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ZIF-67 Derived N-Doped Co/C Nanocubes as High Performance Anode Materials for Lithium-Ion Batteries Lei Wang, Zehua Wang, Lingling Xie, Limin Zhu, and Xiao-Yu Cao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b03365 • Publication Date (Web): 16 Apr 2019 Downloaded from http://pubs.acs.org on April 16, 2019

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ACS Applied Materials & Interfaces

ZIF-67 Derived N-Doped Co/C Nanocubes as High Performance Anode Materials for Lithium-Ion Batteries Lei Wang,†,‡ Zehua Wang,†,‡ Lingling Xie,†,‡ Limin Zhu,*,†,‡ Xiaoyu Cao*,†,‡ † College

of Chemistry, Chemical and Environmental Engineering, Henan University of Technology, Zhengzhou 450001, PR China

‡ Key

Laboratory of High Specific Energy Materials for Electrochemical Power

Sources of Zhengzhou City, Henan University of Technology, Zhengzhou 450001, PR China *Corresponding author. Tel.: +86 371 67756193; fax: +86 371 67756718. E-mail address: [email protected] (X. Cao), [email protected] (L. Zhu) ABSTRACT: Co nanoparticles embedded in nitrogen-doped carbon nanocubes (Co/NCs) for applications as anode materials in rechargeable lithium-ion batteries were synthesized by calcining Co-based metal-organic framework. Sizes of Co nanoparticles were ~15 nm according to X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical performances of as-prepared anode nanocube composite at 700 °C showed high initial capacity of 1375.1 mAh g-1 in the voltage range of 0.01-3.0 V at the current rate of 0.1 A g-1. After 100 cycles, capacity remained at 688.6 mAh g-1. Thereinto, the role of Co nanoparticles in electrochemical reaction was also elucidated by in situ XRD experiment. Capacity increase of Co/NCs at the high currents was observed, which are potentially caused by the activation of electrode and pseudocapacitance during cycling. High surface area and abundant mesopores contributed to the improved electrochemical performances of the anode, providing numerous pathways and sites for Li+ transfer and storage and accordingly 1

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contributing to pseudocapacitance capacity. KEYWORDS: lithium-ion batteries, ZIF-67 precursor, Co/C anode nanocubes, enhanced electrochemical performances, pseudocapacitance behavior

1. INTRODUCTION Because of their environmental friendliness and low cost, lithium-ion batteries (LIBs) are considered as a new generation of energy storage products for electronics products and hybrid vehicles.1-3 Graphite as a conventional anode material for LIBs was unable to meet increasing storage energy needs due to its low theoretical capacity.4-7 Fortunately, Co-based materials, such as Co3O4,8 CoSe29 and CoS2,10 exhibit high theoretical capacity and are considered as candidates for the new generation of high energy anode materials. However, drastic structural changes occurring in electrode material during cycling cause capacity decay, which limits further applications of these materials.11-12 To solve these problems, fabrication of hollow structures and their combination with various carbon materials was proposed as a solution to these drawbacks. 13-15 Various materials of sacrificial templates or precursors synthesized using metal-organic frameworks (MOF) were widely used in energy storage field because of their high specific surface area, porosity and versatility.16-18 For examples, CuO@C derived from Cu3(btc)2 MOF templates,19 Co3ZnC@NC derived from ZnCo-ZIF nanopolyhedra,20 and Co9S8@C and CoP@NC derived from ZIF-67 precursors,21-22 exhibited good electrochemical performance. It's more exactly that rich mesoporous 2


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structure and high surface area can shorten the diffusion distance of lithium ions and increase the surface contact between the electrode and the electrolyte.23 It can also provide additional voids to buffer the volume change, thereby improving electrochemical performance of the material.24-25 ZIF-67 based MOF materials can be used as sacrificial templates during synthesis of various Co-based/carbon anode materials. For example, Co3O4 has a very high reversible capacity (~1200 mAh g-1) at 0.2 A g-1,26 and CoSe exhibits discharge capacity of 787 mAh g-1 at the same current density.27 By contrast, CoS2 has similar electrochemical performance with high reversible capacity of 1040 mAh g-1 when the current density amounts to 0.2 A g-1.28 Although these materials show excellent lithium storage capability, literature data on Co/C anode materials consisting of Co and C only are scarce. As is known, several transition metals, including Fe, Co and Ni, are inert to directly react with Li+ during discharge process, and therefore display inferior electrochemical properties when selected as the anode materials for LIBs.29-30 Nevertheless, recent research has found that when these transition metal nanoparticles were added to the carbon material, the resulting metal-carbon composites can exhibit an exceptionally excellent reversible capacity, although the metal contributes nothing to Li+ electrochemical storage. Yue et al.31 reported that by adding Co nanoparticles into carbon matrix, the C/Co anode retains an improved reversible capacity of 600 mAh g-1 after 40 cycles, which is attributed to the in-situ grown reaction of Co nanoparticles and its high conductivity and catalytic activity. Su′s group found that 3



the hierarchical Ni/C composites and core–shell Fe@C microspheres all present superior cycling stability and reversible capacity than that of pure carbon or metal electrode.29-30 Simultaneously, they proposed a possible reaction principle to explain this unexpected phenomenon, which is the catalysis of metallic Fe and Ni in the formation and decomposition of solid electrolyte interface (SEI). However, for most carbon-based anodes, the primary generation of SEI and the preliminary decomposition of electrolyte mainly occur in the initial discharge process and subsequent few cycles. The consumption of active material, Li+ and electrolyte is the main reason why almost all carbon-based anodes exhibit a low initial columbic efficiency.32 Fortunately, due to the stable physical and chemical properties of SEI, it can become a protective layer during subsequent charge and discharge process, avoiding further reductions of internal active materials.33 Thus, this side reaction will gradually disappear in the successive cycles and thereby enhances cycling stability of anodes. On the other hand, the reversible reaction of SEI formation and decomposition also fails to explain why the reversible capacity of metal-carbon composites significantly increase because its contents are relatively low and the thickness of SEI is generally a few to one hundred nanometers.28 In summary, the mechanism of extra capacity caused by adding Co nanoparticles in carbon materials is still not clear, and further research is urgent. In this work, we synthesized a series of Co/NCs nanocubes with special morphology using ZIF-67 as precursor. Carbon-coated and nitrogen-doped of cobalt nanocubes were obtained by calcination in inert atmosphere. Cubic composite 4


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materials were implemented into LIBs to study their electrochemical performance and reaction mechanism associated with their cycling. LIBs with these anodes showed excellent rate performance and cycle stability: reversible discharge capacity remained 688.6 mAh g-1 after 100 cycles at current density of 0.1 A g-1. At current density of 1.0 A g-1, discharge capacity was 467.6 mAh g-1, showing a promising potential as anode materials for new generation LIBs.

2. EXPERIMENTAL 2.1 Material synthesis All chemicals used in this study were of analytical grade. They were purchased from different vendors and used without any purification. Preparation of ZIF-67 nanocubes was described in previous report.34 Typically, 0.58 g of Co(NO3)2·6H2O was dissolved in deionized water containing hexadecyl trimethyl ammonium bromide (CTAB), and the solution was stirred at room temperature until it became pink and clear. In a separate container, 9.08 g of 2-methylimidazole was also dissolved in deionized water. After that, the pink solution was quickly poured into clear colorless 2-methylimidazole solution under constant stirring. The whole solution quickly became purple. This purples solution was stirred for 20 min, after which purple precipitate was centrifuge, washed one time with water and three times with ethanol and dried under vacuum at 60 °C for 12 h to obtain the ZIF-67. The resulting ZIF-67 nanocube template then placed in Ar atmosphere and calcined at 600, 700 and 800 °C for 2 h, to prepare three Co/NCs. For convenience, these three anode composites are 5



abbreviated as Co/NC-600, Co/NC-700 and Co/NC-800 nanocube, respectively. 2.2 Characterization techniques XRD (Rigaku MiniFlex 600) was used to determine phase compositions of as-prepared samples. Microstructures of the samples were analyzed using scanning electron microscopy (SEM, FEI-Quanta 250 FEG) and TEM (JEM-2100F). Energy dispersive spectrometer (EDS, EDAX Octane Pro) was used to verify the element type and content. Raman (Renishaw-InVia) and X-ray photoelectron spectroscopy (XPS, Kratos Axis Ultra DLD) were recorded to characterize structures and surface characteristics of the samples, respectively. Surface analysis was performed using BET tests (Quantachrome Autosorb iQ2). Surface area and porosity were calculated from the N2 adsorption-desorption isotherms. Thermogravimetric analysis (TGA, Labsys NETZSCH TG-209) was used to investigate thermal stability of the ZIF-67. It was carried out in Ar atmosphere from room temperature to 800 °C with heating rate of 10 °C min-1. Finally, the in situ XRD (Bruker, D8 Advance) was used to determine the exact reaction mechanism of Co/NC-700. 2.3 Electrochemical measurements To prepare electrodes, Co/NCs nanocube powders, Ketjen Black (KB) and Polyvinylidene fluoride (PVDF) binder (at weight ratios equal to 7: 1.5: 1.5) were uniformly mixed with appropriate amount of N-Methyl pyrrolidone (NMP) solvent, coated on a copper foil and vacuum dried at 60 °C for 12 h. The anodes were punched from copper sheet using a punch die, and final surface area of each sheet was ~1.13 cm2, the mass of active material was ~5.5 mg and the thickness of the electrode was 6


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~3.5 μm. Lithium metal foil, Celgard 2400 microporous membrane and gaskets were used as counter electrode, separator and fixture, respectively. Electrolyte was 1 M LiPF6 dissolved in mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) at volume ratio of 1: 1: 1. LAND multi-channel battery tester (CT2001A) was used to perform a constant current charge and discharge test between 0.01 and 3.0 V at various current densities from 0.1 to 1.0 A g-1. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed in the electrochemical workstation (CHI 660D). EIS was performed with ±5 mV amplitude and within the frequency range of 100 kHz−10 mHz. For comparison, the electrochemical performances of commercial Co nanoparticles as well as bare carbon materials that were removed Co particles by soaking concentrated nitric acid were also analyzed. All electrodes were assembled and inspected under the same conditions. In the full-cell, the LiCoO2 was selected as cathode, and was prepared through the same procedure of Co/NC samples. The voltage test range of the full-cell is 0.1−4.0 V.

3. RESULTS and DISCUSSION TGA results of ZIF-67 agreed with previously reported ones35 (Figure S1a). ZIF-67 experienced a severe weight loss at ~500-600 °C, which was caused by the collapse of the MOF skeleton and decomposition of the organic ligand.36 Total weight loss from room temperature to 800 °C was 38.56 wt%. Therefore, the several different Co/NCs were obtained by calcining ZIF-67 at 600, 700 and 800 °C in Ar atmosphere. 7



XRD patterns of Co/NCs calcined at different temperatures are shown in Figure 1a. All Co/NCs had face-centered cubic Fm3m structure with lattice parameters equal to 5.668 Å. Peaks corresponding to (111), (200) and (220) planes were consistent with the Co standard pattern according to JCPDS card #15-0806. Average crystallite sizes of Co/NC-600, Co/NC-700 and Co/NC-800 can be calculated through the Scherrer equation, which were ~14.02, 14.85 and 18.79 nm, respectively. Disorder of these three-dimensional face-center structures obtained at high temperatures was large, resulting in a more stable structure, which facilitates continuous diffusion and storage of Li+. As calcination temperature increased, diffraction peaks become narrower and sharper, indicating an increase in grain size. Besides, intensity of the (111) peak was much higher than that of the other peaks, manifesting a preferred (111) growth direction.37 A small broad peak observed at ~2θ = 24° was indexed as amorphous carbon, derived from the organics decomposition.22 Raman spectra of Co/NCs are shown in Figure 1b. Peaks at ~1344 and 1590 cm-1 were attributed to D- and G-bands, respectively.38 Because of micro-structure rearrangements and incorporation of N atoms into the lattice structure during the conversion process, relative intensity of the D-band reflects structural disorder of the carbon lattice. G-band represents in-plane stretching vibration of the sp2 hybridized carbon bonds.39 Intensity ratio of these two peaks (ID/IG) indicates degree of graphitization.40 ID/IG ratios for Co/NC-600, Co/NC-700 and Co/NC-800 samples were 1.09, 1.05 and 1.04, respectively. Thus, ID/IG value decreased as temperature increases, but not very significantly. Therefore, it is believed that degree of 8


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graphitization of the Co/NCs increased as temperature increased. It is possible that Co nanoparticles acted as a catalysts of carbon graphitization.41 Nitrogen adsorption/desorption curves of ZIF-67 and Co/NCs belong to type I and type II curves with hysteresis hoops according to IUPAC classification (Figure S1b and Figure 1c), respectively.42-43 This indicates that the ZIF-67 was microporous material, while Co/NCs were mainly mesoporous materials. Surface areas of Co/NCs and ZIF-67 were different. ZIF-67 was calcined and its microporous structure transitioned to the mesoporous structure. Co/NC-700 had surface area equal to ~220.1 m2 g-1 in the Co/NCs. The Barrett-Joyner-Halenda (BJH) pore size distribution curve (Figure S1b) confirmed that ZIF-67 and Co/NCs had micro- and meso-pores, respectively. Mesoporous and high surface area of the Co/NCs materials (Figure 1d) will very facilitate electrolyte penetration and diffusion towards the active sites with less resistance. These pores and high surface also relieve huge volume changes during charge/discharge processes.44 XPS demonstrated that surface of all three Co/NCs consisted mainly of Co，C, N, and O (Figure 2a). Sharp peak at 484 eV corresponds to O 1s. The source of oxygen was very likely oxygen absorbed from the air. Peak intensity of C increased while peak intensity of N, O and Co decreased as calcining temperature increased, indicating higher degree of graphitization, which agrees with Raman test results. XPS spectrum of Co/CN-700 (Figure 2) is considered as an example. XPS spectra for CN-600 and Co/CN-800 samples are shown in Figure S2. C 1s spectrum can be resolved into five characteristic peaks located at 284.6, 285.2, 286, 286.9 and 289.0 9



eV (Figure 2b), which can be attributed to C=C, C-C, C-O or C-N and C=O or C=N bonds, respectively.45 Presence of carbon peaks associated with C=C and C-C bonds agrees with Raman results. In addition, the C 1s spectrum also demonstrated the possible presence of carbon atoms attached to N. N 1s spectra was deconvoluted into three peaks at 398.7, 399.5 and 401.2 eV, which correspond to pyridine-N, pyrrole-N and graphitic-N (Figure 2c), respectively.46 These functional groups contribute to pseudocapacitance of this anode and enhance its wettability. Both factors improve electrochemical performance, which will be confirmed by the later electrochemical examinations. Figure 2d depicts the high-resolution spectrum of Co 2p, showing an asymmetric peak. Co 2p3/2 peak was deconvoluted into peaks at 778.4, 780.5 and 784.9 eV. These peaks correspond to Co metal, CoOx, and plasma-loss peak, respectively. Even though, XRD patterns of Co/NCs showed only Co metal, XPS demonstrated CoOx on the surface of Co/NCs which occurs often.47 XPS confirmed successful synthesis of Co/NCs with carbon layer. As shown in Figure 3, SEM demonstrated that Co/NCs inherited morphology of the ZIF-67 nanocubes. However, ZIF-67 has a smooth surface, while Co/NCs have a rough surface, which became even rougher as its synthesis temperature increased. This phenomenon could be attributed to the decomposition of MOF precursor. TEM demonstrated that dark dots with different sizes are not uniformly dispersed in the carbon cube matrix (Figure 4a, b and Figure S3a-d). Sizes of Co/NC-700 particles were ~300 nm. TEM also showed that Co/NC-700 nanoparticles were wrapped by a few layers of carbon sheets (Figure 4c). These sheets formed at high temperature in 10


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situ with assistance of Co as a catalyst.48 High-resolution TEM (HRTEM) showed well-crystalline and ordered lattices (Figure 4d and Figure S3e, f). As displayed in Figure 3d, lattice fringes of the two adjacent planes were ~0.205 nm apart. This distance corresponds to the (111) crystal plane of cubic Co/NC-700. Selected area electron diffraction (SAED) showed that formed Co/NCs were polycrystalline (Figure 4e and Figure S3g, h). Elemental mapping of Co/NC-700 showed distribution of C, Co and N within the cube, further demonstrating presence of Co nanoparticles (Figure 4g-i). Figure 4j depicted that EDS of the Co/NC-700 (without taking into account Cu content from the substrate) demonstrated that weight ratios between C, Co and N were ~66.1: 31.6: 2.3, which further confirmed that the elements in as-prepared Co/NCs were uniform distributed. EDS results are consistent with the XRD observations. Scheme 1 reveals formation mechanism of Co/NCs based on the above characterization results. Figure 5a, c and e demonstrated the CV curves of Co/NC-600, Co/NC-700 and Co/NC-800, respectively. According to previous reports, three irreversible and broad peaks at ~1.7, 1.0 and 0.4 V in the initial negative sweep might be related to the preliminary decomposition of electrolytes and some other irreversible reactions.31, 49-50 The onset potential of SEI formation is below 0.8 V in LiPF6/EC/DMC/EMC electrolytes, therefore, sharp peak at ~0.6 V could be regarded as the formation of SEI, and weak peak at ~1.2 V observed during the first positive CV sweep was also attributed to the partial decomposition of generated SEI. Simultaneously, no obvious peak of electrochemical reaction between metallic Co and Li+ can be found, 11



indicating Co nanoparticles are inactive during the discharge and charge process. All subsequent curves (for the 2nd-5th CV cycles) were overlapped well, and the CV curve corresponds to the voltage platform at current density of 0.1 A g-1 (shown in Figure 5b, d and f, respectively), indicating excellent cyclic stability of Co/NC-700 anode for LIBs. The Co/NCs exhibited excellent cycle stability at different densities in the voltage range of 0.01-3.0 V. At 0.1 A g-1, as shown in Figure 6a, initial specific discharge capacities of Co/NCs anodes made from ZIF-67 calcined at 600, 700 and 800 °C reached 1214.8, 1375.1, and 1097.6 mAh g-1, respectively. Corresponding coulombic efficiencies were 50.5, 49.3 and 50.6%, respectively, due to SEI layer formation and other side reactions.51-52 Specific discharge capacities of the three materials after 100 cycles were 586.5, 688.6 and 500.4 mAh g-1, respectively. Capacity retention after 100 cycles calculated relative to the second discharge was 95.8, 100.8%, and 92.8%. Anodes made from Co/NCs exhibited very stable long-life cycling performance at the current density of 1.0 A g-1, as shown in Figure 6h. Co/NC-700 demonstrated especially stable reversible capacity, which increased gradually during the first 450 cycles and then declined slowly during the next 450 cycles. Long-life coulombic efficiency was very stable and equal 100% and specific discharge capacity of Co/NC-700 after 1000 cycles was 434.5 mAh g-1. Thus, introduced Co nanoparticles can significantly enhance electrochemical performance of the as-prepared composites during charge-discharge process, which is not only associated with their higher electronic conductivity, but is also related to the 12


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synergistic effect between metallic Co nanoparticles and carbon shells that may also promote structural stability of the composites.53-54 Specific discharge capacities of Co/NC-600 and Co/NC-800 after 1000 cycles were 326.9 and 251.5 mAh g-1, respectively. Cycle capacities of Co/NCs at 0.1, 0.2, 0.5, 0.8 (Figure S4) and 1.0 A g-1 were similar to their rate capabilities. Capacity of Co/NCs anodes demonstrated different ascending behavior, which may relate with pseudocapacitance behavior with extended cycling. As presented in Figure 6g, the rate capabilities of Co/NCs electrodes were compared under various current densities. Capacity of the anodes made from the same material was very reproducible. However, the discharge capacity of Co/NC-700 electrode was the largest and demonstrated least attenuation. Therefore, the Co/NC-700 had the optimum rate performance with discharge capacities of 661, 611.5, 532, 487.8 and 467.6 mAh g-1 at current density of 0.1, 0.2, 0.5, 0.8, and 1.0 A g-1. Capacity retention of this electrode was 71%. When the current density returned to the 0.8, 0.5, 0.2 and 0.1 A g-1, the discharge capacities of Co/NC-700 were 494.7, 541.6, 618.9 and 674.1 mAh g-1, respectively, which are slightly higher than the values during the first cycle of rate capability tests. In comparation, anode prepared from Co/NC-800 material showed the lowest capacity at 1.0 A g-1 (equal to 273.7 mAh g-1). As shown in Figure 6d-f, the voltage distribution of the Co/NCs electrodes from 0.1 to 1.0 A g-1 was resemblance. Almost no voltage platform was observed, which implies that electrode processes were capacitive. Currently, LiCoO2 is commercial cathode material for diverse LIBs, which has 13



high capacity, low self-discharge rate and excellent cycle stability.55 Therefore, we chose LiCoO2 as a cathode material to test performance of Co/NC-700 anode in full-cells. Initial charge/discharge capacitates of full cells containing LiCoO2 cathodes and Co/NC-700 anodes were 686.9/1148.7 mAh g−1 as shown in Figure 6b. Even after 80 cycles at the current rate of 0.1 A g−1, capacity of the full-cell was 662.8 mAh g−1. Cyclic efficiency gradually rose during the first 10 cycles, and stabilized at almost 100% for the rest of the battery cycling. It can be seen from Figure 6c that voltage platform of the full-cell is different from the half-cell because it is mainly derived from the voltage gap between LiCoO2 and Co/NC-700. EIS was utilized to gain further insights into electrical conductivity and the charge transfer efficiency of Co/NCs anodes. Nyquist plots of Co/NCs show a depressed semicircle in the high to medium frequency region followed by a sloping straight line in the low-frequency range in Figure S5, corresponding to the charge-transfer resistance between electrodes and electrolyte and solid-state diffusion of Li+, respectively.56-57 Meanwhile, Co/NC-600, Co/NC-700 and Co/NC-800 anodes demonstrated larger semicircles with resistances equal to ~ 281.9, 208.7 and 286.7 Ω (Figure S5a). Nyquist plots of Co/NCs after 50 cycles at 1.0 A g-1 demonstrated significantly reduced semicircles, indicating depressed charge-transfer resistances (Figure S5b): semicircle diameters for Co/NC-600, Co/NC-700 and Co/NC-800 anodes were 62.16, 36.12 and 98.25 Ω, respectively. Charge transfer resistance of Co/NC-700 was still the smallest, indicating its low contact and charge transfer impedances, which enhance electrical conductivity and ionic mobility during Li+ 14


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insertion/extraction reaction. SEM analysis of Co/NCs morphology after 50 cycles at 1.0 A g-1 showed that some anode particles were covered binder and carbon black, while some particles were bare as shown in Figure S6. Anodes made from Co/NC-700 demonstrated no changes and exhibited the stable structures after 50 cycles. Co/NC-800-based anodes demonstrated significant damage, which was probably the reason for capacity reduction of this anode. Thus, SEM analysis confirmed that structural stability of Co/NC-based anodes is the reason for their excellent reversible capacity and cycle stability. Considering that the existing theory cannot perfectly explain the effect of additive Co nanoparticles on the enhanced electrochemical performance of carbon materials, the in-situ XRD measurement has been utilized to further confirm the lithium storage mechanism of Co/NC-700. By observing several changes of XRD peaks throughout the galvanostatic test, the reliable reaction of electrode would be effectively analyzed. As shown in Figure 7a, the whole discharge and charge process of the as-prepared Co/NC-700 has been divided into six regions according to the position of redox peaks shown in CV curves (Figure 5c), and a series of XRD patterns of Co/NC-700 were also shown in Figure 6b. Among them, strongest peaks at 45.8°, 50.9°, 52.8°, and 70.9° were consistent with the standard card of Be (JCPDS card # 22-0111), while three small peaks at 38.6°, 41.4°, and 44.1° were related to its oxide, BeO (JCPDS card # 78-1556). Apart from this, the peak at 44.4° was associated with Co (JCPDS card # 15-0806), and several small peaks at 36.0°, 51.9°, and 64.9° might 15



come from the metallic Li (JCPDS card # 01-1131). Interestingly, there are several small peaks located at lower 2θ region, which were hard to be exactly defined. According to previous reports, those peaks might be related to complicated ingredients of SEI membrane, such as Li2O, LiF, Li2CO3, and the PVDF binder, while the exact proportion of organic and inorganic components depends on the additive of electrolyte, sweep rates or active material.33, 58 As shown in Figure 7b, it is difficult to observe distinct change of characteristic peaks corresponding to the PVDF binder and SEI components during the charge and discharge cycling, suggesting that the composition of SEI is very stable after the formation. Thus, previously proposed mechanism cannot entirely explain the reason of extra capacity in Co/C composites. To clearly understand the role of Co in charge and discharge process, Figure 7c exhibits the detailed survey of Co peak at the selected 2θ region during the initial cycle. Obviously, when the voltage changed between 3.0 V and 0.01 V, the intensity and position of this peak did not occur drastic variation, indicating the lattice of Co was unchanged. For Co electrode, which used commercial Co powder to be the active material, its reversible capacity was very low, showing merely 30 mAh g-1 after 100 cycles at the current density of 0.1 A g-1, thereby suggesting that Co nanoparticles were not directly involved in the electrochemical reaction and the insertion/extraction of Li+. For bare carbon electrode, shown in Figure 7e, its charge-transfer resistance was ~423 Ω, much higher than that of Co/NC-700, further proving that the embedded Co nanoparticles obviously reduce the resistance of as-prepared anode. Dynamic analysis of the Co/NC-700 anode material was shown in Figure 8a 16


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and b, performed using CV at the scanning rates of 0.1-10 mV s-1, respectively. It was found that CV curves showed similar shape at different scan rates. Intensity of oxidation and reduction peaks gradually increased, and the reduction potential positively shifted as scanning rate increased. Thus, reversible electrochemical reaction occurred as the sweep rate increased. Relationship of charge/discharge capacities and cyclic time was described in Figure 8c, demonstrating that charge-storage capacity reached 653.2 mAh g-1 after ~393 min. Reversible capacity could increase to 465.7 mAh g-1 during a short period (only 22 min), indicating existence of a capacitive behavior. Trasatti analysis utilized to further investigate kinetic characteristics of Co/NC-700 is shown in Figure 8d and e. By reciprocating both sides of Equation 1, Equation 2 can be obtained as follows: 59-60 Q(v) = Qcapacitive + α(v-1/2)

(1),

1/Q(v) =1/Qtotal + α(v1/2)

(2),

where Q(v), Qcapacitive, and Qtotal represent galvanostatic charge transferring capacity, capacitance storage capacity derived from the pseudo- or double-layer capacitance, and the total Li storage capacity, respectively; α is a constant, and v is the scan rate. As v increases to infinity, diffusion-dominated behavior of anode is can be neglected. Thus, total capacity will be related to the capacitive-storage. From these formulas and assumptions, Qcapacitive was calculated from the intercept of the lineal fitting as 569.35 mAh g-1. At v = 0, the time of charge process might approach infinity, which indicates that all reactive sites could participate in the electrochemical reaction. Based on the linear fitting of 1/Q(v) vs. v1/2, Qtotal can be adjusted to 657.89 mAh g-1. Qcapacitive/Qtotal, 17



in this case, is 86.5%, which confirms significant contribution from the capacitance storage during cycling. Meanwhile, as shown in Figure S7d, e and S8d, e, Qcapacitive/Qtotal ratios for Co/NC-600 and Co/NC-800 were 77.2% and 76.2%, respectively, indicating their lower capacitance-controlled contribution than for Co/NC-700. These results can also be confirmed based on the correlation between peak current (i) and scan rate (v):61-63 i = avb

(3),

log (i) = blog(v) + log(a)

(4),

where i and v belong to the intensity of major peak and the relevant sweep rate in several CV curves, respectively; a and b are constant, corresponding to the electrochemical mechanism of an electrode. When b is close to 1, the surface reaction rate is controlled by the pseudocapacitance behavior. Value of b = 0.5, indicates lithium-ion diffusion-controlled process. Equation 4 is introduced to determine the b value: slope of the linear curve represents the b value, which is equal to 0.87 and 0.76 for the Co/NC-700-based anode at the scan rates < 1 mV s-1 and > 1 mV s-1, respectively (Figure 8f). These b values indicate that the electrochemical reaction of Co/NC-700 is generally controlled by the pseudocapacitance behavior. Therefore, capacity contribution for Co/NC-700-based anode can be divided into two processes: one is controlled by the pseudocapacitance and the other by diffusion. Thus, Equation 3 can be defined as follow:64 i(V) = k1v + k2v1/2

(5)

i/v1/2 = k1v1/2 + k2

(6) 18


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where

k1v

k2v1/2

and

are

contributions

from

pseudocapacitance

and

diffusion-controlled processes, respectively. Equation 5 was simplified by dividing both sides by v1/2, which resulted in Equation 6. The slope and intercept of Equation 6 are

k1

and

k2,

respectively.

Using

these

values,

percentage

of

pseudocapacitance-controlled contribution can be easily calculated. Figure 8g exhibits behavior of Co/NC-700 anode functions at different potentials. These functions have distinct linear relationships, suggesting the reliability and accuracy of our analysis. In a typical CV curve with 0.5 mV s-1, pseudocapacitance contribution was 78.2% (Figure 8h). Figure 8i shows comparison of pseudocapacitance-controlled contributions at different rates. Pseudocapacitance contribution increased as the sweep rates increased: it was 76.2% at 0.1 mV s-1 and became 78.7% at 1 mV s-1. Thus, pseudocapacitance of Co/NC-700 is a dominant factor contributing to overall capacity. Pseudocapacitance analysis results were the same for Co/NC-600 and Co/NC-800 than for Co/NC-700 (Figure S7f-i and S8f-i). Thus, it is believed that excellent rate performance of Co/NC anodes is directly related to the percentage of pseudocapacitance contribution. Pseudocapacitance contribution is consistent with the surface area of the anode. To the best of our knowledge, the appearance of pseudocapacitance is closely related to maximizing the surface area and minimizing the size of electrode material, which provides abundant storage sites and shorten transport paths for Li+ and electrons.65-66 The high surface area and electronic conductivity of Co/NCs are main reasons for the generation of pseudocapacitance behavior, and therefor contribute to the enhanced electrochemical performances.67 19



4. CONCLUSIONS Anodes prepared from Co/NCs exhibited excellent electrochemical performance, including cyclic stability and rate capability. At current density of 1.0 A g-1, Co/NC-700 delivered reversible capacity of 434.5 mAh g-1 after 1000 cycles. Such high values were observed because of high surface area and abundant mesopores, which improve lithium reversible transfer and storage processes. The presence of carbon network enhances stability of the material. N-doping carbon network also contributed to the structural stability. Co has high electrical conductivity and enhances the electrical conductivity of the Co/NCs. Electrode prepared from Co/NC-700 behaved as a very promising anode for LIBs. This work further advances research progress on carbon composites incorporating metal particles using MOF as precursors. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: xxxxxx. TGA curve and BET result of ZIF-67; XPS spectra, morphology characterizations and the kinetic properties analysis of Co/NC-600 and Co/NC-800; cycling performances, Nyquist plots and SEM images after cycling of Co/NCs.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], [email protected] (L. Zhu). Phone: +86-371-67756193, Fax: +86-371-67756718 (X. Cao). 20


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ORCID Xiaoyu Cao: 0000-0002-6740-4937 Author Contributions Lei Wang performed the experiments and analyzed the data and wrote the initial manuscript draft. Prof. Xiaoyu Cao designed and oversaw the experiments, revised and finalized the manuscript for submission. All authors have discussed the experimental results and commented on the manuscript. Notes The authors declare no conflicts of interest.

ACKNOWLEDGEMENTS This work was supported by National Natural Science Foundation, China (No. 21773057, U1704142, and 21403057), Postdoctoral Science Foundation, China (No. 2017M621833), Program for Innovative Team (in Science and Technology) in University of Henan Province, China (No. 17IRTSTHN003), Program for Science and Technology Innovation Talents in Universities of Henan Province, China (No. 18HASTIT008), Zhongyuan Thousand People Plan-The Zhongyuan Youth Talent Support Program (in Science and Technology), China (No. ZYQR201810139), Cultivation Plan for Young Core Teachers in Universities of Henan Province, China (No. 2016GGJS-068), Natural Science Foundation of Henan Province, China (No. 162300410050), and Fundamental Research Funds for the Henan Provincial Colleges and Universities in Henan University of Technology, China (No. 2018RCJH01).

REFERENCES (1) Ji, L.; Lin, Z.; Alcoutlabi, M.; Zhang, X. Recent Developments in Nanostructured Anode Materials for Rechargeable Lithium-Ion Batteries. Energy Environ. Sci. 2011, 4, 2682−2699. (2) Scrosati, B.; Hassoun, J.; Sun, Y. K. Lithium-Ion Batteries. A Look into the Future. Energy Environ. Sci. 2011, 4, 3287−3295. 21



(3) Goodenough, J. B.; Park, K. S. The Li-Ion Rechargeable Battery: A Perspective. J. Am. Chem. Soc. 2013, 135, 1167−1176. (4) Roberts, A. D.; Li, X.; Zhang, H. Porous Carbon Spheres and Monoliths: Morphology Control, Pore Size Tuning and Their Applications as Li-Ion Battery Anode Materials. Chem. Soc. Rev. 2014, 43, 4341−4356. (5) Goriparti, S.; Miele, E.; De Angelis, F.; Di Fabrizio, E.; Proietti Zaccaria, R.; Capiglia, C. Review on Recent Progress of Nanostructured Anode Materials for Li-Ion Batteries. J. Power Sources 2014, 257, 421−443. (6) Huang, J.; Wei, Z.; Liao, J.; Ni, W.; Wang, C.; Ma, J. Molybdenum and Tungsten Chalcogenides for Lithium/Sodium-Ion Batteries: Beyond MoS2. J. Energy Chem. 2018, 33, 100−124. (7) Liao, J.; Tan, R.; Kuang, Z.; Cui, C.; Wei, Z.; Deng, X.; Yan, Z.; Feng, Y.; Li, F.; Wang, C.; Ma, J. Controlling the Morphology, Size and Phase of Nb2O5 Crystals for High Electrochemical Performance. Chinese Chem. Lett. 2018, 29, 1785−1790. (8) Kang, W.; Zhang, Y.; Fan, L.; Zhang, L.; Dai, F.; Wang, R.; Sun, D. Metal-Organic Framework Derived Porous Hollow Co3O4/N-C Polyhedron Composite with Excellent Energy Storage Capability. ACS Appl. Mater. Interfaces 2017, 9, 10602−10609. (9) Lu, W.; Xue, M.; Chen X.; Chen, C. CoSe2 Nanoparticles as Anode for Lithium Ion Battery. Int. J. Electrochem. Sci. 2017, 12, 1118−1129. (10) Wang, Q.; Zou, R.; Xia, W.; Ma, J.; Qiu, B.; Mahmood, A.; Zhao, R.; Yang, Y.; Xia, D.; Xu, Q. Facile Synthesis of Ultrasmall CoS2 Nanoparticles within Thin N-Doped Porous Carbon Shell for High Performance Lithium-Ion Batteries. Small 2015, 11, 2511−2517. (11) Cabana, J.; Monconduit, L.; Larcher, D.; Palacin, M. R. Beyond Intercalation-Based Li-Ion Batteries: The State of the Art and Challenges of Electrode Materials Reacting through Conversion Reactions. Adv. Mater. 2010, 22, E170−E192. (12) Li, C.; Chen, T.; Xu, W.; Lou, X.; Pan, L.; Chen, Q.; Hu, B. Mesoporous Nanostructured Co3O4 Derived from MOF Template: A High-Performance Anode Material for Lithium-Ion Batteries. J. Mater. Chem. A 2015, 3, 5585−5591. (13) Su, D. S.; Schlogl, R. Nanostructured Carbon and Carbon Nanocomposites for Electrochemical Energy Storage Applications. ChemSusChem 2010, 3, 136−168. (14) Zhao, Y.; Wang, L. P.; Sougrati, M. T.; Feng, Z.; Leconte, Y.; Fisher, A.; Srinivasan, M.; Xu, 22


Page 22 of 39

Page 23 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Z. A Review on Design Strategies for Carbon Based Metal Oxides and Sulfides Nanocomposites for High Performance Li and Na Ion Battery Anodes. Adv. Energy Mater. 2017, 7, No. 1601424. (15) Liu, J.; Liang, J.; Wang, C.; Ma, J. Electrospun CoSe@N-doped Carbon Nanofibers with Highly Capacitive Li Storage. J. Energy Chem. 2018, 33, 160−166. (16) Zhou, H. C.; Kitagawa, S. Metal-Organic Frameworks (MOFs). Chem. Soc. Rev. 2014, 43, 5415−5418. (17) Zhou, H. C.; Long, J. R.; Yaghi, O. M. Introduction to Metal-Organic Frameworks. Chem. Rev. 2012, 112, 673−674. (18) Ke, F. S.; Wu, Y. S.; Deng, H. Metal-Organic Frameworks for Lithium Ion Batteries and Supercapacitors. J. Solid State Chem. 2015, 223, 109−121. (19) Chen, T.; Hu, Y.; Cheng, B.; Chen, R.; Lv, H.; Ma, L.; Zhu, G.; Wang, Y.; Yan, C.; Tie, Z.; Jin, Z.; Liu, J. Multi-Yolk-Shell Copper Oxide@Carbon Octahedra as High-Stability Anodes for Lithium-Ion Batteries. Nano Energy 2016, 20, 305−314. (20) Zhu, G.; Chen, T.; Wang, L.; Ma, L.; Hu, Y.; Chen, R.; Wang, Y.; Wang, C.; Yan, W.; Tie, Z.; Liu, J.; Jin, Z. High Energy Density Hybrid Lithium-Ion Capacitor Enabled by Co3ZnC@N-Doped Carbon Nanopolyhedra Anode and Microporous Carbon Cathode. Energy Storage Mater. 2018, 14, 246−252. (21) Chen, T.; Ma, L.; Cheng, B.; Chen, R.; Hu, Y.; Zhu, G.; Wang, Y.; Liang, J.; Tie, Z.; Liu, J.; Jin, Z. Metallic and Polar Co9S8 Inlaid Carbon Hollow Nanopolyhedra as Efficient Polysulfide Mediator for Lithium-Sulfur Batteries. Nano Energy 2017, 38, 239−248. (22) Zhu, K.; Liu, J.; Li, S.; Liu, L.; Yang, L.; Liu, S.; Wang, H.; Xie, T. Ultrafine Cobalt Phosphide Nanoparticles Embedded in Nitrogen-Doped Carbon Matrix as a Superior Anode Material for Lithium Ion Batteries. Adv. Mater. Interfaces 2017, 4, No. 1700377. (23) Ma, L.; Chen, R.; Hu, Y.; Zhu, G.; Chen, T.; Lu, H.; Liang, J.; Tie, Z.; Jin, Z.; Liu, J. Hierarchical Porous Nitrogen-Rich Carbon Nanospheres with High and Durable Capabilities for Lithium and Sodium Storage. Nanoscale 2016, 8, 17911−17918. (24) Zheng, S.; Li, X.; Yan, B.; Hu, Q.; Xu, Y.; Xiao, X.; Xue, H.; Pang, H. Transition-Metal (Fe, Co, Ni) Based Metal-Organic Frameworks for Electrochemical Energy Storage. Adv. Energy Mater. 2017, 7, No. 1602733. (25) Du, M.; He, D.; Lou, Y.; Chen, J. Porous Nanostructured ZnCo2O4 Derived from MOF-74: 23



High-Performance Anode Materials for Lithium Ion Batteries. J. Energy Chem. 2017, 26, 673−680. (26) Shao, J.; Wan, Z.; Liu, H.; Zheng, H.; Gao, T.; Shen, M.; Qu, Q.; Zheng, H. Metal Organic Frameworks-Derived Co3O4 Hollow Dodecahedrons with Controllable Interiors as Outstanding Anodes for Li Storage. J. Mater. Chem. A 2014, 2, 12194−12200. (27) Hu, H.; Zhang, J.; Guan, B.; Lou, X. W. Unusual Formation of CoSe@carbon Nanoboxes, which have an Inhomogeneous Shell, for Efficient Lithium Storage. Angew. Chem. Int. Edit. 2016, 55, 9514−9518. (28) Zhang, J.; Yu, L.; Lou, X. W. D. Embedding CoS2 Nanoparticles in N-Doped Carbon Nanotube Hollow Frameworks for Enhanced Lithium Storage Properties. Nano Res. 2017, 10, 4298−4304. (29) Su, L.; Zhong, Y.; Zhou, Z. Role of Transition Metal Nanoparticles in the Extra Lithium Storage Capacity of Transition Metal Oxides: A Case Study of Hierarchical Core–Shell Fe3O4@C and Fe@C Microspheres. J. Mater. Chem. A 2013, 1, 15158−15166. (30) Su, L.; Zhou, Z.; Shen, P. Ni/C Hierarchical Nanostructures with Ni Nanoparticles Highly Dispersed in N-Containing Carbon Nanosheets: Origin of Li Storage Capacity. J. Phys. Chem. C 2012, 116, 23974−23980. (31) Yue, J.; Zhao, X.; Xia, D. Electrochemical Lithium Storage of C/Co Composite as An Anode Material for Lithium Ion Batteries. Electrochem. Commun. 2012, 18, 44−47. (32) Zhou, Y.; Tian, R.; Duan, H.; Wang, K.; Guo, Y.; Li, H.; Liu, H. CoSe/Co Nanoparticles Wrapped by in situ Grown N-Doped Graphitic Carbon Nanosheets as Anode Material for Advanced Lithium Ion Batteries. J. Power Sources 2018, 399, 223−230. (33) Pallavi, V.; Pascal, M.; Petr, N. A Review of the Features and Analyses of the Solid Electrolyte Interphase in Li-Ion Batteries. Electrochim. Acta 2010, 55, 6332−6341. (34) Hu, H.; Guan, Bu Y.; Lou, X. W. Construction of Complex CoS Hollow Structures with Enhanced Electrochemical Properties for Hybrid Supercapacitors. Chem. 2016, 1, 102−113. (35) Wang, Y.; Wang, C.; Wang, Y.; Liu, H.; Huang, Z. Superior Sodium-Ion Storage Performance of Co3O4@Nitrogen-Doped Carbon: Derived from a Metal-Organic Framework. J. Mater.Chem. A 2016, 4, 5428−5435. (36) Sun, W.; Cai, C.; Tang, X.; Lv, L. P.; Wang, Y. Carbon Coated Mixed-Metal Selenide Microrod: Bimetal-Organic-Framework Derivation Approach and Applications for Lithium-Ion Batteries. Chem. Eng. J. 2018, 315, 169−176. 24


Page 24 of 39

Page 25 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(37) Zhu, L.; Xie, L.; Cao, X. LiV3O8/Polydiphenylamine Composites with Significantly Improved Electrochemical Behavior as Cathode Materials for Rechargeable Lithium Batteries. ACS Appl. Mater. Interfaces 2018, 10, 10909−10917. (38) Lu, W.; Liu, M.; Miao, L.; Zhu, D.; Wang, X.; Duan, H.; Wang, Z.; Li, L.; Xu, Z.; Gan, L.; Chen, L. Nitrogen-Containing Ultramicroporous Carbon Nanospheres for High Performance Supercapacitor Electrodes. Electrochim. Acta 2016, 205, 132−141. (39) Ferrari, A. C.; Basko, D. M. Raman Spectroscopy as a Versatile Tool for Studying the Properties of Graphene. Nat. Nanotechnol. 2013, 8, 235−246. (40) Ćirić-Marjanović, G.; Pašti, I.; Gavrilov, N.; Janošević, A.; Mentus, S. Carbonised Polyaniline and Polypyrrole: Towards Advanced Nitrogen-Containing Carbon Materials. Chem. Pap. 2013, 67, 781−813. (41) Guo, Y.; Tang, J.; Salunkhe, R. R.; Alothman, Z. A.; Hossain, M. S. A.; Malgras, V.; Yamauchi, Y. Effect of Various Carbonization Temperatures on ZIF-67 Derived Nanoporous Carbons. Bull. Chem. Soc. Jpn. 2017, 90, 939−942. (42) Qin, J.; Wang, S.; Wang, X. Visible-Light Reduction CO2 with Dodecahedral Zeolitic Imidazolate Framework ZIF-67 as an Efficient Co-Catalyst. Appl. Catal. B-Environ. 2017, 209, 476−482. (43) Lin, K. Y.; Chen, B. C. Efficient Elimination of Caffeine from Water Using Oxone Activated by a Magnetic and Recyclable Cobalt/Carbon Nanocomposite Derived from ZIF-67. Dalton Trans. 2016, 45, 3541−3551. (44) Zhu, D.; Zheng, F.; Xu, S.; Zhang, Y.; Chen, Q. MOF-Derived Self-Assembled ZnO/Co3O4 Nanocomposite Clusters as High-Performance Anodes for Lithium-Ion Batteries. Dalton Trans. 2015, 44, 16946−16952. (45) Wang, X.; Li, Y. Nanoporous Carbons Derived from MOFs as Metal-Free Catalysts for Selective Aerobic Oxidations. J. Mater. Chem. A 2016, 4, 5247−5257. (46) Sheng, Z. H.; Shao, L.; Chen, J. J.; Bao, W. J.; Wang, F. B.; Xia, X. H. Catalyst-Free Synthesis of Nitrogen-Doped Graphene via Thermal Annealing Graphite Oxide with Melamine and Its Excellent Electrocatalysis. ACS Nano 2011, 5, 4350−4358. (47) Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S. C. Resolving Surface Chemical States in XPS Analysis of First Row Transition Metals, Oxides and 25



Hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717−2730. (48) Xia, W.; Zhu, J.; Guo, W.; An, L.; Xia, D.; Zou, R. Well-Defined Carbon Polyhedrons Prepared From Nano Metal-Organic Frameworks for Oxygen Reduction. J. Mater. Chem. A 2014, 2, 11606−11613. (49) Sun, X.; Hao, G.; Liu, X.; Li, X.; Liu, B.; Si, W.; Ma, C.; Liu, Q.; Zhang, Q.; Stefan, K.; Oliver, S. High-defect Hydrophilic Carbon Cuboids Anchored with Co/CoO Nanoparticles as Highly Efficient and ultra-stable Lithium-ion Battery anodes. J. Mater. Chem. A 2016, 4, 10166−10173. (50) Guo, B.; Kong, Q.; Zhu, Y.; Mao, Y.; Wang, Z.; Wan, M.; Chen, L. Electrochemically Fabricated Polypyrrole–Cobalt–Oxygen Coordination Complex as High-Performance Lithium-Storage Materials. Chem. Eur. J. 2011, 17, 14878 −14884. (51) Deng, M.; Li, S.; Hong, W.; Jiang, Y.; Xu, W.; Shuai, H.; Zou, G.; Hu, Y.; Hou, H.; Wang, W.; Ji, X. Octahedral Sb2O3 as High-Performance Anode for Lithium and Sodium Storage. Mater. Chem. Phys. 2019, 223, 46−52. (52) Liu, W.; Fu, Y.; Li, Y.; Chen, S.; Song, Y.; Wang, L. Three-dimensional carbon foam surrounded by carbon nanotubes and Co-Co3O4 nanoparticles for stable lithium-ion batteries. Compos. Part B: Eng. 2019, 163, 464-470. (53) Zhao, Y.; Pang, Q.; Wei, Y.; Wei, L.; Ju, Y.; Zou, B.; Gao, Y.; Chen, G. Co9S8/Co as a High-Performance Anode for Sodium-Ion Batteries with an Ether-Based Electrolyte. ChemSusChem 2017, 10, 4778−4785. (54) Shi, X.; Song, H.; Li, A.; Chen, X.; Zhou, J.; Ma, Z. Sn-Co Nanoalloys Embedded in Porous N-Doped Carbon Microboxes as a Stable Anode Material for Lithium-Ion Batteries. J. Mater. Chem. A 2017, 5, 5873−5879. (55) Cao, Q.; Zhang, H. P.; Wang, G. J.; Xia, Q.; Wu, Y. P.; Wu, H. Q. A Novel Carbon-Coated LiCoO2 as Cathode Material for Lithium Ion Battery. Electrochem. Commun. 2007, 9, 1228−1232. (56) Hou, H.; Banks, C. E.; Jing, M.; Zhang, Y.; Ji, X. Carbon Quantum Dots and Their Derivative 3D Porous Carbon Frameworks for Sodium-Ion Batteries with Ultralong Cycle Life. Adv. Mater. 2015, 27, 7861−7866. (57) Wang, Z.; Cao, X.; Ge, P.; Zhu, L.; Xie, L.; Hou, H.; Qiu, X.; Ji, X. Hollow-sphere ZnSe Wrapped Around Carbon Particles as a Cycle-Stable and High-Rate Anode Material for Reversible Li-Ion Batteries. New J. Chem. 2017, 41, 6693−6699. 26


Page 26 of 39

Page 27 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(58) Shinichi, K.; Wataru, M.; Toru, I.; Naoaki, Y.; Tomoaki, O.; Tetsuri, N.; Atsushi, O.; Kazuma, G.; Kazuya, F. Electrochemical Na Insertion and Solid Electrolyte Interphase for Hard-Carbon Electrodes and Application to Na-Ion Batteries. Adv. Funct. Mater. 2011, 21, 3859−3867. (59) Song, Y.; Meng, Y.; Wang, P.; Jiang, L.; Wu, Z.; Jiang, Y.; Hu, L. Epitaxial Growth of NiCo2S4/Co9S8@Graphene

Heterogenous

Nanocomposites

with

High-Rate

Lithium

Storage

Performance. J. Alloys Compd. 2018, 747, 926−933. (60) Ge, P.; Li, S.; Shuai, H.; Xu, W.; Tian, Y.; Yang, L.; Zou, G.; Hou, H.; Ji, X. Engineering 1D Chain-Like Architecture with Conducting Polymer towards Ultra-Fast and High-Capacity Energy Storage by Reinforced Pseudocapacitance. Nano Energy 2018, 54, 26−38. (61) Zhao, G.; Zou, G.; Qiu, X.; Li, S.; Guo, T.; Hou, H.; Ji, X. Rose-Like N-Doped Porous Carbon for Advanced Sodium Storage. Electrochim. Acta 2017, 240, 24−30. (62) Cao, X.; Xie, L.; Ge, P.; Zhu, L. Stabilization of LiV3O8 Rod-Like Structure by Protective Mg2(PO4)3 Layer for Advanced Lithium Storage Cathodes. Energy Technol. 2018, 6, 2497−2487. (63) Liang, J.; Wei, Z.; Wang, C.; Ma, J. Vacancy-Induced Sodium-Ion Storage in N-Doped Carbon Nanofiber@MoS2 Nanosheet Arrays. Electrochim. Acta 2018, 285, 301−308. (64) Zou, G.; Hou, H.; Cao, X.; Ge, P.; Zhao, G.; Yin, D.; Ji, X. 3D Hollow Porous Carbon Microspheres Derived from Mn-MOFs and Their Electrochemical Behavior for Sodium Storage. J. Mater. Chem. A 2017, 5, 23550−23558. (65) Simon, P.; Gogotsi, Y.; Dunn, B. Where Do Batteries End and Supercapacitors Begin? Science 2014, 343, 1210−1211. (66) Yao, X.; Ke, Y.; Ren, W.; Wang, X.; Xiong, F.; Yang, W.; Qin, M.; Li, Q.; Mai, L. Defect-Rich Soft Carbon Porous Nanosheets for Fast and High-Capacity Sodium-Ion Storage. Adv. Energy Mater. 2018, No. 1803260. (67) Zou, G.; Hou, H.; Ge, P.; Huang, Z.; Zhao, G.; Yin, D.; Ji, X. Metal-Organic Framework-Derived Materials for Sodium Energy Storage. Small 2018, 14, No. 1702648.

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Figure captions Figure 1. XRD patterns of Co/NCs (a), Raman spectra of Co/NCs (b), nitrogen adsorption -desorption isotherm of Co/NCs (c), and pore size distribution of Co/NCs (d). Figure 2. XPS spectra of the Co/NCs nanocubes: survey spectrum of Co/NCs (a), C 1s of Co/NC-700 (b), N 1s of Co/NC-700 (c), and Co 2p of Co/NC-700 (d). Figure 3. SEM micrographs of ZIF-67 (a and b), Co/NC-600 (c and d), Co/NC-700 (e and f), and Co/NC- 800 (g and h). Figure 4. TEM micrographs of Co/NC-700 (a-c), HRTEM micrographs of Co/NC-700 (d), SAED of Co/NC-700 (e), elemental mapping images of Co/NC-700 (f-i), and EDS of Co/NC-700 (j). Scheme 1. Schematic illustration of the synthesis process of Co/NCs. Figure 5. The first five CV curves of Co/NC-600 (a), Co/NC-700 (c) and Co/NC-800 (e) at a scan rate of 0.1 mV s-1 in the potential range of 0.01-3.0 V (vs. Li+/Li), and the discharge/charge curves of Co/NC-600 (b), Co/NC-700 (d) and Co/NC-800 (f) at current density of 0.1 A g-1 for the first five cycles. Figure 6. Cycling performances of Co/NCs at 0.1 A g-1 (a). In the full-cell, the cycling properties of Co/NC-700 vs. LiCoO2 (b), and the corresponding charge/discharge profiles (c). The charge/discharge profiles of the Co/NC-600 (d), Co/NC-700 (e) and Co/NC-800 (f) electrode at various current densities from the 1st to 50th cycle. Rate capability of Co/NCs at various current densities (g), and the long-term cycling performances of Co/NCs at 1.0 A g-1 (h). Figure 7. The selected time-potential curves of Co/NC-700 at different potentials (a), and 28


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corresponding in situ XRD patterns (b) and the enlarged view of Co peak (c) at different charge/discharge states. The cycling performance of bare Co nanoparticles (d) and EIS comparison of Co/NC-700 and carbon electrode (e) at open circuit potential. Figure 8. CV curves of Co/NC-700 at different scan rates of 0.1-1.0 mV s-1 (a), at different scan rates of 1.0-10 mV s−1(vs. Li+/Li) (b), the relationship of charge/discharge capacities with cyclic time of Co/NC-700 (c). Kinetic characteristic investigating through Trasatti analysis：v→∞, reflecting the more diffusion-controlled behaviors were overlooked, the Qcapacitive is calculated ~569.35 mAh g−1 (d), v→0, reflecting that the diffusion-controlled redox reaction can replace completely, the Qtotal is calculated ~657.89 mAh g−1 (e). The relationship between logarithm peak currents and logarithm sweep rates for the Co/NC-700 electrode (f), plots of i/v1/2 vs. v1/2 at different redox states for obtaining constants k1 and k2 (g), capacitive charge storage (red) and diffusion-controlled contribution (blue) at 0.5 mV s-1 (h), and the contribution ratio of capacitive (red) and diffusion (blue) charge at different sweep rates (i).

29



Figure 1

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Figure 2

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Figure 3

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Figure 4

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Scheme 1

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Figure 5

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Figure 6

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Figure 8

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Table of Contents Graphic

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C Nanocubes as High ... - ACS Publications

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