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L. Zhao , PKey LaborBeijing KeEnergy MBeijing NaInstitute oChinese ABeijing 10 E-mail: ys Dr. J. M. Zhao Key LaborInstitute oChinese ABeijing 10 Prof. Z. BSchool ofHuazhonWuhan 43

DOI: 10.

In the fi eld of energy storage, lithium (Li)-ion batteries dominate the portable consumer electronic market because of their high energy density. Recently, however, the sodium (Na)-ion battery has again aroused interest for large-scale energy storage due to Na abundance. [ 16 ] Conventionally, the chemistry behind Li-ion and Na-ion batteries involves transition metal elements, [ 4 , 6 ] thus giving rise to problems of cost and environmental concern. Therefore, intensive efforts have been aimed at the development of new Lcompoumaterialdous chea wide rresourceof Li-conto have moderatin Li-ionof such o

In thdisodiumanode mteries. Tan organrial for Ntion voltof 250 m

storage Al 2 O 3 co

SchemThe exiand deincapacityas-receivFourier

200 mAh/g. A fl at plateau was then observed at 0.29 V with a

Liang Zhao , Junmei Zhao , Yong-Sheng Hu * Hong L and Liquan Chen

Disodium Terephthalate (Na 2 C 8 H 4 O 4 ) as High Performance Anode Material for Low-Cost RoomSodium-Ion Battery 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimlibrary.com

atory of Green Process and Engineering f Process Engineering cademy of Sciences 0190, China . Zhou Chemistry and Chemical Engineering g University of Science and Technology 0074, China

1002/aenm.201200166

capacity of 270 mAh/g, in accordance with two Na insertion (255 mAh/g). The charge plateau was located at 0.56 V, and the initial coulombic effi ciency was 50.3%. In contrast, in its coun-terpart Li 2 C 8 H 4 O 4 /Li cell, [ 12 ] the dischargecharge plateaus were located at higher values of 0.8 and 1.0 V. The factor contrib-uting to this large difference is unknown at present, but may be related to the mutual electrostatic repulsion of bulky Na + ions. The low coulombic effi ciency in the fi rst scan is mainly resulted

Adv. Energy Mater. 2012, 2, 962965rofs. Y.-S. Hu , H. Li , M. Armand , L. Q. Chen atory for Renewable Energy y Laboratory for New aterials and Devicestional Laboratory for Condensed Matter Physics f Physicscademy of Sciences0190, Chinahu@aphy.iphy.ac.cn

i storage materials shifting from inorganic to organic nds. [ 7 ] Numerous advantages exist in using organic s as electrodes for energy storage, such as their tremen-mical compounds, the tuning of the redox potential in ange, possible multi-electron reactions, the abundant s from biomass, and ease in recycling. [ 712 ] A number taining organic compounds have been demonstrated high lithium storage capacity, good cycleability, and e rate capability, making them promising applications batteries. [ 7 , 1012 ] However, there is no report on the use rganic compounds in Na-ion batteries.

is contribution, a carboxylate-based organic material, terephthalate (Na 2 C 8 H 4 O 4 ), is introduced as a novel aterial for low-cost room-temperature Na-ion bat-

o the best of our knowledge, this is the fi rst time that ic compound is reported for the use as an anode mate-a-ion batteries. This material exhibits a low Na inser-

age at 0.29 V vs. Na + /Na and a high reversible capacity Ah/g with excellent cycleability. It is found that Na

fraction FTIR respurity ostructureto JCPDconstantc = 18.9XRD paorienteddiffi cult.scopy (Sis shown100 m. ductivity(KB). Aft600 nm,pattern of the (0pears. TFigure 1that the mixed co

The eat a voltaof 0.1 Cper formfi rst 10 charge pa sloped performance can be further improved by a thin layer of ating on the Na 2 C 8 H 4 O 4 electrode surface. e 1 shows the molecular structure of Na 2 C 8 H 4 O 4 .

stence of two carbonyl groups allows for the insertion sertion of two Na ions, corresponding to a theoretical

of 255 mAh/g. In order to confi rm the purity of the ed Na 2 C 8 H 4 O 4 , nuclear magnetic resonance (NMR), transform infrared spectroscopy (FTIR), and X-ray dif-(XRD) measurements were performed. Both NMR and ults as shown in Figures S1 and S2 reveal the high

f the sample. The Na 2 C 8 H 4 O 4 has an orthorhombic and can be indexed in space group Pbc21, according S card No. 00-052-2146 (Figure S3). [ 13 ] The lattice s of Na 2 C 8 H 4 O 4 are a = 3.5480 , b = 10.8160 , and 943 , and its lattice volume is V = 728.92 3 . The ttern of as-received Na 2 C 8 H 4 O 4 showed preferentially (006) and (008) planes. Thus, refi ning the structure is This can be evidenced by the scanning electron micro-EM) image in Figure 1 b, where the as-received sample to have a fl ake-like structure with very large size near To reduce the particle size and increase electronic con-

, the sample was ball-milled with 20 wt.% Ketjen black er ball-milling, the particle size decreases to 50 nm to which is responsible for the broadening of the XRD (Figure 1 a). Moreover, the preferential orientation 06) and (008) planes of the ball-milled sample disap-he transmission electron microscopy (TEM) image in c shows that the particles are surrounded by KB and sample is also porous, resulting in the formation of a nducting network for both electron and ion transport. lectrochemical performance of Na 2 C 8 H 4 O 4 was tested ge range of 0.1 V to 2 V vs. Na + /Na at a current rate

(0.1 C refers to 2 mol Na insertion into Na 2 C 8 H 4 O 4 ula unit in 10 h). The dischargecharge curves for the cycles are shown in Figure 2 . During the initial dis-rocess, the voltage sharply dropped to 0.7 V, following range between 0.7 and 0.23 V with a capacity of about

i , Zhibin Zhou , Michel Armand ,

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Surface modifi cation of electrode materials is an effective way to improve the performance of Li-ion batteries. [ 6 , 14 , 15 ] This has been achieved in both anode materials, such as natural graphite [ 16 ] and silicon, [ 17 ] and high voltage cathode materials, such asapplied Among tion (ALthe surfative met

rh 3

from the large irreversible capacity of the sloped region, which disappears in subsequent cycles. For comparison, the non-ball-milled sample also delivered an irreversible capacity of 75 mAh/g in the sloped region of the fi rst discharge process, as shown in Figure S4. This value is signifi cantly lower than that of the Na 2 C 8 H 4 O 4 /KB composite electrode, but still notice-able. The large irreversible capacity indicates the formation of a solid electrolyte interphase (SEI). [ 5 ] Figure S5 presents the TEM image of electrodes after discharging to 0.01 V. Compared with Figure 1 c, the active material and KB can no longer be distin-guished, and the electrode is surrounded by an amorphous layer. The large irreversible capacity is attributed mainly to the severe electrocatalysis of electrolyte reduction by KB and possibly by Na 2 C 8 H 4 O 4 itself. The distinct plateaus could be assumed to be structural changes from Na 2 C 8 H 4 O 4 to Na 4 C 8 H 4 O 4 with Na ions bonding to the two carbonyl groups in Na 2 C 8 H 4 O 4 in the Na insertion process.

Figure 2 . The fi rst 10 discharge-charge cycles of the Na 2 C 8 H 4 O 4 /KB composite electrode, the voltage range is between 0.1 V and 2 V.

Scheme 1 . Molecular structure of disodium terephthalate (Na 2 C 8 H 4 O 4 ) and the Na insertion/deinsertion mechanism.

Figure Na 2 C 8 Himage oNa 2 C 8 H

Adv. Eneinter-paHere, tmethod Figure the elecas ALD 2012 WILEY-VCH Verlag GmbH & Co. KG

Figure 3 . electrodebetween 50.3%, 62

1 . Structure characterizations: (a) XRD pattern of the pristine 4 O 4 and the ball-milled Na 2 C 8 H 4 O 4 /KB composite; (b) SEM f the pristine Na 2 C 8 H 4 O 4 ; and (c) TEM image of the ball-milled 4 O 4 /KB composite.

rgy Mater. 2012, 2, 962965 LiMn 2 O 4 and LiCoO 2 , [ 16 , 18 ] by metal-oxide coating in terms of long term cycling and rate capability.

the approaches for surface coating, atomic layer deposi-D) is an easy means to form a uniform coating layer on ce of active materials. [ 19 ] More importantly, the protec-

al-oxide coating layer can be applied without disrupting ticle electronic contact through the ALD method. [ 16 ] e Na 2 C 8 H 4 O 4 electrode was coated through the ALD for 20 cycles ( ca. 2 nm) and 50 cycles ( ca. 5 nm). displays the initial discharge and charge curves of

trodes coated by ALD for 20 and 50 cycles (denoted 20 and ALD50). The capacities of the sloped region 963aA, Weinheim wileyonlinelibrary.com

The initial discharge-charge curves of the untreated Na 2 C 8 H 4 O 4 and the ALD20 and ALD50 electrodes in the voltage range 0.1 V and 2 V; the corresponding coulombic effi ciencies are .5% and 60.6%, respectively.

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at 400 rpm for 15 min. The structure of Na 2 C 8 H 4 O 4 samples was ized by XPert Pro MPD X-ray diffractometer (Philips, Holland) Ka radiation (1.5405 ). The morphologies of the samples were

decreased to 159 and 143 mAh/g for the ALD20 and ALD50 electroties. Ctively ielectrothat thtrode slytes d

Figuuntrearates. Aincreaseach raimprovelectro0.05 C respect67.2%,pared 31.5% currenthe elereducean insutradictocoatingsurfacelayer istrode. Al 2 O 3 trode pslowly tion ofchargeand 21respectnique improvfi rst exin enh

In canode Na-ionat 0.29reversielectroforminKB elein termcyclingthe irrprocesin prog

Exper Na 2 C 8 Hfurther Internat

Discharge curves of the untreated Na 2 C 8 H 4 O 4 electrode (a) and 0 (b) and ALD50 (c) electrodes at different discharge-charge tes, the curves shown here are the end ones of each fi ve cycles. ycling performance of the untreated Na 2 C 8 H 4 O 4 electrode and 0 and ALD50 electrodes tested at 0.1C, the voltage range is .01 V and 2 V.

Adv. Energy Mater. 2012, 2, 962965 2012 WILEY-VCH Verlag GmbH & Co. Knelibrary.com

(PM 200)characterusing Cu-

des, respectively, with no decrease in reversible capaci-orrespondingly, the initial coulombic effi ciencies respec-ncreased to 62.5% and 60.6% for the ALD20 and ALD50 des. The increased effi ciency can be attributed to the fact e Al 2 O 3 layer mitigates the formation of SEI on the elec-urface through the reductive decomposition of electro-

uring initial discharge. re 4 a, b, and c show the dischargecharge curves of

ted and Al 2 O 3 -coated electrodes at different current ll cells were successively discharged and charged with

ing current rates from 0.05 C to 2 C for fi ve cycles at te. It is found that the Al 2 O 3 -coating is also effective in ing rate capability (see Figure 4 and S6). For the ALD20 de, 91.1%, 86.2%, 64.9%, and 52.8% of the capacity at were still accessible at current rates of 0.1, 0.2, 1, and 2 C, ively. In the case of the ALD50 electrode, 91.3%, 87.3%, and 57.0% of the capacity at 0.05 C were achieved, com-with capacity retentions of 87.9%, 80.2%, 52.4%, and for the untreated electrode. Moreover, cycling at high

t density does not permanently damage the structure of ctrode, given that the capacity is restored when the rate is d to a low current rate (0.1 C). As it is well known, Al 2 O 3 is lated coating layer, however, this characteristic is not con-ry to the enhanced rate performance, because the Al 2 O 3 layer can reduce the formation of SEI layer on electrode , which results in large impedance; and the Al 2 O 3 coating also benefi cial to the structure maintenance of the elec-Finally, the cycling performance is also improved after coating of the electrode (Figure 4 d). The untreated elec-resented an initial charge capacity of 258 mAh/g, which faded to 192 mAh/g after 50 cycles, with a capacity reten- 74.4%. The ALD20 and ALD50 electrodes exhibited initial capacities of 282 and 255 mAh/g, which decayed to 225 1 mAh/g, with capacity retentions of 79.8% and 82.7%, ively. A thin layer of Al 2 O 3 coating through the ALD tech-on the electrode surface has been shown to effectively e the performance of inorganic electrodes. This is the ample to demonstrate the effectiveness of this technique ancing the performance of an organic electrode. onclusion, Na 2 C 8 H 4 O 4 is fi rstly introduced as a novel material for low-cost rechargeable room-temperature

batteries. The material exhibits low Na insertion voltage V. The Na 2 C 8 H 4 O 4 /KB composite electrode shows a ble capacity of 250 mAh/g, corresponding to a two-n transfer, with excellent cycling performance. By per-g ALD Al 2 O 3 coating on the surface of the Na 2 C 8 H 4 O 4 /ctrode, Na storage performance is signifi cantly improved

s of initial coulombic effi ciency, rate capability, and performance. Future work on the further reduction of eversible capacity during the initial chargedischarge s and on exploring Na storage mechanism is currently ress.

imental Section 4 O 4 was purchased from Alfa Aesar Company and used without treatment. Na 2 C 8 H 4 O 4 and Ketjen black (EC-600JD, Ketjenblack ional, Japan) (80:20) were ball-milled in a planetary ball mill

Figure 4 . the ALD2current ra(d) The cthe ALD2between 0

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observed using a scanning electron microscope (SEM) (Hitachi S-4800) and a transmission electron microscope (TEM) (JEOL 2010). Fourier transform infrared spectroscopy (FTIR) measurements were performed on a Bruker Tensor 27 Spectrometer using KBr pellets. NMR experiments were conducted on a Bruker Avance 600 spectrometer. The sample was dissolved in D 2 O and the solution was sealed in a 5 mm NMR tube.

Both pristine and ball-milled sample electrodes were prepared with active materials, carbon black, and binder (poly (vinylidene difl uoride) (PVdF) is dissolved in N-methyl pyrrolidinone (NMP)) at a weight ratio of 80:10:10. The slurry was cast on the Cu foil and dried at 100 C in vacuum for 10 h. The active material in the composite electrode is 64 wt.%. The specifi c capacity was calculated based on the mass of Na 2 C 8 H 4 O 4 . The coil cells CR2032 were assembled with pure sodium foil as cEC:Dcharsystanhin c

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[ 1 ] [ 2 ]

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[ 4 ]

M. Slater , S. Rood , J. T. Vaughey , N. Karan , M. Balasubramanian , C. S. Johnson , Adv. Energy Mater. 2011 , 1 , 333 ; d) Y. Kawabe , N. Yabuuchi , M. Kajiyama , N. Fukuhara , T. Inamasu , R. Okuyama , I. Nakai , S. Komaba , Electrochem. Commun. 2011 , 13 , 1225 ; e) D. Kim , E. Lee , M. Slater , W. Q. Lu , S. Rood , C. S. Johnson , Elec-trochem. Commun. 2012 , 18 , 66.

[ 5 ] a) J. F. Qian , M. Zhou , Y. L. Cao , X. P. Ai , H. X. Yang , Adv. Energy Mater. 2012 , 2 , 410; b) L. Cao , L. F. Xiao , W. Wang , D. W. Choi , Z. M. Nie , J. G. Yu , L. V. Saraf , Z. G. Yang , J. Liu , Adv. Mater. 2011 , 23 , 3155 ; c) S. Wenzel , T. Hara , J. Janek , P. Adelhelm , Energy. Environ. Sci. 2011 , 4 , 3342 ; d) S. Komaba , W. Murata , T. Ishikawa , N. Yabuuchi , T. Ozeki , T. Nakayama , A. Ogata , K. Gotoh , K. Fujiwara , Adv. Funct. Mater. 2011 , 21 , 3859 ; e) Q. Sun ,

Adv. 2012 WILEY-VCH Verlag GmbH & Co. K

ounter electrode, glass fi ber separator and 1M Na[N(SO 2 F) 2 ] (NaFSI) EC (4:6) electrolyte in an argon-fi lled glove box. The discharge and

ge measurements were carried out on a Land BT2000 battery test em (Wuhan, China). The discharged electrode was washed with ydrous DMC several times and then dispersed in DME and dripped opper grid in the glove box for TEM observation. Savannah-100 ALD system (Cambridge NanoTech Inc.) was used

the Al 2 O 3 layer deposition. The deposition process was performed 00 C using trimethyl aluminum (TMA) and H 2 O as precursors. The kness of Al 2 O 3 layer was about 1 for each precursor pulse cycle.

pporting Information porting Information is available from the Wiley Online Library or the author.

knowledgements work was supported by the National High Technology Research Development Program of China (Grant No. 2009AA033101), the ional Basic Research Program of China (Grant No. 2009CB220104), National Natural Science Foundation of China (Grant No.50972164), ese Academy of Sciences Project (Grant No. KJCX2-YW-W26), and

Hundred-Talent Project of the Chinese Academy of Sciences.

Received: March 9, 2012 Published online: May 11, 2012

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