structures and few 2D nanosheets were detected; suggesting that the PI assembled into 3D structure possesses superior stability in comparison with PI nanosheets which disintegrated largely during pyrolysis. TEM images further depict the morphologies and
Fig. 3. XPS spectra of the PNDCs: survey (a)and N1s (b).
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
27
Fig. 4. SEM images of the PI (a, b, c) and PNDCs (d, e, f). TEM images of the PNDCs (g, h, i, g).
structures of NDPCs. As shown in Fig. 4(g–j), highly graphitic structure was observed in the products and the interlayer spacing is 0.387 nm, agreeing well with the Raman spectra and the calculation based on the XRD of NDPCs. 3.3. Electrochemical performances The electrochemical performances of the as-prepared NDPCs as anode material for SIBs were investigated by the tests of a series of coin-type cells. Na-ion insertion/extraction behaviors in NDPCs were explored by CV and the typical CV curves at a scanning rate of 0.1 mV s1 from 0.01–3.00 V (vs Na+/Na) was shown in Fig. 5a. In the first negative sweep, two irreversible broad peak were observed at around 0.90 and 0.38 V, which can be attributed to the decomposition of the electrolyte, the reactions between sodium ion and surface functional groups,the formation of solid electrolyte interface (SEI) film and some other irreversible reactions [34–36]. In the following negative sweeps, two obvious peaks could be detected. The broad one between 0.8 and 0.5 V was mainly resulted from the charge transfer on the surface of small graphitic clusters and the sharp one around 0.01 V corresponding to the Na-ion insertion in the interlayer of the graphitic microcrystalline [10,37]. In the positive processes, one sharp peak at 0.2 V and another broad peak from 0.6 to 1.0 V corresponded to
the negative processes respectively. Additionally, the good overlap of CV curves after first cycle manifests excellent reversibility and cycle performance of the NDPCs electrode for Na-ion insertion/ extraction reaction. In order to further explore the nature of the electrochemistry process in the NDPCs/Na cell, kinetics analysis was conducted based on the CV curves at a variety of scan rates. As shown in Fig. 5b and c, CV curves at various scan rates from 0.1–50 mV s1 display similar shapes and the intensity of the oxidation and reduction peaks increases progressively with the increase of scan rate. Meanwhile the reduction potential is positive shift with the increase of scan rate. According to the correlation of the current (i) and the scan rate (v): i = avb
(1)
the b-value can indicate the dominant control process of the reaction. Accordingly, the b-value of 0.5 indicates a diffusioncontrol process while the b-value of 1 implies a capacitive process [38–40]. To determinate the value of b, the plot of log (v)-log (i) was carried out and the slope represents the b-value. As shown in Fig. 5d, the b-value of 0.54 can be reckoned according to the plot, which reveals a diffusion-control process, which is in good agreement with the CV curves and demonstrates the interlayer spacing of NDPCs is large enough for Na-ion insertion/extraction,
28
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
Fig. 5. Electrochemical characterization and performance of the NDCs as anode materials for SIBs. (a) CV curves of the PNDCs electrode in a range of 0.01–3.00 V (vs Na+/Na) as a scan rate of 0.10 mV s1. (b) CV curves at various scan rates, from 0.1-1.0 mV s1 in a range of 0.01–3.00 V. (c) CV curves at various scan rates of 2–50 mV s1 in a range of 0.01– 3.00 V. (d) Peak current as a function of root square of scan rate, V1/2 in the respective catholic processes.
consisting with the calculated value based on XRD and the measured value in TEM. Besides, this result can also match with the XPS date of NDPCs, since the tiny amounts of N content cannot enhance the pseudo capacitive significantly [36,41]. Fig. 6a displays the galvanostatic charge/discharge profiles of PNDCs electrodes at a current density of 100 mA g1. The initial capacity of discharge and charge are 350 mAh g1 and 150 mAh g1 respectively and the first coulombic efficiency is 42.8%. The vulgaris first coulumbic efficiency can be attributed to the larger specific surface area of NDPCs, which intensifies the formation of SEI film, the decomposition of electrolyte and some irreversible reactions among the functional groups [42–44]. In the first discharge curve, flat plateaus appear at around 0.9 and 0.4 V apart which can be attributed to the formation of SEI films and irreversible reactions. In the subsequent curves, two broad plateaus were observed close to 0.6 V and 0 V, corresponding to the charge transfer on the surface of small graphitic clusters and Na-ion insertion/extraction reaction in the interlayer of graphitic microcrystalline of NDPCs, agreeing well with the CV results. The cycling performance and coulombic efficiency of NDPCs electrode obtained at a current density of 100 mA g1 for 100 cycles is shown in Fig. 6b. The NDPCs electrode exhibits high specific capacity and good cycling performance. Even after 100 cycles, the remained reversible specific capacity can reach 224 mAh g1. Interestingly, the specific charge capacity increases gradually over
initial cycles, which can be ascribed to the activation progress [45]. In addition, the coulombic efficiency of the NDPCs electrode reached up to 97% after 6 cycles and remained beyond 98% after 15 cycles. The excellent cycling stability may be benefited from the porous structure of NDPCs, which can buffer the change in volume of NDPCs electrode. As an indispensable feature to evaluate electrochemical performances of electrode materials, the rate performance was tested at several current densities of 50, 100, 200, 400, 800, 1600 and 3200 mA g1. As depicted in Fig. 6c, the reversible specific capacities are 253.8, 239.4, 211.4, 175.8, 148.5, 126.7 and 104.1 mAh g1 respectively and the stable specific capacity can still recovery to 247.9 mAh g1 when the current density returns to 50 mA g1 which indicates the outstanding rate performance of NDPCs electrode. The porous rose-like structure play a crucial role in enhancing the electrochemical performance, since micropores/mesopores can supply active sites for insertion/ extraction reaction of Na-ion and enable a good contact with electrolyte and the high specific surface area gives rise to sufficient electrolyte/electrode interface to absorb Na-ion. 4. Conclusion NDPCs were prepared through carbonization of the as-prepared rose-like PI in-situ and the electrochemical performances of NDPCs electrode for SIBs were investigated in detailed. Benefited from the
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
29
Acknowledgment This work was financially supported by the National Postdoctoral Program for Innovative Talents (BX00192), National Natural Science Foundation of China (51622406, 21673298 and 21473258), Innovation Mover Program of Central South University (2016CX020, 2017CX004) and the Fundamental Research Funds for the Central Universities of Central South University (2016zzts022). References
Fig. 6. (a) Galvanostatic charge/discharge profiles of PNDCs electrodes at current density of 100 mA g1. (b) Cycle performance of PNDCs electrodes at current density of 100 mA g1. (c) Rate performance of PNDCs electrodes at various current densities (The cell was pre-cycled at 100 mA g1 for 10 cycles before the cycle performance).
special structure of NDPCs, the reversibility specific capacity of the NDPCs electrode is 224 mAh g1 after 100 cycles at the current density of 100 mA g1 and could persist 104.1 mAh g1 even at high current density of 3.2 A g1. The high specific capacity and good cycling performance of NDPCs electrode suggest that the nitrogendoped carbon materials derived from PI are promising anode alternative for SIBs. In addition, this work also introduces a new insight for the utilization of PI.
[1] X.X. Ning, Y. Wang, W. Qian, L.K. Ping, Advanced materials 24 (75) (2012) 76– 81. [2] B. Kang, G. Ceder, Nature 458 (2009) 190–193. [3] Y. Zhu, X. Ji, C. Pan, Q. Sun, W. Song, L. Fang, Q. Chen, C.E. Banks, Energy & Environmental Science 6 (2013) 3665–3675. [4] J. Liu, P. Kopold, P.A. van Aken, J. Maier, Y. Yu, Angewandte Chemie 54 (2015) 9632–9636. [5] C.K. Chan, H. Peng, G. Liu, K. Mcilwrath, X.F. Zhang, R.A. Huggins, Y. Cui, Nature Nanotechnology 3 (2008) 31–35. [6] Y. Yang, B. Qiao, X. Yang, L. Fang, C. Pan, W. Song, H. Hou, X. Ji, Advanced Functional Materials 24 (2014) 4349–4356. [7] S.W. Kim, D.H. Seo, X. Ma, G. Ceder, K. Kang, Advanced Energy Materials 2 (2012) 710–721. [8] D. Kundu, E. Talaie, V. Duffort, L.F. Nazar, Angewandte Chemie International Edition 54 (2015) 3431–3448. [9] Y. Zhang, C. Wang, H. Hou, G. Zou, X. Ji, Advanced Energy Materials (2016) 1600173. [10] Y. Cao, L. Xiao, M.L. Sushko, W. Wang, B. Schwenzer, J. Xiao, Z. Nie, L.V. Saraf, Z. Yang, J. Liu, Nano letters 12 (2012) 3783–3787. [11] H.G. Wang, Z. Wu, F.L. Meng, D.L. Ma, X.L. Huang, L.M. Wang, X.B. Zhang, ChemSusChem 6 (2013) 56–60. [12] Y. Zhang, C.W. Foster, C.E. Banks, L. Shao, H. Hou, G. Zou, J. Chen, Z. Huang, X. Ji, Advanced materials 28 (2016) 9391–9399. [13] J. Xu, M. Wang, N.P. Wickramaratne, M. Jaroniec, S. Dou, L. Dai, Advanced materials 27 (2015) 2042–2048. [14] B. Qu, C. Ma, G. Ji, C. Xu, J. Xu, Y.S. Meng, T. Wang, J.Y. Lee, Advanced materials 26 (2014) 3854–3859. [15] Y. Zhang, C.W. Foster, C.E. Banks, L. Shao, H. Hou, G. Zou, J. Chen, Z. Huang, X. Ji, Advanced materials 28 (2016) 9233–9233. [16] H. Hou, X. Qiu, W. Wei, Y. Zhang, X. Ji, Advanced Energy Materials (2017) 1602898. [17] T. Sun, Z.J. Li, H.G. Wang, D. Bao, F.L. Meng, X.B. Zhang, Angewandte Chemie International Edition 55 (2016) 10662–10666. [18] J. Ding, H. Wang, Z. Li, A. Kohandehghan, K. Cui, Z. Xu, B. Zahiri, X. Tan, E.M. Lotfabad, B.C. Olsen, Acs Nano 7 (2013) 11004–11015. [19] H. Hou, C.E. Banks, M. Jing, Y. Zhang, X. Ji, Advanced materials 27 (2015) 7861– 7866. [20] Y. Li, L. Mu, Y.S. Hu, H. Li, L. Chen, X. Huang, Energy Storage Materials 2 (2015) 139–145. [21] H. Hou, L. Shao, Y. Zhang, G. Zou, J. Chen, X. Ji, Advanced science 4 (2016) 1600243. [22] M. Wang, Y. Yang, Z. Yang, L. Gu, Q. Chen, Y. Yu, Advanced science (2017) 1600468. [23] D. Li, H. Chen, G. Liu, M. Wei, L.-x. Ding, S. Wang, H. Wang, Carbon 94 (2015) 888–894. [24] M. Ghosh, Polyimides: fundamentals and applications, CRC Press, 1996. [25] K. Vanherck, G. Koeckelberghs, I.F.J. Vankelecom, Progress in Polymer Science 38 (2013) 874–896. [26] P. Heikkilä, A. Taipale, M. Lehtimäki, A. Harlin, Polymer Engineering & Science 48 (2008) 1168–1176. [27] X. Han, C. Chang, L. Yuan, T. Sun, J. Sun, Advanced materials 19 (2007) 1616– 1621. [28] Z. Xu, X. Zhuang, C. Yang, J. Cao, Z. Yao, Y. Tang, J. Jiang, D. Wu, X. Feng, Advanced materials 28 (2016) 1981–1987. [29] Z. Song, H. Zhan, Y. Zhou, Angewandte Chemie 49 (2010) 8444–8448. [30] J. Hou, C. Cao, F. Idrees, X. Ma, Acs Nano 9 (2015) 2556. [31] G. Zou, X. Jia, Z. Huang, S. Li, H. Liao, H. Hou, L. Huang, X. Ji, Electrochimica Acta 196 (2016) 413–421. [32] Y. You, X.L. Wu, Y.X. Yin, Y.G. Guo, Energy & Environmental Science 7 (2014) 1643–1647. [33] Z. Wang, Y. Li, X.J. Lv, Rsc Advances 4 (2014) 62673–62677. [34] J.R. Dahn, T. Zheng, Y. Liu, J.S. Xue, Science 270 (1995) 590–593. [35] R. Alca’Ntara, P. Lavela, G.F. Ortiz, J.L. Tirado, Electrochemical & Solid State Letters 8 (2005) A222–A225. [36] L. Fu, K. Tang, K. Song, P.A. van Aken, Y. Yu, J. Maier, Nanoscale 6 (2014) 1384– 1389. [37] I. Mochida, C.H. Ku, Y. Korai, Carbon 39 (2001) 399–410. [38] C. Chen, Y. Wen, X. Hu, X. Ji, M. Yan, L. Mai, P. Hu, B. Shan, Y. Huang, Nature Communications 6 (2015) 6929. [39] S. Li, J. Qiu, C. Lai, M. Ling, H. Zhao, S. Zhang, Nano Energy 12 (2015) 224–230.
30
G. Zhao et al. / Electrochimica Acta 240 (2017) 24–30
[40] H. Lindström, S. Södergren, A. Solbrand, H. Rensmo, J. Hjelm, A. Anders Hagfeldt, S.E. Lindquist, Journal of Physical Chemistry B 101 (1997) 7717– 7722. [41] F. Su, C.K. Poh, J.S. Chen, G. Xu, D. Wang, Q. Li, J. Lin, X.W. Lou, Energy & Environmental Science 4 (2011) 717–724. [42] Z. Wang, L. Qie, L. Yuan, W. Zhang, X. Hu, Y. Huang, Carbon 55 (2013) 328– 334.
[43] S. Komaba, W. Murata, T. Ishikawa, N. Yabuuchi, T. Ozeki, T. Nakayama, A. Ogata, K. Gotoh, K. Fujiwara, Advanced Functional Materials 21 (2011) 3859– 3867. [44] A. Ponrouch, E. Marchante, M. Courty, J.M. Tarascon, M.R. Palacín, Energy & Environmental Science 5 (2012) 8572–8583. [45] L. Qie, W.M. Chen, Z.H. Wang, Q.G. Shao, X. Li, L.X. Yuan, X.L. Hu, W.X. Zhang, Y. H. Huang, Advanced materials 24 (2012) 2047–2050.