Electrochimica Acta 146 (2014) 218–223

Indanthrone derived disordered graphitic carbon as promisinginsertion anode for sodium ion battery with long cycle life

Anil Suryawanshi a,b,1, Dattakumar Mhamane a,1, Satyawan Nagane a,1, Shankar Patil b,Vanchiappan Aravindan c,*, Satishchandra Ogale a,1, Madhavi Srinivasan c,d,*aCentre of Excellence in Solar Energy, National Chemical Laboratory (CSIR-NCL), Dr Homi Bhabha Road, Pune 411 008, IndiabDepartment of Physics, University of Pune, Pune 411 008, Indiac Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Research Techno Plaza, 637553, Singapored School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore

A R T I C L E I N F O

Article history:Received 25 June 2014Received in revised form 19 August 2014Accepted 12 September 2014Available online xxx

Keywords:Na-ion batteryanodedisordered carbonindanthrone

A B S T R A C T

We report facile, one step synthesis of disordered graphitic carbon by high temperature (1000 �C)pyrolysis of indanthrone dye (ID). The pyrolysed carbon is disordered in nature and the same is clearlyevidenced by various analytical techniques like X-ray diffraction, Raman spectroscopy and highresolution transmission electron microscopy. Na-insertion properties of such indanthrone dye deriveddisordered graphitic carbon (IDDGC) is evaluated in half-cell assembly (Na/IDDGC). The test cell delivereda reversible capacity of �160 mAh g�1 at current density of 25 mA g�1. In addition, excellent cyclingprofiles are noted for such IDDGC, which retains �67% of initial reversible capacity after 500 cycles. Thepresent study clearly highlights the importance of disorder in the graphitic carbon for efficient Na-ionstorage.

ã 2014 Elsevier Ltd. All rights reserved.

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Electrochimica Acta

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1. Introduction

The excellent deliverable specific energy density makes Li-ionbatteries (LIBs) a prospective energy storage system in this new eranot only for portable electronic appliances but also for large scaleapplications like hybrid electric vehicles (HEV) and electricvehicles (EV) [1–3]. Although the LIB aims are focused on zeroemission transportation applications, the complexity is associatedwith Li metal resources, apart from its performance. Hence, themanufacturing cost of LIB is substantially high. In order toovercome such issues, it is necessary to explore beyond Li-ionchemistry with low-cost and eco-friendliness. Na-ion chemistrycould potentially offer interesting options in this regard [4,5,6,7,8]because the alkali metal, Natrium (Na) is one of the highlyabundant, low-cost materials in the earth and exhibits only slightlylower redox potential than metallic Li (�2.71 vs. SHE) [6,8].

Although the Na-ion chemistry is as attractive as Li chemistry,the usage of metallic Na in practical cells is questionable because ofits very lower melting point (�97.7 �C) [5]. Therefore, searchfor alternate insertion materials is highly warranted to fabricatehigh performance Na-ion cells keeping the low-cost and

* Corresponding author.1 Fax: +91 20 2590 2636.

http://dx.doi.org/10.1016/j.electacta.2014.09.0520013-4686/ã 2014 Elsevier Ltd. All rights reserved.

eco-friendliness in mind. Carbonaceous electrodes, particularlygraphite and disordered carbons, are considered as promisinginsertion hosts for reversible accommodation of Li [9]. Byconsidering the insertion potential of Na into graphite andthe interspaces between two graphene layers, graphite is notfavorable for the Na-insertion [9]. Therefore, research direction isfocused on developing disordered carbon as insertion host for thereversible accommodation Na-ions. However, transition metaloxide based insertion anodes have shown higher insertionpotential than carbonaceous electrodes, which results in drasticreduction in the net energy density of the Na-ion batteries [7,10].For the case of carbonaceous electrodes, presence of defects,degree of graphitization and porosity in disordered carbon play avital role in the enhanced Na-storage properties [6,8].

In the recent past, several carbonaceous materials prepared bypyrolysis route have been exploited as anode for Na-ion storage.The precursors have included polymers, petroleum cokes,commercial carbon black, etc [11]. The commercially availablecarbon black and petroleum coke derived carbon have been shownto deliver a reversible capacity of �100 mAh g�1 [12,13]. Generally,the hard carbons exhibit high reversible capacity of �250 mAh g�1,but the severe capacity fading during cycling is a matter of seriousdebate [9]. Carbon microspheres obtained from resorcinol-formaldehyde have shown a very high reversible capacity of�260 mAh g�1, but experience very severe capacity fade (within

Fig. 1. (a) Fig. 1a Structure of Indanthrone (ID) and its single step conversion todisordered graphitic carbon (IDDGC), (b) Photos of Indanthrone Dye (ID) and IDDGCsamples dispersed in water.

A. Suryawanshi et al. / Electrochimica Acta 146 (2014) 218–223 219

8 cycles it fall to �210 mAh g�1) [14]. Hollow structured carbonnanowires [15] and nanospheres [16] are promising for efficientNa-storage, but the suppression of volumetric capacity andscalability remains an issue. Activated carbon nanofibers[17] andreduced graphene oxide (RGO) [18] have also been investigatedfor possible Na-storage. Unfortunately both of them exhibit aturbostatic (capacitance) behavior rather than insertion which isclearly evident from the cyclic voltammetry studies. In generalsuch materials may exhibit higher reversible capacity, but nopractical application because of its very high self-discharge andhigh operating potential irrespective of the Li-ion or Na-ionchemistries. Very recently, Zhou et al. [19] reported the importanceof disordered graphitic carbon obtained from the pyrolysis of poly(sodium 4-styrenesulfonate)-poly(diallyl dimethylammoniumchloride) white precipitate in the context of Na-ion based storage.This material was shown to exhibit a stable reversible capacity of�225 mAh g�1. All these works clearly highlight the importance ofgraphitic materials for efficient Na-ion storage. However, favorablefeatures for efficient Na-storage such as incorporation ofnanocavities, low specific surface area/volume ratio, andmorphology have not been focused substantially till today, asdiscussed in the review by Slater et al. [8] Keeping all this in mind,we attempted to synthesize the disordered carbon in a simple,scalable, and cost effective procedure. Although, the synthesisprocedure is generally simple with most precursors, achieving allthe stated desired properties in a single material is quitechallenging and the choice of the precursor plays the vital rolein this context. We chose Indanthrone dye (ID) as a precursorwhich is an organic dye and has been known for long time as apigment [20]. There are a few reports in which aqueous solution ofammonium salt of indanthrone disulfonate has been employed asnovel and effective carbon precursor to construct ordered all-edgesurface carbon thin films [21,22]. Yan et al. [23] reported use ofindanthrone disulfonate salt for making biocompatible, carbonnaoparticles for cell delivery. Only Indanthrone (unsulfonatedform) is also a planar and poly-aromatic molecule. This planarmolecule forms 3D assembly (Please see Fig. 1) due to strong p-pinteractions and intermolecular hydrogen bonding [24]. The size ofID molecule is very small (Molecular length: 17.99 nm) and due tostrong p-p interactions many layers are stacked together to form3D graphite like structure [24].The p-p spacing is �3.4 Å andmatches well with the separation of graphene layers of graphite. Inspite of such interesting structural features, till today there are noreports for the direct use of only ID as carbon precursor, which mayhelp in getting an interesting morphology because of its 3Dstructure. It is speculated that employing ID as a precursor maylead to a novel graphitic carbon with small graphene sheets withdisorder and nanocavities. This is the reason we selected ID formaking graphitic carbon.

In this work we report on a simple and scalable synthesis ofgraphitic disordered carbon by pyrolyzing ID at 1000 �C underArgon atmosphere and its evaluation as anode for Na-ion batteryapplication. The pyrolyzed carbon is hereafter denoted asIndanthrone derived disordered graphitic carbon (IDDGC).Detailed structural and electrochemical evaluation of IDDGC isperformed and described.

2. Experimental section

Synthesis of IDDGC was carried out by single step pyrolysis of IDin horizontal alumina split tube furnace. In a typical procedure, 1 gof ID was placed in alumina boat followed by heating at 1000 �C for4 h in Argon atmosphere with heating rate of 5 �C min�1. PowderX-ray diffraction (XRD) measurements were carried out usingPhilips X'Pert PRO, diffractometer equipped with CuKa radiation.Raman spectrum was recorded with a confocal micro Raman

spectrometer LabRAM ARAMIS Horiba Jobin Yvon apparatus.Morphological studies were carried out using High resolutiontransmission electron microscopy (HR-TEM) (FEI Tecnai 300)and Field emission scanning electron microscopy (FE-SEM).Brunauer-Emmett-Teller (BET) surface area analysis wasperformed using Quadrasorb automatic volumetric instrument.All the electrochemical studies were performed using CR2016coin-cell assembly. The composite electrodes were formulatedwith accurately weighed active material (5 mg), super-P (1 mg) andteflonized acetylene black (TAB-2, 1 mg) using ethanol. Then theslurry was pressed on a 200 mm2 stainless steel mesh and dried at60 �C for 4 h under vacuum before conducting the cell assemblyunder Ar filled glove box. In the coin-cell assembly, compositeelectrode and metallic sodium was separated by microporous glassfiber separator (Whatman, Cat. No. 1825 047, UK) and filled with

80604020

2θo

Inte

nsi

ty (

a.u

.) IDDGC

101

002

Graphite

Fig. 2. XRD patterns of IDDGC and pure graphite powder.

Fig. 4. UV-Visible absorption spectrum of IDDGC sample.

220 A. Suryawanshi et al. / Electrochimica Acta 146 (2014) 218–223

1 M NaClO4 in ethylene carbonate (EC)/propylene carbonate (PC)(1:1 wt. %). Cyclic voltammetry (CV) traces were recorded usingSolartron, 1470 E and SI 1255B Impedance/gain-phase analyzercoupled with a potentiostat. Galvanostatic charge-dischargecycling profiles were carried out using Arbin battery tester(BT 2000) at ambient temperature conditions.

3. Results and discussions

The structure of ID and its single step conversion to IDDGC isshown in Fig. 1a. The prominent color change from blue to blackwas noted after the pyrolysis which is evident from thephotographic images given in Fig. 1b.

Fig. 2 shows the XRD pattern of IDDGC. The observed reflectionsclearly show the presence of broad and intense reflections at2u = 24.8� and 44� which correspond to the (002) and (101)graphitic planes, respectively. The XRD pattern of pure graphitewas also recorded and compared to ensure the formation of

300020001000

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G Ba nd

IDDGC

2D Ba nd

Inte

nsi

ty (

a. u

.)

1358 cm-1

1320 cm-1

1584 cm-1

Graphite

1590 cm-1

Raman Shif t (c m-1 )

Fig. 3. Raman spectra of IDDGC and pure graphite powder.

disordered graphitic phase. It can be seen that the (002) peak isconsiderably shifted towards lower angles as compared to itsposition for pure graphite powder which signifies significantincrement in the d-spacing. The major broadening of the peakssignifies high degree of disorder in IDDGC. This is one of thedesirable properties for Na-ion storage. Raman spectroscopy isanother important tool to study the structural defects in carbonbased materials [25–27]. The substantial degree of disorder inIDDGC is clearly evidenced from Raman spectra as well. Therecorded Raman spectra for pure graphite and IDDGC are given inFig. 3.

Pure graphite has a prominent and narrow peak at � 1580 cm�1

which is due to the >C=C< symmetric stretching vibration (G banddesignated to E2g phonons of sp2 carbon atom). However, for thecase of IDDGC the D band (designated to the breathing mode ofk-point phonons of A1g symmetry) at �1320 cm�1 is prominent ascompared to G band with very high intensity. The increase in theintensity of D band supports the formation of new sp2 domains.This also confirms the substantial stress in the IDDGC as comparedto the 3D graphitic crystal. The induced stress also results in a smallblue shift of the G band in the case of IDDGC. By considering thepeak intensity we have calculated the ID/IG ratio value for IDDGC.The observed ratio for IDDGC is 1.3 whereas in graphite is only 0.32.The significantly higher value of ID/IG ratio supports the highdegree of disorder in the IDDGC sample. The shift in D bandtowards lower frequency (shown by dotted line) is due tostretching of the C-C bond in IDDGC, which is very common insp2 hybridized carbonaceous based materials [25,28,29]. The fewlayer aggregated structure of IDDGC is confirmed by the absence of2D peak, which is one of the prominent peaks for graphite. The

280 28 1 28 2 28 3 28 4 28 5 28 6 287 288 289 290

Inte

nsi

ty (

a.u

.)

Binding energy (eV )

C 1s plo t

IDDGC

Fig. 5. XPS plot for IDDGC.

Fig. 6. (a, b) FE-SEM images and (c-f) HR-TEM images for IDDGC sample.

A. Suryawanshi et al. / Electrochimica Acta 146 (2014) 218–223 221

presence of >C=C< functionality in IDDGC is further confirmed byUV-Visible absorption spectroscopy. The UV-vis plot for IDDGC isshown in Fig. 4. The absorption peak at � 260 nm is observed due top!p* transition. This confirms, the presence of only >C = C<functionality in IDDGC sample. The observed peak also supportfor the graphitization of ID after pyrolysis. The UV-vis absorptionplot of IDDGC is in good agreement with the literature reports

on chemically obtained graphene samples [30,31]. Additionalinformation towards presence of graphitic structure in IDDGCsample can be seen from X-ray photoelectron spectroscopy (XPS).Fig. 5 shows the core-level C 1s XPS spectrum of the IDDGC sample.The single narrow peak at 284.6 eV designated to graphitic carbonis consistent with the graphitic nature of the material[32].Morphological features of IDDGC were analyzed by FE-SEM and

0.0 0.2 0.4 0.6 0.8 1.0

0

5

10

15

20

25

30V

olu

me

(cc/

g)

Relative Press ure P/Po

Ad sor ption Desorption

Surface area = 6.97 m2/g

IDDGC

Fig. 7. Adsorption-Desorption isotherm of IDDGC sample.

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HR-TEM techniques and are presented in Fig. 6. The mean size ofIDDGC flakes is found to be about few micron scale with roughsurface texture. Further the HR-TEM images also help reveal thepresence of nano-sized cavities/pores in the IDDGC structure.The HR-TEM images for IDDGC are shown in Fig. 6c–f. Due tostrong p!p interactions, the morphology of IDDGC looks quitestacked similar to few layer graphene sheets. However, presenceof nano-cavities is evident from HR-TEM which is one of thefavorable properties for facile Na-ion storage. Generally,the presence of disorder must alter the d-spacing of sample. Thecalculated d-spacing for IDDGC sample is found to be �0.38 nm(Fig. 6f). This value for d-spacing is slightly higher as compared to

2.52.01.51.00.50.0-1.2

-1.0

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0.2

0.4

0.6

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(a)

Cu

rren

t (m

A)

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7060504030201000

40

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200 mA g-1

800 mA g-1

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200 mA g-1

100 mA g-1

50 mA g-1

Cap

acit

y (m

Ah

g-1

)

Cycle numbe r

25 mA g-1

Fig. 8. (a) Cyclic voltammogram of IDDGC in half-cell configuration (Na/IDDGC) betwedischarge–charge cycles of IDDGC in half-cell configuration (Na/IDDGC) at various currenhalf cell at various current densities and (d) Plot of normalized reversible capacity vs.

the ordered graphitic carbons (0.34 nm). This provides additionalactive sites (defective sites) for efficient Na-ion storage.Such defect-tuning of d-spacing has been proposed by Yoo et al.[33] and is very important for advanced energy storage devices.Thus the presence of important properties like nano-cavitiesand disorder is clearly supported by FE-SEM and HR-TEMTechniques. Additional TEM images are provided in SupportingInformation (SI) Fig. S1. Presence of nano-cavities/pores wasfurther validated by BET surface area analysis and correspondingadsorption/de-sorption isotherms are given in Fig. 7. The specificsurface area of IDDGC is found to be 6.97 m2g�1 which is in goodagreement with the previous reports for carbonaceous materialsfor Na-ion storage [14,34]. For instance Alcantara et al. [14]explained the importance of disordered carbon with low surfacearea value for Na+ ion storage. According to authors, the excellentsolution is to avoid unwanted irreversible reactions of Na+ andelectrolyte ions for better storage. This could be possible if a sampleis associated with free space between the graphene layers and lowavailability of external surface. It is concluded that, materials withthese property features are very important for reducing irrevers-ible reactions and allowing reversible sodiation/de-sodiationprocesses. As stated earlier, our one step prepared IDDGC sampleis highly disordered as evident from Raman and HRTEM analysis.Moreover its structure is open and contains stack of smallgraphene layers. Low value of surface area (6.97 m2/g), clearlysuggest that this material carries less number of reactive surfaces,and hence results in minimal reaction of Na+ and electrolyte ions.This allows maximum reversible intercalation/de-intercalationof Na+ ions and hence better electrochemical performance ofNa/IDDGC half cell. The pore size distribution clearly revealed thepredominant pores are lies between 20-50 Å (Fig. S2).

(b)

50040030020010000

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4003002001000

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(d)

Pot

enti

al (

V v

s. N

a+/

Na)

Capacity ( mAh g-1)

(25, 50, 100 , 200, 400, 600 and 800 mA/ g)

en 0.005–2.5 V vs. Na+/Na at slow scan rate of 0.1 mV s�1; (b) Typical galvanostatict densities between 0.005–2.5 V vs. Na+/Na; (c) Rate capability studies of Na/IDDGCcycle number tested at current density of 200 mA g�1.

A. Suryawanshi et al. / Electrochimica Acta 146 (2014) 218–223 223

Na-ion storage profiles of IDDGC were analyzed by cyclicvoltammetry (CV) and galvanostatic charge-discharge studies inhalf cell configuration (Na/IDDGC) under ambient temperatureconditions (Fig. 8). Typical CV signatures of IDDGC are recordedbetween 0.005-2.5 V vs. Na at scan rate of 0.1 mV s�1, the data aregiven in Fig. 8a. During the first cathodic sweep, a small peak at�0.46 V vs. Na is observed which is due to the decomposition ofelectrolyte solution and subsequent solid electrolyte interface (SEI)formation over carbonaceous electrode. The Na-insertion takesplace beyond the decomposition potential of the electrolytesolution (evident from the increase in peak current), and it isunfortunate that the prominent insertion peak is very difficult torecord because, in the negative range the Na-platting severelyoccurs on the working electrode [9]. Conversely, very prominentanodic peak is observed at �0.24 V vs. Na+/Na which corresponds tothe Na-extraction. In the subsequent cycles (up to 10 cycles), thereis no deviation in the peak positions and much reduction in thearea underneath the curves is noted which suggests the excellentreversibility of the system. Galvanostatic cycling profiles were alsoconducted for Na/IDDGC half-cells between 0.005-2.5 V vs. Na+/Naat various current densities from 25 to 800 mA g�1 and the data aregiven in Fig. 8b. As noted from the CV studies, a huge irreversiblecapacity loss is noted in the first cycle, which is mainly due to thedecomposition of electrolyte and subsequent SEI formation, forexample the half-cell delivered the capacity of �447 and �160mA h g�1 at current density of 25 mA g�1 for first discharge andcharge, respectively [11]. Further, the average insertion potential of�0.38 V vs. Na+/Na is noted at a low current density of 25 mA g�1.The observed values are found neither superior nor inferiorcompared to the reported values in the literature (Table S1) whichclearly showed the importance of precursor for the electrochemi-cal profiles. In addition to above, there is no much differencebetween the electrochemical profiles of such carbonaceousmaterials noted when the annealing temperature is lowered.Further studies are in progress to improve the reversible capacityand suppress the irreversible capacity loss in the first cycle by finetuning the synthesis parameters.

It is interesting to observe that the Coloumbic efficiency isdrastically increased from �36 to �89% from initial to second cyclein low current rates. As expected, increasing current density resultsin a decrease in reversible capacity, which is clearly evident fromFig. 8 b-c. At high current rates, decrease in the reversible capacityprofiles is noticed which is attributed to the participation of onlysurface of IDDGC electrode for Na-ion insertion/extraction ratherthan the bulk [35]. It is evident that the Coloumbic efficiency isover 99.5% at high current rates, which indicates the excellentreversibility of IDDGC. Long term cycleability is another importantcriterion to employ them in practical cells, hence the Na/IDDGC cellwas further tested at a current density of 200 mA g�1. The plot ofreversible capacity vs. cycle number is given Fig. 8d. The test cellrendered �67% of initial reversible capacity after 500 cycles, whichis one of the best results reported for the carbonaceous electrodesmentioned above. We strongly believe such an enhanced perfor-mance is mainly because of the presence of defects and disorderednature of the graphitic carbon.

4. Conclusion

We successfully demonstrated the scalable synthesis of novelgraphitic based disordered carbon from indanthrone dye bysingle step pyrolysis. Several analytical techniques were adoptedto study the nature of the carbon thus obtained. The disorderedcarbon was evaluated as an efficient insertion anode forNa-ion rechargeable battery applications in a half-cell assembly.A remarkable performance of IDDGC towards Na-ion storageproperties was observed; for example the cell delivered the

maximum reversible capacity of �160 mAh g�1. Further, excellentlong-term cycleability was also evidenced from the galvanostaticcycling profile.

Acknowledgement

Authors would like to thank Satish Ogale for fruitfuldiscussions. VA and SM thank National Research foundation(NRF, Singapore) for financial support through CompetitiveResearch Programme (CRP) (Grant no. NRF-CRP4-2008-03). ASacknowledges University Grants Commission (UGC), India forJunior and Senior Research Fellowship support.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.elec-tacta.2014.09.052.

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