A Search for the Optimum Lithium Rich Layered Metal Oxide Cathode Material for Li-Ion Batteries (original) (raw)
Related papers
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.
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.
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.
Journal of Alloys and Compounds, 2017
In this work a series of Li-rich layered-layered solid solution of Li 2 MnO 3-LiMnO 2 [Li[Li (1Àx)/3 Mn (xþ2)/3 ]O 2 ; x ¼ 0.0, 0.1, 0.3 and 0.5] nanocomposite structure were successfully synthesized using sol-gel technique. All the synthesized compositions exhibit the main characteristics peaks of m-Li 2 MnO 3 and could be indexed to the C2/m space group except some weak diffraction peaks located around 20e30 which can be attributed to the superlattice structure originate due to the ordering of Mn ion into Li-Mn layers and are typically observed for Li-rich based materials. CV results show that pristine LMO possesses weak anodic peak around 4.7 V and no symmetric cathodic peak in the voltage window of 2.0e4.8 V. Among all the synthesized compositions, x ¼ 0.3 (LMO3) delivers highest specific discharge capacity and best rate and cycling performances at all values of current densities. The LMO3 composition delivers an initial discharge capacity of 177 ± 5 mAhg À1 at a current density of 10 mA/g in the voltage range of 2.0e4.8 V and holds nearly 97% of the initial discharge capacity after 120 charge/discharge cycles at the same current density.
Effects of Lithium Source and Content on the Properties of Li-Rich Layered Oxide Cathode Materials
ChemEngineering
Lithium-rich layered oxide (LLO) are considered high-capacity cathode materials for next-generation lithium-ion batteries. In this study, LLO cathode materials were synthesized via the hydroxide coprecipitation method followed by a two-step lithiation process using different lithium contents and lithium sources. The effects of lithium content and lithium source on structure and electrochemical performance were investigated. This study demonstrated the clear impact of Li/TM ratio on electrochemical performance. Lower Li/TM ratio reduced the irreversible capacity loss in the first cycle and provided better cycling stability among all samples. The best results exhibited an initial discharge capacity of 279.65 mAh g−1 and reached a discharge capacity of 231.9 mAh g−1 (82.9% capacity retention) after 30 cycles. The sample using Li2CO3 as lithium source exhibits better electrochemical performance than the sample using LiOH as lithium source. Therefore, it is important to choose the approp...
Composition of layered oxides are tuned for high capacity and rate capability. LiNi 0.4 Co 0.4 Mn 0.2 O 2 is proposed as one of the promising cathode materials. Lesser structural changes during charging lead to excellent cycling stability. LiNi 0.4 Co 0.4 Mn 0.2 O 2 delivers a capacity over 200 mAh g À1 via single-phase reaction. a b s t r a c t In this study, we target to find a new composition for a layered mixed metal oxide, which has a high structural stability and a good electrochemical performance. Our strategy is to alter the transition metal composition focusing on the relative amounts of redox active Ni and Co to the inactive Mn, based on highly-stabilized LiNi 1/3 Co 1/3 Mn 1/3 O 2. X-ray absorption near-edge structure and X-ray diffraction analyses show that the degree of cation disorder decreases on increasing the ratio of Ni and Co to Mn, by the presence of Ni 3þ , suggesting that slightly higher Ni and Co contents lead to improved structural stability. Electrochemical studies demonstrate that LiNi 0.4 Co 0.4 Mn 0.2 O 2 cathodes exhibit considerable improvements in both the reversible capacity and the rate capabilities at a voltage range of 2.5e4.6 V. In situ XRD measurements reveal that LiNi 0.4 Co 0.4 Mn 0.2 O 2 maintains a single-phase and undergoes lesser structural variations compared to controlled compositions during a delithiation process up to 4.6 V, while achieving a high reversible capacity over 200 mAh g À1. As a result, LiNi 0.4 Co 0.4 Mn 0.2 O 2 experiences fewer structural degradations during electrochemical cycling, which explains the excellent long-term cycling performance.
2013
A nanosized Li-rich layered oxide/carbon composite material is successfully prepared by simple ball milling pulverization of microsphere-shaped Li-rich layered oxide materials with conductive carbon. The nanosized Li-rich layered oxide/carbon composite electrode exhibits a high 1st discharge capacity of 250 mAh g 21 with an excellent rate capability at high current density. The composite also reduces the internal resistance from oxygen release during the electrochemical activation of Li 2 MnO 3. The improvement in the electrochemical performance of nanosized Li-rich layered oxide/carbon composite materials primarily occurs because the nanosized particles facilitate the diffusion of Li within the structure and provide innumerable reaction sites with lithium. Furthermore, the electronic conductivity of the active material is effectively enhanced by the carbon coating on the particles. In addition, unique effects of ball milling on the electrochemical properties of the Li-rich layered oxides are observed: (i) pre-activation of the Li 2 MnO 3 component and (ii) gradual electrochemical activation under 4.3 V during cycling. Adverse effects on the electrochemical stability of the nanosized Li-rich layered oxide are also discussed, and these adverse effects mainly arise due to (i) the structural deformation of hexagonal ordering, (ii) the growth of the spinel component and (iii) the insufficient formation of a protective NiF 2 layer on the surface of the active material.
Electrochimica Acta, 2013
High energy density integrated positive electrode Lithium manganese oxide rich layered-layered composite Lithium-ion battery Solid-state method Self combustion synthesis a b s t r a c t Alternative to LiCoO 2 cathode without sacrificing its structure and capacity, layered-layered composites with Li 2 MnO 3 -LiMO 2 formula have been pursued in this article. In this study, we have optimized the Li 2 MnO 3 content in the composite based on its electrochemical performances (in terms of specific capacity, mAh g −1 ). All the samples are synthesized either by self-combustion reaction (SCR) or solidstate method. Phase composition, morphology, particle size and distribution are characterized by using X-ray diffraction (XRD), field emission gun scanning electron microscope (FEG-SEM) and high resolution transmission electron microscope (HR-TEM), respectively. The X-ray diffraction study confirms that the material has layered LiNi 0.3 Co 0.3 Mn 0.3 O 2 structure with a space group of R3m along with the formation of Li 2 MnO 3 phase with super lattice ordering (C2/m). Charge/discharge capacity of the composite cathode materials increases with cycle number due to more and more activation of the Li 2 MnO 3 and get stabilized after 20th cycle with good coulombic efficiency. A composite of 0.7Li 2 MnO 3 -0.3LiMn 0.33 Co 0.33 Ni 0.33 O 2 composition delivered a maximum stable specific discharge capacity of ∼190 mAh g −1 over 50 cycles at C/10 rate at 20 • C once it reaches the activation stage. A detail electrochemical study has been performed to understand the complicated electrochemistry during charge-discharge reaction at 20 • C.
Chemistry of Materials, 2010
The layered oxide cathode material LiMO 2 , where M = Ni 0.9-y Mn y Co 0.1 and 0.45 e y e 0.60, was synthesized by a coprecipitation method. X-ray diffraction analysis shows that the maximum manganese content in the stoichiometric material, i.e. with Li:M = 1, cannot exceed 50%; otherwise, a second phase is formed. Rietveld refinement reveals that increasing manganese content suppresses the disorder between the lithium and nickel ions. Magnetic measurements show that part of the Mn 4þ ions in the manganese rich compounds is reduced to Mn 3þ ; this results in a larger hysteresis loop due to the increased magnetic moment of the resulting ferrimagnetically ordered clusters. LiNi 0.4 Mn 0.5 Co 0.1 O 2 and LiNi 0.45 Mn 0.45 Co 0.1 O 2 show similar electrochemical capacities of around 180 mAh/g (between 2.5 and 4.6 V at 0.5 mA/cm 2) for the first discharge. However, subsequent cycling of LiNi 0.4 Mn 0.5 Co 0.1 O 2 results in faster capacity loss and poorer rate capability indicating that manganese rich compounds, with Li:M = 1:1, are probably not suitable candidates for lithium batteries.