Optimization of Layered Cathode Materials for Lithium-Ion Batteries (original) (raw)
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Stabilized Layered-Layered-Spinel Cathode Materials for Lithium-Ion Batteries
The concept of embedding a spinel component in high capacity, composite xLi 2 MnO 3 •(1−x)LiMO 2 (M = Mn, Ni) 'layeredlayered' structures to improve their electrochemical properties and cycling stability has been exploited. In this paper, we report the preparation and electrochemical characterization of three-component 'layered-layered-spinel' electrodes, synthesized by lowering the lithium content of a parent 'layered-layered' 0.3Li 2 MnO 3 •0.7LiMn 0.5 Ni 0.5 O 2 material while maintaining a Mn:Ni ratio of 0.65:0.35; such compounds can be designated generically by the system, Li x Mn 0.65 Ni 0.35 O y , for which the end members are 0.3Li 2 MnO 3 •0.7LiMn 0.5 Ni 0.5 O 2 (x = 1.3; y = 2.3), in which the average manganese and nickel oxidation states are 4+ and 2+, respectively, and LiMn 1.3 Ni 0.7 O 4 (x = 0.5; y = 2) in which the corresponding average oxidation states are expected to lie between 4+ and 3.77+ for Mn, and 2.57+ and 3+ for Ni, respectively. For this study, compounds with a lithium content of x = 1.3, i.e., the parent 'layered-layered' composition, and 1.25 were selected for detailed and comparative investigation, the latter value corresponding to a targeted spinel content of 6%. The beneficial effects of 1) using Mg 2+ as a dopant ion and 2) treating the electrode particle surface with an acidic solution of AlF 3 to enhance cycling stability, reduce first-cycle capacity loss, and to slow voltage decay on cycling are discussed.
Composite 'Layered-Layered-Spinel' Cathode Structures for Lithium-Ion Batteries
Journal of the Electrochemical Society, 2012
The concept of embedding a spinel component in high capacity, composite xLi 2 MnO 3 •(1−x)LiMO 2 (M = Mn, Ni) 'layeredlayered' structures to improve their electrochemical properties and cycling stability has been exploited. In this paper, we report the preparation and electrochemical characterization of three-component 'layered-layered-spinel' electrodes, synthesized by lowering the lithium content of a parent 'layered-layered' 0.3Li 2 MnO 3 •0.7LiMn 0.5 Ni 0.5 O 2 material while maintaining a Mn:Ni ratio of 0.65:0.35; such compounds can be designated generically by the system, Li x Mn 0.65 Ni 0.35 O y , for which the end members are 0.3Li 2 MnO 3 •0.7LiMn 0.5 Ni 0.5 O 2 (x = 1.3; y = 2.3), in which the average manganese and nickel oxidation states are 4+ and 2+, respectively, and LiMn 1.3 Ni 0.7 O 4 (x = 0.5; y = 2) in which the corresponding average oxidation states are expected to lie between 4+ and 3.77+ for Mn, and 2.57+ and 3+ for Ni, respectively. For this study, compounds with a lithium content of x = 1.3, i.e., the parent 'layered-layered' composition, and 1.25 were selected for detailed and comparative investigation, the latter value corresponding to a targeted spinel content of 6%. The beneficial effects of 1) using Mg 2+ as a dopant ion and 2) treating the electrode particle surface with an acidic solution of AlF 3 to enhance cycling stability, reduce first-cycle capacity loss, and to slow voltage decay on cycling are discussed.
Layered cathode materials Rate capability and cycle life a b s t r a c t The structure of the layered Li(Ni x Mn y Co 1ÀxÀy)O 2 in different amounts of x and y ranging between 0.2 and 0.6, have been synthesized and investigated by powder X-ray diffraction and electron microscopy techniques. In the current work spray pyrolysis was used to obtain spherical fine-sized morphology followed by heat treatment to obtain better elec-trochemical activity. The precursor powders were prepared using aqueous solution via spray pyrolysis. Synthesized samples were then heat treated at 850 C. X-Ray Diffraction patterns of synthesized cathode materials showed well defined splitting of [006]/[102] and [108]/[110] diffraction peaks indicating layered structure and good hexagonal ordering. In this study, Li(Ni 1/3 Mn 1/3 Co 1/3)O 2 (111), Li(Ni 0.2 Mn 0.2 Co 0.6)O 2 (226), Li(Ni 0.6 Mn 0.2 Co 0.2)O 2 (622) and Li(Ni 0.2 Mn 0.6 Co 0.2)O 2 (262) were synthesized. The morphology of cathode materials was investigated by scanning electron microscopy and average crystallite size was measured to be between 0.2 mm and 0.6 mm. Moreover, particle sizes were verified by particle size measurement and transmission electron microscopy techniques. The electrochemical cells were cycled at 0.1C and 0.3C rate (1C ¼ 170 mAhg À1) and it was found that fast charging and discharging behavior were not sufficient. However, capacity retention after 32 cycles were determined to be 85.3% and 90%, for (111) and (262) samples, respectively.
A new lithium rich composite positive electrode material of the composition 0.3Li 2 MnO 3 .0.7LiNi 0.5 Co 0.5 O 2 (LLNC) was synthesized using the conventional co-precipitation method. Its crystal structure and electrochemistry in Li cells have been compared to that of the previously known material, 0.3Li 2 MnO 3 .0.7LiMn 0.33 Ni 0.33 Co 0.33 O 2 (LLNMC). The removal of Mn from the LiMO 2 (M = transition metal) segment of the composite cathode material allowed us to determine the location of the manganese oxide moiety in its structure that triggers the layered to spinel conversion during cycling. The new material resists the layered to spinel structural transformation under conditions in which LLNMC does. X-ray diffraction patterns revealed that both compounds, synthesized as approximately 300 nm crystals, have identical super lattice ordering attributed to Li 2 MnO 3 existence. Using X-ray absorption spectroscopy we elucidated the oxidation states of the K edges of Ni and Mn in the two materials with respect to different charge and discharge states. The XAS data along with electrochemical results revealed that Mn atoms are not present in the LiMO 2 structural segment of LLNC. Electrochemical cycling data from Li cells further revealed that the absence of Mn in the LiMO 2 segment significantly improves the rate capabilities of LLNC with good capacity maintenance during long term cycling. Removing the Mn from the LiMO 2 segment of lithium rich layered metal oxides appears to be a good strategy for improving the structural robustness and rate capabilities of these high capacity cathode materials for Li-ion batteries.
A Search for the Optimum Lithium Rich Layered Metal Oxide Cathode Material for Li-Ion Batteries
We report the results of a comprehensive study of the relationship between electrochemical performance in Li cells and chemical composition of a series of Li rich layered metal oxides of the general formula xLi 2 MnO 3 · (1-x)LiMn 0.33 Ni 0.33 Co 0.33 O 2 in which x = 0,1, 0.2, 0,3, 0.5 or 0.7, synthesized using the same method. In order to identify the cathode material having the optimum Li cell performance we first varied the ratio between Li 2 MnO 3 and LiMO 2 segments of the composite oxides while maintaining the same metal ratio residing within their LiMO 2 portions. The materials with the overall composition 0.5Li 2 MnO 3 · 0.5LiMO 2 containing 0.5 mole of Li 2 MnO 3 per mole of the composite metal oxide were found to be the optimum in terms of electrochemical performance. The electrochemical properties of these materials were further tuned by changing the relative amounts of Mn, Ni and Co in the LiMO 2 segment to produce xLi 2 MnO 3 · (1-x)LiMn 0.50 Ni 0.35 Co 0.15 O 2 with enhanced capacities and rate capabilities. The rate capability of the lithium rich compound in which x = 0.3 was further increased by preparing electrodes with about 2 weight-percent multiwall carbon nanotube in the electrode. Lithium cells prepared with such electrodes were cycled at the 4C rate with little fade in capacity for over one hundred cycles.
J. Mater. Chem. A, 2015
A Li-rich layered-spinel material with a target composition Li 1.17 Ni 0.25 Mn 1.08 O 3 (xLi[Li 1/3 Mn 2/3 ]O 2 .(1 À x) LiNi 0.5 Mn 1.5 O 4 , (x ¼ 0.5)) was synthesized by a self-combustion reaction (SCR), characterized by XRD, SEM, TEM, Raman spectroscopy and was studied as a cathode material for Li-ion batteries. The Rietveld refinement results indicated the presence of monoclinic (Li[Li 1/3 Mn 2/3 ]O 2 ) (52%), spinel (LiNi 0.5 Mn 1.5 O 4 ) (39%) and rhombohedral LiNiO 2 (9%). The electrochemical performance of this Li-rich integrated cathode material was tested at 30 C and compared to that of high voltage LiNi 0.5 Mn 1.5 O 4 spinel cathodes. Interestingly, the layered-spinel integrated cathode material exhibits a high specific capacity of about 200 mA h g À1 at C/10 rate as compared to 180 mA h g À1 for LiNi 0.5 Mn 1.5 O 4 in the potential range of 2.4-4.9 V vs. Li anodes in half cells. The layered-spinel integrated cathodes exhibited 92% capacity retention as compared to 82% for LiNi 0.5 Mn 1.5 O 4 spinel after 80 cycles at 30 C. Also, the integrated cathode material can exhibit 105 mA h g À1 at 2 C rate as compared to 78 mA h g À1 for LiNi 0.5 Mn 1.5 O 4 . Thus, the presence of the monoclinic phase in the composite structure helps to stabilize the spinel structure when high specific capacity is required and the electrodes have to work within a wide potential window. Consequently, the Li 1.17 Ni 0.25 Mn 1.08 O 3 composite material described herein can be considered as a promising cathode material for Li ion batteries. Fig. 1 Rietveld profiles for (a) LiNi 0.5 Mn 1.5 O 4 and (b) Li 1.17 Ni 0.25 -Mn 1.08 O 3 . The calculated 2q values of the reflections (vertical bars) correspond to (a) LiNi 0.5 Mn 1.5 O 4 and Li 0.3 Ni 0.5 Mn 0.2 O; (b) Li 2 MnO 3 , LiNi 0.5 Mn 1.5 O 4 , and LiNiO 2 (top-down).
Journal of The Electrochemical Society, 2006
Layered Li 1+x (Ni 0.425 Mn 0.425 Co 0.15) 1-x O 2 materials (0 x 0.12) were prepared at 1000°C for 12 h in air by a coprecipitation method. As x increased in Li 1+x (Ni 0.425 Mn 0.425 Co 0.15) 1-x O 2 , the substitution of x Li + ions for x transition metal ions induced for charge compensation an increase in the average transition metal oxidation state. X-ray photoelectron spectroscopy analyses showed that cobalt and manganese were present in these materials in the trivalent and tetravalent states, respectively, and that increasing overlithiation led to the oxidation of Ni 2+ ions into Ni 3+ ions. The refinement of the crystal structure of these materials in the R m space group and magnetic measurements showed a decrease in the Ni occupancy in the Li layers with increasing overlithiation. From an electrochemical point of view, the reversible capacity in the 2-4.3 V range decreased with overlithiation Keywords : Although LiCoO 2 is suitable for the lithium-ion battery application, its high cost and toxicity prevent its use in low-price or large devices. Positive electrodes with LiNiO 2 revealed an attractive reversible capacity 1 but suffered from a quite poor capacity retention 2 and also from a low thermal stability of their deintercalated phases. 3,4,5,6 Partial substitution for nickel allowed an optimization of these properties for compositions such as LiNi (1-x-y) Co x Al y O 2. 7,8,9 Nevertheless, there is still a need for cheaper and safer positive electrode materials with higher electrochemical performances. Recently lithium-rich manganese-based materials such as Li[Ni x Li (1/3-2x/3) Mn (2/3-x/3) ]O 2 and Li[Co x Li (1/3x/3) Mn (2/3-2x/3) ]O 2 were extensively studied by various research groups. 10,11,12,13 Interesting results were obtained, for instance for the Li[Ni 1/3 Li 1/9 Mn 5/9 ]O 2 phase with a capacity of 230 mAh/g between 2.0 and 4.6 V at 55°C. 14 In all these materials, the manganese ions are in the tetravalent state in the pristine material 15 so that they are electrochemically inactive. Because there are no Mn 3+ ions, no structural evolution to the spinel structure is expected to occur upon cycling, on the contrary to what was observed for the layered LiMnO 2. 16,17,18,19 Furthermore, the presence of a large amount of manganese ions at the stable tetravalent oxidation state is thought to be responsible for a higher thermal stability. Differential scanning calorimetry experiments (DSC) on charged electrodes of Li[Ni x Li (1/3-2x/3) Mn (2/3-x/3) ]O 2 for x=5/12 indicate that this material should be thermally safer than LiCoO 2. 10 The DSC profiles of the fully oxidized Li x [Li 0.12 Ni z Mg 0.32-z Mn 0.56 ]O 2 (z=0.3) material also demonstrate much higher thermal stability than Li x CoO 2. 20 Note also that most of these overlithiated materials exhibit an irreversible plateau at around 4.5 V/Li during the first charge. The origin of this plateau was attributed by Lu and Dahn to be due to an irreversible oxygen loss. 14 Ever since LiNi 1/3 Mn 1/3 Co 1/3 O 2 material was shown by Ohzuku et al. to deliver a high discharge capacity close to 200 mAh/g, 21 a lot of research in the lithium-ion battery field has focused on the layered Li(Ni,Mn,Co)O 2 materials. 22,23,24 In a previous paper we discussed the synthesis conditions of the LiNi 0.425 Mn 0.425 Co 0.15 O 2 phases and their optimization from an electrochemical point of view. 24 In this paper, we report the structure and the electrochemical behavior of the Li 1+x (Ni 0.425 Mn 0.425 Co 0.15) 1x O 2 materials (0 x 0.12). The classical coprecipitation method was used for syntheses because it leads to the best electrochemical performance. 24 The relationships between the chemical composition, the physical properties, the structure, and the electrochemical performances are discussed in this paper. Experimental Ni(NO 3) 2 •6H 2 O (97% Prolabo), Mn(NO 3) 2 •4H 2 O (98% Fluka), Co(NO 3) 2 •6H 2 O (98% Prolabo), LiOH (98+% Alfa Aesar), and NH 4 OH (28-30% J.T. Baker) were used as starting materials.
Journal of Alloys and Compounds, 2016
Mesoporous cathode active materials that included undoped and separated Cu 2+ and Co 3+ doped spinels were prepared. The "doped spinel-Layered-Li-rich spinel" composite nanoparticles within the three integrated phased (LiM 0,02 Mn 1,98 O 4-Li 2 MnO 3-Li 1,27 Mn 1,73 O 4 ; where M is Cu 2+ and Co 3+) were synthesized by a microwave assisted hydrothermal synthesis. These materials were investigated with X-Ray powder Diffraction spectroscopy (XRD), Scanning Electron Microscopy (SEM and FE-SEM), High Resolution Transmission Electron Microscopy (HR-TEM), galvanostatic cycling at 0.1 C and 0.5 C rates, Cyclic Voltammetry (CV), and Electrochemical Impedance Spectroscopy (EIS). The effects of the calcination temperature and the partial substitution of Mn 3+ in the spinel by Cu 2+ and Co 3+ , and onto the spinel structure were investigated with XRD. The lattice parameters of the spinel structured compounds were calculated from the XRD data using the Williamson-Hall equation. However, the morphological changes, which depended on the calcination temperature, were examined by SEM, FE-SEM and HRTEM. Furthermore, the two other phases which were different from LiM 0,02 Mn 1,98 O 4 had a great impact on the electrochemical performance over the potential range of the 3-5 V. At the 0.1 C rate, the first discharge capacities of undoped and Cu 2+ , Co 3+ doped materials were 577, 285, 560 mAh/g respectively. After 50 cycles at 0.5 C rate, we achieved 96.2%; 52.5%; 95.4% capacity retention for the undoped and Cu 2+ , Co 3+ doped materials respectively.
Ionics, 2017
The enriched lithium ion containing layered oxide cathode materials Li(Li 0.05 Ni 0.7 -x Mn 0.25 Co x )O 2 have been prepared by using facile sol-gel technique. The phase purity and crystalline nature of the layered oxide cathodes have determined by X-ray diffraction analysis. Surface morphology and elemental analysis have been carried out using scanning electron microscopy with energy dispersive analysis by X-rays and HR-TEM. Cyclic voltammetry analysis of the lithium-enriched cathode material shows a well redox performance at electrode-electrolytic interface. The Li(Li 0.05 Ni 0.7 -x Mn 0.25 Co x )O 2 cathode shows the most promising electrochemical properties under different conditions in which an appropriate rising of discharge capacity (i.e., 167 mAh g -1 at 0.5 C) and cycling stability (i.e., capacity retention: 83% at 1 C after 20 cycles, cutoff voltage 2.8-4.5 V) at ambient temperature. These unique properties allow the effective use of these cathode materials as positive electrodes for the development of rechargeable lithium ion batteries.
Journal of The Electrochemical Society
Layered Li and Mn rich cathode materials of the xLi[Li1/3Mn2/3]O-2 center dot(1-x)LiMn1/3Ni1/3Co1/3O2 (x = 0.2, 0.4, 0.6) were synthesized by a self-combustion method, characterized by XRD, SEM, HRTEM and Raman spectroscopy and studied as positive electrode materials for Li-ion batteries. The cathode material with x = 0.6 exhibits an initial high discharge specific capacity of 270 mAh g(-1) at C/10 rate in galvanostatic charge-discharge cycling, which decreases to 220 mAh g(-1) after 50 cycles. It also exhibits a high rate capability as compared to other composites. Structural studies using the electron diffraction technique with TEM and spectral studies by Raman spectroscopy indicate continuous structural changes upon cycling that include formation of a spinel phase. The electrochemical impedance spectra recorded at various potentials present evidence of a substantial increase in the charge-transfer resistance at potentials higher than 4.4 V during charge and also at potentials low...