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On the electrochemical performance of anthracite-based graphite materials as anodes in lithium-ion batteries
Fuel 89 (2010) 986–991
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On the electrochemical performance of anthracite-based graphite materials as anodes in lithium-ion batteries Ignacio Cameán a, Pedro Lavela b, José L. Tirado b, A.B. García a,* a b
Instituto Nacional del Carbón, CSIC, Francisco Pintado Fe 26, 33011 Oviedo, Spain Laboratorio de Química Inorgánica, Universidad de Córdoba, Campus de Rabanales, 14071 Córdoba, Spain
a r t i c l e
i n f o
Article history: Received 13 March 2009 Received in revised form 25 June 2009 Accepted 30 June 2009 Available online 15 July 2009 Keywords: Graphite material Anthracite Anode Lithium-ion battery Electrochemical properties
a b s t r a c t The electrochemical performance as potential negative electrode in lithium-ion batteries of graphite materials that were prepared from two Spanish anthracites of different characteristics by heat treatment in the temperature interval 2400–2800 °C are investigated by galvanostatic cycling. The interlayer spacing, d002, and crystallite sizes along the c axis, Lc, and the a axis, La, calculated from X-ray diffractometry (XRD) as well as the relative intensity of the Raman D-band, ID/It, are used to assess the degree of structural order of the graphite materials. The galvanostatic cycling are carried out in the 2.1–0.003 V potential range at a constant current and C/10 rate during 50 cycles versus Li/Li+. Larger reversible lithium storage capacities are obtained from those anthracite-based graphite materials with higher structural order and crystal orientation. Reasonably good linear correlations were attained between the electrode reversible charge and the materials XRD and Raman crystal parameters. The graphite materials prepared show excellent cyclability as well as low irreversible charge; the reversible capacity being up to 250 mA h g1. From this study, the utilization of anthracite-based graphite materials as negative electrode in lithiumion batteries appears feasible. Nevertheless, additional work should be done to improve the structural order of the graphite materials prepared and therefore, the reversible capacity. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Lithium-ion batteries are currently the energy source for most of the portable electronic devices, such as cellular phones, notebook computers, and digital cameras. Since their introduction to the market in the early 1990s, much research work has been focused on the performance of different types of carbons as anode materials [1–4]. Thus, natural graphite and several graphite materials [1–18], including powder synthetic graphites, graphitized mesocarbon microbeads, graphite fibers, carbon nanotubes, graphite composites, as well as hard [19–22] and soft carbons [23–25] have been extensively investigated to search for an ideal anode material in terms of capacity, cyclability, operational voltage and cost. Among them, graphite (mainly synthetic) with relatively high specific capacity, high cycling efficiency and low irreversible capacity are nowadays the choice of a majority of the commercially available lithium-ion batteries [1–3,26]. Highly crystalline graphite can insert up to one lithium ion for every six carbons to form the intercalation compound LiC6 what corresponds to a theoretical reversible capacity of 372 mA h g1. However, the capacity loss (irreversible) which is mainly due to the formation of the solid * Corresponding author. Tel.: +34 985118954; fax: +34 985297662. E-mail address: [email protected] (A.B. García). 0016-2361/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2009.06.034
electrolyte interface (SEI) during the first cycle on the graphite anode surface and the limited value of the reversible capacity (about 310 mA h g1) are major drawbacks [1]. The production of graphite involves the selection of carbon materials (precursors) that graphitize readily. Currently, petroleum coke is used as the main precursor material in the manufacturing of synthetic graphite [27]. Different factors, however, have prompted a research interest into other alternative precursors such as coal. Among the different classes of coal, anthracites can graphitize when heated at temperatures above 2000 °C [28]. Anthracites carbon content is over 90%, which is arranged in a macromolecular structure of condensed aromatics rings forming large units bridged or ‘‘cross-linked” by aliphatic and/or ether groups, conferring on them a certain structural order [29]. The removal of the ‘‘crosslinks” by heating the anthracite at high temperatures facilitates the reorganization of the aromatic units into graphite-like structure. Graphite materials with structural characteristics comparable to those of commercially oil-derived synthetic graphite were prepared from anthracites [28,30–33]. In the work described in this paper, the electrochemical performance as the potential negative electrode in lithium-ion batteries of graphite materials that were prepared from Spanish anthracites of different characteristics by high temperature treatment (HTT) were investigated by galvanostatic cycling of lithium test cells.
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Emphasis was placed on the relation between the structural characteristics of the materials and their anodic behaviour. The interlayer spacing, d002, and crystallite sizes along the c axis, Lc, and the a axis, La, calculated from X-ray diffractometry (XRD) as well as the relative intensity of the Raman D-band, ID/It, are used in this study to assess the degree of structural order of the graphite materials. Both XRD and Raman spectroscopy techniques have been extensively used in the structural characterization of carbon materials [34–36]. 2. Materials and methods 2.1. Materials: selection and characterization Two Spanish anthracites, denoted AF and ATO, from Villablino in north-west Spain were selected for this research. Their proximate and elemental analyses are reported in Table 1. A representative sample of both anthracites was ground to 20 lm top size for the carbonization and graphitization experiments. For comparative purposes, two petroleum-based powder synthetic graphites, named SG1 and SG2, were also characterized. These graphites are commercialized to be employed in the manufacturing of lithium-ion battery anodes. 2.2. High temperature treatments The anthracites were carbonized at 1000 °C in a tube furnace, under nitrogen flow, for 1 h with a heating rate of 2 °C min1, and then graphitized. The graphitization experiments were carried out at 2400, 2500, 2600, 2700, and 2800 °C in a graphite furnace for 1 h under argon flow. The heating rates were 25 °C min1 from room temperature to 1000 °C, 20 °C min1 in the range 1000–2000 °C and 10 °C min1 from 2000 °C to the prescribed temperature. The graphite materials thus prepared were identified by the precursor anthracite designation, and the treatment temperature, such as AF/2400 or ATO/2600. 2.3. Structural and textural characterization techniques: XRD, Raman spectroscopy, and nitrogen BET surface area The diffractograms were recorded in a Bruker D8 powder diffractometer equipped with monochromatic Cu Ka X-ray source and an internal standard of silicon powder. Diffraction data were collected by step scanning with a step size of 0.02° 2h and scan step 2 s. For each sample, three diffractograms were obtained, using a different representative batch of sample for each run. The mean interlayer spacing, d002, was evaluated from the position of the (0 0 2) peak applying Bragg’s equation. The mean crystallite sizes, Lc and La, were calculated from the (0 0 2) and (1 1 0) peaks, respectively, using the Scherrer formula, with values of K = 0.9 for Lc and 1.84 for La [37]. The broadening of diffraction peaks due to instrumental factors was corrected with the use of a silicon standard. Table 1 Proximate (dry basis, db) and elemental (dry ash-free basis, daf) analyses of ATO and AF anthracites. ATO
AF
Proximate analyses (wt%, db) Ash Volatile matter
10.12 4.12
19.74 8.72
Elemental analyses (wt%, daf) Carbon Hydrogen Nitrogen Organic sulfur Oxygen (diff.)
93.16 2.04 0.88 1.01 2.91
91.02 3.02 1.41 0.91 3.64
Raman spectra were obtained in a Raman microspectrometer HR 800 Jobin Yvon Horiba using the green line of an argon laser (k = 532 nm) as an excitation source and was equipped with a charge-coupled device (CCD) camera. The 100 objective lens of an Olympus M Plan optical microscope was used both to focus the laser beam (at a power of 25 mW) and to collect the scattered radiation. Extended scans from 1700 to 1225 cm1 were performed to obtain the first-order Raman spectra of the samples, with typical exposure times of 30 s. To assess differences within samples, at least 21 measurements were performed on different particles of each individual sample. The intensity I of the Raman bands was measured using a mixed Gaussian–Lorentzian curve-fitting procedure. Nitrogen adsorption/desorption isotherms were measured at 77 K in a Micromeritics ASAP 2420, after outgassing the samples at 250 °C. The surface area was calculated by applying the BET method to the respective nitrogen adsorption isotherm. 2.4. Cell preparation and electrochemical measurements For the electrochemical measurements, two-electrodes Swagelok-type cells were used. Metallic lithium disks of 12 mm diameter were the counter-electrodes. The working electrodes were prepared by mixing during 24 h, at 60 °C the graphite material (92 wt%) and PVDF binder (8%) in 1-methyl-2-pyrrolidone solution. The slurry was deposited on a copper foil of 12 mm diameter and then vacuum dried at 120 °C for 2 h. Glass micro-fiber disks impregnated with 1 M LiPF6 (EC:DEC, 1:1, w/w) electrolyte solution were the electrode separators. All cells were assembled in an MBraun dry box under argon atmosphere and water content below 1 ppm. The galvanostatic cycling was carried out in the 2.1–0.003 V potential range at a constant current of C/10 (corresponding to a capacity of 372 mA h g1 in 10 h) during 50 cycles versus Li/Li+, using a Biologic multichannel VMP2/Z potentiostat/galvanostat.
3. Results and discussion 3.1. Structural characteristics of the graphite materials prepared The mean interlayer spacing, d002, the mean crystallite sizes, Lc and La, and the relative intensity of the Raman D-band (ID/It, where It = IG + ID + ID0 ) of the graphite materials prepared from AF and ATO anthracites by heat treatment in the temperature interval 2400– 2800 °C are summarized in Table 2. Data corresponding to the reference synthetic graphites SG1 and SG2 are also reported in this table. Experimental errors are not included in the table for clarity. Typical standard errors of crystallite sizes are <1% and <4% of the reported values for Lc and La, respectively. The d002 values are much
Table 2 Interplanar distance d002, crystallite sizes Lc and La, and Raman ratio ID/It of the graphite materials prepared from ATO and AF anthracites by HTT and of the synthetic graphites SG1 and SG2. Material
d002 (nm)
Lc (nm)
La (nm)
ID/It (%)
ATO/2400 ATO/2500 ATO/2600 ATO/2700 ATO/2800 AF/2400 AF/2500 AF/2600 AF/2700 AF/2800 SG1 SG2
0.3412 0.3403 0.3402 0.3393 0.3387 0.3382 0.3382 0.3373 0.3370 0.3369 0.3374 0.3379
8.0 9.3 9.5 11.2 12.8 14.1 14.6 18.8 21.1 21.6 33.6 22.0
21.2 25.7 27.6 34.1 39.1 44.6 42.0 46.7 49.2 48.7 63.0 53.0
29.7 28.0 28.1 22.1 23.9 16.5 18.9 17.7 14.2 12.4 28.7 10.0
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more precise, with standard errors of <0.01%. The relative intensity of the Raman D-band ID/It (It = ID + IG + ID0 ) was calculated with standard errors lower than 8%. The analysis of the XRD data of the materials that have been prepared from the anthracites showed that, as the treatment temperature increases, a significant growth of the crystallite sizes occurs. In a parallel way, the interlayer spacing, d002, decreases. For example, crystallite sizes in the c direction, Lc, of 14, 19, and 22 nm were calculated for AF/ 2400, AF/2600, and AF/2800 materials; the corresponding interlayer spacing, d002, being 0.3382, 0.3373, and 0.3369 nm. The variation with the temperature of the relative intensity of the Raman band, ID/It, follows a similar tendency. A decay of this Raman parameter with increasing temperature was detected. These facts are associated with the improvement of both the degrees of structural order (three-dimensional crystalline structure) and of crystalline orientation of the materials [34–36,38,39]. A comparative analysis of the structural data of the materials prepared from the anthracites appearing in Table 2 leads to the conclusion that materials with higher degree of structural order and crystal orientation were obtained from AF anthracite. Thus, values of d002 and ID/It parameters of 0.3369 and 0.3387 nm, and 12% and 24% were measured for AF/2800 and ATO/2800 materials, respectively. This significant difference in the ability of the anthracites to graphitize has been previously discussed attending to their different characteristics (composition, microstructure, mineral matter) [28,31,32]. Among them, the anthracite mineral matter was found to act as a graphitization catalyst [28,31–33,40,41], thus explaining the more graphite-like materials obtained in this work from AF anthracite (Tables 1 and 2). According to the structural data in Table 2, the HTT of the anthracites can result in graphite materials that have structural characteristics comparable to those of the GS2 graphite of reference. The main structural difference between the GS1 reference graphite and the more graphite-like materials prepared from the anthracites is related to the Lc and La sizes of the coherent domains (Table 2). Thus, the crystallite sizes of the ATO/2800 and AF/2800 materials are lower than that of SG1 graphite. However, this reference material shows a much higher value of the Raman ratio, ID/It, which is used as an indicator of the bi-dimensional order of carbon materials [34–36,39]. It is important to mention that, apart from the La diameter of the coherent domains [39,42] and the degree of crystalline orientation [43], there are other factors that have been suggested to contribute to the Raman D band intensity, such as the presence of disordered carbon or doping [34,43–45] as well as the interstitials or sp3 carbons [42], thus explaining the higher value of ID/It calculated for the SG1 graphite as compared to those of some of the graphite materials prepared from AF and ATO anthracites. 3.2. Electrochemical characterization (galvanostatic cycling) of the graphite anode materials The first voltage profiles of discharge–charge cycle and the second discharge of the lithium cells using ATO/2800 and AF/2800 graphite materials as working electrodes are shown in Fig. 1a. For comparison, the data corresponding to the reference synthetic graphite SG1 appears in the same figure. At the beginning of the discharge, the cell voltage drops quickly to 0.8 V (versus Li/Li+) to form a short plateau which is attributed to the solid electrolyte interface (SEI) film formation on the graphite surface as a result of the electrolyte decomposition [46], and then gradually decreases to the point at what the lithium insertion into the electrode starts. Such voltage profiles are characteristics of graphite materials that do not show exfoliation [1,8,47,48]. As can be seen in Fig. 1b, lithium intercalation in the electrode material takes place in the voltage range below 0.2 V vs. Li/Li+. The Li+ insertion profile of the
graphite material prepared from AF anthracite, AF/2800, was much the same to that of the reference synthetic graphite, SG1, except shorter plateaus at approximately 0.18, 0.10, and 0.06 V. Considering that the structural differences between AF/2800 and the reference graphite, SG1, are much associated with the values of Lc and La, the size of the crystal domain appears as a significant factor governing the extent of the first Li+ intercalation into the graphene layers, thus explaining the different profiles showed by these materials (Fig. 1b, Table 2). A comparison of the differential capacity (absolute value, derived from the first cycle discharge data) versus potential plots of AF/2400 and AF/2800 graphite materials which have been prepared from the same precursor (AF anthracite) makes this fact more evident (Fig. 1c). Thus, although three potential peaks during lithium intercalation can be observed on both materials, those corresponding to AF/2800 with larger mean crystallite sizes, La and Lc, are significantly more intensive. Unlike AF/ 2800 and SG1, only two lithium intercalation stages at the lowest potentials were slightly detectable in the profile of ATO/2800 in Fig. 1b. However, as can be seen in Fig. 1d which shows the differential capacity plot, the lithium intercalation in this material also occurs in three stages at approximately 0.17, 0.09, and 0.06 V. As expected, ATO/2800 material with a lower degree of structural order as compared to that of AF/2800 materials lead to smaller potential peaks. The irreversible charge losses (irreversible capacity, Cirr) during the first discharge–charge cycle of the materials studied are reported in Table 3. Both series of AF/2400–2800 and ATO/2400– 2800 graphite electrodes show a narrow and similar range of irreversible capacity percentages, the absolute values of this electrochemical parameter being low and mostly smaller than that corresponding to the synthetic graphites of reference, SG1 and SG2. Thus, values of Cirr in the ranges 12–19% and 14–18% were, respectively, calculated for these two series of electrodes. It is generally accepted that the irreversible capacity is essentially due to the formation of the solid electrolyte interface on the surface of the graphite electrode [47]. Other surface side reactions may also contribute to this capacity loss [48–50]. Because of the SEI film covers the electrode surface exposed to the electrolyte solution, this irreversible consumption of Li has been related with the surface area of the electrode material [46,48–51]. Specifically, proportionality with the BET specific surface area was found in graphites from the same family with comparable nanotextures [52]. However, as can be seen in Table 3 there is not dependence between these two parameters for the graphite materials prepared from AF or ATO anthracites. It has been previously reported that the value of the irreversible capacity is directly related with the active surface area (ASA) of the carbon material [49,50]. The ASA corresponds to the cumulated area of the different type of defects present on the carbon surface such as stacking faults, dislocations, and vacancies, thus being an indirect estimation of the degree of structural order of the material. A comparison of the Cirr data with the XRD and Raman parameters reveals that there is a certain tendency of the electrode irreversible capacity to decrease as both the degrees of structural order and crystal orientation increases for ATO/2400–2800 series of graphite materials (Tables 2 and 3). However, any proportionality was found in the case of AF/2400–2800 series. In contrast, these materials and the synthetic graphites with higher degree of structural order also show higher Cirr values. Taking into account that exfoliation was not observed during the lithiation of AF/2400–2800 graphite electrodes, other factors different than the degree of structural order and thus the ASA value should influence on the irreversible charge loss. The cycling behaviour of AF/2400–2800 and ATO-2400/2800 graphite materials is presented in Fig. 2a and b. Those corresponding to the SG1 and SG2 reference materials are included in Fig. 2a. As observed, all of the electrodes show a significant stable capacity
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0.6
(a)
ATO/2800 AF/2800 SG1
2.0
Potential (V) vs Li/Li+
Potential (V) vs Li/Li +
2.4
1.6 1.2 0.8 0.4 0.0 0.0
0.2
0.4
0.6
0.8
1.0
0.4 0.3 0.2 0.1 0.0
1.2
0.1
0.3
0.5
8000
(c)
AF/2400 AF/2800
6000 0.10 V
4000
2000 0.18 V
0 0.1
0.2
0.3
0.7
0.9
1.1
x in LixC6 Differential capacity (mAhg -1V-1)
Differential capacity (mAhg-1V-1)
x in LixC6
0.06 V
(b)
ATO/2800 AF/2800 SG1
0.5
0.4
Potencial (V) vs Li/Li
0.5
0.6
+
8000
(d)
ATO/2800
6000
4000 0.06 V 0.09 V
2000
0.17 V
0 0.1
0.2
0.3
0.4
0.5
0.6
Potential (V) vs Li/Li +
Fig. 1. Galvanostatic first discharge–charge cycle and second discharge profiles of ATO/2800, AF/2800, and SG1 graphite materials (a), first Li+ intercalation/de-intercalation in ATO/2800, AF/2800, and SG1 graphite materials (b), and differential capacity from the first cycle discharge vs. potential of AF/2400 and AF/2800 (c), and of ATO/2800 (d).
Table 3 First cycle irreversible capacity (Cirr) and nitrogen BET specific surface area data of the graphite materials prepared from ATO and AF anthracites by HTT and of the synthetic graphites SG1 and SG2. Material
Cirr (mA h/g)
Cirr (%)
BET surface area (m2/g)
ATO/2400 ATO/2500 ATO/2600 ATO/2700 ATO/2800 AF/2400 AF/2500 AF/2600 AF/2700 AF/2800 SG1 SG2
37 30 31 31 28 38 44 53 48 42 49 49
19 15 16 14 12 15 14 18 16 14 12 15
4.9 5.6 5.1 4.7 4.9 6.8 5.3 5.5 6.0 5.6 7.5
Cirr (%) = 100(charge first Li+ intercalation) (charge first Li+ de-intercalation)/ (charge first Li+ intercalation).
on prolonged cycling. In contrast, the reversible capacity of the synthetic graphite of reference, SG1, decreases monotonically with cycling, suggesting the exfoliation of the graphene layers (Fig. 2a). By comparing the galvanostatic cycling results and the crystalline parameters of the graphite materials prepared from the anthracites in Table 2, it is evident that those with higher structural order provide larger reversible lithium storage capacity. As an example, values of approximately 170 and 250 mA h g1 were calculated for ATO/2800 and AF/2800 with crystallites sizes in the c direction,
Lc, of approximately 13 and 22 nm, respectively; the corresponding interlayer spacing being 0.3387 and 0.3369 nm. To explore a possible correlation between the reversible capacity of the electrodes and the degree of structural order of the graphite electrode materials as estimated from XRD and Raman spectroscopy, linear regression analyses were performed with the data appearing in Fig. 2 (after 20 cycles) and Table 2. This type of analysis gave equations with correlation coefficients of R2 = 0.954, 0.973, 0.920, and 0.947 for the interlayer spacing, d002, the thickness of the crystallite, Lc, the width of the crystallite, La, and Raman parameter, ID/ It, respectively, of the graphite materials prepared from the anthracites in this work. On the basis of these results, both the degrees of structural order and crystal orientation of the graphite materials prepared from the anthracites seems to influence the reversible electrochemical intercalation of lithium. When the data of the SG1 and SG2 graphites of reference were included, the correlation was restricted to the materials crystallite sizes. In this approach, values of R2 of 0.924 for Lc and 0.902 for La were found. The dependence of the electrochemical intercalation of lithium in well-ordered (graphite-like) materials prepared from different precursors on their crystal structure has been previously studied by other authors [1,53,54]. The crystal thickness, Lc, was reported to be the most important factor affecting the extent of the material reversible capacity. A tendency of these materials capacity to decrease with the crystallite thickness with no evident dependency on the material crystal length, La, was observed; the minimum capacities being showed by those with Lc values of 10 nm. Nevertheless, no specific correlation between the electrode capacity and the crystal thickness of the graphite material was established in
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300
(a)
AF/2400 AF/2500 AF/2600 AF/2700 AF/2800 SG1 SG2
400 350 300 250 200 150
10
20
30
40
50
Cycle number
(b) Dis. capacity (mAhg-1)
Dis. capacity (mAhg-1)
450
ATO/2400 ATO/2500 ATO/2600 ATO/2700 ATO/2800
250
200
150
100
10
20
30
40
50
Cycle number
Fig. 2. Extended galvanostatic cycling of AF/2400–2800, SG1, and SG2 graphite materials (a) and of ATO/2400–2800 graphite materials (b).
these studies. In fact, significant larger capacities were provided by some of the graphite-like materials studied with lower or similar Lc values, thus inferring the influence on the graphite material electrochemical performance of other structural factors different than the crystal thickness as shown in those prepared from AF and ATO anthracites. 4. Conclusions Larger reversible lithium storage capacities were obtained from those anthracite-based graphite materials with higher structural order and crystal orientation. Reasonably good linear correlations were attained between the electrode reversible charge and the XRD (Lc, La, d002) and Raman (ID/It) crystal parameters of the graphite materials prepared from AF and ATO anthracites. By including graphites prepared from other precursors the correlation was restricted to the crystallite sizes. The graphite materials prepared from anthracites high temperature treatment showed excellent cyclability as well as low irreversible charge loss; the reversible capacity being up to 250 mA h g1. On the basis of that, the utilization of these materials as negative electrode in lithium-ion batteries appears feasible. Nevertheless, additional work should be done to improve the structural order of the graphite materials prepared and therefore, the reversible capacity. Acknowledgements Financial support from the Spanish Ministry of Science and Innovation MICINN (under Project MAT2004-01094), and FICYT (under Project PC07-014)) is gratefully acknowledged. I. Cameán thanks MICINN for a personal grant to develop the work. References [1] Endo M, Kim C, Nishimura K, Fujino T, Miyashita K. Recent development of carbon materials for Li ion batteries. Carbon 2000;38:183–97. [2] Noel M, Sryanarayanan V. Role of carbon host lattices in Li-ion intercalation/ de-intercalation processes. J Power Sources 2002;111:193–209. [3] Wakihara M. Recent development in lithium ion batteries. Mater Sci Eng 2001;R33:109–34. [4] Bruce PG, Scrosati B, Tarascon J-M. Nanomaterials for rechargeable lithium batteries. Angew Chem 2008;47:2930–46. [5] Guoping W, Bolan Z, Min Y, Xiaoluo X, Meizheng Q, Zuolong Y. A modified graphite anode with high initial efficiency and excellent cycle life expectation. Solid State Ion 2005;176:905–9. [6] Wu Y, Jiang C, Wan C, Tsuchida E. A green method for the preparation of anode materials for lithium ion batteries. J Mater Chem 2001;11:1233–6. [7] Yang S, Song H, Chen X. Electrochemical performance of expanded mesocarbon microbeads as anode material for lithium-ion batteries. Electrochem Commun 2006;8:137–42.
[8] Baek J-K, Lee H-Y, Jang S-W, Lee S-M. Electrochemical performance of modified synthetic graphite for lithium ion batteries. J Mater Sci 2005;40: 347–53. [9] Pan Q, Guo K, Wang L, Fang S. Novel modified graphite as anode material for lithium ion batteries. J Mater Chem 2002;12:1833–8. [10] Yang Z, Feng Y, Li Z, Sang S, Zhou Y, Zeng L. An investigation of lithium intercalation into the carbon nanotubes by a.c. impedance. J Electroanalyt Chem 2005;580:340–7. [11] Lee YH, Pan KC, Lin YY, Kumar TP, Fey GTK. Lithium intercalation in graphites precipitated from pig iron melts. Mater Chem Phys 2003;82:750–7. [12] Yao J, Wang GX, Ahn J-H, Liu HK, Dou SX. Electrochemical studies of graphitized mesocarbon microbeads as anode in lithium-ion cells. J Power Sources 2003;114:292–7. [13] Buqa H, Golob P, Winter M, Besenhard JO. Modified carbons for improved anodes in lithium ion cells. J Power Sources 2001;97–98:122–5. [14] Barsukov VZ, Il’in EA, Likhmitskii KV, Zayats OV, Tverdokhleb VS, Kryukov VV, et al. Graphites from the zavalie deposit as active materials fro lithium-ion batteries. Russ J Electrochem 2008;44:579–84. [15] Balasooriya NWB, Touzain Ph, Bandaranayake PWSK. Lithium electrochemical intercalation into mechanically and chemically treated Sri Lanka graphite. J Phys Chem Solids 2006;67:1213–7. [16] Khomenko VG, Barsukov VZ. Characterization of silicon- and carbon-based composite anodes for lithium-ion batteries. Electrochim Acta 2007;52:2829–40. [17] Lee J-H, Kim W-J, Kim J-Y, Lim S-H, Le S-M. Spherical silicon/graphite/carbon composites as anode material for lithium-ion batteries. J Power Sources 2008;176:353–8. [18] Khomenko VG, Barsukov VZ, Doninger JE, Barsukov IV. Lithium-ion batteries based on carbon–silicon–graphite composite anodes. J Power Sources 2007;165:598–606. [19] Chevallier F, Gautier S, Salvetat JP, Clinard C, Frackowiak E, Rouzaud JN, et al. Effects of post-treatments on the performance of hard carbons in lithium cells. J Power Sources 2001;97–98:143–5. [20] Zheng T, Xing W, Dahn JR. Carbons prepared from coals for anodes of lithiumion cells. Carbon 1996;34:1501–7. [21] Kim Y-J, Yang H, Yoon S-H, Korai Y, Mochida I, Ku C-H. Anthracite as a candidate for lithium ion battery anode. J Power Sources 2003;113:157–65. [22] Fransson L, Eriksson T, Edström K, Gustafsson T, Thomas JO. Influence of carbon black and binder on Li-ion batteries. J Power Sources 2001;101:1–9. [23] Bonino F, Brutti S, Piana M, Natale S, Scrosati B, Gherghel L, et al. Structural and electrochemical studies of a hexaphenylbenzene pyrolysed sofá carbon as anode material in lithium batteries. Electrochim Acta 2006;51:3407–12. [24] Concheso A, Santamaría R, Menéndez R, Jiménez-Mateos JM, Alcántara R, Lavela P, et al. Iron-composites as electrode materials in lithium batteries. Carbon 2006;44:1762–72. [25] Machnikowski J, Grzyb B, Weber JV, Frackowiak E, Rouzaud JN, Béguin F. Structural and electrochemical characterisation of nitrogen enriched carbon produced by the co-pyrolysis of coal-tar pich with polyacrylonitrile. Electrochim Acta 2004;49:423–32. [26] Olson DW, 2007. Graphite, 2006 Mineral Year Book. US Geological Survey, US Department of Interior, Washington. [27] Inagaki M. Applications of polycrystalline graphite. In: Delhaès P, editor. Graphite and precursors. Amsterdam: Gordon and Breach; 2001. p. 179–98. [28] Oberlin A, Terriere G. Graphitization studies of anthracites by high resolution transmission electron microscopy. Carbon 1975;13:367. [29] van Krevelen DV. Coal: typology, physics, chemistry and constitution. Amsterdam: Elsevier; 1993. [30] Bustin RM, Rouzaud JN, Ross JV. Natural graphitization of anthracites – experimental considerations. Carbon 1995;33:679–91. [31] Atria JV, Rusinko F, Schobert HH. Structural ordering of Pennsylvania anthracites on heat treatment to 2000–2800 degrees C. Energy Fuels 2002;16:1343–7.
I. Cameán et al. / Fuel 89 (2010) 986–991 [32] Gonzalez D, Montes-Morán MA, Suarez-Ruiz I, Garcia AB. Structural characterization of graphite materials prepared from anthracites of different characteristics: a comparative análisis. Energy Fuels 2004;18:365–70. [33] Gonzalez D, Montes-Morán MA, Garcia AB. Influence of inherent coal mineral matter on the structural characteristics of graphite materials prepared from anthracites. Energy Fuels 2005;19:263–9. [34] Cuesta A, Dhamelincourt P, Laureyns J, Martinez-Alonso A, Tascon JMD. Comparative performance of X-ray diffraction and Raman microprobe techniques for the study of carbon materials. J Mater Chem 1998;8:2875–9. [35] Cuesta A, Dhamelincourt P, Laureyns J, Martinez-Alonso A, Tascón JMD. Raman microprobe studies of carbon materials. Carbon 1994;32:1523–32. [36] Montes-Morán MA, Young RJ. Raman spectroscopy study of HM carbon fibres: effect of the plasma treatment on the interfacial properties of single fibre/ epoxy composites-Part I: fibre characterisation. Carbon 2002;40:845–55. [37] Biscoe J, Warren B. An X-ray study of carbon blacks. J Appl Phys 1942;13:364–71. [38] Franklin RE. The structure of graphitic carbons. Acta Crystal 1951;4:253. [39] Tuinstra F, Koening JL. Raman spectra of graphite. J Chem Phys 1970;53:1126–30. [40] Evans EL, Jenkins JL, Thomas JM. Direct electron microscopic studies of graphitic regions in heat-treated coals and coal extracts. Carbon 1972;10:637–42. [41] Cabielles M, Montes-Morán MA, Garcia AB. Structural study of graphite materials prepared by HTT of unburned carbon concentrated from coal combustion fly ashes. Energy Fuels 2008;22:1239–43. [42] Beny C, Rouzaud JN. Characterization of carbonaceous materials by correlated electron and optical microscopy and Raman microspectroscopy. Scan Electron Microsc 1985:119–32. [43] Katagiri G, Ishida H, Ishitani A. Raman spectra of graphite edges planes. Carbon 1988;26:565–71.
991
[44] Afanasyeva NI, Jawhari T, Klimenko IV, Zhuravleva TS. Micro-Raman spectroscopy measurements on carbon fibers. Vibrat Spectrosc 1996;11:79–83. [45] Nistor LC, van Landuyt J, Ralchenko VG, Kononenko TV, Obraztosova ED, Strelnitsky VE. Direct observation of laser-induced crystallization of A–C–H films. Appl Phys 1994;A58:137–44. [46] Fong R, von Sacken U, Dahn JR. Studies of lithium intercalation into carbons using nonaqueous electrochemical-cells. J Electrochem Soc 1990;137:2009–13. [47] Guerin K, Fevrier-Bouvier A, Flandris S, Couzi M, Simon B, Biensan P. Effect of graphite crystal structure on lithium electrochemical intercalation. J Electrochem Soc 1999;146:3660–5. [48] Spahr ME, Wilhelm H, Palladino T, Dupont-Pavlovsky N, Goers D, Joho F, et al. The role of graphite surface group on graphite exfoliation during electrochemical lithium insertion. J Power Sources 2003;119–121:543–9. [49] Béguin F, Chevallier F, Vix-Guterl C, Saadallah S, Bertagna V, Rouzaud JN, et al. Correlation of the irreversible lithium capacity with the active area of modified carbons. Carbon 2005;43:2160–7. [50] Novák P, Ufheil J, Buqa H, Krumeich F, Spahr ME, Goers D, et al. The importance of the active surface area of graphite materials in the first lithium intercalation. J Power Sources 2007;174:1082–5. [51] Aurbach D, Teller H, Koltypin M, Levi E. On the behaviour of different types of graphite anodes. J Power Sources 2003;119–121:2–7. [52] Winter M, Novak P, Monnier J. Graphites for lithium ion cells: the correlation of the first cycle charge loss with the BET surface area. J Electrochem Soc 1998;145:428–36. [53] Dahn JR, Sleigh AK, Shi H, Reimers JN, Zhong Q, Way BM. Dependence of the electrochemical intercalation of lithium in carbons on the crystal structure of the carbon. Electrochim Acta 1993;38:1179–91. [54] Endo M, Nishimura Y, Takahashi T, Takeuchi K, Dresselhaus MS. Lithium storage behaviour for various kinds of carbon anodes in Li ion secondary battery. J Phys Chem Solids 1996;57:725–8.
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On the electrochemical performance of anthracite-based graphite materials as anodes in lithium-ion batteries Ignacio Cameán a, Pedro Lavela b, José L. Tirado b, A.B. García a,* a b
Instituto Nacional del Carbón, CSIC, Francisco Pintado Fe 26, 33011 Oviedo, Spain Laboratorio de Química Inorgánica, Universidad de Córdoba, Campus de Rabanales, 14071 Córdoba, Spain
a r t i c l e
i n f o
Article history: Received 13 March 2009 Received in revised form 25 June 2009 Accepted 30 June 2009 Available online 15 July 2009 Keywords: Graphite material Anthracite Anode Lithium-ion battery Electrochemical properties
a b s t r a c t The electrochemical performance as potential negative electrode in lithium-ion batteries of graphite materials that were prepared from two Spanish anthracites of different characteristics by heat treatment in the temperature interval 2400–2800 °C are investigated by galvanostatic cycling. The interlayer spacing, d002, and crystallite sizes along the c axis, Lc, and the a axis, La, calculated from X-ray diffractometry (XRD) as well as the relative intensity of the Raman D-band, ID/It, are used to assess the degree of structural order of the graphite materials. The galvanostatic cycling are carried out in the 2.1–0.003 V potential range at a constant current and C/10 rate during 50 cycles versus Li/Li+. Larger reversible lithium storage capacities are obtained from those anthracite-based graphite materials with higher structural order and crystal orientation. Reasonably good linear correlations were attained between the electrode reversible charge and the materials XRD and Raman crystal parameters. The graphite materials prepared show excellent cyclability as well as low irreversible charge; the reversible capacity being up to 250 mA h g1. From this study, the utilization of anthracite-based graphite materials as negative electrode in lithiumion batteries appears feasible. Nevertheless, additional work should be done to improve the structural order of the graphite materials prepared and therefore, the reversible capacity. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Lithium-ion batteries are currently the energy source for most of the portable electronic devices, such as cellular phones, notebook computers, and digital cameras. Since their introduction to the market in the early 1990s, much research work has been focused on the performance of different types of carbons as anode materials [1–4]. Thus, natural graphite and several graphite materials [1–18], including powder synthetic graphites, graphitized mesocarbon microbeads, graphite fibers, carbon nanotubes, graphite composites, as well as hard [19–22] and soft carbons [23–25] have been extensively investigated to search for an ideal anode material in terms of capacity, cyclability, operational voltage and cost. Among them, graphite (mainly synthetic) with relatively high specific capacity, high cycling efficiency and low irreversible capacity are nowadays the choice of a majority of the commercially available lithium-ion batteries [1–3,26]. Highly crystalline graphite can insert up to one lithium ion for every six carbons to form the intercalation compound LiC6 what corresponds to a theoretical reversible capacity of 372 mA h g1. However, the capacity loss (irreversible) which is mainly due to the formation of the solid * Corresponding author. Tel.: +34 985118954; fax: +34 985297662. E-mail address: [email protected] (A.B. García). 0016-2361/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2009.06.034
electrolyte interface (SEI) during the first cycle on the graphite anode surface and the limited value of the reversible capacity (about 310 mA h g1) are major drawbacks [1]. The production of graphite involves the selection of carbon materials (precursors) that graphitize readily. Currently, petroleum coke is used as the main precursor material in the manufacturing of synthetic graphite [27]. Different factors, however, have prompted a research interest into other alternative precursors such as coal. Among the different classes of coal, anthracites can graphitize when heated at temperatures above 2000 °C [28]. Anthracites carbon content is over 90%, which is arranged in a macromolecular structure of condensed aromatics rings forming large units bridged or ‘‘cross-linked” by aliphatic and/or ether groups, conferring on them a certain structural order [29]. The removal of the ‘‘crosslinks” by heating the anthracite at high temperatures facilitates the reorganization of the aromatic units into graphite-like structure. Graphite materials with structural characteristics comparable to those of commercially oil-derived synthetic graphite were prepared from anthracites [28,30–33]. In the work described in this paper, the electrochemical performance as the potential negative electrode in lithium-ion batteries of graphite materials that were prepared from Spanish anthracites of different characteristics by high temperature treatment (HTT) were investigated by galvanostatic cycling of lithium test cells.
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Emphasis was placed on the relation between the structural characteristics of the materials and their anodic behaviour. The interlayer spacing, d002, and crystallite sizes along the c axis, Lc, and the a axis, La, calculated from X-ray diffractometry (XRD) as well as the relative intensity of the Raman D-band, ID/It, are used in this study to assess the degree of structural order of the graphite materials. Both XRD and Raman spectroscopy techniques have been extensively used in the structural characterization of carbon materials [34–36]. 2. Materials and methods 2.1. Materials: selection and characterization Two Spanish anthracites, denoted AF and ATO, from Villablino in north-west Spain were selected for this research. Their proximate and elemental analyses are reported in Table 1. A representative sample of both anthracites was ground to 20 lm top size for the carbonization and graphitization experiments. For comparative purposes, two petroleum-based powder synthetic graphites, named SG1 and SG2, were also characterized. These graphites are commercialized to be employed in the manufacturing of lithium-ion battery anodes. 2.2. High temperature treatments The anthracites were carbonized at 1000 °C in a tube furnace, under nitrogen flow, for 1 h with a heating rate of 2 °C min1, and then graphitized. The graphitization experiments were carried out at 2400, 2500, 2600, 2700, and 2800 °C in a graphite furnace for 1 h under argon flow. The heating rates were 25 °C min1 from room temperature to 1000 °C, 20 °C min1 in the range 1000–2000 °C and 10 °C min1 from 2000 °C to the prescribed temperature. The graphite materials thus prepared were identified by the precursor anthracite designation, and the treatment temperature, such as AF/2400 or ATO/2600. 2.3. Structural and textural characterization techniques: XRD, Raman spectroscopy, and nitrogen BET surface area The diffractograms were recorded in a Bruker D8 powder diffractometer equipped with monochromatic Cu Ka X-ray source and an internal standard of silicon powder. Diffraction data were collected by step scanning with a step size of 0.02° 2h and scan step 2 s. For each sample, three diffractograms were obtained, using a different representative batch of sample for each run. The mean interlayer spacing, d002, was evaluated from the position of the (0 0 2) peak applying Bragg’s equation. The mean crystallite sizes, Lc and La, were calculated from the (0 0 2) and (1 1 0) peaks, respectively, using the Scherrer formula, with values of K = 0.9 for Lc and 1.84 for La [37]. The broadening of diffraction peaks due to instrumental factors was corrected with the use of a silicon standard. Table 1 Proximate (dry basis, db) and elemental (dry ash-free basis, daf) analyses of ATO and AF anthracites. ATO
AF
Proximate analyses (wt%, db) Ash Volatile matter
10.12 4.12
19.74 8.72
Elemental analyses (wt%, daf) Carbon Hydrogen Nitrogen Organic sulfur Oxygen (diff.)
93.16 2.04 0.88 1.01 2.91
91.02 3.02 1.41 0.91 3.64
Raman spectra were obtained in a Raman microspectrometer HR 800 Jobin Yvon Horiba using the green line of an argon laser (k = 532 nm) as an excitation source and was equipped with a charge-coupled device (CCD) camera. The 100 objective lens of an Olympus M Plan optical microscope was used both to focus the laser beam (at a power of 25 mW) and to collect the scattered radiation. Extended scans from 1700 to 1225 cm1 were performed to obtain the first-order Raman spectra of the samples, with typical exposure times of 30 s. To assess differences within samples, at least 21 measurements were performed on different particles of each individual sample. The intensity I of the Raman bands was measured using a mixed Gaussian–Lorentzian curve-fitting procedure. Nitrogen adsorption/desorption isotherms were measured at 77 K in a Micromeritics ASAP 2420, after outgassing the samples at 250 °C. The surface area was calculated by applying the BET method to the respective nitrogen adsorption isotherm. 2.4. Cell preparation and electrochemical measurements For the electrochemical measurements, two-electrodes Swagelok-type cells were used. Metallic lithium disks of 12 mm diameter were the counter-electrodes. The working electrodes were prepared by mixing during 24 h, at 60 °C the graphite material (92 wt%) and PVDF binder (8%) in 1-methyl-2-pyrrolidone solution. The slurry was deposited on a copper foil of 12 mm diameter and then vacuum dried at 120 °C for 2 h. Glass micro-fiber disks impregnated with 1 M LiPF6 (EC:DEC, 1:1, w/w) electrolyte solution were the electrode separators. All cells were assembled in an MBraun dry box under argon atmosphere and water content below 1 ppm. The galvanostatic cycling was carried out in the 2.1–0.003 V potential range at a constant current of C/10 (corresponding to a capacity of 372 mA h g1 in 10 h) during 50 cycles versus Li/Li+, using a Biologic multichannel VMP2/Z potentiostat/galvanostat.
3. Results and discussion 3.1. Structural characteristics of the graphite materials prepared The mean interlayer spacing, d002, the mean crystallite sizes, Lc and La, and the relative intensity of the Raman D-band (ID/It, where It = IG + ID + ID0 ) of the graphite materials prepared from AF and ATO anthracites by heat treatment in the temperature interval 2400– 2800 °C are summarized in Table 2. Data corresponding to the reference synthetic graphites SG1 and SG2 are also reported in this table. Experimental errors are not included in the table for clarity. Typical standard errors of crystallite sizes are <1% and <4% of the reported values for Lc and La, respectively. The d002 values are much
Table 2 Interplanar distance d002, crystallite sizes Lc and La, and Raman ratio ID/It of the graphite materials prepared from ATO and AF anthracites by HTT and of the synthetic graphites SG1 and SG2. Material
d002 (nm)
Lc (nm)
La (nm)
ID/It (%)
ATO/2400 ATO/2500 ATO/2600 ATO/2700 ATO/2800 AF/2400 AF/2500 AF/2600 AF/2700 AF/2800 SG1 SG2
0.3412 0.3403 0.3402 0.3393 0.3387 0.3382 0.3382 0.3373 0.3370 0.3369 0.3374 0.3379
8.0 9.3 9.5 11.2 12.8 14.1 14.6 18.8 21.1 21.6 33.6 22.0
21.2 25.7 27.6 34.1 39.1 44.6 42.0 46.7 49.2 48.7 63.0 53.0
29.7 28.0 28.1 22.1 23.9 16.5 18.9 17.7 14.2 12.4 28.7 10.0
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more precise, with standard errors of <0.01%. The relative intensity of the Raman D-band ID/It (It = ID + IG + ID0 ) was calculated with standard errors lower than 8%. The analysis of the XRD data of the materials that have been prepared from the anthracites showed that, as the treatment temperature increases, a significant growth of the crystallite sizes occurs. In a parallel way, the interlayer spacing, d002, decreases. For example, crystallite sizes in the c direction, Lc, of 14, 19, and 22 nm were calculated for AF/ 2400, AF/2600, and AF/2800 materials; the corresponding interlayer spacing, d002, being 0.3382, 0.3373, and 0.3369 nm. The variation with the temperature of the relative intensity of the Raman band, ID/It, follows a similar tendency. A decay of this Raman parameter with increasing temperature was detected. These facts are associated with the improvement of both the degrees of structural order (three-dimensional crystalline structure) and of crystalline orientation of the materials [34–36,38,39]. A comparative analysis of the structural data of the materials prepared from the anthracites appearing in Table 2 leads to the conclusion that materials with higher degree of structural order and crystal orientation were obtained from AF anthracite. Thus, values of d002 and ID/It parameters of 0.3369 and 0.3387 nm, and 12% and 24% were measured for AF/2800 and ATO/2800 materials, respectively. This significant difference in the ability of the anthracites to graphitize has been previously discussed attending to their different characteristics (composition, microstructure, mineral matter) [28,31,32]. Among them, the anthracite mineral matter was found to act as a graphitization catalyst [28,31–33,40,41], thus explaining the more graphite-like materials obtained in this work from AF anthracite (Tables 1 and 2). According to the structural data in Table 2, the HTT of the anthracites can result in graphite materials that have structural characteristics comparable to those of the GS2 graphite of reference. The main structural difference between the GS1 reference graphite and the more graphite-like materials prepared from the anthracites is related to the Lc and La sizes of the coherent domains (Table 2). Thus, the crystallite sizes of the ATO/2800 and AF/2800 materials are lower than that of SG1 graphite. However, this reference material shows a much higher value of the Raman ratio, ID/It, which is used as an indicator of the bi-dimensional order of carbon materials [34–36,39]. It is important to mention that, apart from the La diameter of the coherent domains [39,42] and the degree of crystalline orientation [43], there are other factors that have been suggested to contribute to the Raman D band intensity, such as the presence of disordered carbon or doping [34,43–45] as well as the interstitials or sp3 carbons [42], thus explaining the higher value of ID/It calculated for the SG1 graphite as compared to those of some of the graphite materials prepared from AF and ATO anthracites. 3.2. Electrochemical characterization (galvanostatic cycling) of the graphite anode materials The first voltage profiles of discharge–charge cycle and the second discharge of the lithium cells using ATO/2800 and AF/2800 graphite materials as working electrodes are shown in Fig. 1a. For comparison, the data corresponding to the reference synthetic graphite SG1 appears in the same figure. At the beginning of the discharge, the cell voltage drops quickly to 0.8 V (versus Li/Li+) to form a short plateau which is attributed to the solid electrolyte interface (SEI) film formation on the graphite surface as a result of the electrolyte decomposition [46], and then gradually decreases to the point at what the lithium insertion into the electrode starts. Such voltage profiles are characteristics of graphite materials that do not show exfoliation [1,8,47,48]. As can be seen in Fig. 1b, lithium intercalation in the electrode material takes place in the voltage range below 0.2 V vs. Li/Li+. The Li+ insertion profile of the
graphite material prepared from AF anthracite, AF/2800, was much the same to that of the reference synthetic graphite, SG1, except shorter plateaus at approximately 0.18, 0.10, and 0.06 V. Considering that the structural differences between AF/2800 and the reference graphite, SG1, are much associated with the values of Lc and La, the size of the crystal domain appears as a significant factor governing the extent of the first Li+ intercalation into the graphene layers, thus explaining the different profiles showed by these materials (Fig. 1b, Table 2). A comparison of the differential capacity (absolute value, derived from the first cycle discharge data) versus potential plots of AF/2400 and AF/2800 graphite materials which have been prepared from the same precursor (AF anthracite) makes this fact more evident (Fig. 1c). Thus, although three potential peaks during lithium intercalation can be observed on both materials, those corresponding to AF/2800 with larger mean crystallite sizes, La and Lc, are significantly more intensive. Unlike AF/ 2800 and SG1, only two lithium intercalation stages at the lowest potentials were slightly detectable in the profile of ATO/2800 in Fig. 1b. However, as can be seen in Fig. 1d which shows the differential capacity plot, the lithium intercalation in this material also occurs in three stages at approximately 0.17, 0.09, and 0.06 V. As expected, ATO/2800 material with a lower degree of structural order as compared to that of AF/2800 materials lead to smaller potential peaks. The irreversible charge losses (irreversible capacity, Cirr) during the first discharge–charge cycle of the materials studied are reported in Table 3. Both series of AF/2400–2800 and ATO/2400– 2800 graphite electrodes show a narrow and similar range of irreversible capacity percentages, the absolute values of this electrochemical parameter being low and mostly smaller than that corresponding to the synthetic graphites of reference, SG1 and SG2. Thus, values of Cirr in the ranges 12–19% and 14–18% were, respectively, calculated for these two series of electrodes. It is generally accepted that the irreversible capacity is essentially due to the formation of the solid electrolyte interface on the surface of the graphite electrode [47]. Other surface side reactions may also contribute to this capacity loss [48–50]. Because of the SEI film covers the electrode surface exposed to the electrolyte solution, this irreversible consumption of Li has been related with the surface area of the electrode material [46,48–51]. Specifically, proportionality with the BET specific surface area was found in graphites from the same family with comparable nanotextures [52]. However, as can be seen in Table 3 there is not dependence between these two parameters for the graphite materials prepared from AF or ATO anthracites. It has been previously reported that the value of the irreversible capacity is directly related with the active surface area (ASA) of the carbon material [49,50]. The ASA corresponds to the cumulated area of the different type of defects present on the carbon surface such as stacking faults, dislocations, and vacancies, thus being an indirect estimation of the degree of structural order of the material. A comparison of the Cirr data with the XRD and Raman parameters reveals that there is a certain tendency of the electrode irreversible capacity to decrease as both the degrees of structural order and crystal orientation increases for ATO/2400–2800 series of graphite materials (Tables 2 and 3). However, any proportionality was found in the case of AF/2400–2800 series. In contrast, these materials and the synthetic graphites with higher degree of structural order also show higher Cirr values. Taking into account that exfoliation was not observed during the lithiation of AF/2400–2800 graphite electrodes, other factors different than the degree of structural order and thus the ASA value should influence on the irreversible charge loss. The cycling behaviour of AF/2400–2800 and ATO-2400/2800 graphite materials is presented in Fig. 2a and b. Those corresponding to the SG1 and SG2 reference materials are included in Fig. 2a. As observed, all of the electrodes show a significant stable capacity
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0.6
(a)
ATO/2800 AF/2800 SG1
2.0
Potential (V) vs Li/Li+
Potential (V) vs Li/Li +
2.4
1.6 1.2 0.8 0.4 0.0 0.0
0.2
0.4
0.6
0.8
1.0
0.4 0.3 0.2 0.1 0.0
1.2
0.1
0.3
0.5
8000
(c)
AF/2400 AF/2800
6000 0.10 V
4000
2000 0.18 V
0 0.1
0.2
0.3
0.7
0.9
1.1
x in LixC6 Differential capacity (mAhg -1V-1)
Differential capacity (mAhg-1V-1)
x in LixC6
0.06 V
(b)
ATO/2800 AF/2800 SG1
0.5
0.4
Potencial (V) vs Li/Li
0.5
0.6
+
8000
(d)
ATO/2800
6000
4000 0.06 V 0.09 V
2000
0.17 V
0 0.1
0.2
0.3
0.4
0.5
0.6
Potential (V) vs Li/Li +
Fig. 1. Galvanostatic first discharge–charge cycle and second discharge profiles of ATO/2800, AF/2800, and SG1 graphite materials (a), first Li+ intercalation/de-intercalation in ATO/2800, AF/2800, and SG1 graphite materials (b), and differential capacity from the first cycle discharge vs. potential of AF/2400 and AF/2800 (c), and of ATO/2800 (d).
Table 3 First cycle irreversible capacity (Cirr) and nitrogen BET specific surface area data of the graphite materials prepared from ATO and AF anthracites by HTT and of the synthetic graphites SG1 and SG2. Material
Cirr (mA h/g)
Cirr (%)
BET surface area (m2/g)
ATO/2400 ATO/2500 ATO/2600 ATO/2700 ATO/2800 AF/2400 AF/2500 AF/2600 AF/2700 AF/2800 SG1 SG2
37 30 31 31 28 38 44 53 48 42 49 49
19 15 16 14 12 15 14 18 16 14 12 15
4.9 5.6 5.1 4.7 4.9 6.8 5.3 5.5 6.0 5.6 7.5
Cirr (%) = 100(charge first Li+ intercalation) (charge first Li+ de-intercalation)/ (charge first Li+ intercalation).
on prolonged cycling. In contrast, the reversible capacity of the synthetic graphite of reference, SG1, decreases monotonically with cycling, suggesting the exfoliation of the graphene layers (Fig. 2a). By comparing the galvanostatic cycling results and the crystalline parameters of the graphite materials prepared from the anthracites in Table 2, it is evident that those with higher structural order provide larger reversible lithium storage capacity. As an example, values of approximately 170 and 250 mA h g1 were calculated for ATO/2800 and AF/2800 with crystallites sizes in the c direction,
Lc, of approximately 13 and 22 nm, respectively; the corresponding interlayer spacing being 0.3387 and 0.3369 nm. To explore a possible correlation between the reversible capacity of the electrodes and the degree of structural order of the graphite electrode materials as estimated from XRD and Raman spectroscopy, linear regression analyses were performed with the data appearing in Fig. 2 (after 20 cycles) and Table 2. This type of analysis gave equations with correlation coefficients of R2 = 0.954, 0.973, 0.920, and 0.947 for the interlayer spacing, d002, the thickness of the crystallite, Lc, the width of the crystallite, La, and Raman parameter, ID/ It, respectively, of the graphite materials prepared from the anthracites in this work. On the basis of these results, both the degrees of structural order and crystal orientation of the graphite materials prepared from the anthracites seems to influence the reversible electrochemical intercalation of lithium. When the data of the SG1 and SG2 graphites of reference were included, the correlation was restricted to the materials crystallite sizes. In this approach, values of R2 of 0.924 for Lc and 0.902 for La were found. The dependence of the electrochemical intercalation of lithium in well-ordered (graphite-like) materials prepared from different precursors on their crystal structure has been previously studied by other authors [1,53,54]. The crystal thickness, Lc, was reported to be the most important factor affecting the extent of the material reversible capacity. A tendency of these materials capacity to decrease with the crystallite thickness with no evident dependency on the material crystal length, La, was observed; the minimum capacities being showed by those with Lc values of 10 nm. Nevertheless, no specific correlation between the electrode capacity and the crystal thickness of the graphite material was established in
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300
(a)
AF/2400 AF/2500 AF/2600 AF/2700 AF/2800 SG1 SG2
400 350 300 250 200 150
10
20
30
40
50
Cycle number
(b) Dis. capacity (mAhg-1)
Dis. capacity (mAhg-1)
450
ATO/2400 ATO/2500 ATO/2600 ATO/2700 ATO/2800
250
200
150
100
10
20
30
40
50
Cycle number
Fig. 2. Extended galvanostatic cycling of AF/2400–2800, SG1, and SG2 graphite materials (a) and of ATO/2400–2800 graphite materials (b).
these studies. In fact, significant larger capacities were provided by some of the graphite-like materials studied with lower or similar Lc values, thus inferring the influence on the graphite material electrochemical performance of other structural factors different than the crystal thickness as shown in those prepared from AF and ATO anthracites. 4. Conclusions Larger reversible lithium storage capacities were obtained from those anthracite-based graphite materials with higher structural order and crystal orientation. Reasonably good linear correlations were attained between the electrode reversible charge and the XRD (Lc, La, d002) and Raman (ID/It) crystal parameters of the graphite materials prepared from AF and ATO anthracites. By including graphites prepared from other precursors the correlation was restricted to the crystallite sizes. The graphite materials prepared from anthracites high temperature treatment showed excellent cyclability as well as low irreversible charge loss; the reversible capacity being up to 250 mA h g1. On the basis of that, the utilization of these materials as negative electrode in lithium-ion batteries appears feasible. Nevertheless, additional work should be done to improve the structural order of the graphite materials prepared and therefore, the reversible capacity. Acknowledgements Financial support from the Spanish Ministry of Science and Innovation MICINN (under Project MAT2004-01094), and FICYT (under Project PC07-014)) is gratefully acknowledged. I. Cameán thanks MICINN for a personal grant to develop the work. References [1] Endo M, Kim C, Nishimura K, Fujino T, Miyashita K. Recent development of carbon materials for Li ion batteries. Carbon 2000;38:183–97. [2] Noel M, Sryanarayanan V. Role of carbon host lattices in Li-ion intercalation/ de-intercalation processes. J Power Sources 2002;111:193–209. [3] Wakihara M. Recent development in lithium ion batteries. Mater Sci Eng 2001;R33:109–34. [4] Bruce PG, Scrosati B, Tarascon J-M. Nanomaterials for rechargeable lithium batteries. Angew Chem 2008;47:2930–46. [5] Guoping W, Bolan Z, Min Y, Xiaoluo X, Meizheng Q, Zuolong Y. A modified graphite anode with high initial efficiency and excellent cycle life expectation. Solid State Ion 2005;176:905–9. [6] Wu Y, Jiang C, Wan C, Tsuchida E. A green method for the preparation of anode materials for lithium ion batteries. J Mater Chem 2001;11:1233–6. [7] Yang S, Song H, Chen X. Electrochemical performance of expanded mesocarbon microbeads as anode material for lithium-ion batteries. Electrochem Commun 2006;8:137–42.
[8] Baek J-K, Lee H-Y, Jang S-W, Lee S-M. Electrochemical performance of modified synthetic graphite for lithium ion batteries. J Mater Sci 2005;40: 347–53. [9] Pan Q, Guo K, Wang L, Fang S. Novel modified graphite as anode material for lithium ion batteries. J Mater Chem 2002;12:1833–8. [10] Yang Z, Feng Y, Li Z, Sang S, Zhou Y, Zeng L. An investigation of lithium intercalation into the carbon nanotubes by a.c. impedance. J Electroanalyt Chem 2005;580:340–7. [11] Lee YH, Pan KC, Lin YY, Kumar TP, Fey GTK. Lithium intercalation in graphites precipitated from pig iron melts. Mater Chem Phys 2003;82:750–7. [12] Yao J, Wang GX, Ahn J-H, Liu HK, Dou SX. Electrochemical studies of graphitized mesocarbon microbeads as anode in lithium-ion cells. J Power Sources 2003;114:292–7. [13] Buqa H, Golob P, Winter M, Besenhard JO. Modified carbons for improved anodes in lithium ion cells. J Power Sources 2001;97–98:122–5. [14] Barsukov VZ, Il’in EA, Likhmitskii KV, Zayats OV, Tverdokhleb VS, Kryukov VV, et al. Graphites from the zavalie deposit as active materials fro lithium-ion batteries. Russ J Electrochem 2008;44:579–84. [15] Balasooriya NWB, Touzain Ph, Bandaranayake PWSK. Lithium electrochemical intercalation into mechanically and chemically treated Sri Lanka graphite. J Phys Chem Solids 2006;67:1213–7. [16] Khomenko VG, Barsukov VZ. Characterization of silicon- and carbon-based composite anodes for lithium-ion batteries. Electrochim Acta 2007;52:2829–40. [17] Lee J-H, Kim W-J, Kim J-Y, Lim S-H, Le S-M. Spherical silicon/graphite/carbon composites as anode material for lithium-ion batteries. J Power Sources 2008;176:353–8. [18] Khomenko VG, Barsukov VZ, Doninger JE, Barsukov IV. Lithium-ion batteries based on carbon–silicon–graphite composite anodes. J Power Sources 2007;165:598–606. [19] Chevallier F, Gautier S, Salvetat JP, Clinard C, Frackowiak E, Rouzaud JN, et al. Effects of post-treatments on the performance of hard carbons in lithium cells. J Power Sources 2001;97–98:143–5. [20] Zheng T, Xing W, Dahn JR. Carbons prepared from coals for anodes of lithiumion cells. Carbon 1996;34:1501–7. [21] Kim Y-J, Yang H, Yoon S-H, Korai Y, Mochida I, Ku C-H. Anthracite as a candidate for lithium ion battery anode. J Power Sources 2003;113:157–65. [22] Fransson L, Eriksson T, Edström K, Gustafsson T, Thomas JO. Influence of carbon black and binder on Li-ion batteries. J Power Sources 2001;101:1–9. [23] Bonino F, Brutti S, Piana M, Natale S, Scrosati B, Gherghel L, et al. Structural and electrochemical studies of a hexaphenylbenzene pyrolysed sofá carbon as anode material in lithium batteries. Electrochim Acta 2006;51:3407–12. [24] Concheso A, Santamaría R, Menéndez R, Jiménez-Mateos JM, Alcántara R, Lavela P, et al. Iron-composites as electrode materials in lithium batteries. Carbon 2006;44:1762–72. [25] Machnikowski J, Grzyb B, Weber JV, Frackowiak E, Rouzaud JN, Béguin F. Structural and electrochemical characterisation of nitrogen enriched carbon produced by the co-pyrolysis of coal-tar pich with polyacrylonitrile. Electrochim Acta 2004;49:423–32. [26] Olson DW, 2007. Graphite, 2006 Mineral Year Book. US Geological Survey, US Department of Interior, Washington. [27] Inagaki M. Applications of polycrystalline graphite. In: Delhaès P, editor. Graphite and precursors. Amsterdam: Gordon and Breach; 2001. p. 179–98. [28] Oberlin A, Terriere G. Graphitization studies of anthracites by high resolution transmission electron microscopy. Carbon 1975;13:367. [29] van Krevelen DV. Coal: typology, physics, chemistry and constitution. Amsterdam: Elsevier; 1993. [30] Bustin RM, Rouzaud JN, Ross JV. Natural graphitization of anthracites – experimental considerations. Carbon 1995;33:679–91. [31] Atria JV, Rusinko F, Schobert HH. Structural ordering of Pennsylvania anthracites on heat treatment to 2000–2800 degrees C. Energy Fuels 2002;16:1343–7.
I. Cameán et al. / Fuel 89 (2010) 986–991 [32] Gonzalez D, Montes-Morán MA, Suarez-Ruiz I, Garcia AB. Structural characterization of graphite materials prepared from anthracites of different characteristics: a comparative análisis. Energy Fuels 2004;18:365–70. [33] Gonzalez D, Montes-Morán MA, Garcia AB. Influence of inherent coal mineral matter on the structural characteristics of graphite materials prepared from anthracites. Energy Fuels 2005;19:263–9. [34] Cuesta A, Dhamelincourt P, Laureyns J, Martinez-Alonso A, Tascon JMD. Comparative performance of X-ray diffraction and Raman microprobe techniques for the study of carbon materials. J Mater Chem 1998;8:2875–9. [35] Cuesta A, Dhamelincourt P, Laureyns J, Martinez-Alonso A, Tascón JMD. Raman microprobe studies of carbon materials. Carbon 1994;32:1523–32. [36] Montes-Morán MA, Young RJ. Raman spectroscopy study of HM carbon fibres: effect of the plasma treatment on the interfacial properties of single fibre/ epoxy composites-Part I: fibre characterisation. Carbon 2002;40:845–55. [37] Biscoe J, Warren B. An X-ray study of carbon blacks. J Appl Phys 1942;13:364–71. [38] Franklin RE. The structure of graphitic carbons. Acta Crystal 1951;4:253. [39] Tuinstra F, Koening JL. Raman spectra of graphite. J Chem Phys 1970;53:1126–30. [40] Evans EL, Jenkins JL, Thomas JM. Direct electron microscopic studies of graphitic regions in heat-treated coals and coal extracts. Carbon 1972;10:637–42. [41] Cabielles M, Montes-Morán MA, Garcia AB. Structural study of graphite materials prepared by HTT of unburned carbon concentrated from coal combustion fly ashes. Energy Fuels 2008;22:1239–43. [42] Beny C, Rouzaud JN. Characterization of carbonaceous materials by correlated electron and optical microscopy and Raman microspectroscopy. Scan Electron Microsc 1985:119–32. [43] Katagiri G, Ishida H, Ishitani A. Raman spectra of graphite edges planes. Carbon 1988;26:565–71.
991
[44] Afanasyeva NI, Jawhari T, Klimenko IV, Zhuravleva TS. Micro-Raman spectroscopy measurements on carbon fibers. Vibrat Spectrosc 1996;11:79–83. [45] Nistor LC, van Landuyt J, Ralchenko VG, Kononenko TV, Obraztosova ED, Strelnitsky VE. Direct observation of laser-induced crystallization of A–C–H films. Appl Phys 1994;A58:137–44. [46] Fong R, von Sacken U, Dahn JR. Studies of lithium intercalation into carbons using nonaqueous electrochemical-cells. J Electrochem Soc 1990;137:2009–13. [47] Guerin K, Fevrier-Bouvier A, Flandris S, Couzi M, Simon B, Biensan P. Effect of graphite crystal structure on lithium electrochemical intercalation. J Electrochem Soc 1999;146:3660–5. [48] Spahr ME, Wilhelm H, Palladino T, Dupont-Pavlovsky N, Goers D, Joho F, et al. The role of graphite surface group on graphite exfoliation during electrochemical lithium insertion. J Power Sources 2003;119–121:543–9. [49] Béguin F, Chevallier F, Vix-Guterl C, Saadallah S, Bertagna V, Rouzaud JN, et al. Correlation of the irreversible lithium capacity with the active area of modified carbons. Carbon 2005;43:2160–7. [50] Novák P, Ufheil J, Buqa H, Krumeich F, Spahr ME, Goers D, et al. The importance of the active surface area of graphite materials in the first lithium intercalation. J Power Sources 2007;174:1082–5. [51] Aurbach D, Teller H, Koltypin M, Levi E. On the behaviour of different types of graphite anodes. J Power Sources 2003;119–121:2–7. [52] Winter M, Novak P, Monnier J. Graphites for lithium ion cells: the correlation of the first cycle charge loss with the BET surface area. J Electrochem Soc 1998;145:428–36. [53] Dahn JR, Sleigh AK, Shi H, Reimers JN, Zhong Q, Way BM. Dependence of the electrochemical intercalation of lithium in carbons on the crystal structure of the carbon. Electrochim Acta 1993;38:1179–91. [54] Endo M, Nishimura Y, Takahashi T, Takeuchi K, Dresselhaus MS. Lithium storage behaviour for various kinds of carbon anodes in Li ion secondary battery. J Phys Chem Solids 1996;57:725–8.