Lithium Manganese Oxide Cathode Research Articles

Diode laser heat treatment of lithium manganese oxide films

The crystallization of lithium manganese oxide thin films prepared by radio frequency magnetron sputtering on stainless steel substrates under 10Pa argon pressure is demonstrated by a laser annealing technique. Laser annealing processes were developed as a function of annealing time and temperature with the objective to form an electrochemically active lithium manganese oxide cathode. It is demonstrated, that laser annealing with 940nm diode laser radiation and an annealing time of 2000s at 600°C delivers appropriate parameters for formation of a crystalline spinel-like phase. Characteristic features of this phase could be detected via Raman spectroscopy, showing the characteristic main Raman band at 627cm−1. Within cyclic voltammetric measurements, the two characteristic redox pairs for spinel lithium manganese oxide in the 4V region could be detected, indicating that the film was well-crystallized and de-/intercalation processes were reversible. Raman post-analysis of a cycled cathode showed that the spinel-like structure was preserved within the cycling process but mechanical degradation effects such as film cracking were observed via scanning electron microscopy. Typical features for the formation of an additional surface reaction layer could be detected using X-ray photoelectron spectroscopy.

Preparation of LiMn 2O 4 with an enhanced performance by mixed liquid and mechanical activations

Spinel lithium manganese oxide (LiMn 2O 4) cathode material was synthesized by an improved solid state reaction method named mixed liquid activation and mechanical activation. Thermal decomposition of the precursor was investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). X-ray diffraction (XRD) was used to identify the phase of the synthesized LiMn 2O 4 powder. The particle of the as-prepared powder was observed by scanning electron microscopy (SEM). Cyclic voltammograms (CV) characterization shows that the LiMn 2O 4 prepared by the improved solid state reaction method possesses an excellent electrochemical property, which is possibly due to its small and homogeneous particle. Galvanostatic charge–discharge tests shows that the LiMn 2O 4 has an initial capacity of 117 mAh/g at a current density of 29.6 mA/g (0.2C) between 3.3 and 4.5 V and good cycle stability, maintaining 94% of its initial capacity after 40 cycles. Moreover, the LiMn 2O 4 prepared by the improved method shows better discharge ability at higher rates than that prepared by the conventional method.

Structure, Morphology, and Electrochemical Investigation of LiMn2O4 Thin Film Cathodes Deposited by Radio Frequency Sputtering for Lithium Microbatteries

Spinel lithium manganese oxide (LiMn2O4) cathode thin films were successfully deposited on different substrates such as Si, Pt/Al, and indium tin oxide (ITO)/Pt/Al by radio frequency (RF) sputtering. These thin films were investigated as positive electrodes for lithium microbatteries. The thickness of the deposited films was estimated by surface-profilometer at different deposition time intervals from 30 min to 15 h, and the thickness was found to be 20−600 nm. The structure and surface morphology deposited thin films of LiMn2O4 were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The phase transformation from amorphous to crystalline phase was found at around 700 °C for the electrode films deposited on Si substrate. The LiMn2O4 deposited with ITO interlayer on Pt/Al substrate was found to be well crystallized relatively at lower temperature (≤300 °C). No significant changes were observed on the surface morphology between the as-deposited and the annealed film. Electrochemical performance was measured for LiMn2O4 films deposited with or without ITO interlayer on Pt/Al substrate. The discharge capacity around 60.9 and 67.5 mAh g−1 are obtained, respectively, for the 500 °C-annealed LiMn2O4/Pt/Al film and as-deposited LiMn2O4/ITO/Pt/Al film. Because the crystallization temperature of LiMn2O4/ITO/Pt/Al film was found to be relatively lower (≤300 °C), this work could possibly be extended to design and fabricate flexible lithium microbatteries using polymer substrates.

Synthesis and physicochemical properties of LiLa 0.01Mn 1.99O 3.99F 0.01 cathode materials for lithium ion batteries

Spinel lithium manganese oxide cathode materials were synthesized using the ultrasonic-assisted sol-gel method. The synthesized samples were investigated by differential thermal analysis (DTA) and thermogravimetry (TG), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and the charge-discharge test. TG-DTA shows that significant mass loss occurs in two temperature regions during the synthesis of LiLa 0.01Mn 1.99O 3.99F 0.01. XRD data indicate that all samples exhibit the same pure spinel phase, and LiLa 0.01Mn 1.99O 3.99F 0.01 and LiLa 0.01Mn 1.99O 4 samples have a better crystallinity than LiMn 2O 4. SEM images indicate that LiLa 0.01Mn 1.99O 3.99F 0.01 has a slightly smaller particle size and a more regular morphology structure with narrow size distribution. The charge-discharge test reveals that the initial capacities of LiMn 2O 4, LiLa 0.01Mn 1.99O 4, and LiLa 0.01Mn 1.99O 3.99F 0.01 are 130, 123, and 126 mAh·g 1, respectively, and the capacity retention rates of the initial value, after 50 cycles, are 84.8%, 92.3%, and 92.1%, respectively. The electrode coulomb efficiency and CV reveal that the electrode synthesized by the ultrasonic-assisted sol-gel (UASG) method has a better reversibility than the electrode synthesized by the sol-gel method.

An alternative method to improve the electrochemical performance of a lithium secondary battery with LiMn 2O 4

The electrochemical properties of the Li-ion battery with a lithium manganese oxide (LiMn 2O 4) cathode are improved by efficiently reducing the reaction between LiMn 2O 4 and hydrofluoric acid (HF) produced in the electrolyte. By introducing fine ZrO 2 particles in the slurry during fabrication, Mn dissolution of the cathode during the charge–discharge cycles is minimized by scavenging the HF produced in the cell. Results from galvanostatic experiments show that the capacity retention of the LiMn 2O 4 fabricated with new method is maintained up to 92% after 50 cycles at room temperature and 76% at high temperature without losing initial capacity. The improvement in the electrochemical properties of the cathode prepared by this method is superior to other approaches in terms of fabrication process and it sheds light on the possibility of further improving the electrochemical properties of LiMn 2O 4.

Stability Improvement of LiMn2O4 Thin-Film Cathodes under High Rate and Over-Discharge Cycling

Thin films of spinel lithium manganese oxides were prepared by sol-gel method. The annealing time and temperatures were optimized to obtain crystalline thin films. The as-synthesized films were coated with a thin layer of alumina or lithium phosphorus oxynitride by radio frequency sputtering. The coatings were amorphous as characterized by X-ray diffraction. The electrochemical properties of the coated and uncoated thin-film cathodes were characterized and compared. The cells made of the lithium manganese oxide cathodes were discharged at different rates. At higher discharge rates, both the alumina and the -coated samples exhibited higher discharge potential plateaus than the uncoated spinel. As the cells were cycled in a wide voltage window of , the coated cathodes exhibited less capacity fading. For samples immersed in acid solution before cycling, the surface-coated samples showed greater stability.

Effects of synthetic parameters on structure and electrochemical performance of spinel lithium manganese oxide by citric acid-assisted sol–gel method

The spinel lithium manganese oxide cathode materials were prepared by citric acid-assisted sol–gel method at 623–1073 K in air. The effects of pH value, raw material, synthesis temperature and time on structure and electrochemical performance of spinel lithium manganese oxide are investigated by X-ray diffraction (XRD), scanning electronic microscope (SEM) and cyclic voltammetry (CV). XRD data results strongly suggest that the synthesis temperature is the dominating factors of the formation of spinel phase, and spinel lithium manganese oxide powder with various crystallites size can be obtained by controlling the sintering time. CV shows that spinel lithium manganese oxide powder formed about 973 K presents the best electrochemical performance with well separated two peaks and the highest peak current. Charge–discharge test indicates that spinel lithium manganese oxide powders calcined at higher temperatures have high discharge capacity and capacity loss, and sintered at lower temperatures has low discharge capacity and high capacity retention.

Characterization of Lithium Manganese Oxide Cathode for All-Solid-State Lithium Rechargeable Batteries

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Electrochemical performance of LBO-coated spinel lithium manganese oxide as cathode material for Li-ion battery

Surface treatment of the lithium manganese oxide cathode material coated by lithium borate glass (Li 2O–2B 2O 3) with improved electrochemical cyclability and structural stability was conducted in this study. The lithium manganese oxide powder doped with various weight percentages of LBO glass was calcined to form a fine powder with single spinel phase, exhibiting different particle size, size distribution and morphology. The surface area decreased with the content of the LBO glass. The average particle size was in the range of 3–8 μm. Cyclic charge/discharge testing of the coin cells, fabricated by lithium manganese oxide and 0.4 wt.% LBO-coated lithium manganese oxide as cathode material, provided the initial discharge capacity of 95.57 and 119.79 mAh/g, respectively. Furthermore, the 0.4 wt.% LBO-coated lithium manganese oxide powder retained 93% of its original capacity after 10 cycles, showing much better cyclability than the uncoated lithium manganese oxide. It is demonstrated that the LBO-coated lithium manganese oxide cathode material exhibited high discharge capacity and the fading rate was evidently decreased after cyclic test.

Nanostructured Lithium Manganese Oxide Cathodes Obtained by a Reduction of Aqueous Lithium Permanganate with Hydrogen

Nanostructured lithium manganese oxides have been synthesized by reducing aqueous lithium permanganate with hydrogen gas at 60°C in the presence and absence of lithium hydroxide followed by firing in vacuum at 250°C. The oxides have been characterized by wet-chemical analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and Brunauer-Emmett-Teller surface area and density measurements. The Li/Mn ratio in the samples increases from 0.47 to 1.09 with increasing amount of lithium hydroxide in the synthesis medium. X-ray diffraction indicates the sample to have spinel- or -like structures. The samples exhibit high capacities of 250-300 mAh/g at 4-1.5 V with good rate capability in lithium cells. The capacity retention and the charge efficiency of the cathodes improve with increasing lithium content. © 2003 The Electrochemical Society. All rights reserved.

A study of layered lithium manganese oxide cathode materials

Substituted layered sodium manganese oxide bronzes with the P2 structure were prepared by glycine-nitrate combustion synthesis. The Na in the as-prepared materials could be completely ion-exchanged for Li under mild conditions. All lithium manganese oxide compounds obtained after ion-exchange have O2 stacking of the layers. Cyclic voltammetry and stepped potential experiments on lithium cells containing these materials show that the main redox reaction around 3.1 V is a diffusion-controlled process and is completely reversible. O2-Li 0.6[Al 0.1Mn 0.85□ 0.05]O 2 and O2-Li 0.6[Ni 0.1Mn 0.85□ 0.05]O 2 are particularly promising as cathode materials in lithium cells because of the high reversible discharge capacities (180 mAh/g).

Nanostructured Lithium Manganese Oxide Cathodes Obtained by Reducing Lithium Permanganate with Methanol

Reduction of lithium permanganate with methanol in acetonitrile and acetonitrile-water media has been investigated to obtain nanocrystalline lithium manganese oxides. The products have been characterized by wet-chemical analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and transmission electron microscopy. The samples synthesized in acetonitrile medium consist of a considerable amount of organic residue even after firing at 250°C in vacuum, which could be lowered by introducing water into the synthesis and washing media (acetonitrile-water mixture). Additionally, introduction of lithium hydroxide into the synthesis medium helps to increase the lithium content and Li/Mn ratio in the product and thereby to improve the electrochemical performance. Optimum compositions synthesized in the acetonitrile-water medium exhibit capacities of mAh/g with good cyclability and charge efficiency. © 2002 The Electrochemical Society. All rights reserved.

6Li MAS NMR Studies of the Local Structure and Electrochemical Properties of Cr-doped Lithium Manganese and Lithium Cobalt Oxide Cathode Materials for Lithium-Ion Batteries

6Li magic-angle spinning NMR spectroscopy has been used to probe the lithium local environments in a series of layered compounds, Cr-doped LiCoO2, Co-doped LiCrO2, Cr-doped LiMnO2, and the Li-rich material Li[Li0.2Cr0.4Mn0.4]O2. A series of resonances are seen for LiCrxCo1-xO2 due to Cr3+ occupancy of the first and second cation coordination sphere surrounding Li. The shifts, which are caused by a transferred hyperfine interaction, differ in size and sign, depending on the Li−O−Cr bond angle. The shift of LiCrO2 cannot be directly extrapolated from those measured in the magnetically dilute Cr3+-doped LiCoO2 compounds, and remains constant with temperature (from room to 283 °C). This behavior is ascribed to the strong antiferromagnetic couplings that exist in LiCrO2. The behavior of Cr3+-doped layered LiMn(III)O2 is qualitatively similar to that of Co3+-doped LiCrO2, both compounds showing additional resonances caused by the dopant cations. Dramatically different NMR spectra are seen for Li[Li0.2Cr0.4Mn0.4...

Polymer gel electrolyte supported with microporous polyolefin membranes for lithium ion polymer battery

A polymer gel electrolyte supported with a microporous polyolefin membrane for lithium ion polymer batteries was prepared and characterized. The polymer gel electrolytes were based on poly(vinylidene fluoride- co-hexafluoropropylene) (PVdF-HFP), lithium salt and carbonate solvents. The gel electrolytes exhibited high ionic conductivity in the order of 10 −3 S cm −1 at room temperature and were electrochemically stable up to +5.0 V against Li +/Li. The membrane-supported gel electrolytes show excellent mechanical properties and good adhesion toward electrodes. Lithium-ion polymer cells, composed of a carbon anode and lithium manganese oxide cathode separated by the membrane-supported polymer electrolytes were assembled. The cells showed good electrochemical and rate performance during cycling.

A causal study of the capacity fading of Li 1.01Mn 1.99O 4 cathode at 80°C, and the suppressing substances of its fading

Discharge capacities of the Li 1.01Mn 1.99O 4 cathode and Mn content dissolved from the cathode were examined on the addition of some chemicals, as the storage temperatures and time were changed. On the addition of 1000 ppm of H 2O to 1.0 M LiPF 6 solution in EC/DMC (1:2 in volume), 41% of capacity of the cathode was lost after 24 h storage at 80°C, in contrast to 5% loss in the case of no additive. Water would be responsible for causing the capacity fading of the cathode under such condition as elevated temperatures. In the EC/DMC solution without LiPF 6, on the contrary, no capacity fading was observed with H 2O additive at 80°C storage, while the CF 3SO 3H addition resulted in 40% of capacity fading. These results show that plausible acid derived from the reaction of LiPF 6 with H 2O causes the capacity fading on the lithium manganese oxide at 80°C, relatively high storage temperature. On the other hand, addition of 500–1000 ppm of (CH 3) 3SiNHSi(CH 3) 3 resulted in less capacity fading of the cathode and made Mn dissolution decrease drastically. Therefore, dehydration and acid-neutralization in the electrolyte solution would restrain the capacity fading of the lithium manganese oxide cathode during high temperature storage, and we confirmed it in some experiments.

Electrode Characteristics of Sputtered Lithium Manganese Oxide Films with Diamond-Like-Carbon Top Layer

ABSTRACTThere have been increasing interests in lithium rechargeable batteries, especially microbatteries, with rapid development of portable electronic equipments and MEMS(Micro electromechanical systems) technology. In this work, lithium manganese oxide, as a strong candidate for the battery materials, which is more abundant, stable in ambient state and less toxic than the other oxides such as lithium nickel oxides and lithium cobalt oxides, was deposited by rf magnetron sputter. The effect of thermal treatment on the microstructure and electrode characteristics of lithium manganese oxide cathode was investigated. In electrochemical experiment using liquid electrolyte, half-cell failure would be caused by manganese dissolution, degradation of electrolyte materials during charging/discharging process and so on. In this research we focus on interface reaction problem that would affect the cyclability and lifetime of microbattery. In order to reduce the interface reaction during operation, we introduce DLC(Diamond-like-Carbon) film that has high electrical resistivity, mechanical hardness and chemical stability. DLC film was deposited on sputtered lithium manganese oxide electrode by ECRCVD(Electron Cyclotron Resonance Chemical Vapor Deposition). DLC-top-layer LiMn2O4 film was more stable during charging/discharging reaction and higher discharge capacity in wide voltage windows than LiMn2O4 film.

New and optimised lithium manganese oxide cathodes for rechargeable lithium batteries

The 3 V spinel, LiMn 2O 4.1, has been prepared by a low temperature solution route which includes the addition of a small amount of carbon to the solution. As a result a significant enhancement of the capacity retention is obtained on cycling, reaching 50% after 300 cycles at discharge and charge rates of C/2 and C/4, respectively. X-ray diffraction of the composite cathode on cycling shows that the improved capacity retention is related to a more complete conversion of the entire electrode between the cubic (charged) and tetragonal (discharged) structures. Layered and anhydrous LiMnO 2 with a structure analogous to LiCoO 2 is reported. The structure, refined using neutron diffraction data, as well as some preliminary results concerning the electrochemical performance are presented. A capacity of 270 mAh g −1 is obtained on the first charge. Capacity fade on cycling is significant for these early materials.

Low-temperature lithium-manganese oxide cathode materials for polymer batteries

Low-temperature spinel phases with physico-chemical characteristics adapted to solid polymer electrolyte environment are prepared as 3 V intercalation material for rechargeable lithium batteries. The lithium intercalation compounds are made by solid-state reaction of an intimate mixture of specifically prepared β-MnO 2 (pyrolusite) and lithium salts at various temperatures between 150 and 450 °C. The experimental results show a direct relation between the composition of the spinel phase obtained and the synthesis temperature. The electrochemical tests show interesting results in terms of reversibility, energy and power density.

3 V and 4 V lithium manganese oxide cathodes for rechargeable lithium batteries

Two lithium manganese oxide materials based on the spinel structure have been synthesised by a new solution method which has the advantage that it can be carried out in air unlike previous sol-gel methods. One material is suitable as a 3 V and the other as a 4 V cathode in rechargeable lithium cells. In the case of the 3 V matherial the addition of a small amount of carbon to the solution during preparation yields a material with a significantly enhanced cycling performance. Cycling at discharge and charge current densities of 1 and 0.5 mA cm −2, respectively (corresponding to a discharge rate of >C/2) and between 3.7 and 2.0 V yields a capacity of 90 mAh g −1 after 300 cycles for the material prepared using carbon. This represents an enhancement of the discharge capacity by 50% on the 300th cycle when compared with the same material without carbon. Cathodes fabricated from the 4 V material have been cycled at discharge and charging current densities of 1 and 0.5 mA cm −2, respectively (corresponding to a discharge rate of >C/2) between limits of 4.4 and 3.3 V. The specific discharge capacity obtained initially is 110 mAh g −1 decreasing to 85 mAh g −1 at 300 cycles.

Solution Synthesis and Characterization of Lithium Manganese Oxide Cathode Materials

ABSTRACTA nonaqueous coprecipitation process has been developed to prepare controlled stoichiometry lithium manganese oxalate precipitates. The process involved mixing a methanolic Li-Mn nitrate solution with a methanolic solution containing tetramethylammonium oxalate as the precipitating agent. The resulting oxalates were readily converted to a variety of phase pure lithium manganese oxides at moderate temperatures (≤600°C), where the phase formed was determined by the initial Li/Mn ratio in the starting solution. Metal cation dopants have been incorporated into the oxalate precipitate by dissolving the appropriate metal nitrate in the Li-Mn precursor solution The various starting solutions, oxalate precipitates, and calcined oxides have been extensively characterized using a variety of techniques, including 7Li NMR, TGA/DTA, SEM, and XRD. Results indicate that a strong interaction occurs between Li and Mn in the nitrate solution which carries over into the oxalate phase during precipitation. The morphology and the crystallite size of the oxide powders were shown to be controlled by the morphology of the oxalate precursor and the oxalate calcination temperature, respectively. The results of initial cathode performance tests with respect to dopant type (Al, Ni, Co) and concentration for LiMn2O4 are also reported.