Spinel LiMn Research Articles

Milling effect on the local structure, site occupation, and site migration in aluminum substituted lithium manganese oxides

7Li and 27Al MAS-NMR, magnetic susceptibility, and complex impedance measurements have been performed to study the local structure and electrical resistivity in Al doped spinel LiMn2−xAlxO4 (x = 0, 0.05) exposed to a ball-milling process. The milling process decreased the effective magnetic moment of the Mn species, arising from the appearance of Mn4+, and lead to the suppression of the antiferromagnetic correlation. A hopping time and an activation energy for hopping charge carrier, estimated from electrical resistivity, relatively became larger above milling time of 2.5 h. 7Li and 27Al MAS-NMR spectra were dependent on milling time, and changes in the spectrum intensities were related to the distribution of Al/Li site occupation. Consequently, we concluded that structural disorder caused by the moderate milling process stimulated a migration of Al3+ ions from the 8a site to the 16d one and the increase of Li+ ions at the 8a site on the diffusion pathway. Such a mutual site migration between the 8a and 16d site for Li+ and Al3+ ions would be favorable to Li+ ion diffusion in the milled samples.

Synthesis and Characterization of Stoichiometric Spinel-LiMn<sub>2</sub>O<sub>4</sub>

In this study, spinel LiMn 2 O 4 powder was synthesized from LiOH.H 2 O and MnO x by conventional and mechanical alloying (MA) methods, followed by heat treatment at 800 °C in O 2 for four hours with cooling to room temperature in the furnace at 60 °C/h. It is found that both samples do not show phase transition in low temperature, and this occurred for different reasons. In the MA sample, the presence of Fe as contamination increased the Mn valence and hindered the occurrence of phase transition. The conventional sample does not show phase transition at low temperature due to stoichiometric content, without any contamination. In general, the absence of phase transition occurred due to synthesis condition employed in this study.

Understanding the Solution Chemistry of Coprecipitation and the Homogeneity of the Precipitated Particle to Achieve Excellent Electrochemical Performance of Transition Metal Oxide Cathode Materials for Lithium-Ion Batteries

Coprecipitation is a widely used method to synthesize multicomponent transition metal cathode materials for lithium-ion batteries. The major advantages of the coprecipitation method are the homogeneity of different transition metal ions within the precipitated particles, and the tunability of the particle morphology through control of the reaction conditions. In this poster, we will show our recent results related to the coprecipitation of precursors for lithium-ion active materials, as well as their conversion to cathode materials. Solution chemistry was chosen to achieve explicit control over particle composition, and a variety of characterization methods including electrochemical evaluation were utilized to demonstrate the structure and performance of the synthesized materials. As an example material, we will use high voltage spinel LiMn1.5Ni0.5O4 synthesized from manganese and nickel blend oxalate precursor. We will present insights into nucleation and particle growth processes during particle formation in the coprecipitation reaction. We will also demonstrate the level of homogeneity that coprecipitation is able to achieve relative to traditional solid-state methods.

Crystal Chemistry and Electrochemistry of LixMn1.5Ni0.5O4 Solid Solution Cathode Materials

For ordered high-voltage spinel LiMn1.5Ni0.5O4 (LMNO) with the P4321 symmetry, the two consecutive two-phase transformations at ∼4.7 V (vs Li+/Li), involving three cubic phases of LMNO, Li0.5Mn1.5Ni0.5O4 (L0.5MNO), and Mn1.5Ni0.5O4 (MNO), have been well-established. Such a mechanism is traditionally associated with poor kinetics due to the slow movement of the phase boundaries and the large mechanical strain resulting from the volume changes among the phases, yet ordered LMNO has been shown to have excellent rate capability. In this study, we show the ability of the phases to dissolve into each other and determine their solubility limit. We characterized the properties of the formed solid solutions and investigated the role of non-equilibrium single-phase redox processes during the charge and discharge of LMNO. By using an array of advanced analytical techniques, such as soft and hard X-ray spectroscopy, transmission X-ray microscopy, and neutron/X-ray diffraction, as well as bond valence sum analysis, th...

Tuning the Cation Ordering with the Deposition Pressure in Sputtered LiMn1.5Ni0.5O4 Thin Film Deposited on Functional Current Collectors for Li-Ion Microbattery Applications

The development of high voltage spinel LiMn1.5Ni0.5O4 (LMNO) sputtered thin films on functional current collector was reported within the framework of this study. We have first solved the technological issue due to the PtSi phase which originates from the interdiffusion between silicon wafer and chromium/platinum current collector to form PtSi phase under annealing treatment. By substituting the Cr layer with a very dense and pinhole free Al2O3 thin film deposited by ALD acting as a barrier diffusion between the silicon substrate and the LMNO layer, the synthesis process (sputtered thin films annealed under air at 700 °C) has been validated. In the second part of this study, the behavior of the sputtered LMNO thin films as a function of the deposition pressure and the film thickness has been investigated. The deposition pressure has been found to play a key role on the Mn–Ni cations ordering in spinel-like structures (P4332 ordered vs Fd3m disordered spinel) and consequently on the electrochemical perfor...

From hydrated layered-spinel lithium manganate composite to high-performance spinel LiMn2O4: A novel synthesis tuned by the concentration of LiOH

Abstract To obtain high-performance spinel LiMn 2 O 4 , various types of hydrated layered-spinel lithium manganate composites have been controllably synthesized through the hydrothermal process. It is found that the composition and morphology of these intermediate products can be tuned by the concentration of LiOH: Li + act as the template and OH - provide the required alkaline environment. In particular, the nanostructure varies from nanowires to nanosheets at different levels, depending on the phase ratio of the spinel phase ranging from 0% to 100%. Phase purity and the corresponding electrochemical properties of the as-prepared LiMn 2 O 4 products are further tailored through the subsequent heat treatment. With the optimized LiOH concentration of 0.08 M, the resulting LiMn 2 O 4 cathode material exhibits the best electrochemical performance with the initial discharge capacity of 121.7 mA h g −1 at 1 C and 117.8 mA h g −1 at 30 C, while a retention over 90% can be achieved after 1500 cycles. This study will help deepen understanding of the function mechanisms and further direct the novel synthesis from hydrated layered-spinel lithium manganate composites to high-performance spinel LiMn 2 O 4 cathode materials.

Effects of Equimolar Co3+ and Ni2+ Co-Doping on the Electrochemical Properties of Spinel LiMn2–2xNixCoxO4 Prepared by Solid-State Reaction Method

Effects of Equimolar Co³⁺ and Ni²⁺ Co-Doping on the Electrochemical Properties of Spinel LiMn₂_–2<i>x</i>Ni_<i>x</i>Co_<i>x</i>O₄ Prepared by Solid-State Reaction Method

Enhanced Electrochemical Performance in Ni‐Doped LiMn2O4‐Based Composite Cathodes for Lithium‐Ion Batteries

AbstractHigh‐voltage and high‐performance Ni‐doped LiMn2O4‐basedcomposite cathodes have been obtained from the nominal formula of Li2Mn1‐xNixSiO4, synthesized by using a citric acid‐assisted sol‐gel method. The spinel Li(Mn,Ni)2O4 and layered Li2SiO3 coexist in the composites with x=0 and 0.05, whereas the materials with x=0.15 and 0.25 consist of Li(Mn,Ni)2O4, Li2SiO3 and layered LiNiO2; at x≥ 0.35, the impurity phases of NiO and Ni6MnO8 are detected. A significant improvement in discharge capacity and rate performance of the materials has been caused by the simultaneous existence of LiNiO2 and Li2SiO3. The composite with x=0.25 givesa very high initial discharge capacity of 168 mAh g−1 in the potential range of 3–5 V and exhibits an excellent rate performance. Our study shows that the composites consisting of Li(Mn, Ni)2O4, Li2SiO3, and LiNiO2may be promising candidates for high‐voltage and high‐performance lithium‐ion batteries.

Phase transformation mechanism in lithium manganese nickel oxide revealed by single-crystal hard X-ray microscopy

Understanding the reaction pathway and kinetics of solid-state phase transformation is critical in designing advanced electrode materials with better performance and stability. Despite the first-order phase transition with a large lattice mismatch between the involved phases, spinel LiMn1.5Ni0.5O4 is capable of fast rate even at large particle size, presenting an enigma yet to be understood. The present study uses advanced two-dimensional and three-dimensional nano-tomography on a series of well-formed LixMn1.5Ni0.5O4 (0≤x≤1) crystals to visualize the mesoscale phase distribution, as a function of Li content at the sub-particle level. Inhomogeneity along with the coexistence of Li-rich and Li-poor phases are broadly observed on partially delithiated crystals, providing direct evidence for a concurrent nucleation and growth process instead of a shrinking-core or a particle-by-particle process. Superior kinetics of (100) facets at the vertices of truncated octahedral particles promote preferential delithiation, whereas the observation of strain-induced cracking suggests mechanical degradation in the material.

First-Principles Modeling of Mn(II) Migration above and Dissolution from LixMn2O4 (001) Surfaces

Density functional theory and ab initio molecular dynamics simulations are applied to investigate the migration of Mn(II) ions to above-surface sites on spinel Li(x)Mn(2)O(4) (001) surfaces, the subsequent Mn dissolution into the organic liquid electrolyte, and the detrimental effects on graphite anode solid electrolyte interphase (SEI) passivating films after Mn(II) ions diffuse through the separator. The dissolution mechanism proves complex, the much-quoted Hunter disproportionation of Mn(III) to form Mn(II) is far from sufficient. Key steps that facilitate Mn(II) loss include concerted liquid/solid-state motions, proton-induced weakening of Mn-O bonds forming mobile OH- surface groups, and chemical reactions of adsorbed decomposed organic fragments. Mn(II) lodged between the inorganic Li(2)CO(3) and organic lithium ethylene dicarbonate (LEDC) anode SEI components facilitates electrochemical reduction and decomposition of LEDC. These findings help inform future design of protective coatings, electrolytes, additives, and interfaces.

Effects of magnesium and chlorine co‐doping on the structural and electrochemical performance of the spinel LiMn2O4cathode materials

The lithium-ion battery cathode materials spinel LiMn2O4 and LiMg0.05Mn1.95O3.9Cl0.1 samples are synthesised by solid state reaction route, the effects of magnesium and chlorine co-doping on the structure, morphology and electrochemical performance of material LiMn2O4 are studied by X-ray diffraction, scanning electron microscope, electron diffraction spectroscope and galvanostatic charge–discharge, respectively. The results indicate that appropriate amount doping of magnesium and chlorine does not change the spinel structure of LiMn2O4, and the results reveal that the LiMg0.05Mn1.95O3.9Cl0.1 has an initial discharge capacity of 125.2 mAh/g at 0.2C, and the capacity retention is still as high as 89.3% even after 100 cycles, which is significantly higher than 79.6% of LiMn2O4. Especially, the LiMg0.05Mn1.95O3.9Cl0.1 shows the discharge capacity of 91.2 mAh/g at 10C, which higher than that of LiMn2O4 (64.3 mAh/g). The LiMg0.05Mn1.95O3.9Cl0.1 exhibits excellent cycling performance and rate capability than that of LiMn2O4. Thus, this is a very effective way for comprehensive improving LiMn2O4 electrochemical performance.

Surface design with spinel LiMn1.5Ni0.5O4 for improving electrochemical properties of LiNi0.5Co0.2Mn0.3O2 at high cut-off voltage

Spinel LiNi0.5Mn1.5O4 is successfully coated on the surface of LiNi0.5Co0.2Mn0.3O2 cathode material by sol-gel method. The results show that the spinel LiNi0.5Mn1.5O4 has been successfully coated on the surface of LiNi0.5Co0.2Mn0.3O2 and exhibits a good electrochemical performance at high cut-off voltage (4.6V), showing initial discharge capacity of 192.1mAhg−1 and retains 92.4%after 100 cycles. The rate capability results show that the reversible capacity retention of LiNi0.5Co0.2Mn0.3O2 increases from 84.1% to 90.6% after being coated with LiNi0.5Mn1.5O4. Electrochemical impedance spectroscopy (EIS) reveals that the coating layer can protect LiNi0.5Co0.2Mn0.3O2 from HF attack, reduce the charge transfer resistance and favor the lithium diffusion of the electrode.

Effects of aluminium and sodium co‐doping on the structural and electrochemical performances of the spinel LiMn2O4cathode materials

The lithium-ion battery cathode materials spinel LiMn2O4, LiAl0.1Mn1.9O4 and Li0.94Na0.06Al0.1Mn1.9O4 materials are synthesised by sol–gel method. The structure, morphology and electrochemical performances of the aluminium and sodium co-doped materials are studied by X-ray diffraction measurement, scanning electron microscopy, and Electron diffraction spectroscopy, respectively. The results reveal that appropriate amount doping of aluminium and sodium does not change the spinel structure of LiMn2O4. Those materials have a good crystallinity and the sizes are approximately 150 nm. The initial discharge capacity of Li0.94Na0.06Al0.1Mn1.9O4 is 113.8 mAh/g at 0.5 C. Compared with the rate capability of LiMn2O4, the discharge capacity of 107.5 mAh/g at 5 C for Li0.94Na0.06Al0.1Mn1.9O4 has 46.8% improvement. Obviously, aluminium and sodium co-doping is a very effective way to improve LiMn2O4 rate capability.

Spinel LiMn2−x Si x O4 (x &lt; 1) through Si4+ substitution as a potential cathode material for lithium-ion batteries

Spinel LiMn2−x Si x O4 (x< 1, through substituting Mn4+ with Si4+ in cubic spinel LiMn2O4) was synthesized successfully by a facile sol-gel method. The as-prepared LiMn2−x Si x O4 consisted of pores with large size distribution range from a few nanometers to over 200 nm and possessed specific surface area of 8.76 m2 g−1. Results of X-ray powder diffraction and X-ray photoelectron spectroscopy confirmed that Si atoms entered the host lattice. As a cathode material for rechargeable lithium-ion batteries, spinel LiMn2−x Si x O4 exhibited excellent structural reversibility and integrity during the charging-discharging process. The result indicated that substitution of Mn4+ by Si4+ in spinel LiMn2O4 material effectively alleviated the phase transition caused by Jahn-Teller effect. The initial discharge capacity of the as-prepared spinel LiMn2−x Si x O4 was 147 mA h g−1 over the voltage range of 1.5–4.8 V. However, after 51 cycles, the specific capacity was 88 mA h g−1 with capacity retention of 60 %. More work is needed to understand the effects of substituting Mn4+ by Si4+ and to improve the cyclic stability.

Synthesis of Spinel LiMn&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;4&lt;/SUB&gt; with Manganese Carbonate by Controlled Crystallization Method

Synthesis of Spinel LiMn&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;4&lt;/SUB&gt; with Manganese Carbonate by Controlled Crystallization Method

Synergetic effects of LiFe0.3Mn0.7PO4–LiMn1.9Al0.1O4 blend electrodes

Composite cathodes are prepared by blending the olivine LiFe0.3Mn0.7PO4 (LFMP) and spinel LiMn1.9Al0.1O4 (LMO) in order to combine the high capacity of LFMP with the rate capability of the spinel. While tap density, capacity and energy density show a linear dependency on the blend ratio, a remarkable synergetic effect between LFMP and LMO improving the electrochemical performance at higher C-rates is demonstrated. Potential curves of blend electrodes at rates of 3C reveal a less pronounced polarization for the Mn2+/3+ plateau than expected from theoretical calculations. This buffer effect is also observed for high current pulses (5C) where blend electrodes resemble the behavior of pure spinel electrodes. In terms of power density at high states of charge (SoC), the performance of the Blend(50LFMP/50LMO cap%) exceeds even that of pure spinel. In addition, the spinel-related manganese dissolution can be drastically reduced by blending spinel with LFMP. This study shows the expected and synergetic effects of LFMP/spinel blends and compares the results with theoretical calculations.

Enhanced Cyclic Stability of Spinel LiMn2O4 for Lithium‐Ion Batteries by Surface Coating with WO3

AbstractWO3‐modified LiMn2O4 was synthesized by using a simple wet‐chemical process followed by solid‐state reaction. After surface coating modification, a high discharge capacity of 125.6 mAh g−1 with retention of 94.8 % was obtained at a current density of 1 C between 3.3 and 4.3 V after 100 cycles. The XRD patterns showed that the crystal structure of LiMn2O4 was not altered by coating WO3 and the HRTEM image showed the solution method had been used to prepare the WO3‐coated LiMn2O4 successfully. From electrochemical impedance spectroscopy and cyclic voltammetry analysis, the WO3 coating was shown to decrease the charge‐transfer resistance and avoid the disproportionation reaction of manganese into the electrolyte solution. The WO3 surface coating is a promising approach to improve the cyclic stability of lithium manganese oxide.

Dual-doping to suppress cracking in spinel LiMn2O4: a joint theoretical and experimental study.

Electrochemical cycling stabilities were compared for undoped and Al/Co dual-doped spinel LiMn2O4 synthesized by solid state reactions. We observed the suppression of particle fracture in Al/Co dual-doped LiMn2O4 during charge/discharge cycling and its distinguishable particle morphology with respect to the undoped material. Systematic first-principles calculations were performed on undoped, Al or Co single-doped, and Al/Co dual-doped LiMn2O4 to investigate their structural differences at the atomistic level. We reveal that while Jahn-Teller distortion associated with the Mn(3+)O6 octahedron is the origin of the lattice strain, the networking -i.e. the distribution of mixed valence Mn ions - is much more important to release the lattice strain, and thus to alleviating particle cracking. The calculations showed that the lattice mismatching between Li(+) intercalation and deintercalation of LiMn2O4 can be significantly reduced by dual-doping, and therefore also the volumetric shrinkage during delithiation. This may account for the near disappearance of cracks on the surface of Al/Co-LiMn2O4 after 350 cycles, while some obvious cracks have developed in undoped LiMn2O4 at similar particle size even after 50 cycles. Correspondingly, Al/Co dual-doped LiMn2O4 showed a good cycling stability with a capacity retention of 84.1% after 350 cycles at a rate of 1C, 8% higher than the undoped phase.

Correction: An acid-free rechargeable battery based on PbSO4 and spinel LiMn2O4.

Correction for 'An acid-free rechargeable battery based on PbSO4 and spinel LiMn2O4' by Yu Liu et al., Chem. Commun., 2014, 50, 13714-13717.

Overcoming the chemical instability on exposure to air of Ni-rich layered oxide cathodes by coating with spinel LiMn1.9Al0.1O4

To overcome the chemical instability on exposure to air of Ni-rich materials, a heterostructure composed of a Ni-rich layered oxide core and a Mn-rich LiMn1.9Al0.1O4 shell is explored. The spinel coating alleviates the chemical instability leading to superior capacity retention even after air-storage.