Microwave-assisted synthesis and electrochemical characterization of α-MnO2 as catalyst for...

ISSN 1023�1935, Russian Journal of Electrochemistry, 2014, Vol. 50, No. 10, pp. 933–939. © Pleiades Publishing, Ltd., 2014.Published in Russian in Elektrokhimiya, 2014, Vol. 50, No. 10, pp. 1037–1044.

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1. INTRODUCTION

With an increasing demand of batteries to provide avery high specific charge some alternatives to lithium�ion batteries were investigated recently. Compared tolithium–ion batteries, lithium–sulphur batteries pro�vide a much higher theoretical charge of 1675 A h kg–1

(relating to the active material content of the elec�trode), which is a magnitude higher than the theoreti�cal specific charge of olivine materials as LiFePO4 (ca.170 A h kg–1). Further, the lithium�air cell is a type ofmetal�air battery of high interest since the theoreticalenergy density of oxygen is about 11140 W h kg–1 [1].Various experimental conditions have been reportedwith different types of catalysts, electrolytes, cell man�ufacturing, separator materials, and thermal condi�tions [2–4]. A very challenging and important pointthat needs to be addressed in the field of lithium�airbatteries is how to enable the reversible reactions (i.e.,

2Li+ + 2e + → Li2O2 and 4Li+ + 4e + →2Li2O) with respect to aprotic electrolytes. Therefore,O2 catalysts are key factor for the development ofeffective lithium–air cathode materials. Moreover, therelation between catalyst materials and carbon needsto be addressed [5, 6]. MnO2 is a very promising cata�lyst and a number of publication already described dif�ferent modifications of this catalyst [7–12]. Neverthe�less, almost all reports used a different preparation ofthe catalyst with a subsequent, second step for theloading of the catalyst onto carbon material.

O2* O2*

All of these traditional preparation processes ofelectrodes for lithium(�ion) cells use organic solvents,such as NMP (JV�Methyl�2�pyrrolidone) or NEP(N�Ethyl�2�pyrrolidone), during the preparation pro�cess. Due to their toxicity these chemicals need to bereplaced [13]. Though other solvents might be usedinstead, dry coating processes for electrodes haveadditional advantages with respect to the energy con�sumption during the preparation process.

In this work the authors describe a microwave�assisted synthesis of an MnO2�catalyst that wasdirectly formed on the particles of a carbon�com�pound. The MnO2�loaded carbon�compound wasthen used for the preparation of lithium�air electrodes.

A Laser Induced Forward Transfer (LIFT) [14–17]method served as dry (solvent free) coating method forthe preparation of the electrodes. LIFT transfers thematerial of interest by the laser beam from a transpar�ent donor substrate (like a ink ribbon) onto an appro�priate receiver substrate (here: current collector). Inparticular, this technique allows one to obtain patternsof materials with high resolution. These patterns aredefined by the shape of the laser beam. In conven�tional LIFT the material to transfer can be directlyirradiated by the laser pulse, in which metals and somepolymers may be used. But this method has a strongimpact on the transferred material which mightdecompose it. As an alternative to the direct irradia�tion, suitable materials to be used as the sacrificiallayer are photosensitive polymers, Triazene polymers(TP) transfer the soft material with a minimum ofthermal load to a receiver substrate, because thesedecompose into gaseous fragments upon UV laserirradiation [18]. Using triazene polymers as dynamic

Microwave�Assisted Synthesis and Electrochemical Characterization of α�MnO2

as Catalyst for Lithium–Air Batteries1

Andreas Hintennachz and Sarah RosenbergCGS, Brachter Str�Bau 7, D�71732 Hohenstange

Received June 13, 2013

Abstract—A novel preparation path for the synthesis of MnO2�based wire�shaped catalyst material for lith�ium�air electrodes is presented. The electrode was prepared with direct laser�transfer, which is solvent freeand considered environmental benign. High specific charge, 869 and 2978 A h kg–1, was achieved for the totalmass of one electrode and carbon content, respectively. The electrode faded about 11% of the initial specificcharge after 60 cycles.

Keywords: laser transfer, MnO2, lithium–air, microwave

DOI: 10.1134/S1023193514100036

1 The article is published in the original.z Corresponding author: [email protected] (Andreas Hintennach).

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RUSSIAN JOURNAL OF ELECTROCHEMISTRY Vol. 50 No. 10 2014

ANDREAS HINTENNACH, SARAH ROSENBERG

releasing layer (DRL) has several advantages, (i) thetriazene polymers have a very low ablation threshold ofapprox. 25 mJ cm–2 for 308 nm irradiation, whichmeans that the transfer can be achieved with low ther�mal impact on the donor layer; (ii) no debris isdetected, and (iii) a high absoiption coefficient at theXeCl excimer laser wavelength (please refer to Fig. 1for the absorption spectrum and the exemplary chem�ical structure of TP). These facts make the LIFT withTP an ideal technique for the dry preparation of elec�trodes.

2. EXPERIMENTAL

2.1. Preparation of Carbon Compounds for the Electrodes

Microwave�assisted synthesis paths are character�ized by very fast reactions, which allows only a shorttime for the formation of networks between solid com�posites or becoming an equilibrium [19–24]. Thebasic condition of the short time requires precursorswith large surfaces, high solubility, and a very intensemixture prior to and during the synthesis. With theserequirements in mind one of the key issues for thepreparation of a working carbon material for the elec�trode was to select precursors which would be pyrolyz�able very fast and could inflate the pyrolyzing carbon�containing compounds. Stearic acid and magnesiumstearate were used to form a stable framework. Thepotassium hydro carbonate served both as an inflatingtool and a wetting additive. For the synthesis of thecarbon compounds the selection of the inflating agent(here: potassium hydro carbonate) was proved to have

a significant influence on the structure of the carboncompound since the kinetic of the inflation varies withthe use of different materials. Ammonium hydro car�bonate might be used as an alternative to potassiumhydro carbonate. But for ammonium hydro carbonatethe whole preparation process was less adjustable dueto higher inflation speed and the begin of the inflationat lower temperatures. In order to avoid an uncon�trolled and irreproducible synthesis, it is essential tofinely adjust the reaction rate. Adjusting the reactionrate could be easily performed by pressing a pill with areasonable surface/volume ratio. This is a sensitivepart within the preparation of the synthesis as the reac�tion kinetic significantly influences the morphology ofthe prepared carbon and, therefore, the mixing withthe sulphur which is applied in the second laser print�ing step.

Carbon compounds were prepared by a micro�wave�assisted pyrolysis of a mixture of saccarose,potassium hydro carbonate, magnesium stearate, andstearic acid (91 : 9 : 1 : 1 by weight). The powders wereground in a mortar and pressed to a thin pill (weightloading 195 kN) with a diameter of about 19 mm anda final height of 14 mm. The amount of material usedfor pressing the pill was always adjusted to achieve thesame pill parameters (height, diameter). Due to themicrowave heating and the limited penetration depthof microwaves into a material constant pill parametersare important to ensure a constant result of the pyrol�ysis process. Afterwards this pill was immersed in2.75 mL of a mixture of ethanoi and acetylacetone(1 : 1 by weight) in an open glass vessel without stir�ring. Only the outer parts of the pill was soaked withthe solvents (>99%, Merck) while most of the pillremained diy. As a heating source a conventionalindustrial microwave oven was slightly modified. Itwas equipped with a second single�pulse voltage dou�bler giving 2 × 2 kV output. In addition, 4 high voltagediodes and 2 high voltage capacitors giving a two pulsevoltage doubler for one magnetron were used. Thissetup allowed a continuous irradiation of the sample[25, 26]. This mixture was heated in this modifiedmicrowave oven at a continuous power of 350 W for2.5 min and 800 W for additional 9 min. During thefirst step of the pyrolysis process the solvents almostcompletely evaporated. With further pyrolysis thepotassium hydro�carbonate inflated the pyrolysis prod�uct. The carbon product could be used without furtherpurification. Please note that these carbon compoundsdo not yet contain any MnO2 or precursors.

2.2. Microwave�Assisted Synthesis of α�MnO2

The carbon�compounds described in section 2.1were stored in nitric acid (10 wt %) for 10 min. Thenthe solution was heated in a microwave to boiling pointfor 5 min and naturally cooled down to room temper�ature. All used chemicals were of analytical grade andused without further purification.

N N N

R2

R1 N

R2

N NX

n

40

0450400350300250200

80

120

Abs

orpt

ion

, cm

–1

Wavelength, nm

Fig. 1. Absorption curve of the Triazene polymer (UV/Vis)and chemical structure of the polymer.


MICROWAVE�ASSISTED SYNTHESIS 935

For the predispersion of carbon�compound andprecursors of MnO2the carbon�compound (0.15 g)was dispersed in deionized water (100 mL) by ultra�sonication for 40 min. Then MnSO4 (15 wt %), a sto�ichiometric quantity of KBr in deionized water, andTriton X�209 (0.8 wt %) was added and sonicated for15 min to absorb deeply onto and into the carbon�structure. Subsequently, the mixture was heated in themicrowave using the heating protocol as shown inFig. 2. It was proved to be important to quench thesynthesis at the end by rapidly cooling the reactionvessel with pressurized air. The suspension was fil�tered, washed with deionized water several times, eth�anol (99%), and then dried at 100°С for 12 h in a vac�uum oven. Finally, the black powder was collected.

2.3. Powder Characterization

Raman spectra were recorded of the surface of dif�ferent electrodes to ensure a homogeneous coating ofthe surface. All Raman spectra were recorded with aHoribaJobinYvon T64k Raman microscope equippedwith a HeNe laser working at 633 nm. A wide�rangeobjective (50×) was used. The laser power during themeasurements was limited by the internal filter set to1.2 mW.

The structure and morphology of the samples wereexamined by an X�ray diffractometer (XRD; Panalyt�ical X’pert) with CuK

α radiation and scanning elec�

tron microscopy (SEM; Zeiss Ultra), respectively.X�ray photoelectron spectroscopy (XPS) was used forcompositional analysis.

2.4. Preparation of Electrodes via LIFT

The preparation of electrodes mainly consists ofthe following steps: First, the pulverulent carbonbinder mixture was prepared. Second, the donor filmswith light sensitive TP was prepared. Third, the laserprinting of electrodes (coating of the current collectorswith electroactive material, binder etc.) was per�formed using the LIFT technique. Finally, these elec�trodes were assembled for characterization.

For the preparation of the carbon�binder mixturedry and ground powder of the as�synthesized carboncompound was used. Dry polyvinylidene fluoride(PVDF SOLEF 1015, Solvay) was used as a binder andmixed prior to the coating of the TP film with a dryblender (Hosokawa Alpine) with the carbon material(92 : 8 by weight). Since PVDF is hygroscopic it isessential to mix the carbon material with the PVDFbinder within a dry atmosphere. In this work, theblender was flushed with nitrogen.

To transfer electrode materials by LIFT, the keyfactor is to get donor films with the correct architec�ture to achieve a successful transfer. An additional TPinterlayer, that is tailored to absorb the laser light pro�duces enough energy to transfer various materials. Theimportant parameters for transfers are the thickness of

the TP layer and the brittleness of the material. The TPused for the following experiments was synthesized asdescribed in the literature [18]. Dry and pristine TPwas dissolved in a mixture of chlorobenzene andcyclohexanone (1 : 1 by volume) with stirring at roomtemperature for 1 h to achieve a TP concentration inthe solution of 1.25% by weight. Donor films were pre�pared by spin coating (2500 rpm, 50 s, nitrogenflushed) the TP solution on glass substrates resulting ina film thickness of ca. 50 nm. For a good wetting of theTP surface, 0.75% (by weight) Triton�X 209 (Sigma�Aldrich) was added. The addition of a surfactant wasproved to be beneficial to obtain homogeneous andcrack free coated surfaces for the donor substrate.Finally, the TP films were dried on a hot plate at 60°Сfor 1 h while the first 10 min the plate was flushed withnitrogen.

For a “dry,” solvent�free, coating of the TP�filmswith the electrode material an electrostatic charge wasapplied to the surface of the as�prepared TP�filmsusing a commercial electrostatic charge device (SirncoIon, 45 kV, linear electrode). Placing the glass sub�strate with the TP film under the electrostatic chargedevice charged the surface of the TP electrostaticallyand, therefore, improved the adhesion of the pulveru�lent materials. Please note, that the TP films are sensi�tive to light and therefore, the electrostatic charginghas to be applied in a shaded environment.

LIFT transfers (please see Fig. 3 for the setup) weremade with a XeCl excimer laser (Lambda Physics, λ =308 nm, τ = 30 ns). The laser beam was shaped using asquare shaped 2 × 2 mm or a circular ∅ = 4.0 mm

200

100

51 3

KBr, MnSO4deion. water

Triton X�209 (0.8 wt %)

Microwavep < 4 bar Wire�shaped

particles ofMnO2

Tem

pera

ture

, °С

Time, min0

Fig. 2. Temperature protocol for the microwave�assistedsynthesis of the MnO2 catalyst material. The inlet showsthe synthesis procedure.

936



aperture in the homogeneous part of the beam anddemagnified four times to ablate pixels of about500 μm side length. A computer�controlled xy�stagewas used in order to prepare larger areas of electrodefoil. The fluences were adjusted with an attenuationplate and varied between 350 and 400 mJ cm–2. Thedonor and the receiver substrate were placed in closecontact (<10 μm) on a motorized translation stage.The described setup was controlled via a programma�ble logic controller (Siemens Simatic S7). All thetransfers were earned out under ambient conditions(atmospheric pressure and 25°С, low humidity with adew point of –35°С).

2.5. Electrochemical Characterization

Pouch type test cells (about 4 × 4 cm) were used forthe electrochemical characterization. The car�bon/MnO2 mixture which had been electrostaticallyloaded onto the TP films was then LIFTed (please seesection 2.4 for the details of the laser�transfer) onto asquare of stainless steel mesh (4 × 4 cm, 20 μm thick�ness, 185 wires per linear inch). The thickness of the finalprinted layer was adjusted to about 60 μm. Please notethat no NMP was needed. A lithium�foil (4 × 4 cm,0.5 mm thickness; 99.89%, Mewack) served both as ananode and reference electrode with a porous polypro�pylene film (Celgard 3401) as separator in between.The cell was gas proof except for the stainless steelmesh window that exposed the porous cathode tohighly dried O2. Drying the gas is critical for the life�time since the moisture of the air reacts with the lith�ium negative electrode and CO2 can react with thelithium�ions of the conductive salt of the electrolyte. Amixture of ethyl carbonate (EC)�diethyl carbonate(DEC) (2 : 3 by volume) with LiTFSI salt (1 M; lith�ium bistrifluoromethanesulfonimidate; 99.95%,Sigma�Aldrich) served as electrolyte. Ail cells wereassembled in an argon filled glove box with concentra�tions of H2O and O2 < 1 ppm.

All cells rested for 2 h under the conditionsdescribed above to allow the formation of an equilib�rium for the gas concentration. The electrochemicalcycling and the charge�discharge profiles were per�formed in a voltage range of 2.0–4.2 V vs. Li/Li+ at aconstant current of 0.2 mA cm–2 in a climate con�trolled chamber at (25 ± 0.1)°C. All results are theaverage of four tests. The specific charge is alwaysrelating to the active material content of the electrode.The electrochemical impedance spectra wererecorded within a frequency range of 0.1–105 Hz withan amplitude of 5 mV.

3. RESULTS

An exemplary SEM image of the formed mixture ofthe carbon compound with the loaded α�MnO2 on thesurface is shown in Fig. 4. The wire�like structure ofthe formed MnO2 catalyst is clearly visible. For theelectrochemical performance the structure and size ofthe as�formed MnO2 are important. With changingsynthesis conditions (pressure, time, concentration,temperature) the size, surface area, and form of thecatalyst particles can be significantly influenced.

The formation of MnO2 is the result of an oxidationof the MnSO4 precursor. An exemplary XRD pattern isshown in Fig. 5. The XRD signals were indexed to thetetragonal α�MnO2 crystal structure with the spacegroup I4/m (87) with lattice constants of a = 9.784 Åand c = 2.863 Å which indicates a very high purity andcrystallinity. In addition, the as�obtained data werecompared to literature values for the tetragonalβ�MnO2 crystal structure with the space groupP42/mnm (136) with lattice constants of a = 4.399 Åand c = 2.874 Å, but no corresponding signals wereobtained which underlines the high purity of the syn�thesized MnO2 [27].

Laser

Glass with

SampleAttenuator and

Mask Objective

xyz�Stage

donor layer

shaping

Fig. 3. Schematic drawing of the setup for the laser trans�fers with LIFT.

200 nm

Fig. 4. Typical SEM�image of the surface of the preparedmixture of carbon�compound and wire�shaped MnO2 cat�alyst. SEM at 3 kV, SN2 lens.



The oxidation states of the obtained α�MnO2(Mn2p) catalyst were investigated with XPS which isshown in Fig. 6. Both the peaks Mn2p3/2 and Mn2p1/2at the positions 642 and 654 eV can be compared withliterature data [28]. These two peaks indicate the man�ganese in MnO2 is mainly of Mn4+ state and, therefore,the synthesis with the described microwave�assistedpath directly led to MnO2 via precipitation [29–31].

Raman spectra were recorded from different posi�tions on the surface of the sample. A representativespectrum is shown in Fig 7. A typical scattering bandof α�MnO2 at about 643 cm–1 is highly visible, whichcorresponds to the Ag spectroscopic species originat�ing from breathing vibrations of the MnO6 octahedra[32]. The absence of peaks at about 304 and 360 cm–1

indicates that no significant laser�induced heatingwith subsequent formation of Mn2O3 and/or Mn3O4(bending modes of O–Mn–O) occurred [33]. The

very strong Ag�mode is ascribed to a very fast and crys�talline formation of α�MnO2. These results are highlyin line with the results of the XRD and XPS�measure�ments, described above.

Typical results of the electrochemical impedancespectroscopy are shown in Fig. 8 for a cell before theelectrochemical cycling and after 20 cycles. The con�tact resistance is represented by the semicircle at highfrequency values. In addition, the discharged productlayer has some influence on this semicircle if the cellwas electrochemically cycled. At low frequency valuesthe ion diffusion within the cell is represented by theinclined line. It can be assumed that the reaction prod�uct of Li2O2 (or Li2O or LiO2 is deposited on the poresof the diffusion layer of the cathode side. This depositreduces the electronic conductivity and increases theresistance and polarization. This effect is mainlyresponsible for the degradation of the cathode during

703010 50

α�MnO2

(110

)

(200

)

(310

)

(211

)

(301

)

(411

)

(600

)(5

21)

(002

)(5

41)

(312

)

Inte

nsi

ty

2θ, deg

Fig. 5. XRD pattern of the composite of the carbon�com�pound and α�MnO2 catalyst material.

640660 650

654 eVMn2p1/2

Mn2p3/2

642 eV

Binding energy, eV

Inte

nsi

ty

Fig. 6. XPS spectra (Mn2p) of the composite of the car�bon�compound and α�MnO2 catalyst material.

800400200 600

MnO2

Inte

nsi

ty

Wavenumber, cm–1

Fig. 7. Typical Raman spectra of the surface of the elec�trode material highlighting the peaks for α�MnO2.

400

200

0 700500300100

Z'',

Oh

m

Z ', Ohm

Before cyclingAfter 20 cycles

Fig. 8. Electrochemical impedance spectra of the lithium�air cell before electrochemical cycling and after 20 cycles.

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the electrochemical cycling and it is assumed to be aresult of accretions on the surface of the electrodereducing the electronic conductivity of the cathode[34, 35].

An exemplary charge/discharge curve of an as�pre�pared electrode is shown in Fig. 9a. High specificcharge, 869 and 2978 A h kg–1, was achieved for thetotal mass of one electrode and carbon content,respectively. The electrode faded about 11% of the ini�

tial specific charge after 60 cycles. Compared to liter�ature data these values are very high. The electro�chemical stability is shown in Fig. 9b. After the veryhigh initial specific charge the specific charge wasdetermined for a higher number of cycles. About 89%of the initial specific charge remain after 60 cycleswhich is a high value for lithium–air (lithium–oxy�gen) cells. Nevertheless, the fading becomes more andmore severe with an increasing number of cycles. Butafter the achieved number of cycles the specific chargeis still acceptable with very high values. This factunderlines the high quality of the as�prepared elec�trodes especially in comparison to published data inliterature [36–38].

4. CONCLUSIONS

Direct laser�printing was verified to be an efficient,fast, and “green” alternative to regular coating pro�cesses of electrodes for lithium batteries. The ability oflaser�based printing processes to fabricate lithium�airelectrodes proved to be a technology of choice for thepreparation of electrodes with a very high electro�chemical performance. Though the novel concept wasdesigned to fabricate working test electrodes of amedium size, scale�up is possible without a major revi�sion of the concept. With a change from the pixel�by�pixel transfer to a line�by�line transfer (comparable toa laser printer of a desktop computer) electrodes of alarge size can be produced with various shapes. Theseshapes can even be three�dimensional. The synthesisof the MnO2 can be easily scaled up by the use of apump�through (forced flow) microwave reactorinstead of the batch reactor without a redesign of thesynthesis.

REFERENCES

1. Beattie, S.D., Manolescu, D.M., and Blair, S.L.,Journal of The Electrochemical Society, 2009, vol. 156,pp. A44–A47.

2. Xu, W., Xiao, J., Wang, D., Zhang, J., and Zhang, J.�G.,Electrochemical and Solid�State Letters, 2010, vol. 13,pp. A48–A51.

3. Lu, Y.C., Gasteiger, H.A., and Shao�Hom, Y., Journalof the American Chemical Society, 2011, vol. 133,pp. 19048–19051.

4. Zhang, X., Hua, L., Yang, E., An, Z., Chen, J., Chen, X.,Chao, X., Yu, J., Wu, M., and Miao, X., Int. J. Electro�chem. Sci., 2012, vol. 7, pp. 10562–10569.

5. Meini, S., Piana, M., Beyer, H., Schwammlein, J., andGasteiger, H.A., Journal of The Electrochemical Society,2012, vol. 159, pp. A2135–A2142.

6. Eswaran, M., Munichandraiah, N., and Scanlon, L.G.,Electrochemical and Solid�State Letters, 2010, vol. 13,pp. A121–A124.

7. Zeng, J., Nair, J.R., Francia, C., Bodoardo, S., andPenazzi, N., International Journal of ElectrochemicalScience, 2013, vol. 8, pp. 3912–3927.

3.0

2.0300020000 1000

4.0

2000

1000

500

0 1406020

2500

3000

1500

100

0.2 mA cm–2

Pot

enti

al,

V v

s. L

i/L

i*

Specific charge, A h kg–1

0.2 mA cm–2

Spe

cifi

c ch

arge

(di

sch

arge

), A

h k

g–1

Cycles

(a)

(b)

Fig. 9. (a) Variation of the potential of the cell with thestate of charge (0.2 mA g–1) for a porous electrode con�taining the as�prepared α�MnO2 on a carbon�compound.Please note: The specific charge is the normalized value forthe carbon content i.e., about 869 A h kg–1 for the totalmass of the electrode. (b) Variation of the specific chargefor the discharge (0.2 mA g–1) process.



8. Li, J., Wang, N., Zhao, Y., Ding, Y., and Guan, L.,Electrochemistry Communications, 2011, vol. 13,pp. 698–700.

9. Thapa, A.K. and Ishihara, T., Journal of Power Sources,2011, vol. 196, pp. 7016–7020.

10. Truong, T.T., Liu, Y., Ren, Y., Trahey, L., and Sun, Y.,ACS Nano, 2012, vol. 6, pp. 8067–8077.

11. Li, L., Nan, C., Lu, J., Peng, Q., and Li, Y., ChemicalCommunications, 2012, vol. 48, pp. 6945–6947.

12. Debart, A., Paterson, A.J., Bao, J., and Bruce, P.G.,Angewandte Chemie, 2008, vol. 47, pp. 4521–4524.

13. Reisch, M., Chemical & Engineering News Archive,2008, vol. 86, pp. 32.

14. Atre, A.C. and Arnold, C.B., in Laser�Based Micro�and Nanopackaging and Assemhly V, vol. 7921, Pfleg�ing, W., Lu, Y., Washio, K., Amako, J., Moving, W.,Eds., 2011, pp. 27–49.

15. Sones, C.L., Kaur, K.S., Ganguly, P., Banks, D.P.,Ying, Y.J., Eason, R.W., and Mailis, S., Applied Physics A:Materials Science & Processing, 2010, vol. 101,pp. 333–338.

16. Rapp, L., Diallo, A.K., Nenon, S., Alloncle, A.P.,Videlot�Ackermann, C., Fages, F., Nagel, M., Lippert, T.,and Delaporte, P., Thin Solid Films, 2012, vol. 520,pp. 3043–3047.

17. Shaw�Stewart, J.R.H., Lippert, T.K., Nagel, M.,Nueesch, F.A., and Wokaun, A., Acs Applied Materials &Interfaces, 2012, vol. 4, pp. 3535–3541.

18. Stebani, J., Nuyken, O., Lippert, T., and Wokaun, A.,Makromolekulare Chemie�Rapid Communications,1993, vol. 14, pp. 365–369.

19. Yu, P., Zhang, X., Chen, Y., Ma, Y.W., and Qi, Z.P.,Materials Chemistry and Physics, 2009, vol. 118,pp. 303–307.

20. Yan, J., Fan, Z.J., Wei, T., Cheng, J., Shao, B., Wang, K.,Song, L.P., and Zhang, M.L., Journal of Power Sources,2009, vol. 194, pp. 1202–1207.

21. Ai, Z.H., Zhang, L.Z., Kong, F.H., Liu, H., Xing, W.T.,and Qiu, J.R., Materials Chemistry and Physics, 2008,vol. 111, pp. 162–167.

22. Cao, J.M., Feng, J., Deng, S.G., Chang, X., Wang, J.,Liu, J.S., Lu, P., Lu, H.X., Zheng, M.B., Zhang, F.,

and Tao, J., Journal of Materials Science, 2005, vol. 40,pp. 6311–6313.

23. Smith, F.E. and Arsenault, E.A., Talanta, 1996, vol. 43,pp. 1207–1268.

24. Cao, Y., Wei, H.�J., and Xia, Z.�N., Transactions ofNonferrous Metals Society of China, 2009, vol. 19, Sup�plement 3, pp. s656–s664.

25. Seifart, M., Analoge Schaltungen, vol. 3, Auflage, Berlin:VEB Verlag Technik, 1989, p. 599.

26. Tietze, U. and Schenk, C., Halbleiter�Schaltungstechnik,Berlin: Springer, 2002, pp. 899–919.

27. Zhang, Z., Li, M., Wu, Z., and Li, W., Nanotechnology,2011, vol. 22, p. 015602.

28. Nesbitt, H.W. and Baneijee, D., American Mineralogist,1998, vol. 83, pp. 305–315.

29. Huang, H. and Wang, X., Nanoscale, 2011, vol. 3,pp. 3185–3191.

30. Li, G.R., Feng, Z.P., Ou, Y.N., Wu, D., Fu, R., andTong, Y.X., Langmuir: the ACS Journal of Surfaces andColloids, 2010, vol. 26, pp. 2209–2213.

31. Dong, X., Shen, W., Gu, J., Xiong, L., Zhu, Y., Li, H.,and Shi, J., The Journal of Physical Chemistry B, 2006,vol. 110, pp. 6015–6019.

32. Gao, T., Fjellvag, R., and Norby, P., Analytica ChimicaActa, 2009, vol. 648, pp. 235–239.

33. Buciuman, F., Patcas, F., Craciun, R., andZahn, R.T.D., Physical Chemistry Chemical Physics,1999, vol. 1, pp. 185–190.

34. Fan, J. and Fedkiw, P.S., Journal of Power Sources,1998, vol. 72, pp. 165–173.

35. Zhang, L., Wang, Z., Xu, D., Xu, J., Zhang, X., andWang, L., Chinese Science Bulletin, 2012, vol. 57,pp. 4210–4214.

36. Chen, Y., Freunberger, S.A., Peng, Z., Barde, F., andBruce, P.G., Journal of the American Chemical Society,2012, vol. 134, pp. 7952–7957.

37. Peng, Z., Freunberger, S.A., Chen, Y., and Bruce, P.G.,Science, 2012, vol. 337, pp. 563–566.

38. Lacey, M.J., Frith, J.T., and Owen, J.R., ElectrochemistryCommunications, 2013, vol. 26, pp. 74–76.

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