Combustion-synthesized LiNi0.6Mn0.2Co0.2O2 as cathode material for lithium ion batteries

Combustion-synthesized LiNi0.6Mn0.2Co0.2O2 as cathode material for lithium ion batteries

Journal of Alloys and Compounds 609 (2014) 143–149 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.e...

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Journal of Alloys and Compounds 609 (2014) 143–149

Contents lists available at ScienceDirect

Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom

Combustion-synthesized LiNi0.6Mn0.2Co0.2O2 as cathode material for lithium ion batteries Wook Ahn a,b, Sung Nam Lim c, Kyu-Nam Jung b, Sun-Hwa Yeon b, Kwang-Bum Kim a,⇑, Hoon Sub Song d, Kyoung-Hee Shin b,⇑ a

Department of Materials Science & Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-Gu, Seoul 120-749, Republic of Korea Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea Department of Chemical & Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea d Department of Chemical Engineering, University of Waterloo, 200 University Ave. W., Waterloo, ON N2L3G1, Canada b c

a r t i c l e

i n f o

Article history: Received 20 February 2014 Received in revised form 14 March 2014 Accepted 17 March 2014 Available online 1 April 2014 Keywords: Lithium ion batteries Cathode Combustion method Layered structure Nickel-rich

a b s t r a c t A nitrate/urea mixture was used as fuel to simply combustion-synthesize LiNi0.6Co0.2Mn0.2O2 as a high-capacity cathode material for lithium ion batteries. The reaction formulas and physical properties of the resultant cathode materials sintered at various temperatures were examined using thermogravimetric analysis/simultaneous differential thermal analysis, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectrometry, and inductively coupled plasma/atomic emission spectrometry. The influence of sintering temperature on the electrochemical performance was evaluated by analyzing the charge/discharge profiles and cycling and rate-capability performances. The LiNi0.6Co0.2Mn0.2O2 cathode sintered at 800 °C exhibited a discharge capacity of 170 mA h g1 measured at a constant 20 mA g1, 98.2% capacity retention after 30 cycles, and better rate capability than the cathodes sintered at 700, 900, and 1000 °C. The experimental results suggest that the enhanced electrochemical performance of the LiNi0.6Co0.2Mn0.2O2 cathode sintered at 800 °C is attributable to the pure, well-organized layered structure containing few mixed cations and to the shorter diffusion path resulting from the uniformly distributed nanoparticles. Ó 2014 Elsevier B.V. All rights reserved.

1. Introduction LiCoO2 is used as a common cathode material for commercial lithium rechargeable batteries because of its high energy density, longevity, ease of manufacture, etc. However, it also shows several disadvantages including high cost, high use of cobalt (which is scarce), and toxicity. As mobile electronic devices and hybrid electric vehicles (HEVs) have become extensively used, the production of lithium rechargeable batteries as power sources has exponentially increased [1–7]. However, an improved cathode material is needed to enhance the energy and power density of lithium rechargeable batteries. Many researchers have developed cathode materials as possible substitutes for LiCoO2 [8–13]. One such candidate is cobalt-free LiNi0.5Mn0.5O2 layered materials. Layered LiNi0.5Mn0.5O2 is a very attractive cathode material for lithium secondary batteries because it is less expensive and less toxic than cobalt oxides and shows a high specific capacity of 260 mA h g1; ⇑ Corresponding authors. Tel.: +82 2 2123 2839; fax: +82 2 312 5375 (K.-B. Kim). Tel.: +82 42 860 3618; fax: +82 42 860 3133 (K.-H. Shin). E-mail addresses: [email protected] (K.-B. Kim), [email protected] (K.-H. Shin). http://dx.doi.org/10.1016/j.jallcom.2014.03.123 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.

however, LiNi0.5Mn0.5O2 is difficult to be synthesized, and the electric conductivity of LiNi0.5Mn0.5O2 is lower than LiCoO2 [14–16]. Ni-rich layered composites such as LiNi0.8Co0.15Al0.05O2 and LiNi0.8Co0.1Mn0.1O2 are other promising cathode materials for lithium ion batteries for plug-in hybrid vehicles (PHVs) and electric vehicles (EVs) because these materials are relatively inexpensive and show a high reversible capacity of approximately 200 mA h g1. Also, LiNi1/3Co1/3Mn1/3O2 was reported to have a capacity of 150 mA h/g in the voltage window of 2.5–4.2 V by Ohzuku and Makimura [17]. However, LiNi0.8Co0.15Al0.05O2 and LiNi0.8Co0.1Mn0.1O2 are thermally unstable and show low rate capabilities. Further, LiNi1/3Co1/3Mn1/3O2 is expensive and requires a significant amount of cobalt, which is scarce. Therefore, another high-capacity material is needed to reduce the amount of cobalt used in and improve the thermal stability of cathode materials. LiNi0.6Co0.2Mn0.2O2 is a progressive material, which has the potential to reduce the amount of cobalt required for producing cathode materials [18] by combining Ni, Co, and Mn in the layered R-3m structure, thereby retaining the advantages of the unique transition metal compounds, such as the high capacity of LiNiO2, the excellent rate capability of LiCoO2, and the good structural

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Fig. 1. TGA–DTA curves for raw-material mixtures heated at 1 °C/min under flowing nitrogen and combusted in urea:nitrate (3:2 mol/mol).

in air without any pulverization, grinding, particle morphology controlling, and particle size controlling of reactants as well as products. All of these features make using combustion synthesis to manufacture materials at lower costs more attractive than using conventional methods to manufacture the materials [22]. Several studies have shown that cathode materials showing desirable electrochemical performances can be easily combustion synthesized [23,24]. We used low-sintering-temperature combustion synthesis to prepare LiNi0.6Co0.2Mn0.2O2, which showed good cycling performance and high rate capability, as a cathode material for lithium-ion batteries. We studied the structural properties and electrochemical performances of LiNi0.6Co0.2Mn0.2O2 sintered at various temperatures. To our knowledge, this is the first report that demonstrates the combustion synthesis of a Ni-rich LiNi0.6Co0.2Mn0.2O2 layered cathode material.

2. Experimental

stability of LiNi0.5Mn0.5O2 while being less expensive and less toxic [19]. LiNi0.6Co0.2Mn0.2O2 has conventionally been synthesized using a wide variety of methods including solid-state reaction and co-precipitation [20,21]. In the previous studies [20,21] using the solid-state reaction and co-precipitation method, the specific capacity presents ca. 170 mA h g1, however, the cyclability is poor. Furthermore, these methods necessarily demanded the controlling pH of solution and long reaction time to prepare the precursor. Combustion synthesis is a simple, cost-effective method of producing LiNi0.6Co0.2Mn0.2O2 in which the chemical composition, crystallite size, and particle shape can be easily controlled. A nitrate/urea mixture can be used as fuel for combustion synthesis to produce submicroparticles because the vast heat generated at low temperature nucleates crystals and disperses the crystal nuclei while simultaneously inhibiting crystal growth. Once the fuel starts to burn, the temperature dramatically increases and nucleation rapidly accelerates producing nanomaterials as the final product. Combustion synthesis also has the advantages of fast heating rates and short reaction times. Using this method, the manufacturing procedure is easily made up just thermal reaction

LiNi0.6Co0.2Mn0.2O2 was simply prepared using combustion synthesis as follows: 0.1 mol LiCH3CO22H2O, 0.02 mol Ni(CH3CO2)24H2O, 0.04 mol Ni(NO3)6H2O, 0.02 mol Mn(CH3CO2)24H2O and 0.02 mol Co(CH3CO2)24H2O were homogeneously mixed and added to a mixture of NH2CONH2 (urea):nitrate (3:2 mol/mol) dissolved in 150 mL of deionized (DI) water and stirred for 2 h. The mixture was then dried in an oven at 80 °C for 24 h and subsequently heated consecutively at 130, 350, and sintered in the range 700–1000 °C for 1, 5, and 12 h, respectively, in air in a muffle furnace. The phases in the synthesized powder were analyzed using X-ray diffraction (XRD; automated HPC-2500 XRD diffractometer, Gogaku) with Cu Ka radiation (k = 1.5405 Å). The XRD measurements were scanned in the range 10–80° in 0.02° increments. The thermogravimetric analysis/simultaneous differential thermal analysis (TGA–SDTA 851e-METTLER TOLEDO) was performed in the range of 25–1000 °C, and the samples were heated at 5 °C min1 in air. The morphologies and microstructures were examined using scanning electron microscopy (SEM; S4700, Hitachi) and field-emission transmission electron microscopy (FE-TEM; JEM-1010, JEOL, Ltd.). X-ray photoelectron spectroscopy (XPS) was conducted using a Thermo MultiLab 2000 spectrometer with a monochromatic Al Ka X-ray source, and the composition of the synthesized powder was analyzed using inductively coupled plasma/atomic emission spectrometry (ICP–AES; OPTIMA 7300DV, Perkin-Elmer). Cathode electrodes were prepared for the electrochemical tests by mixing 10 wt% Super PÒ conductive carbon black (Denka) and 10 wt% poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP, KYNARÒ 2801) binder and dissolving the mixture in N-methyl-2-pyrrolidone (NMP) to form slurry, which was coated using a doctor blade onto 20 lm-thick Al foils. The cathodes were pressed and dried

Fig. 2. FE-SEM morphologies of LiNi0.6Co0.2Mn0.2O2 sintered at (a) 700, (b) 800, (c) 900, and (d) 1000 °C.

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was used to measure the rate capabilities in the range 20–320 mA g1. Electrochemical impedance spectra were recorded by using a Zahner IM6 with application of an ac-amplitude of 5 mV rms on an open circuit potential over a frequency range from 105 Hz down to 102 Hz.

3. Results and discussion

Fig. 3. XRD patterns for LiNi0.6Co0.2Mn0.2O2 sintered in range 700–1000 °C.

Table 1 ICP/AES results for content of each metal in LiNi0.6Co0.2Mn0.2O2. Element

Li Ni Mn Co

Elements composition (%) 700 °C

800 °C

900 °C

1000 °C

98.56 60.65 19.80 19.55

98.44 59.86 20.11 20.03

90.70 61.10 19.17 19.73

89.54 60.78 19.51 19.71

under vacuum at 70 °C, and the final cathodes were 60 lm thick. CR2032 coin-type cells were assembled using an electrolyte consisting of a 1.0 M solution of LiPF6 dissolved in ethylene carbonate and diethyl carbonate (EC/DEC) mixed in a 1:1volumetric ratio. Lithium foil and polypropylene (CelgardÒ 2400) were used as the counter electrode and separator, respectively. The coin cells were completely assembled in an Ar-filled glovebox, and the cells were charged and discharged at 20 mA g1. A MACCOR 4000 series fully automated, computerized test system

TGA and SDTA were performed during combustion to provide information on the reaction formulas. Fig. 1 shows the TGA–SDTA results for the mixed precursor powder measured in the range 25–1000 °C under a nitrogen atmosphere. The TGA curves seem to show two weight losses. The first stage of 19.4% (abrupt) weight loss in the range ca. 25–120 °C reflects dehydration (calculated weight loss = 18%), and the small exothermic DTA peaks up to 80 °C indicate the post-dehydration melting of the acetates and nitrates, which began to decompose in the range 120–500 °C in accordance with the second weight loss of 55.3% and a large exothermic DTA peak at 230 °C. The experimental result is very consistent with the weight loss of 56.1% calculated for the release of 3.3H2O, 4.4CO2, and 0.4N2 and the gain of 5.05O2. Furthermore, the endothermic heat generated from the decomposition of the acetates and the urea/nitrates combusted at 240 °C is probably required to form the hexagonal layered phase. The acetates and nitrates reacted with the urea as fuel, releasing heat and causing a strong endothermic peak to appear after the exothermic one. The weight loss above 550 °C was negligible; thus, the reaction for forming the layered LiNi0.6Co0.2Mn0.2O2 phase finishes below 550 °C. The overall reaction formulas for this material can thus be given as follows:

LiCH3 CO2  2H2 O þ 0:2NiðCH3 CO2 Þ2  4H2 O þ 0:4NiðNO3 Þ2  4H2 O þ 0:2MnðCH3 CO2 Þ2  4H2 O þ 0:2CoðCH3 CO2 Þ2  4H2 O ! LiNi0:6 Mn0:2 Co0:2 ðCH3 CO2 Þ2:2 ðNO3 Þ0:8 þ 6H2 O

ð1Þ

Fig. 4. XPS spectra for Ni, Co, and Mn 2p regions of LiNi0.6Co0.2Mn0.2O2 sintered at various temperatures.

Table 2 Ni oxidation states calculated from fitted XPS spectra for samples sintered in range 700–1000 °C. Oxidation state

Ni content 2+in Ni content 3+in Ni content 3+/(2+ + 3+)

Oxidation state composition of Ni in LiNi0.6Co0.2Mn0.2O2 Theoretical composition

700 °C

800 °C

900 °C

1000 °C

0.60 0.20 0.40 0.667

0.607 0.184 0.423 0.698

0.599 0.186 0.413 0.690

0.611 0.099 0.512 0.839

0.608 0.091 0.517 0.851

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Fig. 5. TEM images and single crystal showing R-3m symmetry of LiNi0.6Co0.2Mn0.2O2 sintered at 800 °C.

LiNi0:6 Mn0:2 Co0:2 ðCH3 CO2 Þ2:2 ðNO3 Þ0:8 þ 5:05O2 ! LiNi0:6 Mn0:2 Co0:2 O2 þ 3:3H2 O þ 4:4CO2 þ 0:4N2 :

ð2Þ

Fig. 2(a–d) shows SEM images of the samples sintered at various temperatures. All the samples consist of spherical particles, and those sintered at 700 and 800 °C were primarily composed of nanoparticles and exhibited more uniform particle size distribution than those sintered at 900 and 1000 °C. Increasing the sintering temperature also caused the particles to aggregate because the grains grew faster. The micrographs show that the morphologies of the combustion-synthesized samples strongly depend on sintering temperature and that optimizing it could produce more uniformly distributed nanoparticles. Fig. 3 presents the powder XRD patterns for the materials sintered in the range 700–1000 °C. All the XRD patterns show peaks characteristic of a hexagonal structure showing the R3m space group. However, the XRD spectrum for the sample sintered at 700 °C exhibits broad diffraction peaks, indicating that the sample showed low crystallinity and should be sintered above 800 °C to combustion synthesize highly crystalline LiNi0.6Co0.2Mn0.2O2. Further, the obvious splitting of the (0 0 6)–(1 0 2) and (1 0 8)–(1 1 0) doublets in the XRD patterns for the samples sintered at 800, 900, and 1000 °C suggests the formation of a layered structure [25,26]. Lattice constants (a, c) were calculated based on Bragg’s law for the samples sintered at 700, 800, 900, and 1000 °C as (2.889 Å, 14.130 Å), (2.893 Å, 14.289 Å), (2.894 Å, 14.238 Å), and (2.899 Å, 14.260 Å), respectively, to compare the crystallinity of the samples sintered at various temperatures. It has previously been reported that the c represents the average metal–metal interslab distance and that a well-defined hexagonal layered structure is strongly related to high c/a [27]. It should be noted that the sample sintered at 800 °C showed a higher c/a (4.938) than the other samples (4.891, 4.920, and 4.919 for the samples sintered at 700, 900, and 1000 °C, respectively), implying that its layered structure was more crystalline than those of the others. In addition, the XRD pattern for the sample sintered at 1000 °C shows peaks of similar intensity between the (0 0 3) and (1 0 4) peaks. The I(003)/I(104) relative intensity can be used to evaluate the degree of the cation mixing, which is one of the main problems that degrades the electrochemical performance of layered Ni-based cathode materials

Fig. 6. Charge/discharge profiles and cycle performances of LiNi0.6Co0.2Mn0.2O2 sintered at various temperatures.

because the Ni and Li ionic sizes are similar. A low I(003)/I(104) represents more cation mixing. I(003)/I(104) = 0.987 for the sample sintered at 1000 °C, lower than those for the other samples (i.e., 1.35, 1.35, and 1.38 for the samples sintered at 700, 800, and 900 °C,

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Fig. 7. (a) Rate capabilities of materials sintered at 800 and 900 °C; and the corresponding charge–discharge profiles sintered at (b) 800 and (c) 900 °C; the corresponding dQ/ dV curves measured at different C-rates for materials sintered at (b) 800 and (c) 900 °C.

respectively), indicating that the cations could be easily mixed at that temperature. Therefore, the sintering temperature used during combustion synthesis plays a critical role in forming well-crystallized layered structures in which the cations do not mix. ICP–AES was used to determine the exact elemental compositions of the samples sintered in the range 700–1000 °C, and the measured contents are listed in Table 1. The elemental compositions of the samples sintered at 700 and 800 °C were (98.44% Li, 59.86% Ni, 20.11% Mn, and 20.03% Co) and (98.56% Li, 60.65% Ni, 19.80% Mn, and 19.55% Co), respectively, meaning that the stoichiometry of those samples was very consistent with that of LiNi0.6Co0.2Mn0.2O2. However, the lithium contents of the samples sintered at 900 and 1000 °C were 90.70% and 89.54%, respectively, which are lower than those of the samples sintered at 700 and 800 °C. Thus, lithium sublimation during higher-temperature sintering seems to form lithium-deficient compounds, LixNi0.6Co0.2 Mn0.2O2 (x < 1.0). XPS was used to determine the electrovalence of the cations in the materials and whether Ni2+ had oxidized to Ni3+ with increasing sintering temperature. The binding energy for each spectrum was calibrated using the C1s peak (284.5 eV). The binding energies for the Mn, Co, and Ni 2p spectra and the oxidation states of the corresponding Mn, Co, and Ni ions are presented in Fig. 4. The experimental binding energies for the Co 2p1/2 and 2p3/2 signals

were 780 and 795 eV, respectively, suggesting that the Co ions in each sample showed an oxidation state of 3+, which is very close to that obtained for LiCoO2 [28]. The experimental binding energies for the Mn 2p1/2 and 2p3/2 signals were 642.5 and 654 eV, respectively, suggesting a single valence of Mn4+. From the chemical perspective, the Co and Mn ions are expected to show the 3+ and 4+ oxidation states, respectively, and the experimentally determined oxidation states are consistent with the theoretical ones. The signals in the Ni 2p spectra are complex, indicating that the Ni ions showed more than one oxidation state, so the signals were deconvoluted into three component curves, and the detailed fitted results are summarized in Table 2. The Ni 2p3/2 fitting reveals two contributing peaks: one around 854.2 eV, corresponding to the NiO binding energy, and the other at 855.2 eV, consistent with Ni3+ ions [29]. Further, a satellite peak (S1) is cluttered the Ni 2p region near 861 eV, which commonly shows peaks attributed to nickel oxide [30]. The Ni2+ and Ni3+ contents changed with increasing sintering temperature because fewer lithium ions were sintered at 900 and 1000 °C than at 700 and 800 °C. From the fitted XPS Ni 2p spectra, the Ni3+/(Ni2+ + Ni3+) ratio was estimated at 0.69 for the sample sintered at 800 °C, which is consistent with the theoretical Ni3+/(Ni2+ + Ni3+) ratio of about 0.67 calculated for LiNi0.6Co0.2 Mn0.2O2. The oxidation states of the ions in the synthesized 3+ 3+ 4+ LiNi0.6Co0.2Mn0.2O2 are LiNi2+ 0.2Ni0.4Co0.2Mn0.2O2.

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hence, the considerably reduced discharge capacities and abrupt decay in the cycle performances of those cathodes can be explained by the suboptimal-sintering-temperature-induced structural inhomogeneity. Fig. 7(a) shows the rate capabilities measured in the range 20–320 mA g1 for the samples sintered at 800 and 900 °C, and Fig. 7(b) and (c) shows the corresponding charge–discharge curves at various current densities. The sample sintered at 800 °C retained high capacities of 116 and 92 mA h measured at 160 and 320 mA g1, respectively. Moreover, the dQ/dV curves in Fig. 7(d) and (e) show that the two-step oxidation had transformed into a single-step one with increasing current rate at the lower current density for the cathode sintered at 900 °C, which is due to the sluggish kinetics of lithium ion diffusion. Since the cathode sintered at 900 °C shows a lower c/a, a more-lithium-deficient stoichiometry, and larger particles than the cathode sintered at 800 °C, the enhanced electrochemical performance of the cathode sintered at 800 °C might be attributed to the well-organized, stoichiometric layered structure containing few mixed cations and to the shorter diffusion path resulting from the uniformly distributed nanoparticles. In order to investigate the lithium diffusion coefficient of the prepared materials, the ac-impedance spectra were measured and the lithium diffusion coefficients were calculated. Fig. 8(a) and (b) illustrates typical Nyquist plots and relationship between real impedance with the low frequencies obtained from the materials sintered at 800 and 900 °C. Rs and Rct were measured at highintermediate frequency ranges for the samples sintered at 800 and 900 °C as (2.18 X, 59.94 X) and (1.88 X, 80.27 X), respectively. A narrow line inclined at a constant angle to the real axis (Warburg impedance) in the low frequency range, and this region is attributed to the diffusion of the lithium ions into the bulk of the electrode. This relation is governed by Eq. (1). Fig. 8. Relationship between real impedance with the low frequencies for synthesized cathode materials sintered at (a) 800 °C and (b) 900 °C.

Z re ¼ Rs þ Rct þ rw  x0:5 D ¼ 0:5ðRT=An2 F 2 rw CÞ

Table 3 Ac-impedance parameters and diffusion coefficients of lithium ion for samples prepared at 800 and 900 °C. Sample (°C)

Re (X)

Rct (X)

r (X s0.5)

D (cm2 s1)

800 900

2.18 1.88

59.94 80.27

14.92 20.21

4.03  1014 2.18  1014

The morphologies and microstructure of the sample sintered at 800 °C were examined using TEM (Fig. 5). From the high-resolution TEM image, the sample shows 300 nm domains, and the d-spacing of the (0 0 0 1) plane was 0.476 nm. The selected-area electron diffraction (SAED) pattern for the [4 4 0 1] zone axis orientation shown in Fig. 5b reveals a set of sharp spots corresponding to the (1 0 1 4) and (1 1 2 0) planes. The discharge/charge capacities and cycle performance were evaluated to investigate the effect of sintering temperature on the electrochemical performance. Fig. 6(a) and (b) displays the typical discharge/charge profiles and cycle performances measured at a constant 20 mA g1, respectively, for the cathode materials sintered at various temperatures. The LiNi0.6Co0.2Mn0.2O2 sintered at 800 °C delivered the highest capacity, 170 mA h g1, and 98.2% capacity retention after 30 cycles. The initial discharge capacity of the prepared cathode material using co-precipitation method presented ca. 170 mA h g1, however, the capacity significantly reduced within 40 cycles [21]. The cathode sintered at 700 °C shows a less crystalline layered structure and that sintered at 1000 °C exhibits more cation mixing in a lithium-deficient structure and larger particles;

2

ð1Þ ð2Þ

where rw is called Warburg impedance coefficient (X s0.5), x: angular frequency in the low frequency region (x = 2pf), D: diffusion coefficient, R: the gas constant, T: the absolute temperature, F: Faraday’s constant, A: the area of the electrode surface, C: molar concentration of Li+ ions in 1 cm3, C = 103 M in 1 cm3 for using 1 mol L1 [31]. From the Eq. (2), the diffusion coefficient of lithium ion into the bulk was calculated and the results were presented in Table 3. The obtained diffusion coefficient (4.03  1014) for the cathode material prepared at 800 °C explains the higher mobility for lithium ion diffusion than prepared at 900 °C and this result is in accordance with the electrochemical properties. 4. Conclusions We used a nitrate/urea mixture as fuel to simply combustionsynthesize LiNi0.6Co0.2Mn0.2O2 cathode materials for lithium ion batteries. TGA–DTA data were used to determine the synthesis mechanism and predict the proper sintering temperature. The XRD patterns suggested that the cathode material sintered at 800 °C showed no impurities and was well crystallized. Further, c and c/a were calculated for the samples sintered at various temperatures. ICP–AES showed that the material sintered at 800 °C was LiNi0.6Mn0.2Co0.2O2. XPS showed that the Ni3+/(Ni2+ + Ni3+) ratio for the Ni in the material sintered at 800 °C was 0.69, which is consistent with the theoretical Ni3+/(Ni2+ + Ni3+) ratio for LiNi0.6Co0.2Mn0.2O2. The morphology and microstructure of the material were determined using TEM and SAED. The LiNi0.6Co0.2Mn0.2O2 cathode material sintered at 800 °C exhibited a good capacity of

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