NASA/TM--1999-209437

Intercalation of Lithium in Pitch-Based

Graphitized Carbon Fibers Chemically

Modified by Fluorine: Soft Carbon

With or Without an Oxide Surface

Ching-cheh Hung

Glenn Research Center, Cleveland, Ohio

Aniko Prisko

Cleveland State University, Cleveland, Ohio

December 1999

https://ntrs.nasa.gov/search.jsp?R=20000018015 2018-05-14T14:05:53+00:00Z
The NASA STI Program Office... in Profile

Since its founding, NASA has been dedicated to

the advancement of aeronautics and space

science. The NASA Scientific and Technical

Information (STI) Program Office plays a key part

in helping NASA maintain this important role.

The NASA STI Program Office is operated by

Langley Research Center, the Lead Center for

NASA's scientific and technical information. The

NASA STI Program Office provides access to the

NASA STI Database, the largest collection of

aeronautical and space science STI in the world.

The Program Office is also NASA's institutional

mechanism for disseminating the results of its

research and development activities. These results

are published by NASA in the NASA STI Report

Series, which includes the following report types:

TECHNICAL PUBLICATION. Reports of

completed research or a major significant

phase of research that present the results of

NASA programs and include extensive data

or theoretical analysis. Includes compilations

of significant scientific and technical data and

information deemed to be of continuing

reference value. NASA's counterpart of peerreviewed formal professional papers but

has less stringent limitations on manuscript

length and extent of graphic presentations.

TECHNICAL MEMORANDUM. Scientific

and technical findings that are preliminary or

of specialized interest, e.g., quick release

reports, working papers, and bibliographies

that contain minimal annotation. Does not

contain extensive analysis.

CONTRACTOR REPORT. Scientific and

technical findings by NASA-sponsored

contractors and grantees.

CONFERENCE PUBLICATION. Collected

papers from scientific and technical

conferences, symposia, seminars, or other

meetings sponsored or cosponsored by

NASA.

SPECIAL PUBLICATION. Scientific,

technical, or historical information from

NASA programs, projects, and missions,

often concerned with subjects having

substantial public interest.

TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific

and technical material pertinent to NASA's

mission.

Specialized services that complement the STI

Program Office's diverse offerings include

creating custom thesauri, building customized

data bases, organizing and publishing research

results.., even providing videos.

For more information about the NASA STI

Program Office, see the following:

• Access the NASA STI Program Home Page

at http-[[www.sti.nasa.gov

• E-mail your question via the Internet to

help@sti.nasa.gov

• Fax your question to the NASA Access

Help Desk at (301) 621-0134

• Telephone the NASA Access Help Desk at

(301) 621-0390

Write to:

NASA Access Help Desk

NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076
NASA/TM--1999-209437

Intercalation of Lithium in Pitch-Based

Graphitized Carbon Fibers Chemically

Modified by Fluorine: Soft Carbon

With or Without an Oxide Surface

Ching-cheh Hung

Glenn Research Center, Cleveland, Ohio

Aniko Prisko

Cleveland State University, Cleveland, Ohio

Prepared for the

1999 Biennial Carbon Conference

sponsored by the American Carbon Society

Charleston, South Carolina, July 11-16, 1999

National Aeronautics and

Space Administration

Glenn Research Center

December 1999
Acknowledgments

The authors greatly appreciate the efforts of Dr. Richard Baldwin of Electrochemistry Branch, NASA Glenn

Research Center, in providing the knowledge and skills needed to conduct electrochemistry

experiments on lithium-ion cells.

This report contains preliminary

findings, subject to revision as

analysis proceeds.

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Price Code: A03

Available from

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Price Code: A03
INTERCALATION OF LITHIUM IN PITCH BASED GRAPHITIZED

CARBON FIBERS CHEMICALLY MODIFIED BY FLUORINE:

SOFT CARBON WITH OR WITHOUT AN OXIDE SURFACE

Ching-cheh Hung

National Aeronautics and Space Administration

Glenn Research Center

Cleveland. Ohio 44135

Aniko Prisko

Cleveland State University,

Cleveland. Ohio 44115

SUMMARY

The effects of carbon structure and surface oxygen on the carbon's performance as the anode in lithium-ion

battery were studied. Two carbon materials were used for the electrochemical tests: soft carbon made from

defluorination of graphite fluoride, and the carbon precursor from which the graphite fluoride was made. In this

research the precursor was graphitized carbon fiber P- 100. It was first fluorinated to form CF,,_. then defluorinated

slowly at 350 to 450 °C in bromoform, and finally heated in 1000 °C nitrogen before exposed to room temperature

air. producing disordered soft carbon having basic surface oxides. This process caused very little carbon loss. The

electrochemical test involved cycles of lithium intercalation and deintercalation using C/saturated Lil-50/50 (vol _ )

EC and DMC/Li half cell. The cycling test had four major results: ( 1) The presence of a basic oxide surface may

prevent solvent from entering the carbon structure and therefore prolong the carbon+s cycle life for lithium

intercalation-deintercalation, (2) The disordered soft carbon can store lithium through two different mechanisms.

One of them is lithium intercalation, which gives the disordered carbon an electrochemical behavior similar to its

more ordered graphitic precursor. The other is unknown in its chemistry, but is responsible for the high-voltage

portion (>0.3V) of the charge-discharge curve, (3) Under certain conditions, the disordered carbon can store more

lithium than its precursor. (41 These sample and its precursor can intercalate at 200 mA/g, and deintercalate at a rate

of 2000 mA/g without significant capacity loss.

INTRODUCTION

Carbon material as the anode of lithium-ion batteries has been the subject of recent research. It has been

reported that both the structure and the surface of the carbon materials are important parameters affecting their

performance as the anode in lithium-ion batteries. The surface is important in forming a surface-electrolyte interface

(SEI) layer during the first cycle of lithium intercalation. The SEI layer, if properly, formed, can effectively allow

lithium ions to enter the carbon layers and at the same time protect the intercalated lithium by keeping the solvent

out of the carbon structure. The carbon structure, on the other hand, is responsible for the capacity of lithium

intercalation. Recently. it has been reported that. for certain types of carbon, the capacity of lithium storage in the

lithium-ion battery, can exceed the value predicted by the generally accepted theory (Li/C = 1/6) (refs. 1 to 3).

The objective of this research is to further investigate the effects of carbon structure and carbon surface on the

performance of the carbon as the anode in the lithium-ion battery. Some o1"the carbon materials to be tested were

modified by fluorine in order to observe the change of the electrochemical behavior due to the modification in

structure and surface. The performance of the carbon materials are characterized from the point of view of capacity,

cycle life. and rate of charge and discharge.

EXPERIMENTAL

To conduct the study, the electrochemical behaviors of two different kinds of carbon materials were compared

whose differences and similarities in surface and structure either were well-documented or characterized. Two such

carbon materials were the precursor (Amoco PI00 graphitized carbon fiber) and the product (soft carbon) of a

process that consists of fluorination of Po100 and defluorination of the fluorinated P-100 thus obtained.

NASA/TM-- 1999-209437 1
Theprecursor andtheproductswerethentestedbythestandardhalf-cellwhereconstant currentwasusedasthe

powersource.Thedatathusobtainedwerethenusedtocharacterize andcomparetheirelectrochemical properties.

Fromsuchstudy,theaffectsofbulkcarbonstructureandsurfaceoxygenontheperformance ofthismaterials

anodeoflithium-ionbatteriescanbeinferred.

CarbonMaterial

AmocoP-100graphitizedcarbonfiberswereusedastheprecursorfthefluorination-defluorination reaction

describedabove.It waschosenbecauseitssynthesisandpropertieshavebeenstudiedingreatdetail.

Surfacesofpitch-basedcarbonfibershavealsobeenstudiedextensively. Itsreactionproductsafterthe

fluorination-defluorination processhavealsobeenexaminedatlengthinthepastseveral years(refs.4to7).

ThecommerciallypurchasedP-100wasfirstfluorinatedtoformCE,_s(refs.7to9).It wasthendefluorinated,

resultinginanewcarbonmaterial.

Dependingontheenvironment andthetemperatureofthisfluorination-defluorination process, alargenumber

ofdifferentdisorderedcarbonproductscanbeobtainedfromtheP-100graphiteprecursor (ref.7).Inthisresearch,

thefluorination-defluorination processwasdesignedsuchthatheproductsweresoftcarbon,whichwasfoundtobe

agoodmaterial foranodeinlithium-ionbatteriesaspreviouslyreported(ref.3).Thiswasaccomplished byslowly

heatingoftheCE6sfibersinbromoformto350to450°Cin 1hrandkeptatthatemperaturefor1.5hr.The

productwasthenstoredinambient airforsometimebeforefurthertreatedin1000°Cnitrogentoremovethe

residual fluorineandoxygeninthecarbonfibers.Theproductwasthenstoredinambient airagainbeforethe

electrochemical experiment.

Thisprocessremovedfluorineinthegraphitefluoridewithoutcausingmuchcarbonloss.Fromthex-ray

diffraction, thediameter andtheresistivitydata.it wasconcludedthatheproductwassoftcarboncontaining

disorderingareasandpossiblycarbonbranchesconnectingadjacent graphenelayersoradjacent crystallites(refs.6

and7).Itsphysical andstructural propertieswerecomparedtoisprecursor andarelistedintableI.

Thiscarbonmaterial maynotcontainoxygenrightafterthe1000°Cnitrogenheating. However, altersome

timeofambientairstorage, itsenergydispersivespectra(EDS)indicatedthepresenceofasmallamountofoxygen.

Itisbelievedthatsomeoxygenatomsfromtheambient airreactedtotheactivesitesonthesurfaceofthecarbon

materialnd,asaresult,producedanoxidesurfacelayer.

Bismarcketal.observedthat,underasimilartreatment of905°Cnitrogenheatingfollowedby25°Cair

exposure, abasic,hydrophobicsurfaceoxidewasformedonthehightensileandhighmoduluscarbonfibers.They

alsoreportedthatthermallyoxidizedfibersofthesametypeswereacidicandhydrophilic(ref.10).It isbelievedthat

thefibersinthisstudyhadthesamebasic,hydrophobicsurfaceasthatdescribedbyBismarcketal.(ref.10).

Eachsampleintheformof 1to1.5cmfiberstrandwastiedbya0.13mmnickelwiretoa0.5mmnickelwire,

whichinturnwasconnectedtoa3mmnickelrodfromwhichtheconstant currentsourcewasconnected. Two

methodswereusedtoremovesurfaceoxidedescribedabove:overnight (about15hr)vacuumheatingat180°C

immediatelybeforeassemblingthehalfcell,andovernight nitrogenheatingat540°Cimmediatelybefore

assemblingthehalfcell.Theformermethodwasbelievedtodegas,removemoistureandsomeoxygenincarbon.

Thelattermethod, ontheotherhand,wasbelievedtocausecarbon-oxygen reactionbecauseofthehightemperature

heatingat540°C.Thisremovednotonlythemajorityoftheoxygen, butalsosomecarbon.

Thepreparationfthecarbonsampleselectrochemically testedinthisresearchissummarized infigure1.

HalfCellTest

Theelectrochemical propertiesof the carbon materials were measured in a three-electrode cell containing a

counter electrode and a reference electrode of lithium metal, and a working electrode made from a carbon material.

Both lithium and carbon fibers were connected to nickel rods. which served as an electrode connecting to the

electrical instruments. The electrolyte used was saturated LiI in a 50/50 (vol %) mixture of ethylene carbonate and

dimethyl carbonate. The half-cell was prepared in a glove box purged with argon.

During tests, the current was controlled, and the voltage measured. For the purpose of visually observing the

possible interference of lithium salt. a pyrex glass weighing bottle was used as the cell, and LiI was used as the

lithium salt. In this arrangement, whenever and wherever I_ is formed in the cell during reaction, it can be identified

by its color. For example, the color of the electrolyte did not change if deintercalation was stopped at 0.7 V. but

gradually turned from light yellow to orange alter several cycles of cell test if the "cut-off voltage" was 3.0 V.

Trial runs were made using commercially purchased crystalline graphite powder as working electrodes. The

capacity for the first intercalation to 0 V was measured to be 380 mAhr/g, within experimental error of the literature

value (390-420 mAhr/g) (ref. 1I).

NAS A/TM-- 1999-209437 2
RESULTSANDDISCUSSION

ImmediatelyafterheatingthesoftcarbondescribedintableIin540°Cnitrogentoremovethesurfaceoxides,

thecarbonsamplewastestedelectrochemically inthehalfcellagainstlithiummetal.Figure2(a)iscomparisonf

reversible(i.e.,deintercalation) capacitybetweenthissampleanditsprecursor (PI00).Theireversiblecapacities

wereaboutthesameif thecut-offvoltageoftheworkingelectrode(V,,0was0.3V.Thehighertotalreversible

capacityforthiscarbonmaterial overitsprecursor ismostlyduetoitsabilitytoreleasemorelithiumafterV,,.was

above0.3V.

Figure2(b)istheenlargement ofthelowervoltageportionoffigure2(a).It canbeseenthathecurvesforboth

samplesshowplateausat80,120,and190mV,representing differentstagesoflithiumdeintercalation.

Theabovedataindicatethathedisorderingofcarbonatomsduetothefluorination-defluorination treatment of

acarbonprecursor maynotaffectitsabilitytoelectrochemically intercalateanddeintercalatewithlithiumwhen

0<V,,r<0.3V,butdoescreatenewlithiumintercalation/absorption sieswhichareactivewhenV,,r>0.3V.Such

creationoflithiumsitesresultsinanincreaseofreversible, oruseablecapacityforalithium-ionbattery.

Whetherthesenewlycreatedlithiumsitesareabsorptionsitesorintercalationsitesisnotknown.However. they

aremorelikelytobeabsorptionsitessinceithasbeenreportedthatmostlithiumdeintercalation takesplacewhen

0<V,,..<0.3V(ref.12).

TableII describestheintercalationaddeintercalation capacitiesofthesetwosamples(PI00astheprecursor

andsoftcarbonwithoutsurfaceoxidesastheproduct). Itisnotedthatforbothsamples, thedeintercalation capacity

wasalwaysmallerthantheintercalationcapacity. Thisindicatesthatineverycharge-discharge cycleasmallbut

significant amountoflithiumwasinsertedintothecarbonstructureandlost.Ifthesecarbonmaterialsaretobeused

astheanodeinalithium-ionbattery,thecyclelifeaswellastheirreversiblecapacitywouldneedtobefurlher

tested. Apossiblerasonforsuchlithiumlossisthatit reactedtosomesolventthatwasalsoinsertedintothecarbon

structureduringthelithiumintercalationprocess. Topreventsuchpossibility, abettercarbonsurfacemaybeneeded

asthesolventbarrier.

Inordertotestheeffectsofcarbonsurfaceonitselectrochemical behavior, theabovexperiment wasslightly

modified. Insteadofovernightightemperature(540°C)preheatingwhichcausedcarbon-oxygen ractionsand

removedsurfaceoxygen,thecarbonsamplewaspreheatedto180°Cinvacuumimmediatelybeforethehalf-cell

preparation. Theresultedintercalationaddeintercalated capacitiesaredescribedintableIII andfigure3.Itcanbe

seenthat.withoxidesontheirsurfaces, boththeprecursor andthesoftcarbonproducthadverysmallnoticeable

lithiumlossalterseveral cyclesoftheintercalation-deintercalation process. Thesedatasuggest thatcarbon

containingsuchsurfaceoxidescanhavealongcyclelifeastheanodeinlithium-ionbattery.

Theeffectofsurfaceoxideonthecarbon'scapacitytostorelithiumiscomplicated. ComparingtableII and

tableIII.it canbeseenthatforthecarboncontainingsurfaceoxides,theprecursor (P100)storedmorelithiumthan

theP-100withoutcarbondid.butthesoftcarbonproductstoredless.

Thedeintercalation curveforthecarboncontainingsurfaceoxides(fig.3)indicatedthathereversiblecapacity

ofthedisorderedcarbonwassmallerthanthatofitsprecursor (PI00).Thisisdifferentfromdataobtainedfromthe

carbonwithoutsurfaceoxide(fig.2).It suggeststhathesurfaceoxidecanpreventlihiumfrombeingintercalated

intocarbon.However, thisdisorderedcarbonshowedthesameabilitytoreleaselithiumwhenV,,rwasabove0.3V.

Theabove-described affectsofcarbon'soxidesurfacesonthecarbon'sperformanceasanodeoflithium-ion

batter), aresummarizedinfigure4.It appearsthatthesurfaceoxidespreventedthesolventfromenteringthecarbon

structure. Italsopreventedlithiumfromenteringthesoftcarbonproduct, butnotthePIO0precursor.

Theaffectsofsurfaceoxideonthecarbon'sperformance asanodeinlithium-ionbatter),appeartobecomplicatedandcritical.Furtherstudyisneededtoidentifythephysical andchemical propertiesofthesurfaceoxide

whichcanimprovethereversiblecapacityandcyclelife,butatthesametimereducetheirreversiblecapacityofthe

carbonanode.

Experimentswerealsomadetotesttherateoflithiumintercalation-deintercalation forthe180°Cvacuum

heatedsampleaswellasitsprecursor. Inthissetofexperiments, carbonmaterialsfullyintercalatedat

10mA/gweredeintercalated atseveral higherrates.Andcarbonmaterialsfullydeintercalated at10mA/gwere

intercalatedatseveral higherrates.Figures5and6show,forthedisorderedsoftcarbonanditsprecursor.

respectively, theV,,rasfunctionsoftheintercalatedquantityatseveral differentintercalationaddeintercalation

rates.Itcanbeseenthatboththedisorderedsoftcarbonanditsprecursor performedwellathighratesof

intercalation(80mA/g)anddeintercalation (2000 mA/g).

CONCLUSION

Disordering of carbon atoms in P-100 graphitized carbon fibers was accomplished. Both the P-100 precursor

and the disordered soft carbon product were electrochemically tested for their performance as anode in lithium ion

battery.

NASA/TM-- 1999-209437 3
The disordering of the graphitized carbon fiber P-100 was made by treating the fiber with the process of

fluorination and then slow defluorination in 450 °C bromoform environments, followed by 1000 °C nitrogen heating

and room temperature air storage.

Immediately after 540 °C heating in nitrogen to remove the oxygen in this product, the sample was

electrochemically tested and was found to have larger reversible and irreversible capacity to intercalated lithium

than their precursor. Data suggests that the sample and its precursor has the same ability to intercalate lithium when

V,,, < 0.3V. which is the only possible voltage range for graphite to intercalate lithium. The reason for the higher

lithium storage capacity in the disordered carbon was the creation of new lithium sites which were active when

V,, r > 0.3 V. If the carbon was heated in 180 °C vacuum before half cell preparation, the surface oxygen was not

totally removed. In that case the surface may prevent solvent from entering the carbon structure and therefore help

increasing the cycle life of the carbon when it is used as the anode material in the lithium-ion battery. The effect of

surface oxide on the carbon's lithium storage capacity is not conclusive. It reduced the capacity of lithium

intercalation (when V,, r <0.3V) in the soft carbon tested in this research, but increased the capacity in its precursor

(P-100). Both this sample and its precursor can have a very high rate of intercalation and deintercalation. It can

intercalate at 200 mA/g, and deintercalate at a rate of 2000 mA/g without significant capacity loss.

REFERENCES

1. Endo, M., Ismail, R., Hiraoka, T.. Karaki. T., Kasai, T., Matthews, M.. Brown, S., and Dresselhaus, M.: in

Extended Abstracts 23rd Biennial Cot!ference on Carbon, University Park, PA, 1997, I, 146.

2. Takami, N.. Satoh. S., Hara, M., and Ohsaki, T.: J. Electrochem. Soc., 1995, 142 (8), 2564.

3. Dahn, J., Sleigh, A., Shi, H., Way, B., Weydanz, W., Reimers, J., Zhong, Q. and von Saken. U.: Carbon

and Graphite as Substitutes for the Lithium Anode in Lithium Batteries, G. Pistoia (ed.) pp. 1-47, Elsevier,

Amsterdam, 1994.

4. Singer, L.: Fuel, 70. 1981, pp. 839-847.

5. Hoffman, W.: Carbon, 30 (3), 1992, pp. 315-331.

6. Hung, C.: U.S. Patent 5,662,683, 1997.

7. Hung, C.: NASA TM-106398, 1994.

8. Hung,C., and Kucera, D.: Extended Abstracts 20th Biennial Conference on Carbon, Santa Barbara. CA, 1991.

674.

9. Hung, C.: U.S. Patent 5,286,471, 1994.

10. Bismarck, A., Wuertz, C., and Springer, J.: Carbon. 1999, 37 (7), pp. 1019-1027.

11. Ohzuku. T., Iwakoshi, Y., and Sawai, K., J. Electrochem. Soc., 1993, 140 (9), p. 2490.

12. Endo, M., Takahashi, T.. Rahim, I., Takamuka, A., and Nakamura, J.: in Extended Abstracts 22nd Biennial

Conference on Carbon. San Diego, CA, 1995, p. 806.

TABLE I.--PROPERTIES OF THE PRECURSOR AND THE PRODUCT OF THE

FOLLOWING REACTIONS

45{I ¢C I()l_0 :C

... C(Sofl carbon) PI00 l:lu_rinalion ) CFI!O8 I_rt_molorm l_,ltrogen

Diameter. Resistivity, X-ray diffraction (002) peak

lain p.fLcm Position. Width at half Intensity

A maximum

Carbon from slow

defluorination of CF_ _ in 1l. 3 900 3.35 1.4° 1

CHBr_

P I(30 10.0 390 3.37 0.454" 100

NASAfYM--1999-209437 4
TABLE II.--INTERCALATION AND

DE[NTERCALATION CAPACITIES FOR THE

CARBON PRODUCTS PRETREATED AT

540 °C NITROGEN

(CI AND C3 DESCRIBED IN F1GURE I)

(a_ CI {Soft cmbon fibersl

r Cycle number 1 2 3 4 5 6

Intercalation 487 293 286 288 276 273

Deintercalation 280 274 270 268 265 260

(b) C3 IGraphitized carbon fibers)

Cycle number 1 2 3 4 5 I 6

Intercalation _49 -.6 ..... 4 _.l -.1

Deintercalation _,-_ ..... z; _30 _.'_'I _"19 _"17 217

TABLE III,--INTERCALATION AND DEINTERCALAT1ON

CAPACITIES FOR THE CARBON PRODUCTS

PRETREATED AT 180 °C VACUUM

(C2 AND C4 DESCRIBED IN FIGURE I )

(a) Soft Carbon Fibers

Cycle number I 2 3 4

Intercalation Capacity t mAHr/_) 210 213 207 197

CuJTent ( mA/_ ) I0 3-6 8 I 0

Deintercalation Capacity (mAHr/_} 208 208 196" 197 _:

Cunent (mA/g) 13 10 50 30

(b) Graphitized Carbon Fibers

Cycle number I 2 3 4

lnlercalation Capaciff (mAHr/2) 257 242 245 194

Current (mA/_l 10 28 10 200

I)einlercalation Capacity ImAHdi. ) 245 241 244 194

Current fmA/_l 10 40 9 40

TABLE IV.--INTERCALATION AND DEINTERCALAT1ON CAPACITIES

AT HIGH CURRENT DENSITIES FOR CARBON PRODUCTS

PRETREATED AT 180 °C VACUUM

(C2 AND C4 DESCRIBED tN FIGURE 1}

(a) C2 (Soft Carbon Fibers)

Imercalation Capacitx (mAHr/_) 197 190 177 161 105

CulTenl (nlA/_) 10 50 80 200 350

Deinlercalalion Capacity (mAHr/g t 197 196 - - 184 163

Cunent (mA/g) 30 50 -- 500 2000

(b) C4 IGraphitized Carbon Fibers_

Intercalation Capacity I mAHr/_.) 245 232 194 79

Cunent I mA/g) 10 8[) 200 350

Deintercalation Capacity _mAHd[} 244 241 235 232

Cunent ImA/g) 9.1 40 50(} 2(}0(}

540 °C

> C1

P1 450 °C 1000 °C Room temp. _ Nitrogen 00_CF 0 68----------> _ > C (Soft carbon)

Fluorination ' Bromoform Nitrogen Air 180 °C

> C2

vacuum

100o °C Room temp.

P100 _ • C (Graphitized carbon)

Nitrogen Air

540 °C

> C3

-_ Nitrogen 180 °C

> C4

Vacuum

Figure 1 ._Preparation of carbon samples electrochemically tested in this study.

NASA/TM-- 1999-209437 5
3.0

2.5

2.0

1.5

1.0

0.5

0.0

P-IO0

carbon

(a)

0.5

0.4

0.3

0.2

0.1

0.0

0 50 100 150 200 250 300

mAHr/g

Soft carbon

P-100

(b)

0 50 100 150 200 250 300

mAHr/g

Figure 2.--Electrochemical deintercalation of lithium from carbon pretreated at 540 °C nitrogen

(C1 (soft carbon) and C3 (P-100) described in Figure 1). (a) The entire voltage range (0 to 3 V).

(b) The lower voltage range only (<0.SV). The half cell (C/saturated Lil-50/50 (vol %) EC and

DMC/Li) was operated at 10 mA/g. The plateaus indicate deintercalation.

NASA/TM--1999-209437 6
3.0

2.5

2.0

1.5

1.0

0.5

0.0

0

0.50

i

5O

_'---- P-100

/

so.c 

150 ' '

100 200 250

mAHr/g

3OO

0.45

0.40

0.35

0.30

> 0.25

0.20

0.15

0.10

0.05

0.00

0

!

i

I"L'--- P-1 O0

so,, car, i I s/

(b)

i F

5_ 100 150 200 25'0 3o(

mAHr/g

Figure 3.--Electrochemical deintercalation of lithium from carbon pretreated at 180 °C vacuum

(C2 (soft carbon) and C4 (P-100) described in Figure 1). (a) The entire voltage range (0 to 3 V).

(b) the lower voltage range only (<0.5V). The half cell (C/saturated Lil-50/50 (vol %) EC and

DMC/Li) was operated at 10 mA/g. The plateaus indicate deintercalation.

NASA/TM-- 1999- 209437 7
PIO0 Slowly defluorinated CF0.68

Capacity $ $

Cycle life $ $

Figure 4.--Effect of removing surface oxide (C and O)

on the performance of carbon materials as anode in

lithium-ion battery.

NASA/TM-- 1999-209437 8
1.0

;>

0.9

0.8 10mA/g

0.7

80 mA/g

0.6

0,5

0.4

\

\

\

0.3 \

0.2 200 mA/g

350 mA/(

0.1

0.0

0 2() 4() 60 80 100 120 140 160 180 200

mAHr/g

3.0

)

2.5 i

i

2.0

1.5 -

1.0 _

0.5 i

F

0.0

0

J

t

2000 mA/g ..-_yf// /

/ /

/ /

// /_ 500 mA/g

 --,0an0 0m.0

T 1 T

5 0 100 150 200

mAHr/g

Figure 5.--Electrochemical behavior as functions of current density in a C/saturated Lil-50/50 (vol %)

EC and DMC/Li half cell. The carbon was a soft carbon pretreated at 180 °C vacuum. (C2 described

in Figure 1). (a) intercalation of a slowy (10mA/g) deintercalated carbon. (b) deintercalation of a slowy

(10mA/g) intercalated carbon.

(b)

250

NASA/TM-- 1999-209437 9
1.00

0.75

> 0.50

0.25

0.00

3.0

i

V10 mA/g

_",,'_-- 200 mA/g

i i

50 1 O0

mAHdg

_

l i

150 200 250

2.5

2.0

1.5

1.0

0.5

o.o-_

/

i

!

/

/ _ 9.1 mA/g

2000 mA/g _ --40 mA/g

_/j.-// _ L 500 mA/g

(b)

0 50 100 150 200 250 300

mAHr/g

Figure 6.--Electrochemical behavior as functions of current density in a C/saturated Lil-50/50 (vol %) EC

and DMC/Li half cell. The carbon was P-100 pretreated at 180 °C vacuum. (C4 described in Figure 1).

(a) intercalation of a slowy (10mA/g) deintercalated carbon. (b) deintercalation of a slowy (10mA/g)

intercalated carbon.

NASA/TM-- 1999-209437 10

REPORT DOCUMENTATION PAGE Form Approved

OMBNO.0704-0188

Public reporting burden tor this collection of information is estimated to average I hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and rewewing the collection of information Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden to Washington Headquarters Services. Directorate for information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arhngtcn, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188) Washington, DC 20503

1. AGENCY USE ONLY (Leave blank) 2, REPORT DATE 3. REPORT TYPE AND DATES COVERED

December 1999 Technical Memorandum

4. TITLE AND SUBTITLE

Intercalation of Lithium in Pitch-Based Graphitized Carbon Fibers Chemically

Modified by Fluorine: Soft Carbon With or Without an Oxide Surface

6. AUTHOR(S)

Ching-cheh Hung and Aniko Prisko

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

5. FUNDING NUMBERS

WU-632-I A-l E--O0

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-11914

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--1999-209437

11. SUPPLEMENTARY NOTES

Prepared for the 1999 Biennial Carbon Conference sponsored by the American Carbon Society, Charleston.

South Carolina, July 11-16, 1999. Ching-cheh Hung, NASA Glenn Research Center. Aniko Prisko. Cleveland State

University. Cleveland, Ohio 44115. Responsible person Ching-cheh Hung, organization code 5480, (216) 433-2302.

12a, DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Categories: 20 and 23 Distribution: Nonstandard

This publication is available from the NASA Center for AeroSpace Information. (301) 621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 worde)

The effects of carbon structure and surface oxygen on the carbon's performance as the anode in lithium-ion battery were studied.

Two carbon materials were used for the electrochemical tests: soft carbon made from defluorination of graphite fluoride, and the

carbon precursor from which the graphite fluoride was made. In this research the precursor was graphitized carbon fiber P-100.

It was first fluorinated to form CF,,_, then defluorinated slowly at 350 to 450 °C in bromolbrm, and finally heated in 1000 °C

nitrogen before exposed to room temperature air, producing disordered soft carbon having basic surface oxides. This process

caused very little carbon loss. The electrochemical test involved cycles of lithium intercalation and deintercalation using

C/saturated Lii-50/50 (vol %) EC and DMC/Li half cell. The cycling test had four major results. (1) The presence of a basic

oxide surface may prevent solvent from entering the carbon structure and therefore prolong the carbon's cycle life for lithium

intercalation-deintercalation. (2) The disordered soft carbon can store lithium through two different mechanisms. One of them is

lithium intercalation, which gives the disordered carbon an electrochemical behavior similar to its more ordered graphitic

precursor. The other is unknown in its chemistry, but is responsible for the high-voltage portion (>0.3V) of the charge-discharge

curve. (3) Under certain conditions, the disordered carbon can store more lithium than its precursor. (4) These sample and its

precursor can intercalate at 200 mA/g. and deintercalate at a rate of 2000 mA/g without significant capacity loss.

14. SUBJECT TERMS

Intercalated; Carbon; Lithium: Batteries

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

15. NUMBER OF PAGES

16

16. PRICE CODE

A03

20. LIMITATION OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102