NiCo2S4 derived from metal-organic foams enables an improved electron transfer and ion diffusion performance

Journal of Alloys and Compounds 817 (2020) 153293

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A novel binary metal sulfide hybrid Li-ion battery anode: Three-dimensional ZnCo2S4/NiCo2S4 derived from metal-organic foams enables an improved electron transfer and ion diffusion performance Haikuo Zhang a, b, Jinyun Liu c, *, Xirong Lin a, b, Tianli Han c, Mengying Cheng c, Jiawei Long c, Jinjin Li a, b, ** a

Key Laboratory for Thin Film and Micro Fabrication of the Ministry of Education, Department of Micro/Nano Electronics, Shanghai Jiao Tong University, Shanghai, 200240, PR China b Center for High-Performance Computing, Shanghai Jiao Tong University, Shanghai, 200240, PR China c Key Laboratory of Functional Molecular Solids of the Ministry of Education, Anhui Laboratory of Molecule-Based Materials, Key Laboratory of Electrochemical Clean Energy of Anhui Higher Education Institutes, College of Chemistry and Materials Science, Anhui Normal University, Wuhu, Anhui, 241000, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 September 2019 Received in revised form 25 November 2019 Accepted 5 December 2019 Available online 6 December 2019

Many binary metal oxides possess poor conductivity and ion diffusion efficiency, even though they have a high theoretical capacity as secondary battery anodes. Herein, we present a double binary metal sulfide composing of ZnCo2S4/NiCo2S4 growing on carbon cloth, which was derived from a ZneCoeNi metal organic foam. Compared to the ZnCo2O4/NiCo2O4, the ZnCo2S4/NiCo2S4 anodes exhibit an obviously improved electrochemical performance including a high areal capacity of 2.4 mAh cm
2 after cycling for 100 times at 0.36 mA cm
2, and a Coulombic efficiency of 99.9%. A well-recoverable rate-performance is also presented. In addition, the enhancement mechanism is investigated by using density functional theory simulations, which show the density of states and Li ion diffusion energies of the ZnCo2S4/NiCo2S4 are improved compared to ZnCo2O4/NiCo2O4. It is expected that the high-performance hybrid and the theoretical enhancement mechanism would enable them to find important applications for developing emerging energy-storage materials. © 2019 Elsevier B.V. All rights reserved.

Keywords: Binary metal sulfides Metal organic foams Secondary batteries Density functional theory calculations

1. Introduction Depending on the increase of energy crisis and environmental pollution, developing clean energy has received broad attention. Clean energy sources need energy storage systems in many cases. Li-ion battery is dominated in the world markets, such as in the portable electronics and new-energy vehicles [1e4]. Currently, the carbon-based anodes are commonly used in Li-ion batteries [5e7]; nevertheless, its theoretical capacity is poor (372 mAh g
1). It is dissatisfactory for the development of high-capacity battery systems which have become more and more significant [8,9]. Many

* Corresponding author. ** Corresponding author. Center for High-Performance Computing, Shanghai Jiao Tong University, Shanghai, 200240, PR China. E-mail addresses: [email protected] (J. Liu), [email protected] (J. Li). https://doi.org/10.1016/j.jallcom.2019.153293 0925-8388/© 2019 Elsevier B.V. All rights reserved.

efforts have been contributed to develop high-performance anode candidates [10e12]. Nanosizing and constructing composites have been considered promising. Recently, several studies have shown that binary metal oxides, such as NiCo2O4, ZnMn2O4, NiFe2O4, are attractive for their electrochemical performance and structural stability [13e17]. However, the low electron and Li ion transfer efficiencies lead to poor cycling capability and rapid capacity decay. Several sulfides possess special advantages compared to their oxide counterparts: i) the lattice spacing of many metal sulfides is enlarged compared to oxide counterparts, which is able to speed up the immigration of Li ions; ii) the enhanced conductivity of sulfides is commonly achievable, so the conversion of binary metal oxides to sulfides would be an efficient strategy to address the issues indicated above. In recent years, metal sulfides have been widely investigated for LieS batteries due to their strong adsorption with

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Fig. 1. (a) Illustration for the ZnCo2S4/NiCo2S4 hybrid coating on CC. (b,c) SEM images of the ZnCo2O4/NiCo2O4 on CC. (d) TEM image of the ZnCo2O4/NiCo2O4 nanoplate. (e,f) SEM (g) TEM images and (h) HRTEM image and corresponding SAED pattern of the ZnCo2S4/NiCo2S4. XRD patterns of (i) ZnCo2S4/NiCo2S4 and (j) ZnCo2O4/NiCo2O4.

polysulfides [18,19], such as SeS2 [20], MoS2 [21], Co9S8 [22,23], and for Li-ion batteries owing to their specific electronic properties, such as the sulfides ReS2 [24,25], FeS2 [26], CoS2 [27,28], MoS2 [29], and VS4 [30]. Zheng et al. synthesized a core-shell CuCo2S4 nanosphere by a solvothermal process, which showed a high capacity (773.7 mAh g
1) after cycling for 1000 times [31]. Wang et al. hydrothermally synthesized NiCo2S4 nanosheets on Ni foam, which remained 1386 mAh g
1 after cycling for 50 times at 200 mA g
1 [32]. However, so far, many investigations focused on single binary metal sulfide anode, and the enhancement mechanism is unclear regarding to the electron and Li ion transfer compared to their oxides. Herein, we present a double binary metal sulfide anode which composes of a novel ZnCo2S4/NiCo2S4 hybrid derived from ZnCo2O4/NiCo2O4 metal-organic foams (MOFs) grown on a threedimensional (3D) carbon cloth (CC), as illustrated in Fig. 1a. The ZnCo2S4/NiCo2S4 anodes exhibit an obviously improved electrochemical performance compared to the oxides. After 100 cycles at 0.36 mA cm
2, the ZnCo2S4/NiCo2S4 anode exhibits an areal capacity of 2.4 mAh cm
2, and a Coulombic efficiency of 99.9%, which exceed those of ZnCo2O4/NiCo2O4. The mechanisms have been studied by using density function theory (DFT) simulations, which show the density of states (DOS) increase significantly after converting ZnCo2O4/NiCo2O4 to ZnCo2S4/NiCo2S4. In addition, the diffusion of Li ions on the ZnCo2S4/NiCo2S4 is improved compared

to the ZnCo2O4/NiCo2O4. 2. Experimental 2.1. Preparation of ZnCo2S4/NiCo2S4 MOFs on CC All the chemicals were purchased from Sinopharm Chemical Reagent Company. First, 0.1725 g of ZnSO4$7H2O, 0.1577 g of NiSO4$6H2O, 0.5821 g of Co(NO3)2$6H2O, and 1.5 g of 2methylimidazole (2-MIM) were separately dissolved in 40 mL of DI water under stirring. Then those two solutions were mixed and stirred for 2 min. The carbon cloth piece at a radius of 0.6 mm, which was cleaned by acetone, ethanol and deionized water was put into the mixed solution and reacted for 4 h at room temperature. Then, the ZneNieCo-MOFs/CC was rinsed with DI water, and dried in an oven. In an air environment, the sample was annealed at 350  C for 2 h to form ZnCo2O4/NiCo2O4. After that, the ZnCo2O4/ NiCo2O4 was placed in an autoclave with 35 mL of 0.1 M Na2S solution. The treatment was kept at 90  C for 6 h. At last, the sample was rinsed and dried for further use. 2.2. Characterization The X-ray diffraction analyzer (XRD, Bruker D8 Advance) was used to measure the phase of samples. The samples were observed

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on a scanning electron microscopy (SEM, Hitachi S-4800) and a transmission electron microscopy (TEM, HT-7700). Energy dispersive X-ray spectroscopy (EDS) and elemental mappings were measured by using the same SEM equipped with an Oxford INCA analyzer. The X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250Xi) was used to study the composition and chemical states. The thermal analysis (TGA) was conducted on Setaram Labsys Evo SDT Q600. 2.3. Computational methods DFT simulations were conducted to demonstrate the enhancement mechanism. In our investigation, a Vienna Ab-initio Simulation Package (VASP) [33] was used. The projector augmented wave pseudopotential [34,35] and the generalized gradient approximation of Perdew-Burke-Ernzerhof were employed. The structures of ZnCo2S4, NiCo2S4, ZnCo2O4, NiCo2O4 with a space group of Fd-3m and carbon were optimized until energy and force lower than 1  10
6 eV atom
1 and 0.01 eV Å
1, respectively. The energy cutoff of 520 eV and k-points grids of 3  3  1 were chose. To calculate Li ion diffusion barrier on the (111) plane of structures mentioned above, the slabs including five atom layers were cleaved, in which a vacuum layer of 15 Å was employed for avoiding layer-layer interaction. The DFT-D3 was employed in all calculations [36]. The diffusion energy was calculated through the climbing image nudged elastic band method. 2.4. Electrochemical tests Electrochemical measurements were conducted using the battery test system (Neware) and electrochemical workstation (Shanghai Cheng Hua, CHI660D). The ZnCo2O4/NiCo2O4 and ZnCo2S4/NiCo2S4 on CC were directly used as binder-free anodes to assemble CR2032-typed coin cells. A piece of Li metal was used as counter electrode. The electrolyte contained 1 M LiPF6 in ethylene carbonate/diethyl carbonate. All cells were assembled in glovebox (Mikrouna Super 1220/750) infilling with ultra-pure argon. The capacity was tested through a galvanostatic method at 0.01e3.0 V. Cyclic voltammetry (CV) profiles were measured at 0.1 mV s
1; and electrochemical impedance spectroscopy (EIS) were recorded on the same workstation.

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3. Results and discussion ZneNieCo-MOFs were synthesized on CC by a facile method at room temperature using 2-methylimidazole (2-MIM) as an organic-ligand. Then, ZnCo2O4/NiCo2O4 (Fig. 1b and c) was prepared by annealing the NieCo-MOFs (Fig. S1). At last, the ZnCo2S4/ NiCo2S4 coating on CC was obtained by a sulfuring treatment using Na2S solution. The zoomed-in SEM image of the ZnCo2O4/NiCo2O4 (Fig. 1c) displays that the nanoplate array is in a height of about 1 mm. The nanoplates were transformed from triangular to slightly bended and rough after heat-treatment. In the TEM image (Fig. 1d), there are many pores throughout the plate which are ascribed to the oxidization of MOFs at a high temperature [37]. In Fig. 1eeg, the morphology of ZnCo2S4/NiCo2S4 changes slightly after sulfidation from ZnCo2O4/NiCo2O4. As seen, the ZnCo2S4/NiCo2S4 nanoplates coat densely on the CC; and a cross-link 3D network architecture is formed. The porous structure would provide abundant redox sites, and enables the penetration of electrolyte through the anode in batteries. In addition, the corresponding HRTEM image (Fig. 1h) shows that the lattice spacings of 0.31 and 0.19 nm are consistent with (1 1 1) and (2 2 0) planes of ZnCo2S4, while the other two lattice spacings of 0.55 and 0.32 nm can be indexed to (1 1 1) and (2 2 0) planes of NiCo2S4. The illustration of SAED pattern also reveals co-existence of ZnCo2S4 and NiCo2S4. The phases of the ZnCo2S4/NiCo2S4 and ZnCo2O4/NiCo2O4 on CC were studied by XRD patterns as shown in Fig. 1i and j. The two strong diffraction peaks at around 25.6 and 43.7 are ascribed to the CC substrate. The peaks at 16.3 , 26.8 , 31.6 , 38.3 , 47.4 and 50.5 correspond to NiCo2S4 (JCPDS No. 20-0782); while the peaks centered at 28.6 , 47.6 , 56.5 , 76.9 are assigned to the ZnCo2S4 (JCPDS No.47-1656) [38]. As for the ZnCo2O4/NiCo2O4, diffraction peaks are assigned to the ZnCo2O4 (JCPDS No.23-1390) and NiCo2O4 (JCPDS No.20-0781). In Fig. 2, the elemental mapping images indicate uniform distribution of elements Co, Ni, Zn, and S throughout the composite; while the C and O are from the CC substrate. EDS spectrum (Fig. 2h) confirms the chemical composition of the ZnCo2S4/NiCo2S4. To demonstrate the elemental composition and chemical states, the XPS measurement of ZnCo2S4/NiCo2S4 was conducted. In Fig. 3a, the survey spectrum indicates the existence of Zn, Ni, Co, S elements besides to the C and O from the CC substrate. In Fig. 3b, peaks

Fig. 2. (a) SEM image, (beg) elemental mappings, and (h) EDS spectrum of the ZnCo2S4/NiCo2S4 on CC.

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Fig. 3. (a) XPS survey spectrum, (b) Zn 2p, (c) Co 2p, (d) Ni 2p, (e) S 2p of the ZnCo2S4/NiCo2S4.

at 1022 and 1045 eV are indexed to the Zn 2p3/2 and Zn 2p1/2, respectively [39]. In Co 2p and Ni 2p regions, spin-orbit peaks and satellites were divided. In Fig. 3c, peaks at 781 and 797 eV for Co 2p3/2 and Co 2p1/2 correspond to Co3þ; and the ones at 782.7 and 798 eV are assigned to the Co2þ, respectively [40]. In Fig. 3d, the peaks at 856 and 873 eV are ascribed to the Ni2þ; while another two peaks at 857 and 875 eV are assigned to Ni3þ [41]. The peaks at 162.5 and 163.5 eV are observed in Fig. 3e, which are indexed to the S 2p [42]. Moreover, TGA curve of the ZnCo2S4/NiCo2S4 on CC is shown in Fig. S1c. The weight loss before 300  C is ascribed to the evaporation of water and decomposition of some organic species on CC. The second weight loss is contributed to that the ZnCo2S4/ NiCo2S4 transforms to ZnCo2O4/NiCo2O4. According to the second weight loss, the content of ZnCo2S4/NiCo2S4 on CC is calculated to

be about 7 wt%. The discharge/charge curves of the ZnCo2S4/NiCo2S4 anode at 0.36 mA cm
2 are presented in Fig. 4a. It should be indicated that the bare CC exhibits some capacity contribution. Fig. S2c shows the cycling capacity of CC electrode. Since the active materials loading mass is about 0.9 mg cm
2 on CC, the gravimetric capacity of the ZnCo2S4/NiCo2S4 can be calculated as 1211, 1311, 1288, and 856 mAh g
1 for the 1st, 2nd, 3rd, and 100th cycles, respectively, which are quite competitive with some other reports [43e45]. Fig. 4b presents the cyclic performances of the ZnCo2S4/NiCo2S4 and ZnCo2O4/ NiCo2O4. The ZnCo2S4/NiCo2S4 anode provides a discharge area capacity of 2.82 mAh cm
2 in the first cycle, along with a high Coulombic efficiency of 98%, which are better than the ZnCo2O4/ NiCo2O4 (2.49 mAh cm
2 in the initial cycle with a Coulombic

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efficiency of 94%). The high initial Coulombic efficiency may be contributed to the porous and tightly-connected morphology of the composite which is beneficial for a stable and thin SEI formation [46,47]. More importantly, the capacity maintains 2.4 mAh cm
2 after 100 cycles, and a Coulombic efficiency of 99.9%. In contrast, the ZnCo2O4/NiCo2O4 anode decays seriously after 100 cycles. When cycling at a relatively high current density of 1 mA cm
2, the ZnCo2S4/NiCo2S4 shows a stable discharge area capacity of 2.54 mAh cm
2 after 30 cycles, as presented in Fig. S3. The rateperformance is displayed in Fig. 4e. At a rate of 1.5 mA cm
2, the ZnCo2S4/NiCo2S4 exhibits a capacity of 2.21 mAh cm
2. When turning back to 0.36 mA cm
2, the capacity recovers to 2.79 mAh cm
2. We can also find that the ZnCo2O4/NiCo2O4 exhibits a lower rate-performance compared to the ZnCo2S4/NiCo2S4. The ZnCo2S4/NiCo2S4 and ZnCo2O4/NiCo2O4 growing on CC were directly used as binder-free anodes. The initial five cyclic CV curves of the ZnCo2S4/NiCo2S4 anode are shown in Fig. 4c. To distinguish the typical peaks of ZnCo2S4/NiCo2S4, the CV curves of the pristine

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CC were also studied under the same testing conditions. As displayed in Fig. 4d, in the first cycle, a cathodic peak located at 0.31 V was detected, which shifted to around 0.84 V in the following cycles. In the anodic sweep, a strong peak appears at 0.32 V, corresponding to Li ion extraction from CC [37]. For the ZnCo2S4/NiCo2S4 anode, a broad peak at 0.53 V is ascribed to the solid electrolyte interphase (SEI) formation. The peak at 1.15 V is related to reduction of Zn2þ, Ni2þ, Co3þ into Zn, Ni, Co metals together with forming Li2S. Then the cathodic peak shifts to 1.35 V, originating from Li ion insertion to electrodes. The anodic peaks at 1.5 and 2.0 V correspond to the Zn, Ni, Co oxidations to form ZnCo2S4 and NiCo2S4 [48]. The curves overlap well in the following cycles, which indicates a good reversibility. The CV curves of the ZnCo2O4/NiCo2O4 anode is displayed in Fig. S2a. Similarly, the first cycle shows the formation of SEI. In the subsequent sweeps, the cathodic peak at 1.28 V and anodic peaks at 1.6 and 2.1 V are associated with the redox reaction during discharge and charge, respectively. Corresponding charge/discharge curves are shown in Fig. S2b. Fig. 4f

Fig. 4. (a) charge/discharge curves of the ZnCo2S4/NiCo2S4 anode. (b) cycling performance at 0.36 mA cm
2. (c) CV curves of the ZnCo2S4/NiCo2S4 and (d) bare CC at 0.l mV s
1. (e) Rate-performance. (f) EIS of the ZnCo2S4/NiCo2S4 and ZnCo2O4/NiCo2O4 on CC. The insert shows the fitted circuit diagram.

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shows the EIS spectra of the ZnCo2S4/NiCo2S4 and ZnCo2O4/NiCo2O4 anodes. Impedance spectra were fitted and shown in the inset of Fig. 4f. The ZnCo2S4/NiCo2S4 exhibits a smaller charge transfer resistance (Rct) of 110.5 U than that of the oxides (223.3 U). After 50 cycles, the charge transfer resistances for the ZnCo2S4/NiCo2S4 and ZnCo2O4/NiCo2O4 increase to 255.9 and 315.9 U, respectively. The electrochemical kinetics were further investigated by measuring CV curves at a variety of rates at 0.2e1.0 mV s
1. In Fig. 5a, the CV curves show a similar shape at different rates, indicating a small polarization [49]. The relation of current (i) and scanning rates (v) follows the formula: i ¼ avb [50]. It is transformed into log(i) ¼ log(a) þ blog(v). The value of b can be calculated according to the plotted Fig. 5b, the slope values of 0.8303,

0.7283 for the anodic and cathodic peaks, respectively, imply a dominated capacitance process. The electrochemical reaction can be quantitatively described by the formula [51]: i(v) ¼ k1v þ k2v1/2, where k1v and k2v1/2 stands for the capacitance and diffusioncontrolled processes, respectively. The values of k1 are obtained by the curves plotted in Fig. 5c. The capacitance ratio of the whole charge storage can be determined at certain rates. In Fig. 5d, a capacitive contribution of 61.5% is obtained at 0.4 mV s
1. Fig. 5e displays all the ratios at different rates. The ratios increase depending on the increase of rates. The capacitance-controlled results confirm the Li ions tend to aggregate on the surface of electrodes in the charge/discharge process, which would avoid pulverization of anodes because of large volume expansion and

Fig. 5. (a) CV curves at different rates. (b) The log(i) vs. Log(v) plots, and (c) i/v1/2 vs. V1/2. (d) CV curve with capacitive contribution at 0.4 mV s
1 marked by green. (e) Ratios of the capacitive contributions at different rates. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

H. Zhang et al. / Journal of Alloys and Compounds 817 (2020) 153293

shorten ion diffusion path [52]. In order to further demonstrate the enhancement mechanism of the ZnCo2S4/NiCo2S4 compared to the ZnCo2O4/NiCo2O4, the DFT analysis was performed. As shown in Fig. 6a and b, DOS results show that the ZnCo2S4 and ZnCo2O4 both possess a band gap,

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indicating a nature semi-conductive property. The band gap values for ZnCo2S4 and ZnCo2O4 are 0.51 eV and 0.58 eV, respectively. Fig. 6c demonstrates that the band gap of NiCo2O4 is smaller than ZnCo2O4 or ZnCo2S4, which means that NiCo2O4 is more conductive. When transformed into NiCo2S4, the DOS (Fig. 6d) is

Fig. 6. DOSs of (a) ZnCo2O4, (b) ZnCo2S4, (c) NiCo2O4, (d) NiCo2S4, (e) ZnCo2S4/C, (f) NiCo2S4/C, models of the (g) ZnCo2S4 and (h) NiCo2S4 on carbon.

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Fig. 7. Li ion diffusion barrier of (a) ZnCo2O4 and ZnCo2S4, (b) NiCo2O4 and NiCo2S4. Li ion diffusion pathway on (c) ZnCo2S4, (d) ZnCo2O4, (e) NiCo2S4, (f) NiCo2O4.

continuous around Fermi level, which reveals that an enhanced conductivity is obtained after sulfidation compared with its oxide. To simulate the real case that ZnCo2S4/NiCo2S4 grows on conductive CC substrate, we constructed a single carbon layer below the ZnCo2S4 and NiCo2S4 layers to examine the whole conductivity. The detailed structural information is illustrated in Fig. 6g and h. In Fig. 6e and f, we can see that there are many electron states emerge around the Fermi level, which is able to greatly speed up reaction kinetics. In addition, the Li ion diffusion barrier energies on the ZnCo2S4, ZnCo2O4, NiCo2S4 and NiCo2O4 were investigated. The (111) plane is commonly exposed for NiCo2S4 and NiCo2O4, so it is cleaved for calculations in our study. We find that the diffusion energy of ZnCo2S4 (0.26 eV) is smaller than that of ZnCo2O4 (0.93 eV), which indicates that Li ions could more easily transfer in the ZnCo2S4 (Fig. 7a). In Fig. 7b, a diffusion energy of 0.15 eV for NiCo2S4 is presented, exhibiting a smaller diffusion energy than NiCo2O4 (0.58 eV). The diffusion pathway is shown in Fig. 7cef. The lowered Li ion diffusion barrier is beneficial for accelerating a fast ions diffusion due to the formation of ZnCo2S4/NiCo2S4.

transfer of electrons and Li ions. It is believed that the binary sulfides hybrid structure and the theoretical mechanism would bring some new inspirations to develop high-performance energy-storage materials for secondary batteries. Author contribution statement Haikuo Zhang: Methodology, Formal analysis, Data curation, Writing- Original draft preparation. Jinyun Liu: Conceptualization, Formal analysis, Writing- Original draft preparation, Writing- Reviewing and Editing, Supervision. Xirong Lin: Formal analysis, Visualization, Investigation. Tianli Han: Data curation, Formal analysis, Visualization, Investigation. Mengying Cheng: Formal analysis, Visualization, Investigation. Jiawei Long: Formal analysis, Visualization, Investigation. Jinjin Li: Conceptualization, Writing- Reviewing and Editing, Supervision. Declaration of competing interest

4. Conclusions In summary, a binary ZnCo2S4/NiCo2S4 hybrid derived from MOFs growing in a CC is presented. The binder-free ZnCo2S4/ NiCo2S4 anodes exhibit a high area capacity of 2.4 mAh cm
2 after cycling at 0.36 mA cm
2 for 100 times, along with a Coulombic efficiency of 99.9%. The cycling capability and rate-performance are improved compared to their oxide counterparts. The DFT calculations show that the conductivity is improved, and the Li ion diffusion energy is reduced after sulfidation, thus accelerating the

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was supported by the National Natural Science Foundation of China (51672176 and 21901157), Science and Technology Major Project of Anhui Province (18030901093), Key

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Research and Development Program of Wuhu (2019YF07), Natural Science Research Project for Universities in Anhui Province (KJ2018ZD034 and KJ2019A0502), Creative Science Foundation of AHNU (2018XJJ108), Foundation of Anhui Laboratory of MoleculeBased Materials (FZJ19014), and the Anhui Provincial Program for Innovation and Entrepreneurship of Returnees from Overseas (2019LCX005). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.153293. References [1] Z.Q. Jia, Y.B. Tan, Z.H. Cui, L.L. Zhang, X.X. Guo, Construction of NiCo2O4@ graphene nanorods by tuning the compositional chemistry of metal-organic frameworks with enhanced lithium storage properties, J. Mater. Chem. A 6 (2018) 19604e19610. [2] D.X. Wang, Y. Wang, Q.Y. Li, W.B. Guo, F.C. Zhang, S.S. Niu, Urchin-like alphaFe2O3/MnO2 hierarchical hollow composite microspheres as lithium-ion battery anodes, J. Power Sources 393 (2018) 186e192. [3] J.Y. Cheong, W.T. Koo, C. Kim, J.W. Jung, I.D. Kim, Feasible defect engineering by employing metal organic framework templates into one-dimensional metal oxides for battery applications, ACS Appl. Mater. Interfaces 10 (2018) 20540e20549. [4] T. Kim, W.T. Song, D.Y. Son, L.K. Ono, Y.B. Qi, Lithium-ion batteries: outlook on present, future, and hybridized technologies, J. Mater. Chem. A 7 (2019) 2942e2964. [5] J. Xu, X. Wang, N.Y. Yuan, B.Q. Hu, J.N. Ding, S.H. Ge, Graphite-based lithium ion battery with ultrafast charging and discharging and excellent low temperature performance, J. Power Sources 430 (2019) 74e79. [6] Y.Y. Zhang, N.N. Song, J.J. He, R.X. Chen, X.D. Li, Lithiation-aided conversion of end-of-life lithium-ion battery anodes to high-quality graphene and graphene oxide, Nano Lett. 19 (2019) 512e519. [7] H. Kim, J. Kim, H.S. Jeong, H. Kim, H. Lee, J.M. Ha, S.M. Choi, T.H. Kim, Y.C. Nah, T.J. Shin, J. Bang, S.K. Satija, J. Koo, Spontaneous hybrids of graphene and carbon nanotube arrays at the liquid-gas interface for Li-ion battery anodes, Chem. Commun. 54 (2018) 5229e5232. [8] Q.H. Cui, Y.T. Zhong, L. Pan, H.Y. Zhang, Y.J. Yang, D.Q. Liu, F. Teng, Y. Bando, J.N. Yao, X. Wang, Recent advances in designing high-capacity anode nanomaterials for Li-ion batteries and their atomic-scale storage mechanism studies, Adv. Sci. 5 (2018) 1700902. [9] J.G. Lee, B.N. Joshi, J.H. Lee, T.G. Kim, D.Y. Kim, S.S. Al-Deyab, I.W. Seong, M.T. Swihart, W.Y. Yoon, S.S. Yoon, Stable high-capacity lithium ion battery anodes produced by supersonic spray deposition of hematite nanoparticles and self-healing reduced graphene oxide, Electrochim. Acta 228 (2017) 604e610. [10] J. Sun, C.X. Lv, F. Lv, S. Chen, D.H. Li, Z.Q. Guo, W. Han, D.J. Yang, S.J. Guo, Tuning the shell number of multishelled metal oxide hollow fibers for optimized lithium-ion storage, ACS Nano 11 (2017) 6186e6193. [11] Y. Li, L.B. Kong, M.C. Liu, W.B. Zhang, L. Kang, Facile synthesis of Co3V2O8 nanoparticle arrays on Ni foam as binder-free electrode with improved lithium storage properties, Ceram. Int. 43 (2017) 1166e1173. [12] W.B. Liu, L. Chen, L. Cui, J.Z. Yan, S.C. Zhang, S.Q. Shi, Freestanding 3D nanoporous Cu@1D Cu2O nanowire heterostructures: from a facile one-step protocol to robust application in Li storage, J. Mater. Chem. A 7 (2019) 15089e15100. [13] Y.D. Zhu, Y. Huang, M.Y. Wang, K. Wang, M. Yu, X.F. Chen, Z. Zhang, Novel carbon coated core-shell heterostructure NiCo2O4@NiO grown on carbon cloth as flexible lithium-ion battery anodes, Ceram. Int. 44 (2018) 21690e21698. [14] Y. Wang, P.C. Liu, K.J. Zhu, J. Wang, K. Yan, J.S. Liu, One-step fabrication of in situ carbon-coated NiCo2O4@C bilayered hybrid nanostructural arrays as freestanding anode for high-performance lithium-ion batteries, Ceram. Int. 273 (2018) 1e9. [15] J.X. Chen, W. Liu, S. Liu, H.L. Wang, Y. Zhang, S.G. Chen, Marine microalgaesderived porous ZnMn2O4/C microspheres and performance evaluation as Liion battery anode by using different binders, Chem. Eng. J. 308 (2017) 1200e1208. [16] Y.L. Zhang, W.Q. Cao, Y.Z. Cai, J.C. Shu, M.S. Cao, Rational design of NiFe2O4rGO by tuning the compositional chemistry and its enhanced performance for a Li-ion battery anode, Inorg. Chem. Front. 6 (2019) 961e968. [17] J.J. Deng, X.L. Yu, X.Y. Qin, D. Zhou, L.H. Zhang, H. Duan, F.Y. Kang, B.H. Li, G.X. Wang, Co-B nanoflakes as multifunctional bridges in ZnCo2O4 micro-/ nanospheres for superior lithium storage with boosted kinetics and stability, Adv. Energy Mater. 9 (2019) 1803612. [18] J.R. He, Y.F. Chen, A. Manthiram, Metal sulfide-decorated carbon sponge as a highly efficient electrocatalyst and absorbent for polysulfide in high-loading Li2S Batteries, Adv. Energy Mater. 9 (2019) 1900584.

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