14034
J. Phys. Chem. C 2009, 113, 14034–14039
High Electrochemical Li Intercalation in Titanate Nanotubes Dong Hyun Kim,*,† Jum Suk Jang,‡ Sang Soo Han,§ Ki Soo Lee,# Sun Hee Choi,$ Ahmad Umar,% Jin Woo Lee,| Dong Wook Shin,† Seung-Taek Myung,r Jae Sung Lee,& Sun-Jae Kim,⊥ Yang Kook Sun,# and Kyung Sub Lee† DiVision of Materials Science and Engineering, Hanyang UniVersity, 133-791 Seoul, Korea, Department of Chemistry and Biochemistry, The UniVersity of Texas at Austin, Austin, Texas 78712, Korea Research Institute of Standards and Science, P.O. Box 102, 305-340 Daejeon, Korea, Department of Chemical Engineering, Hanyang UniVersity, 133-791 Seoul, Korea, Pohang Accelerator Laboratory, Beamline Research DiVision, Pohang, 790-784, Korea, Department of Physics, Faculty of Science, Najran UniVersity, P.O. Box 1988 Najran 11001, Saudi Arabia, Department of Mechanical Engineering, Choongnam National UniVersity, Yuseong-gu, Daejeon 305-764, Korea, Institute/Faculty of Nanotechnology and AdVanced Materials Engineering, Sejong UniVersity, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Korea, Department of Chemical Engineering/School of EnVironmental Engineering, Pohang UniVersity of Science and Technology, Pohang 790-784, Korea, and Department of Chemical Engineering, Iwate UniVersity, JP 020-8551, Japan ReceiVed: April 10, 2009; ReVised Manuscript ReceiVed: June 23, 2009
Titanate nanotubes and Ni doped titanate nanotubes were synthesized by hydrothermal method using rutile powders as starting materials. The electrochemical lithium storage of the nanotubes were investigated by cyclic voltammetric methods, and the crystal structure of the titanate nanotubes were computed by the density functional theory (DFT). The microstructure and morphology of the synthesized nanotubes were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM). Titanate nanotubes were composed of H2Ti2O5 · H2O in accordance with DFT calculation and had outer and inner diameters of ∼10 nm and 6 nm, and the interlayer spacing was about 0.65-0.74 nm. Also, Ni dopants were completely doped in the nanotube matrix. The undoped and the Ni doped nanotubes showed initial electrochemical lithium discharge capacity of 303 and 318 mAh/g, respectively; however, the Ni doped nanotubes revealed poor reversibility due to a large interlayer spacing compared with the undoped nanotubes. On the other hand, the undoped nanotubes exhibited good cycling performance because of the open-end and rolled layers with suitable spacing. The relationships between morphology and electrochemical properties have been discussed. I. Introduction One dimensional titania have been extensively studied for photocatalysis, dye-sensitized solar cell, lithium ion batteries, hydrogen storage, and electrochemical capacitors1-5 because of its large specific surface area, numerous surface defects, and physicochemical potentials.6-8,17 There have been many reports to apply one-dimensional (1D) titania such as nanowires, nanofiber, nanorod, TiO2-B, and nanotubes for electrochemical lithium storage. Zhang et al. reported that a mixture of nanotube and anatase-nanorod exhibited relatively large reversible capacity for lithium intercalation and good reversibility due to the existence of different phases.9 Also, the anatase nanorods by Gao et al. showed a large initial electrochemical lithium insertion capacity of 206 mAh/g and good reversibility which were caused by formation of imperfection in TiO2 nanorod.10 The researchers explained the high electrochemical performance of the onedimensional titania from three aspects: first, the large surface * Corresponding author. Phone: +82-2-2281-4914. Fax: +82-2-22814914. E-mail:
[email protected]. † Division of Materials Science and Engineering, Hanyang University. ‡ The University of Texas at Austin. § Korea Research Institute of Standards and Science. # Department of Chemical Engineering, Hanyang University. $ Pohang Accelerator Laboratory. % Najran University. | Choongnam National University. ⊥ Sejong University. & Pohang University of Science and Technology. R Iwate University.
areas cause the effective contact between electrode and electrolyte; second, the small diameters of 1D structures reduce the distance of Li+ diffusion; finally, the interlayer spacing of the 1D materials accelerates the Li+ diffusion in the open and loose structure.11 However, in spite of these efforts, much work on the characterizations of structural and electrochemical performance of titanate nanotubes are required. Also, systematic study on transition metal doping and interlayer spacing has yet to be done. Most researchers reported that the crystal structures of the titanate nanotubes have A2Ti3O7, H2Ti4O9 · H2O (A ) Na and/or H), and lepidocrocite titanates with monoclinic crystal structure.12-14 However, the corresponding of XRD patterns was not fully coincided with the crystal structure from JCPDS. In the present work, titanate nanotubes and Ni doped titanate nanotubes were synthesized by hydrothermal method using rutile TiO2 with NaOH solution. The morphology, detailed structure of titanate nanotubes, effect of interlayer spacing, and electronic structures of the titanate nanotubes system were investigated. Also, the electrochemical performances of the nanotubes for lithium storage were investigated by galvanostatic method and cyclic voltammetry. II. Experimental Section Synthesis. The rutile powders were prepared by HPPLT method using TiCl4 as a starting material15 while Ni was doped by mechanical alloying for 14 h using planetary ball mill (Fritz mill, P-5) with 8 wt % metal nickel element (Kojundo Chem.
10.1021/jp903344e CCC: $40.75 2009 American Chemical Society Published on Web 07/07/2009
High Electrochemical Li Intercalation
J. Phys. Chem. C, Vol. 113, No. 31, 2009 14035
TABLE 1: Atomic Positions (Cartesian Coordinate, Å) in the Unit Cell of Undoped Titanated Nanotube (H2Ti2O5 · H2O) Obtained from the DFT Calculationa
a
atom
x
y
z
atom
x
y
z
Ti1 Ti2 Ti3 Ti4 O1 O2 O3 O4 O5 O6 O7 O8
4.65414 6.93437 16.08866 18.35623 0.77036 3.61064 6.26015 5.23271 7.87638 9.78193 12.20926 15.00550
-0.10600 1.82428 1.79937 -0.01458 0.17680 -0.15934 -0.09736 1.76439 1.60500 3.07650 1.23725 1.83250
0.12976 1.60002 1.86790 0.44763 0.0418 1.64495 1.59420 0.08071 0.07324 1.67343 1.76726 0.40576
O9 O10 O11 O12 H1 H2 H3 H4 H5 H6 H7 H8
16.69492 17.65874 19.33619 20.90555 1.57500 0.61971 9.69554 10.47285 12.01867 13.01953 20.80766 21.67912
-0.02883 1.86378 0.18639 -1.59467 -0.34222 0.60314 3.38141 2.37894 0.79366 1.74263 -1.88711 -0.94107
1.93427 0.44655 1.95278 0.51509 -0.13743 2.21312 2.60026 1.72811 0.91654 1.57044 1.44542 3.56659
Here the optimized structure has an orthorhombic crystal and lattice parameters of a ) 22.53, b ) 3.74, and c ) 3.03 Å.
Co., LTD, 99.9%). The details of the process have been reported elsewhere.15,16 The Ni doped TiO2 and synthesized rutile powders (0.8 g) and 15 mL of 10 M NaOH aqueous solution were mixed under stirring for 1 h and placed in a Ni-lined stainless-steel autoclave at 120 °C for 24 h and then cooled to room temperature. Next, 0.1 M HCl aqueous solution was added and washed repeatedly with distilled water until the pH of the solution reached 7. Finally, powders were collected by the centrifugal separator (Oak Redge tube) operated at 15 000 rpm for 30 min. Characterization. The structure of the samples were characterized by X-ray diffraction (XRD) using a Rigaku D-MAX 3000 diffractometer equipped with Cu KR and scan rate was 1° (2¥)/min. Also, to determine the exact interlayer spacing of each sample, selected scattering angles (2¥) ranging between 5-15° and 20-27° with a step size of 0.01° were employed. The microstructures were observed with a JEOL 4010 microscope with accelerating voltage of 400 kV. Electrochemical Property. For fabrication of electrodes, the active materials were mixed with acetylene black (Alfa Aesar Co.), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC; 85:10:2:3) in DI water. The slurry was coated onto etched Al foil and roll-pressed. Then, the electrode was dried at 120 °C for 12 h to remove solvent and water. The electrochemical tests were performed on a coin-type cell (CR2032) assembled with working electrode/separator/reference electrode (metallic lithium). The electrolyte solution (Cheil Industries Inc., Korea) was 1 M LiBF4 dissolved in a propylene carbonate (PC). Galvanostatic charge-discharge tests were carried out using TOSCAT 3000 at constant current density (10 mA/g), with cutoff voltage of 1.0 to 3.0 V. Computational Methodology. To investigate an exact crystal structure of pristine titanate nanotubes, the density functional theory (DFT) calculations were performed using the SEQQUEST software,25 a fully self-consistent Gaussian-based linear combination of atomic orbitals (LCAO) DFT method with double-ζ plus polarization basis sets.26 All calculations were based on the Perdew-Burke-Ernzerhof (PBE)27 generalized gradient approximation with PBE pseudoatomic potentials and spin polarization within three-dimensional periodic boundary conditions. The k-point sampling of 6 × 6 × 6 in the Brillouin zone and the real space grid interval of 138 × 23 × 19 in the x-y-z box were carefully determined by energetic convergence. The initial crystal structure was used with a H2Ti2O5 · H2O crystal structure reported by Tasi and Teng28 in which a unitcell of the structure was consisted of 4 Ti, 12 O, and 8 H atoms. Then, we fully optimized the structure through the DFT calculation.
III. Results and Discussion Figure 1 shows the HRTEM images of the Ni doped titanate nanotubes (a) and undoped titanate nanotubes (b). The nanotubes had multiple layers of 4-5 with the interlayer spacing of 0.74 and 0.65 nm, respectively. The diameters of the nanotubes were almost 6-10 nm, with the length of several tens to hundred nanometers and all open at both ends. This interlayer spacing of nanotubes was much larger than that of normal layered metal oxide intercalation compounds which would accelerate the lithium ion diffusion in this open and loose structure.11 The difference in the interlayer spacing between Ni doped nanotubes and undoped nanotubes may be due to the Ni doped between the two interlayers of the nanotubes. The difference of detailed crystal structure is further supported by XRD and DFT studies. The axis of the nanotubes was [001] direction, and the layer stacking was parallel to the axis. The selected area electron diffraction (SAED) patterns of the center area of the Ni doped nanotubes and undoped nanotubes are shown in an inset. It can be seen that both patterns indicate diffraction lines of hydrogen titanate hydrate, (200), (110), (310), (501), (020), except small distortion in Ni doped nanotubes by doping. The typical EDS data collected form the average over five different points of analysis in Ni-doped nanotubes exhibited that the Ni doped nanotubes contained about 7 wt % Ni, and ICP analysis revealed that about 6.87 wt % metallic Ni atoms remained in the nanotubes. A small loss of Ni concentration occurred during the hydrothermal process.38 Figure 2a shows the XRD patterns of the Ni doped titanate nanotubes and undoped titanate nanotubes with the reported crystal structure from JCPDS.18-20 Selected scattering angles (2¥) ranging between 5-15° and 20-27° to calculate d200 and d110 value from XRD patterns are shown in Figure 2b,c. Both powders revealed characteristic peaks at around 2θ ) 10, 24, and 28° which could be assigned to the diffraction of H2Ti2O5 · H2O with peak broadening that was the result of nanometer size and bending of some atom planes of the tubes.22 The results indicate that the crystal structures of the synthesized nanotubes were completely different from those reported by other researchers12-14 in spite of the similar method of synthesizing nanotubes. The interlayer spacing of the Ni doped nanotubes and the undoped nanotubes from the reflection (200) were 0.91 and 0.84 nm, respectively. The difference of interlayer spacing between TEM and XRD could be due to the shrinkage of the interlayer spacing which was caused by dehydration during TEM analysis owing to the electron beams irradiation.23 Both lattice fringes of (110) reflection of nanotubes were not changed by Ni doping (Figure 2c. It shows that the Ni dopant
14036
J. Phys. Chem. C, Vol. 113, No. 31, 2009
Kim et al.
Figure 1. (a) High resolution TEM image of the undoped nanotubes. The selected diffraction patterns of the center area of the nanotube. (b) High resolution TEM image of the Ni doped nanotube with EDS analysis and selected diffraction patterns.
incorporated between two interlayers and expanded the interlayer spacing of the nanotubes. There have been many reports indicating a controversial point about titanate nanotubes for electrochemical lithium storage due to thermal unstability;9,31,32 however, these titanate nanotubes were stable up to 450 °C as shown in Figure 2a. To clarify a crystal structure of the undoped titanate nanotube, we have performed the DFT calculation and found that the optimized crystal has an orthorhombic structure with lattice parameters of a ) 22.53, b ) 3.74, and c ) 3.03 Å where an axis of the tube is along the [001] direction (Figure 3). In a unit cell of the nanotube structure, there are two layers of a composition of 2(TiO2) and two H2O molecules which are physically bonded in the structures with strong bonding energy between them, leading to a composition of H2Ti2O5 · H2O. In addition, our simulated structure is very similar to a recent HRTEM result from Figure 3d.29 The O-H bond distance of H2O in the undoped nanotube is 1.0 Å, same as that in pure water; however, the O-O distance between two H2O molecules is 3.1 Å, which is higher than in pure water (2.8 Å).30 For clarity, we tabulate all atomic positions in a unit cell of the nanotube
optimized by DFT calculation in Table 1. We simulated a XRD pattern of the optimized structure, which is inserted in Figure 1a. The optimized XRD pattern is indeed in good agreement with our experimental data and the JCPDS data for H2Ti2O5 · H2O. Tsai and Teng28 reported a crystal structure of the H2Ti2O5 · H2O in which the hydrogen atoms in interlayer H2O molecule face each other. In their structure, the hydrogen atoms should have positive charges because of charge polarization between oxygen and hydrogen atoms. Thus, two hydrogen atoms should repel each other. In our model in Figure 3, two hydrogen atoms do not face each other. We also optimized the nanotube structure without H2O in the interlayer through the DFT calculation. The structure is almost similar to that in Figure 3, and its lattice parameters are a ) 18.12, b ) 3.74, and c ) 3.02 Å. Compared with the hydrated nanotube, the only difference is that the dehydrated structure has smaller interlayer distance, which is also supported by XRD result of Figure 2a. Figure 4 shows the initial charge-discharge voltage profiles of Li intercalation in the undoped nanotube (TNT) and the Nidoped nanotube at the charge and discharge current density of 10 mA/g. The initial charge and discharge capacities of the
High Electrochemical Li Intercalation
J. Phys. Chem. C, Vol. 113, No. 31, 2009 14037
Figure 3. Optimized structure for a pristine titanate nanotube (TiO2 · H2O) from the DFT calculation: (a) an overview of the crystal structure, (b) [001] projection, and (c) [010] projection. Here, all structures are shown by a 1 × 2 × 2 supercell and the color codes are hydrogen for white, oxygen for red, titanium for gray. (d) Enlarged one side image of titanate nanotubes from [001].
Figure 2. XRD patterns of undoped nanotubes, Ni doped nanotubes, and heated titanate nanotubes. The standard diffraction peaks are indexed according to H2Ti2O5 · H2O, H2Ti3O7, and Na2Ti3O7 from JCPDS.
undoped nanotubes were 303 and 187 mAh/g, respectively, indicating a reversible efficiency of 61%, and the first charge and discharge capacities of Ni-doped nanotubes were 318 and 147 mAh/g, representing a reversible efficiency of 46%. The interlayer spacing of Ni-doped nanotubes is much larger than that of undoped nanotubes which could facilitate the lithium ion diffusion in the structure. Because of large interlayer spacing, the Ni-doped nanotubes revealed a higher discharge capacity than the undoped nanotubes at the first cycle. However, the reversible efficiency of Ni-doped nanotube was conspicuously lower than that of the undoped nanotubes. There are two plausible reasons for TNT materials to have large irreversible capacities. The first is the interlayer spacing of titanate nanotubes.24 Generally, the high specific surface area of nanotube could provide efficient contact between the titanate nanotubes and the nonaqueous electrolyte, and the thin diameter of the titanate nanotubes can reduce the distance of lithium ion diffusion in the nanotube electrodes. However, the nanotubes had a characteristic of the one way path. At the first discharge, lithium intercalation occurred at both the inner and the outer surface of the nanotube. Some of these intercalated lithium ions could not be extracted from inner surface of the nanotube electrode and remained in the nanotube during the first cycle.
Figure 4. Initial charge/discharge profile of (a) undoped nanotubes and (b) Ni-doped nanotubes at a current rate of 10 mA/g between 1.0 and 3.0 V.
The second reason is that hydrate existed in the titanate nanotube structure. The lithium ion could react with hydrate during discharge and may form the Li2O or LiOH on the surface and inner side of the layer, which are very stable and do not easily liberate Li+9. To remove all of the hydrates in the nanotube structures is too difficult and needs a high temperature over 800 °C9 because a hydrate is a part of the structure in the nanotube material. Therefore, the removing hydrate could be important to improve their reversible efficiency. Figure 5 shows the differential capacity versus voltage of the undoped nanotubes and Ni-doped nanotubes. It can be seen that there were two pairs of cathodic and anodic peaks that were found in the both nanotubes. In Figure 5a, two cathodic peaks of lithium intercalation at 1.68 and 1.8 V versus Li/Li+ were observed; meanwhile, two anodic peaks of lithium deintercalation were found in the voltage at about 1.75 and 1.9 V versus Li/Li+, respectively. However, the dramatic decreasing of peaks occurred during the cathodic process (discharge process) at the
14038
J. Phys. Chem. C, Vol. 113, No. 31, 2009
Kim et al. IV. Conclusion
Figure 5. Differential capacity vs voltage for each cycle of (a) undoped nanotubes and (b) Ni-doped nanotubes at a current rate of 10 mA/g between 1.0 and 3.0 V.
In summary, titanate nanotube and Ni doped nanotubes were synthesized by hydrothermal method using rutile powders as starting materials. The nanotubes were composed of H2Ti2O5 · H2O with outer and inner diameter of ∼10 nm and 6 nm, and the interlayer spacing was about 0.65-0.74 nm, These results were totally different from the other results as previously reported. In a unit cell of the nanotube structure from DFT calculation, there are two layers with a composition of 2(TiO2) and two H2O molecules incorporated between the two layers, leading to a composition of H2Ti2O5 · H2O. The undoped titanate nanotubes showed the highest cycle stability compared with Nidoped tubes which may be due to the formation of suitable interlayer spacing for lithium intercalation. Acknowledgment. This work was supported by Korea Research Foundation Grant (KRF-2006-005-J04103) and by KOSEF (R01-2006-000-10342-0). Supporting Information Available: SAD patterns of both undoped nanotube and Ni-doped nanotube, EDS spectrum of Ni doped nanotubes, and simulated XRD pattern in Figure 2. This material is available free of charge via the Internet at http:// pubs.acs.org.
Figure 6. Cycle performances of undoped nanotubes (vs Li/Li+) in the electrolyte of 1.0 M LiBF4; PC at a current rate of 10 mA/g (cutoff voltage: 1.0-3.0 V).
second cycle because of the remaining extracted Li ion in the nanotubes as previous mentioned. In addition, a pair of cathodic/ anodic peaks is clearly shown at 1.8 and 1.9 V that originates from the inserted/extracted lithium in the nanotubes.31,32 Another pair of peaks at the lower potential represents the pseudocapacitive behavior which could be explained in terms of the interaction taking place on the nanotube surface. The pseudocapacitive behavior means that it can store energy via surface faradaic redox reactions on the interface of the material and electrolyte.39 These pair of peaks which show lower potential are also presented in the Ni-doped nanotubes in Figure 4b. However, the pair of cathodic/anodic peaks of the Ni doped nanotubes at 1.9 and 2.0 V versus Li/Li+ is much lower than that of the undoped nanotubes, which means that the Ni-doped nanotubes have a little reaction with electolyte. Therefore, in spite of large discharge capacity at the first cycle, Ni-doped nanotubes are not suitable for application in lithium ion batteries or electrochemical capacitors because of poor reversible efficiency. Thus, a galvanostatic charge-discharge test was only carried out for the undoped nanotubes, and it is displayed in Figure 6. The cutoff potentials for charge-discharge were set to be 1.0 and 3.0 V versus Li/Li+, respectively. It shows that the titanate nanotubes exhibited excellent cycle stability in spite of an obvious drop of discharge capacity observed during the first several cycles that may be due to the decomposition of solvent on the surface of the electrode33 and nanoscale morphology changes.34 It is also observed that the charge capacity of titanate nanotubes was gradually increased until 30th cycle because of slow penetration of electrolyte through the nanotubes, and the Li ion has a chance to be moved into the inner of nanotubes during the cycles incorporating in the defects such as micropore and hollows.35-37
References and Notes (1) Zhu, H. Y.; Lan, Y.; Gao, X. P.; Ringer, S. P.; Zheng, Z. F.; Song, D. Y.; Zhao, J. C. J. Am. Chem. Soc. 2005, 127, 6730. (2) Park, J. H.; Bard, A. J. Electrochem. Solid-State Lett. 2006, 9, E5. (3) Kaven, L.; Kalbac, Martin.; Zukalova, M.; Exnar, I.; lorenzen, V.; Nesper, R.; Graetzel, M. Chem. Mater. 2004, 16, 477. (4) Lim, S. H.; Luo, J.; Zhong, Z.; Ji, W.; Lin, J. Inorg. Chem. 2005, 44, 4124. (5) Li, J.; Tang, Z.; Zhang, Z. Electochem. Commun. 2005, 7, 62. (6) Yoshida, R.; Suzuki, Y.; Yoshikawa, S. Mater. Chem. Phys. 2005, 91, 409. (7) Ding, X.; Xu, X. G.; Peng, L. M. Nanotechnology 2006, 17, 5423. (8) Bavykin, D. V.; Friedrich, J. M.; Walsh, F. C. AdV. Mater. 2006, 18, 2807. (9) Zhang, H.; Li, G. R.; An, L. P.; Yan, T. Y.; Gao, X. P.; Zhu, H. Y. J. Phys. Chem. C 2007, 111, 6143. (10) Gao, X.; Zhu, H.; Pan, G.; Ye, S.; Lan, Y.; Wu, F.; Song, D. J. Phys. Chem. B 2004, 108, 2868. (11) Li, J.; Tang, Z.; Zhang, Z. Chem. Mater. 2005, 17, 5848. (12) Du, G. H.; Chen, Q.; Che, R. C.; Yuan, Z. Y.; Peng, L.-M. Appl. Phys. Lett. 2001, 79, 3702. (13) Yang, J.; Jin, Z.; Wang, X.; Li, W.; Zhang, J.; Zhang, S.; Guo, X.; Zhang, Z. Chem. Soc., Dalton Trans. 2003, 3898. (14) Zhang, M.; Jin, Z.; Zhang, J.; Guo, X.; Yang, J.; Ki, W.; Wang, X.; Zhang, Z. Mol. Catal. A: Chem. 2004, 217, 203. (15) Kim, D. H.; Hong, H. S.; Song, J. S.; Kim, S. J.; Lee, K. S. J. Alloy Compd. 2004, 375, 259. (16) Kim, D. H.; Park, H. S.; Kim, S. J.; Lee, K. S. Catal. Lett. 2005, 100, 48. (17) Thorne, A.; Kruth, A.; Tunstall, D.; Irvine, J. T. S.; Zhou, W. J. Phys. Chem. B 2005, 109, 5439. (18) Chen, Q.; Zhou, W. Z.; Du, G. H.; Peng, L. M. AdV. Mater. 2002, 14, 1208. (19) Armstrong, A. R.; Armstrong, G.; Canales, J.; Bruce, P. G. Angew. Chem., Int. Ed 2004, 43, 2286. (20) Ma, R.; Bando, Y.; Sasaki, T. Chem. Phys. Lett. 2003, 380, 577. (21) Han, S. S.; Kim, H. S.; Han, K. S.; Lee, J. Y.; W, S. I.; Duin, A. D.; Goddard III, W. A. Appl. Phys. Lett. 2005, 87, 213113. (22) Yuan, Z. Y.; Su, B. L. Colloids Surf., A 2004, 241, 173. (23) Huang, A.; Liu, X.; Kong, L.; Lan, W.; Su, Q.; Wang, Y. Appl. Phys. A: Mater. Sci. Process. 2007, 87, 781. (24) Junrong, L.; Zilong, T.; Zhongtai, Z. Chem. Mater. 2005, 17, 5848. (25) Schultz, P. A.; Sandia National Labs, Albuquerque, NM, 2005. http://dst.sandia.gov/Quest. (26) Mattsson, A. E.; Schultz, P. A.; Desjarlais, M. P.; Mattsson, T. R.; Leung, K. Modell., Simul. Mater. Sci. Eng. 2005, 13, R1–R31. (27) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV. Lett. 1996, 77, 3865. (28) Tasi, C.-C.; Teng, H. Chem. Mater. 2006, 18, 367–373.
High Electrochemical Li Intercalation (29) Renzhi, M.; Takayoshi, S.; Yoshio, B. Chem. Commun. 2005, 948. (30) Tuckerman, M.; Lassonen, K.; Sprik, M.; Parrinello, M. J. Chem. Phys. 1995, 103, 150. (31) Zhao, Z. W.; Guo, Z. P.; Wexler, D.; Ma, Z. F.; Wu, X.; Liu, H. K. Electrochem. Commun. 2007, 9, 697. (32) He, B. L.; Dong, B.; Li, H. L. Electrochem. Commun. 2007, 9, 425. (33) Shu, Z. X.; McMillan, R. S.; Murra, J. J. J. Electrochem. Soc. 1993, 140, 922. (34) Kavan, L.; Kalbac, M.; Zukalova, M.; Exnar, I.; Lorenzen, V.; Nesper, R.; Graetzel, M. Chem. Mater. 2004, 16, 477.
J. Phys. Chem. C, Vol. 113, No. 31, 2009 14039 (35) Ni, J. F.; Zhou, H. H.; Chen, J. T.; Zhang, X. X. Mater. Lett. 2007, 61, 1260. (36) Franger, S.; Cras, L. F.; Bourbon, C.; Rouault, H. J. Power Sources 2003, 119, 252. (37) Dominko, R.; Goupil, J. M.; Bele, M.; Gaberscek, M.; Remaskar, M.; Hanzel, D.; Jamnik, J. J. Electrochem. Soc. 2005, 5, 152–A858. (38) Wu, D.; Chen, Y.; Liu, J.; Zhao, X.; Li, A.; Ming, N. Appl. Phy. Lett. 2005, 87, 112501. (39) Hwang, S. W.; Hyun, S. H. J. Power Sources 2007, 172, 451.
JP903344E
