Mg-doped LiNi0.5Mn1.5O4 spinel for cathode materials

Lithium-ion batteries are becoming more and more important not only for portable electronic devices, but also in prevision of high power electric vehicles. In such an optic, deep studies regarding all the components of a secondary battery are in development. In this study, high voltage cathode materials have been selected. Crystals with spinel structure have a 3D vacancy pathway suitable for Li-ions transport. The material under study was LiNi_0.5Mn_1.5O₄ doped with magnesium replacing the nickel. Various samples were synthesized via three different routes: a solid-state method, a modified sol–gel method and a xerogel method. The structure and morphology of the powders were analyzed with HRTEM and XRD. Electrochemical tests were also performed. A wide range of particle sizes (from micro to nanosize) was the result of the different synthesis routes. Unfortunately pure materials were not always obtained. The electrochemical tests showed improvement of the material's cyclability, by reducing the particle size. The electrochemical tests further confirmed the existence of a Li_1+dMn_2−dO₄ impurity. The results are quite promising, however, further improvement of the purity of the electrode composition are needed.     

Synthesis and electrochemical properties of spherical spinel Li1.05M0.05Mn1.9O4 (M = Mg and Al) as a cathode material for lithium-ion batteries by co-precipitation method

Cation (Mg and Al)-substituted spinel were synthesized using metal oxide precursor by co-precipitation method. XRD revealed that the prepared substituted spinel has spinel structure with Fd3m space group. In order to compensate the decreased initial capacity of cation-substituted spinel, partial anion (F) substitution was also carried out. The cycling performance of all the substituted spinel was improved, compared to the Li_1.05Mn_1.95O₄ at 55 °C. Li_1.05Al_0.1Mn_1.85O_3.95F_0.05 showed better capacity retention than the other substituted spinels. Both cation and anion substitution appeared to be effective for improving the cycling performance of spinel material at elevated temperature.     

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.     

Improved electrochemical performance of AlPO4-coated LiMn1.5Ni0.5O4 electrode for lithium-ion batteries

LiMn_1.5Ni_0.5O₄ materials coated with AlPO₄ are prepared by a sol-gel method with citric acid to improve their electrochemical performance; the physical and electrochemical properties are characterized by various analytical techniques. The coated AlPO₄ layer completely covers the surfaces of the LiMn_1.5Ni_0.5O₄ particles and the thickness of the coated layer is ∼15 nm. 1 wt.% AlPO₄-coated LiMn_1.5Ni_0.5O₄ has much lower surface and charge-transfer resistances and shows a higher lithium diffusion rate in comparison with the pristine sample. The modified material demonstrates dramatically enhanced electrochemical reversibility and stability under elevated temperature conditions. This is because the coated AlPO₄ layer reduces the contact area between the electrode and electrolyte and suppresses the formation of undesirable solid electrolyte interface films.     

Electrochemical performance of ZnO-coated LiMn1.5Ni0.5O4 cathode material

LiMn_1.5Ni_0.5O₄ cathode material was prepared by sol–gel method and annealed at 850 °C for 15 h. The prepared powder was coated with ZnO by dissolving zinc acetate in methanol and LiMn_1.5Ni_0.5O₄ powder was mixed in this solution followed by the continuous stirring for 4 h. The LiMn_1.5Ni_0.5O₄ and ZnO-coated LiMn_1.5Ni_0.5O₄ powder was structurally characterized using X-ray diffraction and scanning electron microscopy (SEM). The coin cell was fabricated using ZnO-coated LiMn_1.5Ni_0.5O₄ as cathode materials, LiPF₆, dissolved in ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:1 wt ratio) as electrolyte, and Li foil as anode. It was found that ZnO-coated LiMn_1.5Ni_0.5O₄ cathode materials had the initial discharge capacity of about 146 mA h g⁻¹. The discharge capacity retention after 50 cycles was found to be nearly 97%.     

Synthesis of high power type LiMn1.5Ni0.5O4 by optimizing its preparation conditions

LiMn_1.5Ni_0.5O₄ has been synthesized by an ultrasonic-assisted sol-gel method. The precursor is heat treated at a series of temperatures from 650 °C to 1000 °C. The structure and physical-chemical properties of the as-prepared powder are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) thermal gravimetric and galvanostatic charge-discharge tests in detail. As temperature goes up, the particle size increases, the reactivity of the material in 4 V region becomes more obvious, the structure of the samples become more stable and it behaves optimal electrochemical properties as the material is heat treated at 850 °C. When it is used as cathode active material in a lithium battery, it delivers high initial capacity of 134.5 mAh g⁻¹ (corresponding to 91.7% of the theoretical capacity), and high rate discharge capability, e.g., 133.4, 120.6, 111.4, 103.2 and 99.3 mAh g⁻¹ as discharged at 0.5, 1, 5, 10 and 15 C (1 C = 148 mA g⁻¹)-rates, respectively. It also shows satisfactory capacity retention even at high rate of 5 C, which is about 99.83% of the capacity retention per cycle.     

X-ray absorption spectra of the spinel LiCu0.5Mn1.5O4

X-ray absorption spectra of the spinel LiCu_0.5Mn_1.5O₄ were recorded at the Cu K and L₃, Mn K and L₃, and O K edge. The spectra are aligned on a common energy scale with the aim to establish an experimental picture of the conduction band structure. The fine structures observed a few electron volts around the absorption thresholds are discussed in terms of hybridisation of cation and anion orbitals. Emphasis is put on the identification of spectral features correlated with the presence of lithium on the tetrahedral sites of the spinel structure. The consequences of lithium insertion/extraction on the intensities of these spectral structures are discussed. Previous studies by X-ray absorption spectroscopy of lithium insertion/extraction in various spinels are found to agree with our expectations.     

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.     

Effect of protecting metal oxide (Co3O4) layer on electrochemical properties of spinel Li1.1Mn1.9O4 as a cathode material for lithium battery applications

Metal oxide (Co₃O₄) was coated on spinel Li_1.1Mn_1.9O₄ using glutamic acid. Powder X-ray diffraction pattern of Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ showed that the Co₃O₄ coating medium was not incorporated in the spinel bulk structure. Morphology of the Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ was observed by scanning electron microscopy and transmission electron microscopy. The cycling performance of the Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ was obviously improved, compared to the pristine Li_1.1Mn_1.9O₄ at elevated temperature (55 °C). Improvement of rate capability was also achieved at high C-rates.     

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.     

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.     

Improvement of electrochemical properties of Li1.1Al0.05Mn1.85O4 achieved by an AlF3 coating

The electrochemical performance of AlF₃-coated Li_1.1Al_0.05Mn_1.85O₄ spinel was investigated. The morphology of the AlF₃-coated Li_1.1Al_0.05Mn_1.85O₄ was observed by SEM and TEM, and the thickness of the coating layer was approximately 10 nm. Capacity retention and rate capability were substantially improved by the AlF₃-coating, as compared to pristine Li_1.1Al_0.05Mn_1.85O₄. Manganese dissolution was also dramatically reduced for the AlF₃-coated Li_1.1Al_0.05Mn_1.85O₄, which may reflect lower impedance for the coated spinel. The thermal stability of the AlF₃-coated Li_1.1Al_0.05Mn_1.85O₄ was improved, exhibiting an exothermic reaction at higher temperature with reduced heat generation, compared to the pristine Li_1.1Al_0.05Mn_1.85O₄.     

Improvement of cathode performance of LiMn2O4 as a cathode active material for Li ion battery by step-by-step supersonic-wave treatments

As a novel partial substitution and surface modification process, we focused on a step-by-step (double-step) supersonic-wave treatment in a Zn-containing aqueous solution without any heat-treatments, and performed the treatment on LiMn₂O₄ powder. From XRD measurements, it was demonstrated that the lattice constant of LiMn₂O₄ decreased slightly by the treatments, indicating a partial substitution of Zn for Mn. It was also suggested by SEM–EDX and XPS that Zn was well dispersed in/on the samples and their surfaces were modified by Zn compounds. Such a partial substitution and surface modification was supported by crystal structure analysis based on the Rietveld method using neutron diffraction. Cycle performance of LiMn₂O₄ was significantly improved by the step-by-step supersonic-wave treatments. In the processes, it was especially effective for the improvement to apply lower and higher frequencies at the first and second steps, respectively, keeping the power higher. The cathode property improvement was considered due to the partial substitution and the surface coating caused by the step-by-step supersonic-wave treatments. From the investigation on the cathodes and electrolytes after the cycle tests, it was suggested that the crystal structure of LiMn₂O₄ was stabilized by the treatments.     

Synthesis and electrochemical performance of Li2CoSiO4 as cathode material for lithium ion batteries

Li₂CoSiO₄ has been prepared successfully by a solution route or hydrothermal reaction for the first time, and its electrochemical performance has been investigated primarily. Reversible extraction and insertion of lithium from and into Li₂CoSiO₄ at 4.1 V versus lithium have shown that this material is a potential candidate for the cathode in lithium ion batteries. At this stage reversible electrochemical extraction was limited to 0.46 lithium per formula unit for the Li₂CoSiO₄/C composite materials, with a charge capacity of 234 mAh g⁻¹ and a discharge capacity of 75 mAh g⁻¹.     

Li2MnSiO4 as a potential Li-battery cathode material

Recently we synthesized and preliminary characterized a new material for potential use in Li-battery cathodes: Li₂MnSiO₄. Although its theoretical capacity is about 330 mAh g⁻¹, the actual measurements showed a much smaller value (about 120 mAh g⁻¹). One of the reasons for the poor performance could be the poor electronic conductivity (<10⁻¹⁴ S cm⁻¹ at RT) causing a huge polarization during charge–discharge. However, in the present paper we show that reducing the particle size down to the range of 20–50 nm and additional particle embedment into a carbon phase does not significantly improve the electrochemistry of Li₂MnSiO₄. Observations of structural changes during the first charge shows a complete loss of peaks when reaching the nominal composition of ca. Li₁MnSiO₄. The peaks are not recovered during subsequent cycling. It is supposed that extraction of Li causes significant structural changes so that the resulting material is only able to reversibly exchange a limited amount of Li.     

PMMA-assisted synthesis of Li1−xNi0.5Mn1.5O4−δ for high-voltage lithium batteries with expanded rate capability at high cycling temperatures

In this work, poly(methyl methacrylate) (PMMA), a non-surfactant polymer was used to synthesize nonstoichiometric Li_0.82Ni_0.52Mn_1.52O_4−δ (0 ≤ δ ≤ 0.25) spinels. The presence of the polymer was found to be beneficial with a view to facilitating the use of the spinel in electrodes for lithium batteries. Thus, PMMA allowed spinel particles of a high crystallinity and uniform size and shape to be obtained, and particle size to be tailored by using an appropriate calcining temperature and time. By controlling these variables, spinels in nanometric, submicrometric and micrometric particle sizes were prepared and characterized by chemical analysis, X-ray diffraction, electron microscopy, thermogravimetry and nitrogen adsorptions measurements. The spinels were obtained as highly crystalline phases with lithium and oxygen deficiency and some cation disorder as revealed by chemical analysis, thermogravimetric and XRD data. Their electrochemical performance in two-electrode cells was tested at room temperature and 50 °C over a wide range of charge/discharge rates (from C/4 to 4C). Cell performance was found to depend on particle size rather than on structural properties. Thus, the spinel best performing at 50 °C was that consisting of submicrometric particles, which delivered a high capacity and exhibited the best capacity retention and rate capability. Particles of submicronic size share the advantages of nanometric particles (viz. the ability to withstand high charge/discharge rates) and micrometric particles (a high capacity and stability at low rates).     

Structural and thermal properties of LiNi0.6−xMgxCo0.25Mn0.15O2 cathode materials

For improving the electrochemical performance and thermal stability, magnesium was chosen as the doping element in Li(NiCoMn)O₂ cathode materials. LiNi_0.6−xMg_xCo_0.25Mn_0.15O₂ (x = 0 and 0.03) were successfully synthesized via the mixing hydroxide method. These materials exhibited α-NaFeO₂ structure as indicated by the XRD patterns. The intensity ratio of (0 0 3) to (1 0 4) showed that the Mg substitution could reduce the cation mixing. The pristine material exhibited the initial discharge of capacity 199 mAh g⁻¹ and remained retention of 79% after 20 cycles in the voltage range of 3–4.5 V. When magnesium ions were substituted, the initial capacity was reduced due to the less active ions. However, the capacity retention was increased to 95%. Not only cycleability, but also the thermal stability was improved by Mg substitution at every delithiated state of electrodes with electrolytes. The in situ synchrotron X-ray diffraction patterns showed that the boundary of phase transition for H1 to H2 was much clearer in Mg-doped sample, indicating that the LiNi_0.57Mg_0.03Co_0.25Mn_0.15O₂ material exhibited higher structural integrity. The improvements of both electrochemical retention and thermal stability were possibly attributed to the reduced cation mixing and complete structural changes.     

Structural characteristics and electrochemical performance of layered Li[Mn0.5−xCr2xNi0.5−x]O2 cathode materials

Li[Mn_0.5−xCr_2xNi_0.5−x]O₂ (0 < 2x <0.2) (Mn/Ni = 1) cathode materials have been synthesized by a solution method. X-ray diffraction patterns of the as-prepared materials were fitted based on a hexagonal unit cell (α-NaFeO₂ layer structure). The extent of Li/Ni intermixing decreased, and layering of the structure increased, with increasing Cr content. Electrochemical cycling of the oxides, at 30 °C in the 3–4.3 V range vs. Li/Li⁺, showed that the first charge capacity increased with increasing Cr content. However, maximum discharge capacity (∼143 mAh g⁻¹) was observed for 2x = 0.05. X-ray absorption near edge spectroscopic (XANES) measurements on the K-edges of transition metals were carried out on pristine and delithiated oxides to elucidate the charge compensation mechanism during electrochemical charging. The XANES data revealed simultaneous oxidation of both Ni and Cr ions, whereas manganese remains as Mn⁴⁺ throughout, and does not participate in charge compensation during oxide delithiation.     

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.     

Cerium and zinc: Dual-doped LiMn2O4 spinels as cathode material for use in lithium rechargeable batteries

Pristine spinel lithium manganese oxide (LiMn₂O₄) and zinc- and cerium-doped lithium manganese oxide [LiZn_xCe_yMn_2−x−yO₄ (x = 0.01–0.10; y = 0.10–0.01)] are synthesized for the first time via the sol–gel route using p-amino benzoic acid as a chelating agent to obtain micron-sized particles and enhanced electrochemical performance. The sol–gel route offers shorter heating time, better homogeneity and control over stoichiometry. The resulting spinel product is characterized through various methods such as thermogravimetic and differential thermal analysis (TG/DTA), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrochemical galvanostatic cycling studies. Charge–discharge studies of LiMn₂O₄ samples heated at 850 °C exhibit a discharge capacity of 122 mAh g⁻¹ and a corresponding 99% coulombic efficiency in the 1st cycle. The discharge capacity and cycling performance of LiZn_0.01Ce_0.01Mn_1.98O₄ is found to be superior (124 mAh g⁻¹), with a low capacity fade (0.1 mAh g⁻¹ cycle⁻¹) over the investigated 10 cycles.