Synthesis and cycling performance of double metal doped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode materials for rechargeable lithium ion batteries

In order to improve the cycling performance of LiMn₂O₄, the spinel phases LiCo_0.15Mn_1.85O₄ and LiCo_0.05M_0.1Mn_1.85O₄ (M = Ni, Zn, Cu) were prepared by the sol-gel method. Their structures have been investigated by x-ray diffraction. Electrochemical studies were carried out using the Li | Li _x Mn₂O₄ (x = 1.05, 1.1), LiCo_0.15Mn_1.85O₄, and LiCo_0.05M_0.1Mn_1.85O₄ (M = Ni, Zn, Cu) cells. The capacity loss of Li | Li _x Mn₂O₄ (x = 1.05, 1.1) cells is about 21.7 and 6.4% after 30 cycles, whereas that for Co, Co-Ni, Co-Zn, and Co-Cu doped spinel materials is about 4.0, 2.0, 1.0, and 1.9%, respectively. The good capacity retention of LiCo_0.05M_0.1Mn_1.85O₄ (M = Ni, Zn, Cu) electrodes is attributed to stabilization of spinel structure by double metal doping for Mn ion sites. Double substituted spinels display better performance in terms of cycle-life compared with LiMn₂O₄. The text was submitted by the authors in English.     

Er-Doped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

LiMn_2-x Er_xO₄ (x ≤ 0.02) materials were synthesized by a rheological phase reaction method. The thermal behavior of the materials was examined by thermogravimetric and differential scanning calorimetry. X-ray diffraction showed that the samples (x ≤ 0.02 ) exhibited the same phase as the pure spinel. The lattice parameter of the Er-doped spinel was smaller than that of the undoped one and decreased with increasing doping level. Cyclic voltammograms showed two reversible processes corresponding to the typical response of spinel LiMn₂O₄ and revealed an insertion-extraction reaction occurring at two stages in the 4-V region. The electrochemical performances of the samples were studied and displayed a better reversibility and cyclability.__________From Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 740–743.Original English Text Copyright © 2005 by Haowen Liu, Li Song, Kelli Zhang.This article was submitted by the authors in English.     

Modeling effects of particle size in LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material on peak current level in lithium-ion batteries

Mathematical simulation of the current transfer characteristics of submicron and nanodimensional objects has been used to predict some properties of a structured electrode material in lithium-ion batteries. A diffusion model of the intercalation-deintercalation (ID) process is presented. Using this model, the current density in cathode material particles (nanocrystals) has been numerically simulated and an equation for the current density in the absence of diffusion polarization is derived. The proposed model can be used to optimize the ID process for improving the functional properties of cathode materials and increasing the working life of cathodes. Results are illustrated by examples for LiMn₂O₄ cathode material.     

Hierarchical porous onion-shaped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> as ultrahigh-rate cathode material for lithium ion batteries

Spinel LiMn₂O₄ is a widely utilized cathode material for Li-ion batteries. However, its applications are limited by its poor energy density and power density. Herein, a novel hierarchical porous onion-like LiMn₂O₄(LMO) was prepared to shorten the Li⁺ diffusion pathway with the presence of uniform pores and nanosized primary particles. The growth mechanism of the porous onion-like LiMn₂O₄ was analyzed to control the morphology and the crystal structure so that it forms a polyhedral crystal structure with reduced Mn dissolution. In addition, graphene was added to the cathode (LiMn₂O₄/graphene) to enhance the electronic conductivity. The synthesized LiMn₂O₄/graphene exhibited an ultrahigh-rate performance of 110.4 mAh·g^–1 at 50 C and an outstanding energy density at a high power density, maintaining 379.4 Wh·kg^–1 at 25,293 W·kg^–1. Besides, it shows durable stability, with only 0.02% decrease in the capacity per cycle at 10 C. Furthermore, the (LiMn₂O₄/graphene)/graphite full-cell exhibited a high discharge capacity. This work provides a promising method for the preparation of outstanding, integrated cathodes for potential applications in lithium ion batteries.

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Preparation and electrochemical properties of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> 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°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. The text was submitted by the authors in English.     

Modeling the effects of particle size and intercalation-deintercalation rate of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material on the level of mechanical stresses in lithium-ion batteries

A mathematical model of the appearance and development of intercalation-deintercalation (ID) mechanical stresses in particles of an electrode material is presented. Results of simulations of the effects of particle size (including submicron level) and ID rate on the magnitude of mechanical stresses are presented. Analytical expressions are obtained that describe the distribution of mechanical stresses in a submicron particle, depending on the dimensionless ion current density. Results are illustrated by examples for LiMn₂O₄ cathode material.     

LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> microspheres: Synthesis,characterization and use as a cathode in lithium ion batteries

Solid and hollow microspheres of LiMn₂O₄ have been synthesized by lithiating MnCO₃ solid microspheres and MnO₂ hollow microspheres, respectively. The LiMn₂O₄ solid microspheres and hollow microspheres had a similar size of about 1.5 ?m, and the shell thickness of the hollow microspheres was only 100 nm. When used as a cathode material in lithium ion batteries, the hollow microspheres exhibited better rate capability than the solid microspheres. However, the tap density of the LiMn₂O₄ solid microspheres (1.0 g/cm³) was about four times that of the hollow microspheres (0.27 g/cm³). The results show that controlling the particle size of LiMn₂O₄ is very important in terms of its practical application as a cathode material, and LiMn₂O₄ with moderate particle size may afford acceptable values of both rate capability and tap density.     

Preparation of ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel whiskers from zinc cobalt oxalate

ZnCo₂O₄ whiskers 2–5 µm in diameter and up to 50 µm in length, retaining their composition and shape up to 800°C, are prepared via decomposition of the mixed oxalate Zn_1/3Co_2/3C₂O₄ 2H₂O in air and are characterized using chemical analysis, x-ray diffraction, IR spectroscopy, and scanning electron microscopy.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 348–352.Original Russian Text Copyright © 2005 by Bazuev, Gyrdasova, Grigorov, Koryakova.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Effect of in situ spinel seeding on synthesis of MgO-rich MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> composite

MgO-rich MgAl₂O₄ spinel was prepared by adopting solid-state reaction of commercially available sintered seawater magnesia and α-alumina. Starting materials were mixed in weight ratio (Al₂O₃: MgO) of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, where the developed MgAl₂O₄ spinel crystal seed in calcined powder varied (5–50%) with respect to addition of MgO content and temperature. Around 70% spinellisation could be noticed in Al₂O₃: MgO (1:1) batch through double stage sintering. Densification and grain size of the sintered specimen was found to be greatly dependent on initial calcination temperature and content of primary spinel seed. The diametrical compressive strength of sintered specimen was ∼115 MPa for highest amount of spinel content. The hardness of MgO-rich spinel composite was varied with spinel addition.     

Nano-domain structure of Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript> spinel

XRD-pure Li₄Mn₅O₁₂ spinels are obtained below 600 °C from oxalate and acetate precursors. The morphology consists of nanometric particles (about 25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn⁴⁺ are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li₄Mn₅O₁₂ reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of the cubic spinel structure and the (001) plane of monoclinic Li₂MnO₃. For Li₄Mn₅O₁₂ compositions annealed between 400 and 800 °C, EPR spectroscopy shows the appearance of two types of Mn⁴⁺ ions having different metal environments: (i) Mn⁴⁺ ions surrounded by Li⁺ and Mn⁴⁺ and (ii) Mn⁴⁺ ions in Mn⁴⁺-rich environment. The composition of the Li⁺, Mn⁴⁺-shell around Mn⁴⁺ mimics the local environment of Mn⁴⁺ in monoclinic Li₂MnO₃, while the Mn⁴⁺-rich environment is related with that of the spinel phase. The structure of XRD-pure Li₄Mn₅O₁₂ comprises nano-domains with a Li₂MnO₃-like and a Li_4/3−x Mn_5/3+x O₄ composition rather than a single spinel phase with Li in tetrahedral and Li_1/3Mn_5/3 in octahedral spinel sites. The annealing of Li₄Mn₅O₁₂ at temperature higher than 600 °C leads to its decomposition into monoclinic Li₂MnO₃ and spinel Li_4/3−x Mn_5/3+x O₄.     

Enhancement of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel formation from coprecipitated precursor by powder processing

Although low temperature fast coprecipitation technique has been used to synthesize stoichiometric (MgO-nAl₂O₃, n = 1) MgAl₂O₄ spinel forming precursor, delayed spinellization has always been the concern in this process. In this article, the precursor of this ‘fast technique’ has been used for bulk production by further processing by high speed mixing with solvents and mechanical activation by attrition milling in terms of superior spinellization. At 1000°C, MgAl₂O₄ — γ-Al₂O₃ solid solution and MgO phases are formed (spinel formed by 1000°C is regarded as primary spinel). At higher temperatures, due to large agglomerate size, MgO can not properly interact with the exsolved α-Al₂O₃ from spinel solid solution to form secondary spinel; and consequently spinellization gets affected. Solvent treatment and attrition milling of the coprecipitated precursor disintegrate the larger agglomerates into smaller size (effect is more in attrition). Then MgO comes in proper contact with exsolved alumina, and therefore total spinel formation (primary + secondary) is enhanced. Extent of spinellization, for processed calcined samples where some alumina exists as solid solution with spinel, can be determined from the percentage conversion of MgO. Analysis of the processed powders suggests that the 4 h attrited precursor is most effective in terms of nano size (< 25 nm) stoichiometric spinel crystallite formation at ≤ 1100°C.     

Effect of particle size on the conductive and electrochemical properties of Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript>

We have studied the effect of final annealing temperature on the formation of lithium zinc titanate, its electrical conductivity, and its electrochemical performance. Li₂ZnTi₃O₈ has been shown to form in a wide range of annealing temperatures, from 673 to 1073 K. Its particle size increases systematically with increasing annealing temperature, whereas its conductivity decreases. The highest electrochemical capacity at low currents is offered by the materials annealed at 773 and 873 K, and the highest cycling stability is offered by the material prepared at 873 K.     

LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> particles prepared by spray pyrolysis from spray solution with citric acid and ethylene glycol

Spinel LiMn₂O₄ particles with fine sizes and regular morphologies were successfully synthesized by ultrasonic spray pyrolysis at the severe preparation conditions from a spray solution with citric acid and ethylene glycol. The as-prepared particles with spherical shapes, porous structures and micron sizes turned into LiMn₂O₄ particles with submicron size and narrow size distribution at the post-treatment temperature of 800 °C. The discharge capacities of the particles prepared from the spray solution with citric acid and ethylene glycol changed from 90 to 127 mAh/g when the post-treatment temperature was changed from 700 to 1,000 °C. The LiMn₂O₄ particles had maximum discharge capacities at the post-treatment temperature of 800 °C. The discharge capacity of the LiMn₂O₄ particles dropped from 127 to 108 mAh/g by the 30th cycle.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.     

Characterization and electrical properties of semiconducting Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

Semiconducting glasses of the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system were prepared by the press-quenching method and their dc conductivity in the temperature range 223–393 K was measured. The glass transition temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The density for these glasses was consistent with the ionic size, atomic weight and amount of different elements in the glasses. Mössbauer results revealed that the relative fraction of Fe increases with increasing Fe₂O₃ content. Electrical conductivity showed a similar composition dependency as the fraction of Fe. The glasses had conductivities ranging from 10 to 10 Scm at temperatures from 223 to 393 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

A facile method to enhance electrochemical performance of high-nickel cathode material Li(Ni<Subscript>0.8</Subscript>Co<Subscript>0.1</Subscript>Mn<Subscript>0.1</Subscript>)O<Subscript>2</Subscript> via Ti doping

The cycle stability of Li(Ni_0.8Co_0.1Mn_0.1)O₂ is enhanced obviously by titanium doping via a facile solid-state method. The property of crystal structure is evaluated by XRD, which illustrates the samples possessed a layered α-NaFeO₂ structure with R-3m space group. According to the charge/discharge studies, the capacity retention of pristine sample is around 51% after 125 cycles at 5 C, and the sample with Ti dopant displays a good cyclic stability, after 125 cycles, the capacity retention increases to 75% under 5 C, suggesting it could be possibly applied in fast charge Lithium-ion battery area. The superb electrochemical performance might be attributed to the Ti⁴⁺ occupy the layer structure to broaden the Lithium-ion channel, which is benefit to lithium intercalation and deintercalation during cycling.     

Reactions of V<Subscript>2</Subscript>O<Subscript>5</Subscript>, Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>, and Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> with AlN

Reactions of vanadium, niobium, and tantalum pentoxides with aluminum nitride have been studied using X-ray diffraction. At temperatures from 1000 to 1600°C, we have identified various V, Nb, and Ta nitrides. The composition of the niobium and tantalum nitrides depends on the reaction temperature. The tendency toward nitride formation becomes stronger in the order V₂O₅ < Ta₂O₅ < Nb₂O₅.     

Effect of Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the crystallization behavior of BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We gave studied the crystallization behavior of 30BaO · 25Bi₂O₃ · 45B₂O₃ glasses doped with Eu₂O₃ to different levels. At a Eu₂O₃ content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.     

Synthesis of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowders

A procedure has been developed for the synthesis of MgAl₂O₄ nanopowders with a characteristic particle size of 10–40 nm. Translucent hydrous xerogels have been synthesized as precursors to MgAl₂O₄. The synthesized magnesium aluminum spinel nanopowders are promising for the fabrication of optical ceramics.