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Nano Energy (2014) 8, 17–24

http://dx.doi.org/12211-2855/& 2014 E

nCorresponding aunnCorresponding annnCorrespondingE-mail addresses

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DNA metallization for high performance Li-ionbattery anodes

Dong Jun Kima, Min-Ah Woob, Ye Lim Jungb, K. Kamala Bharathia,Hyun Gyu Parkb,n, Do Kyung Kima,nn, Jang Wook Choic,nnn

aDepartment of Materials Science and Engineering, Korea Advanced Institute of Science and Technology(KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of KoreabDepartment of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science andTechnology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of KoreacGraduate School of Energy, Environment, Water, and Sustainability (EEWS), Center for Nature-inspiredTechnology (CNiT), KAIST Institute NanoCentury, Korea Advanced Institute of Science and Technology(KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea

Received 29 January 2014; received in revised form 9 April 2014; accepted 8 May 2014Available online 23 May 2014

KEYWORDSBiological template;DNA nanostructure;DNA metallization;Lithium ion battery

0.1016/j.nanoen.2lsevier Ltd. All rig

thor. Tel.: +82 42uthor. Tel.: +82 4author. Tel.: +82 4: hgpark@kaist.ac.

AbstractMetal cluster formation on the DNA backbone, known as so-called DNA metallization, hascaught much attention for both biological and non-biological research areas. DNA metallizationis particularly useful for overcoming intrinsically low electronic conductivity of DNA and hasbeen used for generating conductive wires for various applications such as molecularelectronics. Meanwhile, designing effective nanostructure electrodes are very critical foradvanced lithium ion batteries (LIBs) especially in achieving high energy densities and longcycle lives. Among various LIB anode candidates, metal oxides offer several times highertheoretical capacities compared to those of conventional graphite anodes, utilizing uniqueconversion reaction mechanism. Herein, we report a 1D nickel oxide nanostructure whosemorphology was directed by DNA metallization. The unique 1D DNA nanostructure deliveredhigh reversible capacity of 850 mA h g�1 and robust cycling performance for 150 cycles. Thepresent study suggests that various nanostructures in biological systems and nature, especiallyafter simple chemical reactions, can be key elements for high capacity LIB electrodes thatsuffer from large volume changes during battery operations.& 2014 Elsevier Ltd. All rights reserved.

014.05.007hts reserved.

350 3932; fax: +82 42 350 3910.2 350 4118; fax: +82 42 350 3310.2 350 1719; fax: +82 42 350 2248.kr (H.G. Park), dkkim@kaist.ac.kr (D.K. Kim), jangwookchoi@kaist.ac.kr (J.W. Choi).

dx.doi.org/10.1016/j.nanoen.2014.05.007dx.doi.org/10.1016/j.nanoen.2014.05.007dx.doi.org/10.1016/j.nanoen.2014.05.007dx.doi.org/10.1016/j.nanoen.2014.05.007dx.doi.org/10.1016/j.nanoen.2014.05.007http://crossmark.crossref.org/dialog/?doi=10.1016/j.nanoen.2014.05.007&domain=pdfmailto:hgpark@kaist.ac.krmailto:dkkim@kaist.ac.krmailto:jangwookchoi@kaist.ac.krdx.doi.org/10.1016/j.nanoen.2014.05.007

D.J. Kim et al.18

Introduction agglomerate during repeated aggressive Li (de)insertion

Since the structure of DNA was first discovered, DNA hasbeen a popular research object in a variety of areas. Notonly has it served as a carrier encoding genetic informationin biological fields, but has also expanded the territory intothe field of materials science. DNA has been regarded as asmart functional biopolymer due to its unique capabilities ofbuilding self-assembled structures by complementary recog-nition, amplifying same sequences of strands by severalorders of magnitude, recognizing specific functional groupsin the end of strands, and maintaining stable structures invarious environments [1–6]. Above all, it is the smallest one-dimensional (1D) structure in nature. Recently, it was foundthat utilizing complementary binding between specificnucleobases, strands of DNA can be assembled into compli-cate 3D structures, so-called ‘DNA origami’, and the desig-nated structures can be designed by controlling thesequences of the involved DNA strands [7–9]. Besides theorigami concept, binding of metal ions to DNA, namely DNAmetallization, has been studied for various fields, andprevious studies have revealed that DNA can form metalcomplexes with the nucleobases and/or phosphate groups inthe DNA backbone, and can thus lead to diverse metal ormetal oxide nano-structures [10,11]. In the materialsscience perspective, DNA metallization has been intensivelystudied to overcome intrinsically moderate conductivity ofDNA and has thus been applied for molecular-scale electro-nic circuits [6,12,13]. For example, Braun et al. [14]synthesized DNA-templated nanowires by metallization ofsilver ions and constructed functional circuits. Similarmetallization processes were employed for other applica-tions including nano-patterning, nano-electronics, drugdelivery, etc. [15–19].

So far lithium ion batteries (LIBs) have been verysuccessful in powering diverse portable electronic devices,and are currently expanding their applications to supportelectric vehicles, stationary utility grids, as well as moreadvanced electronic devices [20,21]. These new emergingapplications impose more challenging standards with regardto energy/power densities, lifetime, and safety. Amongthese parameters, high energy density together with longcycle life has been very critical for green transportationapplications, as the energy density of LIB is directly relatedto driving distance per each charge. Along this direction,metal oxide materials have attracted a great deal ofattention as alternative anodes to conventional graphiteones because metal oxides can engage conversion reactionsand can thus deliver several times larger specific capacities(�800 mA h g�1) compared to those of the conventionalgraphite anodes (�300 mA h g�1) [22–24]. For this reason, avariety of metal oxides have been investigated as LIBelectrodes and have been well summarized in recentreviews [25–30]. Despite the large capacities, metal oxideanodes still suffer from limited cycle lives since theyundergo large volume changes over repeated cycles, whichresult in stress-involved pulverization. As in the cases ofalloy electrodes such as silicon and tin, nanostructurescould overcome the pulverization because small dimensionsof active materials can afford to relax the stress built upduring the volume changes [31,32]. However, it shouldalso be noted that nanostructured metal oxides could

depending on the morphology, losing the advantages ofthe original nanostructures. In this viewpoint, 1D nanos-tructures are more advantageous [33] than other nanos-tructures because 1D nanostructures are typically lessvulnerable to agglomeration.

Having noticed the intrinsic morphology of DNA in nan-ometer dimensions and its capability of metallization aswell as the advantages of 1D nanostructures for robustcycling of metal oxide anodes, in the present study, wecreated 1D nickel oxide (NiO) nanostructures using DNA as astructural template. Taking advantages of unique 1D nanos-tructures, the synthesized NiO exhibited stable capacityretention for 150 cycles and decent rate performance whiledelivering large reversible capacities of 850 mA h g�1.

Experimental section

Materials

Esherichia coli W (ATCC1105) was obtained from AmericanType Culture Collection (ATCC, MD, USA) and was grownovernight in lysogeny broth at 37 1C with shaking at200 rpm. Genomic DNA from E. coli was extracted by usingcommercialized E. coli DNA Extraction Kit (iNtRON Biotech-nology, Korea) according to the manufacturer's protocoldeveloped for gram-negative bacteria. Briefly, the culturedbacterial cells were mixed with lysis buffer containingRNase A and Proteinase K and incubated at 65 1C for15 min for complete cell lysis. The cell lysates were thencentrifuged in the column for 1 min and washed twice usingwashing buffer (10 mM Tris–HCl pH 7.5, 80% EtOH). The DNAwas finally obtained by washing the membrane in the givenKit with elution buffer and then incubating it for 1 min atroom temperature. After the incubation, the genomic DNAbound to column was eluted in distilled water. All of thecentrifugation was performed at 13,000 rpm.

Nickel metallization of E. coli DNA

The Ni metallized DNA was prepared by modifying theprocedures reported in the literature [34]. The extractedgDNA from E. coli was mixed with a NiCl2 solution and themixture was then incubated for 30 min at room tempera-ture. Next, 20 mM of CHES solution (pH 9) with 50 mM ofNaCl were added into the mixture solution. The solution wasagain incubated for 2 hr at room temperature. After incuba-tion, gDNA was converted to Ni-metallized DNA. The solu-tion was filtered and washed through molecular weight cut-off membrane (Amicon Ultra, EMD Millipore Corporation,MA, USA) by centrifugation at 13,000 rpm and dried in 70 1Coven for overnight.

Characterization of DNA metallization

Fluorescence spectroscopy was conducted for characteriza-tion of Ni-DNA. The metallized samples were stained withDNA staining dye, EvaGreen™ (1X). The fluorescence inten-sity was measured at various NiCl2 concentrations (0.15–15 mM) while the DNA concentration remained constant.

19DNA metallization

The fluorescence intensity was measured using a TecanInfinite M200 pro-microplate reader (Mnnedorf, Switzer-land) and black 384-well Greiner Bio-One microplates(Courtaboeuf, France). The excitation and emission inten-sities were measured at 488 and 525 nm, respectively. Forgel electrophoresis, 10 μL of the Ni-DNA solution (100 μM)was mixed with 2 μL of 6X loading buffer (10 mM Tris–HCl(pH 7.6), 0.03% bromophenol blue, 0.03% xylene cyanol, 60%glycerol and 60 mM EDTA) for visual tracking of DNA migra-tion during electrophoresis. The mixed DNA solution wassubjected to electrophoresis consisting of 2% agarose gelcontaining ethidium bromide (EtBr) and the electrophoreticbands were observed upon UV-B (305 nm peak) illuminationusing a gel imaging equipment (Gel Doc™ EZ System, Bio-Rad, CA, USA). The NiCl2 � 6H2O and 2-Cyclohexylaminoethanesulfonic acid (CHES) were purchased from Sigma-Aldrich (St. Louis, MO, USA). The DNA staining dye used inthis study, EvaGreen™, was obtained from Biotium (Hay-ward, CA, USA).

Transmission electron microscopy, field-emissionscanning electron microscopy, X-ray photoelectronmicroscopy, and X-ray diffraction

The morphologies of metallized DNA was characterized bytransmission electron microscopy (FE-TEM (300 kV) TecnaiG2 F30), and field-emission scanning electron microscopy(FESEM FEI Nova 230). The XPS analysis was carried out withX-ray Photoelectron Spectroscopy (Thermo VG scientific,Sigma Probe). The XRD analysis was performed using aRigaku D/MAX-RB(12KW) X-ray diffractometer.

Electrode preparation and electrochemicalcharacterization

All of the electrochemical measurements were carriedout by preparing 2032 coin cells in an argon-filled glovebox. The working electrode was prepared by dispersingNiO-DNA, carbon black, and polyvinylidene fluoride (PVDF)in N-methylpyrrolidone (NMP) in a mass ratio of 50:40:10.The prepared slurry was cast on Cu-foil and the cast samplewas dried inside a vacuum oven at 60 1C overnight. Metalliclithium foil (Hosen, Japan) was used as counter/referenceelectrodes. The microporous membrane (Celgard 2400) wasused as separator and 1 M solution of lithium hexafluoropho-sphate (LiPF6) in ethylene carbonate (EC) and diethylcarbonate (DEC) (v:v=1:1, Soulbrain Co., Ltd.) was usedas an electrolyte. All of the C-rates in this study were basedon the current density with respect to the 1C value, notactual charge or discharge times. The potential range ofNiO-DNA was 0.05–2.5 V vs Li/Li+. Galvanostatic charge anddischarge tests were carried out using a Biologic VMP3 multichannel system at room temperature.

Magnetic characterization

Magnetic properties were measured using a superconductingquantum interference device (SQUID, Quantum Design(MPMS XL-7)). Zero field cooled (ZFC) and field cooled (FC)measurements were carried out at under 100 Oe in the

temperature range of 300–40 K. Temperature and fielddependent magnetization were measured in the magneticfield range of �60 to 60 kOe and in the temperature rangeof 2–300 K.

Results and discussions

Since efficient electronic transport is critical for highperformance LIBs, we applied the concept of DNA metalli-zation (M-DNA) [34–38] into our electrode design. Thesynthesis of Ni-incorporated M-DNA nanostructure was sche-matically illustrated in Figure 1a. In detail, the genomicDNA (gDNA) of E. coli was selected as our scaffold andextracted by using commercialized DNA extraction kit(iNtRON Biotechnology, Korea). The DNA metallization wasfirst processed by replacing the imino protons of guanineand thymine with Ni2+ ions at pH above 8.5, forming Ni-DNAchelates in the buffer [34,36,38]. The precise pH control atthis step is crucial for structural stability of the DNA. TheNi-DNA complexes were followed by Ni clustering onto theNi-DNA chelates and also onto the DNA backbone, resultingin the Ni-metallized DNA hybrid structure. More detailedexperimental procedures are described in the Experimentalsection. It should be noted that a majority portion of Ni isnaturally oxidized into nickel oxide (NiO) and so we here-after denote this final material as NiO-DNA.

In order to investigate the Ni metallization of DNA,fluorescence spectroscopy and gel electrophoresis wereemployed. Once the metallization was completed, thesamples were stained using a DNA fluorometric dye (Eva-Green™). The EvaGreen dye has been known [39] to emitfluorescence signal at λmax=525 nm when forming dye-DNAcomplex, and was thus used for double-stranded DNAtracing in the current study. Figure 1b shows differentlevels of fluorescent intensity depending on the Ni ionconcentration. As the Ni ion concentration increased, thefluorescence intensity decreased reflecting the situationthat the fluorometric dye does not bind to Ni-DNA as muchas before the metallization. Accordingly, the non-metallizedDNA sample showed the highest intensity peak. The gelelectrophoresis (Supplementary Figure S1) also exhibited con-sistent results. The distance of the band from the top startingpoint became shortened with the increased Ni ion concentra-tion, as the Ni-metallization reduced the mobility of DNA. Bothanalysis results indicate the successful metallization of Ni-DNA.

To investigate the chemical composition of Ni-metallizedDNA, X-ray photoelectron spectroscopy (XPS) was performedin the range of 850–870 eV (Figure 1c). The location of theNi 2p3/2 peak center at 856.9 eV and the satellite peak at862.7 eV, which is attribute to the X-ray source that givesadditional emission with higher energy, indicating that Niexists mainly in the divalent state [40]. Also, the reasonableGaussian peak-fitting with a single peak (SupplementaryFigure S2a), instead of double peaks, implies that Ni existssolely in the divalent state in NiO-DNA [41]. In addition,NiO-DNA was characterized further by X-ray diffraction(XRD) analysis, and the obtained XRD pattern matched wellwith the NiO phase (JCPDS ♯04-0835, Supplementary FigureS2b). Both XPS and XRD results confirm the unstable natureof Ni in air and its natural oxidation to NiO during electrodepreparation in the air-exposed environment [42].

Figure 1 (a) The schematic description of DNA metallization process. The DNA metallization process can be separated into foursteps. (i) Activation: the metal ion complexes bind to the specific binding sites of nucleotide bases or phosphate backbone of DNA.(ii) Ni-chelate formation: the imino protons of guanine and thymine were replaced by nickel ions. (iii) Ni seeds formation andclustering: the reduced metal atoms grow into clusters on the activated nucleotide bases. (iv) DNA metallized 1D nanostructure: themetal clusters constitute continuous metal 1D nanostructure. (b) Fluorescence spectra results of Ni-DNA at various Ni ionconcentration. The concentration of DNA was constant. The nickel ion concentration was the highest in D1 samples while D6 was thelowest. The inset shows the fluorescence intensity at 525 nm. (c) XPS spectrum of NiO-DNA in the Ni 2p3/2 branch. (d) ATEM image ofthe synthesized NiO-DNA.

D.J. Kim et al.20

The NiO-DNA was further characterized by transmissionelectron microscopy (TEM). From the TEM images (Figure 1dand Supplementary Figure S3a), it was found that themetallization produced 100–200 nm Ni clusters connected inseries, forming a necklace-like 1D structure. By contrast, thesame clusters but without using the DNA scaffold showedfar more agglomerated morphology in �2 μm dimensions(Supplementary Figure S3b), verifying the importance ofthe DNA-mediated metallization for realization of theagglomeration-free 1D morphology of NiO-DNA. Moreover, ahigh-resolution TEM (HRTEM) image of NiO-DNA showed alattice distance of 2.42 Å corresponding to the NiO (111)plane (Supplementary Figure S3c). Additionally, energy dis-persive spectroscopy (EDS) characterization was performedfor elemental analysis, and, consistent with the XPS results,nickel and oxygen were detected (Supplementary Figure S3d).

The electrochemical properties of NiO-DNA were evalu-ated by preparing 2032 coin-type half-cells in which Limetal was used as the reference/counter electrodes. 1 Mlithium hexafluorophosphate (LiPF6) dissolved in co-solventsof ethylene carbonate (EC) and diethyl carbonate (DEC) in a1:1 volume ratio was used as electrolyte. More detailedelectrode preparation and measurement conditions aredescribed in the Experimental section. All the potentialsaddressed hereafter are with respect to that of Li/Li+.As shown in Figure 2a, NiO-DNA exhibited plateaus at 0.85and 1.3 V during charge (lithiation) and discharge (delithia-tion), which are characteristic of the well-known conversionreaction: NiO+2Li+ +2e�2Ni+Li2O [43,44]. In terms ofthe gravimetric capacity, when measured in the potential

range of 0.05–2.5 V, NiO-DNA provides 1750 and 985 mA h g�1

for the first charge and discharge capacities respectively.These values lead to a relatively low first Coulombicefficiency (CE) of 56.3%. This tendency is indeed consistentwith most conversion reactions that are accompanied withunavoidable formation of solid–electrolyte-interphase (SEI)and Li2O in the first cycle. In the second and subsequentcycles, persistent capacities around 840 mA h g�1 werepreserved when measured at a C-rate of 0.14 C (=100 mA g�1),suggesting robust structural character of NiO-DNA. In thisstudy, all of the C-rates are based on 1 C (=718 mA g�1),not actual durations.

NiO-DNA exhibited decent rate capability (Figure 2b)when tested by applying various C-rates. Even when theC-rate increased a 10-fold from 0.14 C (=100 mA g�1) to1.4 C (=1000 mA g�1), the original capacity of 882 mA h g�1

dropped only to 643 mA h g�1, corresponding to 73% capa-city retention. Also, the initial capacities were recoveredwhen the C-rate returned to 0.14 C (=100 mA g�1), recon-firming the robust nanostructure of NiO-DNA (Figure 2c).The good rate capability of NiO-DNA is ascribed to the smalldimensions of NiO directed by the unique 1D structure ofDNA that allows Li ions to diffuse only in short distances.Also, it is speculated that the very core of the givennecklace-like structure still preserves metallic Ni even afterthe NiO formation in the shell, and the metallic Nicontributes to efficient electronic transport, which is desir-able for the good rate capability. Such core–shell structurewas confirmed further by the magnetic characterization, aswill be described at the end of this section.

Figure 2 Electrochemical properties of NiO-DNA when tested as an LIB anode. (a) The galvanostatic test voltage profiles of NiO-DNA in the first five cycles when measured at 0.14 C (=100 mA g�1). (b) The galvanostatic voltage profiles of NiO-DNA at variousC-rates. (c) The rate capability test of NiO-DNA. The C-rate was the same for lithiation and delithiation in each cycle. (d) The cyclingperformance of NiO-DNA. For all of the results in this figure, the potential range of NiO-DNA was 0.05–2.5 V. Also, all of the specificcapacities were calculated based on total weight of both NiO and DNA. The same current rate was applied for charging anddischarging of each cycle.

21DNA metallization

NiO-DNA exhibited excellent cycling performance. As shownin Figure 2d, when measured at 0.28 C (=200 mA g�1),the capacity became stabilized after a certain capacitydecay in the first three cycles. In the first three cycles, thecapacity decayed from 969 to 871 mA h g�1. But, thecapacity was retained quite well thereafter, as 840 mA h g�1

was preserved at the end of 150 cycles, indicating 96%capacity retention in the cycle range of 3–150 cycles. Evenwhen the C-rate was increased to 1.4 C (=1000 mA g�1),average capacity of 625 mA h g�1 was obtained. At thishigher current rate, a good capacity retention of 86% wasachieved in the same cycle range of 3–150 cycles. Theaverage Coulombic efficiency of 3–150 cycles was 98.8%. Wehave also carried out galvanostatic cycling test with anincreased portion of the active material (70 wt%) andobserved comparable performance (Supplementary FigureS4). The capacity retention during 20 cycles was 83% andaverage Coulombic efficiency was 98%. The initial capacitydecay may be associated with the structure stabilizationduring the conversion reaction. Once the structure reachesthe stabilization point, it appears that the structure remainsvery stable. Behind the excellent cycling performance, the1D structure directed by the DNA backbone should play adecisive role as the 1D structure contributes to preventionof agglomeration of nano-NiO during aggressive Li diffusionover cycling (Supplementary Figure S5).

In an attempt to elucidate the composition and redoxstate of the NiO-DNA electrode, magnetic characterizationwas carried out from 300 to 2 K employing a superconductingquantum interference device magnetometer (SQUID). Forthis, the samples were prepared at three different states:(i) as-synthesized state, (ii) Li insertion state, and (iii) Liextraction state. For the sample collection, the coin cellswere disassembled inside an argon-filled glove box, and theelectrodes were removed from the Cu current collectors.

Zero field cooled (ZFC) and field cooled (FC) magnetizationcurves were obtained for all of the three samples in thetemperature range of 300–40 K under a magnetic field of100 Oe (Figure 3a–c). From the temperature dependence ofthe magnetic moment, the redox state of Ni can be clarifiedbecause NiO and Ni have distinctive magnetic characters ofantiferromagnetism (AFM) and ferromagnetism (FM), respec-tively. In the case of the as-synthesized sample (Figure 3a),the magnetic moment in both ZFC and FC measurementsdecreased with the decreasing temperature down to 90 K butstarted to increase thereafter. The negative slope of themagnetic moment with respect to the temperature has beenknown as a characteristic of AFM materials, thus verifyingthat the as-synthesized NiO-DNA has dominant NiO phase.This dominant NiO phase is also related to the large specificcapacity. By contrast, in the case of the Li insertion state(Figure 3b), the negative slope disappeared, suggesting the

Figure 3 Magnetization measurements of NiO-DNA. Zero field cooled (ZFC) and field cooled (FC) magnetization curves of NiO-DNAat 100 Oe for (a) the as-synthesized state, (b) the Li insertion state, and (c) the Li extraction state. (d) Field variation of themagnetization measurements of NiO-DNA at 2 K and at 300 K.

D.J. Kim et al.22

elimination of the temperature dependence of the magneticmoment, due to the dominant phase of FM Ni. In fact, thedominant Ni phase after Li insertion is consistent with thesuggested conversion reaction mechanism. Upon Li extrac-tion (Figure 3c), the magnetic moment behavior returnedsimilarly to that of the as-synthesized sample, confirmingthe reversible nature of NiO-DNA throughout a full cycle.In addition, the consistent trends between ZFC and FC mea-surements for all of the three states indicate exchangeinteraction between AFM and FM domains [45]. The reversi-bility of ZFC and FC curves during the electrochemicalreaction indicates the absence of frustrated magneticmoments or clustering glass behavior. The magnetization(M–H) curves as a function of magnetic field was alsomeasured at 300 K and 2 K (Figure 3d). The linear M–Hobtained at 300 K indicates a dominant NiO AFM exchangeinteraction over FM Ni at RT. At 2 K, magnetization curveshows clear ferromagnetic loop (from Ni) along with theunsaturated straight line at high field (from AFM NiO)confirming the presence of FM and AFM exchange interaction.Overall, the magnetic characterization is consistent with ourview on the NiO-DNA structure, that is Ni/NiO core–shellstructure, and, once again, the excellent electrochemicalproperties are synergetic outcomes of small dimensions ofNiO-DNA and presence of its metallic Ni core.

Conclusion

In conclusion, we report high capacity LIB anodes consistingof the 1D NiO nanostructure by employing well-establishedDNA metallization. This unique 1D nanostructure of DNAdelivered reversible capacity of 850 mA h g�1, that is sub-stantially higher than those of current graphite anodes.Utilizing the small dimensions of the diameters in the 1D

structure and its unique Ni/NiO core–shell structure, NiO-DNA exhibited excellent capacity retention for 150 cycles aswell as decent rate performance. The present investigationsuggests that a variety of simple nanomaterial synthesesengaging bio-templates [46] can be useful platforms for highcapacity LIB electrodes that suffer from large volumechanges and formation of insulating phases during batteryoperations.

Acknowledgment

We are pleased to acknowledge the financial support by theNational Research Foundation of Korea (NRF) Grant fundedby the Korea Government (MEST) (NRF-2010-C1AAA001-0029031 and NRF-2012-R1A2A1A01011970).

Appendix A. Supplementary information

Supplementary data associated with this article can befound in the online version at http://dx.doi.org/10.1016/j.nanoen.2014.05.007.

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Dong Jun Kim received his B.S. degree inthe Materials Science Engineering from Yon-sei University, Korea in 2010. He is currentlya Ph.D. student in Prof. Jang Wook Choi’sgroup at KAIST, Korea. His current researcharea includes energy storage materials andredox active organic materials.

Min-Ah Woo is currently a senior researcherat Korea Food Research Institute, Korea.She has received her M.S. degree at SeoulNational University, Korea in 2008, andPh.D. degree in Chemical & BiomolecularEngineering at KAIST, Korea in 2013. Herresearch focuses on the design of diagnosticsystems using genetically engineeredmutant E. coli.

Ye Lim Jung is currently a senior researcherat Korea Institute of Science and TechnologyInformation, Korea. She has completed herM.S. and Ph.D. degrees in Chemical &Biomolecular Engineering at KAIST, Koreain 2014. Her research focuses on the devel-opment of colorimetric biosensors based onthe regulation of metal ion reduction.

K. Kamala Bharathi received his masters(M.Sc.) from The American College, Maduraiat India and Ph.D. from IIT Madras, Chennaiat India in 2010. He has worked as apostdoctoral fellow in Prof. C.V. Ramana’sgroup at UTEP, Texas, USA from 2010 – 2011and Prof. Do Kyung Kim’s group at KAIST,Korea from 2012 – 2014. His research inter-est includes magnetoelectric materials,multiferroic thin films, rare earth doped Ni

ferrite materials, synthesis and characterization of nanocrystallineperovskite oxides, X-ray Phosphor materials, Li battery materialsand their magnetic properties.

Hyun Gyu Park received his B.S., M.S. andPh.D. degrees from Department of ChemicalEngineering at KAIST in 1996. He was avisiting Scholar at Department of BiochemicalEngineering at University of Iowa in 1993 anda senior researcher at Samsung AdvancedInstitute of Technology in 1996. He has beenthe faculty in the Department of ChemicalBiomolecular Engineering at KAIST since 2002.He was awarded Innovative Research Award

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D.J. Kim et al.24

(Samsung Advanced Institute of Technology) in 1998, AcademicExcellence Award (KAIST) and The Award for Innovative Excellencein Technology (KAIST) in 2011. His current research interests includenucleic acid bioengineering, microarray technology, electrochemicaltechnology for molecular diagnostics, and nanobiotechnology &enzyme engineering.

Prof. Do Kyung Kim has been the faculty ofDepartment of Materials Science and Engi-neering, KAIST, Korea since 1994. He hasreceived his B.S. degree from SeoulNational University, Korea in 1982 and M.S.and Ph.D. degrees from the Department ofMaterials Science and Engineering at KAIST,Korea in 1984 and 1987, respectively.Before joining KAIST, he has worked forthe Agency for Defense Development

(1987–1994), Korea. He had several visiting professor positions atUC San Diego (1992), NIST (2002), and UC Berkeley (2008). He wasawarded a Top 20 Most Outstanding Research Award from KoreaScience and Engineering Foundation (KOSEF) in 1997 and Top Most

Outstanding Research Award from Korea Research Foundation (KRF)in 2011. In 2007, he was awarded the Promising Scientist forOverseas Research by SBS Foundation. He has authored more than150 technical articles, and has filled 17 Patents in US, Japan andKorea.

Jang Wook Choi received his B.S. degreefrom Seoul National University, Korea in2002 and Ph.D. degree from Division ofChemistry and Chemical Engineering at Cal-tech, USA in 2007. He was a PostdoctoralResearcher at the University of Chicago(2007) and Stanford University (2008). Hehas been the faculty of Graduate School ofEEWS (Energy, Environment, Water, Sustain-ability), KAIST, Korea in 2010. He was

awarded Top 10 KAIST R&D Project (2012), Best KAIST CollaborationAward (2013), and Scientist of the Month Award from Daejeon City(2014). His research area encompasses materials for rechargeablebatteries, supercapacitors, and CO2 storage.

DNA metallization for high performance Li-ion battery anodesIntroductionExperimental sectionMaterialsNickel metallization of E. coli DNACharacterization of DNA metallizationTransmission electron microscopy, field-emission scanning electron microscopy, X-ray photoelectron microscopy, and X-ray...Electrode preparation and electrochemical characterizationMagnetic characterization

Results and discussionsConclusionAcknowledgmentSupplementary informationReferences