Performance Of LiMn2O4 Cathode Materials Research Articles

Alkaline-earth metal doping in spinel LiMn2O4 cathode materials for Li-ion batteries: Insights from first-principles calculations

Spinel LiMn2O4 is regarded as a promising cathode material candidate due to its advantages of environmental friendliness and low cost. However, its development is hindered by unstable cyclic performance and limited energy density. Herein, alkaline-earth metal Mg doping in spinel LiMn2O4 cathode material was investigated based on first-principles calculations. The results show that the substitution of Mg2+ for Mn3+ is thermodynamically favorable. At the same time, adjacent Mn3+ is oxidized to Mn4+, which weakens the Jahn-Teller distortion of the LiMn2O4 cathode. The study also found that Mg and O have strong coupling near the Fermi level, which improves cycling stability. In addition, it is found that alkaline-earth metal doping is beneficial to the enhancement of intercalation potential. These findings will provide a theoretical reference for improving the performance of LiMn2O4 cathode material and promote the development of LiMn2O4 in power batteries.

New strategy for enhancing the electrochemical performance of LiMn2O4 cathode material

Despite spinel-structured LiMn2O4 (LMO) cathode material has been successfully commercialized for large scale energy storage, its cycling stability in practical applications still awaits for further improvement. Herein, we provided an effective strategy by adding phosphate in the preparation process, and this modification play a dual effect on LMO materials. Impressively, HRTEM indicated that Li3PO4 generated on the particle surface protects the LMO particles from electrolyte corrosions, while the fast ion conductor can effectively improve the lithium ion diffusion coefficient from 4.506 × 10−12 cm2 s−1 to 1.570 × 10−11 cm2 s−1. Meanwhile, the tetrahedral ion doped into the octahedrally transition metal oxide units, enhances the p-type carrier effect, resulting in the carrier density and Hall mobility are improved by a factor of ∼5 and ∼10, respectively. Electrochemical performance among the LMOP0.50 cathode with a high initial discharge capacity of ∼140 mA h g−1 at 0.1 C, and a capacity retention of 95.5 % after 500 cycles at 1 C. Consequently, the introduction of phosphate provides a new strategy for modifying LMO cathode material.

Effects of AgNPs-coating on the electrochemical performance of LiMn2O4 cathode material for lithium-ion batteries

Effects of AgNPs-coating on the electrochemical performance of LiMn2O4 cathode material for lithium-ion batteries

Improved long cycle performance of LiMn2O4 cathode material by Ni-B co-doping combined with truncated octahedron morphology

The rapid capacity fading of spinel LiMn2O4 cathode materials still suffers from Jahn-Teller effect and Mn dissolution. Herein, various spinel LiMn1.90-xNi0.10BxO4 cathode materials with truncated octahedron morphology are obtained by a solid-state combustion method. Owing to the substitution of Ni-B dual-doping for Mn, the MnO6 octahedron in the LiMn2O4 generates a contraction that leads to the increased average Mn oxidation state and the suppressed Jahn-Teller effect. Simultaneously, the expansive LiO4 tetrahedron is conducive to boosting the fast Li+ diffusion. Moreover, the growth of {110} crystal planes in the LiMn1.90-xNi0.10BxO4 (x = 0.02–0.15) is also restrained by the Ni-B co-doping, hence alleviating the Mn dissolution. So the Ni-B co-doping accompanied with truncated octahedron morphology presents the preferential growth of {111} and {100} planes. Among the various counterparts of Ni-B co-doping, the optimized LiMn1.84Ni0.10B0.06O4 exhibits the optimal rate performance and cycle life. At 5 C, a capacity retention of 73.5% with an initial discharge capacity of 101.8 mAh g−1 is achieved after ultra-long 2000 cycles. Even at 10 C, the capacity retention of 62.2% is also maintained after 2000 cycles. This combination of element doping and morphology regulation will provide a feasible strategy to synthesize high-performance spinel LiMn2O4 cathode materials for lithium-ion batteries.

The crystal shape algorithm as a tool for the characterization of agglomerated morphologies: Cubic and hexagonal crystal habits of LiMn2O4

The crystal shape algorithm as a tool in the quantitative characterization of agglomerated morphologies of materials is reviewed. Irrespective of whether there is agglomeration or not, the material morphology is made up of a fundamental unit known as the crystal habit, which is captured by the crystal shape algorithm. Using this algorithm both agglomerated and un-agglomerated morphologies were studied. Enhanced electrochemical performance of LiMn2O4 cathode material is achieved not only from a preferred crystal orientation along the 400 direction, but also when the crystal growth completely stops along the 311 direction. The cubic crystal habit of LiMn2O4 thus shows much better electrochemical performance as compared to the hexagonal crystal habit.

Improved electrochemical performance of LiMn2O4 cathode material by Ce doping

Lithium manganese oxide nanopowders doped with Ce ions are synthesized using modified sol-gel method and the effect of annealing atmosphere (air vs. nitrogen) on the structure, morphology, and phase composition is studied thoroughly. Electrochemical testing is conducted to evaluate the effect of annealing atmosphere on electrochemical performance. The X-ray diffraction indicates the cubic spinel structure for all the obtained samples. The lattice parameter is observed to slightly decrease with increasing concentration of Ce3+ ions substituting Mn3+ ions from 8.230 to 8.228 Ẵ and from 8.227 to 8.224 Ẵ for air annealing and for nitrogen-air annealing, respectively. A limited solubility of cerium in LiMn2O4 is also observed, as small amounts of cerium dioxide is detected on the surface of LiMn2-xCexO4 grains and confirmed by XPS analysis of cerium which shows only the spectrum of Ce4+ ions. Electrochemical testing is conducted to evaluate the effect of annealing atmosphere on electrochemical performance. It is shown that annealing in nitrogen and then in air results in excellent capacity retention with minimal, 4–8% capacity loss after 150 cycles. LiMn1.99Ce0.01O4 samples prepared that way display better high rate performance in comparison with pristine LiMn2O4.

Mn4+ rich surface enabled elevated temperature and full-cell cycling performance of LiMn2O4 cathode material

LiMn2O4 (LMO) cathode exhibiting improved electrochemical performance is reported. X-ray diffraction confirms spinel cubic structure in the bulk with localized structural integrity confirmed by high-resolution Transmission Electron Microscopy (TEM) analysis showing lattice fringes with spacing of 0.48nm corresponding to (111) of spinel LMO. X-ray photoelectron spectroscopy (XPS) study quantified the Mn4+/Mn3+∼2 instead of 1 on the surface of pristine LMO nanoparticles. Mn4+ rich surface improved elevated temperature cycling stability inhibiting Mn-dissolution. The surface rich Mn4+ and almost equal concentration of Mn4+ and Mn3+ in the sub-surface/bulk was confirmed by XPS analysis upon ion-etching. At room temperature, high discharge capacity of ∼110 mAh/g at 2C rate and ∼102 mAh/g at 10C rate is reported for long cycles (over 500). Cycling at 55°C, capacity retention of 81.2% and 72% at the end of 200 cycles for 1C and 10C discharge rates respectively are testified for the electrochemical stability. This is superior elevated temperature performance of LMO electrodes especially, without any surface coating or doping. To demonstrate LMO cathode’s potential, a full-cell against Li4Ti5O12 and commercial graphite anodes were tested that exhibit discharge capacity of 95 mAh/g and 82 mAh/g respectively with retention of ∼82% over 100 cycles. Finally, electrodes after first charge and discharge have been investigated by ex situ XPS to correlate the oxidation states of manganese with pristine LMO.

Nature of the Electrochemical Properties of Sulphur Substituted LiMn₂O₄ Spinel Cathode Material Studied by Electrochemical Impedance Spectroscopy.

In this work, nanostructured LiMn2O4 (LMO) and LiMn2O3.99S0.01 (LMOS1) spinel cathode materials were comprehensively investigated in terms of electrochemical properties. For this purpose, electrochemical impedance spectroscopy (EIS) measurements as a function of state of charge (SOC) were conducted on a representative charge and discharge cycle. The changes in the electrochemical performance of the stoichiometric and sulphur-substituted lithium manganese oxide spinels were examined, and suggested explanations for the observed dependencies were given. A strong influence of sulphur introduction into the spinel structure on the chemical stability and electrochemical characteristic was observed. It was demonstrated that the significant improvement in coulombic efficiency and capacity retention of lithium cell with LMOS1 active material arises from a more stable solid electrolyte interphase (SEI) layer. Based on EIS studies, the Li ion diffusion coefficients in the cathodes were estimated, and the influence of sulphur on Li+ diffusivity in the spinel structure was established. The obtained results support the assumption that sulphur substitution is an effective way to promote chemical stability and the electrochemical performance of LiMn2O4 cathode material.

Influences of polyethylene glycol (PEG) on the performance of LiMn2O4 cathode material for lithium ion battery

Spinel phase LiMn2O4 is synthesized by a polyethylene glycol (PEG)-assisted co-precipitation method. The samples are characterized by X-ray diffraction and scanning electron microscopy techniques. The LiMn2O4 samples synthesized have similar morphology and uniform size of about 150–350 nm. The electrochemical measurements show that as-prepared LiMn2O4 nanoparticle sample using PEG with the molecular weight as 4000 (PEG-4000) shows the best cycling performance and highest rate capability among all samples, its initial discharge capacity is 133 mAhg−1 and maintains at 122 mAhg−1 under 0.5 °C after 50 cycles. The loss of its capacity was just 5.1 %. To control the particle size of LiMn2O4 is one of important factors for its application as a cathode material.

Improved cycle performance of LiMn2O4 cathode material for aqueous rechargeable lithium battery by LaF3 coating

LaF3-coated LiMn2O4 composites were prepared by a simple co-precipitation method using pristine LiMn2O4, La(NO3)3·6H2O, NH4F and polyvinyl pyrrolidone (PVP) as raw materials and the physical and electrochemical properties of the composites were investigated. The results indicate that LaF3 coating is beneficial to improving the electrochemical performance of LiMn2O4 used as a cathode material for aqueous rechargeable lithium battery (ARLB) in 1 mol/L LiNO3 solution. The optimal LaF3-coated LiMn2O4 composite (L-3-LMO) containing 3 wt% LaF3 exhibits much improved electrochemical performance as compared with the pristine LiMn2O4. When galvanostatically charged and discharged at 2 C (296 mA g−1), L-3-LMO displays initial discharge capacity of 118.4 mAh g−1 and capacity retention of 99.7% after 50 cycles, while the pristine LiMn2O4 presents initial discharge capacity of 109.2 mAh g−1 and capacity retention of 89.4%. Even at high current density of 10 C, L-3-LMO delivers discharge capacity of 109.5 mAh g−1 and the capacity remains 107.9 mAh g−1 after 100 cycles, while the highest discharge capacity of pristine LiMn2O4 is only 101.6 mAh g−1 and the capacity is as low as 86.3 mAh g−1 after 100 cycles. The effects of LaF3 coating on Li+ diffusion coefficient, dissolution of manganese ion of electroactive materials are also investigated.

Influences of the surfactant on the performance of nano-LiMn2O4 cathode material for lithium-ion battery

This study synthesized spinel LiMn2O4 materials using a solid-state reaction processing technology. Neutral surfactants and the tri-block copolymer P123 (template) formed an organic self-assembly in alcohol (solvent), with LiCH3COO·2H2O and Mn(CH3COO)2·4H2O as precursors of the inorganic skeleton. Changes in the structure, particle size, and surface area of LiMn2O4 powder in relation to different surfactant contents were investigated. The changes in surface area should affect the wetting effect of the electrolyte on the cathode material, thereby further influencing the actual reaction area and charge–discharge efficiency. The results were analyzed to assess the effect of surface area on electrochemical performance of LiMn2O4 cathode materials. X-ray diffraction (XRD) analysis data showed that LiMn2O4 materials synthesized through the solid-phase reaction method are single-phase spinel, whose original structure is unaffected by the addition of surfactants. Scanning electron microscopic (SEM) observation revealed that LiMn2O4 forms different spherical particles after the addition of different concentrations of surfactants. Furthermore, Brunauer–Emmett–Teller (BET) analysis showed that specific surface areas of 0.4–1.2m2/g are relatively effective in enhancing the capacitance, similarly the formation of spherical particles is beneficial in enhancing the capacitance, and the high-current discharge efficiency is similar to the low-current discharge efficiency. As for the different concentrations of P123, the experiments added with 1.42M P123 achieved optimum results.

Study on the enhanced electrochemical performance of LiMn2O4 cathode material at 55 °C by the nano Ag-coating

In this paper, the nano-sized Ag particles were coated on the surfaces of the spinel LiMn2O4 nanoparticles through a one-step combustion method. It was shown that the rate performance and cycling performance of LiMn2O4 could be effectively improved by the appropriate amount of Ag (5wt%) not only at room temperature (25°C) but also at high temperature (55°C). This was because the Ag particles dispersed on the surface of LiMn2O4 had dramatically increased its electronic conductivity. Definitely, the electrochemical performance of the Ag-coated LiMn2O4 particles at 55°C was not as excellent as that at 25°C. Besides, the Ag-coated LiMn2O4 displayed much better cycling performance at higher C-rates (2C and 5C) at 55°C, compared with that at lower C-rate (0.5C). This was because Ag was just dispersed rather than being densely coated on the surface of LiMn2O4, so the dissolution of LiMn2O4 at 55°C could not be completely inhibited by Ag. Moreover, the dissolution of LiMn2O4 at 2C and 5C at 55°C was much weaker than that at 0.5C, caused by the faster transformation between Mn3+ and Mn4+. As a result, the electrochemical performance of LiMn2O4 could be enhanced by the Ag-coating at high temperature.

Effect of “Nano Inclusion” On Cycle Performance of LiMn2O4 Cathode Material At 3V Range

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Effect of LLT Coating on Elevated Temperature Cycle Life Performance of LiMn2O4 Cathode Material

LiMn2O4 compound are synthesized by polymer precursor method using polyvinyl pyrrolidone (PVP) at temperatures (T), 650, 750 and 850°C which was coated by a thin La0.61Li0.17TiO3 (LLT). The structure and the morphology of the compounds are studied by the Rietveld refined X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques, respectively. To investigate the effect of LLT coating galvanostatic charge–discharge cycling (60 mA g−1) studies are made in the voltage range of 3.5–4.3 V vs. Li at elevated temperature (55 deg. C). The high-temperature electrochemical performance of the LiMn2O4 was significantly improved by the LLT coating.

The Effect of LiFePO4 Coating on Electrochemical Performance of LiMn2O4 Cathode Material

LiMn2O4 spinel cathode materials have been successfully synthesized by solid-state reaction. Surface of these particles were modified by nanostructured LiFePO4 via sol gel dip coating method. Synthesized products were characterized by thermally analyzed by Thermogravimetric and Differential Thermal Analysis(TG/DTA), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) spectroscopy. The results of electrochemical tests showed that the charge/discharge capacities improved up to 120 mAh/g and charge retention of battery enhanced over %95. This improved electrochemical performance is caused by LiFePO4 phosphate layer on surfaces of LiMn2O4cathode particles.

Effects of LLTO Coating on High Temperature Cycle Life Performance of LiMn2O4 Cathode Material

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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.

Cycle Performance of LiMn2O4 Cathode Material with "Nano Inclusion" for Lithium Ion Battery

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Influence of surface effect to the performance of LiMn2O4 cathode material for lithium ion batteries

The surface geometrical and electronic structure of LiMn2O4 (001) are investigated via a density functional approach within the spin-dependent generalized gradient approximation (GGA). Large relaxations perpendicular to the (001) plane of surface and subsurface atoms are observed, which is partly responsible for the Mn dissolution problem of the material when used as cathode material for lithium ion batteries. Because of the surface effect, only Mn3+ ions are observed at the LiMn2O4 (001) surfaces, which is very active for the disproportionation reaction occurs at the electrode/electrolyte interface. The calculated results are also in good agreements with experimental observations.

Electrochemical characterization of surface-modified LiMn2O4 cathode materials for Li-ion batteries

To improve the performance, the surface of LiMn2O4 was coated with very fine MgO, Al2O3 and ZnO by sol-gel method, respectively. The structure and morphology of the coated materials were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The charge and discharge performance of uncoated and surface modified LiMn2O4 spinel at 25°C and 55°C were tested, using a voltage window of 3.0–4.35 V and a current density of 0.1 C rate. There is a slight decrease in the initial discharge capacity relative to that of uncoated LiMn2O4, but the cycle ability of Li LiMn2O4 coated by metal-oxide has remarkably been improved. The EIS measurements of uncoated and Al2O3-coated LiMn2O4 were carried out by a model 273 A potentiostat/galvanistat controlled by a computer using M270 software, and using a frequency response analyzer (Zsimpwin) combined with a potentiostate (PAR 273). Consequently, the reason for the improved cycle properties is that the surface modification reduces the dissolution of Mn, which results from the suppression of the electrolyte decomposition, and suppresses the formation of passivation film that acts as an electronic insulating layer. In conclusion, the use of surface modification is an effective way to improve the electrochemical performance of LiMn2O4 cathode material for lithium batteries.