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Synthesis of layered cathode materials Li[CoxNiyMn1−x−y]O2 from layered double hydroxide precursors
Particuology 8 (2010) 202–206
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Synthesis of layered cathode materials Li[Cox Niy Mn1−x−y ]O2 from layered double hydroxide precursors Yanluo Lu ∗ , Yang Zhao State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China
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Article history: Received 23 March 2009 Accepted 17 June 2009 Keywords: Layered Li[Cox Niy Mn1−x−y ]O2 Layered double hydroxides Precursor method Cathode materials
a b s t r a c t Cathode materials Li[Cox Niy Mn1−x−y ]O2 for lithium secondary batteries have been prepared by a new route using layered double hydroxides (LDHs) as a precursor. The resulting layered phase with the ␣NaFeO2 structure crystallizes in the rhombohedral system, with space group R-3m having an interlayer spacing close to 0.47 nm. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation states of Co, Ni and Mn. The effects of varying the Co/Ni/Mn ratio on both the structure and electrochemical properties of Li[Cox Niy Mn1−x−y ]O2 have been investigated by X-ray diffraction and electrochemical tests. The products demonstrated a rather stable cycling behavior, with a reversible capacity of 118 mAh/g for the layered material with Co/Ni/Mn = 1/1/1. © 2010 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.
1. Introduction Recently, layered Li[Co1/3 Ni1/3 Mn1/3 ]O2 materials have attracted considerable interest as an alternative cathode material to LiCoO2 for commercial lithium-ion batteries. Li[Ni1/3 Co1/3 Mn1/3 ]O2 provides higher battery capacity in a wider voltage range, and shows better safety characteristics than conventional LiCoO2 (Belharouak, Sun, Liu, & Amine, 2003; Cho, Shiosaki, & Noguchi, 2006; Choi & Manthiram, 2005; Kang, Abraham, Yoon, Nam, & Yang, 2008; Kang, Yoon, Nam, Yang, & Abraham, 2008; Lee, Kang, Myung, & Sun, 2004; Ohzuku & Makimura, 2001; Thackeray, Kang, Johnson, Vaughey, & Hackney, 2006; Todorov & Numata, 2004; Yabuuchi, Koyama, Nakayama, & Ohzuku, 2005; Yoon et al., 2005). However, Li[Ni1/3 Co1/3 Mn1/3 ]O2 generally shows a poorer first cycle efficiency (<90%) than LiCoO2 (98%), which cancels out the energy density of a lithium-ion battery adopting the former as the cathode active material (Choi & Manthiram, 2005; Cho et al., 2006; Kang, Abraham, et al., 2008; Kang, Yoon, et al., 2008). It is well known that the performance of the powders used as cathode materials in lithium-ion batteries is strongly affected by their preparation processes (Li, Muta, Zhang, Yoshio, & Noguchi, 2004; Lin, Wen, Gu, & Huang, 2008), thus indicating how important it is to select a suitable method to prepare high-performance Li[Co1/3 Ni1/3 Mn1/3 ]O2 (Shaju, Subba Rao, & Chowdari, 2002). Li[Co1/3 Ni1/3 Mn1/3 ]O2 was first prepared by
∗ Corresponding author. Tel.: +86 10 64412115; fax: +86 10 64425385. E-mail address: [email protected] (Y. Lu).
conventional solid-state reaction methods (Kim & Chung, 2004; Ohzuku & Makimura, 2001), which require prolonged heat treatment at relatively high temperatures with repeated intermediate grinding because of the heterogeneity of the precursors. In order to overcome these disadvantages, various new techniques, such as glycine-nitrate combustion (Patoux & Doeff, 2004), hydroxide co-precipitation (Lee et al., 2004; Myung, Kim, & Sun, 2004), carbonate co-precipitation (Cho, Park, & Yoshio, 2004; Cho, Park, Yoshio, Hirai, & Hideshima, 2005), ultrasonic spray pyrolysis (Park et al., 2004), solution spray drying (Li et al., 2004), and sol–gel (Hwang, Tsai, Carlier, & Ceder, 2003) processes have been developed for preparing high-quality Li[Co1/3 Ni1/3 Mn1/3 ]O2 . Although they led to homogeneous materials with small particle size, these synthetic routes are complex, calling for precursors which require expensive initial or intermediate reagents, and long time for drying. Moreover, the use of organic acids or hydroxides, which are corrosive to the production equipment, makes these methods less than ideal for the industrial-scale production of the materials. Layered double hydroxides (LDHs) or hydrotalcite-like compounds (Canavi, Trifiro, & Vaccari, 1991; Vaysse, GuerlouDemourgues, & Delmas, 2002), already known for a considerable time, have been widely studied. The basic layer structure of LDHs is based on that of brucite [Mg(OH)2 ], which consists of magnesium ions surrounded approximately octahedrally by hydroxide ions. These octahedral units form infinite layers by edge sharing, with the hydroxide ions sitting perpendicular to the plane of the layers. The layers then stack on top of one another to form a three-dimensional structure. The basic structure of an LDH may be derived by
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doi:10.1016/j.partic.2010.03.006
Y. Lu, Y. Zhao / Particuology 8 (2010) 202–206
substitution of a fraction of the divalent cations in a brucite lattice by trivalent cations such that the layers acquire a positive charge, which is balanced by intercalation of anions between the layers (Vaccari, 1998). LDHs may be described by the general formula [M1−x II Mx III (OH)2 ]x+ [Ax/n n− ·yH2 O]x− , where MII and MIII are divalent and trivalent metal cations, and An− is an n-valent anion. It is often said that pure LDH phases can be formed for stoichiometries in the range of 0.20 < x < 0.33 (Han, Guerlou-Demourgues, & Delmas, 1997; Jones & Chibwe, 1990; Trave, Selloni, Goursot, Tichit, & Weber, 2002), i.e., for MII /MIII ratios in the range of 2–4. The MII /MIII isomorphous substitution in the octahedral sites of the hydroxide sheets results in a well-distributed single phase in these materials when they are prepared by the co-precipitation method (Canavi et al., 1991; Dunn, Peacor, & Palmer, 1979; Goswamee, Sengupta, Bhattacharyya, & Dutta, 1998; Kovanda, Grygar, & Dorniˇcák, 2003). In this work, layered Li[Cox Niy Mn1−x−y ]O2 materials were prepared by using LDHs as precursor. The precursor CoNiMn LDHs were first synthesized by co-precipitation, and after mixing with an appropriate amount of LiOH·H2 O, were calcined in air at 900 ◦ C. The structure and the initial electrochemical performance of the resulting Li[Cox Niy Mn1−x−y ]O2 products have been examined.
2. Methods and materials CoNiMn LDHs with Co/Ni/Mn molar ratios of 1/1/1, 2/1/1 and 1/2/1 were prepared by a co-precipitation method similar to that described previously for CoMn LDHs (Lu, Wei, Yang, & Li, 2007). A solution containing the metallic nitrate salts Ni(NO3 )2 ·6H2 O, Co(NO3 )2 ·6H2 O and Mn(NO3 )2 (0.6 M) with the chosen molar ratio was added to a beaker at room temperature. A second aqueous solution containing 100 mL NaOH (1 M) and Na2 CO3 (0.5 M) was added dropwise over 3 h into the metallic nitrate salts solution with vigorous stirring. Air was bubbled throughout the reaction mixture during the entire addition period. The resulting suspension was aged at room temperature for 12 h, and the precipitate obtained was collected by centrifugation and washed thoroughly with distilled water. It was then well mixed with the appropriate amount of LiOH·H2 O (Li/(Co + Ni + Mn) = 1.1) by grinding, and the resulting mixture dried at 70 ◦ C for 12 h. The mixture was calcined at 900 ◦ C for 24 h in air and cooled to room temperature. The product was washed thoroughly with distilled water and dried at 70 ◦ C for 12 h in air. XRD data were collected from 2Â = 10◦ to 2Â = 85◦ with 0.04◦ step size, each step lasting 10 s. Unit cell parameters were obtained by least squares refinement of the powder XRD data. Elemental analysis was performed by ICP spectroscopy using a Shimadzu ICPS-7500 instrument. X-ray photoelectron spectra (XPS) were collected using a Thermo VG Sigma Probe X-ray photoelectron spectrometer with an Mg K␣ X-ray source (200 W). The base pressure, in both the main and the preparation chambers, was 3 × 10−9 mbar. All spectra were charge referenced to the C 1s XPS peak (284.6 eV). In order to evaluate the electrochemical performance of the materials, composite electrodes were formed by mixing the active material with acetylene black and polytetrafluoroethylene (PTFE) in the weight ratio 85/10/5, and then pressing into pellets. The composite electrodes were dried at 120 ◦ C in vacuum for 24 h before use. Button-type cells were assembled in a glove box filled with argon with less than 1 ppm H2 O and O2 . A cell was prepared by assembling the cathode, separator, and the anode in a sandwich structure. The anode was lithium metal and the electrolyte was a 1 M solution of LiClO4 in a mixture of ethylene carbonate and diethyl carbonate (EC/DEC) in the volume ratio 1/1. The galvanostatic charge–discharge tests were carried out between 2.8 and 4.3 V (versus Li/Li+ ) at a constant current density of 0.2 mA/cm2
203
Fig. 1. Powder XRD patterns of CoNiMn LDHs with different Co/Ni/Mn ratios. (A) Co/Ni/Mn = 1/1/1; (B) Co/Ni/Mn = 2/1/1; C. Co/Ni/Mn = 1/2/1.
(corresponding to the 0.07 C rate) using a LAND CT2001A cycle life tester. 3. Results and discussion 3.1. Structural study of LDHs precursor The powder XRD patterns of the CoNiMn LDHs with different Co/Mn/Ni ratios are shown in Fig. 1. The phases crystallize in the trigonal system (space group: R-3m) with a basal spacing of 0.755 nm in each case, similar to that reported for MgAl LDHs containing interlayer carbonate anions (Trave et al., 2002). During the co-precipitation, most of the MnII was oxidized to MnIII by the oxygen in air which was bubbled through the solution. As a result, the MII /MIII molar ratio in the LDHs should be in accordance with the (Ni + Co)/Mn ratio in the precursor mixture. The ideal formula of the LDH with a precursor mixture with (Co/Ni/Mn = 1/1/1) can therefore be written as follows. 3.2. Structure and composition of the layered Li[Cox Niy Mn1−x−y ]O2 The powder XRD patterns of Li[Cox Niy Mn1−x−y ]O2 with different Co/Ni/Mn ratios, shown in Fig. 2, can be indexed on the basis of the ␣-NaFeO2 type structure. The layered phase crystallizes in the rhombohedral system, space group R-3m with an interlayer spacing close to 0.47 nm. The lattice parameters of Li[Cox Niy Mn1−x−y ]O2 calculated from the XRD patterns are listed in Table 1. Increasing the Mn content results in a slight expansion of the unit cell parameters. It has been reported that large c/a ratios suggest a well-defined layered structure (Armstrong, Robertson, & Bruce, 1999), so the c/a ratios for the materials prepared in this work (all close to 5) indicate a well-defined layered structure and a high degree of cation ordering. Table 1 Lattice parameters for Li[Cox Niy Mn1−x−y ]O2 with different Co/Ni/Mn ratios. Co/Ni/Mn ratio
d003 /nm
d110 /nm
a/nm
c/nm
c/a
1/1/1 2/1/1 1/2/1
0.4754(9) 0.4694(5) 0.4685(9)
0.1430(7) 0.1419(7) 0.1426(4)
0.2861 0.2839 0.2853
1.4265 1.4082 1.4058
4.986 4.960 4.927
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Fig. 2. Powder XRD patterns of Li[Cox Niy Mn1−x−y ]O2 with different Co/Ni/Mn ratios. (A) Co/Ni/Mn = 1/1/1; (B) Co/Ni/Mn = 2/1/1 and (C) Co/Ni/Mn = 1/2/1.
Elemental analytical data for the Li[Cox Niy Mn1−x−y ]O2 products, as obtained by ICP spectroscopy, are listed in Table 2. The Co/Ni/Mn molar ratio in each product was close to the ratio in the corresponding synthesis mixture, while the lithium content increased as the value of x increased and the value of y decreased (Table 2). This may be because larger amounts of Ni (i.e., large values of y) lead to the formation of Ni(OH)2 which results in a reduced charge density in the layers and less intercalation of Li+ ions between the layers. It should also be noted that it has been reported that a native surface film, mainly composed of Li2 CO3 , exists on all transition metal oxide cathode materials based on manganese, cobalt, and nickel (Armstrong et al., 1999). This surface component could arise from the precursors used to synthesize these metal oxides or, more likely, from the reaction between the metal oxides and the CO2 in the atmosphere during the processing of these oxidizing materials (Aurbach, 2000). X-ray photoelectron spectroscopy (XPS) can provide chemical information such as the oxidation state, as well as the semiquantitative composition of the surface, and is thus a very useful method for studying surface properties. Fig. 3 displays the XPS results for Li[Co0.50 Ni0.25 Mn0.25 ]O2 . The binding energy of Mn 2p3/2 is 642.5 eV, which is in agreement with that reported in the literature (Galakhov et al., 2000) for MnO2 , indicating that the predominant Mn species near the surface is MnIV . As a rule, compounds containing high-spin CoII ions have strong shake-up satellites in Co
Fig. 3. X-ray photoelectron spectra of Co, Ni, Mn and O in Li[Co0.50 Ni0.25 Mn0.25 ]O2 .
Y. Lu, Y. Zhao / Particuology 8 (2010) 202–206
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Table 2 Elemental analysis of Li[Cox Niy Mn1−x−y ]O2 by ICP. Co/Ni/Mn molar ratio
1/1/1 2/1/1 1/2/1
Content (%)
Composition
Li
Mn
Ni
Co
6.275 6.154 6.611
15.765 12.032 11.539
19.192 28.447 13.719
17.317 12.593 24.999
Li1.00 [Co0.32 Ni0.36 Mn0.32 ]O2 ·xH2 O Li1.10 [Co0.49 Ni0.27 Mn0.24 ]O2 ·xH2 O Li0.97 [Co0.23 Ni0.53 Mn0.24 ]O2 ·xH2 O
2p XPS spectra, while CoIII is diamagnetic and has no satellite peak (Oswald & Brückner, 2004), and the valence of cobalt can therefore be determined by XPS spectroscopy. The Co 2p3/2 and Co 2p1/2 peaks in Fig. 3 at 780.1 and 795.5 eV respectively, are close to those reported previously (Oku & Hirokawa, 1975) for CoIII in ZnCo2 O4 . No visible satellite peaks can be observed, confirming that most of CoII has been oxidized to CoIII during the calcination. The Ni 2p3/2 peak at 855.1 eV is close to the overlapping peaks reported previously for Ni(OH)2 and Ni2 O3 (Oswald & Brückner, 2004). The O 1s spectrum contains two peaks: one component at 529.8 eV is typical of metal–oxygen bonding and the other at 531.0 eV is usually associated with oxygen in OH− groups. The presence of this latter peak indicates that the surface of the materials was hydroxylated to some extent. XPS gives an elemental Co/Ni/Mn ratio of 45/31/24 near the surface of Li[Co0.50 Ni0.25 Mn0.25 ]O2 . Compared to that in the bulk, as determined by ICP (Co/Ni/Mn = 49/27/24), the Ni content near the surface is higher, and Co content is lower. This shows that Ni is stabilized near the surface, perhaps by the formation of Ni(OH)2 , as suggested above. 3.3. Electrochemical performance of Li[Cox Niy Mn1−x−y ]O2 The charge–discharge curves of the cell for the first cycle with the Li[Cox Niy Mn1−x−y ]O2 samples with Co/Ni/Mn = 1/1/1, 2/1/1 and 1/2/1 used as cathode materials are illustrated in Fig. 4, and the cycling behavior is shown in Fig. 5. The three samples have an initial EMF of 2.7–3.2 V. It can be seen in Fig. 4 that the molar ratio of Co/Ni/Mn has a significant influence on the charge–discharge capacity. The first charge and discharge capacities of sample A (Co/Ni/Mn = 1/1/1) were 145.5 and 118.1 mAh/g, respectively. The specific capacity of sample A after the 10th cycle was 74.6 mAh/g (Fig. 5). The capacity of sample B (Co/Ni/Mn = 2/1/1) was improved with the increase of Co content, and the reversible
Fig. 5. Cycle performance of Li[Cox Niy Mn1−x−y ]O2 as cathode materials. (A) Co/Ni/Mn = 1/1/1; (B) Co/Ni/Mn = 2/1/1 and (C) Co/Ni/Mn = 1/2/1.
capacity of sample B was 126.5 mAh/g. In contrast, the capacity was decreased with the increase of Ni content, and sample C (Co/Ni/Mn = 1/2/1) had a reversible capacity of 86.2 mAh/g (Fig. 4). This indicates that higher Co content is favorable for the intercalation–deintercalation of lithium ions, while higher Ni content restricts the intercalation–deintercalation of lithium ions. The specific capacity of sample C after the 10th cycle was 80.0 mAh/g (Fig. 5). 4. Conclusions Layered rhombohedral Li[Cox Niy Mn1−x−y ]O2 materials with the ␣-NaFeO2 structure have been synthesized by solid-state reaction of CoNiMn LDH precursors and LiOH. XRD patterns and ICP results demonstrated that the crystal integrity and the capacity of lithium intercalation were improved by increasing the Co content and decreasing the Ni content. XPS revealed that NiII , MnIV and CoIII predominate near the surface of the sample, and Ni is preferentially stabilized near the surface. The electrochemical behavior of Li[Co1/3 Ni1/3 Mn1/3 ]O2 as a cathode material in lithium secondary batteries showed that this material exhibits high charge–discharge capacities of over 118 mAh/g between 2.8 and 4.3 V and viable cycling stability. Acknowledgments
Fig. 4. Charge–discharge curves of Li[Cox Niy Mn1−x−y ]O2 as cathode materials. (A) Co/Ni/Mn = 1/1/1; (B) Co/Ni/Mn = 2/1/1 and (C) Co/Ni/Mn = 1/2/1.
This work was supported by the National Natural Science Foundation of China, the 111 Project (grant no.: B07004) and the Natural Science Foundation for Young Teachers of Beijing University of Chemical Technology (grant no.: QN0723).
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References Armstrong, A. R., Robertson, A. D., & Bruce, P. G. (1999). Structural transformation on cycling layered Li(Mn1−y Coy )O2 cathode materials. Electrochimica Acta, 45, 285–294. Aurbach, D. (2000). Review of selected electrode–solution interactions which determine the performance of Li and Li ion batteries. Journal of Power Sources, 89, 206–218. Belharouak, I., Sun, Y.-K., Liu, J., & Amine, K. (2003). Li(Ni1/3 Co1/3 Mn1/3 )O2 as a suitable cathode for high power applications. Journal of Power Sources, 123, 247–252. Canavi, F., Trifiro, F., & Vaccari, A. (1991). Hydrotalcite-type anionic clays: Preparation, properties and applications. Catalysis Today, 11, 173–301. Cho, T. H., Park, S. M., & Yoshio, M. (2004). Preparation of layered Li[Ni1/3 Mn1/3 Co1/3 ]O2 as a cathode for lithium secondary battery by carbonate coprecipitation method. Chemistry Letters, 33, 704–705. Cho, T. H., Park, S. M., Yoshio, M., Hirai, T., & Hideshima, Y. (2005). Effect of synthesis condition on the structural and electrochemical properties of Li[Ni1/3 Mn1/3 Co1/3 ]O2 prepared by carbonate co-precipitation method. Journal of Power Sources, 142, 306–312. Cho, T.-H., Shiosaki, Y., & Noguchi, H. (2006). Preparation and characterization of layered LiMn1/3 Ni1/3 Co1/3 O2 as a cathode material by an oxalate co-precipitation method. Journal of Power Sources, 159, 1322–1327. Choi, J., & Manthiram, A. (2005). Investigation of the irreversible capacity loss in the layered LiNi1/3 Mn1/3 Co1/3 O2 cathodes. Electrochemical and Solid-State Letters, 8, C102–C105. Dunn, P. J., Peacor, D. R., & Palmer, T. D. (1979). Desautelsite, a new mineral of the pyroaurite group. American Mineralogist, 64, 127–130. Galakhov, V. R., Korotin, M. A., Ovechkina, N. A., Kurmaev, E. Z., Gorshkov, V. S., Kellerman, D. G., et al. (2000). Electronic structure of LiMnO2 : X-ray emission and photoelectron spectra and band structure calculations. The European Physical Journal B, 14, 281–286. Goswamee, R. L., Sengupta, P., Bhattacharyya, K. G., & Dutta, D. K. (1998). Adsorption of Cr(VI) in layered double hydroxides. Applied Clay Science, 13, 21–34. Han, K. S., Guerlou-Demourgues, L., & Delmas, C. (1997). Intercalation process of metavanadate chains into a nickel–cobalt layered double hydroxide. Solid State Ionics, 98, 85–92. Hwang, B. J., Tsai, Y. W., Carlier, D., & Ceder, G. (2003). A combined computational/experimental study on LiNi1/3 Co1/3 Mn1/3 O2 . Chemistry of Materials, 15, 3676–3682. Jones, W., & Chibwe, M. (1990). The synthesis, chemistry and catalytic applications of layered double hydroxides. In I. V. Mitchell (Ed.), Pillared latered structures (pp. 67–78). London: Elsevier. Kang, S.-H., Abraham, D. P., Yoon, W.-S., Nam, K.-W., & Yang, X.-Q. (2008). Firstcycle irreversibility of layered Li–Ni–Co–Mn oxide cathode in Li-ion batteries. Electrochimica Acta, 54, 684–689. Kang, S.-H., Yoon, W.-S., Nam, K.-W., Yang, X.-Q., & Abraham, D. P. (2008). Investigating the first-cycle irreversibility of lithium metal oxide cathodes for Li batteries. Journal of Materials Science, 43, 4701–4706. Kim, J. M., & Chung, H. T. (2004). The first cycle characteristics of Li[Ni1/3 Co1/3 Mn1/3 ]O2 charged up to 4.7 V. Electrochimica Acta, 49, 937–944. Kovanda, F., Grygar, T., & Dorniˇcák, V. (2003). Thermal behaviour of Ni–Mn layered double hydroxide and characterization of formed oxides. Solid State Sciences, 5, 1019–1026.
Lee, M. H., Kang, Y. J., Myung, S. T., & Sun, Y. K. (2004). Synthetic optimization of Li[Ni1/3 Co1/3 Mn1/3 ]O2 via co-precipitation. Electrochimica Acta, 50, 939–948. Li, D. C., Muta, T., Zhang, L. Q., Yoshio, M., & Noguchi, H. (2004). Effect of synthesis method on the electrochemical performance of LiNi1/3 Mn1/3 Co1/3 O2 . Journal of Power Sources, 132, 150–155. Lin, B., Wen, Z., Gu, Z., & Huang, S. (2008). Morphology and electrochemical performance of Li[Ni1/3 Co1/3 Mn1/3 ]O2 cathode material by a slurry spray drying method. Journal of Power Sources, 175, 564–569. Lu, Y., Wei, M., Yang, L., & Li, C. (2007). Synthesis of layered cathode material Li[Cox Mn1−x ]O2 from layered double hydroxides precursors. Journal of Solid State Chemistry, 180, 1775–1782. Myung, S. T., Kim, G. H., & Sun, Y. K. (2004). Synthesis of Li[Ni1/3 Co1/3 Mn1/3 ]O2 -zFz via coprecipitation. Chemistry Letters, 33, 1388–1389. Ohzuku, T., & Makimura, Y. (2001). Layered lithium insertion material of LiCo1/3 Ni1/3 Mn1/3 O2 for lithium-ion batteries. Chemistry Letters, 30, 642–643. Oku, M., & Hirokawa, K. (1975). X-ray photoelectron spectroscopy of Co3 O4 , Fe3 O4 , Mn3 O4 and related compounds. Journal of Electron Spectroscopy and Related Phenomena, 7, 405–473. Oswald, S., & Brückner, W. (2004). XPS depth profile analysis of non-stoichiometric NiO films. Surface and Interface Analysis, 36, 17–22. Park, S. H., Yoon, C. S., Kang, S. G., Kim, H.-S., Moon, S.-I., & Sun, Y.-K. (2004). Synthesis and structural characterization of layered Li[Ni1/3 Co1/3 Mn1/3 ]O2 cathode materials by ultrasonic spray pyrolysis method. Electrochimica Acta, 49, 557–563. Patoux, S., & Doeff, M. M. (2004). Direct synthesis of LiNi1/3 Co1/3 Mn1/3 O2 from nitrate precursors. Electrochemistry Communications, 6, 767–772. Shaju, K. M., Subba Rao, G. V., & Chowdari, B. V. R. (2002). Performance of layered Li(Ni1/3 Co1/3 Mn1/3 )O2 as cathode for Li-ion batteries. Electrochimica Acta, 48, 145–151. Thackeray, M. M., Kang, S.-H., Johnson, C. S., Vaughey, J., & Hackney, S. A. (2006). Comments on the structural complexity of lithium-rich Li1+x M1−x O2 electrodes (M = Mn, Ni, Co) for lithium batteries. Electrochemistry Communications, 8, 1531–1538. Todorov, Y. M., & Numata, K. (2004). Effects of the Li:(Mn + Co + Ni) molar ratio on the electrochemical properties of LiMn1/3 Co1/3 Ni1/3 O2 cathode material. Electrochimica Acta, 50, 495–499. Trave, A., Selloni, A., Goursot, A., Tichit, D., & Weber, J. (2002). First principles study of the structure and chemistry of Mg-Based hydrotalcite-like anionic clays. The Journal of Physical Chemistry B, 106, 12291–12296. Vaccari, A. (1998). Preparation and catalytic properties of cationic and anionic clays. Catalysis Today, 41, 53–71. Vaysse, C., Guerlou-Demourgues, L., & Delmas, C. (2002). Thermal evolution of carbonate pillared layered hydroxides with (Ni, L) (L = Fe, Co) based slabs: Grafting or nongrafting of carbonate anions? Inorganic Chemistry, 41, 6905–6913. Yabuuchi, N., Koyama, Y., Nakayama, N., & Ohzuku, T. (2005). Solid-State chemistry and electrochemistry of LiCo1/3 Ni1/3 Mn1/3 O2 for advanced lithium-ion batteries: II. Preparation and characterization. Journal of the Electrochemical Society, 152, A1434–A1440. Yoon, W.-S., Balasubramanian, M., Chung, K. Y., Yang, X.-Q., McBreen, J., Grey, C. P., et al. (2005). Investigation of the charge compensation mechanism on the electrochemically Li-ion deintercalated Li1−x Co1/3 Ni1/3 Mn1/3 O2 electrode system by combination of soft and hard X-ray absorption spectroscopy. Journal of the American Chemical Society, 127, 17479–17487.
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Synthesis of layered cathode materials Li[Cox Niy Mn1−x−y ]O2 from layered double hydroxide precursors Yanluo Lu ∗ , Yang Zhao State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China
a r t i c l e
i n f o
Article history: Received 23 March 2009 Accepted 17 June 2009 Keywords: Layered Li[Cox Niy Mn1−x−y ]O2 Layered double hydroxides Precursor method Cathode materials
a b s t r a c t Cathode materials Li[Cox Niy Mn1−x−y ]O2 for lithium secondary batteries have been prepared by a new route using layered double hydroxides (LDHs) as a precursor. The resulting layered phase with the ␣NaFeO2 structure crystallizes in the rhombohedral system, with space group R-3m having an interlayer spacing close to 0.47 nm. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation states of Co, Ni and Mn. The effects of varying the Co/Ni/Mn ratio on both the structure and electrochemical properties of Li[Cox Niy Mn1−x−y ]O2 have been investigated by X-ray diffraction and electrochemical tests. The products demonstrated a rather stable cycling behavior, with a reversible capacity of 118 mAh/g for the layered material with Co/Ni/Mn = 1/1/1. © 2010 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.
1. Introduction Recently, layered Li[Co1/3 Ni1/3 Mn1/3 ]O2 materials have attracted considerable interest as an alternative cathode material to LiCoO2 for commercial lithium-ion batteries. Li[Ni1/3 Co1/3 Mn1/3 ]O2 provides higher battery capacity in a wider voltage range, and shows better safety characteristics than conventional LiCoO2 (Belharouak, Sun, Liu, & Amine, 2003; Cho, Shiosaki, & Noguchi, 2006; Choi & Manthiram, 2005; Kang, Abraham, Yoon, Nam, & Yang, 2008; Kang, Yoon, Nam, Yang, & Abraham, 2008; Lee, Kang, Myung, & Sun, 2004; Ohzuku & Makimura, 2001; Thackeray, Kang, Johnson, Vaughey, & Hackney, 2006; Todorov & Numata, 2004; Yabuuchi, Koyama, Nakayama, & Ohzuku, 2005; Yoon et al., 2005). However, Li[Ni1/3 Co1/3 Mn1/3 ]O2 generally shows a poorer first cycle efficiency (<90%) than LiCoO2 (98%), which cancels out the energy density of a lithium-ion battery adopting the former as the cathode active material (Choi & Manthiram, 2005; Cho et al., 2006; Kang, Abraham, et al., 2008; Kang, Yoon, et al., 2008). It is well known that the performance of the powders used as cathode materials in lithium-ion batteries is strongly affected by their preparation processes (Li, Muta, Zhang, Yoshio, & Noguchi, 2004; Lin, Wen, Gu, & Huang, 2008), thus indicating how important it is to select a suitable method to prepare high-performance Li[Co1/3 Ni1/3 Mn1/3 ]O2 (Shaju, Subba Rao, & Chowdari, 2002). Li[Co1/3 Ni1/3 Mn1/3 ]O2 was first prepared by
∗ Corresponding author. Tel.: +86 10 64412115; fax: +86 10 64425385. E-mail address: [email protected] (Y. Lu).
conventional solid-state reaction methods (Kim & Chung, 2004; Ohzuku & Makimura, 2001), which require prolonged heat treatment at relatively high temperatures with repeated intermediate grinding because of the heterogeneity of the precursors. In order to overcome these disadvantages, various new techniques, such as glycine-nitrate combustion (Patoux & Doeff, 2004), hydroxide co-precipitation (Lee et al., 2004; Myung, Kim, & Sun, 2004), carbonate co-precipitation (Cho, Park, & Yoshio, 2004; Cho, Park, Yoshio, Hirai, & Hideshima, 2005), ultrasonic spray pyrolysis (Park et al., 2004), solution spray drying (Li et al., 2004), and sol–gel (Hwang, Tsai, Carlier, & Ceder, 2003) processes have been developed for preparing high-quality Li[Co1/3 Ni1/3 Mn1/3 ]O2 . Although they led to homogeneous materials with small particle size, these synthetic routes are complex, calling for precursors which require expensive initial or intermediate reagents, and long time for drying. Moreover, the use of organic acids or hydroxides, which are corrosive to the production equipment, makes these methods less than ideal for the industrial-scale production of the materials. Layered double hydroxides (LDHs) or hydrotalcite-like compounds (Canavi, Trifiro, & Vaccari, 1991; Vaysse, GuerlouDemourgues, & Delmas, 2002), already known for a considerable time, have been widely studied. The basic layer structure of LDHs is based on that of brucite [Mg(OH)2 ], which consists of magnesium ions surrounded approximately octahedrally by hydroxide ions. These octahedral units form infinite layers by edge sharing, with the hydroxide ions sitting perpendicular to the plane of the layers. The layers then stack on top of one another to form a three-dimensional structure. The basic structure of an LDH may be derived by
1674-2001/$ – see front matter © 2010 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.partic.2010.03.006
Y. Lu, Y. Zhao / Particuology 8 (2010) 202–206
substitution of a fraction of the divalent cations in a brucite lattice by trivalent cations such that the layers acquire a positive charge, which is balanced by intercalation of anions between the layers (Vaccari, 1998). LDHs may be described by the general formula [M1−x II Mx III (OH)2 ]x+ [Ax/n n− ·yH2 O]x− , where MII and MIII are divalent and trivalent metal cations, and An− is an n-valent anion. It is often said that pure LDH phases can be formed for stoichiometries in the range of 0.20 < x < 0.33 (Han, Guerlou-Demourgues, & Delmas, 1997; Jones & Chibwe, 1990; Trave, Selloni, Goursot, Tichit, & Weber, 2002), i.e., for MII /MIII ratios in the range of 2–4. The MII /MIII isomorphous substitution in the octahedral sites of the hydroxide sheets results in a well-distributed single phase in these materials when they are prepared by the co-precipitation method (Canavi et al., 1991; Dunn, Peacor, & Palmer, 1979; Goswamee, Sengupta, Bhattacharyya, & Dutta, 1998; Kovanda, Grygar, & Dorniˇcák, 2003). In this work, layered Li[Cox Niy Mn1−x−y ]O2 materials were prepared by using LDHs as precursor. The precursor CoNiMn LDHs were first synthesized by co-precipitation, and after mixing with an appropriate amount of LiOH·H2 O, were calcined in air at 900 ◦ C. The structure and the initial electrochemical performance of the resulting Li[Cox Niy Mn1−x−y ]O2 products have been examined.
2. Methods and materials CoNiMn LDHs with Co/Ni/Mn molar ratios of 1/1/1, 2/1/1 and 1/2/1 were prepared by a co-precipitation method similar to that described previously for CoMn LDHs (Lu, Wei, Yang, & Li, 2007). A solution containing the metallic nitrate salts Ni(NO3 )2 ·6H2 O, Co(NO3 )2 ·6H2 O and Mn(NO3 )2 (0.6 M) with the chosen molar ratio was added to a beaker at room temperature. A second aqueous solution containing 100 mL NaOH (1 M) and Na2 CO3 (0.5 M) was added dropwise over 3 h into the metallic nitrate salts solution with vigorous stirring. Air was bubbled throughout the reaction mixture during the entire addition period. The resulting suspension was aged at room temperature for 12 h, and the precipitate obtained was collected by centrifugation and washed thoroughly with distilled water. It was then well mixed with the appropriate amount of LiOH·H2 O (Li/(Co + Ni + Mn) = 1.1) by grinding, and the resulting mixture dried at 70 ◦ C for 12 h. The mixture was calcined at 900 ◦ C for 24 h in air and cooled to room temperature. The product was washed thoroughly with distilled water and dried at 70 ◦ C for 12 h in air. XRD data were collected from 2Â = 10◦ to 2Â = 85◦ with 0.04◦ step size, each step lasting 10 s. Unit cell parameters were obtained by least squares refinement of the powder XRD data. Elemental analysis was performed by ICP spectroscopy using a Shimadzu ICPS-7500 instrument. X-ray photoelectron spectra (XPS) were collected using a Thermo VG Sigma Probe X-ray photoelectron spectrometer with an Mg K␣ X-ray source (200 W). The base pressure, in both the main and the preparation chambers, was 3 × 10−9 mbar. All spectra were charge referenced to the C 1s XPS peak (284.6 eV). In order to evaluate the electrochemical performance of the materials, composite electrodes were formed by mixing the active material with acetylene black and polytetrafluoroethylene (PTFE) in the weight ratio 85/10/5, and then pressing into pellets. The composite electrodes were dried at 120 ◦ C in vacuum for 24 h before use. Button-type cells were assembled in a glove box filled with argon with less than 1 ppm H2 O and O2 . A cell was prepared by assembling the cathode, separator, and the anode in a sandwich structure. The anode was lithium metal and the electrolyte was a 1 M solution of LiClO4 in a mixture of ethylene carbonate and diethyl carbonate (EC/DEC) in the volume ratio 1/1. The galvanostatic charge–discharge tests were carried out between 2.8 and 4.3 V (versus Li/Li+ ) at a constant current density of 0.2 mA/cm2
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Fig. 1. Powder XRD patterns of CoNiMn LDHs with different Co/Ni/Mn ratios. (A) Co/Ni/Mn = 1/1/1; (B) Co/Ni/Mn = 2/1/1; C. Co/Ni/Mn = 1/2/1.
(corresponding to the 0.07 C rate) using a LAND CT2001A cycle life tester. 3. Results and discussion 3.1. Structural study of LDHs precursor The powder XRD patterns of the CoNiMn LDHs with different Co/Mn/Ni ratios are shown in Fig. 1. The phases crystallize in the trigonal system (space group: R-3m) with a basal spacing of 0.755 nm in each case, similar to that reported for MgAl LDHs containing interlayer carbonate anions (Trave et al., 2002). During the co-precipitation, most of the MnII was oxidized to MnIII by the oxygen in air which was bubbled through the solution. As a result, the MII /MIII molar ratio in the LDHs should be in accordance with the (Ni + Co)/Mn ratio in the precursor mixture. The ideal formula of the LDH with a precursor mixture with (Co/Ni/Mn = 1/1/1) can therefore be written as follows. 3.2. Structure and composition of the layered Li[Cox Niy Mn1−x−y ]O2 The powder XRD patterns of Li[Cox Niy Mn1−x−y ]O2 with different Co/Ni/Mn ratios, shown in Fig. 2, can be indexed on the basis of the ␣-NaFeO2 type structure. The layered phase crystallizes in the rhombohedral system, space group R-3m with an interlayer spacing close to 0.47 nm. The lattice parameters of Li[Cox Niy Mn1−x−y ]O2 calculated from the XRD patterns are listed in Table 1. Increasing the Mn content results in a slight expansion of the unit cell parameters. It has been reported that large c/a ratios suggest a well-defined layered structure (Armstrong, Robertson, & Bruce, 1999), so the c/a ratios for the materials prepared in this work (all close to 5) indicate a well-defined layered structure and a high degree of cation ordering. Table 1 Lattice parameters for Li[Cox Niy Mn1−x−y ]O2 with different Co/Ni/Mn ratios. Co/Ni/Mn ratio
d003 /nm
d110 /nm
a/nm
c/nm
c/a
1/1/1 2/1/1 1/2/1
0.4754(9) 0.4694(5) 0.4685(9)
0.1430(7) 0.1419(7) 0.1426(4)
0.2861 0.2839 0.2853
1.4265 1.4082 1.4058
4.986 4.960 4.927
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Fig. 2. Powder XRD patterns of Li[Cox Niy Mn1−x−y ]O2 with different Co/Ni/Mn ratios. (A) Co/Ni/Mn = 1/1/1; (B) Co/Ni/Mn = 2/1/1 and (C) Co/Ni/Mn = 1/2/1.
Elemental analytical data for the Li[Cox Niy Mn1−x−y ]O2 products, as obtained by ICP spectroscopy, are listed in Table 2. The Co/Ni/Mn molar ratio in each product was close to the ratio in the corresponding synthesis mixture, while the lithium content increased as the value of x increased and the value of y decreased (Table 2). This may be because larger amounts of Ni (i.e., large values of y) lead to the formation of Ni(OH)2 which results in a reduced charge density in the layers and less intercalation of Li+ ions between the layers. It should also be noted that it has been reported that a native surface film, mainly composed of Li2 CO3 , exists on all transition metal oxide cathode materials based on manganese, cobalt, and nickel (Armstrong et al., 1999). This surface component could arise from the precursors used to synthesize these metal oxides or, more likely, from the reaction between the metal oxides and the CO2 in the atmosphere during the processing of these oxidizing materials (Aurbach, 2000). X-ray photoelectron spectroscopy (XPS) can provide chemical information such as the oxidation state, as well as the semiquantitative composition of the surface, and is thus a very useful method for studying surface properties. Fig. 3 displays the XPS results for Li[Co0.50 Ni0.25 Mn0.25 ]O2 . The binding energy of Mn 2p3/2 is 642.5 eV, which is in agreement with that reported in the literature (Galakhov et al., 2000) for MnO2 , indicating that the predominant Mn species near the surface is MnIV . As a rule, compounds containing high-spin CoII ions have strong shake-up satellites in Co
Fig. 3. X-ray photoelectron spectra of Co, Ni, Mn and O in Li[Co0.50 Ni0.25 Mn0.25 ]O2 .
Y. Lu, Y. Zhao / Particuology 8 (2010) 202–206
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Table 2 Elemental analysis of Li[Cox Niy Mn1−x−y ]O2 by ICP. Co/Ni/Mn molar ratio
1/1/1 2/1/1 1/2/1
Content (%)
Composition
Li
Mn
Ni
Co
6.275 6.154 6.611
15.765 12.032 11.539
19.192 28.447 13.719
17.317 12.593 24.999
Li1.00 [Co0.32 Ni0.36 Mn0.32 ]O2 ·xH2 O Li1.10 [Co0.49 Ni0.27 Mn0.24 ]O2 ·xH2 O Li0.97 [Co0.23 Ni0.53 Mn0.24 ]O2 ·xH2 O
2p XPS spectra, while CoIII is diamagnetic and has no satellite peak (Oswald & Brückner, 2004), and the valence of cobalt can therefore be determined by XPS spectroscopy. The Co 2p3/2 and Co 2p1/2 peaks in Fig. 3 at 780.1 and 795.5 eV respectively, are close to those reported previously (Oku & Hirokawa, 1975) for CoIII in ZnCo2 O4 . No visible satellite peaks can be observed, confirming that most of CoII has been oxidized to CoIII during the calcination. The Ni 2p3/2 peak at 855.1 eV is close to the overlapping peaks reported previously for Ni(OH)2 and Ni2 O3 (Oswald & Brückner, 2004). The O 1s spectrum contains two peaks: one component at 529.8 eV is typical of metal–oxygen bonding and the other at 531.0 eV is usually associated with oxygen in OH− groups. The presence of this latter peak indicates that the surface of the materials was hydroxylated to some extent. XPS gives an elemental Co/Ni/Mn ratio of 45/31/24 near the surface of Li[Co0.50 Ni0.25 Mn0.25 ]O2 . Compared to that in the bulk, as determined by ICP (Co/Ni/Mn = 49/27/24), the Ni content near the surface is higher, and Co content is lower. This shows that Ni is stabilized near the surface, perhaps by the formation of Ni(OH)2 , as suggested above. 3.3. Electrochemical performance of Li[Cox Niy Mn1−x−y ]O2 The charge–discharge curves of the cell for the first cycle with the Li[Cox Niy Mn1−x−y ]O2 samples with Co/Ni/Mn = 1/1/1, 2/1/1 and 1/2/1 used as cathode materials are illustrated in Fig. 4, and the cycling behavior is shown in Fig. 5. The three samples have an initial EMF of 2.7–3.2 V. It can be seen in Fig. 4 that the molar ratio of Co/Ni/Mn has a significant influence on the charge–discharge capacity. The first charge and discharge capacities of sample A (Co/Ni/Mn = 1/1/1) were 145.5 and 118.1 mAh/g, respectively. The specific capacity of sample A after the 10th cycle was 74.6 mAh/g (Fig. 5). The capacity of sample B (Co/Ni/Mn = 2/1/1) was improved with the increase of Co content, and the reversible
Fig. 5. Cycle performance of Li[Cox Niy Mn1−x−y ]O2 as cathode materials. (A) Co/Ni/Mn = 1/1/1; (B) Co/Ni/Mn = 2/1/1 and (C) Co/Ni/Mn = 1/2/1.
capacity of sample B was 126.5 mAh/g. In contrast, the capacity was decreased with the increase of Ni content, and sample C (Co/Ni/Mn = 1/2/1) had a reversible capacity of 86.2 mAh/g (Fig. 4). This indicates that higher Co content is favorable for the intercalation–deintercalation of lithium ions, while higher Ni content restricts the intercalation–deintercalation of lithium ions. The specific capacity of sample C after the 10th cycle was 80.0 mAh/g (Fig. 5). 4. Conclusions Layered rhombohedral Li[Cox Niy Mn1−x−y ]O2 materials with the ␣-NaFeO2 structure have been synthesized by solid-state reaction of CoNiMn LDH precursors and LiOH. XRD patterns and ICP results demonstrated that the crystal integrity and the capacity of lithium intercalation were improved by increasing the Co content and decreasing the Ni content. XPS revealed that NiII , MnIV and CoIII predominate near the surface of the sample, and Ni is preferentially stabilized near the surface. The electrochemical behavior of Li[Co1/3 Ni1/3 Mn1/3 ]O2 as a cathode material in lithium secondary batteries showed that this material exhibits high charge–discharge capacities of over 118 mAh/g between 2.8 and 4.3 V and viable cycling stability. Acknowledgments
Fig. 4. Charge–discharge curves of Li[Cox Niy Mn1−x−y ]O2 as cathode materials. (A) Co/Ni/Mn = 1/1/1; (B) Co/Ni/Mn = 2/1/1 and (C) Co/Ni/Mn = 1/2/1.
This work was supported by the National Natural Science Foundation of China, the 111 Project (grant no.: B07004) and the Natural Science Foundation for Young Teachers of Beijing University of Chemical Technology (grant no.: QN0723).
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References Armstrong, A. R., Robertson, A. D., & Bruce, P. G. (1999). Structural transformation on cycling layered Li(Mn1−y Coy )O2 cathode materials. Electrochimica Acta, 45, 285–294. Aurbach, D. (2000). Review of selected electrode–solution interactions which determine the performance of Li and Li ion batteries. Journal of Power Sources, 89, 206–218. Belharouak, I., Sun, Y.-K., Liu, J., & Amine, K. (2003). Li(Ni1/3 Co1/3 Mn1/3 )O2 as a suitable cathode for high power applications. Journal of Power Sources, 123, 247–252. Canavi, F., Trifiro, F., & Vaccari, A. (1991). Hydrotalcite-type anionic clays: Preparation, properties and applications. Catalysis Today, 11, 173–301. Cho, T. H., Park, S. M., & Yoshio, M. (2004). Preparation of layered Li[Ni1/3 Mn1/3 Co1/3 ]O2 as a cathode for lithium secondary battery by carbonate coprecipitation method. Chemistry Letters, 33, 704–705. Cho, T. H., Park, S. M., Yoshio, M., Hirai, T., & Hideshima, Y. (2005). Effect of synthesis condition on the structural and electrochemical properties of Li[Ni1/3 Mn1/3 Co1/3 ]O2 prepared by carbonate co-precipitation method. Journal of Power Sources, 142, 306–312. Cho, T.-H., Shiosaki, Y., & Noguchi, H. (2006). Preparation and characterization of layered LiMn1/3 Ni1/3 Co1/3 O2 as a cathode material by an oxalate co-precipitation method. Journal of Power Sources, 159, 1322–1327. Choi, J., & Manthiram, A. (2005). Investigation of the irreversible capacity loss in the layered LiNi1/3 Mn1/3 Co1/3 O2 cathodes. Electrochemical and Solid-State Letters, 8, C102–C105. Dunn, P. J., Peacor, D. R., & Palmer, T. D. (1979). Desautelsite, a new mineral of the pyroaurite group. American Mineralogist, 64, 127–130. Galakhov, V. R., Korotin, M. A., Ovechkina, N. A., Kurmaev, E. Z., Gorshkov, V. S., Kellerman, D. G., et al. (2000). Electronic structure of LiMnO2 : X-ray emission and photoelectron spectra and band structure calculations. The European Physical Journal B, 14, 281–286. Goswamee, R. L., Sengupta, P., Bhattacharyya, K. G., & Dutta, D. K. (1998). Adsorption of Cr(VI) in layered double hydroxides. Applied Clay Science, 13, 21–34. Han, K. S., Guerlou-Demourgues, L., & Delmas, C. (1997). Intercalation process of metavanadate chains into a nickel–cobalt layered double hydroxide. Solid State Ionics, 98, 85–92. Hwang, B. J., Tsai, Y. W., Carlier, D., & Ceder, G. (2003). A combined computational/experimental study on LiNi1/3 Co1/3 Mn1/3 O2 . Chemistry of Materials, 15, 3676–3682. Jones, W., & Chibwe, M. (1990). The synthesis, chemistry and catalytic applications of layered double hydroxides. In I. V. Mitchell (Ed.), Pillared latered structures (pp. 67–78). London: Elsevier. Kang, S.-H., Abraham, D. P., Yoon, W.-S., Nam, K.-W., & Yang, X.-Q. (2008). Firstcycle irreversibility of layered Li–Ni–Co–Mn oxide cathode in Li-ion batteries. Electrochimica Acta, 54, 684–689. Kang, S.-H., Yoon, W.-S., Nam, K.-W., Yang, X.-Q., & Abraham, D. P. (2008). Investigating the first-cycle irreversibility of lithium metal oxide cathodes for Li batteries. Journal of Materials Science, 43, 4701–4706. Kim, J. M., & Chung, H. T. (2004). The first cycle characteristics of Li[Ni1/3 Co1/3 Mn1/3 ]O2 charged up to 4.7 V. Electrochimica Acta, 49, 937–944. Kovanda, F., Grygar, T., & Dorniˇcák, V. (2003). Thermal behaviour of Ni–Mn layered double hydroxide and characterization of formed oxides. Solid State Sciences, 5, 1019–1026.
Lee, M. H., Kang, Y. J., Myung, S. T., & Sun, Y. K. (2004). Synthetic optimization of Li[Ni1/3 Co1/3 Mn1/3 ]O2 via co-precipitation. Electrochimica Acta, 50, 939–948. Li, D. C., Muta, T., Zhang, L. Q., Yoshio, M., & Noguchi, H. (2004). Effect of synthesis method on the electrochemical performance of LiNi1/3 Mn1/3 Co1/3 O2 . Journal of Power Sources, 132, 150–155. Lin, B., Wen, Z., Gu, Z., & Huang, S. (2008). Morphology and electrochemical performance of Li[Ni1/3 Co1/3 Mn1/3 ]O2 cathode material by a slurry spray drying method. Journal of Power Sources, 175, 564–569. Lu, Y., Wei, M., Yang, L., & Li, C. (2007). Synthesis of layered cathode material Li[Cox Mn1−x ]O2 from layered double hydroxides precursors. Journal of Solid State Chemistry, 180, 1775–1782. Myung, S. T., Kim, G. H., & Sun, Y. K. (2004). Synthesis of Li[Ni1/3 Co1/3 Mn1/3 ]O2 -zFz via coprecipitation. Chemistry Letters, 33, 1388–1389. Ohzuku, T., & Makimura, Y. (2001). Layered lithium insertion material of LiCo1/3 Ni1/3 Mn1/3 O2 for lithium-ion batteries. Chemistry Letters, 30, 642–643. Oku, M., & Hirokawa, K. (1975). X-ray photoelectron spectroscopy of Co3 O4 , Fe3 O4 , Mn3 O4 and related compounds. Journal of Electron Spectroscopy and Related Phenomena, 7, 405–473. Oswald, S., & Brückner, W. (2004). XPS depth profile analysis of non-stoichiometric NiO films. Surface and Interface Analysis, 36, 17–22. Park, S. H., Yoon, C. S., Kang, S. G., Kim, H.-S., Moon, S.-I., & Sun, Y.-K. (2004). Synthesis and structural characterization of layered Li[Ni1/3 Co1/3 Mn1/3 ]O2 cathode materials by ultrasonic spray pyrolysis method. Electrochimica Acta, 49, 557–563. Patoux, S., & Doeff, M. M. (2004). Direct synthesis of LiNi1/3 Co1/3 Mn1/3 O2 from nitrate precursors. Electrochemistry Communications, 6, 767–772. Shaju, K. M., Subba Rao, G. V., & Chowdari, B. V. R. (2002). Performance of layered Li(Ni1/3 Co1/3 Mn1/3 )O2 as cathode for Li-ion batteries. Electrochimica Acta, 48, 145–151. Thackeray, M. M., Kang, S.-H., Johnson, C. S., Vaughey, J., & Hackney, S. A. (2006). Comments on the structural complexity of lithium-rich Li1+x M1−x O2 electrodes (M = Mn, Ni, Co) for lithium batteries. Electrochemistry Communications, 8, 1531–1538. Todorov, Y. M., & Numata, K. (2004). Effects of the Li:(Mn + Co + Ni) molar ratio on the electrochemical properties of LiMn1/3 Co1/3 Ni1/3 O2 cathode material. Electrochimica Acta, 50, 495–499. Trave, A., Selloni, A., Goursot, A., Tichit, D., & Weber, J. (2002). First principles study of the structure and chemistry of Mg-Based hydrotalcite-like anionic clays. The Journal of Physical Chemistry B, 106, 12291–12296. Vaccari, A. (1998). Preparation and catalytic properties of cationic and anionic clays. Catalysis Today, 41, 53–71. Vaysse, C., Guerlou-Demourgues, L., & Delmas, C. (2002). Thermal evolution of carbonate pillared layered hydroxides with (Ni, L) (L = Fe, Co) based slabs: Grafting or nongrafting of carbonate anions? Inorganic Chemistry, 41, 6905–6913. Yabuuchi, N., Koyama, Y., Nakayama, N., & Ohzuku, T. (2005). Solid-State chemistry and electrochemistry of LiCo1/3 Ni1/3 Mn1/3 O2 for advanced lithium-ion batteries: II. Preparation and characterization. Journal of the Electrochemical Society, 152, A1434–A1440. Yoon, W.-S., Balasubramanian, M., Chung, K. Y., Yang, X.-Q., McBreen, J., Grey, C. P., et al. (2005). Investigation of the charge compensation mechanism on the electrochemically Li-ion deintercalated Li1−x Co1/3 Ni1/3 Mn1/3 O2 electrode system by combination of soft and hard X-ray absorption spectroscopy. Journal of the American Chemical Society, 127, 17479–17487.