16338
J. Phys. Chem. 1995,99, 16338-16343
Structural and Electrochemical Properties of Lithiated Polymerized Aromatics. Anodes for Lithium-Ion Cells Michikazu Hara,* Asako Satoh, Norio Takami, and Takahisa Ohsaki Materials & Devices Lab., R&D Center, Toshiba Corporation I , Komukai Toshiba-cho, Saiwai-ku Kawasaki 210, Japan Received: April 6, 1995; In Final Form: August 8, 1995@
Structural and electrochemical properties of lithiated polymerized aromatics as anodes for lithium-ion cells have been studied using 3,4,9,lO-perylenetetra-3,4,9,lO-carboxylic dianhydride (PTCDA) heated at 5501000 "C in inert gas. Lithium can be reversibly doped in PTCDA heated at 550 "C with the largest specific capacity of 660 mA h g-' between 0 and 2 V vs Li/Li+. The capacity of the pyrolyzed PTCDA decreased with increasing heat-treatment temperature (HTT). IR and XRD measurements revealed that the structure of pyrolyzed PTCDA shifted from a polymerized perylene to a disordered carbon composed of small graphite layers with increasing HTT. The IR spectra of lithiated pyrolyzed PTCDA suggested that the reversible lithium doping in the pyrolyzed PTCDA heated at temperatures of less than 650 "C was attributed to an ionic complex composed of lithium ions and aromatic rings with negative charges. The relationship between the lithium-doping mechanism and the structure of the pyrolyzed PTCDA has been discussed.
1. Introduction Lithium-ion cells have been awaited as power sources with high-energy densities. Early secondary batteries with metallic lithium anodes were studied in expectation of high-energy densities. However, these batteries have poor cycle life because there is considerable difficulty in preventing intemal short circuits caused by lithium dendrite which penetrates the separators. For long cycle life and safety, various kinds of carbons as anodes for lithium-ion cells have been investigated instead of the metallic lithium anode. Carbons and graphite can intercalate lithium ions into their layered planar lattice structure by electrochemical methods. However, the graphite anodes cannot have capacities over 372 mA h g-'.' This is because graphite cannot form more lithium composition than LiC6 electrochemically. Recently, disordered carbons prepared by the heat treatment of mesocarbon microbeads and polymers (polyacene, poly@phenylene), and poly(furfury1 alcohol)) at 600-800 "C have been proposed as anodes for lithium-ion cells.2-6 These carbon materials have large specific capacities of more than 400 mA h g-' and formed more lithium compositions than LiC6 in graphite. The origin of the large capacities and the lithiumdoping (insertion) mechanism for these disordered carbons have not been well analyzed yet. It is known that organic compounds heated at the above temperature range are not so much carbon as carbon precursor composed of polymerized condensed aromatic^.^^^ These studies show that polymerized condensed aromatics have larger capacities than graphite. In this study, the charge-discharge characteristics zind the structures of pyrolyzed 3,4,9,10-perylenetetra-3,4,9, lo-carboxylic dianhydride (PTCDA) as anodes for lithium-ion cells were investigated by infrared spectroscopy (IR), X-ray diffraction (XRD), and charge-discharge test. PTCDA decomposes and generates perylene tetraradicals at 516 "C as shown in Scheme 1.9 The radical polymerization of perylene tetraradicals are expected to form polymerized condensed aromatics with large capacities. In the present article, lithium doping-undoping mechanisms into the polymerized condensed aromatics are discussed. @
Abstract published in Advance ACS Abstracts, October 1, 1995.
SCHEME 1
PTCDA
P e r y I e n e T e t r a r a d i c a l s
2. Experimental Section The carbon materials were prepared by the pyrolytic treatment of PTCDA (CZ~HSOS). PTCDA (powder, purity >98%, MerckSchuchardt) in an alumina melting pot was heated at 530 "C for 5 h in an electric furnace under an argon atmosphere. After pyrolytic treatment, a black powder in the melting pot and black whiskerlike materials on the wall in the electric furnace were obtained. The product yields of the black powder and the whiskerlike materials are 40% and 5%, respectively. The whiskerlike materials are considered to be polyperinaphthalene. Polyperinaphthalene whiskers grow on a pellet of PTCDA heated at temperatures of more than 520 "C9 Perylenetetraradicals from PTCDA form whiskerlike polyperinaphthalene in vapor phasea9 However, the characteristics of the PTCDA pellet after the pyrolysis have not been investigated yet. In this study, we used not the whiskerlike materials (polyperinaphthalene) but the black powder as a carbon precursor. The carbon materials were prepared by the heat-treatment of the black powder at 550-1000 "C for 5 h in an argon atmosphere. The prepared samples are listed in Table 1. Table 1 shows heattreatment temperatures and the hydrogen atodcarbon atom (W C) ratio for each sample. The structures of the samples were investigated by means of IR and XRD. The IR spectra for the samples were measured using the KBr disks of the samples. XRD was measured by a Rigaku Rint 1200 V with Ni-filtered Cu K a radiation. The sample was set on a silica sample holder in the diffractometer. The electrochemicalproperties of the samples were evaluated by a charge-discharge cycling test. Charge-discharge cycling tests for the sample electrodes were carried out using a threeelectrode glass cell.Io The sample working electrodes (2 x 2
0022-365419512099-16338$09.0010 0 1995 American Chemical Society
Lithiated Polymerized Aromatics
J. Phys. Chem., Vol. 99, No. 44, 1995 16339
TABLE 1: Pyrolyzed PTCDA Used in This Study sample A
B
preparation temp("C1 550 650
WC 0.26
sample C
0.16
D
preparation temp('C) 800
lo00
WC 0.05 10.01
cm) were prepared by mixing a sample obtained with a 3 wt % Teflon powder binder by pressing them on a stainless steel mesh collector. The carbon electrodes had a coverage of 10- 11 mg cm-2 and a thickness of about 100 pm. A reference electrode was a lithium tip on a Ni wire. A counter electrode was a lithium foil (2 x 2 cm) on a Ni mesh. A glass filter as the separator and the reference electrode were sandwiched between the carbon working electrode and the counter electrode. Both electrodes were supported by two polypropylene plates. The electrolytes used in these cells were a 1 M solution of LiPF6 in an ethylene carbonate/propylene carbonate ( E C R ) mixed solvent (1:l by volume). Typical charge-discharge cycling tests for the carbon electrodes were carried out using galvanostatic cycling at 0.25 mA cm-2 between 0 and 2 V vs Li/Li+. To measure the IR spectra for the lithiated samples, the samples were electrochemically doped with Li using a binderfree electrode. The binder-free electrodes, which had a coverage of 3-4 mg cm-2 and a thickness of about 80 pm, were prepared by drying a suspension of a sample and acetone on a Ni foil (2 x 2 cm). The electrodes were charged or discharged in the above cells with a 1 M solution of LiPF6 in an ethylene carbonate/l ,Zdimethoxyethane (ECDME) mixed solvent (1: 1 by volume). The electrodes were charged or discharged with Li in a similar manner. After charge or discharge, the lithiated samples were washed with DME several times. Then, the KBr disks of the samples, which were vacuum-dried about 1 h, were prepared for the IR measurements. All of the above operations, the IR measurements and the charge-discharge cycling tests were performed at 24-25 "C in an Ar atmosphere (299.99%).
3. Results and Discussion 3.1. Structure of Pyrolyzed PTCDA. Figure 1 shows the IR spectra for PTCDA and the prepared samples. Each spectrum name corresponds to each sample name. As shown in Figure 1, the IR spectrum of PTCDA has vibrational modes based on aromatics and carboxylic dianhydride. The vibrational modes of aromatics are aroamtic v(C=C) (1594, 1510, 1405 cm-l) and aromatic C-H bending d(C-H) (in-plane 11201150 cm-l, out-of-plane 1000-700 cm-l). The absorptions due to carboxylic dianhydride consist of v(C=O) (1770 cm-I), C-0-C (1299, 1234 cm-I), and -CO-0-CO(1022 ~ m - ' ) . ~Spectrum A is an Ir spectrum for sample A, which is the pyrolyzed PTCDA heated at 550 "C, and consists of the very weak peak of v(C=O) (1770 cm-') and the broad peaks which are assigned to v(C=C) (1594, 1400 cm-') and d(CH) (in-plane 1130 cm-I, out-of-plane 900-700 cm-I). Spectrum A shows that PTCDA is almost pyrolyzed and forms an aromatic at 550 "C. This aromatic is expected to be a polymerized perylene because perylene tetraradicals generated by the pyrolysis of PTCDA radical polymerize each other. The peak intensities for aromatic v(C=C) and 6(C-H) (out of plane) are decreased with H". The vibrational modes due to aromatics are little observed in spectrum D for sample D prepared at lo00 "C. The identified vibrational modes in Figure 1 are listed in Table 2. The XRD patterns for the samples are shown in Figure 2. The peaks around 28 = 25" and 45" correspond to the (002) diffraction based on the layer-by-layer structure and the (10)
1
1
1
1
I
I
,
.
,
.
,
.
,
3600 2 8 0 0 2 0 0 0 1600 1 2 0 0 800
Wave Number/cm-' Figure 1. IR spectra for PTCDA (samples A-D). Vertical axis represents IR transmittance and all of the spectra are in scale.
TABLE 2: Assignment for the Observed IR Peaks sample PTCDA
peak/cm-l 1770 1594
I [:E1
:A:[
1130
A
B C D
assignment v(C=O)
aromatic v(C=c)
c-0-c d(C-H)
1022
-co-0-co-
900-750
d(C-H) v(C=c)
900-750 1600 900-850 1610
d(C-H) v(C=C) d(C-H) v(C=c)
[EI
diffractions for carbon, respectively. Both peaks are moderately diffuse, and the (1 10) diffraction due to the width of graphite layer does not appear in all of the XRD patterns. These XRD results indicate that the pyrolyzed PTCDAs in this study are not amorphous carbon but "disordered carbon" comprised of buckled small graphite layers.'1,12 The (002) diffraction in Figure 2 slightly sharpens with increasing H'IT. The above IR and XRD results reflect the carbonization process of an organic compound. As shown in Scheme 2, the initial carbonization process at 500-1000 "C begins at the polymerization and aromatization of the organic compund (l), followed by the plane growth for small condensed aromatics to large condensed aromatics as small graphite layers by the condensation of aromatics (2) and three-dimensional growth that buckled small graphite layers are stacked (3). Although the carbon compounds in this process are called "disordered carbon",'* disordered carbon has several aspects as above. The phase shown in 1 of Scheme 2 is the polymers of aromatics or condensed aromatics rather than carbon. The layer-by-layer structure composed of buckled graphite layers in disordered carbon approximates to the three-dimensional structures in
Hara et al,
16340 J Phys. Chem., Vol. 99, No. 44, 1995 ( 0 0 2)
I I
-1
I
A
D
C
> +. .M C 0)
0
+.
200
C
-
600
4UO
800
1000
CaPacity/mAh.g’
Figure 3. Charge-discharge curves for samples A-D.
600
5
20
40
60
80
2e/deg Figure 2. XRD patterns for samples A-D.
2
500
c:
2 k
SCHEME 2
:.
400 300
0
m Q
m 0
200
1
Irreversible
100
0
500
1
2
3
“turbostratic carbon” or “hexagonal graphite” with increasing HTT. In turbostratic carbon, graphite layers are basically parallel, but each layer is randomly translated or rotated with respect to its neighbors. The H atom/C atom ratio decreases and the conjugated n orbitals spread with the plane growth of condensed aromatics by the dehydrogenation condensation of aromatic rings, so that the carbon compound with large condensed aromatics or small graphite layers has a large absorption in the visible region. Large absorption at visible region influences infrared region and enhances the background absorption of the IR spectrum. Consequently, the behavior in Figure 1, which is the decrease of the IR peak intensities due to aromatics with increasing HTT,represents the structural shift from the polymer of condensed aromatics (1 in Scheme 2) to carbons with large condensed aromatics or small graphite layers (2,3).We could not determine the structure because the small graphite layer was so small that the (1 10) diffraction due to the width of graphite layer was not detected by XRD. The slight sharpening of the (002) diffraction with increasing H’lT in Figure 2 suggests that the three-dimensional arrangement in the disordered carbon is gradually ordered. 3.2. Electrochemical Characteristics. Figure 3 shows the charge (lithium doping)-discharge (lithium undoping) curves for the sample electrodes at the first cycle. The reversible/ irreversible capacities for pyrolyzed FTCDA as a function of HTT are shown in Figure 4. As shown in Figures 3 and 4 (sample A) prepared at 550 “C exhibits the capacity of 660 mA h g-l and a irreversible capacity of 380 mA h ggl at the first cycle. The reversible capacity at the first cycle decreases with HTT. Samples B, C, and D have the reversible capacities of 565, 405, and 295 mA h g-’, respectively. We should note a few significant features in Figure 3. First, the samples prepared
600
700
800
HTT/
“c
900
1000
Figure 4. Reversible/irreversible capacities for pyrolyzed PTCDA as a function of HTT.
at the temperature of less than 800 OC have the larger reversible capacities than graphite with a theoretical capacity of 372 mA h g-I. The reversible capacity decreases with increasing HTT as shown in Figure 4. Second, the discharge curves for samples A and B are different from those of disordered carbons such as coke and graphitic carbons. The voltage profiles of disordered carbons as coke are “slanted” such as those of samples C and D.’* The voltage profiles of graphitic carbons have several flat regions.I2 The disordered carbons prepared at 600-800 “C with large specific capacities over 400 mA h g-I show discharge curves similar to those of samples A and B.2*3,6Last, the large reversible capacities of samples A and B depend on the discharge capacities from 0.8 to 1.4 V vs Li/Li+. The reversible capacities of carbons heated above 1000 “C are mostly obtained between 0 and 1.2 V vs Li/Li+. These features indicate in conformity that the structural shift from the polymer to the disordered carbon with small graphite layer results in the decrease of the reversible capacities and the change of the lithium doping-undoping mechanism. The irreversible capacities of samples A-D at the first cycle are 380, 340, 295, and 515 mA h g-I, respectively, and are appreciably large compared to those of graphitic carbons.I2 Although the irreversible capacity decreases with increasing HTT up to 800 “C (sample C), sample D (1000 “C) has the largest irreversible capacity in the prepared samples. Generally, the irreversible capacity at the first cycle of carbon anodes is attributed to the decomposition of electrolyte at the first charge or the residual lithium in carbons after the discharge.I3 The cause for the irreversible capacities at the pyrolyzed FTCDA seems complex because the lithium doping-undoping mechanism may shift with the structural shift. The decreases of the reversible capacities for the samples were observed with the
LiUuated Polymerized Aromatics ,
,
a
,
J. Phys. Chem., Vol, 99, No. 44, 1995 16341 ,
,
SCHEME 3
,
1590cm'
, A
1540cm I
I
1800
I
1600
I
I
I
1400
Wave Number/cm-' Figure 5. IR spectra for sample A at the first charge-discharge cycle. (A) Before charge: B, 230 mA h g-l; C, 380 mA h g-I; D, 1080 mA h g-]; E, 700 mA h g-' (discharge). Vertical axis represents IR transmittance and all of the spectra are in scale. Spectra B-D are for the charged samples. Spectrum E is the sample after the most lithiated sample A is discharged up to 2 V vs Li/Li+.
charge-discharge cycle. The reversible capacities of sample A-D at the 30th cycles were 420, 370, 320, and 280 mA h g-l, respectively, and constant after the 30th cycle. Each sample showed a precipitous reduction of the irreversible capacity after the second cycle. The irreversible capacities after fifth cycle are less than 3 mA h g-l. 3.3. Lithium-Doping Mechanism at Pyrolyzed PTCDA. Figure 5 shows the IR spectra for the lithiated sample A in the range 1900-1300 cm-' at the first charge-discharge cycle. The discharge capacity at spectrum E is the reversible capacity when the most lithiated sample A was discharged up to 2 V vs Li/ Li+. We can neglect the reactions between the lithiated Sample A in the KBr disk and H20 or oxygen in an AI atmosphere during the IR measurements, because the change of each spectrum with the elapse of time had not been observed over several hours. Spectrum A for the sample that is not charged shows the broad peak due to aromatic v(C=C) around 1600 cm-I. Spectrum B at the charge capacity of 230 mA h g-l is composed of a peak at 1540 cm-' and a shoulder around 1460 cm-' and does not have the peak around 1600,cm-I. Both peaks are attributed to the vibrational modes of aromatic v(C=C). The peak intensity around 1460 cm-' increases with increasing the charge capacity, so that a broad peak is observed from 1600 to 1370 cm-' at spectrum D for the most lithiated sample A. Spectrum E for the sample after the first chargedischarge cycle shows an asymmetrical peak with a peak top at 1540 cm-' and does not coincide with spectrum A. Figure 5 indicates that the peak around 1460 cm-' is reversible and the peak at 1540 cm-I is irreversible for the first chargedischarge. The reversible peak around 1460 cm-' and the irreversible peak at 1540 cm-' were observed at the first charge-discharge cycle of sample B (650 "C) in a similar manner. However, these peaks at the first charge-discharge cycle were not detected sufficiently in the lithiated samples C and D because the IR adsorptions due to aromatic v(C=C) for these samples were very weak. At the 30th cycle, it was confirmed at samples A and B that the peak around 1460 cm-I
was reversible for the charge-discharge cycling and the peak at 1540 cm-' was independent of the charge-discharge cycling. The reversible peak can be assigned to the aromatic v(C-C) of an organometallic complex composed of lithium and aromatic ring. It is known that the aromatic v(C=C) for organometallic complexes with an ionic bond, a-bond, and n-bond between metallic atom and aromatic ring appears at 1400-1480 cm-' in the IR spectra.I3 In this study, we do not have to take n-complex into account because lithium cannot bind to aromatic ring using n-bond. The lithium-aromatic ring complexes with a-bond and ionic bond are shown in Scheme 3A,B, respectively. Phenyllithium (CsHsLi) shown in Scheme 3A is a o-complex which is formed by the reaction between metallic lithium and bromobenzene. Scheme 3B displays the formation of lithium naphthalene as an ionic complex. Condensed aromatics such as naphthalene or anthracene directly react with metallic lithium in THF or DME at room temperat~re.'~.'~ The 2s electron of lithium moves into antibonding n-orbitals in condensed aromatics at the reaction, so that condensed aromatics anions with negative charges generate and ionic complexes are formed by the anions and lithium ion after charge transfer. To charge and discharge the pyrolyzed FTCDA with Li through a-complex as shown in Scheme 3A, reversible exchange reaction of lithium ion for hydrogen of aromatic ring must be repeated electrochemically. Such a reversible exchange reaction is not probable in this study because no reversible pathway of hydrogen is found. It is more probable that the reversible doping-undoping arises from an ionic complex such as lithium naphthalene because the reaction shown in Scheme 3B will be reversible when negative charges are given for naphthalene and negative charges are removed from naphthalene anions. The pyrolyzed FTCDAs consist of the polymer of condensed aromatics and carbon mentioned in section 3.1. Samples A and B prepared at 550-650 OC have the characteristics of the polymer of condensed aromatics rather than carbon because the IR spectra for these samples have obvious IR peaks due to aromatics as shown in Figure 1. Consequently, the reversible IR peak around 1460 cm-' is expected to represent the formation of an ionic complex composed of lithium ion and the aromatic rings with negative charges in the polymer of condensed aromatics. The reversible charge-discharge of at least samples A and B is supposed to arise from the ionic complex although we could not investigate the lithium doping-undoping mechanism for the samples prepared at 800-1000 OC (samples C and D). The irreversible IR peak at 1540 cm-' at the first chargedischarge cycle relates to the large irreversible capacity at the first charge-discharge cycle. As mentioned in section 3.2, the irreversible capacity at the f i s t charge-discharge cycle is due to the decomposition of electrolyte at the charge or the residual lithium in the electrodes after the discharge.I2 The aromatic compounds which originate from these factors might cause the irreversible peak. 3.4. Structural Sh& and the Capacities of Pyrolyzed PTCDA. In lithium naphthalene shown in Scheme 3A, a lithium ion is supposed to bind to every aromatic ring.I5.l6It is well-known that alkali metals form ionic complexes with
Hara et al.
16342 J, Phys, Chem., Vol, 99, No. 44, I995 naphthalene. However alkali metals besides lithium only form the ionic complexes composed of an alkali ion and a naphthalene monoanion because the repulsion between the ions with the larger ionic radiuses than lithium ion is considerably strong. The LiC6 stage of graphite consists of a lithium bonded to three six-membered rings on graphite layer. Lithium naphthalene suggests that condensed aromatics can f o m more lithium compositions than LiC6 of graphite. The large reversible capacities of the pyrolyzed PTCDAs heated at relatively low temperatures (samples A and B) are attributed to such an ionic complex of condensed aromatics, because samples A and B are not so much the disordered carbon with small graphite layer as the polymer of condensed aromatics and considered to be charged (or discharged) through the ionic complex as lithium naphthalene. In disordered carbons as coke, the amount of lithium atoms which 6 carbon atoms can accommodate is 0.91.0 as graphite although the mechanism has not been clarified.I2 Graphite, which pyrolyzed PTCDA or carbon precursors finally shift by heat-treatment, cannot have more lithium composition than LiC6. As a result, the drastic decrease of the reversible capacity with increasing HTT in Figures 3 and 4 represents the structural shift from the polymer as carbon precursor toward graphite. The polymers of condensed aromatics as carbon precursor are different from carbons with respect to the size of condensed aromatics and the three dimensional structure in the layer-by-layer direction. Condensed aromatics or graphite layers become large and the layer-by-layer structure is ordered with progressing carbonization, so that the a axis length (La)and c axis length (15,)at graphite lattice increase and the interlayer distance (d(002))among graphite layers decreases up to 0.335 nm. Lo represents the two-dimensional size of graphite layer and the three-dimensional structure is expressed by L, and d(002). Yata et al. attributed the large capacities of polyacene heated at 600-700 "C to the three-dimensional ~tructure.~The interlayer distance of the polyacene heated at 600 "C was estimated at 0.419 nm using XRD when the XRD pattem was able to be analyzed as that of graphite. The authors strongly suggested in the report that polyacene with the reversible capacities of 450-530 mA h g-' had larger interlayer distances than graphite (0.335 nm) and the large capacities were based on the large interlayer distances. In this study, analyzing the (002) diffractions at the XRD pattems in Figure 2 in a manner similar to that for graphite, the interlayer distances ( 4 0 0 2 ) ) of samples A (550 "C) and D (1000 "C) were estimated at 0.369 and 0.360 nm, respectively. In a similar manner, the c-axis lengths (15,)of samples A and D, which are the size of the layerby-layer direction at graphite lattice, were estimated at 1.22 and 1.56 nm, respectively. These results indicate that the threedimensional structure of the pyrolyzed PTCDA grows little within the HTT from 550 to 1000 "C, although the estimated 4 0 0 2 ) and L, are relative. The decrease of the reversible capacity with increasing HTT is drastic despite the slight threedimensional growth. Hence, lithium composition of the pyrolyzed PTCDA as carbon precursor should not be simply attributed to the three-dimensional structure. The H a t o d C ratio shown in Table 1 drastically decreases with increasing HTT. The drastic decrease represents the two-dimensional growth of condensed aromatics resulting from the dehydrogenation condensation of condensed aromatics. The IR results in Figure 1 also support the two-dimensional growth as mentioned in section 3.1. Consequently, the decrease of the reversible capacities with the carbonization of the pyrolyzed PTCDA depends on the two-dimensional growth rather than the threedimensional growth. The two-dimensional size of the large
condensed aromatics is considered to be fairly small compared to the general graphite layer because the (1 10) X R D diffraction based on the size of graphite layers was not observed in the XRD patterns. It is known that graphite forms "superdense phase" of LiC2 under high pressure.I7 The superdense phase reveals that the graphite layer can link lithium atom to every carbon sixmembered ring and carbon compounds with graphite layers can form a "superdense phase". The reason that graphite cannot electrochemically realize superdense phase is probably the strong repulsion among lithium on six-membered ring. The above results strongly suggest that the two-dimensional spread of condensed carbon six-membered rings in addition to the threedimensional structure considerably influences the repulsion among lithium and the lithium composition in carbon compounds from polymerized aromatics to graphite. The investigation of pyrolyzed PTCDA shows that polymerized aromatics have far larger specific capacities than graphite. The pyrolyzed PTCDA heated at 550 "C has the capacity of 660 mA h g-' at the first cycle. It is possible that the polymers of condensed aromatics as pyrolyzed PTCDA may prove to be useful alternatives to carbon materials heated above 1000 "C for the anodes of lithium-ion cells. The details of the structures, the mechanisms for lithium doping-undoping and the decline of the capacity with the charge-discharge cycle of pyrolyzed PTCDA are under investigating.
4. Conclusions The structure, the electrochemical characteristics, and the charge-discharge mechanism for pyrolyzed PTCDA as anodes for lithium-ion cells have been investigated by IR, XRD, and charge-discharge test. There are three major findings in the present study: (1) The pyrolyzed PTCDAs with the structure of the polymer of condensed aromatics have the specific capacities of 565660 mA h g-l. ( 2 ) In the case of the pyrolyzed PTCDA heated at the temperatures of less than 650 "C, the IR spectra for the lithiated samples revealed that the reversible doping-undoping was attributed to the ionic complex as lithium naphthalene. (3) The structural shift due to the carbonization of the pyrolyzed PTCDA causes the decrease of the reversible capacity with increasing HTT. The decrease of the reversible capacity depends on the two-dimensional growth of condensed aromatics or graphite layer rather than the three-dimensional growth with the carbonization.
Acknowledgment. We are grateful to Dr. Motoya Kanda and Mr. Masayuki Suzuki for warm support and valuable discussion. References and Notes (1) Fischer, J. E. Solid State Phys. 1979, 9 , 93. (2) Ohsaki, T.; Satoh, A,; Takami, N. Proceedings of the 34th Battery Symposium in Japan, Hiroshima, 1993; p 19. ( 3 ) Yata, S . ; Kinoshita, H.; Komori, M.; Ando, N.; Kashiwamara, T.; Harada, T.; Tanaka, K.; Yamabe, T. Synth. Met. 1994, 62. 153. (4) Sato, K.; Noguchi, M.; Demachi, A,; Oki, N.; Endo, M. Science 1994, 264, 556. (5) Nishi, Y. European Patent Application 89115940.2, Aug. 1989, 29. (6) Alamgir, M.; Zuo, Q.;Abraham, K. M. J . Electrochem. SOC.1994, 141, L143. ( 7 ) Otani, S. Sekiyu 1975, 18, 606. (8) Otani, S . Tanso 1970, 61, 65. (9) Murakami, M.; Yoshimura, S. Mol. Crysr. Liq. Cryst. 1985, 118, 95.
Lithiated Polymerized Aromatics (10) Takami, N.; Satoh, A.; Hara, M.; Ohsaki, T. J . Electrochem. SOC. 1995, 142, 371. (11) Dahn, J. R.; Sligh, A. K.; Hang Shi; Reimers, J. N.; Zhong, Q.; Way, B. M. Electrochim. Acta 1993, 38, 1179. (12) Dahn, J. R.; Sligh, A. K.; Hang Shi; Way, B. M.; Wegdanz, W. J.; Reimers, J. N.; Zhong, Q.;von Sachen, U. Lithium Batteries New Materials, Developments and Perspectives; Elsevier: New York, 1993; Vol. 5, Chapter 1. (13) Sleigh, A. K.; von Sacken, U. Solid State Ionics 1992, 57, 99.
J. Phys. Chem., Vol. 99, No. 44, 1995 16343 (14) Fritz, H. P. Adv. Organomet. Chem. 1964, I , 239. (15) Schlenk, W.; Bergmann, E. Justus Liebigs Ann. Chem. 1928, 1, 463. (16) Scott, N. D.; Walker, J. F.; Hansley, V. L. J. Am. Chem. SOC.1936, 58, 2442. (17) Avdev, V. V.; Nalimova, V. A.; Semenenko, K. N. High Pressure Res. 1990, 6, 11.
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