Rate-capability response of graphite anode materials in advanced energy storage systems: a structural comparison
Rate-capability response of graphite anode materials in advanced energy storage systems: a structural comparison
Carbon letters. 2016. Jan, 17(1): 39-44
Copyright © 2016, Korean Carbon Society
  • Received : October 28, 2015
  • Accepted : December 17, 2015
  • Published : January 31, 2016
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About the Authors
Umer, Farooq
Korea Electrotechnology Research Institute (KERI), Changwon 51543, Korea
Chil-Hoon, Doh
Korea Electrotechnology Research Institute (KERI), Changwon 51543, Korea
Syed Atif, Pervez
Korea Electrotechnology Research Institute (KERI), Changwon 51543, Korea
Doo-Hun, Kim
Korea Electrotechnology Research Institute (KERI), Changwon 51543, Korea
Sang-Hoon, Lee
Korea Electrotechnology Research Institute (KERI), Changwon 51543, Korea
Mohsin, Saleem
Korea Electrotechnology Research Institute (KERI), Changwon 51543, Korea
Seong-Ju, Sim
Korea Electrotechnology Research Institute (KERI), Changwon 51543, Korea
Jeong-Hee, Choi
Korea Electrotechnology Research Institute (KERI), Changwon 51543, Korea

The work presented in this report was a detailed comparative study of the electrochemical response exhibited by graphite anodes in Li-ion batteries having different physical features. A comprehensive morphological and physical characterization was carried out for these graphite samples via X-ray diffraction and scanning electron microscopy. Later, the electrochemical performance was analyzed using galvanostatic charge/discharge testing and the galvanostatic intermittent titration technique for these graphite samples as negative electrode materials in battery operation. The results demonstrated that a material having a higher crystalline order exhibits enhanced electrochemical properties when evaluated in terms of rate-capability performance. All these materials were investigated at high C-rates ranging from 0.1C up to 10C. Such improved response was attributed to the crystalline morphology providing short layers, which facilitate rapid Li + ions diffusivity and electron transport during the course of battery operation. The values obtained for the electrical conductivity of these graphite anodes support this possible explanation.
1. Introduction
At present, the total amount of human power consumption is around 14 terawatts and that is expected to increase up to three times by 2050 [1] . Oil is currently the major source of energy that is accountable for CO 2 emission, and it is considered to be a major cause of geopolitical instability. Since oil is the main fuel used to run automotive applications, a necessary transition to electrified transportation systems is of utmost urgency [2] . Hybrid electric vehicles have been commercialized that are accelerating as plug-in hybrid vehicles, and finally, electric vehicles are on the verge of entering their commercialization phase. The greatest challenges to the secure establishment of the electrified automobile industry are insufficient storage capacity and the low power density of current battery systems [3 - 4] . Liion batteries (LIBs) are currently used in portable electronic devices because they offer high energy density for application in small mobile devices [5 - 7] . However, they are difficult to use in electric vehicles because they need better energy storage systems with high rate-capability. To address the increased energy demand for LIBs with higher power density, intensive research has been carried out to design novel and efficient electrode materials structures [8] . Efforts have been made to introduce transition metal oxides, silicon, and several other materials as anodes for high power LIBs, but the electrochemical results have revealed no major success [9 - 13] .
Carbon-based materials have already received much attention as negative electrode materials for LIBs because of their excellent features, such as low cost as well as chemical and thermal stability [14 - 16] . Many carbon based materials, such as hard carbon, carbon nanotubes, carbon composites, and disordered carbons have been widely studied as anode materials [17 - 20] . However, various explanations have been suggested for the storage mechanism of lithium ions for various samples. Among all carbonaceous materials, graphite has shown the greatest potential because of its stable and favorable physical structure [21 - 22] . In this work, a comprehensive comparative study was conducted to examine the effects of various physical properties on the electrochemical performance of graphitic anodes. This study revealed that the physical features of graphitic anodes have a definite role in Li + ion diffusion and the high-rate capability performance of LIBs.
2. Experimental
Various kinds of artificial graphite samples were received from three different companies (A, B, and C). These samples were named A1, B1, B2, C1, and C2 for later discussion in this report. First, physical characterization was performed via field emission scanning electron microscopy (Hitachi FE-SEM S4800; Hitachi, Tokyo, Japan). X-ray diffraction (XRD) was performed on an X’pert Philips PMD (Philips) with a panalytical X’celerator detector (Panalytical, Almelo, The Netherlands) using graphite monochromized Cu Kα radiation (wavelength = 1.54056 Å). To investigate electrochemical charge/discharge performance, working electrodes were prepared by respectively mixing the various graphite sample powders, carbon black (Super P, M.M.M. Carbon, Brussels, Belgium), and binder (polyvinylidene fluoride) in the ratio of 90:5:5. Then, each mixture was compressed onto a copper foil and dried at 100℃ for 1 h. Lithium foil (purity 99.9%) was used as a counter electrode, polypropylene membrane separator (Celgard 2400; Celgard, Charlotte, NC, USA) and 1.2 MLiPF 6 in EC/EMC (1:1 v/v) + 2 wt% VC as the electrolyte. Coin cells were assembled in a dry room at room temperature. Rate capability experiments were performed using a multi-channel battery tester (Toscat-3100U; Toyo System, Fukushima, Japan). The potential range was kept between 0.005 to 1.5 V, and the current density was varied between 0.1C to 10C in the experiments. The electronic conductivity of these samples was measured using impedance spectroscopy. The galvanostatic intermittent titration technique (GITT) was used to calculate the diffusion coefficient. Values were recorded after 2 cycles at 0.5C, and a constant current pulse was provided for 5 min with a rest time of 4 h at 20% depth of discharge (DOD).
3. Results and Discussion
XRD is a fundamental characterization technique that has been established for the determination of structural parameters. The XRD pattern presented in Fig. 1 shows that all the reflections of 002, 100, 004, and 110 can be indexed to graphite in all of the five samples [23] . The XRD patterns of these graphite samples show a common diffraction peak, which is attributed to disordered carbon structure. Crystallite size was calculated based on Sherrer’s equation:
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X-ray diffraction patterns of various artificial graphite samples.
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where K is a dimensionless shape factor (typical value = 0.9), λ is the X-ray wavelength, β is the line broadening at full width at half maximum intensity (FWHM), and θ is the Bragg angle. In Fig. 2a the inter-layer spacing (d-spacingd 002 ) values of various samples are presented. Sample B1 had the highest value of d 002 , while sample C2 exhibited the lowest values. The lateral size (L a ) and the stacking height (L c ) were also calculated by Sherrer’s equation, and the values obtained are presented in Fig. 2b . The highest values of L a and L c were recorded for the C2 sample.
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(a) d002 values for all graphite materials and (b) La, Lc, and Lc/La values calculated by Sherrer’s equations. La, lateral size; Lc, stacking height.
Fig. 3a compares the particle size distributions of various graphite materials. The average particle size for most of the samples was calculated to be around 20 μm. Brunauer, Emmett, and Teller (BET) theory was applied to measure the surface area of all samples. The results in Fig. 3b show that sample C2 had a larger surface area, which is likely to have a more positive impact on the electrochemical performance of the material as an anode since there would be a larger reaction area. SEM images were taken to investigate other physical features of the microstructures. Fig. 4 presents SEM images of all the graphite samples. Samples C1 and C2 have relatively non-uniform particle sizes and elliptic or plate-like shapes, while samples of the B1 type have uniform particle distribution among all samples. Differences in size and shape of these graphite samples are related to the manufacturing processes employed by the companies that produced them.
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(a) Particle size analysis of graphite materials, (b) specific surface area calculated by Brunauer, Emmett, and Teller (BET) theory for all graphite materials.
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Scanning electron microscopy micrographs for all graphite samples.
Fig. 5 presents the conductivity features of particles that showed the lowest resistance values for C2. All the obtained values for these samples presented in Fig. 5 suggest that electrical conductivity is inversely proportional to the d 002 spacing of graphite materials [24] . Higher electronic conductivity is one of the key characteristics of high-performance battery systems in terms of rate capability and power density [25 , 26] .
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Electrical conductivity of graphite samples as function of pressure.
The GITT is a useful tool to obtain information about the diffusion coefficient of electrode materials during delithiation. To calculate the diffusion coefficients of the samples, the following equation was used:
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here τ is the constant current pulse time (s), m B is the mass of the insertion electrode material (g), V M is the molar volume of the electrode material (cm 3 mol −1 ), M B is the molar mass of the insertion electrode material (g mol −1 ), S is the area of the electrodeelectrolyte interface (cm 2 ), Δ Es is the change of the steady-state voltage during a single-step GITT experiment (V), and Δ Et is the total change of cell voltage during a constant current pulse τ of a single-step GITT experiment neglecting the IR-drop (V). Table 1 show diffusion coefficient values obtained through careful calculations for these samples. In Fig. 6 , diffusion coefficient results are presented for all the samples calculated under the same experimental conditions. These calculations were carried out during delithiation when the DOD was 20%. The results clearly demonstrate that the C2 sample had the highest diffusion coefficient values during delithiation because this material has low specific resistance and high electronic conductivity.
Calculations performed for diffusion coefficient using GITT at depth of discharge 20%
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GITT, galvanostatic intermittent titration technique.
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(a) Potential vs. time and (b) diffusion coefficient values for all the graphite samples during delithiation at depth of discharge 20%.
To investigate the electrochemical response of these materials, rate-capability testing was performed at room temperature. These samples were tested at variable C-rates ranging from 0.1C to 10C. The results presented in Fig. 7 reveal that the best performance was achieved by the C2 sample. The capacity shown by the sample at 0.1C was considered standard, and it was compared with the capacities observed at 3C, 5C, and 10C. The C2 sample showed remarkably good electrochemical performance in terms of high rate-capability. The capacity recorded for this sample at 0.1C was around 360 mAh·g −1 (consider to be 100%), and it decreased to 89.45% at 3C, 65.23% at 5C, and 28.10% at 10C. This high electrochemical performance can be attributed to the high diffusion coefficient and electrical conductivity of the material that was observed during physical characterization. This high crystalline order of the material enhanced its electronic and ionic conductivity, which in turn improved the rate-capability of material. These high values facilitated the Li-ions to intercalate during the course of battery cycling, which enhanced the performance of battery.
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(a) Rate capability of graphite samples and (b) delithiation profiles of C2 at various C-rates.
4. Conclusions
To conclude this work, a comprehensive comparative study among the physical properties and electrochemical responses of five different graphite anodes was performed. The C2 sample, which was more crystalline in nature, as proven by XRD analysis, exhibited enhanced electrochemical performance in terms of high rate capability. The strong performance shown by this particular material can be attributed to the high diffusion coefficient that was measured by GITT. Moreover, improved ionic and electronic conductivity was observed in this sample, which played a key role in enhancing electrochemical performance. Improved crystallinity and suitable morphology of a material are the main characteristics that can provide high rate capability in a battery system.
No potential conflict of interest relevant to this article was reported.
This research was supported by the Korea Electrotechnology Research Institute (KERI) Primary research program of MSIP/ISTK (No. 15-12-N0101-57).
Girishkumar G , McCloskey B , Luntz AC , Swanson S , Wilcke W (2010) Lithium−air battery: promise and challenges J Phys Chem Lett 1 2193 -    DOI : 10.1021/jz1005384
Sakti A , Michalek JJ , Fuchs ERH , Whitacre JF (2015) A techno-economic analysis and optimization of Li-ion batteries for light-duty passenger vehicle electrification J Power Sources 273 966 -    DOI : 10.1016/j.jpowsour.2014.09.078
Winter M , Besenhard JO , Spahr ME , Novák P (1998) Insertion electrode materials for rechargeable lithium batteries Adv Mater<725::aid-adma725>;2-z 10 725 -    DOI : 10.1002/(SICI)1521-4095(199807)10:10<725::AID-ADMA725>3.0.CO;2-Z
Kang K , Meng YS , Breger J , Grey CP , Ceder G (2006) Electrodes with high power and high capacity for rechargeable lithium batteries Science 311 977 -    DOI : 10.1126/science.1122152
Tarascon JM , Armand M (2001) Review article: issues and challenges facing rechargeable lithium batteries Nature 414 359 -    DOI : 10.1038/35104644
Farooq U , Choi JH , Kim D , Pervez SA , Yaqub A , Hwang MJ , Lee YJ , Lee WJ , Choi HY , Lee SH , You JH , Ha CW , Doh CH (2014) Electrically exploded silicon/carbon nanocomposite as anode material for lithium-ion batteries J Nanosci Nanotechnol 14 9340 -    DOI : 10.1166/jnn.2014.10132
Yaqub A , Lee YJ , Hwang MJ , Pervez SA , Farooq U , Choi JH , Kim D , Choi HY , Cho SB , Doh CH (2014) Low temperature performances of graphite and LiNi0.6Co0.2Mn0.2O2 electrodes in Li-ion batteries J Mater Sci 49 7707 -    DOI : 10.1007/s10853-014-8479-6
Park CM , Kim JH , Kim H , Sohn HJ (2010) Li-alloy based anode materials for Li secondary batteries Chem Soc Rev 39 3115 -    DOI : 10.1039/b919877f
Pervez SA , Kim D , Farooq U , Yaqub A , Choi JH , Lee YJ , Doh CH (2014) Comparative electrochemical analysis of crystalline and amorphous anodized iron oxide nanotube layers as negative electrode for LIB ACS Appl Mater Interfaces http://dx.doi. org/10.1021/am501370f 6 11219 -    DOI : 10.1021/am501370f
Farooq U , Yaqub A , Choi JH , Pervez SA , Kim DH , Lee YJ , Doh CH (2014) Metal-assisted silicon based negative electrode for Li-ion batteries Mater Lett 126 291 -    DOI : 10.1016/j.matlet.2014.04.061
Takami N , Inagaki H , Tatebayashi Y , Saruwatari H , Honda K , Egusa S (2013) High-power and long-life lithium-ion batteries using lithium titanium oxide anode for automotive and stationary power applications J Power Sources 244 469 -    DOI : 10.1016/j.jpowsour.2012.11.055
Yu Y , Zhu Y , Lianga J , Fan L , Qian Y (2013) Synthesis of a novel carbon network-supported Fe3O4@C composite and its applications in high-power lithium-ion batteries Electrochim Acta 111 809 -    DOI : 10.1016/j.electacta.2013.08.088
Ahmed B , Shahid M , Nagaraju DH , Anjum DH , Hedhili MN , Alshareef HN (2015) Surface passivation of MoO3 nanorods by atomic layer deposition toward high rate durable Li-ion battery anodes ACS Appl Mater Interfaces 7 13154 -    DOI : 10.1021/acsami.5b03395
Mukherjee R , Krishnan R , Lu TM , Koratkar N (2012) Nanostructured electrodes for high-power lithium ion batteries Nano Energy 1 518 -    DOI : 10.1016/j.nanoen.2012.04.001
Yu L , Kim KJ , Park DY , Kim MS , Kim KI , Lim YS (2008) Preparation and characterization of pitch/cokes composite anode material for high power lithium secondary battery Carbon Lett 9 210 -    DOI : 10.5714/CL.2008.9.3.210
Bruce PG , Scrosati B , Tarascon JM (2008) Nanomaterials for rechargeable lithium batteries Angew Chem Int Ed 47 2930 -    DOI : 10.1002/anie.200702505
Dahn JR , Seel JA (2000) Energy and capacity projections for practical dual-graphite cells J Electrochem Soc 147 899 -    DOI : 10.1149/1.1393289
Kim KJ , Lee TS , Kim HG , Lim SH , Lee SM (2014) A hard carbon/microcrystalline graphite/carbon composite with a core-shell structure as novel anode materials for lithium-ion batteries Electrochim Acta 135 27 -    DOI : 10.1016/j.electacta.2014.04.171
de las Casas C , Li W (2012) A review of application of carbon nanotubes for lithium ion battery anode material J Power Sources 208 74 -    DOI : 10.1016/j.jpowsour.2012.02.013
Brutti S , Hassoun J , Scrosati B , Lin CY , Wu H , Hsieh HW (2012) A high power Sn–C/C–LiFePO4 lithium ion battery J Power Sources 217 72 -    DOI : 10.1016/j.jpowsour.2012.05.102
Bresser D , Mueller F , Buchholz D , Paillard E , Passerini S (2014) Embedding tin nanoparticles in micron-sized disordered carbon for lithium- and sodium-ion anodes Electrochim Acta 128 163 -    DOI : 10.1016/j.electacta.2013.09.007
Park DY , Lim YS , Kim MS (2010) Performance of expanded graphite as anode material for high power Li-ion secondary batteries Carbon Lett 11 343 -    DOI : 10.5714/CL.2010.11.4.343
Pang H , Wang X , Zhang G , Chen H , Lv G , Yang S (2010) Characterization of diamond-like carbon films by SEM, XRD and Raman spectroscopy Appl Surf Sci 256 6403 -    DOI : 10.1016/j.apsusc.2010.04.025
Rani A , Nam SW , Oh KA , Park M (2010) Electrical conductivity of chemically reduced graphene powders under compression Carbon Lett 11 90 -    DOI : 10.5714/CL.2010.11.2.090
Nam S , Lee JM , Pukha VE , Seo HO , Kim YD , Lee HJ (2014) Carbon anode thin films for lithium batteries Curr Appl Phys 14 1010 -    DOI : 10.1016/j.cap.2014.04.012
Zhang WH (2011) Calculation model of edge carbon atoms in graphite particles for anode of lithium-ion batteries Trans Nonferrous Met Soc China 21 2466 -    DOI : 10.1016/S1003-6326(11)61038-8