Multicomponent Effects on the Crystal Structures and Electrochemical

Jan 24, 2012 - Ternary metal fluorides as high-energy cathodes with low cycling hysteresis. Feng Wang , Sung-Wook Kim , Dong-Hwa Seo , Kisuk Kang , Li...
0 downloads 9 Views 2MB Size
Download PDF
Article pubs.acs.org/cm

Multicomponent Effects on the Crystal Structures and Electrochemical Properties of Spinel-Structured M3O4 (M = Fe, Mn, Co) Anodes in Lithium Rechargeable Batteries Haegyeom Kim,† Dong-Hwa Seo,† Hyungsub Kim,‡ Inchul Park,§ Jihyun Hong,† Kyu-Young Park,§ and Kisuk Kang*,† †

Department of Materials Science and Engineering, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea ‡ Department of Materials Science and Engineering, §Graduate School of EEWS, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea ABSTRACT: The structural and electrochemical properties of the multicomponent oxide MnFeCoO4, which has a cubic spinel AB2O4 structure, are studied experimentally and by using first principles calculations. A solid solution of the spinels Mn3O4, Fe3O4, and Co3O4 forms the spinel MnFeCoO4, with Co preferentially occupying tetrahedral sites (A site). First principles calculations predict that the valence states of each transition metal would shift from +8/3 for the single component oxide to +3, +3, and +2 for the Mn, Fe, and Co ions, respectively, in the mixed spinel. The charge ordering of the transition metals (Co2+ vs Mn3+, Fe3+) in the multicomponent oxide is speculated to be the reason for the strong preference of Co for the A site. As a result, the characteristic redox potential of each transition metal shifted, as demonstrated in an anode test of the multicomponent oxide in a lithium cell. This represents an example how the electrochemical performance could be tuned by multicomponent substitution. KEYWORDS: conversion, rechargeable batteries, spinel, electrode

■

INTRODUCTION Lithium rechargeable batteries are important power sources for portable electronic devices. They have been considered as one of the most favorable options for large scale energy storage units.1−10 However, new electrode materials with high energy densities need to be developed to satisfy the demand for longlasting energy storage units. Accordingly, much attention has been given to transition metal oxide anodes because they potentially have much higher theoretical capacities than the current commercial anode material, graphite.2 Since transition metal oxides can react with more than one Li ion per transition metal atom through a conversion reaction, exceptionally high specific capacities can be achieved.11−14 Among several transition metal oxides reported,10−18 Co3O4 has been proposed as a promising anode material for Li rechargeable batteries because of its excellent electrochemical activity and high specific capacity of about 900 mAh g−1.14−18 Nevertheless, the high production cost and toxicity of Co are still problematic.4 Thus, compounds with partial substitution of Co in Co3O4, such as ZnCo2O4, NiCo2O4, and FeCo2O4, have been suggested as alternative anode materials to Co3O4.19−21 Partial substitution, or doping, of elements is commonly used to improve the electrochemical properties of the parent material.22−28 Materials for cathodes have been studied in particular. For example, Ni and Mn substitution into LiCoO2 to form mixed-metal oxides, such as LiNi1/3Co1/3Mn1/3O2 or © 2012 American Chemical Society

LiNi0.5Mn0.5O2, has resulted in higher energy densities and better safety. This is because Ni is electrochemically active between Ni2+ and Ni4+, thereby increasing the capacity. The Mn4+ serves to stabilize the layered structure.3,29−31 More recently, interesting multicomponent effects have been revealed for an olivine cathode. It has been reported that Li(Mn1/3Fe1/3Co1/3)PO4 has fundamentally different electrochemical properties than a single olivine component, such as one phase-based de/lithiation mechanism, and the shifted transition metal redox potential.32 In this work, we further explored the effect of multicomponent in the M3O4 spinel framework. We found that the valence states of Mn, Fe, and Co in the solid solution MnFeCoO4 (MFC) were different from the average of +8/3. This changed the redox potential of each transition metal. The difference in valence states affected the site occupancy among the transition metals in the AB2O4 spinel structure. The relationship between the structure and the electrochemical properties are discussed in this paper. Furthermore, we fabricated nanosized MFC (∼10 nm) particles using a simple and economically viable solid-state route at low temperature (300 °C) and demonstrated that MFC can be used as a high-performance anode material. Received: December 8, 2011 Revised: January 24, 2012 Published: January 24, 2012 720

dx.doi.org/10.1021/cm2036794 | Chem. Mater. 2012, 24, 720−725

Chemistry of Materials

■

Article

EXPERIMENTAL SECTION

Fabrication of a Nanoszied Multicomponent Oxide. The nanosized muticomponent oxide MFC was fabricated using a simple solid-state method at a relatively low temperature. Manganese acetate tetrahydrate (Sigma-Aldrich, ≥99%), iron acetate (Sigma-Aldrich, ≥99%), and cobalt acetate (Sigma-Aldrich, ≥99%) were used as precursors. The precursors (1:1:1 ratio) were ball-milled (250 rpm) with acetone for 12 h and dried overnight. The dried powder was sintered at 300 °C for 6 h under a flow of argon (1.5 L/min). Calculations. Energies were calculated using the Vienna Ab-Initio Simulation Package (VASP).33 This program uses a spin-polarized generalized gradient approximation (GGA) with the Perdew−Burke− Ernzerhof (PBE) exchange-correlation parametrization to the density functional theory (DFT),34 with a plane−wave basis set and the projector−augmented wave (PAW) method. All calculations used a unit cell of eight formula units of M3O4 (M = Mn, Fe, Co, or Mn1/3Fe1/3Co1/3). The kinetic energy cutoff used in all calculations was 500 eV. Appropriate k-point meshes were chosen to ensure that the total energies converged within 1 meV per formula unit. All structures were fully relaxed with ferromagnetic orderings. The GGA + U approach was employed to accurately calculate the structural and electronic properties of the transition metal oxides.35,36 U values (5.0 eV for Mn and Fe ions and 4.3 eV for Co ion) and J values (1 eV) were used in all calculations.37 For the calculation of transition metals and metal alloy of Mn1/3Fe1/3Co1/3 with space group of cubic Fm3̅m, the same calculation details were used for those of metal oxides, but a 1 × 2 × 3 supercell and the GGA method were used.37 Structural Characterization of the Multicomponent Oxide. The nanosized MFC was analyzed with an X-ray diffractometer (XRD, D8-Advance) using Cu Kα radiation over a scan range of 15−65°. The lattice parameters were determined by the UnitCell program.38 X-ray photoelectron spectroscopy (XPS, AXIS-HSi) was used to establish the valence states of Mn, Fe, and Co in the MFC. To correct for possible charging of the materials by the X-ray irradiation, the binding energy was calibrated using the C 1s (248.6 eV) spectrum for the hydrocarbon that remained in the XPS analysis chamber as a contaminant. The morphology and particle size of the MFC was investigated using field-emission scanning electron microscopy (FE-SEM, SUPRA 55VP) and high-resolution transmission electron microscopy (HR-TEM, JEM-3000F). The ex-situ XRD data was recorded using Cu Kα radiation over a scan rate of 10−60°. Electrochemical Characterization. Electrodes were prepared by simply mixing the MFC (70 wt %) with polyvinylidene fluoride binder (10 wt %) and a conductive agent (super-P) (20 wt %) in N-methyl-2-pyrrolidone solvent. The resultant slurry was uniformly pasted onto Cu foil. The electrodes were dried at 120 °C for 2 h and then roll-pressed. Test cells were assembled in a glovebox into two-electrode cells with a Li metal counter electrode, a separator (Celgard 2400), and an electrolyte of 1 M lithium hexafluorophosphate in a 1:1 mixture of ethylene carbonate and dimethyl carbonate (Techno Semichem). Electrochemical profiles were obtained in the voltage range from 3.0 to 0.001 V at a current rate of 45.9 mA g−1 (C/20, 1 C = 917.5 mA g−1), using a multichannel potentiogalvanostat (WonATech).

Figure 1. XRD data for the MFC, which has a cubic spinel AB2O4 structure. A represents the tetrahedral sites and B represents the octahedral sites.

pattern of the cubic spinel AB2O4 structure for the MFC was that of a single phase and had no peak splitting into single component oxides (Mn3O4, Fe3O4, or Co3O4). This indicated that a solid solution of Mn, Fe, and Co in an AB2O4 spinel structure had been formed. It should be noted that the cubic spinel structure (Fd3m ̅ ) was obtained even though 1/3 of the M in M3O4 were occupied by Mn ions. It has been reported that Mn3O4 can be transformed into the cubic spinel structure (Fd3̅m) at high temperature, that is, above the Jahn−Teller transition (JTT) temperature of 1000 °C.41 However, the cubic spinel structure forms below the JTT temperature for M3O4 containing 33% Mn. The lattice parameters measured for the synthesized MFC are presented in Table 1 along with data 40,41,43 for Table 1. Lattice Parameters of Mn3O4, Fe3O4, and Co3O4 and the MFC with Cubic Spinel AB2O4 Structure from Experimental Results and the Literaturea Mn3O4 Fe3O4 Co304 MnFeCo04

a(A)

ref

8.420 8.397 8.065 8.384

40 41 43 this work

a

The experimental lattice parameters for Mn3O4, Fe3O4, and Co3O4 have been reported elsewhere, and that for the MFC was obtained in this work with the UnitCell program.

Mn3O4, Fe3O4, and Co3O4. The structural refinement with an Fd3m ̅ space group gave the lattice parameter of MFC as 8.384 Å. This value is comparable to the average lattice parameters of Mn3O4, Fe3O4, and Co3O4, consistent with a single-phase solid solution for the MFC. The solid-solution behavior of the MFC was also predicted from first principles calculation of the formation energy. First principles calculations were performed for various configurations of transition metals in the octahedral and tetrahedral sites to determine the most energetically favorable sites for Mn, Fe, and Co in the cubic spinel AB2O4 structure. Figure 2a compares the total energies of cases having a random distribution of transition metals in octa/tetrahedral sites with those having a particular ordering of transition metals. According to general alloy theory, the interaction among the

■

RESULTS AND DISCUSSION Structural information was obtained from XRD analysis (Figure 1). A typical cubic spinel structure was observed that was free of impurities. In general, Co3O4 and Fe3O4 have the cubic spinel AB2O4 structure (space group Fd3̅m), in which 2/3 of the Co (or Fe) atoms occupy octahedral sites (B sites) and 1/3 of the Co (or Fe) occupies tetrahedral sites (A sites),39,40 while Mn3O4 has a distorted spinel structure (tetragonal hausmannite structure, space group I41/amd) with Mn3+ in the octahedral sites and Mn2+ in the tetrahedral sites because of the Jahn− Teller effect of Mn3+ ions at room temperature.41,42 The XRD 721

dx.doi.org/10.1021/cm2036794 | Chem. Mater. 2012, 24, 720−725

Chemistry of Materials

Article

Table 2. Comparison of XPS Peaks between Our Experimental Data and Previously Reported Data Establishing the Valence States of Co, Fe, and Mn. 2+

Co (this work) Co2+ (CoO) Co3+ (Co2Os) Co2++Co3+ (Co304)

Co p3/2

Co p1/2

780.0 eV

795.6 eV

786.2 eV

802.0 eV

780.2 eV 779.2 eV 779.5 eV

796.9 eV 794.4 eV 794.8 eV

786.9 eV 790.0 eV 788.6 eV

802.8 eV 804.9 eV

Fe p3/2 Fe3+ (this work) Fe2+ (Fe2SiO4) Fe2+ (Fe0.94O) Fe3+ (Fe2O3) Fe2+ + Fe3+ (Fe3O4) Mn3+ Mn3+ Mn3+ Mn2+

Figure 2. (a) Total energy comparison between single-phase Mn3O4, Fe3O4, and Co3O4 and the solid solution when Mn, Fe, and Co occupy tetrahedral sites (A sites). (b) Integrated spin as a function of integration radius (Å) around Mn, Fe, and Co in the MFC.

641.5 eV 641.41 eV 641.9 eV 642.6 eV

Fe p1/2 724.5 eV 722.6 eV 723.2 eV 724.6 eV 724.1 eV Mn p1/2 653.0 eV 653.11 eV 652.4 eV 654.5 eV

ref this work 45 45 46

satellite 718.6 714.7 715.5 718.8

eV eV eV eV

satellite

ref this work 47 47 47 47 ref this work 48 49 49

than the phase separated case, the preference of Co to occupy A sites still prevails. To understand this phenomenon in more detail, the valence state of each transition metal was calculated by integrating the electron spin around each atom. Figure 2b shows the net spin moment integrated as a function of distance from the ion core for the transition metals in the MFC. The spin counts of Mn, Fe, and Co indicate that the oxidation states of Mn and Fe are +3, while that of Co is +2. Slight underestimation of the moment compared to the expected value is normal because the remainder of the moment is likely to be on the oxygen ions.29,32,44 The valence change for the Mn, Fe, and Co in the MFC is consistent with published data for the Li(Mn1/3Fe1/3Co1/3)PO4 olivine compound, where the charge density around Fe2+ and Mn2+ decreases while the Co2+ gains charge.27,32 This is due to the electronegativity difference among Mn, Fe, and Co cations in the structure; Co ion has the stronger electron affinity. In the same vein, it is well-known that the redox potential of Co2+/Co3+ is higher than that of Mn2+/ Mn3+ and Fe2+/Fe3+. It is generally observed that A sites in AB2O4 are preferentially occupied by the lower-valent cation, as seen in numerous spinels such as Mn2+Mn3+2O4, Mg2+Al3+2O4, Mg2+Cr3+2O4, Cu2+Fe3+2O4, and Li+Mn3.5+2O4. Therefore, the preference of Co for the A sites in the MFC AB2O4 structure is closely related to the fact that the Co ion is in a lower oxidation state than the Mn and Fe ions. XPS analysis confirmed the valence states of the metal ions (Figure 3). In the Co region, the two characteristic peaks for

transition metals (Mn, Fe, and Co) can be estimated as follows:32 ΔEmix = E(MnFeCoO4 ) −

(this work) (Mn2O3) (Mn2O3) (MnO2)

711.4 eV 709.0 eV 709.5 eV 711.0 eV 710.6 eV Mn p3/2

satellite

1 [E(Mn3O4 ) + E(Fe3O4 ) 3

+ E(Co3O4 )]

A negative ΔEmix indicates that Mn, Fe, and Co ions have an attractive interaction in this framework and will be either randomly mixed or ordered depending on the strength of the interaction and the synthesis condition. A positive ΔEmix indicates that phase separation to Mn3O4, Fe3O4, and Co3O4 is energetically favorable. From the calculation results, it was found that ΔEmix is −279 meV per formula unit when Co occupies tetrahedral sites (A sites, ● in Figure 2a), while ΔEmix is +148 meV or +7 meV per formula unit when Mn or Fe occupy tetrahedral sites (A sites), respectively. These results indicate that Co preferentially occupies the tetrahedral sites (A sites), and this drives the formation of the solid solution rather than segregation into Mn3O4, Fe3O4, and Co3O4. We also calculated the energy of M3O4 for a random distribution of Mn, Fe, and Co in octa/tetrahedral sites. The range of ΔEmix for all the configurations considered in the given supercell size is indicated by the shaded area in Figure 2a. While the M3O4 with a random distribution of transition metals is more stable

Figure 3. XPS data for the MFC in the (a) Co, (b) Fe, and (c) Mn regions, revealing the valence states of Co, Fe, and Mn, respectively. 722

dx.doi.org/10.1021/cm2036794 | Chem. Mater. 2012, 24, 720−725

Chemistry of Materials

Article

Figure 4. (a) Charge/discharge profiles of a simple mixture of Mn3O4, Fe3O4, and Co3O4 and (b) of the MFC electrode at different cycles. (c) Results of dQ/dV analysis for the MFC electrode and the simple mixture of Mn3O4, Fe3O4, and Co3O4. Figure 5. Morphology of the MFC. (a) SEM and (b, c) HR-TEM analysis of the MFC (inset electron diffraction pattern of the selected area).

Co 2p3/2 and Co 2p1/2 at 780.0 and 795.6 eV were observed with two additional satellite peaks at 786.2 and 802.0 eV. For Fe, the two main peaks for Fe 2p3/2 and Fe 2p1/2 at 711.4 and 724.5 eV were found with an additional satellite peak at 718.6 eV. Lastly, in the Mn region, two sharp peaks for Mn 2p3/2 and Mn 2p1/2 were observed at 641.5 and 653.0 eV. Literature data for transition metals in various oxidation states are given in Table 2. The satellite peaks are distinct for Co2+ and Co3+ and can be indicators of the Co valence.45,46 The satellite peaks in our sample corresponded to Co2+.45 For Fe, the two main peaks and a satellite peak for Fe2+ and Fe3+ are also distinct. Comparison with the literature reference values indicated that the valence of Fe in the MFC is +3.47 The Mn of our MFC sample corresponded to Mn3+.48,49 Summarizing, in our MFC, the valence states of Mn and Fe were +3 and that of Co was +2, in a good agreement with first principles calculation.

To investigate the effect of valence shift on the electrochemical properties, we tested the MFC electrode in a Li cell with a galvanostatic measurement and compared the results to those for a mixture electrode composed of Mn3O4, Fe3O4, and Co3O4 as single components. The electrochemical test of the MFC electrode used a current rate of 45.9 mA g−1, corresponding to C/20 (1C = 917.5 mA g−1), from 0.001 to 3.0 V. Figure 4a shows the first and second charge/discharge profiles of the mixture electrode. Three distinct plateaus were observed, which is attributable to the electrochemical reduction of Co, Fe, and Mn ions in each potential. However, only one voltage plateau was identified for MFC in contrast to the mixture of Mn3O4, Fe3O4, and Co3O4, presenting three different plateaus 723

dx.doi.org/10.1021/cm2036794 | Chem. Mater. 2012, 24, 720−725

Chemistry of Materials

Article

Figure 6. (a) ex-situ XRD analysis of MFC electrode during battery cycling from 3.0 to 0.001 V, (b) XRD patterns generated from first principles calculation of metals (Mn, Fe, and Co) and metal alloy (Mn1/3Fe1/3Co1/3) with space group of cubic Fm3̅m, and (c) ex-situ TEM analysis result of fully discharged sample of the MFC.

stable than phase separation of each transition metal by about −2.44 meV per formula unit. For better understanding of the lithiated phase, we performed ex-situ TEM analysis. To aid the comparison of interplanar distances of transition metals or metal alloy, XRD patterns were generated from first principles calculation for metals (Mn, Fe, and Co) and metal alloy (Mn1/3Fe1/3Co1/3) with space group of cubic Fm3m ̅ (Figure 6b). By ex-situ TEM analysis, as shown in Figure 6c, the interplanar distances of 0.201 nm, 0.175 nm, and 0.270 nm were identified, which match to those of the (111) and (200) planes of the metal alloy (Mn1/3Fe1/3Co1/3) and that of the (111) plane of Li2O, respectively. From these data, we suggest the electrochemical reaction mechanism of the MFC as follows:

during battery cycling, which was not altered during extended cycling as well (Figure 4b). It indicates that the electrochemical reaction of the MFC is highly reversible and the multicomponent effect is still active, even after the first cycle, which involves the conversion reaction. The shift of the electrochemical potentials was more evident with a dQ/dV analysis of the two electrodes (Figure 4c). Only a single redox potential was observed for the MFC electrode, even though the three transition metals participated in the electrochemical reaction. This was because charge redistribution occurred among the transition metals when mixed at the atomic scale in the crystal. It presents that metal substitution can substantially affect the electrochemical performance of the multicomponent electrode. The charge/discharge profiles at the first, second, third, and fourth cycles are presented in Figure 4b. After the first discharge, the capacity saturated at about 1000 mAh g−1. The shape of the profiles was not significantly altered, except for the first discharge, indicating that the electrochemical reaction was highly reversible. The high electrochemical activity of the sample can be explained from the extremely small particle size of our synthetic MFC. An FE-SEM image (Figure 5a) shows that very fine MFC particles formed a few hundred nanometer-sized secondary particles. HR-TEM was used to verify the morphology and particle size of the MFC (Figure 5b and c). The primary particle size of MFC was about 7 nm. The magnified TEM image in Figure 5c shows that the spacing between the lattice fringes was 0.291 and 0.250 nm, corresponding to the (220) and (311) planes of the MFC. The high-resolution image and electron diffraction pattern of the selected area indicated that highly ordered spinel nanoparticles were synthesized. It is emphasized that the fabrication of the MFC only involved a mild heat treatment (300 °C) following simple mixing of the precursors. This is an economically viable process suitable for mass production. To identify the electrochemical reaction mechanism of the multicomponent oxide (MFC), ex-situ XRD analysis was carried out for the electrode at different lithiated states. (Figure 6a) As the MFC electrode was discharged, it converts to an amorphouslike phase. It is expected that the final products by lithiation are amorphous-like Li2O and M metal phase. Whether M metal alloy of Mn, Fe, and Co is formed or separation of each transition metal (Mn, Fe, and Co) phase occurs is not clear. However, first principles calculation indicated that solid solution of transition metals (Mn, Fe, Co) was slightly more

MnFeCoO4 + 8Li+ + 8e− ↔ 3Mn1/3Fe1/3Co1/3(metal alloy) + 4Li2O

■

CONCLUSIONS

■

AUTHOR INFORMATION

The structural and electrochemical properties of the multicomponent oxide, MFC, were investigated experimentally and using first principles calculation. We found that the solid solution of MFC had a cubic spinel structure, with Co preferentially occupying tetrahedral sites (A sites) in an AB2O4 spinel structure. It is believed that the strong preference of Co for the A sites was due to the charge-ordering among the transition metals (Co2+ vs Mn3+, Fe3+) in the MFC, a result of electronegativity differences among the cations. As a result, the redox potential of the MFC electrode was quite different from that made from a mixture of the single component spinels. This suggests that the electrochemical properties of metal oxides can be tuned by metal substitution. Furthermore, we demonstrated an economically viable approach for the fabrication of a highperformance MFC nanoparticle anode.

Corresponding Author

* Tel.: +82-2-880-7165. E-mail: [email protected]. Notes

The authors declare no competing financial interest. 724

dx.doi.org/10.1021/cm2036794 | Chem. Mater. 2012, 24, 720−725

Chemistry of Materials

■

ACKNOWLEDGMENTS

■

REFERENCES

Article

(30) Hinuma, Y.; Meng, Y. S.; Kang, K.; Ceder, G. Chem. Mater. 2007, 19, 1790. (31) Breger, J.; Meng, Y. S.; Hinuma, Y.; Kumar, S.; Kang, K.; ShaoHorn, Y.; Ceder, G.; Grey, C. P. Chem. Mater. 2006, 18, 4768. (32) Gwon, H.; Seo, D. -H.; Kim, S. -W.; Kim, J.; Kang, K. Adv. Funct. Mater. 2009, 19, 3285. (33) Kresse, G.; Furthmuller, J. Comput. Mater. Sci. 1996, 6, 15. (34) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865. (35) Anisimov, V. I.; Zaanen, J.; Andersen, O. K. Phys. Rev. B 1991, 44, 943. (36) Xu, B.; Meng, S. J. Power Sources 2010, 195, 4971. (37) Wang, L.; Maxisch, T.; Ceder, G. Phys. Rev. B 2006, 73, 195107. (38) Holland, T. J. B.; Redfern, S. A. T. Mineral. Mag. 1997, 61, 65. (39) Tripathy, S. K.; Christy, M.; Park, N. -H.; Suh, E. -K.; Anand, S.; Yu, Y. -T. Mater. Lett. 2008, 62, 1006. (40) Tarrach, G.; Burgler, D.; Schaub, T.; Wiesendanger, R.; Guntherodt, H. -J. Surf. Sci. 1993, 285, 1. (41) Gorbenko, O. Y.; Graboy, I. E.; Amelichev, V. A.; Bosak, A. A.; Kaul, A. R.; Guttler, B.; Svetchnikov, V. L.; Zandbergen, H. W. Solid State Commun. 2002, 124, 15. (42) Kim, H.; Kim, S. -W.; Hong, J.; Park, Y. -U.; Kang, K. J. Mater. Res. 2011, 26, 2665. (43) Hu, L.; Peng, Q.; Li, Y. J. Am. Chem. Soc. 2008, 130, 16136. (44) Reed, J.; Ceder, G. Electrochem. Solid-State Lett. 2002, 5, A145. (45) Chambers, S. A.; Farrow, R. F. C.; Maat, S.; Toney, M. F.; Folks, L.; Catalano, J. G.; Trainor, T. P.; Brown, G. E. Jr J. Magn. Magn. Mater. 2002, 246, 124. (46) Wang, Y.; Fu, Z. -W.; Qin, Q. -Z. Thin Solid Films 2003, 441, 19. (47) Yamashita, T.; Hayes, P. Appl. Surf. Sci. 2008, 254, 2441. (48) Yang, Z.; Zhang, W.; Wang, Q.; Song, X.; Qian, Y. Chem. Phys. Lett. 2006, 418, 46. (49) Castro, V. D.; Polzonetti, G. J. Electron Spectrosc. Relat. Phenom. 1989, 48, 117.

The authors are grateful to KISTI (Grant No. KSC-2010-C20006) for providing supercomputing resources and this work was supported by the Converging Research Center Program through the Ministry of Education, Science and Technology (2011K000691). This work was also supported by Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (20114010203120).

(1) Tarascon, J. −M.; Armand, M. Nature 2001, 414, 359. (2) Armand, M.; Tarascon, J. -M. Nature 2008, 451, 652. (3) Kang, K.; Meng, Y. S.; Breger, J.; Grey, C. P.; Ceder, G. Science 2006, 311, 977. (4) Kim, H.; Kim, S. -W.; Park, Y. -U.; Gown, H.; Seo, D. -H.; Kim, Y.; Kang, K. Nano Res 2010, 3, 813. (5) Kim, H.; Kim, S. -W.; Hong, J.; Lim, H. -D.; Kim, H. S.; Yoo, J. −K.; Kang, K. J. Electrochem. Soc. 2011, 158, A930. (6) Han, S.; Jang, B.; Kim, T.; Oh, S. M.; Hyeon, T. Adv. Funct. Mater. 2008, 15, 1845. (7) Yamada, A.; Chung, S. C.; Hinokuma, K. J. Electrochem. Soc. 2001, 148, A224. (8) Hong, J.; Seo, D. -H.; Kim, S. -W.; Gwon, H.; Oh, S. -T.; Kang, K. J. Mater. Chem. 2010, 20, 10179. (9) Ryu, J.; Kim, S. -W.; Kang, K.; Park, C. B. ACS Nano 2010, 4, 159. (10) Ji, L.; Lin, Z.; Alcoutlabi, M.; Zhang, X. Energy. Environ. Sci. 2011, 4, 2682. (11) Liu, H.; Wang, G.; Park, J.; Wang, J.; Liu, H.; Zhang, C. Electrochim. Acta 2009, 54, 1733. (12) Zhang, W. -M.; Wu, X. L.; Hu, J. -S.; Guo, Y. -G.; Wan, L. -J. Adv. Funct. Mater. 2008, 18, 3941. (13) Wang, H.; Cui, L. -F.; Yang, Y.; Casalongue, H. S.; Robinson, J. T.; Liang, Y.; Cui, Y.; Dai, H. J. Am. Chem. Soc. 2010, 132, 13978. (14) Kim, H.; Seo, D. -H.; Kim, S. -W.; Kim, J.; Kang, K. Carbon 2011, 49, 326. (15) Liu, Y.; Mi, C.; Su, L.; Zhang, X. Electrochim. Acta 2008, 53, 2507. (16) Liu, H. -J.; Bo, S. -H.; Cui, W. -J.; Li, F.; Wang, C. -X.; Xia, Y. -Y. Electrochim. Acta 2008, 53, 6497. (17) Zhan, F.; Geng, B.; Guo, Y. Chem.Eur. J. 2009, 15, 6469. (18) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J. -M. Nature 2000, 407, 496. (19) Sharma, Y.; Sharma, N.; Rao, G. V. S.; Chowdari, B. V. R. Adv. Funct. Mater. 2007, 17, 2855. (20) Alcantara, R.; Jaraba, M.; Lavela, P.; Tirado, J. L. Chem. Mater. 2002, 14, 2847. (21) Sharma, Y.; Sharma, N.; Rao, G. V. S.; Chowdari, B. V. R. Solid State Ion 2008, 179, 587. (22) Shaju, K. M.; Bruce, P. G. Adv. Mater. 2006, 18, 2330. (23) Wang, Y.; Jiang, J.; Dahn, J. R. Electrochem. Commun. 2007, 9, 2534. (24) Hwang, B. J.; Tsai, Y. W.; Carlier, D.; Ceder, G. Chem. Mater. 2003, 15, 3676. (25) Whitacre, J. F.; Zahgib, K.; West, W. C.; Ratnakumar, B. V. J. Power Sources 2008, 177, 528. (26) Yoon, W. -S.; Grey, C. P.; Balasubramanian, M.; Yang, X. -Q.; McBreen, J. Chem. Mater. 2003, 15, 3161. (27) Seo, D. -H.; Gwon, H.; Kim, S. -W.; Kim, J.; Kang, K. Chem. Mater. 2010, 22, 518. (28) Park, Y. -U.; Kim, J.; Gwon, H.; Seo, D. -H.; Kim, S. -W.; Kang, K. Chem. Mater. 2010, 22, 2573. (29) Kang, K.; Carlier, D.; Reed, J.; Arroyo, E. M.; Ceder, G.; Croguennec, L.; Delmas, C. Chem. Mater. 2003, 15, 4503. 725

dx.doi.org/10.1021/cm2036794 | Chem. Mater. 2012, 24, 720−725