Na‐Doped C70 Fullerene/N‐Doped Graphene/Fe‐Based Quantum Dot

Author Manuscript

Title: Na-doped C70 fullerenes/N-doped graphene/Fe-based quantum dots nanocomposites for sodium-ion batteries with ultra-high coulombic efﬁciency

Authors: Chunlian Wang; Yang Zhang; Wen He; Xudong Zhang; Zhaoyang Wang; Guihua Yang; Manman Ren; Lianzhou Wang

This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofrea- ding process, which may lead to differences between this version and the Version of Record.

To be cited as: ChemElectroChem 10.1002/celc.201700899

Link to VoR: https://doi.org/10.1002/celc.201700899 ARTICLE

1 Na-doped C70 fullerenes/N-doped graphene/Fe-based quantum dots nanocomposites 2 for sodium-ion batteries with ultra-high coulombic efficiency

3 Chunlian Wang,[a] Yang Zhang,[b] Wen He,*[ad] Xudong Zhang,*[a] Guihua Yang,[c] Zhaoyang Wang,[a] Manman Ren,[ad] 4 Lianzhou Wang[d]

[5-8] 6 Abstract: We fabricate Na-doped C70 fullerenes (Na-C70)/N-doped39 better performance. Carbon materials showing potential using

7 graphene (N-GN)/Fe-based nanocomposites (Na-C70/N-GN/FBNCs)40 in other area, such as carbon silicon composites for 8 with the multiple morphologies via an in situ one step method used41 electromagnetic materials[9], poly/multi-walled carbon nanotubes 9 the multifunction sodium lignosulfonate (SLS) as the structural42 with conductive segregated structure[10], graphene quantum dots 10 template and the main raw material. Fe-based nanoparticles can43 decorated oxide as solar cells[11]. Nanocarbon materials are 11 embed in ordered mesoporous hybrid carbon structure of Na-C7044 recognized as the leading electrode material for commercial 12 and N-GN via spontancous chelation reaction of SLS with iron ions45 LIBs anodes because of their high electrical conductivity, low 13 and carbonization under relatively mild hydrothermal treatment. We46 cost, and high chemical stability. However, these carbon-based 14 investigate the influences of molar ratio of SLS:Fe on the structure,47 anode materials used in LIBs cannot be used in SIBs because 15 component and electrochemical properties of the nanocomposites.48 the pure graphite anode only has a low capacity of 35 mAh g- 16 Its unique hybrid carbon structure offers metallicity and49 1.[12,13] The hard carbon (so-called nongraphitizable carbon) 17 superconductivity, countless bonding sites of Na ions, and facilitate50 anode can deliver a capacity of 300 mAh g-1 due to the 18 the transfer of electrons and Na ions during prolonged cycling. The 51 difference of lithium and sodium between molecular radius, but 19 nanocomposites for sodium-ion batteries (SIBs) anodes can achieve 52 its electrical conductivity and rate performance is poor.[14] 20 the highest discharge capacities of 1898 mAh g-1 at the current -1 53 To develop high performance anode materials for SIBs, Fe- 21 density of 1000 mA g , and retain a reversible capacity of 238 mAh [15] [16-18] [19] -1 54 based materials, such as FeNb11O29 , Fe2O3 , Fe3O4 , 22 g after 100 cycles, which are dramatically better than that of lithium- [20-23] [24] [25] -551 FeS , and FeS , and Fe S , have been extensively 23 ion batteries (LIBs). The discharge and charge capacity at 1 A g 2 1-x -1 56 studied because of their high theoretical capacities, low cost, 24 after 30th cycles are 356 and 119 mAh g , respectively, with the 25 ultra-high coulombic efficiency of 299% and the highest coulombic57 earth-abundance and nontoxicity. Among them, Fe2O3 and FeS2 26 efficiencies of 463% after 220 cycles. 58 have been considered as promising candidates for SIBs. 59 However, pure Fe-based electrodes in SIBs showed low 60 reversible capacities, poor cycle life and rate performance, 61 owing to low electrical conductivity, larger Na-ion radius, slower 27 Introduction 62 reaction kinetics, and huge volume expansion from Na-ion 63 insertion. The overall electrochemical performances of the pure 28 Designing and fabricating low-cost nanocomposites are64 Fe-based electrodes are still far from practical application. To 29 considerable interests in improving and optimizing65 mitigate these problems, Fe-based carbon and graphene electrochemical performances of energy storage and conversion 30 66 nanocomposites with various structures have also been studied 31 electrodes. In recent years, great efforts have been devoted to67 for Na-ion storage. [16-18,23] Inclusion of carbon coating materials 32 the research of sodium-ion batteries (SIBs) to obtain low cost,68 improves the structural stability of these Fe-based composites 33 high capacity, and long cycling life batteries and meet the69 during cycling and augments the conductivity of the active 34 demands of different fields, such as sensor, controller and power70 materials. Jun Chen et al. [16] synthesized three-dimensional 35 source.[1-4] The research on the electrode materials of SIBs has 71 (3D) porous γ-Fe2O3@C nanocomposite by using an aerosol 36 made important progress, in part because developments in 72 spray pyrolysis technology, in the nanocomposite the γ-Fe2O3 37 nanocomposite materials are making it possible to achieve 73 nanoparticles (5 nm) uniformly embedded in a porous carbon 74 matrix, which shows high-rate capability and long-term cyclability 75 when applied as an anode material for SIBs. Yiben Shao et al. [24] [a] C-L Wang, Prof. W. He, Prof. X-D Zhang, Z-Y Wang,Prof. M-M Ren 76 prepared FeS2 quantum-dots/functionalized graphene-sheet College of Material Science and Engineering, Qilu University of 77 (QDs/FGS) composites by a facile and scalable method, which Technology, Jinan 250353, China 78 were used as anode materials for sodium-ion batteries and E-mail: [email protected]; [email protected] -1 [b] Dr.Y. Zhang 79 achieved large specific discharge capacities of 742 mAh g at -1 school of information science and technology, Tsinghua university, 80 the current density of 0.5 A g in the first cycle, retained a Beijing, 100084, China 81 reversible charge capacity of 552 mAh g-1 after 100 cycles and [c] Prof. G-H Yang 82 displayed a high specific capacity of 315 mAh g-1 at the high Key Laboratory of Pulp and Paper Science and Technology of -1 Ministry of Education, Qilu University of Technology, Jinan 250353, 83 current densities of 5 A g . These results indicate that the Fe- China 84 based carbon and graphene nanocomposites can significantly [d] Prof. L-Z Wang 85 enhance cycle performance and high rate capability. But the Nanomaterials Centre, School of Chemical Engineering and AIBN, The University of Queensland,Brisbane, QLD 4072, Australia 86 synthesis of these nanocomposites is complex, high cost and 87 low productivity, which severely limits its practical application. Supporting information for this article is given via a link at the end of the document. 88 Besides, as iron exists in different stoichiometric forms and 89 crystallographic structures, synthesis of Fe-based carbon 38

ARTICLE

1 nanocomposite with controllable morphologies remains a28 storage system. Recently, we have been interested in rational 2 challenge. 29 utilizations of Fe-based nanocomposite electrode materials. 3 The application area of polymer, such as co-polymer, flame30- In this study, Fe-based nanoparticles were uniformly

4 retardant foam, recycled plastic, ethyl oleate esterification, is31 anchored onto hybrid carbon structure of Na-C70 and N-GN and

5 wide and could match with different compound and simple32 formed the Na-C70/N-GN/FBNCs with various morphologies via a 6 substance, for example, react with inorganic substance for33 simple in situ synthesis method. We explored the possibility of

7 TiO2/SnO2 nanofibers, with negative permittivity flexible34 using multifunction sodium lignosulfonate (SLS) as the structural

8 membranous metacomposites, and energy materials, such as35 template and the main raw material to fabricate Na-C70/N- 9 battery or supercapacitor electrode materials, except these,36 GN/FBNCs anodes for SIBs and LIBs. The results show that the 10 polymer usually as surfactant to participant synthesis37 skeleton of SLS and a large amount of sulfonic group in SLS 11 composites. [25-31] In this article, we use polymer sodium38 enable its use as carbon and sulfur sources that can control the

12 lignosulfonate and inorganic ferric nitrate to synthesis composite39 formation of Fe-based nanoparticles and Na-C70/N-GN by 13 and as sodium ion battery anode. Commercial sodium40 means of ion exchange and crosslinking reaction. The various 14 lignosulfonate (SLS) is a cheap anionic polymeric surfactant41 polar functional groups in SLS, such as hydroxyl and carboxyl 15 derived from by-products of the cooking process in sulfite42 groups, might easy chelate iron ions and control self-assembly [32] 16 pulping in the manufacture of paper. Molecular mass of SLS43 of particles, thus achieving the in situ synthesis of Na-C70/N- 17 ranges from several hundred to several million according to the44 GN/FBNCs nanocomposite. The particles with different 18 preparation conditions. The degree of sulfonation of SLS45 morphologies in the nanocomposite might be able to affect the 19 molecules is 0.4-0.5 per phenylpropane unit (Fig. 1c) and its46 Na-ion storage and transport synergistically, and importantly, 20 carbon content is greater than 60% with a quite high ash47 this kind of synergistic effect, if exists, cannot be easily attained [33] 21 content. Since SLS owns a three dimensional cross-linked48 with some other synthesis methods. As expected, the Na-C70/N-

22 structure containing C6–C3 hydrophobic basic structure with a49 GN/FBNCs anodes exhibited larger specific capacity, higher rate 23 variety of reactive groups in its molecules, such as hydrophilic50 performance, ultra-high coulombic efficiency as well as

24 hydroxyl, carboxyl, and sulfonic acid groups, an aqueous51 outstanding cycling stability compared to the pristine FeS2 and [34] 25 solution of SLS shows amphiphilic properties. Unfortunately,52 Fe2O3 nanoparticles. This study opens a new way for rational 26 until now, the potential of SLS as a raw material to use in value53- utilization of this waste biomass in designing and preparing high- 27 added applications is underexploited in energy conversion and54 efficiency energy storage and transformation materials.

Results and Discussion

SLS molecules with iron ions was obtained by using polarizing A simple and effective synthesis method was developed for microscopy as shown in Fig. S1 (ESI†), showing self-assembly fabricating low-cost Fe-based/carbon nanocomposites via a aggregation behavior of SLS solution (Fig. S1a) and the biomass converting route, and the synthesis procedure is spontancous chelation and crosslinking reactant of linear SLS illustrated in Fig. 1. This synthesis method is based on the ion exchange, chelation and crosslinking reactions of multifunction SLS molecules with iron ions. The interaction evidence of the

Fig. 1. (a-d) The schematic diagram of the in situ synthesis of Na-C70/N-GN/FBQDs. (e) SEM image of the Na-C70/N-GN/FBQDs sample with different morphologies.

1 2

2 molecules with Fe3+ ions (Fig. S1b). Fig. 1a-d show the 58 observed in the elemental mapping images of Fe and S (Fig. 3 schematic diagram of the synthesis procedure to prepare the 59 3fh). HRTEM images in Fig. 3b-d show its fine microstructure. 4 nanocomposites. The aqueous solution of SLS shows 60 In Fig. 3b some spheroidal nanoparticles with the size of

5 amphiphilic properties, enabling spontaneous adsorption of the 61 approximately 10 nm are embedded in Na-C70/N-GN, 3+ 6 Fe from Fe(NO3)3 solution through coordination or 62 7 electrostatic interactions. In this process, the abundant reactive 8 groups in SLS can effectively induce the nucleation of FBQDs 9 on the SLS surface, whereas SLS is depolymerized to formed

10 hybrid carbon nanosheets of Na-C70 and N-GN through a 11 carbothermic reaction. Firstly, the self-assembly of reactant 12 particles was completed under the hydrothermal conditions and 13 formed the precursor with various morphologies (Fig.1c). Then 14 the precursor was heated at 500 °C for 8h to obtain the Na-

15 C70/N-GN/FBQDs composites with different morphologies (Fig. 16 1d). The SEM image in Fig.1e can confirm that the synthetic 17 mechanism is reasonable. 18 The crystal structure and phase composition of the synthetic 19 samples are revealed by X-ray diffraction (XRD). Fig. 2 shows 20 the XRD patterns of the samples prepared with different molar 21 ratio of SLS:Fe. The standard XRD patterns of different 22 substances are also included at the bottom of Fig. 2 for 23 comparison. The XRD results show that the A sample prepared 24 with SLS:Fe molar ratio of 2:1 is composed of the main crystal

25 phases (cubic FeS2 and Fe2O3, showing the stronger diffraction 26 peaks), second phase (FeS showing the smaller humps) and , 63 27 amorphous carbon (no peak), namely, the Na-C70/N- 64 Fig. 2 XRD patterns of the different samples prepared with different molar

28 GN/FeS2/Fe2O3 (Fig. 2A). According to elemental analysis (Fig. 65 ratio of SLS:Fe, A: Na-C70/N-GN/FeS2/Fe2O3 sample prepared with SLS:Fe

29 S3i) and Raman spctrum (Figs. 4bc), the mass ratio of every 66 molar ratio of 2:1, B: Na-C70/N-GN/Fe1-xS/Fe3O4 sample prepared with

30 phase in the composite is Fe2O3 (8.265Wt%), FeS2 (8.56Wt%), 67 SLS:Fe molar ratio of 1:1, C: Na-C70/N-GN/Fe1-xS sample prepared with

31 FeS (4.13Wt%), C70 (32.45Wt%), N-graphene (36.36Wt%) and 68 SLS:Fe molar ratio of 1:2. 32 amorphous carbon (10.23Wt%), respectively. The phase 69

33 evolutions of pyrrhotite Fe1-XS→pyrite FeS2 and Fe3O4 →Fe2O3 70 34 occurred at 500 °C with the increase of SLS:Fe molar ratio. The 71 showing the combination way of nanoparticles and carbon, 35 B sample prepared with SLS:Fe molar ratio of 1:1 is composed 72 where the light contrast can be assigned to the amorphous

36 of the main crystal phases (Fe1-XS and Fe3O4), second phases 73 carbon nanosheets while the dark contrast suggests the

37 (FeS2, Fe2O3 and Fe) and amorphous carbon, namely, the Na- 74 Fe-based quantum dots with higher projected mass

38 C70/N-GN/Fe1-xS/Fe3O4 (Fig. 2B). The C sample prepared with 75 density. Fig. 3c shows clearly that a FeS QD (about 8 nm) 39 SLS:Fe molar ratio of 1:2 is composed of the main crystal 76 has lattice fringes with interplanar spacings of 0.50 nm,

40 phase (Fe1-XS), second phases (FeS2, FeS, Fe2O3, Fe3O4 and 77 which can be attributed to the (001) plane of FeS. Fig. 3d

41 Fe) and amorphous carbon, namely, the Na-C70/N-GN/Fe1-xS 78 shows that the FeS2 QD (about 9.6 nm) and Fe2O3 QD 42 (Fig. 2C). The XRD results show that the molar ratio of SLS/Fe 79 (about 6 nm) have lattice fringes of 0.34 nm (101) and 0.37

43 has a great influence on the phase component of the Na-C70/N- 80 nm (012), respectively. These results show that SLS 44 GN/FBQDs. 81 played important role in the synthesis process of Na-C70/N-

45 The SEM images of the A (Na-C70/N-GN/FeS2/Fe2O3) sample 82 GN/FeS2/Fe2O3 with various morphologies and unique 46 prepared with SLS:Fe molar ratio of 2:1 show its laminar 83 nanostructures. The reactive groups of SLS can provide 47 microstructure with mushroom-shaped particles on the layer, 84 the nucleation site of FBQDs and control its growth, what’s 48 graininess structure with coarse surface, various morphologies 85 more iron ions have regulating effect on the crosslinking 49 and porous structure (Fig. S2, ESI†). It also showed that some 86 reactions of SLS molecules and the particle morphology of 50 irregularity particle reunite together forming nanosheets. The 87 Na-C70/N-GN/FeS2/Fe2O3. Fig. S3 (ESI†) reveals the 51 fine microstructure, element composition and distribution of the 88 morphology and elemental composition of the A sample by 52 A sample are shown in Fig. 3. A wafer particle in the red square 89 using energy dispersive X-ray spectroscopy (EDS), which 53 area was also observed in TEM image (Fig. 3a), which is 90 is a further confirmation of the reliability of the XRD 54 consisted of stacked structures of the nanoparticles. Elemental 91 analysis (Fig. 2A). The EDS spectrum in Fig. S3hi show 55 mapping images of this wafer particle, shown in Figs 3e-h, 92 that the A sample consist of carbon (67.3%), iron (16.5%), 56 revealed that all of C, Fe, O and S are uniformly distributed in 93 oxygen (12.8%), sulfur (1.80%), sodium (0.90%) and 57 this particle. However, some spheroidal nanoparticles are also 94 nitrogen (0.79%). Fig. S3b-g show differrent EDS map

1 images of various elements in the white square area in Fig. 3 Na, and N indicate the in situ adulteration of sodium and 2 S3a. As shown in Fig. S3bfg, the uniform distributions of C, 4 nitrogen in carbon structure. 5

6 7 Fig. 3 (a-d) HRTEM images and (e-h) elemental mapping images of C, Fe, O and S components in the red square area in (a) for the A (Na-C70/N-

8 GN/FeS2/Fe2O3) sample prepared with SLS:Fe molar ratio of 2:1 9

10 45 D to G band (ID/IG) is 1.61. These also mean the low 11 To further investigate the nature of the carbon and 46 degree of graphitization and disordered arrangement of the 12 porous structure formed in the different samples, XRD, 47 graphene sheets[44], which is consistent with the results of 13 Raman spectrum, HRTEM and nitrogen adsorption- 48 XRD patterns in Fig. 4a. The third Raman peak (12.29%, 14 desorption isotherm were carried out as shown in Fig. 4. 49 blue line) represents amorphous carbon.[45] The results in 15 Fig. 4a shows XRD patterns of different samples in low 50 Fig. 4c show that the hybrid carbon in the A sample is 16 angle range of 10°-30°. The XRD pattern (Fig. 4aA) of the 51 composed of disorder carbon (54.13%), graphitized carbon [35-37] 17 A sample is similar to Na-C70 (PDF no. 47-1577). A 52 (33.58% Area) and amophous carbon (12.29%), which 18 broad diffraction peak at around 25° in Fig. 4aA is 53 contributes to improving the electronic conductivity and 19 observed, which is indexed to that of N-doped graphene, 54 electrochemical performance of the nanocomposite.[46]This 20 implying the low degree of graphitization and disordered 55 carbon structure has significant advantage on SIBs anode 21 arrangement of the graphene sheets.[38,39] The XRD results 56 material, which could offer larger surface with more active 22 in low angle range of 10°-30° show that the molar ratio of 57 sites. Nitrogen sorption isotherms and the Barrentt-Joyner- 23 SLS:Fe has a great influence on the carbon structure of 58 Halenda pore-size distribution are carried out to investigate 24 the composites (Fig. 4 aBC). Fig. 4b shows that the 59 the pore structure. The A sample delivers type-IV 25 characteristic peaks located at around 1332 and 1592 cm-1 60 adsorption-desorption isotherm, indicating mesoporous 26 are attributed to the D-band (representing the dissociative 61 characteristics (Fig. 4e). The hysteresis loop of the A 27 disordered graphitic lattice) and G-band (representing 62 sample consists of distinct H4-type hysteresis in the low [40,41] 28 graphitized carbon) , respectively. The bands labeled 63 pressure area (P/P0=0.1-0.9) and H1-type hysteresis in the

29 with red rhombus are that of Na-C70 (inset in Fig. 4 aA), 64 high pressure area (P/P0=0.9-1.0). H4 is caused by slit 30 other bands labeled with green circle are that of N-doped 65 shaped holes with uniform shape and size. H1 is caused 31 graphene.[42] The Raman results confirm that the 66 by holes heaped up by uniform spherical particles.[47] Fig. 32 graphitized carbon in the A sample is composed of Na- 67 4f shows that the size distribution of these ordered

33 doped C70 (47.18% Area) and N-doped graphene (52.82%), 68 mesopores rang from 2 to 20 nm, which is also validated 34 which is also validated by HRTEM image in Fig. 4d. The 69 by the XRD patterns (Fig. S4a, ESI† ) in low angle range 35 strong and wide 2D-band in Fig. 4b is a second-order two- 70 of 0.5°-4.5° show that the molar ratio of SLS:Fe also 36 phonon process mode of graphene between nonequivalent 71 influences on the ordered mesoporous structure of the 37 K points in the Brillouin zone (BZ), which can be used in 72 composites (Fig. S4bc). 38 the characterization of few-layer graphene samples.[43] The 73 The elechrochemical performances of different samples with

39 value of the peak intensity ratio of the D to G band (ID/IG) 74 the mass loading of the active materials (80wt%) in the cells 40 indicates the degree of graphitization. From the Raman 75 were characterized as anode eletrodes for LIBs and SIBs. The 41 spectrum of the A sample deconvoluted by three Gaussian 76 charge and discharge curves of different samples in Fig. S5ab 42 peaks (Fig. 4c), we found that the D band (54.13% Area, 77 (ESI†) show that the A electrode for both LIBs and SIBs has 43 red line) appears to be stronger than the Gband (33.58%, 78 superior discharge capability and coulombic efficiency than that 44 green line) and the value of the peak intensity ratio of the 79 of other samples. Fig. 5a is the charge and discharge curves of 4

1 the A electrode at the different current density for SIBs. It is 3 charge capability, the A sampe has a ultra-high coulombic 2 found that the discharge capability is always greater than the 4 efficiency due to its unique structure and composition. Fig. 5b

5 Fig. 4 (a) XRD patterns of different samples in low angle range, A: Na-C70/N-GN/FeS2/Fe2O3 sample, B: Na-C70/N-GN/Fe1-xS/Fe3O4 sample, C: Na-

6 C70/N-GN/Fe1-xS sample. (b) Raman spectra of A sample, the inset in (b) shows the Raman spectrum of C70, G-band is deconvoluted by two Gaussian 7 peaks in the orange rectangle area in (b). (c) The D and G peaks of A sample are deconvoluted by three Gaussian peaks. (d) HRTEM image of the A

8 sample, the insets in (d) show the structural representation of C70 and N-doped grapgene, respectively. (e) Nitrogen adsorption-desorption isotherm 9 and Barrentt-Joyner-Halenda pore-size distribution histogram (f) of A sample. 10 11 40 electrode has ultra-high coulombic efficiency. A nuclear 12 shows that the coulombic efficiency of the A electrode at the 41 magnetron resonance (NMR) study has also revealed the -1 [50] 13 current density of 1000 mA g increases with the increase of 42 reversible insertion of Na in the carbon compounds. Although 14 cycle number. The discharge and charge capacity of the A 43 15 electrode at the current density of 1000 mA g-1 after 30th cycles 44 16 are 356 and 119 mAh g-1, respectively, with the ultra-high 17 coulombic efficiency of 299% (Fig. 6b). The highest coulombic 18 efficiency of of the A electrode after 220th cycles is 453%. It is

19 mainly because of synergistic action of FeS2/Fe2O3

20 nanoparticles and Na-C70/N-GN. This may be attibute to the

21 Na-C70 with larger surface area and the more Na ion storage 22 sites are released, the more electron reactions in N-GN are 23 reactivated by cycling reactions. The content of sodium of 24 composites is 0.9% (seeing in the Fig S3). Figs. 4aA and 4b 25 show no crystal phase of sodium, which expresses that sodium

26 implanted in the C70 was amorphous form. In the discharge and 27 charge processes, no apparent plateau can be observed, which 28 is possibly attributed to the presence of small nanoparticles of

29 FeS2 and Fe2O3. The reactions can be described as follows:

0   30 Fe 2O 3  6Na  6e  2Fe  3Na 2O (1)

  31 FeS 2  2Na  2e  Na 2FeS 2 (2) 32 Notably, the average Na+ insertion potential is increased with 33 increasing the current density, but it is nearly unchanged when 34 increasing the cycle number. Since there's a lot of free

35 electrons in Na-C70 molecular structure, Na ions can be doped 45

36 into these voids of the cage-like fused-ring structure of C70 to 46 47 Fig. 5 (a) First charge and discharge curves of the A electrode at the 37 form Na-doped C70 fullerene with metallicity and [48] 48 different current density under the potential window of 0.01-3.00 V for SIBs. 38 superconductivity. Na-C70 is an electron acceptor, Na atoms [49] 49 (b) Charge and discharge curves of the A electrode for the different cycles at 39 in C70 can also be released in discharge process, so the A 5

1 a current density of 1000 mA g-1 for SIBs. (c) Na storage mechanism of in 40 capacity is nearly not affect by the current density at 10–1000 -1 2 hybrid carbon structure of Na-C70/N-GN/FBQDs. 41 mA g . Fig. 6d presents the reversible capacities and 3 42 coulombic efficiency of the A electrode at a current density of 4 43 1000 mA g-1 for 300 galvanostatic cycles for SIBs. It can 5 Na ion can not intercalatethe interlayers of grapgene because 44 achieve the highest discharge capacity of 1898 mAh g-1 and the 6 its interlaminar spacing is smaller, Na has better reactivity with 45 charge capacity of 1150 mAh g-1 at the current density of 1000 7 the disordered graphene layers, giving countless bonding 46 mA g-1, respectively. The large capacity loss in the following [51] 8 sites. Besides N-doped graphene could effectively improve 47 discharge stages is mainly due to the irreversible formation of 9 the electronic conductivity and cyclability of Fe-based quantum 48 SEI layer. After 300 cycles, a capacity of 85 mA h g−1 can be 10 dots and buffer structural change of the A electrode in the 49 maintained and the coulombic efficiency is almost 120%, 11 process of sodium ions intercalation and de-intercalation as 50 showing good cycling stability, which is also revealed in the CV 12 shown in Fig. 5c. So the contribution of Na-C70 and N-doped 51 measurement (Fig. 6e). The results of electrochemical test

13 graphene to the reversible capacity cannot be ignored. 52 indicate that Na-C70/N-GN/FeS2/Fe2O3 nanocomposites for LIBs 14 Fig. 6a shows the cycling stability and coulombic efficiency 53 and SIBs have better electrochemical properties than that of -1 15 of the different samples at the current density of 1000 mA g for 54 other electrodes, especially for SIBs. But the coulombic 16 the first 100 galvanostatic cycles for LIBs, indicating that the A 55 efficiency values fluctuated severely because of 17 electrode has better cycling stability and coulombic efficiency. 56 its complex structure and composition. 18 The A electrode shows superior discharge capability of 920 57 To further research the electrochemical reaction kinetics of -1 -1 19 mAh g at the first cycle and finally settled about 156 mAh g 58 Na-C70/N-GN/FeS2/Fe2O3 nanocomposites as SIB anode, cycle 20 after 100 cycles and the coulombic efficiency is almost 100%. 59 voltammograms (CV) and electrochemical impendence 21 Fig. 6b shows the cycling stability and coulombic efficiency of 60 spectroscope (EIS) were characterized. CV tests were 22 the different samples as SIBs anodes with the same test 61 presented at a scan rate of 0.1 mV s-1 between 0.01 V-3.00 V 23 condition as LIBs. By comparison, we find that the A electrode 62 after different charge/discharge cycles for SIBs, as shown in Fig. 24 for SIBs shows higher reversible capacities and coulombic 63 6e. There are three unapparent peaks in the CV profile of A 25 efficiency, better cycling stability than that of other samples, 64 electrode in first cycle, which was consistent with the reversible

26 which also are higher than those of LIBs. The first discharge 65 electrochemical reaction of Fe2O3 and FeS2 nanoparticles. The 27 and charge capacities for the A electrode are 1080 and 375 mA 66 peaks in the vicinity of 0.75 and 1.6 V are the oxidation and −1 28 h g , respectively, with a ultra-high coulombic efficiency of 67 reduction peaks of Fe2O3, respectively. The peak at 0.5 V is the [23,53,54] 29 122%, which may be mainly attributed to the unique structure 68 reduction peak of FeS2. And most striking, the CV curve 30 and composition. Although the B and C electrodes deliver the 69 is still in its original form in the subsequent 300 cycles although 31 lower reversible capacities, they also have high coulombic 70 the three small peaks disappeared due to decomposition [24,32] 32 efficiency and good cycling stability. Besides, C electrode for 71 reactions of Fe2O3 and FeS2 nanoparticles. This results 33 SIBs delivers unconventional feature that the capacity of 72 demonstrates the surprising cycling stability, in keeping with 34 previous 40 cycles is lower than posterior 40 cycles and a 73 theresults of Fig. 6d. The Nyquist plots of of the A electrode 35 broad peak is presented in 40th-60th. The main reason is the 74 before and after 300 charge/discharge cycles at the range from 36 Fe1-xS with Fe vacancy in the samples shows exceptional 75 10 mHz to 10 kHz include two parts of semicircle and oblique [52] 37 superconductivity. Fig. 6c is the rate capability of the different 76 line. The semicircle rang from high frequency to medium

38 samples for SIBs. By comparison, it is found that the A 77 frequency indicates the charge transfer resistance (Rct) and 39 electrode for SIBs has very stable rate capability, its reversible 78 constent phase elements. 79

1 Fig. 6 Electrochemical characterizations of the different anodes, A: Na-C70/N-GN/FeS2/Fe2O3 sample, B: Na-C70/N-GN/Fe1-xS/Fe3O4 sample, C: Na-C70/N- -1 2 GN/Fe1-xS sample. Reversible capacities and and coulombic efficiency of different electrodes at a current density of 1000 mA g for LIBs (a) and for SIBs (b). (c) 3 Rate capacity of A electrode for SIBs. (d) Reversible capacities and and coulombic efficiency of the A electrode at a current density of 1000 mA g-1 for 300 4 galvanostatic cycles for SIBs. Cyclic voltammograms (e) and Nyquist plots (f) of the A electrode before and after 300 charge/discharge cycles. 5 55 electrochemical measurements can be found in the experimental section of 6 56 Supporting Information.

7 The Nyquist plots show that the charge transfer resistances (Rct) befor 8 and after 300 cycles are 48 Ω and 562 Ω, respectively (Fig. 6f). The 9 oblique line at the medium frequency to low frequency is attributed to 57 Acknowledgements

10 Warburg impedance (Zw) and offers the diffusion of sodium ion in the [55] 11 solid matrix. By comparison, Rct value significantly increases after 58 The authors thank National Natural Science Foundation of

12 300 cycles, which also is because of the decomposition of Fe2O3 and 59 China (Grant No. 51672139, 51472127, and 51272144) and the

13 FeS2 nanoparticles. Fig S6 shows XRD patterns of the different 60 Taishan Scholars Program Special Funds for the financial 14 electrodes after different cycles. The results show that the diffraction 61 support. They also thank the Projects Supported by the Key 15 peaks of the A electrode after 100 cycles have disappeared and 62 Laboratory of Pulp and Paper Science and Technology of 16 appeared a peak of Fe. But the B electrode after 100 cycles and the C 63 Ministry of Education (No.KF2016-01).

17 electrode after 300 cycles all show the diffraction peaks of Fe3O4 and

18 Fe, which indicates that Fe3O4 and Fe have better cycling stability 64 Keywords: sodium lignosulfonate template • Na-doped C70 19 than that of FeS2 and Fe2O3 . 65 fullerenes • N-doped graphene • multilevel structure • sodium- 66 ion battery anode

20 Conclusions 67 [1] C. Alippi, CAAI TIT, 2016, 1, 1-3 . 68 [2] H. Jin, Q. Chen, Z. Chen, Y. Hu, and J. Zhang, CAAI TIT, 2016, 1, 104- 21 In this study, an in situ one step method was employed to 69 113. 70 [3] X. Zhang, H. Gao, M. Guo, G. Li, Y. Liu, D. Li, CAAI TIT, 2016, 1, 4-13. 22 fabricate Na-doped C70 fullerenes (Na-C70)/N-doped graphene 71 [4] S. Padhy, and S. Panda, CAAI TIT, 2017, 2, 12-25. 23 (N-GN)/Fe-based quantum dots (FBQDs) (including Fe O , 2 3 72 [5] D. Kundu, E. Talaie, V. Duffort and L. F. Nazar, Angew. Chem. Int. Ed. 24 FeS2 and FeS) nanocomposites (Na-C70/N-GN/FBQDs) with 73 2015, 54, 3431–3448. 25 various morphologies. In the synthesis the multifunction sodium 74 [6] Y. Kim, Y. Park, A. Choi, N. S. Choi, J. Kim, J. Lee, J. H. Ryu, S. M. Oh 26 lignosulfonate (SLS) is used as the structural template and the 75 and K. T. Lee, Adv. Mater. 2013, 25, 3045–3049. 27 main raw material (including sodium, sulfur and carbon 76 [7] C. Wu, P. Kopold, Y. L. Ding, P. A. van Aken, J. Maier and Y. Yu, Acs 77 Nano, 2015, 9, 6610–6618. 28 sources). FBQDs are embedded in ordered mesoporous hybrid 78 [8] Z. M. Liu, X. Y. Yu, X. W. Lou and U. Paik, Energy Environ. Sci. 2016, 9, carbon structure of Na-C and N-GN via spontancous chelation 29 70 79 2314–2318. 30 reaction of SLS with iron ions and carbonization under relatively 80 [9] C. B. Cheng, R. F. Fan, Z. Y. Wang, Q. Shao, P. T. Xie, Carbon, 2017,

31 mild hydrothermal treatment. The Na-C70/N-GN/FeS2/Fe2O3 81 doi: 10.1016/j.carbon.2017.09.037. 32 sample synthesized with the SLS:Fe molar ratio of 2:1 exhibits 82 [10] K. Zhang, G-H. Li, L. M. Feng, J. Mater. Chem. C. 2017.doi: 33 the multiple morphologies and has the unique ordered 83 10.1039/C7TC02948A. 34 mesoporous hybrid carbon structure. The nanocomposites 84 [11] T. Liu, K. Yu, H. Chen, N.Wang, L. H. Hao, T. X. Li, J. Mater. Chem. A. 35 used as sodium-ion battery anodes can achieve the high 85 2017. 5. 17848-17855. 86 [12] Y. Li, S. Xu, X. Wu, J. Yu, Y. Wang, Y. S. Hu, H. Li, L. Chen and X. 36 reversible capacity and the ultra-high coulombic efficiency at 87 Huang, J. Mater. Chem. A. 2014, 3, 71–77. 37 1000 mA g-1. This work successfully demonstrates a simple and 88 [10] K. Hong, Q. Long, R. Zeng, Z. Yi, W. Zhang, D. Wang, W. Yin, C. Wu, Q. 38 effective method to fabricate low-cost Fe-based/carbon 89 Fan and W. Zhang, J. Mater. Chem. A. 2014, 2, 12733–12738. 39 nanocomposites via a biomass converting route, which 90 [11] Z Jian, Z Xing, C Bommier, Z Li and X. Ji, Adv. Energy Mater. 2016, 6, 40 represents a great step towards the development of low-cost 91 1501874. 41 energy storage and conversion electrodes. 92 [12] N. Zhang, X. Han, Y. Liu, X. Hu, Q. Zhao and J. Chen, Adv. Energy 93 Mater. 2015, 5, 1401123. 94 [13] X. Zhu, Y. Zhu, S. Murali, M. D. Stoller and R. S. Ruoff, Acs Nano, 2011, 95 5, 3333–3338. 42 Experimental Section 96 [14] H Li, L Xu, H Sitinamaluwa, K Wasalathilake and C. Yan, Composites 97 Communications. 2016, 1, 48–53. 98 [15] X. M. Lou, C. F. Lin, Q. Luo, J. B. Zhao, Chemelectrochem. 2017, 19, 99 3288-3298. 43 The Na-C70/N-GN/FBDQs nanocomposites were prepared through a 100 [16] S. M. Oh, S. T. Myung, C. S. Yoon, J. Lu, J. Hassoun, B. Scrosati, K. 44 hydrothermal method. We used Fe(NO3)3·9H2O (99%, Tianjin Kermel 45 Chemical Reagent Co., Ltd) and sodium lingosulfonate (SLS) as raw101 Amine and Y. K. Sun, Nano lett. 2014, 14, 1620–1626. [17] J. Chen, Z. Hu, Z. Zhu, F. Cheng, K. Zhang, J. Wang and C. Chen, 46 materials. Firstly, SLS and (Fe(NO3)3 solutions were mixed with SLS:Fe102 47 molar ratio of 2:1, 1:1 and 1:2, respectively. After stirring at room temperature103 Energy Environ. Sci. 2015, 8, 1309–1316. 48 for 1 h, the mixed precursor solution was transferred into a 100 ml Teflon104 [18] M. Walter, T. Zünd and M. V. Kovalenko, Nanoscale, 2015, 7, 9158 - 49 lined stainless autoclave, and kept at 180 °C for 48 h. The final obtained105 9163. 50 precursor was dried in air in an oven at 60 °C. Finally, the resulting samples106 [19] A. Douglas, R. Carter, L. Oakes, K. Share, A. P. Cohn and C. L. Pint, 51 were calcined at 500 °C for 8 h in a tube furnace with a heating rate of 2 °C107 Acs Nano, 2015, 9, 11156–11165. 52 min-1 in an nitrogen atmosphere. Eventually, the nanocomposites synthesized108 [20] W. Chen, S. Qi, M. Yu, X. Feng, S. Cui, J. Zhang and L. Mi, Electrochim. 53 with SLS:Fe molar ratio of 2:1, 1:1 and 1:2 were named as the A, B and C109 Acta. 2017, 230, 1–9. 54 sample, respectively. More details of material characterization and110 [24] Y Shao, J Yue, S Sun and H Xia, Chinese Journal of Chemistry, 2017, 111 35, 73–78. 7

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Chunlian Wanga, Dr. Yang Zhangb, Prof. Dr. Wen Head* Prof., Dr. Xudong Zhanga*,Prof. Dr. Guihua Yang,c Zhaoyang Wanga,Prof. Dr. Manman Renad and Prof. Dr. Lianzhou Wangd

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