Transition Metal Oxide Cathode Materials Research Articles

Electrochemical Characteristics of Layered Transition Metal Oxide Cathode Materials for Lithium Ion Batteries: Surface, Bulk Behavior, and Thermal Properties.

Layered lithium transition metal oxides, in particular, NMCs (LiNixCoyMnzO2) represent a family of prominent lithium ion battery cathode materials with the potential to increase energy densities and lifetime, reduce costs, and improve safety for electric vehicles and grid storage. Our work has focused on various strategies to improve performance and to understand the limitations to these strategies, which include altering compositions, utilizing cation substitutions, and charging to higher than usual potentials in cells. Understanding the effects of these strategies on surface and bulk behavior and correlating structure-performance relationships advance our understanding of NMC materials. This also provides information relevant to the efficacy of various approaches toward ensuring reliable operation of these materials in batteries intended for demanding traction and grid storage applications. In this Account, we start by comparing NMCs to the isostructural LiCoO2 cathode, which is widely used in consumer batteries. Effects of changing the metal content (Ni, Mn, Co) upon structure and performance of NMCs are briefly discussed. Our early work on the effects of partial substitution of Al, Fe, and Ti for Co on the electrochemical and bulk structural properties is then covered. The original aim of this work was to reduce the Co content (and thus the raw materials cost) and to determine the effect of the substitutions on the electrochemical and bulk structural properties. More recently, we have turned to the application of synchrotron and advanced microscopy techniques to understand both bulk and surface characteristics of the NMCs. Via nanoscale-to-macroscale spectroscopy and atomically resolved imaging techniques, we were able to determine that the surfaces of NMC undergo heterogeneous reconstruction from a layered structure to rock salt under a variety of conditions. Interestingly, formation of rock salt also occurs under abuse conditions. The surface structural and chemical changes affect the charge distribution, the charge compensation mechanisms, and ultimately, the battery performance. Surface reconstruction, cathode/electrolyte interface layer formation, and oxygen loss are intimately related, making it difficult to disentangle the effects of each of these phenomena. They are driven by the different redox activities of Ni and O on the surface and in the bulk; there is a greater tendency for charge compensation to occur on oxygen anions at particle surfaces rather than on Ni, whereas the Ni in the bulk is more redox active than on the surface. Finally, our latest research efforts are directed toward understanding the thermal properties of NMCs, which is highly relevant to their safety in operating cells.

Research Progress of Ternary Layered Oxide Cathode Materials for Lithium Ion Batteries

Lithium-ion battery is considered to be one of the most promising energy storage systems that are able to satisfy the requirements of power battery, but the current energy density, power density and safety performance for lithium-ion batteries can't meet the needs of the development of electric vehicles. As the only lithium ions supplier, the cathode materials for lithium-ion batteries greatly limit the performance of lithium-ion battery.Therefore, the development of cathode materials with a higher energy density, higher power density and better safety performance is highly desired. Owing to high theoretical capacity, low cost, and low toxicity, ternary layered transition metal oxide cathode materials are considered to be the most promising cathode materials for the next-generation lithium-ion batteries. And in order to fully release the capacities of ternary layered transition metal oxide cathode materials high voltage is necessary, but the cycle stability is not good enough when ternary layered transition metal oxide cathode materials are set with a high voltage range. What’s more, the poor storage performance is another factor that restricts the wide application in electric vehicles. This review describes several common cathode materials, highlighting the advantages and disadvantages of ternary layered transition metal oxide cathode materials and modification progress.

Fluorination of Lithium‐Excess Transition Metal Oxide Cathode Materials

AbstractFluorination of Li‐ion cathode materials is of significant interest as it is claimed to lead to significant improvements in long‐term reversible capacity. However, the mechanism by which LiF incorporates and improves performance remains uncertain. Indeed, recent evidence suggests that fluorine is often present as a coating layer rather than incorporated into the bulk of the material. In this work, first‐principles calculations are used to investigate the thermodynamics of fluorination in transition metal oxide cathodes to determine the conditions under which bulk fluorination is possible. It is found that unlike classic well‐ordered cathodes, which cannot incorporate fluorine, disordered rock salt‐structured materials achieve significant fluorination levels due to the presence of locally metal‐poor, lithium‐rich environments that are highly preferred for fluorine. As well as explaining the fluorination process in known materials, this finding is encouraging for the development of new disordered rock salt lithium‐excess transition metal oxides, a promising new class of Li‐ion battery cathode materials that offer superior practical capacity to traditional layered oxides. In particular, it is found that bulk fluorination may serve as an alternative source of Li‐excess in these compounds that can replace the conventional substitution of a heavy redox‐inactive element on the transition metal sublattice.

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.

Lithium-Ion Battery Precursor Chemistry: Understanding the Role of Solution Conditions on Composition and Structure of Transition Metal Oxalates

Coprecipitation is a popular approach to synthesize precursors for transition metal oxide cathode materials used in lithium-ion batteries. Many papers in the literature have reported tuning the particle morphology using careful control of reaction conditions, and the morphology of the precursor particles can also be retained after calcination to obtain final active materials of tunable size and shape. Oxalate coprecipitation provides a route to substitute the more common hydroxide and carbonate coprecipitation; and oxalate provides an advantage where most transition metal ions form stable oxalate precipitates in aqueous solutions exposed to air. Different oxalate polymorphs may occur; however, depending on the detailed reaction conditions. In this talk, we will present studies of pure and blend oxalate coprecipitations using manganese and nickel, and will discuss the impact of feed conditions on the precipitate composition and structure. We will also demonstrate a method to determine the rate of loss of individual transition metals from solution to the solid phase.

Development of Li(Ni1/3Mn1/3Co1/3-x Na x )O2 cathode materials by synthesizing with glycine nitrate combustion technique for Li-ion rechargeable batteries

Glycine nitrate combustion technique was investigated for synthesizing Li(Ni1/3Mn1/3Co1/3-x Na (x) )O-2, x = 0-0.11 based transition metal oxide cathode materials for the rechargeable Li-ion battery (LIB) under this study. X-ray diffraction and scanning electron microscopy analysis showed that the synthesized powder samples were well crystalline rather spherical secondary particles. These secondary particles were composed of softly agglomerated nano-scale primary particles. The room temperature electrical conductivity of these Na-doped materials was significantly higher than that of the base material (2.60 x 10(-7) S/cm). Among them, the x = 0.04 material reported the highest electrical conductivity of 1.02 x 10(-03) S cm(-1). The half-cell assembled with cathode fabricated from Li(Ni1/3Mn1/3Co1/3)O-2 base material showed an initial discharge capacity of 187 mA h(-1) g(-1) with 25 mA h(-1) g(-1) irreversible capacity loss and 88.47% columbic efficiency at C/5 rate with a cut-off voltage of 2.5-4.6 V at 25 A degrees C. The electrochemical behavior of the x = 0.04 cathode showed a comparable initial discharge capacity as of the base material but with improved capacity retention.

Engineering Diffusivity and Operating Voltage in Lithium Iron Phosphate through Transition-Metal Doping

At base, creating better lithium-ion batteries is all about understanding the diffusion of Li${}^{+}$, particularly its reversible intercalation in materials like olivine phosphates. This study shows that for a given diffusion path for Li${}^{+}$, the forward and backward activation barriers can be manipulated simply by choosing the level of doping $x$ in LiFe${}_{1-x}{M}_{x}$PO${}_{4}$. This simple knob can tune three of the most important electrochemical parameters: diffusivity, operating voltage, and band gap. The insight from this study should also apply to other transition-metal oxide cathode materials.

Identifying the Distribution of Al3+ in LiNi0.8Co0.15Al0.05O2

The doping of Al into layered Li transition metal (TM) oxide cathode materials, LiTMO2, is known to improve the structural and thermal stability, although the origin of the enhanced properties is not well understood. The effect of aluminum doping on layer stabilization has been investigated using a combination of techniques to measure the aluminum distribution in layered LiNi0.8Co0.15Al0.05O2 (NCA) over multiple length scales with 27Al and 7Li MAS NMR, local electrode atom probe (APT) tomography, X-ray and neutron diffraction, DFT, and SQUID magnetic susceptibility measurements. APT ion maps show a homogeneous distribution of Ni, Co, Al, and O2 throughout the structure at the single particle level in agreement with the high-temperature phase diagram. 7Li and 27Al NMR indicates that the Ni3+ ions undergo a dynamic Jahn–Teller (JT) distortion. 27Al NMR spectra indicate that the Al reduces the strain associated with the JT distortion, by preferential electronic ordering of the JT lengthened bonds directed to...

Defect Physics and Chemistry in Layered Mixed Transition Metal Oxide Cathode Materials: (Ni,Co,Mn) vs (Ni,Co,Al)

Although layered lithium transition-metal oxides with different compositions of (Ni,Co,Mn) [NCM] or (Ni,Co,Al) [NCA] have been used in commercial lithium-ion battery cathodes, their defect physics and chemistry is still not well understood, despite having important ramifications for cycling properties, particularly capacity fade. Herein we report a hybrid density functional study of the crystal and electronic structures of and intrinsic point defects in the compositions LiNi1/3Co1/3Mn1/3O2 (NCM1/3) and LiNi1/3Co1/3Al1/3O2 (NCA1/3), which also serve as model compounds for NCM and NCA. We find that the transition metals can exist in different charge and spin states at different lattice sites. In NCM1/3, nickel/lithium antisite pairs, i.e., NiLi–LiNi, are estimated to be about 3% in samples prepared at 1000 °C. In NCA1/3, in addition to nickel antisites NiLi, aluminum antisites AlLi can also occur with a very high concentration. The AlLi defect has a high energy except when it is located between two Al atoms...

Spatially resolved surface valence gradient and structural transformation of lithium transition metal oxides in lithium-ion batteries

Layered lithium transition metal oxides are one of the most important types of cathode materials in lithium-ion batteries (LIBs) that possess high capacity and relatively low cost. Nevertheless, these layered cathode materials suffer structural changes during electrochemical cycling that could adversely affect the battery performance. Clear explanations of the cathode degradation process and its initiation, however, are still under debate and not yet fully understood. We herein systematically investigate the chemical evolution and structural transformation of the LiNixMnyCo1-x-yO2 (NMC) cathode material in order to understand the battery performance deterioration driven by the cathode degradation upon cycling. Using high-resolution electron energy loss spectroscopy (HR-EELS) we clarify the role of transition metals in the charge compensation mechanism, particularly the controversial Ni2+ (active) and Co3+ (stable) ions, at different states-of-charge (SOC) under 4.6 V operation voltage. The cathode evolution is studied in detail from the first-charge to long-term cycling using complementary diagnostic tools. With the bulk sensitive 7Li nuclear magnetic resonance (NMR) measurements, we show that the local ordering of transition metal and Li layers (R3[combining macron]m structure) is well retained in the bulk material upon cycling. In complement to the bulk measurements, we locally probe the valence state distribution of cations and the surface structure of NMC particles using EELS and scanning transmission electron microscopy (STEM). The results reveal that the surface evolution of NMC is initiated in the first-charging step with a surface reduction layer formed at the particle surface. The NMC surface undergoes phase transformation from the layered structure to a poor electronic and ionic conducting transition-metal oxide rock-salt phase (R3[combining macron]m → Fm3[combining macron]m), accompanied by irreversible lithium and oxygen loss. In addition to the electrochemical cycling effect, electrolyte exposure also shows non-negligible influence on cathode surface degradation. These chemical and structural changes of the NMC cathode could contribute to the first-cycle coulombic inefficiency, restrict the charge transfer characteristics and ultimately impact the cell capacity.

Thermal Stability Studies in Charged Layered Sodium Transition Metal Oxide Cathode Materials for Na-Ion Batteries

Layered alkali transition metal oxides (i.e., LiMO2 and NaMO2, M=transition metal) are the premier class of cathode materials in lithium- and sodium-ion battery system. The safety characteristics of LiMO2 cathode based LIBs are one of the most critical barriers to be overcome for the large scale application such as EV. One of the main reasons that might cause safety hazards of the LIB is associated with the thermal instability of charged Li1-xMO2 cathode materials, which is related to the occurrence of exothermic reactions between flammable electrolyte and liberating oxygen from charged Li1-xMO2 at high temperature. Based on the structural homology between the layered LiMO2 and NaMO2, we expect that the investigation of thermal stability of charged Na1-xMO2cathode materials is also important for the practical use of SIBs. However, few attentions have been paid on safety issue of SIBs. In this study, the thermal stability of charged Na1-xMO2 cathode materials is investigated by using combined in situ time-resolved X-ray diffraction and mass spectroscopy (TR-XRD/MS), which allows simultaneous observation of the structural changes and gas species that are evolved during thermal decomposition of charged cathode materials, especially O2 gas in our interest. In addition, the ex situ/in situ X-ray absorption spectroscopy (XAS) has been also utilized to look at the local and electronic structural changes occurring during thermal decomposition in an elemental selective way. By utilizing combined X-ray techniques, we are able to get better understanding of structural and electronic structure changes in charged cathode materials during thermal decomposition. In this presentation, the thermal decomposition behavior of charged Na1-xMO2(M=Co, Cr) cathodes will be covered. Acknowledgement The work done at Brookhaven National Lab. was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. DOE under Contract No. DE-SC0012704.

A high performance layered transition metal oxide cathode material obtained by simultaneous aluminum and iron cationic substitution

The method of self-combustion synthesis was applied to prepare double Al- and Fe-substituted LiNi0.6Mn0.2Co0.15Al0.025Fe0.025O2 (NMCAF) and non-substituted LiNi0.6Mn0.2Co0.2O2 (NMC-3:1:1) cathode materials for lithium ion batteries. The novel NMCAF structure obtained by simultaneous cationic substitution showed an improved capacity and high stability during electrochemical cycling. X-ray diffraction patterns proved that both materials have a layered α-NaFeO2 type structure with a good hexagonal ordering. It was found that NMCAF has increased a and c lattice parameters due to a structural expansion caused by Al and Fe ion substitution. Rietveld refinement analysis revealed a significant decrease of the cationic mixing after the metal substitution, suggesting a structural stabilization. Electron paramagnetic resonance (EPR) spectroscopy showed that Al and Fe substitution markedly influenced the EPR spectrum of NMC-(3:1:1). The EPR spectral lines of both materials are attributed to Mn4+ and Ni2+ present in the structure. The change in the Ni2+ line after the metal substitution suggests a redistribution of the Ni ions in the structure, which can be related to the diminished cation mixing in the NMCAF. The improved electrochemical behavior of NMCAF is closely connected to the stabilization of the layered structure and the reduction of the cation mixing after metal substitution.

Synthesis and Electrochemical Properties of Novel Co2+/Co3+ Layered Ordered Rock-Salt Structure Type Li0.75Ca0.25CoO¬2

New layered transition metal oxide cathode material, Li0.75Ca0.25CoO2 (Space Group = P63/mmc; a = 2.817 Å, b = 2.817 Å, c = 10.79 Å ß = 120{degree sign}) was prepared by a multistep synthetic technique. Electrochemical cycling of 0.75 Li+ per formula unit utilizes both the Co3+/Co4+ and Co2+/Co3+ redox couples. The presence of Ca2+ between CoO2 layers results in low volume difference (~0.8%) between fully lithiated and delithiated materials.

Synthesis and electrochemical properties of layered lithium transition metal oxides

Layered lithium transition metal oxide cathode materials (Li1.2Ni0.2Mn0.6O2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2), of spherical morphology with primary nanoparticles assembled in secondary microparticles, were generally synthesized through a simple carbonate co-precipitation method. In this method, various carbonates such as Na2CO3, NaHCO3 and (NH4)2CO3 could be employed as the precipitants without careful control of the pH value. Aging treatment on the carbonate slurries at 80 °C could yield spherical microparticles assembled with very fine primary nanoparticles. The carbonate microparticle precursors were calcined at 500 °C and further lithiated at 900 °C to prepare the layered cathode materials. The as-prepared Li1.2Ni0.2Mn0.6O2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2 cathode materials could deliver a capacity of 230, 190 and 153 mAh g−1, respectively, at a charge–discharge current density of 25 mA g−1 in the voltage range of 2.5–4.6 V. When the charge–discharge current density was increased to 250 mA g−1, the Li1.2Ni0.2Mn0.6O2 and LiNi1/3Co1/3Mn1/3O2 showed an initial discharge capacity of 150 and 166 mAh g−1; as for the LiNi0.5Mn0.5O2, the discharge capacity decreased to 67 mAh g−1. After 150 cycles at a current density of 250 mA g−1, both LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2 showed a capacity decay rate of >25%, while the Li1.2Ni0.2Mn0.6O2 exhibited an excellent cycling performance with almost no capacity decay.

Mass production of cathode materials for lithium ion battery by flame type spray pyrolysis

Lithium transition metal oxide cathode materials such as LiAl0.05Mn1.95O4, LiNi0.5Mn1.5O4, LiCo1/3Ni1/3Mn1/3O2 were successfully produced at a rate of 2 kg/h by large flame type spray pyrolysis. The continuous spray pyrolysis of 250 h exhibited the good stability for powder production. The powder characteristics of them were determined by SEM, XRD, BET and AAS. Cathode materials had spherical morphology with a particle size of about 8 μm and porous microstructure with specific surface area of 10 m2/g. Their geometrical standard deviation of particle size ranged from 1.2 to 1.5. The chemical composition of them was in good agreement with that of the starting solution. The electrochemical measurement revealed that these cathode materials exhibited the higher rechargeable capacity, good cycle performance and thermal stability.

Electronic Properties of LiFePO4 and Li Doped LiFePO4

LiFePO4 has several advantages in comparison to transition metal oxide cathode material in commercial rechargeable lithium batteries. It has a high theoretical capacity (170 mAh/g). It occurs as the mineral triphylite in nature and is inexpensive, thermally stable, non-toxic and non-hygroscopic. However, its low intrinsic electronic conductivity (~ 10-9 S/cm) is problematic. We report here a study of the electronic properties of undoped LiFePO4 and Li doped material in which Li+ are substituted for Fe2+ ions in an attempt to increase the intrinsic electronic conductivity.

Soft mechanochemical synthesis: Preparation of cathode materials for rechargeable lithium batteries

To prepare intercalation lithium — transition metal oxide cathode materials for rechargeable lithium batteries, the reactions in the mixtures of the correspondent hydroxides in highly energetic planetary activators, so called ‘soft mechanochemical synthesis’ were studied. The method can be used for direct preparation of final products in a high dispersed and disordered state, as well as for obtaining high reactive precursors yielding final products by the subsequent brief heating at considerably lower temperatures as compared to conventional ceramic method. The as prepared products were analyzed using X-ray diffraction, TG, IRS, XPS, 7Li NMR, EPR, diffuse reflectance spectroscopy, electron microscopy, BET, and electrochemical measurements. The peculiarities of crystal structure, electronic state of transition metal ions and cycling behaviour of materials are discussed. The method as proposed is concluded to be economically effective and ecologically clean.

A theoretical study of lithium intercalation into V6O13—a combined classical, quantum mechanical approach

A theoretical study of lithium intercalation into the transition metal oxide cathode material, V6O13, is presented. A combination of classical and quantum mechanical computational simulation techniques are used to predict the stable sites occupied by inserted lithium ions, changes to the unit cell dimensions as lithium ions are incorporated, and changes to the electronic structure of the transition metal oxide host. Calculated total energies are used to determine the approximate discharge voltage of LixV6O13s. an anode of metallic lithium. Results obtained with different theoretical methods and experimental data are found to compare favourably. The LixV6O13 material represents a system of significant complexity, which clearly benefits from an approach using both classical and quantum mechanical methods.

Solution processing approaches for solid electrolytes and electrode materials

Solution processing methods have been used to prepare a solid electrolyte, copper-doped bismuth vanadate, and several different lithium transition metal oxide cathode materials. Dense thin films of the bismuth vanadate were prepared by pyrolysis of metal organic precursors deposited on various oxide substrates. A high degree of crystal orientation was obtained using single crystal MgO substrates. The Pechini process was used to prepare powders of the different materials and a variety of results were obtained. The bismuth vanadate exhibited a second phase of BiVO4 while LiNiO2 and the LiCoxNi1−xO2 solid solution require further efforts at obtaining the proper phase and stoichiometry. The LiCoO2 system formed readily and exhibited good electrochemical performance.

Structural aspects of transition metal oxide cathode materials for lithium batteries

Structural aspects of transition metal oxide cathode materials for lithium batteries