Lamellar compounds of graphite fibers were prepared by electrochemical intercalation. The dependence of the electrical resistance on the intercalate concentration was determined by a quasi simultaneous method. A factor 30 decrease of the relative fiber resistance was obtained with fluorosulfuric acid

Besenhard, J. O.

Fritz, H. P.

Moehwald, H.

Nickl, J. J.

English

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NASA TPCH'NICAL ,MEMORANDUM
	
NASA TM-7700,8
ELECTROCHEMICAL INTERCALATION AND ELECTRICAL
CONDUCTIVITY OF GRAPHITE FIBERS
J. 0. Besenhard, H. P. Fritz, H. Moehwald and J. J. Nickl
(NASA-TH-77008) ELEC'TROCHEhICAL 	 N83-33979
INTERCALATION AND ELECTRICAL CONDUCTIVITY OF
GRAPHITE FIBERS (National Aeronautics and
Space Administration) 8 p HC 
A02/NFCSCL 07D G3/25 360925
Translation of "Elektrochemische Intercalation and elektrische Leitfae-
higkeit. von Graphitfasern; 11 Zeitschrift fuer Neturforschung, B: Anorg. Chem.,
Org. Chem. 1978, v01. 33B, no. 7, PP . 737-739-
Vl.
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 2054E	 DECEMBFR 1982
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STANDARD TITLE PAGE
1. Report Ne.	 2. Government Accession No. 7:	 Recipient's Catalog No.
NASA TM-77008	 •
S. Repeit DateI. Title end Subtitle
ELECTROCP EPIICAT, TNTERC'ALATION • AND ELEC- "A
d. Porkrinino Organisation CodeTRICAL CONDUCTIVITY OF GRAPHITE FIBERS
7. Auiher(o) S. Performing Organisation Report No.J. 0. Besenhard, 4. P ..Fritz, 11. Moehwal
Work Unit No.and J. J. Nickl	 10.
9.	 Performing Organi action Nome and Address	 11. Contract or Grant No.
NASw- 541
Lea Kanner Associates
Redwood City, California	 94063
	
13. Type of Report and Period Coverer!
Translation
12. Sponsoring Agency Name anal ANross'
National Aeronautics and Space Adminis-
tration, Washington, D.C.	 20546 1^. Sponsoring Agency Cods
IS. Supplementary Notes
'Translation of "Elektrochem.ische Intercalation and elektrische
Leitfaehigkei^ von Graphitfasern, "	 Zeitschrift fuer Na•turforschung,
B: Anorg. Chem., Org. Chem. 1978, Vol. 33B, no. i pp. 737-739•
16.	 Abstract
Lamellar compounds of graphite fibers, have been prepared by
electrochemical intercalation.' The . dependence of the electric
resistance on the i .ntercalate concentratidn was determined by
a quasi simultaneous method.
	 A factor 30 decrease'of the
relative fiber'res stance ` was obtained ,with`fluorosulfuric aci
' ORIGINAL, PAGE 18r
OF POOR QUALITY
17. Key Words (Selected by Author(%)) 18. Distribution Statement
Unlimited-Unclassified
19.	 Security Clossil. (of this repo,,) 20.	 Security Clossil. (of Chit page) 21. No. of Pages 22.
Unclassified Uhclassified. 6
P	 i
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ORIGINAL PAGE 19
OF POOR QUALITY
ELECTROCHEMICAL INTERCALATION AND ELECTRICAL
CONDUCTIVITY OF G11APHITE FIBERS
J. O. Besenhard, H. P. Fritz, H. Moehwald and J. J. Nickl
Inorganic Chemistry Institute,
Technical University of Munich
Introduction	 " /'737*
Through the investigations of Ruedorff (1) and Ubbelohde (2-5) we
know that the electrical conductivity of lamellar graphite compounds is
greater than that of graphite. Vogel (6) found in the treatment of
graphite fibers with red, fuming HNO3 a reduction of the specific res-
istance of 7.5 X 10 4 .l2, cm to 7 X 10-5 " cm, therefore by a factor 10.
This article reports on the electrochemical interaction of graphite
fibers with very high modulus of elasticity in strong acids; here the
relation between the degree of intercalation and the electrical conduc-
tvity is of particular interest.
The authors used the commercial graphite fibers Celion GY 70 of the
company Celanese,, USA (modulus of elasticity = 5.17 .X 1011 NM-2) 4nd
"^'iorne1R50 of Union Carbide, UM . (modulus of elasticity = 4 X 1011 Nm-2).
The incorporation and subsequent measurement of resistance took place
at room temperature on individual fibers 3 to 4 cm long; to this end these
were in u-shaped contact on Cu bars and the contact points were subse-
quently gold-plated by galvanic means.
To adjust certain degrees of intercalation the fibers were oxidized
anodically with 2 hA direct c-rrent, while Pt was used as counterelectrode.
Numbers in the margin indicate pagination in the foreign text.
I
.'W
ORIGINAL rjsjt-;E
 
E,S
OF POOR QUALITY
By this method as we know it is possible to prepare even very small
degrees of incorporation (3,7).
The intercalation was interrupted periodically (alternating switch)
f	 and the resistance of the fiber was determined practically free from
r	 debt time through the drop in voltage for 10A A direct current.
Test measurements showed that with this method the flow of current
through the electrolyte is negligible so that the resistance of the
fibers could be determined directly in the electrolyte solution.
Raster electron microscopy photographs showed that the fibers used
were not at all round or uniform in cross-section; therefore the specific
electrical resistance was not indicated 1.
i
The measurement results were represented by the dependence of the
relative fiber resistance R/Ro on the mass standardized charge quantity
Q standardized. Thus it is assured that a certain Q standardized gives
for all studied fibers a certain degree of intercalation (Figures 1 and
R
2). The weights of the individual fibers could not be determined with
sufficient precision, so that the standardization was carried out to a
factor proportional to weight 12/Ro	 (1 =fiber length, Ro = resis-
tance of the initial fiber.
Results and Discussion
Figure 1 shows a variation of R/Ro as a function of Q standardized
for Celion GY 70 in about 96 percent HUN.
For a typical cross-section of 7 X 107 cm 2
 for Cel.ion GY 70 the
specific resistance is calculated at about 7 X 10-4
2
M ^^ (J
ORIGINAL PAOF- Ej
OF POOR QUALIV
/738
0.
0
0	 500	 1000	 1500	 2000	 2500
	
O normiert	 As) 1
Figure 1: Relative resistance of Celion GY 70 as a
function of Q standardized.
Key: (1) Q standardized.
. t•0oa	 °
0•SO •	 °
• °
°
00,20-°	 2
0.10	 •^ ••°	 a °
005	 •••'	 •
..•• O
0 1.00
a
0
0.50
0
0
0
0.20	 0
0
0
°o
0-10-°OO 0
	
°°	
O0000
0.05	 ° o
00
°0*00=00
0-02
20	 50	 100	 200	 500 1000 2000
0normiert (P As) (1)
Figure 2: Relative resistanci^ of Celion GY 70 as a function
of (the double logarithmic) degree of intercalation; electrolyte
(1) about 96 percent H2SO4, (2) 70 percent H2SO4, (3) 100
percent FS03H. Key: (1) Q standardized..
The very sharp drop of R/Ro for a low degree of incorporation is
characteristic. An estimate shows that for about 96 percent H2SO4 and
100 percent FS03H (Figure 2, curve 3) a reduction of R/Rc to half of the
initial value is achieved already for a ratio of the C atoms/intercalate
3
ORIGINAL PAGE I&
OF POOR QUALITY
= 1500 to 1; this corresponds to an incorporation density of about 7 by
l0powerl9 anions per cm3. There is no linear relation between anion
density and the relative resistance R/Ro, ratheki,,R/Ro tends with
increasing degree of incorporation to a saturation value.
Figure 2 shows R/Ro plotted in double logarithmic representation
againg;t Q standardized.
In this representation we obtain a case of nondehydrated acid, a
clear minimum; the latter for about 96 percent H2SO4 lies in the range
of C24 + HSO4= ( =first stage) and for 70 percent H2SO4 for a lower degree
of incorporation. This may be explained by the fact that intercalation
takes place initially and after passing through a minimum the formation
of "graphite oxide" begins. This minimum does not appear for 100 percent
FS03H; here there is no water needed to form the "graphite oxide". With
decreasing acid concentration this minimum is observed earlier (Figure 2,
curve 2) since the hydrolysis of the graphite salt takes place earlier
according to
Cn + HSO4- + H2O = CnOH + H2SO4.
The greatest variation of resistance was found for dehydrated FS03H
as electrolyte; here a ratio was obtained Ro/Rmin 30.
The table shows further re sults:.
Ele^ktrolyt (1) 'Ro/11m;
H2SO4	 ca. 100-proz. (2 ) 23	
F
H2SO4	 ca.	 96-proz. 23-26 ,1
H2804	90-proz. 23
H2804
	
80-proz. 16
H2804	 70-proz. 16 t
HC104	70-proz. 13 `	 r
FS03H	 100-proz. 30-33
HNO3
	
100-proz. 19
CF3CO2H	 100-proz. 20
Key: (1) Electrolyte; (2) percent.
4
if p
rrom the table it may be seen that in the case of sulfuric acid
in a concentration range of 100 to 90 percent acid practically the same
value is obtained for Ro/Rmin.
For Thornel R50 fibers similar values were found for Ro/Rmin, of
course the specific resistance of the initial fibers is higher by a
factor of about 3 than for Celion GY 70.
For all intercalation tests it was observed that the mechanical
properties and the diameter of the fibers nary only a little.
	 Since
	
"/739
the density of Celion GY 70 is about 1.6 gcm 3	 (graphite 2.25 gcm-3),
it may be assumed that internal cavities are filled predominantly by
the expansion of the layers.
Pri
If organic electrolyte solutions are used for the electrochemical
oxidation (incorporation of anions) or reduction (incorporation of
^i
cations) considerable decreases of resistance are also found.
	 A forth-
k coming report will be published on th.s area and on the dependence of
incorporation on the modulus of elasticity.
f i^
We thank Dr. A. Lerf, of the Central Institute of how Temperature
Research of the Bavarian Academy of Sciences in Garching for many
stimulating discussions.
J
t
ri
5
a	 t
Literature
(1) W. Ruedoff; Advances in Inorganic Chemistry and Radiochemistry,
Volume I, Academic Press, Inc., New York 1,959.
(2) A. R. Ubbelohde and F. A. Lewis; Graphite and its Crystal Compounds,
Oxford University Press, Oxford 1960,
(3) M. J. Bottomley, G. S. Parry, A. R. Ubbelohde and D. A. Young; J.
Chem. Soc., 1963, 5674.
(4) A. R. Ubbelohde, Carbon 14, 1 (1976).
(5) A. R. Ubbelohde; Proc. Roy. Soc. A., 309, 297 (1969).
(6) F. L. Vogel; Carbon 14, 175 (1976).
(7) J. 0. Besenhard; Carbon 14, 111 (1976).
6
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Electrochemical intercalation and electrical conductivity of graphite fibers

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