Electrochemical Properties Of LiMn2O4 Research Articles

Study and Property Characterization of LiMn2O4 Synthesized from Octahedral Mn3O4

The structure of Mn3O4 with an octahedron structure was similar to that of LiMn2O4, and the lithium manganate prepared with it had good electrochemical performance. During the preparation of octahedron Mn3O4, the effects of the pH regulator, temperature, and reaction pH on its morphology, specific surface area, and other properties were studied in this paper. LiMn2O4 was prepared from Octahedron Mn3O4 obtained by using better technology. The effects of calcination time and temperature on the physicochemical and electrochemical properties of LiMn2O4 were studied. The research results indicated that the optimal synthesis conditions for Mn3O4 were as follows: ammonia water was used as a pH regulator and complexing agent, reaction pH was 8, reaction temperature was 80 °C, reaction time was 12 h, and oxygen flow rate was 3 L∙min−1. The LiMn2O4 synthesized had a good octahedron morphology when the calcination temperature was 800 °C and the calcination time was 10 h. The first discharge-specific capacity was 121.9 mAh∙g−1 at a current density of 0.2 C, the discharge-specific capacity was 114.1 mAh∙g−1 after 100 cycles, and the capacity retention rate was 93.6%. Therefore, the lithium manganate prepared by using octahedron manganous oxide had good electrochemical reversibility and a good application prospect.

Li-Mn Bimetallic Metal-Organic Framework and Its Derivative as a Cathode for Lithium-Ion Batteries.

The bimetallic organic-inorganic hybrid complex [Li2Mn3(ipa)4(DMF)4]n (ipa = deprotonated 1,3-isophthalic acid, DMF = N,N'-dimethyl formamide) was synthesized via a solvothermal method and then further calcined at high temperature to prepare a spinel-type lithium manganate (LiMn2O4) cathode under different atmospheres with various calcination conditions. The structure of the complex [Li2Mn3(ipa)4(DMF)4]n was represented by single-crystal X-ray diffraction (XRD), powder XRD, and thermogravimetric (TG) analysis. The morphology and elements of LiMn2O4 were analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of LiMn2O4 indicated that the direct calcination in an air atmosphere at 850 °C for 12 h was the optimal synthetic condition. The initial discharge specific capacity can reach 95.9 mA h g-1 with an open-circuit voltage of ca. 3.0 V and an upper cutoff voltage of ca. 4.3 V at 0.1 C. The initial discharge-specific capacity of 89.8 mA h g-1 at 1 C had a Coulombic efficiency of 95.3%. This was 73 mA h g-1 at a high rate of 5 C increasing to 91.6 mA h g-1 after returning to 0.1 C. After 500 cycles at 1 C, the system remained at 80.7 mA h g-1 with 89.9% of the initial discharge specific capacity. These features exhibit better stability than that of the reported LiCoO2 and LiNiO2 in battery material for LiMn2O4 enforcement.

Effect of Co3+ Doping on Crystal Structure and Electrochemical Properties of Spinel LiMn2O4 Cathode Material

To inhibit the influence of structural distortion caused by the Jahn–Teller effect on LiMn2O4 (LMO), the spinel LMO doped with cobalt ions is prepared by a simple solid-state calcining method. The effects of different cobalt doping amounts on the structure and electrochemical properties of LMO are investigated. The XRD refinement results show that Co3+ successfully enters the lattice of LMO, and its spinel structure is not changed. Due to the smaller radius of Co3+ and the larger bond energy, the unit cell of the LMO material shrinks, and the spinel structure is more stable. The initial capacity of the material decreases with the increase of Co doping content, but the cycle performance is significantly improved. Impressively, when Co doped at x = 0.04, the initial discharge specific capacity of the LMO-0.04 sample is 115.5 mAh·g–1 at 0.1C, and the capacity retention rate is still 81.04% after 500 cycles. The cycle times are much higher than that of the pure LMO sample. Additionally, the diffusion coefficient of Li+ calculated by the Randles–Sevcik equation shows that the doping of Co3+ significantly improves the mobility of Li+ compared with pure LMO. Hence, Co3+ doping can effectively inhibit the structural distortion caused by the Jahn–Teller effect and improve the electrochemical performance of LMO.

The advantages of mass normalized electrochemical impedance spectra for the determination of the kinetic parameters of LiMn2O4 cathodes

The electrochemical properties of LiMn2O4 (LMO) based cathode material with conducting polymer binder containing poly-3,4-ethylenedioxythiophene/polystyrene sulfonate (PEDOT:PSS) dispersion and carboxymethylcellulose (СМС) were investigated for electrodes of three different thicknesses. The effect of the thickness of LMO cathode layer on the kinetic parameters of electrode processes (Rct, Dapp, i0) derived from electrochemical impedance spectroscopy (EIS) has been experimentally analyzed. A simple approach for estimating the possible influence of various real surface areas of electrodes with different active masses by plotting the dependencies normalized to the mass of the active component was proposed. This approach assumes that the real active surface area is defined as the total surface of all particles of the active component, and their mass is proportional to the area given that size of active grains is subject to random statistical distribution. It leads to determination of more reliable values of kinetic parameters and gives the base for more reasonable comparison of results of different works, as was illustrated in the example of LMO.It has been shown that the large difference in the values of charge transfer resistance Rct and apparent diffusion coefficients Dapp for electrodes with various thicknesses becomes insignificant after EIS data normalization to mass loading. While the values obtained from as-recorded non-normalized EIS data referred to the visible area of electrode differ considerably, the normalization of EIS spectra to LMO mass and calculation referred to the real surface area estimated from Brunauer-Emmet-Teller (BET) yields closer values.

Preparation and Electrochemical Properties of LiMn2O4 by Solid-State Combustion Synthesis Method Using Starch as a Fuel

Preparation and Electrochemical Properties of LiMn2O4 by Solid-State Combustion Synthesis Method Using Starch as a Fuel

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn2O4

Thickness variation of the solid electrolyte interphase (SEI) produced during charge-discharge cycling is investigated to analyze the effect of SEI on the electrochemical properties of LiMn2O4. Atomic force microscopy (AFM) is used to measure the SEI thickness and elastic modulus on the LiMn2O4 surface. The SEI shows a broad thickness distribution due to the random nature of the LiMn2O4 electrode surfaces, while the average SEI thickness increases with cycling and stabilizes after the 20th cycle. Formation of a relatively thin SEI on the LiMn2O4 surface accompanies low Coulombic efficiency at early cycling stages. The SEI produced in the early stages of cycling is vulnerable to capacity fading due to inefficient surface protection against possible side reactions. A fully-grown stable SEI after 20 cycles shields the cathode surface from the electrolyte, minimizing capacity fading.

Synthesis and electrochemical properties of LiMn2O4 and LiCoO2-coated LiMn2O4 cathode materials

The synthesis of spinel LiMn2O4 material by a spherical MnO2 precursor route is reported in this paper. Hydrothermal and solid-state reactions were adopted to investigate the effects of synthetic methods on the morphologies and electrochemical characteristics of the LiMn2O4 products, respectively. LiCoO2-coated LiMn2O4 microspheres were also prepared by a sol–gel route based on the as-prepared LiMn2O4 microspheres. The products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDX), and inductively-coupled plasma emission spectrograph (ICP-ES). The results show that LiMn2O4 octahedrons can be obtained under hydrothermal conditions while LiMn2O4 microspheres can be prepared by the solid-state reaction. Electrochemical characterization reveals that the resulting LiMn2O4 microspheres and LiCoO2-coated LiMn2O4 microspheres display much better cycling properties than those of LiMn2O4 octahedrons.

Synthesis, Structure and Properties of Super Fine LiMn<sub>2</sub>O<sub>4</sub>

In this paper, super fine LiMn2O4 powder was synthesized by mechanochemical method starting from Li2CO3 and Mn2O3. The structure, size and morphology of LiMn2O4 were explored with X-ray diffraction and scanning electron microscopy (SEM). The electrochemical properties of LiMn2O4 were studied in 2 mol/L (NH4)2SO4 solution. The result showed that pure spinel LiMn204 powder was prepared after 8h grinding with 3.0KW of power and the particle size was about 1µm. Cyclic vohammetry curve indicate LiMn2O4 electrode material has better capacitive performances.

STUDY ON LITHIUM MANGANESE OXIDE SPINEL SYSTEM AS CATHODE MATERIALS FOR LITHIUM ION BATTERY: SYNTHESIS, MORPHOLOGICAL AND ELECTROCHEMICAL CHARACTERISTICS

Lithium manganese oxide (LiMn2O4) spinel compounds were synthesized by melting impregnation method using manganese dioxide (MnO2) and lithium nitrate (LiNO3). Four sources of MnO2 raw materials were used: a commercial electrochemical manganese dioxide (EMD) supplied by Pin Con O factory; EMD thermal pretreated (EMDt); and MnO2 synthesized chemically (CMD) by oxidation of MnSO4 solution with K2S2O, and EMD synthesized in our laboratory. The effect of the MnO2 materials on the microstructure and electrochemical properties of LiMn2O4 is investigated by X-ray diffraction, scanning electron microscopy, and electrochemical measurements. The charge-discharge cycling behavior in Swagelok model of lithium-ion cells, using synthesized LiMn2O4 as cathode, lithium metal as anode and LiPF6 as electrolyte with Whatman glass separator, showed that the spinels from thermal treated EMDt and CMD gave higher (3100 mAh/g) and more stable values of specific capacity than the spinels from non-treated EMD.

Enhancement of the electrochemical properties of LiMn2O4 by glycolic acid-assisted sol-gel method

LiMn2O4 spinel cathode was synthesized by the sol–gel method by using glycolic acid as a chelating agent. The sample exhibited a pure cubic spinel structure without any impurities in the X-ray diffraction (XRD) patterns. The result of the electrochemical performances on the sample compared to those of electrodes based on LiMn2O4 spinel synthesized by solid state. LiMn2O4 synthesized by glycolic acid-assisted sol–gel method improves the cycling stability of electrode. The capacity retention of sol–gel-synthesized LiMn2O4 was about 90• after 100 cycles between 3.0 and 4.4 V at room temperature. The electrochemical performance of the LiMn2O4 (sol–gel) and LiMn2O4 (solid state) were investigated under 40• between 3.0 and 4.4 V. XRD results of the cathode material after 50 cycles at 40• revealed that LiMn2O4 (sol–gel) could effectively suppress the LiMn2O4 dissolving of into electrolyte and resulted in a better stability.

Preparation and electrochemical properties of LiMn2O4 by a rheological-phase-assisted microwave synthesis method

By using LiCO3 and MnO2, a rheological-phase-assisted microwave synthesis method has been applied in the fast preparation of spinel LiMn2O4 in order to reduce the cost of cathode materials. Comparing with the pristine LiMn2O4 obtained by the traditional solid-state reaction method, the structure and surface morphology of the samples synthesized by the rheological-phase-assisted microwave synthesis method have been investigated. The powders were used as positive materials for lithium-ion battery, whose charge/discharge properties and cycle performance have been examined in detail. As a result, the powders prepared by the rheologicalphase-assisted microwave synthesis method at 750 degrees C are pure spinel LiMn2O4 with regular shapes and uniform distribution, which exhibit higher capacity and much better reversibility than the sample prepared by the traditional solid-state reaction.

Synthesis and electrochemical properties of LiMn2O4 by microwave-assisted sol–gel method

In this work, a timesaving and efficient method, which is microwave-assisted sol–gel method, has been used for synthesis of LiMn2O4 spinel as a cathode material for lithium ion batteries. The influence of synthesis conditions on the structural and electrochemical properties of LiMn2O4 was investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and charge–discharge experiments. The powders resulting from the microwave-assisted sol–gel method are pure, spinel-structure LiMn2O4 particles of regular shapes that exhibit promising electrochemical behavior for battery. In addition, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to analyze the reason of capacity fading of LiMn2O4 electrodes.

Structure and electrochemical properties of LiMn2O4−xF x

LiMn2O4−xFx prepared by the sol-gel method has a perfect crystal formation. The crystal particle size of the material was medium and distributed uniformly. The substitution of F for O increased the specific capacity of the material at the cost of the cycleability. The explanation of this results is that the F decreases the valence of Mn, that is, more Mn3+ and less Mn4+ exist in the material. The increase of Mn3+ will improve the initial specific capacity and Mn3+ is the original reason for Jahn-Teller effect that caused the poor cycleability of the cathode material by the micro-distortion of the crystal structure. In addition, the expanded measurement of the crystal lattice is also the reason for the poor cycleability. Therefore, the results of F-substitution and cation-substitution are opposite. If the two methods are combined, they can compensate the inability each other and the satisfactory results may be obtained.

Synthesis and electrochemical studies of LiMn1−xCuXO4 cathode material

LiMn1.8Cu0.2O4 was investigated in order to improve the electrochemical properties of LiMn2O4. We report the synthesis and characterization of materials prepared by solid-state reaction. The structural properties evaluated by the X-ray diffraction and vibrational spectroscopy show that a single phase was formed. Conductivity of LiMn1.8Cu0.2O4 cathode is found to be 8×10−6 S/cm at 25 °C. The cyclic voltammetry data shows the reversibility of the electrode material.

Effect of Doping of Magnesium on Electrochemical Property of LiMn2O4.

The effect of partial substitution of magnesium on the electrochemical property of LiMn2O4 has been investigated. As a result of magnesium doping, the specific surface area decreased. In addition the lattice constant decreased along with the polarization at a high discharge rate and an excellent cycle performance was realized in exchange for somewhat of reduction of the capacity. The voltage jump of 4.1V for the discharge curve of LiMn2O4 became indistinct with the magnesium doping. The reaction of LiMn1.8SMg0.2O4 during lithium insertion and desertion was a homogeneous phase reaction. Electrochemical measurements revealed that LiMn1-xMgxO4 is a cathode active material appropriate for use at high rates. The optimum x value in LiMn1-x MgxO4 was found to be in the range of about 0.1 to 0.2.

Effect of Particle Morphology on Electrochemical Property of LiMn2O4.

Two types of LiMn2O4 particles were synthesized from metallic nitrates and acetates by ultrasonic spray pyrolysis. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis revealed that the starting precursor solution influenced the particle morphology, i.e., the nitrate precursor solution led to the formation of porous particles, and the acetate led to the formation of hollow particles. No differences in crystal phase or crystallinity between the two types of LiMn2O4s were detected by X-ray diffraction (XRD) analysis. It was found that the morphology and microstructure of the particles were important factors in determining their electrochemical properties.