Spinel LiMn Research Articles

Spinel LiMn 2O 4 active material with high capacity retention

Heating the mixture of LiMn 2O 4 and NiO at 650 °C was employed to enhance the cyclability of spinel LiMn 2O 4. The results of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy analyses implied that a LiNi x Mn 2− x O 4 solid solution was formed on the surface of LiMn 2O 4 particles. And charge–discharge tests showed that the enhancement of the capacity retention of modified LiMn 2O 4 is significant, maintained 97.2% of the maximum capacity after 100 cycles at charge and discharge rate of C/2, while the pure one only 75.2%. The modified LiMn 2O 4 also results in a distinct improvement in rate capability, even at the rate of 12 C. The improvement of electrochemical cycling stability is greatly attributed to the suppression of Jahn–Teller distortion at the surface of spinel LiMn 2O 4 particles.

Atomic force microscopy study of surface morphology change in spinel LiMn 2O 4: Possibility of direct observation of Jahn–Teller instability

Surface morphology in 3.5 × 3.5 μm 2 area of spinel LiMn 2O 4, which is a typical cathode material for Li ion secondary batteries, is studied using an atomic force microscopy (AFM) with a conductive probe. Negative bias voltage is applied to the probe to attract Li + ions toward LiMn 2O 4 surface during the AFM observation. Before applying the voltage (0 V), the whole LiMn 2O 4 surface is covered with scale-shaped grains. Under the negative voltage of 5.5 V, electric current abruptly increases, indicating Li + ionic conduction. Simultaneously, part of the scale-shaped grains expand and flatten. Jahn–Teller phase transition, which is induced by the repulsive interaction between the Mn-e g and O-2p electrons in Li accumulated layer, is proposed as a possible origin of these results.

Synthesis of highly crystalline spinel LiMn 2O 4 by a soft chemical route and its electrochemical performance

Highly crystalline spinel LiMn 2O 4 was successfully synthesized by annealing lithiated MnO 2 at a relative low temperature of 600 °C, in which the lithiated MnO 2 was prepared by chemical lithiation of the electrolytic manganese dioxide (EMD) and LiI. The LiI/MnO 2 ratio and the annealing temperature were optimized to obtain the pure phase LiMn 2O 4. With the LiI/MnO 2 molar ratio of 0.75, and annealing temperature of 600 °C, the resulting compounds showed a high initial discharge capacity of 127 mAh g −1 at a current rate of 40 mAh g −1. Moreover, it exhibited excellent cycling and high rate capability, maintaining 90% of its initial capacity after 100 charge–discharge cycles, at a discharge rate of 5 C, it kept more than 85% of the reversible capacity compared with that of 0.1 C.

Synthesis and electrochemical properties of nanostructured LiMn 2O 4 for lithium-ion batteries

Spinel LiMn 2O 4 crystal with the grain sizes of about 15 nm is firstly synthesized by hydrothermal route at 180 °C using MnO 2 as a precursor. The LiMn 2O 4 powders synthesized by hydrothermal technique and sol–gel reaction were investigated by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The LiMn 2O 4 samples were used as cathode materials for lithium-ion battery, whose electrochemical properties were investigated. The results show that the sample obtained by hydrothermal route has higher capacity than that prepared by sol–gel method.

An Overview of Chemically/Surface Modified Cubic Spinel LiMn2O4Electrode for Rechargeable Lithium Batteries

The present article is concerned with the overview of the chemically/surface modified cubic spinel <TEX>$LiMn_2O_4$</TEX> as a cathode electrode far lithium ion secondary batteries. Firstly, this article presented a comprehensive survey of the cubic spinel structure and its correlated electrochemical behaviour of <TEX>$LiMn_2O_4$</TEX>. Subsequently, the various kinds of the chemically/surface modified <TEX>$LiMn_2O_4$</TEX> and their electrochemical characteristics were discussed in detail. Finally, this article reviewed our recent research works published on the mechanism of lithium transport through the chemically/surface modified <TEX>$Li_{1-\delta}Mn_2O_4$</TEX> electrode from the kinetic view point by the analyses of the experimental potentiostatic current transients and ac-impedance spectra.

Magnetic properties of the calcium ferrite-type [formula omitted

Magnetic properties of the calcium ferrite-type Li 0.92 Mn 2 O 4 are reported. The static susceptibility data reveal a cusp at ∼ 10 K , suggesting a magnetic glassy transition. Although the crystal structure is essentially different from that of the spinel LiMn 2 O 4 , the compound shows a similarity of the frustrated magnetism of the spinel. The probable magnetic frustration of the calcium ferrite-type compound might be due to a freezing of geometrically frustrated Mn magnetic moments in a triangular-like alignment.

Improvement of electrochemical stability of LiMn 2O 4 by CeO 2 coating for lithium-ion batteries

CeO 2-coated LiMn 2O 4 spinel cathode was synthesized using two-step synthesis method. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The results of the electrochemical performances on CeO 2-coated electrode are compared to those of electrodes based on LiMn 2O 4 spinel without CeO 2 coating. CeO 2-coated LiMn 2O 4 cathode improved the cycling stability of the electrode. The capacity retention of 2 wt% CeO 2-coated LiMn 2O 4 was more than 82% after 150 cycles between 3.0 and 4.4 V at room temperature and 82% after 40 cycles at elevated temperature of 60 °C. The amounts of dissolved manganese-ions in CeO 2-coated LiMn 2O 4 significantly are smaller than pristine LiMn 2O 4 systems especially at elevated temperatures. Surface-modified LiMn 2O 4 can suppress the dissolution reaction of manganese-ions at elevated temperature and clearly improve the cyclability of the spinel LiMn 2O 4 cathode materials.

Preparation and electrochemical properties of LiMn 2O 4 by the microwave-assisted rheological phase method

Pure-phase and well-crystallized spinel LiMn 2O 4 powders as cathode materials for lithium-ion batteries were successfully synthesized by a new simple microwave-assisted rheological phase method, which was a timesaving and efficient method. The physical properties of the as-synthesized samples compared with the pristine LiMn 2O 4 obtained from the rheological phase method were investigated by thermogravimetry analysis (TGA), X-ray diffraction (XRD) and scanning electronic microscope (SEM). The as-prepared powders were used as positive materials for lithium-ion battery, whose charge/discharge properties and cycle performance were examined in detail. The powders resulting from the microwave-assisted rheological phase method were pure, spinel structure LiMn 2O 4 particles of regular shapes with distribution uniformly, and exhibited promising electrochemical properties for battery. Furthermore, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the reactions of Li-ion insertion into and extraction from LiMn 2O 4 electrode.

Novel urea assisted polymeric citrate route for the synthesis of nanocrystalline spinel LiMn 2O 4 powders

Urea assisted polymeric citrate route was investigated for the synthesis of nanocrystalline spinel LiMn 2O 4 powders using metal nitrates/acetates, citric acid and urea under acidic condition at 300 °C. Optimum total metal ions to urea ratio was identified for the synthesis of organic free, phase pure nanocrystalline LiMn 2O 4 powders. Addition of urea changes the microstructure and combustion mechanism of polymeric intermediates as well as the structural coordination and phase formation of the LiMn 2O 4 powders, which are, respectively, confirmed through SEM, TG/DTA, FTIR and XRD analysis. Organic free phase pure nanocrystalline LiMn 2O 4 powder was synthesized by urea assisted polymeric citrate route with the total metal ions to urea ratio of 1:2 at 300 °C and the average crystallite size was found to be 19 nm.

Surface modification and characterization of F-Co doped spinel LiMn 2O 4

Spinel LiCo 0.09Mn 1.91O 3.92F 0.08 as cathode material was modified with LiCoO 2 by the sol-gel method, and the crystal structure, morphology and electrochemical performance were characterized with XRD, SEM, EDS, AAS and charge-discharge test in this paper. The results show that a good clad coated on parent material can be synthesized by the sol-gel method, and the materials with modification have perfect spinel structure. LiCo 0.09Min 0.09O 3.92F 0.08 materials coated by LiCoO 2 improve the stability of crystal structure and decrease the dissolution of Mn into electrolyte. With the LiCoO 2 content increasing, the specific capacity and cycle performance of samples are improved. The capacity loss is also suppressed distinctly even at 55 °C.

Synthesis and electrochemical properties of sol-gel derived LiMn 2O 4 cathode for lithium-ion batteries

Spinel LiMn 2O 4 has been considered to be the most promising alternative cathode material for the new generation of lithium-ion batteries in terms of its low cost, non-toxicity and easy manufacture. The spinel lithium manganese mixed oxides were prepared from lithium nitrate, manganese nitrate and citric acid by a sol-gel method and were characterized by thermogravimetric analysis, X-ray diffraction, cyclic voltam-metry and constant current charging-discharging technique. The different sintering temperatures for different time have strong influence on the structure, initial discharge capacity and cycling performance of the lithium manganese oxide. It shows that the lithium manganese oxides sintered at 700 °C for 10 h have a single spinel structure and better electrochemical properties. The initial discharging capacity can be up to 125.9 mAh·g −1, even after six cycles, it still retains 109.1 mAh·g −1.

Synthesis and electrochemical properties of Th-doped LiMn 2O 4 powders for lithium-ion batteries

To improve the cycle performance of eco-friendly and cost-effective spinel LiMn 2O 4 as the La secondary batteries, the Th-doped LiTh x Mn 1 − x O 4 spinel powers were synthesized by solid-state method. The starting materials, Li 2CO 3, MnO 2 and Th(NO 3) 4·4H 2O, were mixed uniformly using a traditional ball milling, which resulted in a uniform particle size distribution in the mixed powers. Tests of X-ray diffraction, SEM, impedance spectra and charge-discharge were carried out for LiTh x Mn 1− x O 4 cathode materials. Results show that the synthesized LiTh 0.01Mn 1.99O 4 material exhibits standard spinel structure, regular particle morphology and excellent property of charge-discharge for big current. The capacity retention of the material modified by doping Th is more than 85.1 % of the first discharge specific capacity of 111.5 mAh·g −1 after 20 cycles at the current rate 1C, while the pristine LiMn 2O 4 is only 57% of the first discharge specific capacity of 110.2 mAh·g −1 after the same cycles at the same current rate.

Influence of Crystallinity on the Kinetics of Li Ion Insertation and Deinsertation in Spinel LiMn_(2)O_(4)

Influence of Crystallinity on the Kinetics of Li Ion Insertation and Deinsertation in Spinel LiMn_(2)O_(4)

Preparation of LiMn 2O 4 at the low temperature of 250 °C using eutectic self-mixing method

Spinel LiMn 2O 4 as a cathode material for lithium rechargeable batteries is prepared at the low temperature of 250 °C without any artificial mixing procedures of reactants. The phase transitions of lithium manganese oxide are found three times on heating at 250 °C. The prepared material exhibits the initial discharge capacity of 85.5 mAh g −1 and the discharge capacity retention of 91.5% after 50 cycles.

Eutectic self-mixing method for the preparation of LiMn 2O 4 without any artificial mixing procedures

Spinel LiMn 2O 4 as a cathode material for lithium rechargeable batteries is economically prepared by a novel eutectic self-mixing method without any artificial mixing procedures of reactants. The phase transitions of lithium manganese oxide are found three times on the preparation. Thus, those process controls are discussed and emphasized. The prepared LiMn 2O 4 exhibits the initial discharge capacity of 124.8 mAh g −1 and the discharge capacity retention of 98.2% after 20 cycles.

One-step synthesis LiMn 2O 4 cathode by a hydrothermal method

Spinel LiMn 2O 4 powders have been successfully synthesized by a hydrothermal method directly, which is no any pretreatment and following treatment in the process. The structure and morphology of the powders were studied in detail by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA). The data reveal that the products have well-defined stable spinel structure, and the particles show distinctive crystal faces with 50–300 nm in particle sizes. The electrochemical characteristics of the spinel materials are measured in the coin-type cells in a potential range of 3.2–4.35 V versus Li/Li +. The as-synthesized LiMn 2O 4 delivers reversible capacity of about 121 mAh g −1 at a current density of 1/10 C. Cycled the cell to 40 cycles, the capacity remains at about 111 mAh g −1 at 1/2 C.

LiPF 6-EC-MPC electrolyte for LiMn 2O 4 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 LiMn 2O 4 cathode. Thus, we attempted to add EC to MPC in order to form LiPF 6-EC-MPC electrolyte; the effects of solvent ratio and salt concentration on the cycling performance of LiMn 2O 4 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 LiMn 2O 4/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 LiMn 2O 4 cathode have been dramatically enhanced. From the point of view of operation at low temperature (− 20 °C), 1 M LiPF 6 EC/MPC (1/3) electrolyte is highly recommended for spinel LiMn 2O 4 cathode in lithium-ion battery.

Spray-drying technology for the synthesis of nanosized LiMn 2O 4 cathode material

Spinel LiMn 2O 4 cathode material has been synthesized by a spray-drying method for lithium ion batteries. During the entire process, the as-prepared powders were characterized using TGA/DTA, XRD, FTIR, SEM and TEM. The results showed that this method not only reduces the sintering time to 5 h at 750 °C, but also decreases the average particle size of LiMn 2O 4 powders to the order of nanometers. The electrochemical performance of nanosized LiMn 2O 4 was investigated by the galvanostatic charge–discharge tests. The data indicate that the nanosized LiMn 2O 4 has a specific capacity of about 130 mA h g − 1 (1/5 C), and at higher rate (1 C), still has good cycling stability.

The effect of ZnO coating on LiMn 2O 4 cycle life in high temperature for lithium secondary batteries

The surface of the spinel LiMn 2O 4 was modified with zinc oxide by a chemical process to improve its electrochemical performance at high temperatures. The physical properties of the prepared products have been investigated by thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-rays analysis (EDAX). The charge/discharge of the materials was carried at 1 mA/cm 2 in the range of 3.0 and 4.4 V at 55 °C. The discharge capacity of ZnO-coated LiMn 2O 4 (117 mAh/g) showed only 3% loss of the initial capacity (121 mAh/g) over 60 cycles. The cycle ability improvement of the spinel LiMn 2O 4 coated with ZnO is demonstrated at high temperatures. From the analysis of electrochemical impedance spectroscopy (EIS), the improvement of cycle ability may be attributed to the suppression on the formation of the passivation film and the reduction of Mn dissolution, which result from the modifying the surface of the spinel LiMn 2O 4 with zinc oxide.

Effect of chitosan addition on the electrochemical behavior and crystallization of LiMn 2O 4 film derived from acetates-containing solution

Spinel LiMn 2O 4 films were obtained by spin-coating the lithium/manganese acetates-containing precursor solution on a Pt-coated silicon substrate. The effect of chitosan addition in the acetates-containing precursor solution on the formation of the LiMn 2O 4 films was investigated by TG/DTA, FT-IR spectroscopy, glancing-angle XRD and cyclic voltammetry. It was demonstrated that the addition of chitosan is very beneficial to the deposition of a single-phase LiMn 2O 4 film due to the fact that chitosan is able to chelate with lithium/manganese ions and form a stable complex compound. Moreover, the electrochemical measurements also showed that the deposited LiMn 2O 4 film from the chitosan-added precursor solution exhibits a higher discharge capacity of 134 mAh/g at 1 C and a better rate performance (86.4% of the discharge capacity at 1 C can be maintained when the discharge rate increases from 1 up to 8 C) in comparison with one from the chitosan-free solution.