Novel method to enhance the cycling performance of spinel LiMn2O4

In this study, a novel method was presented to improve the cycle performance of the spinel LiMn₂O₄ This method is quite different from the traditional way of coating LiMn₂O₄ particle itself with inorganic and organic compounds. First we covered the current collector with the mixture of LiMn₂O₄ particle, conductive agents and binders, and then deposited an aluminum film onto it by means of vacuum evaporation. The pure electrode and the modified electrode were investigated using a combination of scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and charge–discharge tests. The enhancement of the capacity retention of modified electrode is significant, maintaining 93.5% of the maximum capacity after 200 cycles at charge–discharge rate of C/2, while pure electrode only 63.7%. It was found that the improvement of cycling performance is greatly ascribed to the good electrical conductivity of aluminum film deposited on the surface of spinel LiMn₂O₄.     

Excellent cycling stability of spherical spinel LiMn2O4 by Y2O3 coating for lithium-ion batteries

The Y₂O₃ nano-film is coated on the surface of the spherical spinel LiMn₂O₄ by precipitation method and subsequent heat treatment at 550 °C for 5 h in air. The structure and performance of the bare LiMn₂O₄ and Y₂O₃-coated LiMn₂O₄ are characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis X-ray spectroscopy, galvanostatic charge–discharge, cyclic voltammetry, and impedance spectroscopy. It has been found that the addition of Y₂O₃ does not change the bulk structure of LiMn₂O₄, and the thickness of the Y₂O₃ coating layer is approximate to 3.0 nm. The 1 wt% Y₂O₃-coated LiMn₂O₄ electrode reveals excellent cycling performance with 80.3 % capacity retention after 500 cycles at 1 C at 25 °C. When cycling at elevated temperature 55 °C, the as-prepared sample still shows 76.7 % capacity retention after 500 cycles. These remarkable improvements indicate that thin Y₂O₃ coating on the surface of LiMn₂O₄ is an effective way to improve the electrochemistry performance. Besides, the suppression of Mn dissolution into the electrolyte via the Y₂O₃ coating layer can be accounted for the improved performances.     

PVP-Assisted ZrO2 coating on LiMn2O4 spinel cathode nanoparticles prepared by MnO2 nanowire templates

LiMn₂O₄ spinel nanorods prepared from nanowire MnO₂ templates were capped with polyvinyl pyrrolidone (PVP) and coated with ZrC₂O₄ precursors in aqueous solution. Upon annealing at 600 °C in air, an amorphous ZrO₂ nanoscale coating layer was obtained on the spinel nanoparticles with a particle size of <100 nm that formed from the splitting of the original spinel nanorods. The electrochemical cycling results clearly showed that nanoscale ZrO₂ coating significantly improved the rate capability and cycle life at 65 °C in spite of very high surface area of the spinel nanoparticles.     

Enhanced high power and long life performance of spinel LiMn2O4 with Li2MnO3 coating for lithium-ion batteries

Journal of Solid State Electrochemistry - Li2MnO3 coated spinel lithium manganese oxide (LiMn2O4) materials have been successfully synthesized by a sol-gel method. Scanning electron microscopy...     

尖晶石LiMn_2O_4的表面改性研究

采用溶胶_凝胶法合成尖晶石LiMn2 O4 ,并以LiCoO2 对其进行包覆 ,用XRD、SEM、EPMA等方法对修饰的尖晶石结构和性能进行研究 .结果表明 ,经包覆的LiMn2 O4 在 70 0℃焙烧 10h所得的晶粒是表层富含Co的立方尖晶石 ,而且晶粒中Co3+的含量呈现出从表到里递减的梯度分布 .以该材料作锂离子电池正极 ,虽初始容量稍有降低 ,但能有效地降低Mn2 +在电解质中的溶解 ,而且对Jahn_Teller效应有一定的抑制作用 ,包覆的LiMn2 O4 尖晶石正极材料比未包覆的有更好的循环性能     

Synthesis and electrochemical properties of spinel LiMn2O4 prepared by the rheological phase method

Pure-phase and well-crystallized spinel LiMn₂O₄ powders were successfully synthesized by a simple rheological phase method. The thermal behavior and structure properties of the powders prepared by the rheological phase method compared with the solid-state reaction were investigated by thermogravimetry, powder X-ray diffraction , scanning electron microscopy and transmission electron microscopy. According to the results of the electrochemical tests, it is obvious that the sample resulting from the rheological phase method shows higher discharge capacity and better cycling stability than one formed in the solid-state reaction. The cyclic voltammogram and columbic efficiency curves also confirm that the product by the rheological phase method has a good cycling performance due to its fine cubic spinel structure and morphology.     

The electrochemical performance of sodium-ion-modified spinel LiMn2O4 used for lithium-ion batteries

The spinel LiMn₂O₄ cathode material has been considered as one of the most potential cathode active materials for rechargeable lithium ion batteries. The sodium-doped LiMn₂O₄ is synthesized by solid-state reaction. The X-ray diffraction analysis reveals that the Li_1?x Na _x Mn₂O₄ (0?≤?x?≤?0.01) exhibits a single phase with cubic spinel structure. The particles of the doped samples exhibit better crystallinity and uniform distribution. The diffusion coefficient of the Li_0.99Na_0.01Mn₂O₄ sample is 2.45?×?10^?10 cm^?2 s^?1 and 3.74?×?10^?10 cm^?2 s^?1, which is much higher than that of the undoped spinel LiMn₂O₄ sample, indicating the Na⁺-ion doping is favorable to lithium ion migration in the spinel structure. The galvanostatic charge–discharge results show that the Na⁺-ion doping could improve cycling performance and rate capability, which is mainly due to the higher ion diffusion coefficient and more stable spinel structure.     

Electrochemical properties of tetravalent Ti-doped spinel LiMn2O4

Ti-doped spinel LiMn₂O₄ is synthesized by solid-state reaction. The X-ray photoelectron spectroscopy and X-ray diffraction analysis indicate that the structure of the doped sample is Li( Mn^{3 +} Mn_{1 - x} ^{4 +} Ti_x^{4 +} )O₄ {\hbox{Li}}\left( {{\hbox{M}}{{\hbox{n}}^{3 + }}{\hbox{Mn}}_{1 - x\,}^{4 + }{\hbox{Ti}}_x^{4 + }} \right){\hbox{O}}{}_4 . The first principle-based calculation shows that the lattice energy increases as Ti doping content increases, which indicates that Ti doping reinforces the stability of the spinel structure. The galvanostatic charge–discharge results show that the doped sample LiMn_1.97Ti_0.03O₄ exhibits maximum discharge capacity of 135.7 mAh g⁻¹ (C/2 rate). Moreover, after 70 cycles, the capacity retention of LiMn_1.97Ti_0.03O₄ is 95.0% while the undoped sample LiMn₂O₄ shows only 84.6% retention under the same condition. Additionally, as charge–discharge rate increases to 12C, the doped sample delivers the capacity of 107 mAh g⁻¹, which is much higher than that of the undoped sample of only 82 mAh g⁻¹. The significantly enhanced capacity retention and rate capability are attributed to the more stable spinel structure, higher ion diffusion coefficient, and lower charge transfer resistance of the Ti-doped spinel.     

Effect of MgF2 coating on the electrochemical performance of LiMn2O4 cathode materials

Spinel LiMn₂O₄ cathode materials were coated with 1.0, 3.0 and 5.0?wt.% of MgF₂ by precipitation, followed by heat treatment at 400?°C for 5?h in air. The effects of MgF₂ coating on the structural and electrochemical properties of LiMn₂O₄ cathodes were investigated using XRD, SEM, and electrochemical tests. XRD and SEM results show that no significant bulk structural differences are observed between the coated and pristine LiMn₂O₄. The charge–discharge tests show that the discharge capacity of LiMn₂O₄ decreases slightly, but the cyclability of LiMn₂O₄ is clearly improved when the amount of the MgF₂ coated was increased to 3.0?wt.%. The 3.0?wt.% MgF₂-coated LiMn₂O₄ exhibits capacity retention of 80.1 and 76.7 % after 100 cycles at room temperature (25?°C) and elevated temperature (55?°C) at a rate of 1?C, respectively, much higher than those of the bare LiMn₂O₄ (70.1 and 61.6 %). The improvement of electrochemical performance is attributed to the suppression of Mn dissolution into the electrolyte via the MgF₂ coating layer.     

Comparative performance of LiMn2O4 spinel compositions with carbon nanotubes and graphite in Li prototype battery

We reported previously the superiority of electrochemical characteristics of the mechanical mixtures of micrometer LiMn₂O₄ spinel with multiwall carbon nanotubes (MCNT) over those of spinel compositions with natural graphite in the prototypes of the Li-ion batteries. In the presented work, we extended the investigation of the kinetic and interfacial characteristics of the spinel in the redox reaction with the Li ion. Slow-rate scan cyclic voltammetry and impedance spectroscopy were used. Carbon electroconductive fillers, their nature, and particle sizes play the key role in the efficiency of the electrochemical transformation of spinel in Li-ion batteries. Electrodes based on the composition of the spinel and MCNT show a good cycling stability and efficiency at the discharge rate of 2C. Chemical diffusion coefficients of Li ion, which were determined in spinel composite with MCNT and graphite near potentials of peak activity in deintercalation/intercalation processes, change within one order of 10^?12 cm² s^?1. The value of this chemical diffusion coefficient for the composition of the spinel with MCNT and with graphite change within one order of 10^?12 cm² s^?1. The data of the impedance spectroscopy shows that the resistance of surface films on the spinel (R _s) is low and does not considerably differ from R _s in composites of the spinel with MCNT and graphite. The investigation shows that the resistance of charge transport (R _ct) through the boundary of surface film/spinel composite is dependent on the conductive filler. Value of R _ct in spinel electrode decreases by the factor of thousand in the presence of carbon filler. Exchange current of spinel electrode increases from the order of 10^?7 to 10^?4 A cm^?2 under the influence of MCNT. At the potentials of maximum activity in deintercalation processes, exchange current of spinel composite electrode with MCNT is 2.2–3.0 times more than one of the composite with graphite. Determining role of the resistance of charge transport in electrode processes of spinel is established. The value of R _ct is dependent on the resistance in contacts between spinel particles and also between particles and current collectors. Contact resistance decreases under the influence of MCNT with more efficiency than under the influence of graphite EUZ-M because of small the size of its particles with high surface area of the MCNT.     

Physical properties and electrochemical performance of LiMn2O4 cathode materials prepared by a precipitation method

LiMn₂O₄ powder for lithium-ion batteries was prepared by a precipitation method, and the effects of calcination temperature on the physical properties and electrochemical performance of the samples were investigated by various methods. The results of X-ray diffraction (XRD) showed that the lattice parameter (a) and the unit cell volume (v) decrease with the increasing calcination temperature, and the LiMn₂O₄ sample calcined at 750°C has smaller particle size and higher crystallinity than other samples. The results of the electrochemical experiments showed that the sample calcined at 750°C has larger peak currents, higher initial capacity, and better cycling capability, because of its lower charge-transfer resistance and larger diffusion coefficient of Li⁺ ions than those of other samples.     

Electrochemical performance of LiMn2O4 microcubes prepared by a self-templating route

LiMn₂O₄ microcubes with a size of 10–15 μm have been synthesized by a facile self-templating route starting from cubic MnCO₃. The LiMn₂O₄ microcubes exhibit a hierarchical structure, where the cubes are stacked from parallel plates with a thickness of 200 nm, where each plate is composed of interconnected nanoparticles with a size of around 200 nm. The cubic LiMn₂O₄ shows excellent rate capability and high-rate cycling stability. At 10 C, it can yield a discharge capacity of 108 mAh g^?1. A discharge capacity of 88 mAh g^?1 can be retained after 100 cycles at 10 C. The excellent electrochemical performance makes it a promising cathode for high-power Li-ion batteries.     

合成条件对尖晶石LiMn_2O_4的电化学性能的影响

以Li2 CO3、LiOH、LiNO3以及电解MnO2 (EMD)作原料 ,用固相反应法合成了尖晶石LiMn2 O4 .结果表明 ,反应物种类及合成条件对LiMn2 O4 的电化学性质有很大的影响 .其中以LiNO3和EMD为合成原料制得的LiMn2 O4 性能最佳 .其制备条件分两步 :先在 2 80℃加热 6h ,使熔融的LiNO3渗入EMD微孔 ,然后在 75 0℃下焙烧合成     

Preparation of spherical spinel LiMn2O4 cathode material for lithium ion batteries

A novel process is proposed for synthesis of spinel LiMn₂O₄ with spherical particles from the inexpensive materials MnSO₄, NH₄HCO₃, and NH₃H₂O. The successful preparation started with carefully controlled crystallization of MnCO₃, leading to particles of spherical shape and high tap density. Thermal decomposition of MnCO₃ was investigated by both DTA and TG analysis and XRD analysis of products. A precursor of product, spherical Mn₂O₃, was then obtained by heating MnCO₃. A mixture of Mn₂O₃ and Li₂CO₃ was then sintered to produce LiMn₂O₄ with retention of spherical particle shape. It was found that if lithium was in stoichiometric excess of 5% in the calcination of spinel LiMn₂O₄, the product had the largest initial specific capacity. In this way spherical particles of spinel LiMn₂O₄ were of excellent fluidity and dispersivity, and had a tap density as high as 1.9 g cm^–3 and an initial discharge capacity reaching 125 mAh g^–1. When surface-doped with cobalt in a 0.01 Co/Mn mole ratio, although the initial discharge capacity decreased to 118 mAh g^–1, the 100th cycle capacity retention reached 92.4% at 25°C. Even at 55°C the initial discharge capacity reached 113 mAh g^–1 and the 50th cycle capacity retention was in excess of 83.8%.     

Nanofibers of LiMn2O4 by electrospinning

Through sol-gel processing and electrospinning technique, extrathin fibers of poly(vinyl alcohol) (PVA)/lithium chloride/manganese acetate composite fibers were prepared. After calcination of the above precursor fibers at 600 degrees C, the spinel lithium manganese oxide (LiMn2O4) nanofibers, with a diameter of 100-200 nm, were successfully obtained. The fibers were investigated by TG-DTA, XRD, FT-IR, and SEM, respectively. The results showed that the crystalline phase and morphology of the fibers were largely influenced by the calcination temperature.     

Improvement in stability of LiMn2O4 thin-film electrodes by oxygen-plasma irradiation to precursor gel

LiMn₂O₄ thin-film electrodes were prepared by the sol?Cgel method combined with oxygen-plasma irradiation. Oxygen plasma with a power of 10 or 90?W was irradiated to the precursor thin film prepared from lithium acetate, manganese acetate tetrahydrate and polyvinylpyrrolidone on a Pt plate, and then it was fired at 723 or 973?K. X-ray diffraction and Raman measurements indicated that oxygen-plasma irradiation was effective to increase the crystallinity of the resulting LiMn₂O₄. Atomic force microscope observation showed that the particle size of LiMn₂O₄ in the resulting thin-film electrode was decreased and homogeneous distribution of LiMn₂O₄ particles was achieved. Oxidation of the electrolyte at higher potentials was suppressed and capacity retention at 328?K was dramatically improved for the LiMn₂O₄ thin-film electrode obtained at 973?K. The improved electrochemical stability is ascribed to the elimination of organic materials from precursor by oxygen-plasma irradiation.     

Enhanced electrochemical performance of LiNi0.8Co0.1Mn0.1O2 cathode via wet-chemical coating of MgO

Journal of Solid State Electrochemistry - LiNi0.8Co0.1Mn0.1O2 (NCM811) has a high potential for using as the cathode material for lithium–ion batteries (LIBs) for electric vehicles owing to...     

Preparation of Spinel LiMn2O4 by a Spray-drying Method

Spinel LiMn₂O₄ has already become an attractive cathode material for rechargeable lithium-ion battery. Compared with other layered compounds LiCoO₂ and LiNiO₂,LiMn₂O₄ offers several advantages:inexpensive, nontoxic, abundant and easy to prepare. These characteristics induce many researchers to study it to make it commercialized.     

The effects of crystal structure of the precursor MnO2 on electrochemical properties of spinel LiMn2O4

Journal of Solid State Electrochemistry - The spinel LiMn2O4 samples for lithium-ion battery have been synthesized through one-step solid-state method using four different polymorphs of MnO2, e.g.,...