Electrochemical and theoretical investigation on the reaction of transition metals with Li3N

The electrochemical reactivity of Li₃N with transition metals (M = Mn, Fe, Co, Ni) is examined by discharge/charge, cyclic voltammetry, X-ray diffraction and X-ray photoelectron spectroscopy measurements. An attempt is made to understand this reversible electrochemical reaction of transition metals with Li₃N from the chemical reactions point of view. Density functional theoretical calculation results suggest that a stable complex MNLi₃ could be formed by the insertion of transition metal in Li₃N with exothermic as an intermediate, subsequent the decomposition process of these insertion compounds should make a main contribution to release Li.     

Mn/Co oxide on Ni foam as a bifunctional catalyst for Li–air cells

Binary Mn/Co oxide sheets with spherical flower-like hierarchical structure are grown directly on the surface of a Ni foam skeleton as a cathode for Li–O₂ batteries using a hydrothermal method. This integrated cathode architecture eliminates the negative effects of a conductive carbon additive and binder on the electrochemical performance of Li–O₂ batteries and minimizes the processing steps in fabrication of cathodes for Li–O₂ batteries. The porous Ni foam acts as a scaffold and current collector, and the highly hierarchical porous flower-like structure of the binary Mn/Co oxide sheet acts as a highly active catalyst. Together, they facilitate effective diffusion of oxygen gas as well as rapid ion and electron conduction during electrochemical reactions. When assembled in Li–O₂ cells, the prepared catalyst exhibits excellent catalytic activities, including the oxygen reduction and oxygen evolution reactions. In particular, the Li–O₂ cell using the cathode delivers an extremely high specific discharge capacity of 9690 mAh g^-1 under a applied specific current of 200 mA g^-1 and operate successfully in a long lifespan of 66 cycles even under a high specific current of 600 mA g^-1 and a limited discharge-charge capacity mode of 1000 mAh g^-1. The simultaneous effect of the fast electron transport kinetics provided by the free-standing structure and the high catalytic activity of the binary Mn/Co oxide show promise for use in air electrodes for Li–O₂ batteries.     

Recovery of Al,Co, Cu,Fe, Mn,and Ni from Spent LIBs after Li Selective Separation by the COOL-Process. Part 1: Leaching of Solid Residue from COOL-Process

Lithium recycling from spent LIBs along the COOL-process produces a Li-free metal rich black mass, which still contains the entire fraction of valuable metal such as Co, Ni, and Mn. A recycling process was developed, which allows for mobilizing these metals. The first process stage is the selective leaching of Li via COOL-process. Subsequently, two inorganic (H₂SO₄ and HCl) and two organics acids (citric and gluconic acid) were tested for mobilizing the metals from the solid residue. To optimize this process stage, acid concentration as well as addition of H₂O₂ as a reduction reagent were investigated. The optimal conditions to dissolve valuable metals such as Co, Cu, Fe, Mn, and Ni was identified as 2 N H₂SO₄ and 2 vol % H₂O₂.     

Electrochemical and quantum chemical studies of the reactions of transition metals M (M = Co, Fe and Ni) with LiF and Li2O

It has been a puzzle that transition metals can unexpectedly react with lithium-based matrixes of LiF and Li₂O in the potential versus Li/Li⁺ range from 0.01 to 3.5 V at room temperature. The electrochemical and theoretical investigations on the reactions of transition metals M (M = Co, Fe and Ni) with LiF and Li₂O were carried out. The electrochemical reactivity of metal cobalt with LiF and Li₂O has been examined by the discharge and charge, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. Density functional theoretical calculation results suggested that the stable compounds MLiF and MLi₂O could be formed by the insertion of transition metal (M) in lithium-based matrixes with exothermic as an intermediate. The theoretical calculations provide an understanding in chemical reaction of M with LiF and Li₂O. The small molecular or clusters reaction may play an important role in the electrochemical reaction of metal with transition Li₂O or LiF, which could be used to explain for the unexpectedly reaction of transition metal with LiF and Li₂O.     

High-voltage performance of concentration-gradient Li[Ni0.67Co0.15Mn0.18]O2 cathode material for lithium-ion batteries

A novel Li[Ni_0.67Co_0.15Mn_0.18]O₂ cathode material encapsulated completely within a concentration-gradient shell was successfully synthesized via co-precipitation. The Li[Ni_0.67Co_0.15Mn_0.18]O₂ has a core of Li[Ni_0.8Co_0.15Mn_0.05]O₂ that is rich in Ni, a concentration-gradient shell having decreasing Ni concentration and increasing Mn concentration toward the particle surface, and a stable outer-layer of Li[Ni_0.57Co_0.15Mn_0.28]O₂. The electrochemical and thermal properties of the material were investigated and compared to those of the core Li[Ni_0.8Co_0.15Mn_0.05]O₂ material alone. The discharge capacity of the concentration-gradient Li[Ni_0.67Co_0.15Mn_0.18]O₂ electrode increased with increasing upper cutoff voltage to 4.5 V, and cells with this cathode material delivered a very high capacity, 213 mAh/g, with excellent cycling stability even at 55 °C. The enhanced thermal and lithium intercalation stability of the Li[Ni_0.67Co_0.15Mn_0.18]O₂ was attributed to the gradual increase in tetravalent Mn concentration and decrease in Ni concentration in the concentration-gradient shell layer.     

Structural and magnetic characterizations of Co2MnO4 doped with Cr,Mn, Fe and Cu

The structural and magnetic properties of Co_2-xM_xMnO₄ (M= Cr, Mn, Fe and Cu) samples are investigated. Element substitution does not change the cubic lattice structure within a range of concentrations. There is a structural transition from cubic to tetragonal with the excessive addition of Mn atoms. The site preference of transition metal atoms influences the interatomic interactions in the oxide system. The interatomic interactions of Co₂MnO₄ and CoMn₂O₄ samples are analyzed though ZFC/FC curves, the transition temperatures of which are attributed to the combined effect of magnetic interactions in different sublattices. The magnetic structure is restructured by atomic substitution and site preference, resulting in the compositional dependence of magnetic properties.     

SHS of transition metal-oxide systems in a DC magnetic field: Part 2. TRXRD,thermal imaging,and chemomagnetic studies of metal-oxide systems

The effect of an external magnetic field of 0.2 T on the SHS of a mixture of first row transition metals (Fe, Ti, Mn, Co, and Ni) and their oxides (Fe₃O₄, TiO₂, MnO, Co₃O₄, and NiO) with solid-state oxidizer (NaClO₄) was studied. Time resolved X-ray diffraction (TRXRD) was used to study the kinetics of intermediate product formation. Thermal imaging experiments were used to measure the reaction temperature and velocity as well as chemomagnetic signals to look for the phase transformations in combustion wave. We show that under conditions of applied field in the Fe/Fe₃O₄ system the fcc iron is formed during the metal-oxide transformation. For the Ni/NiO/NaClO₄ system, a new metastable cubic phase eith lattice parameter 3.6 d metal-oxide systems (such as Ti, Mn, Co, and Ni) combustion are briefly described.     

Structure and electrochemical characterization of LiNi<Subscript>0.3</Subscript>Co<Subscript>0.3</Subscript>Mn<Subscript>0.3</Subscript>Fe<Subscript>0.1</Subscript>O<Subscript>2</Subscript> cathode for lithium secondary battery

A lithium insertion material having the composition LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ was synthesized by simple sol-gel method. The structural and electrochemical properties of the sample were investigated using X-ray diffraction spectroscopy (XRD) and the galvanostatic charge-discharge method. Rietvelt analysis of the XRD patterns shows that this compound can be classified as α-NaFeO₂ structure type (R3m; a=2.8689(5) Å and 14.296(5) Å in hexagonal setting). Rietvelt fitting shows that a relatively large amount of Fe and Ni ion occupy the Li layer (3a site) and a relatively large amount of Li occupies the transition metal layer (3b site). LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ when cycled in the voltage range 4.3–2.8 V gives an initial discharge capacity of 120 mAh/g, and stable cycling performance. LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ in the voltage range 2.8–4.5 V has a discharge capacity of 140 mAh/g, and exhibits a significant loss in capacity during cycling. Ex-situ XRD measurements were performed to study the structure changes of the samples after cycling between 2.8–4.3 V and 2.8–4.5 V for 20 cycles. The XRD and electrochemical results suggested that cation mixing in this layered structure oxide could be causing degradation of the cell capacity.     

Electrochemical Quartz Microbalance characterization of Ni(OH)2-based thin film electrodes

The use of the Electrochemical Quartz Crystal Microbalance (EQCM) to study the proton intercalation performance of thin film Ni(OH)₂ layers, nowadays widely used as cathode electrode material in rechargeable Ni(OH)₂-based battery systems such as NiMH and NiCd, is reviewed. In addition, the impact of incorporating foreign metals in these layers on the electrochemical performance will be highlighted.Using EQCM much information can be obtained, as both the electrochemical response and accompanying mass changes can be measured simultaneously. EQCM was extensively used to investigate the effect of the conditions on the formation of Ni(OH)₂ thin layers, the α-to-β modification changes and the details of the redox mechanism. The proposed redox mechanisms differ in whether H⁺ or OH⁻ is transferred, the reactants and/or products are hydrated and cations from the solution take part in the reaction.By incorporation of other metals in the structure, the characteristics of thin Ni(OH)₂ layers can be tuned. This affects the oxidation and reduction potential, the reversibility, the stability of the structure and the oxygen evolution side reaction. Co²⁺ and Fe²⁺ were shown to replace Ni-sites in the hydrous oxide lattice, thereby forming very dense structures with higher stability. However, structural changes still occur in most cases. Due to this inhomogeneity, the layers are usually a combination of different structures, depending on the distribution of the incorporated metal(s). Suppression of the oxygen evolution reaction is reported for Co, Pb, Pd, Zn and Mn. The effects of Co and Mn are shown to depend on the incorporated amount. Co shifts the standard redox potential for the oxygen evolution reaction towards more cathodic potentials and decreases the oxygen overpotential significantly. Light-weight rare-earth elements also catalyze the oxygen evolution reaction.     

锂离子正极材料Li（Ni_（1/3）Co_（1/3）Mn_（1/3））O_（2-x）F_x的合成与电化学性能

采用沉淀法合成一系列Li（Ni1/3Co1/3Mn1/3）O2-xFx正极材料（0≤x≤0.5）;用X射线衍射仪和扫描电镜仪分析了合成产物的晶体结构及表面形貌;利用充放电仪测定产物的电化学性能,结果表明Li（Ni1/3Co1/3Mn1/3）O1.7F0.3的电化学性能最佳,首次充放电比容量分别达181.9、174.0 mA.h/g,材料的结构在循环过程中保持稳定,倍率性能变好,电化学阻抗明显降低。     

Hydrothermal synthesis of LiNixCo1−xO2 cathode materials

Ultrafine powders of LiCoO₂, nonstoichiometric LiNiO₂ and LiNi_0.9Co_0.1O₂ were prepared under mild hydrothermal conditions. The influence of the molar ratio of Li/Co, Li/Ni and Li/(Ni + Co) was studied. The final products were investigated by XRD, TEM and EDS. To synthesize a stoichiometric LiNiO₂ under mild hydrothermal conditions was found to be a big challenge. Transmission electron microscopies (TEM) revealed the formation of well-crystallized LiCoO₂ and LiNi_0.9Co_0.1O₂ with average size of 100 nm and 10 nm, respectively.     

Effect of lithium extraction on the stabilities,electrochemical properties,and bonding characteristics of LiFePO4 cathode materials: A first-principles investigation

The impact of lithium extraction on the structural stabilities, electronic structures, bonding characteristics, and electrochemical performances of LiFePO₄ compound was investigated by first-principles technique. The results demonstrated that the partition scheme of electrons not only affects the calculated atomic charges but also the magnetic properties. In FePO₄ and LiFePO₄ compounds, all Fe ions take high spin arrangements and have large magnetic moments (MMs), while the MMs of other ions are very small. The magnetisms of Li_xFePO₄ compounds are mainly originated form Fe ions. It was found that the changes in d band electrons of the transition metals do play an important role in determining the voltage of a battery (versus Li/Li⁺). Furthermore, the variations in d band electrons also provide us a method to control the density of states (DOS) and carrier concentration at the Fermi energy. Our calculations confirmed that the substitution of Fe by Co and Ni ions leads to a voltage increase by about 0.70 V and 1.23 V respectively. According to the bond populations, it can be identified that strong covalent bonds are formed between O and P ions. The P–O bonds are much stronger than Fe–O ones. The partial DOSs further revealed that the covalent bonds in Li_xFePO₄ are derived from the orbital overlaps between O_2s,2p and P_3s,3p states, and the overlap between Fe_3d and O_2p states. Such covalent bonds are of particularly importance for the excellent thermodynamic stabilities of the two-ends structures of Li_xFePO₄.     

Exafs investigations of Fe-, Ni-, Co- and Cu- MoS2/γ-Al2O3 hydrodesulphurization catalyst systems

In-situ EXAFS studies have been carried out on several transition metal (T)-MoS₂ (T = Fe, Co, Ni or Cu) catalysts supported on -Al₂O₃. While Mo is present in small crystallites of MoS₂ in all the systems studied, the local sulphidic environment around the transition metal atom varies significantly with the catalytic activity. Short T-S distances (compared to the bulk sulphides) are found in the case of the Ni and Co catalysts due to the formation of the active Ni(Co)-Mo-S state. In the case of Fe, which is not a good promoter, the Fe-S distance in the catalyst is only slightly shorter than in the bulk sulphides. No such short distance is found in the Cu-MoS₂/Al₂O₃ system since Cu acts as a poison; instead only bulk sulphides are formed. Effects of the method of preparation, order of impregnation, metal loading and other factors have been examined to arrive at the conditions favourable for the formation of the active Ni(Co)-Mo-S state.Contribution No. 774 from the Solid State & Structural Chemistry Unit.     

Local atomic characterization of LiCo1/3Ni1/3Mn1/3O2 cathode material

Co, Ni and Mn K-edge XAFS investigation of LiCo_1/3Ni_1/3Mn_1/3O₂ as alternative cathode material to commercially used LiCoO₂ in lithium rechargeable battery has been performed. Parameters of a local atomic structure such as radii of metal-oxygen and metal-metal coordination shells and disorder in those shells have been determined. It has been found that the radius of the first coordination shell (metal-oxygen) as well as a local disorder in the second shell (metal-metal) around each of the 3d-metals are in a good agreement with obtained for superlattice model of [√3 × √3] R30° type in triangular lattice of sites by first principle calculation. Other parameters of the local atomic structure around Co, Ni and Mn atoms do not provide evidence for presence of superstructure in LiCo_1/3Ni_1/3Mn_1/3O₂.     

镍钴锰酸锂三元正极材料的研究与应用

镍钴锰酸锂三元材料的化学组成最初出现在20世纪90年代末期的钴酸锂和镍酸锂的掺杂研究中,其作为独立体系材料的研发开始于2001年。在该化合物中,镍呈现正二价,是主要的电化学活性元素;锰呈现正四价,不参与电化学反应,只对材料的结构稳定性和热稳定性提供保证;钴是正三价,部分参与电化学反应,其主要作用是保证材料层状结构的规整度、降低材料电化学极化、提高其倍率性能。该材料具有比容量高、高电压下结构稳定、安全性较好等优点,是目前看来最有应用前景的一种锂离子电池正极材料。     

Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

CO₂ reforming of methane was studied over modified Ni/Al₂O₃ catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al₂O₃, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO₂ reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of A- and B-site doping on the properties of the system La2CoO4±δ

In the present paper the compounds LaSrCo_0.5M_0.5O_4±δ (M = Co, Fe, Mn, Ni) and La_1.4Sr_0.6Co_0.5M_0.5O_4±δ (M = Co, Ni) were prepared and characterised in order to elucidate the influence of strontium doping on A-site as well as doping with transition metals on B-site of the mixed conductor La₂CoO_4±δ. All the prepared oxides of this paper possessed the K₂NiF₄ structure, exhibited high electrical conductivity (>100 S/cm) and adequately low linear thermal expansion coefficient. Therefore, they are very promising materials for high temperature electrochemical applications.     

Electrochemical properties of Li[Ni1/3Mn1/3Al1/3−xCox]O2 as a cathode material for lithium ion battery

Layered Li[Ni_1/3Mn_1/3Al_1/3−xCo_x]O₂ (0 ≤ x ≤ 1/3) cathode materials are synthesized by a solvent evaporation method. Although XRD shows that Li[Ni_1/3Mn_1/3Al_1/3]O₂ has no obvious impurity phase, it has poor electrochemical properties. To improve its capability, part of Al in Li[Ni_1/3Mn_1/3Al_1/3]O₂ compound is replaced by Co in this study. The samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and charge–discharge test. The results indicate that the introduction of Co has a large influence on the morphology, structure and electrochemical performances of the samples, which become more excellent with an increase of Co content in compounds. Meanwhile, the high-temperature behavior of the samples is also investigated.     

Preparation,characterization and comparative electrochemical studies of MgMXMn2-XO4 (x=0, 0.5; M= Ni/Co)

In this study, the structural, electrical and electrochemical properties of the compounds MgM_xMn_2-xO₄ [M = Ni/Co: x = 0,0.5] were investigated by preparing the materials by the citric acid assisted simple, cost effective sol-gel method. X-ray Diffraction (XRD) confirmed that Ni/Co doping created a phase transition of MgMn₂O₄ from tetragonal spinel-structure with a space group of I4₁/amd to a cubic spinel structure with a space group of Fd-3m. HRTEM and SAED analysis showed the bare compound to be polycrystalline and doped compounds to be single crystalline in nature. SEM analysis showed the agglomerated submicron sized particles for all the three compounds. The electrical properties of the compounds have been investigated through AC impedance spectroscopy. The electrical conductivity of the bare compound MgMn₂O₄ was found to be 5.09 × 10⁻⁶ S/cm at 583 K. Cyclic Voltammetry (CV) and Galvanostatic Charge-Discharge (GCD) studies made by the three electrode system shows that all the samples under study could undergo reversible redox reactions in the aqueous magnesium nitrate solution. MgMn₂O₄ sample exhibited highest specific discharge capacity of 263 mAh/g at the current density of 30 mA/g.     

Spray-drying synthesized LiNi0.6Co0.2Mn0.2O2 and its electrochemical performance as cathode materials for lithium ion batteries

Layered LiNi_0.6Co_0.2Mn_0.2O₂ materials were synthesized at different sintering temperatures using spray-drying precursor with molar ratio of Li/Me = 1.04 (Me = transition metals). The influences of sintering temperature on crystal structure, morphology and electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and charge-discharge test. As a result, material synthesized at 850 °C has excellent electrochemical performance, delivering an initial discharge capacity of 173.1 mAh g^− 1 between 2.8 and 4.3 V at a current density of 16 mA g^− 1 and exhibiting good cycling performance.