Research Article Morphology and Electrical Conductivity of …downloads.hindawi.com/journals/jnm/2014/103418.pdf · 2019-07-31 · e electrical conductivity of the composites was

Research ArticleMorphology and Electrical Conductivity of Carbon NanocoatingsPrepared from Pyrolysed Polymers

Marcin Molenda MichaB UwiwtosBawski Marek Drozdek Barbara Dudekand Roman Dziembaj

Faculty of Chemistry Jagiellonian University Ingardena 3 Street 30-060 Krakow Poland

Correspondence should be addressed to Marcin Molenda molendamchemiaujedupl

Received 1 December 2013 Revised 13 March 2014 Accepted 14 March 2014 Published 13 April 2014

Academic Editor Yu-Lun Chueh

Copyright copy 2014 Marcin Molenda et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Conductive carbon nanocoatings (conductive carbon layersmdashCCL) were formed on 120572-Al2O3model support using three different

polymer precursors and deposition methods This was done in an effort to improve electrical conductivity of the material throughcreating the appropriate morphology of the carbon layers The best electrical properties were obtained with use of a precursorthat consisted of poly-N-vinylformamide modified with pyromellitic acid (PMA) We demonstrate that these properties originatefrom a specific morphology of this layer that showed nanopores (3-4 nm) capable of assuring easy pathways for ion transport inreal electrode materials The proposed water mediated method of carbon coating of powdered supports combines coating fromsolution and solid phase and is easy to scale up process The optimal polymer carbon precursor composition was used to prepareconductive carbon nanocoatings on LiFePO

4cathode material Charge-discharge tests clearly show that CLiFePO

4composites

obtained using poly-N-vinylformamide modified with pyromellitic acid exhibit higher rechargeable capacity and longer workingtime in a battery cell than standard carbonlithium iron phosphate composites

1 Introduction

There are many reports on the improvement of electro-chemical performance of electrode materials for lithium-ion batteries using carbon coatings [1ndash9] The compoundsreported for the coating formation include carboxylic acids[2] polyalcohols [3] resins [4 5] and sugars [6] To formthe carbon coatings the compounds were deposited on theelectrode material grains and pyrolysed However morphol-ogy of these layers was not discussed in detail Characteristicof carbon coatings deposited on electrodes is that they canreact with the electrolyte thereby giving rise to the formationof passive insulating layers To avoid these destructive effectsthe carbon conductive layers should stickwell to the electrodematerial and be able to reduce an interface area of theelectrodeelectrolyte composite This reduction is needed toretard the growth of the solid electrolyte interface (SEI) that isresponsible for the magnitude of the ion transport across theinterface In view of the above the formation of nanochannels(the appropriate porous structure) in the conductive carbon

layers (CCL) can provide suitable pathways for the transportof ions (eg Li+) from the electrolyte to the cathode andvice versa Such a composite material should assure also asufficient electrical conductivity

The aim of the present work was to study the influenceof different polymer precursors methods of their depositionand transformation into CCL on the morphology electricalproperties and the performance of formed layers on thesurface of LiFePO

4active cathode material in lithium battery

cell Amodel composite system consisting of the CCL formedon fine grains of 120572-Al

2O3was chosen The 120572-alumina is

a well-defined inert support for the CCLs preparation andcharacterization because of its chemical and thermal stabilityand insulating behaviorThe systemwas studied with thermalgravimetric analysis (TGA) Raman spectroscopy (RS) elec-trical conductivity (EC) specific surface area (BET-N

2) mea-

surements and finally by transmission electron microscopy(TEM) Optimal composition of polymer carbon precur-sor was used to prepare CLiFePO

4cathode composites

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 103418 7 pageshttpdxdoiorg1011552014103418

2 Journal of Nanomaterials

Composites with 7wt of carbon were characterized usingelectrical conductivity measurements (EC) and transmissionelectronmicroscopy (TEM)The galvanostatic tests using CR2032 cells were carried out to reveal electrochemical behaviorof CLiFePO

4nanocomposite material

2 Material and Methods

The idea of C120572-Al2O3composite preparation is presented in

Figure 1 Twomethods of the composite precursors formationwere applied

In the first the free radical precipitation polymerizationof freshly distilled acrylonitrile (AN) was performed inthe presence of 120572-Al

2O3grains (POCh Poland 9999

119878BET = 24m2 gminus1) The procedure was described in our pre-

vious paper [10] Briefly C120572-Al2O3grains were suspended

in water solution of AN (7wt) and the polymerizationwas initiated by 221015840-azobis(isobutyramidine hydrochloride)(Aldrich) upon which the obtained PAN120572-Al

2O3samples

were washed filtered and dried in the vacuum at 50∘C Inthe second method the 120572-Al

2O3grains were impregnated

with polymers in water solutions The polymers used werepoly-N-vinylformamide (PNVF) obtained by radical-freepolymerization from N-vinylformamide (Aldrich) [11] andpyromellitic acid modified (5ndash10wt) PNVF (MPNVF)[12] To achieve the impregnation 120572-Al

2O3grains were

suspended in the solutions of respective polymers in water(8ndash15wt) Suspensions were stirred continuously until thesolvent evaporated and the viscosity of the solutions becamehigh enough to avoid sedimentation Then the samples weredried in an air drier at 90∘C overnight Mass ratios at whichthe polymer precursors were combined with 120572-Al

2O3in

the above composite precursors preparation procedures arecompiled in Table 1

To obtain C120572-Al2O3composites following the prepa-

ration the PAN120572-Al2O3 PNVF120572-Al

2O3and MPNVF120572-

Al2O3composite precursors were pyrolysed in a tube furnace

under the flowof 99999argon (5 dm3 hminus1) at 550 and 600∘Cfor 24 h Active carbon was placed in front of the samples toconsume traces of oxygen and thus minimize losses in thecarbon layers

The obtained C120572-Al2O3composites were deep black

with foamed slag-like structure the one prepared from theMPNVF precursor being special in that it looked glassy andlustrous like graphite

LiFePO4powder was produced using high tempera-

ture ceramic synthesis which is described in detail in [13]CLiFePO

4composites were prepared from the PNVF and

MPNVF precursor (with 5 content of pyromellitic acid)by wet polymer impregnation followed by controlled pyrol-ysis PNVFLiFePO

4and MPNVFLiFePO

4were calcined in

600∘C for 12 h under constant argon (999997) flowCarbon content in composites was determined by the

temperature programmed oxidation (TPO) using TGA [12]All the samples prepared were subjected to further analysis

The Raman spectroscopy measurements were performedfor model composites (C120572-Al

2O3) on thin pellets containing

10mg of the carbon sample and 200mg of KBr The carbon

Table 1 Mass ratios of polymer precursors to 120572-Al2O3 applied inthe composite precursors preparation and the carbon content in theresulting C120572-Al2O3 composites

Polymerprecursor (PP)

PP120572-Al2O3ratio

Carbon content inC120572-Al2O3 wt

Carbonizationefficiency wt

PAN

04 16 4008 51 6912 103 9616 206 16320 372 296

PNVF

10 66 7012 81 7314 96 7516 115 8124 253 14132 319 14648 477 147

MPNVF

02 20 11704 56 16006 97 18208 135 18711 174 18618 238 17433 400 200

samples were prepared by pyrolysis under the same pro-cess conditions as those applied in composites preparationSpectra were recorded at room temperature using a triplegrating spectrometer (JobinYvon T 64000) equipped witha liquid nitrogen cooled CCD detector (JobinYvon ModelCCD3000) The spectral resolution of 2 cmminus1 was set Anexcitation wavelength at 5145 nm was provided by an Ar-ion laser (Spectra-Physics Model 2025) The laser power atthe sample position was about 20mW Raman scattered lightwas collected with a 135∘ geometry and 5000 scans wereaccumulated to ensure acceptable signal-to-noise ratio

The electrical conductivity of the composites was mea-sured using the 4-probe method at temperatures from therange between minus40∘C and +55∘C Due to their high elasticitythe carbon coated composite powders failed to be preparedin the form of pellets by the standard procedure Instead thepowders were placed in a glass tube and pressed by a screw-press between parallel gold disc electrodes (120601 = 5mm) till themeasured resistance remained constant

The specific surface areameasurements of the compositeswere performed in Micrometrics ASAP 2010 using the BETisotherm method For that about 500mg of each sample wasdegassed at 250ndash300∘C for 8 h under a pressure of 026ndash04 Pa and subjected to N

2sorption at minus1958∘CThe pore size

distribution was determined using the BJH methodTransmission electron microscopy investigation was per-

formed using TECNAI G F20 (200 kV) coupled with anenergy dispersive X-ray spectrometer (EDAX) In order tofully describe morphology of obtained composite grains

Journal of Nanomaterials 3

1

2

Grain ofhost material


Suspension inacrylonitrile

water solutionPrecipitation

polymerization

N-vinylformamideradical

polymerizationWet polymer

impregnation

Compositeprecursor Grain of

CCL composite

Controlledpyrolysis

Figure 1 Schematic of theC120572-Al2O3composite formation performed by polymer precipitation in suspension (1) or by polymer impregnation

in water medium (2)

500 1000 1500 2000 2500 3000

Inte

nsity

(au

)

D G

Raman shift (cmminus1)

PAN at 600∘C

PNVF at 600∘C

MPNVF at 600∘C

Figure 2 Raman spectra of the pyrolysed carbons derived fromPAN PNVF and MPNVF precursors

analysis was carried out in a bright field (BF) and highresolution (HREM) modes

The charge-discharge cycling studies were conductedin two-electrode configuration using CR 2032 coin cellLiLi+(CLiFePO

4) between 27 and 42V at different C

rates in room temperature conditions LiPF6(1mol) solution

in ECDEC (1 1) was used in cells as an electrolyte Allgalvanostatic measurements were carried out using ATLAS0961 MBI system

3 Results and Discussion

The results of the Raman spectroscopy (RS) measurementsare presented in Figure 2 The degree of carbon materialsgraphitization was characterized using the integral inten-sity ratio DG where the D band (defect mode at about1350 cmminus1) corresponds to sp3 diamond-like carbon struc-tures and the G band (about 1600 cmminus1) to sp2 graphiticstructures [14ndash17]

It was found that the graphitization degree increased witha decrease in the DG ratio The lowest value of the DGratio was observed for MPNVF precursor This indicates theformation of the highest amounts of the graphite domainsin the carbonized sample compared to the other precursorsAlso the G peak of the carbonized MPNVF precursor wasdownshifted and its width decreased which suggests 2Dordering (1st phase of graphitization) [14ndash16] Thus themodification of PNVF by pyromellitic acid improves thepolymer carbonization and the carbon layer formation Thismay result from the fact that the planar structure of the PMAmolecules serves as a nucleus of the graphite domains whichcompete with the formation of the disordered structuresLikewise for the same precursor the highest carbonizationefficiency (the lowest loss of the carbon atoms from theprecursor) was achieved (Table 1)

The results of the electrical conductivity measurementscarried out on the C120572-Al

2O3samples are presented in

Figure 3(a) As expected the electrical conductivity of thecomposites increased with an increase in carbon loading Forthe PNVF precursor however this increase was found muchslower above 12 wt of C Such an effect was not observedfor the CCL obtained from the PAN andMPNVF precursorsBy contrast the activation energy of electrical conductivityremained nearly constant in the range of carbon content stud-ied suggesting a preservation of the conductivity mechanismof the CCL Of the samples examined the best electricalproperties that is the highest conductivity and the lowestactivation energy were revealed by the composite based onthe MPNVF precursor Taking into account the results of theRSmeasurements it may be concluded that the improvementof the electrical conductivity arose from the action of thepyromellitic acid modifier facilitating the achievement of the2D ordered graphite structure This way the desired valueof the electrical conductivity of 10minus2 S cmminus1 was achievedSimultaneously the lowest activation energy (about 008 eV)of the electrical conductivity for these composite materialswas observed

The change in specific surface area with the carbon con-tent on the C120572-Al

2O3composites is presented in Figure 3(b)


015

012

009

006

003

PANPNVFMPNVF

minus8

minus6

minus4

minus2

log120590

(Scm

minus1)

Open symbols Ealog 120590Solid symbols

0 10 20 30 40 50

C on Al2O3 ()

Ea

(eV

)

(a)

PANPNVFMPNVF

50

100

150

200

0 10 20 30 40 50

C on Al2O3

BET

(m2gminus

1)

()

(b)

Figure 3 Electrical properties (a) and dependence of the specific surface area (b) of the C120572-Al2O3composites on carbon content

For all studied samples specific surface areas increasedlinearly with carbon loading up to 25ndash30wt the rate ofthis increase being dependent on the polymer precursorThis suggests that the initial porous structure of the CCLwas preserved regardless of the carbon content Interestinglyfor the PNVF precursor surface areas measured in the lowcarbon loading region were found much higher than thosefor MPNVF This difference means that the modification ofPNVF with the PMAmodifier resulting in MPNVF broughtabout the formation of another type of CCL where mostprobably the formed graphite domains are locally arranged ina manner that they limit the formation of disordered carbon

The N2-adsorption-desorption isotherms and pore size

distributions in the C120572-Al2O3composites are presented in

Figure 4The observed shapes of the isotherms (Figures 4(a)ndash4(c)) correspond to the mixed I and IV types of isotherms(according to IUPAC nomenclature) Such shapes indicatethe presence of micro- and mesopores within the CCLThe hysteresis loop of the H4 type (IUPAC) suggests theslotted pores located within the intergranular spaces Thetextural properties of the composites on the other hand aregenerally similar but there are differences in the pore sizedistribution (Figures 4(d)ndash4(f)) The smallest pores werefound in the composite obtained from the PAN precursorThis fact can be related to the applied preparation methodthat is the precipitation polymerization resulting in fillingof the pores by carbon particles Unlike the PAN derivedcomposite the PNVF derived composite (Figures 4(b) and4(e)) revealed a highly porous structure with a relativelyhigh number of micropores (about 30) this morphologybeing in agreement with the highest specific surface area(Figure 3(b)) By contrast the composite derived from theMPNVF precursor showed a very uniform distribution ofthe mesopores with sizes within the range of 3ndash45 nm(Figure 4(f)) Also the specific surface area of this compositethat is lower by about 50 than that of the unmodifiedprecursor (PNVF) (Figure 3(b)) suggests that a tighter carbon

film with a lower content of the disordered carbon wasformed in this sample

Based on the electrical and morphological propertiesdetermined for the C120572-Al

2O3composites derived from the

polymer precursors under investigation the following struc-tural model of these materials may be proposed (Figure 5)The CCL obtained from the PAN precursor (Figure 5(a))consists of tightly packed small carbon particles while thatobtained from the PNVF precursor (Figure 5(b)) is built ofcarbon whiskers this latter structure being reflected in ahigh specific surface area and a high share of micropores inthis sample This same PNVF precursor when modified withpyromellitic acid (MPNVF precursor) strongly diminishesthe specific surface area of the resulting composite whichis due to the formation of a tight highly conductive carbonfilm with the defined porous structure that is dominated bymesopores with an arrow size distribution (Figure 5(c))

The result of the performed TEM studies on C120572-Al2O3

composites obtained fromMPNVF precursor is presented inFigures 6(a) and 6(b) A uniformdispersion of ceramic grainsin an amorphous carbon matrix is observed in Figure 6(a)Moreover Figure 6(b) revealed that obtained nanosized car-bon coatings adhered closely to the ceramic support

The C120572-Al2O3composite morphology together with the

electrical properties (Figure 3(a)) indicates that the MPNVFis an optimal polymer carbon precursorThus the CLiFePO

4

composite was prepared from MPNVF precursor with 5 ofPMA with carbon content of 6wt

TEM observations of CLiFePO4obtained fromMPNVF

correspond to those of the model composites Formed car-bon coatings adhere well to the surface of active materialgrains no voids can be visible at the CCLmaterial interface(Figures 6(c) and 6(d)) Figure 6(c) presents part of a singlegrain of LiFePO

4covered with conductive carbon layer

with thickness of about 10 nm The high resolution electronmicroscopy micrograph (Figure 6(d)) shows a boundarybetween LiFePO

4grain and amorphous carbon layer


20

40

60

80

PA

AdsorptionDesorption

N

00 02 04 06 08 10

Relative pressure (ppminus10 )

Volu

me a

dsor

bed

(cm

3gminus

1ST

P)

(a)

PNVF

00 02 04 06 08 10



(b)

MPNVF

00 02 04 06 08 10


BET

N2-is

othe

rm


(c)

00000

00005

00010

00015

00020PAN

Pore

vol

ume (

cm3(gmiddot

)minus1)

0 25 50 75 100

Pore diameter (A

A

)

(d)

PNVF

0 25 50 75 100

Pore diameter (A)

(e)

dVdD

por

es d

istrib

utio

n

MPNVF

0 25 50 75 100

Pore diameter (A)

(f)

Figure 4 Typical BET N2-isotherms of the C120572-Al

2O3composites

(a) (b) (c)

Figure 5 Model cross-section of the CCL composites derived from PAN (a) PNVF (b) and MPNVF (c) precursors

50nm500nm

Figure 6 TEMmicrographs of CAl2O3and CLiFePO

4composites (a) and (b) bright field micrographs of the CAl

2O3composite obtained

from the MPNVF precursor (c) bright field micrograph of a part of the LiFePO4grain coated with amorphous carbon (marked with black

arrow) and (d) high resolution micrograph of carbonactive material interface


0 20 40 60 80 100 120 140

26

28

30

32

34

36

38

40

42

44

Pote

ntia

l (V

)

Capacity (mAh gminus1)

CLiFePO4 (MPNVF precursor)

1st cycle

2nd cycle

10th cycle

Figure 7 Chargedischarge voltage profiles (1st 2nd and 10th cycle)of CLiFePO

4composites obtained fromMPNVF precursor

Carbon coating improved electrical conductivity ofLiFePO

4cathodematerial from 10minus9 S cmminus1 to the satisfactory

level of sim10minus2 S cmminus1 Electrical conductivity measurementsof CLiFePO

4composites confirmed better performance of

composites obtained from MPNVF carbon precursor (con-ductivity of CLiFePO

4obtained from MPNVF is ca one

order of magnitude higher then conductivity of CLiFePO4

obtained from PNVF)Charge-discharge cycling tests were carried out under

C10 rate Figure 7 shows chargedischarge profiles ofCLiFePO

4composites prepared form MPNVF Curves for

first second and tenth cycles are presented From voltageprofile shapes it can be seen that carbon layer undergoesactivation during the first few cycles Discharge capacity isca 130mAh gminus1 after 10th cycle Long term cycling stabilitytests show that composites with carbon coating preparedfrom PNVF precursor stopped working after 40 cycles andthose with carbon prepared fromMPNF were working stablywith retained capacity after 100 cycles

Complete structural and electrochemical analysis ofCLiFePO

4composites obtained from different polymer pre-

cursors can be found in our previous work [17]

4 Conclusions

The electrical and morphological properties of the modelC120572-Al

2O3composites showed a strong dependence on the

nature of the polymer carbon precursors used to form carbonnanocoatingsThis leads to the conclusion that the propertiesof CCL may be controlled by a proper composition ofthe polymer precursor It was shown that the modificationof poly-N-vinylformamide precursor with pyromellitic acidimproved the electrical properties of the carbon coating andgave rise to the formation of the optimal pore structure Theproposed water mediated method of carbon coating of pow-dered supports consisting of the use of polymer precursorsis capable of creating an appropriate mesoporous structure of

the CCL which may assure easy pathways for ion transport(eg Li+) The method combines coating from solution andsolid phase and is easily scalable This feature may be used inpreparation of carbon coated cathodematerials composite forlithium-ion batteries Moreover these carbon films exhibitgood electrical properties which already fulfill the demandfor low-conducting cathode materials (eg LiFePO

4) to be

applied in lithium-ion batteries Also due to its tightnessthe CCL formed with use of the MPNVF precursor shouldbe capable of improving chemical resistance of the cathodematerials to the action of the electrolyte in the battery On theother hand the proposed method of C120572-Al

2O3composites

formation showing relatively high specific surface area andcontrolled porous structure of carbon layers may be appliedin preparation of novel composite adsorbents

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors acknowledge a financial support from theNational Science Center of Poland under research Grantno N N209 088638 and from the European Institute ofInnovation and Technology under the KIC InnoEnergyNewMat project One of the authors (Michał Swiętosławski)acknowledges a financial support from the InternationalPhD-studies programme at the Faculty of Chemistry Jagiel-lonian University within the Foundation for Polish ScienceMPD ProgrammeThe part of the measurements was carriedout with the equipment purchased thanks to the financialsupport of the European Regional Development Fund inthe framework of the Polish Innovation Economy Oper-ational Program (Contract no POIG020100-12-02308)TEM analysis was carried out in Laboratory of TransmissionAnalytical Electron Microscopyat the Institute of Metallurgyand Material Science Polish Academy of Sciences

References

[1] M Armand and J-M Tarascon ldquoBuilding better batteriesrdquoNature vol 451 no 7179 pp 652ndash657 2008

[2] B Lin Z Wen J Han and X Wu ldquoElectrochemical propertiesof carbon-coated Li[Ni

13Co13Mn13]O2cathode material for

lithium-ion batteriesrdquo Solid State Ionics vol 179 no 27ndash32 pp1750ndash1753 2008

[3] R Guo P Shi X Cheng and C Du ldquoSynthesis and characteri-zation of carbon-coated LiNi

13Co13Mn13O2cathode material

prepared by polyvinyl alcohol pyrolysis routerdquo Journal of Alloysand Compounds vol 473 pp 53ndash59 2009

[4] B L Cushing and J B Goodenough ldquoInfluence of carboncoating on the performance of a LiMn

05Ni05O2cathoderdquo Solid

State Sciences vol 4 no 11-12 pp 1487ndash1493 2002[5] J Hassoun G Derrien S Panero and B Scrosati ldquoThe role

of the morphology in the response of Sb-C nanocompositeelectrodes in lithium cellsrdquo Journal of Power Sources vol 183no 1 pp 339ndash343 2008


[6] J-K Kim G Cheruvally J-H Ahn and H-J Ahn ldquoElectro-chemical properties of LiFePO4C composite cathode materialcarbon coating by the precursor method and direct additionrdquoJournal of Physics and Chemistry of Solids vol 69 no 5-6 pp1257ndash1260 2008

[7] J-K Kim G Cheruvally and J-H Ahn ldquoElectrochemicalproperties of LiFePO4C synthesized by mechanical activationusing sucrose as carbon sourcerdquo Journal of Solid State Electro-chemistry vol 12 no 7-8 pp 799ndash805 2008

[8] G Ting-Kuo Fey T-L Lu F-Y Wu and W-H Li ldquoCarboxylicacid-assisted solid-state synthesis of LiFePO4C compositesand their electrochemical properties as cathode materials forlithium-ion batteriesrdquo Journal of Solid State Electrochemistryvol 12 no 7-8 pp 825ndash833 2008

[9] Y-J Choi Y-D Chung C-Y Baek K-W Kim H-J Ahn andJ-H Ahn ldquoEffects of carbon coating on the electrochemicalproperties of sulfur cathode for lithiumsulfur cellrdquo Journal ofPower Sources vol 184 no 2 pp 548ndash552 2008

[10] M Molenda R Dziembaj Z Piwowarska and M DrozdekldquoA new method of coating powdered supportswith conductivecarbon filmsrdquo Journal ofThermal Analysis and Calorimetry vol88 no 2 pp 503ndash506 2007

[11] M Molenda R Dziembaj Z Piwowarska and M DrozdekldquoElectrochemical properties of CLiMn

2O4minus119910

S119910(0 le y le 01)

composite cathodematerialsrdquo Solid State Ionics vol 179 no 1ndash6pp 88ndash92 2008

[12] M Molenda R Dziembaj A Kochanowski E Bortel MDrozdek and Z Piwowarska ldquoProcess for the preparation ofconductive carbon layers on powdered supportsrdquo PAT 216549US Patent Application 20110151112

[13] W Ojczyk J Marzec K Swierczek et al ldquoStudies of selectedsynthesis procedures of the conducting LiFePO

4-based com-

posite cathode materials for Li-ion batteriesrdquo Journal of PowerSources vol 173 no 2 pp 700ndash706 2007

[14] A C Ferrari and J Robertson ldquoInterpretation of Raman spectraof disordered and amorphous carbonrdquo Physical Review BCondensed Matter and Materials Physics vol 61 no 20 pp14095ndash14107 2000

[15] C Fauteux R Longtin J Pegna and M Boman ldquoRamancharacterization of laser grown carbonmicrofibers as a functionof experimental parametersrdquoThin Solid Films vol 453-454 pp606ndash610 2004

[16] S Osswald E Flahaut H Ye and Y Gogotsi ldquoElimination ofD-band in Raman spectra of double-wall carbon nanotubes byoxidationrdquo Chemical Physics Letters vol 402 no 4ndash6 pp 422ndash427 2005

[17] M Molenda M Swietoslawski A Milewska et al ldquoCarbonnanocoatings for CLiFePO

4composite cathoderdquo Solid State

Ionics vol 251 pp 47ndash50 2013

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Composites with 7wt of carbon were characterized usingelectrical conductivity measurements (EC) and transmissionelectronmicroscopy (TEM)The galvanostatic tests using CR2032 cells were carried out to reveal electrochemical behaviorof CLiFePO

4nanocomposite material

2 Material and Methods

The idea of C120572-Al2O3composite preparation is presented in

Figure 1 Twomethods of the composite precursors formationwere applied

In the first the free radical precipitation polymerizationof freshly distilled acrylonitrile (AN) was performed inthe presence of 120572-Al

2O3grains (POCh Poland 9999

119878BET = 24m2 gminus1) The procedure was described in our pre-

vious paper [10] Briefly C120572-Al2O3grains were suspended

in water solution of AN (7wt) and the polymerizationwas initiated by 221015840-azobis(isobutyramidine hydrochloride)(Aldrich) upon which the obtained PAN120572-Al

2O3samples

were washed filtered and dried in the vacuum at 50∘C Inthe second method the 120572-Al

2O3grains were impregnated

with polymers in water solutions The polymers used werepoly-N-vinylformamide (PNVF) obtained by radical-freepolymerization from N-vinylformamide (Aldrich) [11] andpyromellitic acid modified (5ndash10wt) PNVF (MPNVF)[12] To achieve the impregnation 120572-Al

2O3grains were

suspended in the solutions of respective polymers in water(8ndash15wt) Suspensions were stirred continuously until thesolvent evaporated and the viscosity of the solutions becamehigh enough to avoid sedimentation Then the samples weredried in an air drier at 90∘C overnight Mass ratios at whichthe polymer precursors were combined with 120572-Al

2O3in

the above composite precursors preparation procedures arecompiled in Table 1

To obtain C120572-Al2O3composites following the prepa-

ration the PAN120572-Al2O3 PNVF120572-Al

2O3and MPNVF120572-

Al2O3composite precursors were pyrolysed in a tube furnace

under the flowof 99999argon (5 dm3 hminus1) at 550 and 600∘Cfor 24 h Active carbon was placed in front of the samples toconsume traces of oxygen and thus minimize losses in thecarbon layers

The obtained C120572-Al2O3composites were deep black

with foamed slag-like structure the one prepared from theMPNVF precursor being special in that it looked glassy andlustrous like graphite

LiFePO4powder was produced using high tempera-

ture ceramic synthesis which is described in detail in [13]CLiFePO

4composites were prepared from the PNVF and

MPNVF precursor (with 5 content of pyromellitic acid)by wet polymer impregnation followed by controlled pyrol-ysis PNVFLiFePO

4and MPNVFLiFePO

4were calcined in

600∘C for 12 h under constant argon (999997) flowCarbon content in composites was determined by the

temperature programmed oxidation (TPO) using TGA [12]All the samples prepared were subjected to further analysis

The Raman spectroscopy measurements were performedfor model composites (C120572-Al

2O3) on thin pellets containing

10mg of the carbon sample and 200mg of KBr The carbon

Table 1 Mass ratios of polymer precursors to 120572-Al2O3 applied inthe composite precursors preparation and the carbon content in theresulting C120572-Al2O3 composites

Polymerprecursor (PP)

PP120572-Al2O3ratio

Carbon content inC120572-Al2O3 wt

Carbonizationefficiency wt

PAN

04 16 4008 51 6912 103 9616 206 16320 372 296

PNVF

10 66 7012 81 7314 96 7516 115 8124 253 14132 319 14648 477 147

MPNVF

02 20 11704 56 16006 97 18208 135 18711 174 18618 238 17433 400 200

samples were prepared by pyrolysis under the same pro-cess conditions as those applied in composites preparationSpectra were recorded at room temperature using a triplegrating spectrometer (JobinYvon T 64000) equipped witha liquid nitrogen cooled CCD detector (JobinYvon ModelCCD3000) The spectral resolution of 2 cmminus1 was set Anexcitation wavelength at 5145 nm was provided by an Ar-ion laser (Spectra-Physics Model 2025) The laser power atthe sample position was about 20mW Raman scattered lightwas collected with a 135∘ geometry and 5000 scans wereaccumulated to ensure acceptable signal-to-noise ratio

The electrical conductivity of the composites was mea-sured using the 4-probe method at temperatures from therange between minus40∘C and +55∘C Due to their high elasticitythe carbon coated composite powders failed to be preparedin the form of pellets by the standard procedure Instead thepowders were placed in a glass tube and pressed by a screw-press between parallel gold disc electrodes (120601 = 5mm) till themeasured resistance remained constant

The specific surface areameasurements of the compositeswere performed in Micrometrics ASAP 2010 using the BETisotherm method For that about 500mg of each sample wasdegassed at 250ndash300∘C for 8 h under a pressure of 026ndash04 Pa and subjected to N

2sorption at minus1958∘CThe pore size

distribution was determined using the BJH methodTransmission electron microscopy investigation was per-

formed using TECNAI G F20 (200 kV) coupled with anenergy dispersive X-ray spectrometer (EDAX) In order tofully describe morphology of obtained composite grains


1

2





polymerization



impregnation


CCL composite

Controlledpyrolysis


in water medium (2)

500 1000 1500 2000 2500 3000

Inte

nsity

(au

)

D G


PAN at 600∘C

PNVF at 600∘C

MPNVF at 600∘C
















015

012

009

006

003

PANPNVFMPNVF

minus8

minus6

minus4

minus2

log120590

(Scm

minus1)


0 10 20 30 40 50

C on Al2O3 ()

Ea

(eV

)

(a)

PANPNVFMPNVF

50

100

150

200

0 10 20 30 40 50

C on Al2O3

BET

(m2gminus

1)

()

(b)














4








20

40

60

80

PA


N

00 02 04 06 08 10


Volu

me a

dsor

bed

(cm

3gminus

1ST

P)

(a)

PNVF

00 02 04 06 08 10



(b)

MPNVF

00 02 04 06 08 10


BET

N2-is

othe

rm


(c)

00000

00005

00010

00015

00020PAN

Pore

vol

ume (

cm3(gmiddot

)minus1)

0 25 50 75 100

Pore diameter (A

A

)

(d)

PNVF

0 25 50 75 100

Pore diameter (A)

(e)

dVdD

por

es d

istrib

utio

n

MPNVF

0 25 50 75 100

Pore diameter (A)

(f)


2O3composites

(a) (b) (c)


50nm500nm







0 20 40 60 80 100 120 140

26

28

30

32

34

36

38

40

42

44

Pote

ntia

l (V

)



1st cycle

2nd cycle

10th cycle

















4 Conclusions





4) to be


2O3composites




Acknowledgments


References



















2O4minus119910

S119910(0 le y le 01)




4-based com-















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




1

2





polymerization



impregnation


CCL composite

Controlledpyrolysis


in water medium (2)

500 1000 1500 2000 2500 3000

Inte

nsity

(au

)

D G


PAN at 600∘C

PNVF at 600∘C

MPNVF at 600∘C
















015

012

009

006

003

PANPNVFMPNVF

minus8

minus6

minus4

minus2

log120590

(Scm

minus1)


0 10 20 30 40 50

C on Al2O3 ()

Ea

(eV

)

(a)

PANPNVFMPNVF

50

100

150

200

0 10 20 30 40 50

C on Al2O3

BET

(m2gminus

1)

()

(b)














4








20

40

60

80

PA


N

00 02 04 06 08 10


Volu

me a

dsor

bed

(cm

3gminus

1ST

P)

(a)

PNVF

00 02 04 06 08 10



(b)

MPNVF

00 02 04 06 08 10


BET

N2-is

othe

rm


(c)

00000

00005

00010

00015

00020PAN

Pore

vol

ume (

cm3(gmiddot

)minus1)

0 25 50 75 100

Pore diameter (A

A

)

(d)

PNVF

0 25 50 75 100

Pore diameter (A)

(e)

dVdD

por

es d

istrib

utio

n

MPNVF

0 25 50 75 100

Pore diameter (A)

(f)


2O3composites

(a) (b) (c)


50nm500nm







0 20 40 60 80 100 120 140

26

28

30

32

34

36

38

40

42

44

Pote

ntia

l (V

)



1st cycle

2nd cycle

10th cycle

















4 Conclusions





4) to be


2O3composites




Acknowledgments


References



















2O4minus119910

S119910(0 le y le 01)




4-based com-















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




015

012

009

006

003

PANPNVFMPNVF

minus8

minus6

minus4

minus2

log120590

(Scm

minus1)


0 10 20 30 40 50

C on Al2O3 ()

Ea

(eV

)

(a)

PANPNVFMPNVF

50

100

150

200

0 10 20 30 40 50

C on Al2O3

BET

(m2gminus

1)

()

(b)














4








20

40

60

80

PA


N

00 02 04 06 08 10


Volu

me a

dsor

bed

(cm

3gminus

1ST

P)

(a)

PNVF

00 02 04 06 08 10



(b)

MPNVF

00 02 04 06 08 10


BET

N2-is

othe

rm


(c)

00000

00005

00010

00015

00020PAN

Pore

vol

ume (

cm3(gmiddot

)minus1)

0 25 50 75 100

Pore diameter (A

A

)

(d)

PNVF

0 25 50 75 100

Pore diameter (A)

(e)

dVdD

por

es d

istrib

utio

n

MPNVF

0 25 50 75 100

Pore diameter (A)

(f)


2O3composites

(a) (b) (c)


50nm500nm







0 20 40 60 80 100 120 140

26

28

30

32

34

36

38

40

42

44

Pote

ntia

l (V

)



1st cycle

2nd cycle

10th cycle

















4 Conclusions





4) to be


2O3composites




Acknowledgments


References



















2O4minus119910

S119910(0 le y le 01)




4-based com-















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




20

40

60

80

PA


N

00 02 04 06 08 10


Volu

me a

dsor

bed

(cm

3gminus

1ST

P)

(a)

PNVF

00 02 04 06 08 10



(b)

MPNVF

00 02 04 06 08 10


BET

N2-is

othe

rm


(c)

00000

00005

00010

00015

00020PAN

Pore

vol

ume (

cm3(gmiddot

)minus1)

0 25 50 75 100

Pore diameter (A

A

)

(d)

PNVF

0 25 50 75 100

Pore diameter (A)

(e)

dVdD

por

es d

istrib

utio

n

MPNVF

0 25 50 75 100

Pore diameter (A)

(f)


2O3composites

(a) (b) (c)


50nm500nm







0 20 40 60 80 100 120 140

26

28

30

32

34

36

38

40

42

44

Pote

ntia

l (V

)



1st cycle

2nd cycle

10th cycle

















4 Conclusions





4) to be


2O3composites




Acknowledgments


References



















2O4minus119910

S119910(0 le y le 01)




4-based com-















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 20 40 60 80 100 120 140

26

28

30

32

34

36

38

40

42

44

Pote

ntia

l (V

)



1st cycle

2nd cycle

10th cycle

















4 Conclusions





4) to be


2O3composites




Acknowledgments


References



















2O4minus119910

S119910(0 le y le 01)




4-based com-















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










2O4minus119910

S119910(0 le y le 01)




4-based com-















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Research Article Morphology and Electrical Conductivity of …downloads.hindawi.com/journals/jnm/2014/103418.pdf · 2019-07-31 · e electrical conductivity of the composites was