Significance of Mg doped LiMn2O4 spinels as attractive 4 V cathode materials for use in lithium batteries

LiMn₂O₄ spinel is one of the most promising cathode materials for lithium-ion batteries because of its cheapness and eco-friendliness. Due to Jahn-Teller distortion, the capacity fades, however, upon repeated cycling. Attempts are being made to improve the cycle life of the spinel by substitution of manganese with other cations. In this paper we report the effect of partial substitution of manganese by Mg²⁺ ions in the LiMn₂O₄ phase. LiMg_yMn_2−yO₄ (y=0 – 0.3) has been synthesized by a thermal method and characterized using XRD, TG/DTA and FTIR. The electrochemical performance is correlated with the dopant concentration.     

A novel method for preparing lithium manganese oxide nanorods from nanorod precursor

Lithium manganese oxide nanorods were prepared from manganese dioxide nanorods precursor. The structure and morphology were confirmed by X-ray diffraction (XRD) and transmission electron microscope (TEM). The data of the Rietveld refinement indicate that the nanorods preferentially grow along the [111] direction. After charge–discharge test at 1.0 mA cm⁻² in 3.0–4.4 V, the nanorods LiMn₂O₄ showed the 134.5 mAh g⁻¹ initial discharge capacity and only lost 1.1% of initial capacity after 30 cycles, which is better than that of bulk particles LiMn₂O₄ prepared by traditional solid-state reaction method. This effective and simple route to synthesis nanorods LiMn₂O₄ from one-dimensional (1D) precursor could also be extended to prepare 1D other nanomaterials with special electrochemical properties.     

Preparation, characterization and electrochemical performance of γ-MnO2 and LiMn2O4 as cathodes for lithium batteries

The spinel LiMn₂O₄ is a very promising cathode material with economical and environmental advantages. LiMn₂O₄ materials have been synthesized by solid state method using γ-MnO₂ as manganese source, and Li₂CO₃ or LiNO₃ as Li sources. γ-MnO₂ is a commercial battery grade electrolytic manganese dioxide (TOSOH-Hellas GH-S) and LiMn₂O₄ samples were synthesized at a calcinations temperature up to 800 °C. γ-MnO₂ and LiMn₂O₄ samples were characterized by X-ray diffraction, thermal and electrochemical measurements. X-ray powder diffraction of as prepared LiMn₂O₄ showed a well-defined highly pure spinel single phase. The electrochemical performance of LiMn₂O₄ and its starting material γ-MnO₂ was evaluated through cyclic voltammetry, galvanostatic (constant current charge-discharge cycling) The electrochemical properties in terms of cycle performance were also discussed. γ-MnO₂ showed fairly high initial capacity of about 200 mAhg⁻¹ but poor cycle performance. LiMn₂O₄ samples showed fairly low initial capacity but good cycle performance.     

Enhanced cyclability of triple-metal-doped LiMn2O4 spinel as the cathode material for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn₂O₄ spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.     

Malonic acid assisted sol-gel synthesis and characterization of chromium doped LiMn2O4 spinel

Pristine LiMn₂O₄ and LiCr_xMn_2-xO₄ (x=0.01−0.20) have been synthesized by sol-gel method using malonic acid as chelating agent. This technique involves less impurities, shorter heat treatment time, sub-micron sized particles, good surface morphology, better homogeneity, good agglomeration and better crystallinity. The synthesized spinel materials have been characterized by XRD, SEM, TEM, EDAX and electrochemical studies like charge-discharge studies, cyclic voltammogram, cycleability studies have also been carried out. All the results exhibit that chromium substitution improves the structural stability of LiMn₂O₄ spinel upon repeated cycling.     

Improvement of cycling stability of LiMn2O4 cathode by Fe2O3 surface modification for Li-ion battery

The surface of spinel LiMn₂O₄ was modified with Fe₂O₃ (1.0, 2.0, 3.0, 4.0, and 5.0 wt%) by a simple sol-gel method to improve its electrochemical performance at room temperature. Compared with bare LiMn₂O₄, surface modification improved cycling stability of the material. Among the surface-modified cathode materials, the 3.0- and 4.0-wt% surface-modified cathodes have lesser capacity loss than the others. While the bare LiMn₂O₄ showed 25.4 % capacity loss in 70 cycles at room temperature, 3.0 and 4.0 wt% of Fe₂O₃-modified LiMn₂O₄ only exhibited the capacity loss of 2.6 and 2.3 % in 70 cycles at room temperature, respectively. The structure and phase were identified with X-ray diffractometer along with the lattice constant calculated by a Win-Metric program.     

Solution synthesis of boron substituted LiMn2O4 spinel oxide for use in lithium rechargeable battery

An attempt has been made to synthesize LiMn₂O₄ spinel and boron substituted LiMn₂O₄ with atomic concentration of boron ranging from 0.01–0.20 and using glutaric acid as a chelating agent. The spinels have been characterized using PXRD, CV and galvanostatic charge-discharge studies. The precursor obtained from the glutaric acid assisted gel was calcined initially at 300 °C for 4 h to obtain the compound and finally at 800 °C for 4 h so as to obtain homogeneity, high degree of purity and crystallinity for better electrochemical performance. This paper suggests that glutaric acid assisted B³⁺ doped (LiB_xMn_2−xO₄) spinel was found to be as an apt candidate with good electrochemical performance for use in lithium battery.     

Three-dimensionally ordered composite electrode between LiMn2O4 and Li1.5Al0.5Ti1.5(PO4)3

A novel electrode system composed of three-dimensionally ordered macroporous (3DOM) Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) and LiMn₂O₄ was fabricated by the colloidal crystal templating method and sol–gel process. A LATP nanoparticle for the fabrication of 3DOM-LATP was prepared by a sol–gel process. A suspension containing polystyrene (PS) beads and the LATP nanoparticles was filtrated by using a polycarbonate filter to accumulate PS beads and LATP. The accumulated PS beads had a close-packing structure, and the void between PS beads was filled with LATP nanoparticles. 3DOM-LATP was obtained by heat treatment of the accumulated composite. Li–Mn–O sol was injected by a vacuum impregnation process into the macropores of 3DOM-LATP and then was heated to form three-dimensionally ordered composite materials consisting of LiMn₂O₄ and LATP. The formation of the composite between 3DOM-LATP and LiMn₂O₄ were confirmed with scanning electron microscopy and X-ray diffraction method. The prepared composite electrode system exhibited a good electrochemical performance. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Synthesis,structure, and electrochemistry of Ag-modified LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode materials for lithium-ion batteries

The composite of silver-modified lithium manganese oxide were prepared using thermal decomposition method of different mole ratio. Structural characterization was carried out by X-ray diffraction (XRD). XRD analysis revealed different patterns as the content of the dopant in the spinel increases. Phase analysis shows that Ag particles were dispersed on the LiMn₂O₄ surface instead of entering the spinel structure. On the other hand, the electrochemical behavior of cathode powder was examined by using two-electrode test cells consisting of a cathode, metallic lithium as anode, and a solid polymer electrolyte of 0.87PEO-0.13LiCF₃SO₃-0.10DBP. According to the electrochemical tests results, the influence of the Ag additive content on the electrochemical properties of Ag/LiMn₂O₄ composites is clearly shown.     

Synthesis of Co-coated lithium manganese oxide and its characterization as cathode for lithium ion battery

Co-coated LiMn₂O₄ was synthesized by electroless plating. The phase identification, surface morphology, and electrochemical properties of the synthesized powders were studied by X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic charge–discharge experiments, respectively. The result shows that Co-coated LiMn₂O₄ particle has a coarse surface with a lot of holes. The specific capacity of Co-coated LiMn₂O₄ is 118 mAh g⁻¹, which is a bit less than 123 mAh g⁻¹ for the uncoated LiMn₂O₄. The capacity retention of Co-coated LiMn₂O₄ is 11% higher than the uncoated LiMn₂O₄ when the electrode is cycled at room temperature for 20 times. When cycled at the temperature of 55 °C, the capacity retention of Co-coated LiMn₂O₄ becomes 15% higher than the uncoated one.     

Effect of ultrasonic irradiation on structure and electrochemical properties of LiMn2O4 thin films cathode material for Li-ion micro-batteries

Two kinds of spinel LiMn₂O₄ thin film for lithium ion micro-batteries were successfully prepared on polycrystal Pt substrates by spin coating methods, which were carried out under ultrasonic irradiation (USG) and magnetic stirring (MSG), respectively. The microstructures and electrochemical performance of LiMn₂O₄ thin films were characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge-discharge measurements. It was found that the crystalline structure of USG samples grew better than that of the MSG samples. At the same time, higher discharge capacity and better cycle stability were obtained for the LiMn₂O₄ thin films of USG at the current density of 50 μAh/cm² between 3.0 and 4.3 V. The 1st discharge capacity was 57.8 μAh/cm²-μm for USG thin films and 51.7 μAh/cm²-μm for MSG thin films. After 50 cycles, 91.4% and 69% of discharge capacity could be retained respectively, indicating that ultrasonic irradiation condition during spin coating was more suitable for preparing spinel LiMn₂O₄ thin films with better electrode performance for lithium ion micro-batteries.     

Feasibility studies on newly identified LiCrP2O7 compound for?lithium insertion behavior

A new category of lithium intercalating cathode candidates, namely LiCrP₂O₇, was synthesized at 800°C using a citric acid assisted modified (CAM) sol–gel method and examined for possible lithium insertion behavior. The formation of a phase pure and monoclinic LiCrP₂O₇ compound with finer crystallite size was confirmed from the X-ray diffraction patterns. The presence of nano-sized particles as observed from a transmittance electron microscope image of LiCrP₂O₇ and the presence of a preferred local cation environment, evidenced from Fourier transform infra-red and ⁷Li nuclear magnetic resonance studies, are the added advantages of the present study. Further, cyclic voltametry study performed on 2016 coin cells consisting of the synthesized LiCrP₂O₇ cathode revealed an excellent cycling reversibility and structural stability. Hence, CAM sol–gel synthesized LiCrP₂O₇ is found to possess desirable physical as well as electrochemical properties, leading one to consider the same as a possible lithium intercalating cathode material.     

LiPF6-EC-MPC electrolyte for LiMn2O4 cathode in lithium-ion battery

Methyl propyl carbonate (MPC) is a promising single solvent for lithium-ion battery without addition of ethylene carbonate (EC), but it is unstable upon cycling because of exposure to the spinel LiMn₂O₄ cathode. Thus, we attempted to add EC to MPC in order to form LiPF₆-EC-MPC electrolyte; the effects of solvent ratio and salt concentration on the cycling performance of LiMn₂O₄ cathode were also investigated. The experiments were characterized by conductivity measurements, charge-discharge at a constant current density and voltage–capacity curves at low temperature. To further enhance our understanding of the performance improvement of LiMn₂O₄/Li cells, the electrochemical characterization techniques (such as, LSV, EIS) were performed on these cells. The results show that the ionic conductivity of the electrolyte and the cycling performance of the spinel LiMn₂O₄ cathode have been dramatically enhanced. From the point of view of operation at low temperature (− 20 °C), 1 M LiPF₆ EC/MPC (1/3) electrolyte is highly recommended for spinel LiMn₂O₄ cathode in lithium-ion battery.     

Synthesis of sea urchin-like LiMn2O4 hollow macrospheres via in situ conversion for rechargeable lithium-ion batteries

Among several materials (transition metal oxide) under development for use as a cathode in lithium-ion batteries, cubic spinel LiMn₂O₄ is one of the most promising cathode materials. In this study, the sea urchin-like LiMn₂O₄ hollow macrospheres were synthesized by using sea urchin-like α-MnO₂ precursors through solid-state in situ self-sacrificing conversion route. The as-prepared LiMn₂O₄ was assembled by many single-crystalline “thorns” of ca.10–20 nm in diameter and ca. 400–500 nm in length. Galvanostatic battery testing showed that sea urchin-like LiMn₂O₄ had an initial discharge capacity of 126.8 mAh/g at the rate of 0.2 C in the potential range between 3.0 and 4.5 V. More than 96.67 % of the initial discharge capacity was maintained for over 50 cycles. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by the materials. This particular sea urchin-like structured composite conceptually provides a new strategy for designing electrodes in energy storage applications.     

Effect of fluorine in Li1.27Cr0.2Mn0.53O2 cathode for secondary lithium batteries

Fluorine substituted Li_1.27Cr_0.2Mn_0.53O₂ electrode, prepared by sol–gel method, was investigated in the present work. Thermal analysis was done on this cathode material and found to be thermally stable with a loss of weight near 300 °C. Influence of fluorine substitution on the structural and electrochemical properties of the Li_1.27Cr_0.2Mn_0.53O₂ electrode was studied by X-ray diffraction (XRD) and field emission scanning electron microscope. XRD pattern of the fluorine-doped Li_1.27Cr_0.2Mn_0.53O₂ cathode material quenched at 900 °C indicates a phase pure material. The charge–discharge profile of the prepared cathode material showed that the fluorine substitution for oxygen in the cathode material resulted in improved capacity retention. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006.     

Structural stability in partially substituted lithium manganese spinel oxide cathode

LiMn₂O₄ is one of the most promising cathode materials for lithium secondary battery because of natural abundance of manganese in the crust and its low toxicity to environment. Lithium ion can almost reversibly intercalate into or deintercalate from lithium manganese spinel oxide LiMn₂O₄. A part of substitution of manganese with other transition metals brings the improvement of cycle life. We focused on the local structure of the spinels and considered the effect of the local distortion on the cycle life of the spinel cathodes. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Finite size effects on the structural and magnetic properties of sol–gel synthesized NiFe2O4 powders

Nanoparticles of nickel ferrite have been synthesized by the sol–gel method and the effect of grain size on its structural and magnetic properties have been studied in detail. X-ray diffraction (XRD) studies revealed that all the samples are single phasic possessing the inverse spinel structure. Grain size of the sol–gel synthesized powders has been determined from the XRD data and the strain graph. A grain size of 9 nm was observed for the as prepared powders of NiFe₂O₄ obtained through the sol–gel method. It was also observed that strain was induced during the firing process. Magnetization measurements have been carried out on all the samples prepared in the present series. It was found that the specific magnetization of the nanosized NiFe₂O₄ powders was lower than that of the corresponding coarse-grained counterparts and decreased with a decrease in grain size. The coercivity of the sol–gel synthesized NiFe₂O₄ nanoparticles attained a maximum value when the grain size was 15 nm and then decreased as the grain size was increased further.     

Novel approach to preparation of LiMn2O4 core/LiNixMn2−xO4 shell composite

Combining two methods, coating and doping, to modify spinel LiMn₂O₄, is a novel approach we used to synthesize active material. First we coated the LiMn₂O₄ particles with the nickel oxide particles by means of homogenous precipitation, and then the nickel oxide-coated LiMn₂O₄ was calcined at 750 °C to form a LiNi_xMn_2−xO₄ shell on the surface of spinel LiMn₂O₄ particles. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cyclic voltammetry (CV) and charge-discharge test were performed to characterize the spinel LiMn₂O₄ before and after modification. The experimental results indicated that a spinel LiMn₂O₄ core is surrounded by a LiNi_xMn_2−xO₄ shell. The resulting composite showed excellent electrochemical cycling performance with an average fading rate of 0.014% per cycle. This improved cycle stability is greatly attributed to the suppression of Jahn-Teller distortion on the surface of spinel LiMn₂O₄ particles during cycling.     

Synthesis and characterization of pristine Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript> and Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript>/C cathode materials for lithium ion batteries

The cathode materials, pristine Li₂MnSiO₄ and carbon-coated Li₂MnSiO₄ (Li₂MnSiO₄/C), were synthesized by the sol–gel method. Power X-ray diffraction and scanning electron microscopy analyses show that the presence of carbon during synthesis can weaken the formation of impurities in the final product and decrease the particle size of the final product. The effects of carbon coating on electrochemical characteristics were investigated by galvanostatic cycling test and electrochemical impedance spectroscopy. The galvanostatic cycling test results indicate that Li₂MnSiO₄/C cathode exhibits better electrochemical performance with an initial discharge capacity of 134.4 mAh g⁻¹ and a capacity retention of 63.9 mAh g⁻¹ after 20 cycles. Electrochemical impedance analyses confirm that carbon coating can increase electronic conductivity, which results in good electrochemical performance of Li₂MnSiO₄/C cathode. The two semicircles and the large arc obtained in this study can be attributed to the migration of lithium ions through the solid electrolyte interphase films, the electronic properties of the material, and the charge transfer step, respectively.     

Synthesis and characterization of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles prepared by high-energy milling and hydrothermal method

Spinel LiMn₂O₄ has been known to be a technologically important, environmental-friendly, and low-cost cathode material used in Li-based rechargeable batteries, and it is also widely available. Nanoparticle spinel LiMn₂O₄ has been synthesized by the top-down, high-energy milling, and hydrothermal methods. SEM images, X-ray diffraction patterns, and neutron high-resolution powder diffraction patterns have confirmed the nanocrystalline nature of the spinel LiMn₂O₄ samples. Raman and Fourier transform infrared (FTIR) measurements show typical absorption and vibration spectra typical for the spinel LiMn₂O₄ showing the formation of various metallic bonds in the sample. The strongest Raman and FTIR signals come from the higher frequency region, with weaker signals appearing in the lower frequency range.