Cobalt-based metal organic framework with superior lithium anodic performance

Author’s Accepted Manuscript Cobalt-based metal organic framework with superior lithium anodic performance Xiaoshi Hu, Huiping Hu, Chao Li, Tian Li, Xiaobing Lou, Qun Chen, Bingwen Hu www.elsevier.com/locate/yjssc

PII: DOI: Reference:

S0022-4596(16)30281-X http://dx.doi.org/10.1016/j.jssc.2016.07.021 YJSSC19468

To appear in: Journal of Solid State Chemistry Received date: 1 April 2016 Revised date: 18 July 2016 Accepted date: 19 July 2016 Cite this article as: Xiaoshi Hu, Huiping Hu, Chao Li, Tian Li, Xiaobing Lou, Qun Chen and Bingwen Hu, Cobalt-based metal organic framework with superior lithium anodic performance, Journal of Solid State Chemistry, http://dx.doi.org/10.1016/j.jssc.2016.07.021 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 galley proof before it is published in its final citable 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.

Cobalt-based metal organic framework with superior lithium anodic performance Xiaoshi Hu1, Huiping Hu, Chao Li, Tian Li, Xiaobing Lou, Qun Chen, Bingwen Hu* School of Physics and Materials Science, Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai 200062, PR China. [email protected] *

Corresponding author.

ABSTRACT: The reversible charging of a Co-1,4-benzenedicarboxylate MOF (Co-BDC MOF) prepared via an one-pot solvothermal method was studied for use as the anode in a Li-ion cell. It was found that this MOF anode provides high reversible capacities (1090 and 611 mAh g−1 at current densities of 0.2 and 1 A g-1, respectively), and an impressive rate performance. Such an outstanding Li-ion storage property has not been reported previously for the LIB anodes within the MOFs category. Ex-situ X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) studies of this material at different state of charge suggest that cobalt stays at Co2+ state during discharge/charge process, so that in this case Li + may be inserted into the organic moiety without the direct participation of cobalt ions.

1

Equal Contributions. 1

Graphical abstract Co-1,4-benzenedicarboxylate MOF, synthesized through a straightforward solvothermal method, shows outstanding lithium storage performance.

Keywords: Metal organic frameworks, Cobalt, Benzenedicarboxylate, Lithium-ion battery, Anode

1. Introduction Although the performance of lithium-ion batteries (LIBs) has been steadily improved for several decades, their energy density and lifespan remain insufficient for future applications in grid-scale energy storage, portable electronic devices, and hybrid electric vehicles [1-5]. Recent efforts in this realm have focused on high-capacity electrode materials such as alloys, metal oxides, or transition-metal dichalcogenide as anodes, and monoclinic Li3V2(PO4)3 as cathodes [6-13]. Metal organic frameworks (MOFs) or porous coordination polymers (PCPs) constructed

2

from the bonding of metal ions and polyfunctional organic ligands have garnered considerable attentions over the past decade due to their diverse applications, such as in gas storage and separation, catalysis, electron and proton conductivity [14-20]. This structural tunability of MOFs enables us to control their physical properties like particle size, pore size distribution, active specific surface area, and crystallinity by selecting suitable metal ions and organic moieties. Particularly, the electrochemical properties of MOFs, such as electrolyte accessibility and diffusion rates, are expected to affect the insertion/extraction of Li+; hence, it is not astonishing that MOFs, with their specific topologies, are being emerged as promising electrode materials in LIBs in recent years [21-23]. In 2007, Tarascon et al. firstly reported FeIII(OH)0.8F0.2(BDC)·H2O (MIL-53(Fe)), a MOF with higher oxidation state metal, as a cathode material successfully [24]. Since then, a growing number of MOFs have been investigated either as a cathode or as an anode material. A series of formate-based MOFs Zn3(HCOO)6, Co3(HCOO)6 and Zn1.5Co1.5(HCOO)6 were used as anode materials for lithium storage through conversion reaction, and the capacities of these compounds maintained at 560, 410 and 510 mAh g-1 at a current rate of 60 mA g-1 after 60 cycles, respectively [25]. 2,6-Naph-(COOLi)2 also showed superior lithium storage performance, which can retain a reversible capacity of ~210 mAh g-1 at 1C (C= 220 mA g-1) within a voltage window of 0.5−2.0 V [26]. More recently, Zn(IM)1.5(abIM)0.5 (IM=imidazole, abIM=2-aminobenzimidazole), a new functionalized MOF with remarkable thermal

3

and chemical stability has been synthesized. The functionalized pores in MOF result in a good lithium storage capacity with high coulombic efficiency [27]. These stimulating researches demonstrate the potential of MOFs as LIB electrodes, however, these MOFs electrode materials, with either the restricted reversible capacity or the deficient rate performance, are not satisfactory for future applications [28-35]. In order to develop novel MOF electrode materials, we focus our attention on 1,4-benzenedicarboxylate based MOFs because terephthalic acid (H2BDC), with carboxylate functional groups as nucleation sites, has constructed many MOFs architectures that could provide affluent candidates for continuous development [17, 36]. Furthermore, H2BDC is available in abundance from the recycling of polyethylene terephthalate and the metabolites of aromatic hydrocarbon oxidation, meeting the requirement of future mass production [37]. In this work, we have synthesized a Co-1,4-benzenedicarboxylate MOF (referred as Co-BDC MOF) by a straightforward

solvothermal

process

and

investigated

its

electrochemical

performance as LIB anode for the first time. The cell tests exhibited outstanding reversible capacities of 1090 and 611 mAh g−1 at current densities of 200 and 1000 mA g-1 within a cutoff voltage window of 0.01−3.0 V (vs. Li+/Li), as well as superior rate performance. As far as we know, such an outstanding Li-ion storage property has not been reported previously for the LIB anodes within the MOFs category.

2. Experimental Details Materials Synthesis

4

All chemicals and solvents were purchased from commercial suppliers and used as received. The cobalt-based Co-BDC MOF was synthesized through a simple solvothermal method [36]. Typically, Co(NO3)2·6H2O (0.75g, 2.577 mmol) and terephtalic acid (0.428 g, 2.577 mmol) were firstly dissolved in 24 mL N,N-dimethylformamide (DMF) and 6 mL absolute ethyl alcohol (EtOH). After magnetic stirring to obtain a settled solution, the solution was transferred into a 50 mL Teflon-lined high pressure autoclave. The autoclave was then placed in an oven at 105 C for 20 h. After cooling down to room temperature in a fume hood, the resultant crystalline material was collected by removing the mother liquor, followed by rinsing thoroughly with EtOH. The purple powder of Co-BDC MOF was finally obtained after drying in vacuum at 110 C for 12 h. Materials Characterizations Fourier transform infrared spectroscopy (FT-IR) spectra were recorded on a Nicolet-Nexus 670 infrared spectrometer within a wavenumber range of 400-4000 cm-1. Powder X-ray diffraction (PXRD) patterns were collected using a Holland Panalytical PRO PW3040/60 Diffractometer with high-density Cu-Kα radiation (V = 35kV, I = 25 mA, λ=1.5418 Å) in the range 2θCuKα = 5°–50° with a step size of 0.01°, scan size per minutes of 0.1°. Thermogravimetric analysis (TGA) was carried out by using STA 449 F3 Jupiter® simultaneous thermo-analyzer at a ramping rate 10 ℃/min from room temperature to 800 ℃ under nitrogen atmosphere. X-ray photoelectron spectroscopy (XPS) measurements were performed on a Perkin-Elmer PHI 5000C

5

ESCA spectrometer operating at 250W (Al-Kα radiation=1486.6 eV, pass energy=93.9 eV). Field emission scanning electron microscope (FESEM) images were recorded using an S-4800 (HITACHI, Japan) operating at 10 kV, 100 µA. The nitrogen adsorption isotherm was measured at 77 K with an ASAP 2020 Accelerated Surface Area and Porosimetry System (Microeritics, Norcross, GA), the specific surface area was calculated by the Brunauer–Emmett–Teller (BET) method, and the corresponding pore size distribution was determined by Barrett-Joyner-Halenda (BJH) method using the desorption part. Battery Performance Measurements The electrochemical properties were evaluated by assembly of CR2032 coin cells in an argon filled glovebox with oxygen and water content below 1 ppm. The working electrode was prepared by mixing the active materials, acetylene black (conducting additive), and polyacrylic acid (binder) at a weight ratio of 70:20:10. The slurry was then casted onto a piece of Cu foil and dried under a vacuum oven at 110 °C for at least 12 h. The loading of active materials was about 2.0 mg cm−2. Lithium pellets were used as the counter/reference electrode. The electrolyte was composed of 1 M LiPF6 dissolved in ethylene carbonate (EC)/ diethyl carbonate (DEC)/ dimethyl carbonate (DMC) (1:1:1 vol %). Galvanostatic discharge/charge cycling was recorded within a voltage window of 0.01−3.0 V (vs. Li/Li+) with a multichannel battery cycler (LAND CT2001A). All the specific capacities were calculated based on the mass of Co-BDC. Cyclic voltammetric (CV) measurement was conducted using an

6

electrochemical workstation (CHI 660a) at a scan rate of 0.2 mV s-1. Electrochemical impedance spectra (EIS) were also carried out on a CHI 660a electrochemical workstation within the frequency range of 104 Hz-10-2 Hz.

3. Results and Discussion The Co-BDC MOF in this work was synthesized through a simple solvothermal method. The reaction conditions such as temperature, solvent, reaction time and cooling rate play a dominant role in the morphologies and dimensions of MOFs, thus affecting their lithium storage ability. Based on this consideration, the synthesis process must be rigidly controlled (as can be seen in the experimental section). Figure 1a presents the FT-IR spectrum of the as-synthesized Co-BDC MOF, and the corresponding FT-IR spectrum for 1,4-H2BDC is also shown for comparison. The complete deprotonation of 1,4-H2BDC upon reaction with Co2+ is confirmed by the disappearance of the characteristic bands of the nonionized carboxyl groups (νC=O, 1684 cm-1). The new bands arise in the regions of 1672-1508 cm-1 can be ascribed to the asymmetric stretching vibrations of carboxylate groups, while the bands in the regions of 1444-1375 cm-1 can be ascribed to the asymmetric stretching vibrations of carboxylate groups. These new bands demonstrate that Co2+ ions have coordinated with the 1,4-H2BDC ligands successfully. The PXRD patterns of Co-BDC are shown in Figure 1b. The intensive and sharp peaks indicate a well-crystallized MOF structure. The crystalline structure remains unknown, but it might be similar to MOF-71 (Figure S1) with its simulated PXRD pattern in Figure S2. TGA for

7

Co-BDC (Figure 1c) shows that weight loss begins at 226 ℃, indicating the framework of Co-BDC is stable below 226 ℃. Weight loss from 226 to 310 ℃ corresponds to the removal of coordinated DMF molecules, and another weight loss between 435 and 585 ℃ is ascribed to the totally decomposition of the MOF structure, while the residual materials are converted into Co3O4. According to the amount of solvent lost during heating, the molecular formula of the present material was estimated to be Co(1,4-BDC)(DMF)0.61. Figure 1d presents the high-resolution Co 2p XPS spectrum of the as-synthesized Co-BDC MOF. It is observed that two distinct peaks appear at binding energies of 781.54 eV for Co 2p 3/2 and 797.49 eV for Co 2p 1/2, respectively, along with two pronounced satellite peaks (786.44 eV and 803.11 eV) beside them, which prove that Co ions are predominantly in the Co2+ state. Morphology and microstructure of the as-prepared Co-BDC MOF were investigated through FESEM. Figure 2a shows a low magnification FESEM image of Co-BDC, from which we can see a large quantity of shale-shaped microcrystals with coarse surface. The magnified FESEM image in Figure 2b further confirms that the shale-shaped crystals have a two-dimensional layered architecture which contains irregular walls. Such laminar architecture might lead to improved electrolyte accessibility by forming ion-buffering reservoir, thus reducing the Li+ diffusion length to the interior surfaces. The elemental distribution of the material was further characterized by energy-dispersive X-ray spectroscopy (EDS, Figure S3a), where Co, C, O, and N elements are found to be incorporated within the microcrystals.

8

Furthermore, EDS elemental maps of Co, C, O and N (Figure S3b) clearly confirm the relatively homogeneous dispersion of the four elements in the Co-BDC particles. The porosity of the as-synthesized Co-BDC MOF was characterized by measuring nitrogen adsorption-desorption isotherms at 77 K. As depicted in Figure 3a, Co-BDC shows typical type IV isotherms with a hysteresis loop, indicating its mesoporous feature. In addition, Co-BDC also has a wide pore-size distribution from 3 nm to 50 nm (Figure 3b), suggesting the coexistence of structural pores as well as interparticle pores. Specific surface area of Co-BDC is calculated to be 21.7 m2 g-1 by BET method, which is much lower than traditional MOFs with an extremely high specific area. An ultra-high specific surface of the electrode materials often lead to superfluous side reactions with the electrolyte, especially at low potentials (vs. Li/Li+) and thus cause the LIB performance to deteriorate [21]. For this reason, a low BET specific surface area of the as-synthesized Co-BDC MOF may be beneficial. To evaluate the electrochemical performance of the as-synthesized Co-BDC MOF for Li-ion storage, lithium metal foils were used as both the counter and reference electrodes. The electrochemical data of Co-BDC were obtained using polyacrylic acid (PAA) binder. Cyclic voltammetry (CV) was tested for 4 cycles at a scan rate of 0.2 mV s-1 within the potential window of 3.0-0.01 V vs. Li/Li+. As depicted in Figure 4a, the CV curve of the first cycle is quite different from those of the subsequent cycles, particularly for the discharge branches. A broad peak centered at 0.60 V is observed in the first cathodic scan, this peak is slightly shifted to the positive direction (~0.75V)

9

in the subsequent scans, which might be related to some activation processes for the Li-ion insertion during the first cycle [38]. In the first anodic scan, a broad peak located at ~1.25 V is observed, which deconvolutes into two broad peaks centered at 1.25 and 1.89 V in the subsequent cycles. Moreover, all the other peaks after the initial scan are perfectly overlapped, suggesting that similar reactions are occurring during the charge/discharge processes and the formation of a stable solid electrolyte interface (SEI) layer. To learn about the Li-storage mechanism of Co-BDC MOF, ex-situ FT-IR and XPS measurements of the anodes were conducted at the fully discharged state (0.01 V) and charged state (3.0 V). The FTIR results (Figure 5a) indicates absence of Co(0) in the discharged condition or CoO/Co3O4 in the charged condition. In addition, identical XPS spectra are observed for the fully discharged state and charged state (Figure 5b), the nearly unchanged binding energy positions of the peaks and the well-resolved satellite peaks compared with the pristine sample (Figure 1d) clearly demonstrate the presence of cobalt in the Co2+ state during discharge/charge process. Thus, in our case, Li-ions are inserted into the organic moiety without the direct participation of cobalt ions, similar to the insertion mechanism proposed by Mahanty et al. (Scheme 1) [28]. Therefore, the observed reduction peak (~0.75 V) could tentatively be ascribed to the insertion of Li-ions to the organic moiety, while the observed anodic peaks at ~1.25 V and ~1.89 V could be probably attributed to reversible Li-ions deinsertion from the carboxylate moieties and the benzene ring, respectively (or vice versa). However, the involvement of

10

carboxylate group is not so evident from Figure 5a. Figure 4b shows the galvanostatic charge/discharge profiles of the as-prepared Co-BDC samples for different cycles within the potential window of 3.0-0.01 V vs. Li/Li+ and at a current density of 100 mA g−1. In the first cycle, an obvious potential plateau at ~0.85 V and a gradual slope from 0.65 to 0.01 V were observed for the first discharge profile, which was replaced by the slope from 0.80 V to 0.01 V in the subsequent cycles. The initial discharge and charge capacities of Co-BDC are 1963.6 and 780.6 mA h g−1, respectively. The relatively low Coulombic efficiency of 39.75% may be caused by the occurrence of side reactions on the electrode surfaces and interfaces due to SEI layer formation [39-41]. After 20 cycles, the Co-BDC still exhibits a discharge capacity of 1002.2 mAh g−1, much higher than the electrode prepared by the conventional PVDF binder (507.1 mAh g−1, as can be seen in Figure S4). PAA is anticipated to enhance the anodic performance of MOFs-based materials due to thermally cross-linked three-dimensional interconnection of this binder [42]. The specific capacity of the Co-BDC anode versus cycle number was evaluated over a voltage range of 3.0-0.01 V vs. Li/Li+ under 200 mA g-1. As depicted in Figure 4c, the Co-BDC MOF shows an excellent cyclic stability with high reversible capacity. Even after 100 cycles, the electrode still maintained a discharge capacity of 1090.2 mAh g-1, which is approximately 70.7% of the initial discharge capacity (1542.2 mAh g-1). The increase of the specific capacity during unremitting cycles may partly be attributed to the reversible growth of a polymeric gel-like layer resulting

11

from kinetically activated electrolyte degradation [40, 43, 44]. More detailed investigation of such a high specific capacity is in progress. It should be highlighted here that such a high reversible capacity has never been reported previously for the MOFs-based anode materials. Furthermore, the average Coulombic efficiency for cycles from the 3rd to 100th is 99.46%, and the nearly 100% Coulombic efficiency implies the stability of the SEI film and minimal side reactions [45-47]. The rate performance of the Co-BDC electrode was measured at various current densities, as illustrated in Figure 4d. With the gradually increase of current densities from 100 to 2000 mA g-1, the Co-BDC electrode shows discharge capacities of ~1180, ~1046, ~885, ~592, and ~345 mAh g-1 at current densities of 100, 200, 400, 1000, and 2000 mA g-1, respectively. More importantly, over 1010 mA h g-1 can be recovered when the rate was switched back to 100 mA g-1 again, demonstrating the robustness of the MOF structure in response to abrupt current changes. Such outstanding cycling and rate performances demonstrate that the as-prepared Co-BDC MOF has a great potential as a promising anode material for LIBs. High-rate charge/discharge performance is an important factor for futuristic anode materials. In this case, the Co-BDC MOF electrode was also cycled at larger current densities to investigate the long-life performance. As shown in Figure 4e, the Co-BDC electrode maintained a discharge capacity of 795 mAh g-1 at 500 mA g-1 and 611 mAh g-1 at 1 A g-1 after 200 cycles while maintaining a nearly 100% Coulombic efficiency. The capacity retention remains 96.8% after 200 cycles at 500 mA g-1

12

(capacity retention = final specific capacity/the highest specific capacity during cycling). Such cycling stability at high charge/discharge rates of Co-BDC MOF are significantly better than in previously reported works on MOFs-based anode materials (Table S1). Figure 4f displays the EIS spectra of the Co-BDC electrode at different cycles. The semicircle in the high-frequency range corresponds to the charge-transfer resistance (Rct) caused by the Faradic reaction, which was correlated with the intercalation and deintercalation of cations [39, 48]. The Rct are relatively small and nearly unchanged with cycling, indicating a fast solid-state Li+ diffusion rate and limited growth of SEI layers during cycling process.

4. Conclusion In summary, we have synthesized a Co-1,4-benzenedicarboxylate MOF by an one-pot solvothermal method and investigated lithium anodic performance for the first time. This cell tests exhibited outstanding reversible capacities of 1090 and 611 mAh g−1 at current densities of 200 and 1000 mA g-1 within a cutoff voltage window of 0.01−3.0 V (vs. Li+/Li), along with an impressive rate performance. To the best of our knowledge, such an outstanding Li-ion storage property has not been reported previously for the LIB anodes within the MOFs category. Ex-situ FT-IR and XPS studies of this material at the fully discharged state (0.01 V) and charged state (3.0 V) suggest that cobalt stays at Co2+ during discharge/charge process, so that Li ions may be inserted into the organic moiety (including the benzene ring and the carboxylate

13

moieties) without the direct participation of cobalt ions. More detailed studies of the lithium storage mechanism are still in progress.

Acknowledgements This work was supported by National Natural Science Foundation of China for Excellent Young Scholars (21522303), National Natural Science Foundation of China (21373086), Large Instruments Open Foundation of East China Normal University, Basic Research Project of Shanghai Science and Technology Committee (No. 14JC1491000), National Key Basic Research Program of China (2013CB921800), and National High Technology Research and Development Program of China (Grant No. 2014AA123401).

References [1] J. Cabana, L. Monconduit, D. Larcher, M. R. Palacín, Adv. Mater. 22 (2010) E170. [2] F. Cheng, J. Liang, Z. Tao, J. Chen, Adv. Mater. 23 (2011) 1695. [3] J. B. Goodenough, Y. Kim, Chem. Mater. 22 (2010) 587. [4] N. Nitta, F. Wu, J. T. Lee, G. Yushin, Mater. Today 18 (2015) 252. [5] D. Larcher, J. Tarascon, Nat. Chem. 7 (2014) 19. [6] L. Shen, Q. Che, H. Li, X. Zhang, Adv. Funct. Mater. 24 (2014) 2630. [7] X. Xiao, W. Zhou, Y. Kim, I. Ryu, M. Gu, C. Wang, G. Liu, Z. Liu, H. Gao, Adv. Funct. Mater. 25 (2015) 1426. [8] J. Bai, X. Li, G. Liu, Y. Qian, S. Xiong, Adv. Funct. Mater. 24 (2014) 3012.

14

[9] P. Chen, Y. Su, H. Liu, Y. Wang, ACS Appl. Mater. Interfaces 5 (2013) 12073. [10] T. Zhou, W. K. Pang, C. Zhang, J. Yang, Z. Chen, H. K. Liu, Z. Guo, ACS Nano 8 (2014) 8323. [11] X. Cao, B. Zheng, X. Rui, W. Shi, Q. Yan, H. Zhang, Angew. Chem. Int. Ed. 53 (2014) 1404. [12] X. Rui, Q. Yan, M. Skyllas-Kazacos, T. M. Lim, J. Power Sources 258 (2014) 19. [13] L. Zhang, G. Liang, G. Peng, F. Zou, Y. Huang, M. C. Croft, A. Ignatov, The Journal of Physical Chemistry C 116 (2012) 12401. [14] N. L. Rosi, J. Eckert, M. Eddaoudi, D. T. Vodak, J. Kim, M. O'Keeffe, O. M. Yaghi, Science 300 (2003) 1127. [15] H. Furukawa, N. Ko, Y. B. Go, N. Aratani, S. B. Choi, E. Choi, A. O. Yazaydin, R. Q. Snurr, M. O'Keeffe, J. Kim, O. M. Yaghi, Science 329 (2010) 424. [16] R. Banerjee, A. Phan, B. Wang, C. Konbler, H. Furukawa, M. O'Keeffe, O. M. Yaghi, Science 319 (2008) 939. [17] H. Deng, C. J. Doonan, H. Furukawa, R. B. Ferreira, J. Towne, C. B. Knobler, B. Wang, O. M. Yaghi, Science 327 (2010) 846. [18] A. Shigematsu, T. Yamada, H. Kitagawa, J. Am. Chem. Soc. 133 (2011) 2034. [19] S. Bureekaew, S. Horike, M. Higuchi, M. Mizuno, T. Kawamura, D. Tanaka, N. Yanai, S. Kitagawa, Nat. Mater. 8 (2009) 831. [20] S. L. James, Chem. Soc. Rev. 32 (2003) 276.

15

[21] W. Xia, A. Mahmood, R. Zou, Q. Xu, Energy Environ. Sci. 8 (2015) 1837. [22] L. Shun-Li, Q. Xu, Energy Environ. Sci. 6 (2013) 1656. [23] A. Morozan, F. Jaouen, Energy Environ. Sci. 5 (2012) 9269. [24] G. Férey, F. Millange, M. Morcrette, C. Serre, M. Doublet, J. Grenèche, J. Tarascon, Angew. Chem. Int. Ed. 119 (2007) 3323. [25] K. Saravanan, M. Nagarathinam, P. Balaya, J. J. Vittal, J. Mater. Chem. 20 (2010) 8329. [26] N. Ogihara, T. Yasuda, Y. Kishida, T. Ohsuna, K. Miyamoto, N. Ohba, Angew. Chem. Int. Ed. 53 (2014) 11467. [27] Y. Lin, Q. Zhang, C. Zhao, H. Li, C. Kong, C. Shen, L. Chen, Chem. Commun. 51 (2015) 697. [28] S. Maiti, A. Pramanik, U. Manju, S. Mahanty, ACS Appl. Mater. Interfaces 7 (2015) 16357. [29] X. Han, F. Yi, T. Sun, J. Sun, Electrochem. Commun. 25 (2012) 136. [30] Q. Liu, L. Yu, Y. Wang, Y. Ji, J. Horvat, M. Cheng, X. Jia, G. Wang, Inorg. Chem. 52 (2013) 2817. [31] L. Gou, H. Zhang, X. Fan, D. Li, Inorg. Chim. Acta 394 (2013) 10. [32] T. An, Y. Wang, J. Tang, Y. Wang, L. Zhang, G. Zheng, J. Colloid Interf. Sci. 445 (2015) 320. [33] X. Li, F. Cheng, S. Zhang, J. Chen, J. Power Sources 160 (2006) 542.

16

[34] R. Fernández De Luis, A. Ponrouch, M. Rosa Palacín, M. Karmele Urtiaga, M. I. Arriortua, J. Solid State Chem. 212 (2014) 92. [35] C. Luo, R. Huang, R. Kevorkyants, M. Pavanello, H. He, C. Wang, Nano Lett. 14 (2014) 1596. [36] N. L. Rosi, J. Kim, M. Eddaoudi, C. Banglin, M. O'Keeffe, O. M. Yaghi, J. Am. Chem. Soc. 127 (2005) 1504. [37] M. Armand, S. Grugeon, H. Vezin, S. Laruelle, P. Ribière, P. Poizot, J. M. Tarascon, Nat. Mater. 8 (2009) 120. [38] G. Gao, H. B. Wu, B. Dong, S. Ding, X. W. D. Lou, Adv. Sci. 2 (2015) 1400014. [39] L. Chao, C. Taiqiang, X. Weijing, X. Lou, L. Pan, Q. Chen, B. Hu, J. Mater. Chem. A 3 (2015) 5585. [40] B. Liu, J. Zhang, X. Wang, G. Chen, D. Chen, C. Zhou, G. Shen, Nano Lett. 12 (2012) 3005. [41] K. Shihichi, M. Wataru, I. Toru, Y. Naoaki, O. Tomoaki, N. Tetsuri, A. Ogata, K. Gotoh, K. Fujiwara, Adv. Funct. Mater. 21 (2011) 3859. [42] Y. Kim, Y. Kim, A. Choi, S. Woo, D. Mok, N. Choi, Y. S. Jung, J. H. Ryu, S. M. Oh, K. T. Lee, Adv. Mater. 26 (2014) 4139. [43] X. Xu, R. Cao, S. Jeong, J. Cho, Nano Lett. 12 (2012) 4988. [44] R. Wu, X. Qian, F. Yu, H. Liu, K. Zhou, J. Wei, Y. Huang, J. Mater.Chem. A 1 (2013) 11126.

17

[45] F. Zheng, Y. Yang, Q. Chen, Nat. Commun 5 (2014) 5261. [46] C. Wang, H. Wu, Z. Chen, M. T. McDowell, Y. Cui, Z. Bao, Nat. Chem.5 (2013) 1042. [47] Z. Cai, L. Xu, M. Yan, C. Han, L. He, K. M. Hercule, C. Niu, Z. Yuan, W. Xu, L. Qu, K. Zhao, L. Mai, Nano Lett. 15 (2015) 738. [48] L. Mai, Y. Fan, Z. Yun-Long, X. Xu, X. Lin, L. Yan-Zhu, Nat. Commun. 2 (2011) 381.

Figure 1. (a) FT-IR spectra of Co-BDC MOF and 1,4-H2BDC. (b) PXRD patterns of Co-BDC MOF. (c) TGA and DSC curves of Co-BDC MOF under nitrogen atmosphere. (d) High-resolution Co 2p XPS spectra of Co-BDC MOF. 18

b

a

Figure 2. (a, b) FESEM micrographs of the as-prepared Co-BDC MOF at low and high magnifications.

19

Figure 3. (a) N2 adsorption−desorption isotherms and (b) BJH pore size distributions of the as-synthesized Co-BDC MOF.

20

21

Figure 4. Electrochemical performance of the as-synthesized Co-BDC MOF: (a) cyclic voltammetry curves at a scan rate of 0.2 mV s-1. (b) galvanostatic charge-discharge profiles at a current density of 100 mA g-1. (c) cycling performance at a current density of 200 mA g-1. (d) rate performance at different current densities from 0.1−2.0 A g-1. (e) cycling performance at high current density (500 mA g-1 and 1 A g-1). A current density of 100 mA g-1 was used for the first two cycles to activate the electrode. (f) EIS spectra for Co-BDC MOF after different numbers of cycles.

Figure 5. (a) FT-IR spectra of Co-BDC MOF bare electrode, electrode at the fully discharged state (0.01 V), and electrode at the fully charged state (3.0 V). Asterisks denote the characteristic peaks from electrolyte (Figure S5). (b) High−resolution Co 2p XPS spectra of Co-BDC MOF at the fully discharged state (0.01 V), and the fully

22

charged state (3.0 V). The peak at ~2300 cm-1 is due to carbon dioxide (air) not compensated in the background spectra.

Scheme 1. Possible lithiation/delithiation sites for coordination with Li+ in the organic moiety of Co-BDC MOF

Highlights    

Co-1,4-benzenedicarboxylate MOF is synthesized by a one-pot solvothermal method. Reversible capacity of 1090 mAh g−1 is achieved at a current density of 200 mA g-1. Reversible capacity of 611 mAh g−1 is achieved at a current density of 1 A g-1. Li-ions may be inserted into the organic moieties.

23