Covalently Functionalized Graphene by Radical Polymers for

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Covalently Functionalized Graphene by Radical Polymers for Graphene-Based High-Performance Cathode Materials Yongjun Li, Zukai Jian, Meidong Lang, Chunming Zhang, and Xiaoyu Huang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05271 • Publication Date (Web): 22 Jun 2016 Downloaded from http://pubs.acs.org on June 23, 2016

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ACS Applied Materials & Interfaces

Covalently Functionalized Graphene by Radical Polymers for Graphene-Based High-Performance Cathode Materials

Yongjun Li,a,* Zukai Jian,a,b Meidong Lang,b Chunming Zhang,c Xiaoyu Huanga,* a

Key Laboratory of Synthetic and Self-Assembly Chemistry for Organic Functional

Molecules, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, People’s Republic of China， b

Key Laboratory for Ultrafine Materials of Ministry of Education, School of

Materials Science and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, People’s Republic of China c

National Engineering Research Center for Nanotechnology, 28 East Jiangchuan

Road, Shanghai, 200241, People’s Republic of China

* To whom correspondence should be addressed, E-mail: [email protected] (Tel: +86-21-54925310, Fax: +86-21-64166128); [email protected], (Tel: +86-2154925309, Fax: +86-21-64166128).

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ABSTRACT Polymer-functionalized graphene sheets play an important role in graphenecontaining composite materials. Herein, functionalized graphene sheets covalently linked with radical polymer, graphene-graft-poly(2,2,6,6-tetramethylpiperidin-1oxyl-4-yl methacrylate) (G-g-PTMA), were prepared via surface-initiated atom transfer radical polymerization (SI-ATRP). A composite cathode with G-g-PTMA as major active materials and reduced graphene oxide (RGO) as conductive additives was fabricated via a simple dispersing-depositing process and this composite cathode material exhibited a relatively high specific capacity up to 466 mAh g-1 based on the mass of PTMA, which is much higher than the theoretical capacity of PTMA. This extraordinary electrochemical performance is attributed to the fast one-electron redox reaction of G-g-PTMA and surface Faradaic reaction of RGO boosted by G-g-PTMA, which suggested that G-g-PTMA sheets play dual-role in the composite materials, that is, on the one hand provided the fast one-electron redox reaction of PTMA and on the other hand, worked as nanofiller for facilitating the surface Faradaic reaction-based lithium storage of RGO. Keywords: graphene; covalent functionalization; radical polymer; composite material; cathode.

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1. Introduction Graphene, a two-dimensional carbon nanomaterial, has recently illustrated a bright future as next-generation energy storage material for lithium ion batteries (LIBs) and supercapacitors due to the advantages such as high electronic conductivity, high specific surface areas, and good mechanical and chemical stability.1-4 In general, incorporation of graphene sheets into electrodes is aimed to improve the transportation of lithium ion and/or electron in electrodes,5-7 or provide scaffold to host the redox species that is soluble in electrolytes.8-10 For example, hybrid materials of metal oxide nanoparticles (NPs) with reduced graphene oxide (RGO) show increased specific capacities and rate capabilities when compared with free inorganic nanoparticles.5,6 For organic electrode active materials, replacement of conductive acetylene black by graphene sheets resulted in an improved rate performance and good cycling stability.8,9 In these composite electrode materials, the presence of inorganic NPs or organic compounds prevented graphene sheets from restacking during preparation process, which to some extent facilitated ions and electrons transporting efficiently in the electrodes during charge/discharge cycling.10,11 Very recently, entirely carbon nanomaterials, RGO and/or oxidized carbon nanotubes, were developed for freestanding cathodes of LIBs, in which surface oxygen functional species functioned as active sites without adding conventional redox active materials.2,3,12,13 The energy storage mechanism of the cathodes is the Faradaic reaction between surface oxygen functional groups and Li-ion. The Faradaic contribution to specific capacity of graphene-containing electrodes depends on the



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content of surface oxygen functional gruops.3,13 In most cases, the synthetic procedure of graphene/metal oxide NPs hybrid materials includes the pyrolysis of graphene/metal ions complex into well-crystallized NPs, which uniformly distributed on the surface of graphene sheets.5,6 However, during the procedure of high-temperature treatment, most of oxygen-containing groups were removed, which resulted in an increased electronic conductivity while eliminating the interaction of lithium ions with oxygen functional groups, therefore, a decreased Faradaic contribution of specific capacity from oxygen functional groups.3,13 Besides an appropriate percentage of oxygen functional groups which acted as active sites, accessing these surface active sites by ions and electrolyte is also of great importance to maximize the lithium storage performance of graphene-based electrode materials. Surface covalent functionalization of graphene sheets by polymers has been verified as an effective approach to keep the sheets from restacking in the composite materials,14,15 which is a different solution to allow utilization of the surface groups of graphene sheets. Poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA) is a typical radical polymer with potential application in cathodic materials, which consists of polymethacrylate mainchain and persistent TEMPO radicals in each ester groups.16-18 Some recent works have involved the combination of radical polymers with carbon nanotubes or graphene sheets, via physical blending or chemical bonding methods, which has been proved to be a practical way to improve the electric conductivity of composite materials while keeping the high-rate charge-storage capability of radical polymers.19-22 For instance, the composite cathode material


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prepared by directly mixing PTMA with RGO showed a much higher specific capacity (222 mAh g-1) than the theoretical one of PTMA (111 mAh g-1), which was contributed to the two-electron redox reaction of PTMA.20 However, in these reports, graphene or carbon nanotubes only functioned as conductive additives and no obvious Faradaic reaction was detected. Thus, the capacities of the composite electrodes were limited to a lower level. In this work, we prepared PTMA-functionalized graphene sheets, graphene-graft-poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (G-g-PTMA), and then a composite cathode of G-g-PTMA/RGO was fabricated via a simple dispersing-depositing process. Because chemically reduced graphene oxide was used as conductive additives and meanwhile covalent bonding method was adopted for the preparation of composite materials, the cathode showed a higher specific capacity up to 466 mAh g-1 with good cycling performance and excellent rate capability, highlighting importance of covalent functionalization of graphene sheets by radical polymers for the practical application of radical polymeric cathode materials.

2. Results and Discussion G-g-PTMA was synthesized through a surface-initiated atom transfer radical polymerization (SI-ATRP) from graphene sheets (Scheme 1).23,24 Graphene oxide (GO) was firstly prepared according to the modified Hummers’ method and reduced into RGO by hydrazine hydrate. RGO was then treated with 2-(4-aminophenyl) ethanol via in situ diazonium addition reaction to introduce hydroxyls onto the surface



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of RGO. Hydroxyls were then reacted with 2-bromo-2-methylpropionyl bromide to afford the initiating group functionalized graphene, G-Br. Subsequently, using G-Br as the initiator and HMTETA/CuBr as the catalytic system, the precursor monomer, 2,2,6,6-tetramethyl-piperidin-4-yl methacrylate (TMPM), was polymerized by SI-ATRP from the surface of graphene sheets, offering PTMPM-functionalized graphene sheets, G-g-PTMPM, which was finally oxidized to G-g-PTMA with H2O2 in the presence of Na2WO4 catalyst at 60°C.20,21

Scheme 1. Preparation of PTMA-functionalized graphene sheets. The PTMPM- and PTMA-functionalized graphene sheets were firstly characterized by FT-IR (Fig. 1a). Typical vibration absorption of C=O at 1729 cm-1 was both observed in FT-IR spectra of G-g-PTMPM and G-g-PTMA, which was attributed to polymethacrylate backbone. Typical vibrations of -CH2- and -CH3 units were located at around 2960 and 2930 cm-1, respectively. Moreover, a new absorption peak of nitroxyl radical moieties appeared at 1359 cm-1 in FT-IR spectrum after oxidization,25,26 which indicated the successful preparation of G-g-PTMA. Besides 6 ACS Paragon Plus Environment

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these characteristic signals, a weak band at 1631 cm-1 in the spectrum of G-g-PTMPM should be assigned to the vibration of adsorbed water molecules.27 XPS analysis of G-g-PTMA (Fig. 1b) gave an atomic N content of 5.59%, and the weight percentage of N was calculated as 5.57%, which was very close to the result of elemental analysis (5.50%). After oxidization, the N 1s peak of G-g-PTMA showed a slight shift from 398.7 eV to 401.2 eV compared to that of G-g-PTMPM (Fig. S1, Supporting Information), and the deconvolution of N 1s peaks gave the peak at 401.2 eV corresponding to the nitroxyl radicals.28 The successful grafting of PTMA on the surface of graphene sheets was also directly confirmed by visualizing their pattern shapes of graphene sheets via AFM (Fig. 2). In comparison with the clean and flat surface of GO with an average height of 1.5 nm (Fig. 2a), G-g-PTMA exhibited a rough surface profile and the average thickness increased to ca. 7 nm (Fig. 2b), which were formed by anchoring abundant polymeric chains. A hills-like morphology was found in AFM image of G-g-PTMA, which was originated from the inter-tangled neighboring polymer chains.29,30

Figure 1. (a) FT-IR spectra of G-g-PTMPM and G-g-PTMA, and (b) XPS survey scan and N 1s spectra (inset) of G-g-PTMA. 7 ACS Paragon Plus Environment


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Figure 2. Tapping mode AFM images of GO (a) and G-g-PTMA (b). Thermogravimetric analysis (TGA) shown in Fig. 3a was applied to investigate the thermal stability and to determine the polymer content of G-g-PTMA, which was conducted in N2 atmosphere with a heating rate of 10°C/min. Compared to the thermal decomposition of RGO and GO, the major mass loss of G-g-PTMA occurred from 250°C to 450°C, which was contributed by the thermolysis of PTMA. From the weight loss of G-g-PTMA and RGO at 450°C, the weight percentage of PTMA in G-g-PTMA was calculated as 59.4%. The N-O· centered radicals of PTMA and G-g-PTMA were characterized by the electron spin resonance (ESR) spectroscopy in which a clear singlet signal with a g-value of 2.0019 was clearly observed (Fig. 3b).31 The broad featureless ESR spectra of PTMA and G-g-PTMA were assigned to a large population of unpaired electrons in polymers, which led to a spin-spin interaction between the locally populated unpaired electrons. By comparing the ESR intensity of G-g-PTMA with that of PTMA, the weight content of PTMA in G-g-PTMA was determined to be 60.4%, which is very close to the result obtained from TGA.


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Figure 3. (a) TGA curves (in N2) of GO, RGO, and G-g-PTMA with a heating rate of 10oC/min, and (b) ESR spectra of PTMA and G-g-PTMA. To evaluate the electrochemical performance of G-g-PTMA-containing electrode materials, a composite cathode material (G-g-PTMA/RGO) containing G-g-PTMA and RGO (10 wt% of PTMA in the form of G-g-PTMA (16.7 wt%) and 53.3 wt% of RGO) were fabricated through a conventional dispersing-depositing process according to the reported procedure.20,32,33 In the galvanostatical charge/discharge measurement at a current density of 0.2 A g-1 based on the weight of PTMA within a voltage window of 2.0-4.0 V (vs. Li) (Fig. 4a), the composite cathode of G-g-PTMA/RGO delivered a high reversible capacity up to 466 mAh g-1, which exhibited a combination of a typical voltage plateau of PTMA at ca. 3.6 V 16,21 and a slope-shaped curve in the range of 2.0 V to 3.5 V. In order to elucidate the energy storage mechanism of G-g-PTMA/RGO composite cathode, we also measured the charge/discharge profiles of control cathodes based on PTMA, PTMA/RGO or G-g-PTMA (Fig. 4b), which delivered specific capacities of 106 mAh g-1 for PTMA, 181 mAh g-1 for G-g-PTMA, and 262 mAh g-1 for PTMA/RGO, respectively. The physically blended PTMA/RGO cathode showed a similar discharge curve with a



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capacity as 262 mAh g-1 but a shorter voltage platform than that of G-g-PTMA/RGO (Fig. 4b), and this phenomena could also be found in the discharge curves of G-g-PTMA and PTMA. This result may be attributed to the improved transport kinetics of electrons and ions between PTMA and RGO in G-g-PTMA/RGO composite cathode, which is originated from a higher homogeneity on molecular level with more efficient contact of PTMA with RGO in covalent bonding state.34

Figure 4. (a) Galvanostatic charge/discharge curves of G-g-PTMA/RGO at a current rate of 0.2 A g-1; (b) comparison of the third charge/discharge cycle of G-g-PTMA/ RGO, G-g-PTMA, PTMA/RGO, and PTMA at a current rate of 0.2 A g-1; (c) comparison of galvanostatic discharge/charge behaviors of G-g-PTMA/RGO, G-g-PTMA/RGO (20 wt% PTMA), and RGO when normalized to the whole


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electrode weight; and (d) SEM image of as-prepared G-g-PTMA/RGO cathode slurry. The theoretical capacity of PTMA is only 111 mAh g-1 when per repeated unit assuming one-electron redox reaction, and it has been reported by Guo et al that the specific capacity of PTMA-based cathode could be promoted by thermally reduced graphene sheets to 222 mAh g-1 in a two-electron redox reaction mode, which was verified by two voltage plateaus at 3.1 V and 3.6 V, respectively.20 However, thermal annealing reduction of GO can remove a large portion of oxygen functional groups and thereby reduce the contribution of the surface Faradaic reaction to the specific capacity of the cathode.

3,13,35

Relative to thermal annealing treatment, chemical

reduction of GO by hydrazine can preserve most of carboxyl, carbonyl, and ester group at the edge or defective area, which are active for surface Faradaic reactions.12,13 Comparing the charge/discharge profiles of G-g-PTMA/RGO composite and RGO based cathodes (Fig. 4c), in which the specific capacities were normalized to the mass of whole cathode, it was found that the sloping segment of the discharge curve of G-g-PTMA/RGO cathode was almost coincided with the discharge curve of RGO cathode, which should be the evidence of surface Faradaic reactions of RGO. In this work, because chemically reduced graphene oxide was used as conductive additive and only one voltage plateau was found in the charge/discharge profile of G-g-PTMA/RGO, we thus can deduce that the remarkable capacity of G-g-PTMA/RGO composite should be attributed to the fast one-electron redox reaction of PTMA and surface Faradaic reactions of RGO with lithium. Taking account of the contribution of the surface Faradaic reaction of RGO to the



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specific capacity of G-g-PTMA/RGO composite, we also compared the increased capacities of G-g-PTMA or PTMA when RGO was added as conductive additives. For PTMA, the specific capacity increased by 156 mAh g-1 from 106 mAh g-1 (PTMA) to 262 mAh g-1 (PTMA/RGO) after the adding of RGO while the specific capacity of G-g-PTMA/RGO composite increased by 285 mAh g-1 from 181 mAh g-1 (G-g-PTMA) to 466 mAh g-1 (G-g-PTMA/RGO) after RGO was added (Fig. 4b). The increased specific capacities should be resulted from the improved electronic conductivities of the composites and surface Faradaic reactions of RGO. However, in the case of G-g-PTMA, the increased specific capacity is much higher than that for PTMA after RGO was added as conductive additive. This phenomenon should be explained by the fact that PTMA-functionalized graphene sheets can prevent RGO from restacking more efficiently than free PTMA polymer, and that means G-g-PTMA/RGO composite owns more active surface area than PTMA/RGO,3 which increased the lithium storage capability based on the surface Faradaic reactions between oxygen functional groups and lithium. The loosely stacked graphene sheets and well-dispersed carbon black particles as observed by scanning electron microscopy (Fig. 4d and Fig. S2) also supported the supposition that G-g-PTMA could help the dispersion of RGO in the composite, and correspondingly, well-distributed RGO could enhance the electronic conductivity effectively and accommodate more lithium ions. When the proportion of PTMA in the composite cathode was doubled to 20 wt%, i.e. the content of G-g-PTMA increased to 33.4 wt% and the content of RGO decreased to 36.6 wt%, however, the specific capacity of the


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composite cathode containing 20 wt% of PTMA did not increase accordingly and instead, slightly decreased to 39.6 mAh g-1 based on the whole weight of the cathode compared to the value of 46.6 mAh g-1 with 10 wt% of PTMA (Fig. 4c). The discharge curve of the cathode (green line in Fig. 4c) shows a longer voltage platform in comparison with that of G-g-PTMA/RGO containing 10 wt% of PTMA (blue line in Fig. 4c), but a reduced contribution from the surface Faradaic reaction. The total effect of increased proportion of G-g-PTMA on the energy storage capability was to decrease the specific capacity, which was mainly attributed to the reduced surface active sites of RGO resulting from the higher content of radical polymer and lower content of RGO. The electrochemical behavior of G-g-PTMA/RGO composite were further explored by solid-state cyclic voltammetry (CV) analyses of the electrodes over the potential window ranging from 2.0 V to 4.0 V at a sweep rate of 0.5 mV s-1. From the CV curves of G-g-PTMA/RGO electrode (Fig. 5a), a couple of chemically reversible redox peaks with nearly symmetrical shapes was found at around 3.6 V (vs. Li/Li+), which corresponded to the redox reaction between PTMA nitroxyl radicals and oxoammonium cations. This couple of redox peaks was also observed in the CV curves at various sweeping rates (from 0.5 mV s-1 to 100 mV s-1), and the small gap of anodic and cathodic peaks corresponded with its fast electrode reaction rate (Fig. S3). The almost overlapped CV curves with narrow gap of the anodic and cathodic waves suggested the fully reversible redox process without discernible loss of PTMA during the charging/discharging cycles.21 Except for the couple of redox peaks centered at



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Figure 5. (a) Cyclic voltammogram curves of G-g-PTMA/RGO electrode with initial three scans (0.5 mV s-1), and (b) comparison of CV curves of G-g-PTMA/RGO, G-g-PTMA, and RGO electrodes (0.5 mV s-1); and (c) schematic illustration of the energy storage mechanism of G-g-PTMA/RGO cathode. 3.6 V, a nearly rectangular CV shape was observed in the CV profile of G-g-PTMA/RGO electrode compared to those of G-g-PTMA and RGO electrodes (Fig 5b), which indicated a typical pseudo-capacitive behavior contributed from the Faradaic reactions of surface oxygen-containing functional groups of RGO and lithium ions.3,12,13 Additionally, the CV curve of G-g-PTMA/RGO electrode showed a much larger loop area than that of G-g-PTMA or RGO electrodes, revealing better


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utilization of the surface functional groups of RGO in G-g-PTMA/RGO electrode.2,3,12,13 These phenomena also suggested that the high energy storage capability of G-g-PTMA/RGO came from the fast one-electron redox reaction of PTMA and surface Faradaic reaction of RGO, moreover, G-g-PTMA could reduce the restacking degree of RGO and increase the electrochemical activity of the composite cathodic materials. The possible energy storage mechanism may be that the charge process consists of the oxidation of nitroxide radicals to their oxoammonium cation counterparts and the release of lithium ions from RGO, and the discharging process consists of the reduction of oxoammonium cations to nitroxide radicals and the capturing of lithium ions by RGO (Fig. 5c). Rate capability of G-g-PTMA/RGO was measured by cycling the electrode at different current densities ranging from 0.2 A g-1 to 20.0 A g-1 based on the weight of PTMA (Fig. 6a). The gravimetric capacity of G-g-PTMA/RGO cathode was found to be 466 mAh g-1 at a low rate of 0.2 A g-1. Even at a high rate as 20.0 A g-1, the capacity remained as high as 228 mAh g-1, demonstrating exceptional rate performance. When the cathode discharged at 0.2 A g-1 again, a reversible capacity of 362 mAh g-1 was obtained, suggesting the perfect stability at different rates. The cycling performance of G-g-PTMA/RGO cathode at a rate of 0.4 A g-1 was demonstrated in Fig. 6b. After 250 cycles, the reversible capacity of G-g-PTMA/RGO remained at 289 mAh g-1. The charge-discharge profiles of G-g-PTMA/RGO cathode after 50, 150, and 250 cycles show the typical voltage platform at ca. 3.6 V (Fig. S4), which indicated that no polymer obviously dissolved into the electrolyte solution



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during cycling. Electrochemical impedance spectroscopy (EIS) measurement was also performed for G-g-PTMA/RGO cathode (Fig. S5). The composite cathode showed a low charge transfer resistance (about 20 Ω, determined by the diameter of the semicircle in the high frequency area), indicating good electrical conductivity promoted by graphene sheets.15,36 After 220 cycles, the charge transfer resistance slightly decreased, suggesting the long-cycling stability of the cathode material. When comparing the surface morphologies of G-g-PTMA/RGO cathode before and after 250 charge-discharge cycles (Fig. S6), we can also find that the cathode structure maintains nearly as its initial state, except for the covered lithium salt and solid electrolyte.

Figure 6. Electrochemical performance of G-g-PTMA/RGO cathode at various current rates (a) and at 0.4 A g-1 over 250 cycles (b).

3. Conclusions In summary, we presented a covalent functionalization strategy to deal with the crucial facts faced by the application of radical polymer and carbon nanomaterials in high-energy density cathode materials. A composite material containing radical 16 ACS Paragon Plus Environment

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polymer functionalized graphene sheets, G-g-PTMA, and RGO was prepared, in which the covalently bonded radical polymer of PTMA could interact with graphene sheets in a molecular level with improved electron and ion transportation, and G-g-PTMA could also inhibit the restacking of graphene sheets during the electrode fabrication process. This dual-function of G-g-PTMA in G-g-PTMA/RGO composite imparted high specific capacity, as high as 466 mAh g-1, and good cycle performance to the cathode with fast one-electrode redox reaction of PTMA, and enhanced the surface Faradaic reaction of RGO. This strategy clearly provides a new direction for designing high-energy organic storage devices, which concerns more about the cost and recyclability of the cathode materials.

4. Experimental Section Polymerization of TMPM via grafting from G-Br: The initiating group functionalized graphene, G-Br, was prepared via the same procedure reported previously.28,29 First, in a 10 mL pre-dried Schlenk flask, G-Br (35 mg) and TMPM (1.0 g, 4.4 mmol) was charged and the flask was sealed with a rubber septum under N2. After three cycles of evacuating and purging with N2, HMTETA (12.1 µL, 0.044 mmol) and acetone (1.5 mL) were added to the flask via a gastight syringe. This mixture is degassed by three cycles of freezing-pumping-thawing, and then CuBr (6.3 mg, 0.044 mmol) was added under positive N2. The flask is ultrasonicated for 30 min. Polymerization took place under N2 at 70°C and it lasted 8 h. The reaction was terminated by quickly putting the flask into liquid N2 for 20 min and exposing the



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mixture to air. The mixture was diluted by acetone and the crude product was recovered by centrifugation and re-suspended in acetone three times and in n-hexane once. The recovered G-g-PTMPM was dried at 40°C in vacuo overnight. Oxidation of G-g-PTMPM into G-g-PTMA: G-g-PTMPM (69 mg, 0.184 mmol, 50 equiv. of amino group), EDTA-2Na (1.4 mg, 0.0037 mmol), and Na2WO4·2H2O (1.8 mg, 0.0055 mmol) were dissolved in methanol (30 mL) followed by ultrasonic dispersion for 30 min. H2O2 (2 mL in 25 mL of deionized water) was added dropwise (5 mL) every 1 h and the suspension was stirred at room temperature for 48 h. The mixture was dialyzed against deionized water for two days to remove the residual salts. The product was recovered by filtration and dried in vacuo at 40°C overnight. Electrochemical

measurements:

The

electrochemical

performance

of

G-g-PTMA/RGO was measured with 2025 coin cells assembled in a N2-filled glove box. The working electrodes were prepared through a dispersing-depositing process by mixing 16.7 wt% G-g-PTMA (PTMA, 10.6 wt%), 53.3 wt% of RGO, 20 wt% of acetylene black, and 10 wt% of poly(vinylidene fluoride) (PVDF) in NMP to form a slurry. Then the slurry was pressed on an aluminum current collector. For a comparison, cathodes using G-g-PTMA, PTMA/RGO, or RGO as active cathodic materials were also prepared as controls and the compositions were listed in Table S1 (Supporting Information). The electrodes were dried in vacuo at 100°C for 12 h to remove the solvent before test. Lithium foil was used as the counter and reference electrodes, and a porous Celgard 2400 membrane was used as a separator. The mass of the electrode material


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was estimated to be 0.9-1.0 mg depending on the thickness of the sample. The electrolyte was prepared by LiPF6 (1 mol/L) dissolved in the mixture (1:1 by volume) of ethylene carbonate (EC) and diethyl carbonate (DEC). Cyclic voltammetrys (CV) and chemical impedance spectroscopy (EIS) spectroscopies were carried out on a CHI 660D electrochemistry workstation. Galvanostatic cycling tests of the assembled cells were performed on a NEWARE CT3008W system in the range of 2.0 to 4.0 V (vs. Li/Li+).

Supporting Information Experimental details about XPS spectra of G-g-PTMPM, SEM images of as-prepared cathode slurries, schematic illustration of fabrication procedures for composite cathodes and the half-cells, and composition of the cathodes. This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgements The authors thank the financial support from National Basic Research Program of China (2015CB931900), National Natural Science Foundation of China (21204098), and Shanghai Scientific and Technological Innovation Project (14JC1493400).

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for Table of Contents use only


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Covalently Functionalized Graphene by Radical Polymers for

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