Synthesis of Few-Layer Reduced Graphene Oxide for Lithium-Ion

Article pubs.acs.org/IECR

Synthesis of Few-Layer Reduced Graphene Oxide for Lithium-Ion Battery Electrode Materials Jihao Li, Linfan Li, Bowu Zhang, Ming Yu, Hongjuan Ma, Jianyong Zhang, Cong Zhang, and Jingye Li* CAS Key Lab of Nuclear Radiation and Nuclear Energy Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, P. R. China S Supporting Information *

ABSTRACT: We report here a rapid and cost-effective approach to synthesize few-layer reduced graphene oxide (FL-RGO) in graphene oxide solution using EDA as a reducing agent and a cross-linker, and where the resulting FL-RGO was characterized by means of AFM, TEM, XPS, UV−vis, and XRD spectroscopies. A mechanism for forming the FL-RGO via removal of epoxide and hydroxyl groups from GO and stitching of the GO sheets by EDA in a water solution was proposed. FL-RGO was also tested as the electrolyte for a Li+-ion battery and showed advantages with a 346 mAh g−1 capacity at a charge/discharge current density of 1C even after 60 cycles, which is comparable to the theoretical capacity of the graphite (372 mAh g−1).

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INTRODUCTION Nanostructured carbon materials are well-known for their excellent capability to store energy.1−4 As a part of carbon materials, graphite, the commercial anode carbon material, also encounters some disadvantages such as low theoretical specific capacity and poor rate performance.5 In combination with the advantages of the nanomaterial and the graphite in lithium-ion battery application, the emergence of graphene nanomaterial for the preparation and application of new lithium-ion battery anode material provides a new way of thinking. Graphene, a novel 2-D carbon nanomaterial, has attracted wide attention because of its unique mechanical,6 thermal,7 optical,8 and electrical properties,9 and it holds great promise for many technological applications.10−12 Lately, graphene materials have been used as prospective anode materials in rechargeable lithium-ion batteries.13 Graphene4,14−16 has shown high reversible capacity values when used as anode materials in lithium-ion batteries. Additionally, graphene-based nanomaterials are classified according to their restriction of the axes perpendicular to the basal plane of the graphene as doublelayer graphene, few-layer graphene (FLG) (3−9 layers), or multilayer graphene (10 or more layers).17 Among these types, few-layer graphene, which can be regarded as a quasi-2D nanomaterial, has been reported in use as field effect transistors (FET) and is prepared by mechanical exfoliation (repeated peeling) of small mesas of highly oriented pyrolytic graphite18 or by atomic layer deposition and physical vapor deposition.19 Few-layer graphene (FLG) was also synthesized from grapheme oxide (GO) using microwave-assisted exfoliation as an anode material for Li-ion batteries.20 Despite a relatively large number of methods developed to produce graphene, the lack of reliable synthesis methods to produce FLG on a largescale continues to inhibit its application. Graphene oxide (GO), which has 2-D carbon backbones decorated with hydrophilic functional groups,21−23 can be easily prepared from graphite by various approaches, such as the modified Hummers method24−27 at large-scale and low cost,28 and is dispersible in water or other polar solvents.28,29 GO is an © 2014 American Chemical Society

excellent precursor to prepare reduced graphene oxide (RGO) via many reduction approaches.30−37 Meanwhile, GO can also be piled up during the chemical reactions which results in complex 3-D carbon nanomaterials, depending on the nature of the host GO and the intercalant, pillaring and stitching that can be accomplished by ion exchange, intercalation or reaction with the difunctional reagent and reassembly. Matsuo et al.38 reported the intercalation of polyaniline into GO in N-methyl-2-pyrrolidone (NMP) through a previous intercalation of N-hexadecylamine.39 Rajamathi et al.36 describe the delamination and colloidal dispersion of various N-alkylamine intercalated GO in different organic solvents. Robert et al.40 describes a detailed study of the intercalation reaction of α,ω-diaminoalkanes, H2N(CH2)nNH2 (n = 4−10), with GO to produce chemically bridged GO derivatives in an ethanol/water system at room temperature. Hung et al. describe cross-linking with diamine monomers to prepare composite GO framework membranes and show its stability in a separation ethanol−water mixture by pervaporation.41 In our very recent work, we successfully synthesized porous graphene aerogel by one-step reduction and selfassembly of graphene oxide with ethylenediamine.42 Combined with stitching, reduction, and self-assembly, this aerogel has good stability and compressibility. On the basis of the cross-linking and reduction of GO for 3D structure carbon nanomaterial construction, we herein report one step preparation of few-layer reduced graphene oxide (FLRGO) in water medium using EDA as a reducing agent and a cross-linker. The addition of EDA into GO dispersion was accompanied by a fast and unexpected color change, and finally the FL-RGO agglomerated in water or organic solvents such as ethanol and DMF was obtained. The as-produced FL-RGO was characterized by a variety of complementary methods, including Received: Revised: Accepted: Published: 13348

May 4, August August August

2014 5, 2014 8, 2014 14, 2014

dx.doi.org/10.1021/ie5018282 | Ind. Eng. Chem. Res. 2014, 53, 13348−13355

Industrial & Engineering Chemistry Research

Article

atomic force microscopy (AFM), transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fouriertransform infrared spectroscopy (FT-IR), thermo gravimetric analysis (TGA), ultraviolet visible spectroscopy (UV−vis), and Raman spectroscopy. The FL-RGO samples were also used as the anode in lithium-ion batteries, and sheet resistance and charge/discharge cycling performance were characterized.

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Figure 1. Photographs of the dispersions of GO (0) and GO reacted with EDA for 2, 4, 8, 16 and 24 h, at 0.1 mg/mL in water settled for 2 weeks after preparation and ultrasoniation.

EXPERIMENTAL SECTION Materials. Graphite powder (CP grade), EDA, and other chemical reagents (AR grade) were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. All chemicals were used as received without further purification. Milli-Q water was used for all experiments unless otherwise stated. A commercial PVDF membrane with 0.22 μm pore-sizes was used for filtration. Preparation of FL-RGO. GO was prepared from graphite powder through a modified Hummers method as described in our previous work.43,44 In a typical experiment of the FL-RGO preparation, 3 g of EDA was added into 50 mL of ultrapure water, and then to the mixture, 50 mL of 2 mg/mL aqueous suspension of GO was slowly added under magnetic stirring in an ice−water bath at 0−5 °C. The GO concentration was about 1 mg/mL in the final mixture. The mixture was deoxygenated by nitrogen bubbling in a 250 mL flask and then heated in a water bath at 80 °C for various time periods (0, 2, 4, 8, 16, 24 h); the reaction pH value was adjusted with hydrochloric acid or sodium hydroxide. After that, extra EDA and ions were removed by dialysis with a hydrochloric acid solution (pH = 2) and ultrapure water more than ten times, and finally, the asgenerated FL-RGO was separated from the reaction mixture through filtration with a PVDF membrane and washed with ultrapure water three times. Measurements. The instruments and methods for the characterization of the materials are listed in the Supporting Information. Electrochemical measurements were performed in a LANDCT2001A cell test system using lithium metal as a counter/ reference electrode for a voltage scan from 0.005 to 3.0 V. Charge/discharge characteristics for Li+-ion battery performance were examined with CR2032 coin cells, assembled in an Ar-filled glovebox. Working electrodes were prepared by pasting a mixture of 60 wt % (∼3−5 mg) FL-RGO material with 20 wt % conductive black and 20 wt % PVDF onto circular Cu foil (diameter = 12 mm). The electrolyte was 1.0 M LiPF6 in ethylene carbonate (EC)/diethylcarbonate (DEC) (1:1 v/v).

AFM analysis was performed to check the morphology of the products, and the samples are prepared by drop-casting the ultrasonicated dispersion of the products on a freshly cleaved mica surface. Figure 2a presents an AFM image of GO under a

Figure 2. AFM topology analysis of (a, b) GO and (c, d) FL-RGO-8h on freshly cleaved mica.

tapping mode where there are many large GO sheets of a diameter of 200 nm, and the thickness of GO is about 0.95 nm which is measured from the cross-section profile curve in Figure 2b indicating the single layer structure of GO. Figure 2c reveals that the products of the GO reacted with EDA for 8 h are not uniform, and the cross-section analyses of the height profiles in Figure 2d showed that the thickness varied from about 1 to 5 nm, which is an indication that there are many accumulated RGO besides the small portion of a single layer RGO. This means that our goal material, FL-RGO, was obtained. Herein, the products are named as FL-RGO-2h, 4h, 6h, 8h, 16h, and 24h, for those GO reacted with EDA for 2, 4, 6, 8, 16, and 24 h, respectively. The picture of dried FL-RGO-8h is presented in Figure S2 in the Supporting Information. The mechanism of the formation of FL-RGO during the reduction reaction is due to the covalent binding of amine groups with the epoxy groups and carboxyl groups on GO, thus the biamine groups of EDA can play a role as a cross-linker, as illustrated in Scheme S1 in the Supporting Information, which occurred just as the two hands (biamine groups) of one person (EDA) came into contact with the neighboring GO sheets: combination of stitching, reduction, and functionalization.

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RESULTS AND DISCUSSION GO was reacted with EDA in water at 80 °C for 2, 4, 8, 16, and 24 h, and the color of the mixture changed from yellowish brown to homogeneous black with the elongated reaction time which indicated that the reduction reaction had taken place. Figure 1 shows optical pictures of the products dispersed in water settled for 2 weeks after sonication, where it can be found that the GO dispersion is still uniform after the settlement, but the longer reaction time results in poor stability of the products dispersed in water. The agglomeration of the products in water or organic solvents such as ethanol and DMF (Supporting Information, Figure S1) is another indication of the formation of RGO sheets compared with that reported phenomena.32,37 13349



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characteristics of reduction products of GO.43 We should mention that there was no free EDA molecular residual in the FL-RGO sample, since the absorption peak of EDA around 210 nm disappeared. The XRD patterns of the GO and the FL-RGO are given in Figure 4b. Instead of the diffraction peak at 2θ of 10.09° with dspacing of 8.76 Å for GO, a new broadened diffraction peak at 2θ of 23.77° with d-spacing of 3.73 Å appeared in the pattern for FL-RGO-8h, which is close to the position of the (002) peak for the graphite (d-spacing 3.37 Å, 2θ = 26.43°). The overall results demonstrate that the FL-RGO has an inhomogeneous crystalline state and similar structure to graphite, which can be regarded as a nanosized graphite. XPS analysis was performed to analyze both the chemical state and weight percentage of the C, O, and N elements in GO and FL-RGO. The XPS wide-scan spectrum of FL-RGO shows an intensified nitrogen peak at 399 eV and a decreased oxygen peak at 530 eV, as compared to that of GO in Figure 5a, which indicates deoxygenation and oxygen substitution by nitrogen. The weight percentage of the C, O, and N elements are listed in Table 1, and the elemental ratios of C/O and C/N are calculated from that data. It is easy to find that the amount of the N element in GO is very low but rises after the reaction between GO and EDA. This means the additive reaction of EDA with those epoxy and carboxyl groups on GO is a quick step corresponding to the ring opening reaction and the amidation reaction in 2 h and the attached nitrogen-containing groups with almost no change afterward. However, the change of the O element is a slow step corresponding to two parts: before and after 8 h of the reaction. At the beginning of the reaction the O element quickly decreases corresponding to the deoxidization reaction in 8 h; then the O element almost does not change after 8 h of the reaction. Since the amount of the N element is constant in FL-RGO, we can try to write an imaging molecular formula considering a certain amount of a polycyclic carbon structure that is reacted with one EDA molecule (NH2− CH2−CH2−NH2, in short, N2C2) and that some amount of the N element in pristine GO should be considered together. Based on this point, we can calculate that there are about 26 C atoms, equal to about 13 polycyclic rings, which will be attached with one EDA molecule, assuming that the original N element attached is unchanged. The resulted imaging formulas are listed in the last column of Table 1 and show that there are about 7.3 O atoms in the 13 polycyclic rings and half of them were substituted by EDA at the beginning of the 2 h reaction, which should be attributed to the amidation. After being reacted for another 6 h, there was a decrease of 1.3 extra O

The morphology and structure of the FL-RGO sheets were further confirmed using TEM imaging, which is presented in Figure 3a, with FL-RGO sheets deposited on a Cu grid. Except

Figure 3. TEM images of (a) FL-RGO and (b) the diffraction pattern of FL-RGO sheets by SAED, (c) HR-TEM image of the wrinkle of FLRGO sheet, and (d) the surface intensity analysis of the wrinkle.

for a few wrinkles, the inhomogeneous and relatively high contrast of the TEM image demonstrates that the FL-RGO sheets were generated successfully. To gain some insight into the crystalline structure of the FLRGO sheets, the SAED patterns are given in Figure 3b and the HRTEM image in Figure 3c. The corresponding SAED pattern shows multihexagonal symmetry diffraction spots revealing that the FL-RGO sheets have a crystalline state, and the corresponding HRTEM image shows the few-layers and the interlamellar spacing (0.380 nm) of the FL-RGO in Figure 3c and 3d. Here, we should mention that the distance of the interlamellar spacing of the FL-RGO is higher than the graphite (0.335 nm) as reported. In Figure 4a, the UV−vis spectra show that the shoulder peak of GO around 290 nm (n → π* transition of C−O bonds) disappears, and the sharp absorption peak around 230 nm (π → π* transitions of aromatic C−C bonds) red-shifted to 265 nm after reaction with EDA, which is consistent with the

Figure 4. (a) UV−vis spectra of EDA, GO, and FL-RGO-8h in water and (b) XRD pattern of graphite, GO, and FL-RGO-8h. 13350



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Figure 5. (a) XPS wide-scan spectra of GO and FL-RGO-8h, (b) XPS C 1s spectrum of GO, (c) XPS C 1s spectrum of FL-RGO-8h, and (d) XPS N 1s spectrum of FL-RGO-8h.

due to the reaction between the epoxy groups of GO with EDA.42 Figure 6a shows the typical FT-IR spectra of GO and FLRGO-8h. Before the reaction, the stretching vibration band of CO is at 1732 cm−1, and the stretching vibration bands C−O of epoxy and alkoxy are at 1124 and 1043 cm−1, respectively, demonstrating that the GO has abundant oxygen-containing groups. In the FL-RGO-8h spectrum, however, it is markedly different from that of GO and graphite, where the intensities of all the absorption bands correlated to the oxygen-containing groups decreased dramatically, while two new broad bands occurred at 1578 cm−1, which is associated with the vibration of N−H groups, and a band at 1130−1230 cm−1, which is associated with the vibration of the C−N bond. The Raman spectra of FL-RGO is similar to that of GO, as presented in Figure 6b, but the relative intensities ratio of the D band at 1352 cm−1, which corresponds to the breathing mode of κ-point phonons of A1g symmetry, with a G band at 1586 cm−1, which corresponds to a first-order scattering of the E2g mode,47,51 increased from 0.98 to 1.11, which is also evidence for the reduction.33,47 Figure 6c shows the TGA curves of graphite, GO, and FLRGO-8h, where there is an obvious decomposition stage from 150 to 230 °C for GO, while it is a slowly downward sloping line for FL-RGO, which indicates the enhanced thermal stability due to the removal of oxygen-containing groups. All these results prove that the prepared FL-RGO is thermally stable. To evaluate the electrical conductance of the FL-RGOs, circular pallets with a thickness of 0.2 mm and a diameter of 10 mm for FL-RGO powders were prepared using a tablet compression machine (with a force of 150 kN). The electrical conductivity of FL-RGO was measured using a digital fourpoint probe system. To obtain reliable electrical conductance data, the probes were carefully placed on the samples, and five different sites were chosen on each sample for measurement.

Table 1 weight percentage (%)

GO FL-RGO2h FL-RGO4h FL-RGO8h FL-RGO16h FL-RGO24h

elemental ratio

C

O

N

C/O

C/N

71.43 77.8

26.66 13.78

1.91 8.42

3.57 7.53

43.63 10.78

78.95

12.44

8.61

8.46

10.70

81.55

9.25

9.2

11.75

10.34

81.57

9.37

9.06

11.61

10.50

81.61

9.23

9.15

11.79

10.41

imaging formula C26O7.3N0.6 C26O3.7N0.6(C2N2) C26O3.3N0.6(C2N2) C26O2.4N0.6(C2N2) C26O2.4N0.6(C2N2) C26O2.4N0.6(C2N2)

atoms, which should be attributed to the elimination corresponding deoxidization and chemical cross-linking similar to the formation of FL-RGO in Scheme S1. Combined with the dispersibility of the products given in Figure 1, it can be concluded that the formation of FL-RGO mainly happened at the beginning of the 8 h. Figure 5b and 5c show the XPS C 1s spectra of GO and FLRGO-8h. The spectrum of GO can be deconvoluted into three different peaks that correspond to carbon atoms assuming different binding status. The peaks are centered at the binding energies of 284.8 eV for CC/C−C bonds in aromatic rings, 286.7 eV for epoxy and alkoxy bonds, and 288.7 eV for O−C O bonds, respectively.45 In the spectrum of FL-RGO, apart from those peaks attributed to the aromatic rings and carbonyl groups, there are new peaks at 285.9 eV for C−N bonds46,47 and at 287.9 eV for HN−CO bonds,48−50 which also validate the amidation of the polycyclic rings in the FL-RGO. Figure 5d presents the XPS N 1s narrow scan of the pristine aerogel, and there are peaks at 399.7 eV that are attributed to the amide groups and 401.2 eV attributed to the amine groups which are

Figure 6. (a) FT-IR spectra of graphite, GO, and FL-RGO-8h; (b) Raman spectra of GO and FL-RGO-8h; and (c) TGA curves of graphite, GO, and FL-RGO-8h at the heating rate of 10 °C min−1 under N2. 13351



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decomposition, the formation of lithium organic compounds, and the generation of irreversible capacity.54,55 In subsequent cycles, the sloped plateau in the first discharge curve disappears and was replaced by a smooth curve, which can be attributed to the Li+ insertion into the FL-RGO with SEI film protection. Cycle performances of the FL-RGO based electrode demonstrate high specific capacity with a low current density (∼710 mAh g−1 with a current density of 35 mA g−1 (0.1C) and ∼410 mAh g−1 with 175 mA g−1 (0.5C)). The FL-RGO material showed good reversible capacity (346 mAh g−1) and good cyclic stability performance with Coulombic efficiencies around 98% in LIB with a current density of 350 mA g−1 (1C) even after cycling charge/discharge at stepwise current rates with a high current density of 1750 mA g−1 (5C) in Figure 8b. Compared with the commercial graphite, the cross-linked small RGO sheets increase the FL-RGO vacancy sites (such as edgetype sites and other nanopore defects) for Li+ insertion, which may enhance the capacity in FL-RGO nanosheets.56 Just as with other reported high-specific-capacity carbon anodes,52,54 the FL-RGO anode material also exhibits a low first-cycle Coulombic efficiency (∼58%) due to the formation of SEI and the irreversible reaction between Li+ with some remaining function groups on the FL-RGO.54,55 According to previous results, we include a table of comparison of our FLRGO anode with the commercial graphite anode, GNS (graphene), N-GNS anode in terms of initial lithiation capacity, initial Coulombic efficiency, and reversible capacity in Table 2.

The sheet resistance of GO was so large that it ran out of the measurement range of the instruments. Just as we have reported,43 GO sheet resistance is greater than 107Ω□−1, while the FL-RGO products are found to be semiconductors and their resistances quickly decrease with increasing reaction time as presented in Figure 7. The rate of decrease slowed down

Figure 7. Variation in the sheet resistance of FL-RGO block with reaction time.

after being reacted for 8 h. The lowest sheet resistance was about 190 Ω□−1 for the FL-RGO-24h, which was still improved by 5 orders of magnitude as compared with the GO. Although the resistance of the FL-RGO is still much higher than graphite, FL-RGO can be regarded as nanofied graphite. Therefore, it is easy to see the use of FL-RGO as an anode material in a Li+-ion battery. Thus, the electrochemical performance in a coin cell was studied. The first to fourth discharge/charge curves of FL-RGO were measured at a current density of 35 mA g−1 (0.1 C), as shown in Figure 8a. This shows similar charge/discharge profiles with a large charge/discharge voltage hysteresis in the first discharge/charge curve, as previously reported for graphene-based samples.52,53 For example, the first discharge curve shows a sloped plateau at about 0.75 V. This discharge plateau can be attributed to the formation of an SEI film (solid electrolyte interface) on the surface of the FL-RGO, which is associated with electrolyte

Table 2. Comparison of Various Carbon Anode Materials

samples FL-RGO commercial SFG10 graphite GNS (graphene) GNS (graphene) GNS N-GNS

initial lithiation capacity (mAh/g)

initial Coulombic efficiency (%)

reversible capacity (mAh/g) (current density)

ref

1580 486

58 52

∼410 (175 mA/g) ∼230 (25 mA/g)

57

1014

40.6

∼252 (100 mA/g)

58

1472

26

∼250 (200 mA/g)

59

780 1300

44 37

∼269 (200 mA/g) ∼360−390 (200 mA/g)

60 60

Figure 8. Electrochemical performances of FL-RGO as the anode of Li+-ion battery: (a) discharge (solid line) and charge (dash and dot line) curves of the first four cycles (1, black, 2, red, 3, blue, 4, olive) at the rate of 0.1c and (b) cycling discharge(red)-charge(black) performance at stepwise current rates. 13352



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From Table 2, we can learn that the first-cycle Coulombic efficiency (∼58%) of the FL-RGO anode material is higher than other anode materials (commercial graphite anode (52%),57 GNS (40.6%),58 N-GNS anode (44%)60). Except for the initial Coulombic efficiency, the initial lithiation capacity of the FL-RGO anode is also higher than other anode materials in Table 2. We think that the high initial lithiation capacity (1580 mAh/g) of the FL-RGO is due to its more vacancy sites (3-D structure for edge-type sites and other nanopore defects and some remaining function groups on the FL-RGO), and the Coulombic efficiencies of other cycles of the FL-RGO anode can reach a high Coulombic efficiency (95−99%). Notably, the charge curves of the FL-RGO were almost consistent in the subsequent cycles. At the same time, the reversible capacity of the FL-RGO anode is also higher than other anode materials, which could be attributed to the well SEI film protection and some reversible reaction with function groups from RGO and nitrogen groups, because the N-groups from an organic molecule (EDA) may act as a film that reduces the activity of the FL-RGO surface thus reducing their reversible reactions with the electrolyte, which also decrease the initial irreversible capacity and increase the reversible capacity.61 The prepared FL-RGO provides the possibility of producing improved LIB carbon electrode materials due to its 3-D nanostructure, which may provide more vacancy sites for Li+-ion insertion and a significantly shortened Li+ diffusion pathway.62−65 The smaller crystallite structure, high specific surface area, and disorganized graphene stack14,15 of the FL-RGO was confirmed by the presence of a strong D band in the Raman spectra (Figure 6b). Several points also should be addressed here: first, the FLRGO, which is not subjected to further thermal and reduction treatments, is electronically conductive and can be directly applied as the electrode of the LIBs; second, in the present case, the small RGO sheets increase the FL-RGO vacancy sites (such as edge-type sites and other nanopore defects), which enhanced the capacity in disordered FL-RGO nanosheets; and third, the cross-linking via EDA molecular between the RGO sheets in the FL-RGO stabilized the materials in the process of Li+ insertion and extraction. So, this method can be used for preparing new cross-linking “sandwich” graphene composites for new anode material. All the results of the as-prepared FLRGO show good electrochemical performance in lithium-ion batteries.

interlayer spacing through the introduction of a foreign force to interfere in the assembly process for potential application in electrochemical energy storage devices and other areas.

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ASSOCIATED CONTENT

S Supporting Information *

The instruments and methods for the characterization of the materials. Photographs of FL-RGO sheets (8h) of dispersion in different solvents. Photographs of synthesized GO and FLRGO (8h) powders. Illustration of the reaction between GO and EDA and formation of FL-RGO. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 11175234 and 11105210), the “Strategic Priority Research Program” of the Chinese Academy of Sciences (Grant XDA02040300), the “Knowledge Innovation Program” of the Chinese Academy of Sciences (Grant KJCX2-YW-N49), and Shanghai Municipal Commission for Science and Technology (Grant 12ZR1453300).

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REFERENCES

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CONCLUSIONS In summary, we have demonstrated that the GO sheets could be reduced and functionalized efficiently by EDA in an aqueous system under moderate conditions for preparation of the FLRGO. This type of a few-layer structured macroassembly shows good conductivity and excellent electrochemical performance for use in energy storage and other applications. The mechanism for chemical functionalization of GO has been proposed and will be helpful for exploitation of novel strategies for three-dimensional (3D) RGO framework preparation. This XPS result illustrates that the reaction might reach an equilibrium state within 8 h, revealing that the EDA has a strong reduction capability for GO. Additionally, the asprepared FL-RGO shows good electrochemical stability performance in lithium-ion batteries and provides the possibility of producing improved LIB carbon electrode materials. Further work is underway to use different diaminoalkanes as a reducing agent and functional group to fabricate pillared few-layer graphene sheets with tailored 13353



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Synthesis of Few-Layer Reduced Graphene Oxide for Lithium-Ion

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