Performance of LiNi0.5Mn1.5O4 prepared by solid-state reaction

LiNi_0.5Mn_1.5O₄ was prepared through a solid-state reaction using various Ni precursors. The effect of precursors on the electrochemical performance of LiNi_0.5Mn_1.5O₄ was investigated. LiNi_0.5Mn_1.5O₄ made from Ni(NO₃)₂·6H₂O shows the best charge–discharge performance. The reversible capacity of LiNi_0.5Mn_1.5O₄ is about 145 mAh g⁻¹ and remained 143 mAh g⁻¹ after 10 cycles at 3.0–5.0 V. The XRD results showed that the precursors and the dispersion methods had significant effect on their phase purity. Pure spinel phase can be obtained with high energy ball-milling method and Ni(NO₃)₂·6H₂O as precursor. Trace amount of NiO and Li₂MnO₃ phase were detected in LiNi_0.5Mn_1.5O₄ with manual-mixture method and using Ni(CH₃COO)₂·6H₂O, NiO and Ni₂O₃ as precursors.     

Research progress in high voltage spinel LiNi0.5Mn1.5O4 material

Lithium-ion batteries are now considered to be the technology of choice for future hybrid electric and full electric vehicles to address global warming. LiCoO₂ has been the most widely used cathode material in commercial lithium-ion batteries. Since LiCoO₂ has economic and environmental issues, intensive research has been directed towards the development of alternative low cost, environmentally friendly cathode materials as possible replacement of LiCoO₂. Among them, spinel LiNi_0.5Mn_1.5O₄ material is one of the promising and attractive cathode materials for next generation lithium-ion batteries because of its high voltage (4.7 V), acceptable stability, and good cycling performance. Research advances in high voltage spinel LiNi_0.5Mn_1.5O₄ are reviewed in this paper. Developments in synthesis, structural characterization, effect of doping, and effect of coating are presented. In addition to conventional synthesis methods, several alternative synthesis methods are also summarized. Apart from battery performance, the application of spinel LiNi_0.5Mn_1.5O₄ material in asymmetric supercapacitors is also discussed.     

Effect of Bi oxide surface treatment on 5 V spinel LiNi0.5Mn1.5−xTixO4

The effect of Bi surface treatment on LiNi_0.5Mn_1.5−xTi_xO₄ was examined. As a result, Bi surface film around 20 nm thick was confirmed to be fabricated on the surface of 5 V spinel LiNi_0.5Mn_1.5−xTi_xO₄ by transmission electron microscopy (TEM) and energy dispersion X-ray spectrometer (EDX) analysis. The Bi compound was confirmed to be Bi₂O₃ by X-ray diffraction analysis. Cycle behavior was also found to be improved by Bi treatment. A retention capacity of up to around 85% was achieved after 500 cycles at 20 °C, while a retention capacity as high as 70% was obtained after 500 cycles, even at 45 °C. Storage performance was also improved with Bi treatment. Recovery capacity of more than 90% was obtained with Bi treatment after storage for 1 week at 60 °C. The increased resistance in storage was also suppressed with Bi treatment, which would be due to the suppression of electrolyte decomposition by the Bi coating film. It was found that Bi treatment had the effect of decreasing the dissolution of Mn, Ni and Ti of the elements of the cathode active material, due to inductively coupled plasma (ICP) analysis. Based on these results, the Bi surface coating was found to have a remarkable effect on the improvement of the cells with 5 V spinel.     

Understanding the sucrose-assisted combustion method: Effects of the atmosphere and fuel amount on the synthesis and electrochemical performances of LiNi0.5Mn1.5O4 spinel

The present paper comprises results of our studies about the influence of the atmosphere and fuel amount on the synthesis and electrochemical performance of LiNi_0.5Mn_1.5O₄ spinel (LNMS). Reaction of mixtures of metal nitrates with and without sucrose (fuel) in Ar and in air flow has been studied by thermal analysis and coupled mass spectrometry (TG/DTA/MS). Products obtained after the thermal study have been identified and characterized by powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Gases evolved along the thermal treatment have been identified by coupled mass spectrometry (MS). From all these results the synthesis reactions have been put forward. When the reaction is conducted in air sub-micrometric LiNi_0.5Mn_1.5O₄ spinel is obtained independently of the amount of sucrose. When the reaction is done in Ar the spinel is only obtained in absence of fuel. The electrochemical performances at 25 °C and 55 °C of the synthesized LNMSs have been evaluated by galvanostatic cycling. The samples prepared in air furnish high capacity (≈120 mAh g⁻¹) and they work at high voltage (≈4.7 V). Besides, they exhibit remarkable cycling properties, even at elevated temperature (55 °C), with capacity retentions higher than 90% after 50 cycles.     

High power and high capacity cathode material LiNi0.5Mn0.5O2 for advanced lithium-ion batteries

Single-phase lithium nickel manganese oxide, LiNi_0.5Mn_0.5O₂, was successfully synthesized from a solid solution of Ni_1.5Mn_1.5O₄ that was prepared by means of the solid reaction between Mn(CH₃COO)₂·4H₂O and Ni(CH₃COO)₂·4H₂O. XRD pattern shows that the product is well crystallized with a high degree of Li–M (Ni, Mn) order in their respective layers, and no diffraction peak of Li₂MnO₃ can be detected. Electrochemical performance of as-prepared LiNi_0.5Mn_0.5O₂ was examined in the test battery by charge–discharge cycling with different rate, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The cycling behavior between 2.5 and 4.4 V at a current rate of 21.7 mA g⁻¹ shows a reversible capacity of about 190 mAh g⁻¹ with little capacity loss after 100 cycles. High-rate capability test shows that even at a rate of 6C, stable capacity about 120 mAh g⁻¹ is retained. Cyclic voltammetry (CV) profile shows that the cathode material has better electrochemical reversibility. EIS analysis indicates that the resistance of charge transfer (R_ct) is small in fully charged state at 4.4 V and fully discharged state at 2.5 V versus Li⁺/Li. The favorable electrochemical performance was primarily attributed to regular and stable crystal structure with little intra-layer disordering.     

Solution combustion synthesis of layered LiNi0.5Mn0.5O2 and its characterization as cathode material for lithium-ion cells

LiNi_0.5Mn_0.5O₂, a promising cathode material for lithium-ion batteries, is synthesized by a novel solution-combustion procedure using acenaphthene as a fuel. The powder X-ray diffraction (XRD) pattern of the product shows a hexagonal cell with a = 2.8955 Å and c = 14.1484 Å. Electron microscopy investigations indicate that the particles are of sub-micrometer size. The product delivers an initial discharge capacity of 161 mAh g⁻¹ between 2.5 and 4.6 V at a 0.1 C rate and could be subjected to more than 50 cycles. The electrochemical activity is corroborated with cyclic voltammetric (CV) and electrochemical impedance data. The preparative procedure presents advantages such as a low cation mixing, sub-micron particles and phase purity.     

Nonflammable electrolyte for 3-V lithium-ion battery with spinel materials LiNi0.5Mn1.5O4 and Li4Ti5O12

The compatibility between dimethyl methylphosphonate (DMMP)-based electrolyte of 1 M LiPF₆/EC + DMC + DMMP (1:1:2 wt.) and spinel materials Li₄Ti₅O₁₂ and LiNi_0.5Mn_1.5O₄ was reviewed, respectively. The cell performance and impedance of 3-V LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ lithium-ion cell with the DMMP-based nonflammable electrolyte was compared with the baseline electrolyte of 1 M LiPF₆/EC + DMC (1:1 wt.). The nonflammable DMMP-based electrolyte exhibited good compatibility with spinel Li₄Ti₅O₁₂ anode and high-voltage LiNi_0.5Mn_1.5O₄ cathode, and acceptable cycling performance in the LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ full-cell, except for the higher impedance than that in the baseline electrolyte. All of the results disclosed that the 3 V LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ lithium-ion battery was a promising choice for the nonflammable DMMP-based electrolyte.     

Mitigation of the irreversible capacity and electrolyte decomposition in a LiNi0.5Mn1.5O4/nano-TiO2 Li-ion battery

Nanosized titanium oxides can achieve large reversible specific capacity (above 200 mAh g⁻¹) and good rate capabilities, but suffer irreversible capacity losses in the first cycle. Moreover, due to the intrinsic safe operating potential (1.5 V), the use of titanium oxide requires to couple it with high-potential cathodes, such as lithium nickel manganese spinel (LNMO) in order to increase the energy density of the final cell. However the use of the 4.7 V vs. Li⁺/Li⁰ LNMO cathode material requires to tackle the continuous electrolyte decomposition upon cycling. Coupling these two electrodes to make a lithium ion battery is thus highly appealing but also highly difficult because the cell balancing must account not only for the charge reversibly exchanged by each electrode but also for the irreversible charge losses. In this paper a LNMO-nano TiO₂ Li-ion cell with liquid electrolyte is presented: two innovative approaches on both the cathode and the anode sides were developed in order to mitigate the electrolyte decomposition upon cycling. In particular the LNMO surface was coated with ZnO in order to minimize the surface reactivity, and the TiO₂ nanoparticles where activated by incorporating nano-lithium in the electrode formulation to compensate for the irreversible capacity loss in the first cycle. With these strategies we were able to assemble balanced Li-ion coin cells thus avoiding the use of electrolyte additives and more hazardous and expensive ex-situ SEI preforming chemical or electrochemical procedures.     

LiCr0.2Ni0.4Mn1.4O4 spinels exhibiting huge rate capability at 25 and 55 °C: Analysis of the effect of the particle size

The comparison of the rate capability of LiCr_0.2Ni_0.4Mn_1.4O₄ spinels synthesized by the sucrose aided combustion method at 900, 950 and 1000 °C is presented. XRD and TEM studies show that the spinel cubic structure remains unchanged on heating but the particle size is notably modified. Indeed, it increases from 695 nm at 900 °C to 1465 nm at 1000 °C. The electrochemical properties have been evaluated by galvanostatic cycling at 25 and 55 °C between 1 C and 60 C discharge rates. At both temperatures, all samples exhibit high working voltage (∼4.7 V), elevated capacity (∼140 mAh g⁻¹) and high cyclability (capacity retention ∼99% after 50 cycles even at 55 °C). The samples also have huge rate capability. They retain more than 70% of their maximum capacity at the very fast rate of 60 C. The effect of the particle size on the rate capability at 25 and at 55 °C has been investigated. It was demonstrated that LiCr_0.2Ni_0.4Mn_1.4O₄ annealed at 900 °C, with the lowest particle size, has the best electrochemical performances. In fact, among the LiNi_0.5Mn_1.5O₄-based cathodes, SAC900 exhibits the highest rate capability ever published. This spinel, able to deliver 31,000 W kg⁻¹ at 25 °C and 27,500 W kg⁻¹ at 55 °C is a really promising cathode for high-power Li-ion battery.     

Preparation and characterization of sub-micro LiNi0.5−xMn1.5+xO4 for 5 V cathode materials synthesized by an ultrasonic-assisted co-precipitation method

Sub-micro spinel LiNi_0.5−xMn_1.5+xO₄ (x < 0.1) cathode materials powder was successfully synthesized by the ultrasonic-assisted co-precipitation (UACP) method. The structure and electrochemical performance of this as-prepared powder were characterized by powder XRD, SEM, XPS, CV and the galvanostatic charge–discharge test in detail. XRD shows that there is a small Li_yNi_1−yO impurity peak placed close to the (4 0 0) line of the spinel LiNi_0.5−xMn_1.5+xO₄, and the powders are well crystallized. XPS exhibits that the Mn oxidation state is between +3 and +4, and Ni oxidation state is +2 in LiNi_0.5−xMn_1.5+xO₄. SEM shows that the prepared powders (UACP) have the uniform and narrow size distribution which is less than 200 nm. Galvanostatic charge–discharge test indicates that the initial discharge capacities for the LiNi_0.5−xMn_1.5+xO₄ (UACP) at C/3, 1C and 2C, are 130.2, 119.0 and 110.0 mAh g⁻¹, respectively. After 100 cycles, their capacity retentions are 99.8%, 88.2%, and 73.5%, respectively. LiNi_0.5−xMn_1.5+xO₄ (UACP) at C/3 discharge rate exhibits superior capacity retention upon cycling, and it also shows well high current discharge performance. CV curve implies that LiNi_0.5−xMn_1.5+xO₄ (x < 0.1) spinel synthesized by ultrasonic-assisted co-precipitation method has both reversibility and cycle capability because of the ultrasonic-catalysis.     

Surface modification of LiNi0.5Mn1.5O4 by ZrP2O7 and ZrO2 for lithium-ion batteries

The spinel LiNi_0.5Mn_1.5O₄ has been surface modified separately with 1.0 wt.% ZrO₂ and ZrP₂O₇ for the purpose of improving its cycle performance as a cathode in a 5-V lithium-ion cell. Although the modifications did not change the crystallographic structure of the surface-modified samples, they exhibited better cyclability at elevated temperature (55 °C) compared with pristine LiNi_0.5Mn_1.5O₄. The material that was surface modified with ZrO₂ gave the best cycling performance, only 4% loss of capacity after 150 cycles at 55 °C. Electrochemical impedance spectroscopy demonstrated that the improved performance of the ZrO₂-surface-modified LiNi_0.5Mn_1.5O₄ is due to a small decrease in the charge transfer resistance, indicating limited surface reactivity during cycling. Differential scanning calorimetry showed that the ZrO₂-modified LiNi_0.5Mn_1.5O₄ exhibits lower heat generation and higher onset reaction temperature compared to the pristine material. The excellent cycling and safety performance of the ZrO₂-modified LiNi_0.5Mn_1.5O₄ electrode was found to be due to the protective effect of homogeneous ZrO₂ nano-particles that form on the LiNi_0.5Mn_1.5O₄, as shown by transmission electron microscopy.     

Improved electrochemical properties of BiOF-coated 5 V spinel Li[Ni0.5Mn1.5]O4 for rechargeable lithium batteries

The electrochemical properties of BiOF-coated 5 V spinel Li[Ni_0.5Mn_1.5]O₄ were investigated at elevated temperatures (55 °C). As observed by scanning and transmission electron microscopy, BiOF nanolayers with ∼10 nm thickness were coated on the surface of Li[Ni_0.5Mn_1.5]O₄. The BiOF coating layer protected the surface of the active materials from HF generated by the decomposition of LiPF₆ in the electrolyte during electrochemical cycling. The dissolution of transition metal elements was also suppressed upon cycling. Therefore, the capacity retention of the BiOF-coated Li[Ni_0.5Mn_1.5]O₄ was obviously improved compared to the pristine Li[Ni_0.5Mn_1.5]O₄ at 55 °C.     

Nanosized high voltage cathode material LiMg0.05Ni0.45Mn1.5O4: Structural,electrochemical and in situ investigation

In this study a modified solid state synthesis (auto-ignition method) is used to form nanosized spinel type material LiMg_0.05Ni_0.45Mn_1.5O₄. This material presents a high voltage plateau at 4.75 V vs. Li/Li⁺. Structural and electrochemical characterisations have been performed using a wide range of techniques (TEM, neutron diffraction, galvanostatic measurements, and impedance spectroscopy). Besides, in situ XAS has been performed to monitor the evolution of Ni and Mn oxidation state during Li intercalation. The material presents an ordered cubic spinel structure, good capacity retention upon cycling (131 mAh g⁻¹ at C/10 and 117 mAh g⁻¹ at 1C) and good electronic conductivity (10⁻⁶ S cm⁻¹ at RT). The simultaneous presence of Mn³⁺/Mn⁴⁺ in the structure has been investigated and explained by inclusion of disordered nanodomains in the structure.     

Evaluation of nano-structured Ir0.5Mn0.5O2 as a potential cathode for intermediate temperature solid oxide fuel cell

A novel Ir_0.5Mn_0.5O₂ cathode has been synthesized by thermal decomposition of mixed H₂IrCl₆ and Mn(NO₃)₂ water solution. The Ir_0.5Mn_0.5O₂ cathode has been characterized by XRD, field emission SEM (FESEM) and AC impedance spectroscopy. XRD result shows that rutile-structured Ir_0.5Mn_0.5O₂ phase is formed by thermal decomposition of mixed H₂IrCl₆ and Mn(NO₃)₂ water solution. FESEM micrographs show that a porous structure with well-necked particles forms in the cathode after sintering at 1000 °C. The average grain size is between 20 and 30 nm. Two depressed arcs appear in the medium-frequency and low-frequency region, indicating that there are at least two different processes in the cathode reaction: charge transfer and molecular oxygen dissociation followed by surface diffusion. The minimum area specific resistance (ASR) is 0.67 Ω cm² at 800 °C. The activation energy for the total oxygen reduction reaction is 93.7 kJ mol⁻¹. The maximum power densities of the Ir_0.5Mn_0.5O₂/LSGM/Pt cell are 43.2 and 80.7 mW cm⁻² at 600 and 700 °C, respectively.     

Surface modification of LiNi1/2Mn3/2O4 thin-films by zirconium alkoxide/PMMA composites and their effects on electrochemical properties

Three kinds of surface modifications were carried out on LiNi_1/2Mn_3/2O₄ thin-films to improve the charge and discharge characteristics of LiNi_1/2Mn_3/2O₄ positive electrodes. Among them, Zr(OBu)₄/poly(methyl methacrylate) (PMMA)-treated LiNi_1/2Mn_3/2O₄ thin-film electrodes showed charge and discharge efficiency of 80–84% in the first cycle, which was much higher than that for an untreated LiNi_1/2Mn_3/2O₄ thin-film electrode (73%). The values of the charge and discharge efficiency were still higher than that for an untreated electrode after the 30th cycle. The charge and discharge curves gave two plateaus at around 4.72 and 4.76 V, which were very similar to those for the untreated electrode. Ac impedance spectroscopy revealed that the surface film resistance should not increase by Zr(OBu)₄/PMMA treatment. XPS measurements suggest that a composite layer should be formed on a LiNi_1/2Mn_3/2O₄ thin-film electrode from PMMA and Zr(OBu)₄-derived compounds introducing an electrolyte. This composite layer was lithium-ion conductive, and was sustainable enough to suppress subsequent decomposition of an electrolyte at potentials as high as 4.7 V.     

Effect of equivalent and non-equivalent Al substitutions on the structure and electrochemical properties of LiNi0.5Mn0.5O2

Pristine, equivalently and non-equivalently Al substituted LiNi_0.5Mn_0.5O₂ materials were prepared by a combination of co-precipitation and solid-state reaction. As shown by XRD and XPS, lattice volume shrinkage of LiNi_0.5(Mn_0.45Al_0.05)O₂ was attributed to the presence of Ni in both 2+ and 3+, while the lattice volume expansion of Li(Ni_0.45Al_0.05)Mn_0.5O₂ was caused by lowering the average oxidation state of Mn. Electrochemical performance of LiNi_0.5Mn_0.5O₂ materials can be greatly affected by the change of oxidation states of the transition metals by Al substitution. Non-equivalent substitution of Al for Ni leads to deteriorated discharge performance and cyclic stability due to the reduction of the electrochemical active Ni²⁺ and structure supported Mn⁴⁺, while an increase in the amount of Ni²⁺ in LiNi_0.5(Mn_0.45Al_0.05)O₂ brings obvious improvement of the electrochemical properties. EIS analyses of the electrode materials at pristine and charged states indicate that the poor electrochemical performance of Li(Ni_0.45Al_0.05)Mn_0.5O₂ material can be ascribed to the higher charge transfer resistance and surface film resistance, and the observed higher current rate capability of LiNi_0.5(Mn_0.45Al_0.05)O₂ can be understood due to the better charge transfer kinetics.     

Effects of supersonic treatment on the electrochemical properties and crystal structure of LiMn1.5Ni0.5O4 as a cathode material for Li ion batteries

The electrochemical properties and crystal structure of LiMn_1.5Ni_0.5O₄ treated with supersonic waves in an aqueous Ni-containing solution were investigated by performing charge-discharge tests, inductively coupled plasma (ICP) analysis, scanning electron microscopy (SEM), iodometry, X-ray diffraction (XRD), powder neutron diffraction and synchrotron powder XRD. The charge-discharge curve of LiMn_1.5Ni_0.5O₄ versus Li/Li⁺ has plateaus at 4.1 and 4.7 V. The 4.1 V versus Li/Li⁺ plateau due to the oxidation of Mn^3+/4+ was reduced by the supersonic treatment. During the charge-discharge cycling test at 25 °C, the supersonic treatment increased the discharge capacity of the 50th cycle. Rietveld analysis of the neutron diffraction patterns revealed that the Ni occupancy of the 4b site in LiMn_1.5Mn_0.5O₄, which is mainly occupied by Ni, was increased by the supersonic treatment. This result suggests that Ni²⁺ is partially substituted for Mn^3+/4+ during the supersonic treatment.     

Effect of Ag additive on the performance of LiNi1/3Co1/3Mn1/3O2 cathode material for lithium ion battery

The LiNi_1/3Co_1/3Mn_1/3O₂/Ag composite used for cathode material of lithium ion battery was prepared by thermal decomposition of AgNO₃ added to commercial LiNi_1/3Co_1/3Mn_1/3O₂ powders to improve the electrochemical performance of LiNi_1/3Mn_1/3Co_1/3O₂. Structure and morphology analysis showed that Ag particles were dispersed on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ instead of entering the crystal structure. The results of charge–discharge tests showed that Ag additive could improve the cycle performance and high-rate discharge capability of LiNi_1/3Mn_1/3Co_1/3O₂. Extended analysis indicated that Ag was unstable in the commercial electrolyte at high potential. The improved electrochemical performance caused by Ag additive was associated not only with the enhancement of electrical conductivity of the material and the lower polarization of the cell, but also with the increased “c” parameter of LiNi_1/3Mn_1/3Co_1/3O₂ after repeated charge/discharge cycles and the compact and protective SEI layer formed on the surface of LiNi_1/3Mn_1/3Co_1/3O₂.     

La0.75Sr0.25Cr0.5Mn0.5O3 as hydrogen electrode for solid oxide electrolysis cells

La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) has been applied as hydrogen electrode (cathode) material in solid oxide electrolysis cells operating with different steam concentrations (20, 40, 60 and 80 vol.% absolute humidity (AH)) using 40 sccm H₂ carrier gas at 800, 850 and 900 °C, respectively. Impedance spectra and voltage-current curves were measured as a function of cell electrolysis current density and steam concentration to characterize the cell performance. The cell resistance decreased with the increase in electrolysis current density while increased with the increase in steam concentration under the same electrolysis current density. At 1.6 V applied electrolysis voltage, the maximum consumed current density increased from 431 mA cm⁻² for 20 vol.% AH to 593 mA cm⁻² for 80 vol.% AH at 850 °C. Polarization and impedance spectra experiments revealed that LSCM-YSZ hydrogen electrode played a major role in the electrolysis reaction.