Li Secondary Batteries Research Articles

In Situ XAFS Analysis of Li(Mn, M)2O4 (M=Cr, Co, Ni) 5V Cathode Materials for Lithium-Ion Secondary Batteries

Chemical states and structural changes accompanying the electrochemical Li deintercalation of Li1−x(Mn, M)2O4 (M=Cr, Co, Ni) were studied by the in situ X-ray absorption fine structure (XAFS) technique. The X-ray absorption near-edge structures (XANES) of Mn and M as a function of x showed that the high voltage (∼5 V) in the cathode materials of an Li secondary battery is due to the oxidation of M3+ to M4+ (M=Cr, Co) and M2+ to M4+ (in the case of M=Ni), while the origin of the low voltage (3.9–4.3 V) can be ascribed to the oxidation of Mn3+ to Mn4+. The extended X-ray absorption fine structure (EXAFS) analysis of Li1−x(Mn,Ni)2O4 revealed that Ni2+ is oxidized to Ni4+ via the Ni3+ state with a Jahn–Teller distorted Ni3+–O octahedron.

Relationship between the charge capacity of a turbostratic carbon anode for a Li secondary battery and its structure

Relationship between the charge capacity of a turbostratic carbon anode for a Li secondary battery and its structure

Synthesis and characterization of MnV 2O 6 as a high capacity anode material for a lithium secondary battery

Crystalline MnV 2O 6 has been synthesized by a polymer gellation method and investigated for its physical and electrochemical properties as an anode material for Li secondary battery. The physical characterization was carried out by thermal analysis (TG/DTA), FT–IR and SEM. Structural analysis by powder XRD and spectroscopic analysis by XANES showed that the synthesized compound is MnV 2O 6 with brannerite structure. The Li insertion of MnV 2O 6 anode during the first charge showed a large capacity of about 1400 mAh/g, accompanied by irreversible structural transformation into amorphous material. Despite its structural transformation to amorphous during the first lithiation, subsequent cycles showed a capacity of about 800 mAh/g. This paper presents the advantage of this material over existing anode material and discusses the mechanism underlying the electrode process.

Degradation mechanisms in doped spinels of LiM 0.05Mri 1.95O 4 (M = Li, B, Al, Co, and Ni) for Li secondary batteries

Degradation mechanisms in doped spinels of LiM 0.05Mri 1.95O 4 (M = Li, B, Al, Co, and Ni) for Li secondary batteries

The charge/discharge mechanism of polyaniline films doped with LiBF 4 as a polymer electrode in a Li secondary battery

The electrical conductivity of polyaniline films doped with 1 M LiBF 4 is ∼0.082 S/cm. The discharge capacity is increased with cycling and then saturates at more than 15 cycles. We obtained a saturated discharge capacity of about ∼40 mAh/g, which is only about 28% of the theoretical capacity. The solution conductivity is continuously decreased as the Li salt concentration is reduced. The Li salt concentration in the electrolyte and the concentration of Li salt as a doping agent affects the charge/discharge reaction. By the analysis of dc conductivity, XPS, and ESR data, the charging mechanism is explained by a charge separation mechanism which depends on the concentration of ionic salt in the electrolyte.

Electrochemical characteristics of Mg–Ni alloys as anode materials for secondary Li batteries

The electrochemical characteristics of Mg and several Mg–Ni alloys were studied as alternatives to anode materials for secondary Li batteries. Li was alloyed and dealloyed reversibly with Mg at very low voltage region (below 100 mV vs. Li/Li +), and the initial capacity obtained was approximately 3070 mA h/g. Alloys of Mg 50Ni 50, Mg 67Ni 33 and Mg 75Ni 25 were prepared by mechanical alloying and characterized using X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Mg 50Ni 50 and Mg 67Ni 33 were found amorphous and crystalline, respectively, while Mg 75Ni 25 was a mixture of Mg and Mg 2Ni phases. Electrochemical tests with these Mg–Ni alloys demonstrated that only Mg 75Ni 25 reacted significantly with Li at room temperature while Mg 67Ni 33 reacted with Li at high temperature. Mg 75Ni 25 showed enhanced cycle performance compared to that of pure Mg.

Chemical and Electrochemical Characterization of a Novel Nanocomposite Formed from V 2 O 5 and Poly(N‐propane sulfonic acid aniline), a Self‐Doped Polyaniline

Synthesis and characterization of new nanocomposites of and a sulfonated, alkylated polyaniline derivative [poly(N‐propane sulfonic acid aniline), PSPAN] are described. Two types of nanocomposites have been produced, one by reaction of vanadium triisopropoxide solutions with N‐propane sulfonic acid aniline and one by addition of to these same solutions. Nanocomposites are characterized using thermal gravimetric analysis, differencial scanning calorimetry (DSC), cyclic voltammetry, chronopotentiometry, and impedance spectroscopy. The increase of the 001 reflection spacing, X‐ray diffraction results show that the polymer is intercalated into the interlayer region, consistent with the nanocomposite nature of the material. The DSC and infrared data suggest that water coordinated to vanadium sites exposed to the interlayer region is lost during formation of the nanocomposite. SEMs show that, in contrast to the relatively flat and featureless thin films, the nanocomposites are highly textured and have quite small feature sizes. Electrochemical results show that some of the nanocomposites have larger specific capacity (307 Ah/kg) and faster reduction kinetics than and similar cyclability. The relevance of these results to general approaches to the production of nanocomposites for Li secondary battery cathodes is discussed. © 2000 The Electrochemical Society. All rights reserved.

Degradation mechanisms in doped spinels of LiM 0.05Mn 1.95O 4 (M=Li, B, Al, Co, and Ni) for Li secondary batteries

Spinel lithium manganese oxides with a nominal composition of LiM 0.05Mn 1.95O 4 (M=Mn, Li, Al, Co, Ni, or B) are prepared and their degradation mechanisms encountered in lithium secondary cells are investigated. Among the degradation mechanisms proposed in previous reports, those arising either from cation mixing or from the formation of oxygen-deficient spinels are negligible in these materials, but a certain amount of spinel dissolution is observed. X-ray diffraction (XRD) analysis indicates that the spinel lattice experiences an appreciable change in volume during charge–discharge cycling. The extent of this change depends on the nature of dopant. Compared to the undoped spinel, the lattice expansion/contraction according to Li + insertion/removal is more significant in the B-doped spinel, but it is smaller in the case of Ni-, Co-, Al-, or Li-doped spinels. Spinels experiencing a smaller volume change maintain their structural integrity, even after prolonged cell cycling, such that there is a better capacity retention. In the B-doped spinel, however, the spinel lattice is largely collapsed and new phases are formed after cell cycling. This results in poor cycleability. It is proposed that the structural breakdown due to the repeated change in lattice volume is the most important failure mode in these materials. Spinel dissolution plays a second major role.

Electrolytic characteristics of ethylene carbonate–diglyme-based electrolytes for lithium batteries

Dependencies of viscosity ( η) and conductivity ( κ) on temperature and solvent composition are examined for solutions of LiPF 6 and of LiClO 4 in ethylene carbonate (EC):diglyme (DG) binary mixtures to identify organic electrolyte systems with the highest conductivity as possible at room temperature. The energies of activation for viscous flow and for conductivity, determined as functions of the composition of the mixed solvent, show these two transport processes to be strongly related. Conductivities of electrolyte solutions prepared with LiPF 6 and LiClO 4 are comparable, but lower activation energy is required for LiClO 4. A flat maximum of conductivity at about 50% (v/v) in EC is observed when the composition of the mixed solvent is varied. A high value, independent of the considered temperature, has been found for the product κ η, meaning that free ions are the predominant ionic species in these media. As a consequence, the macroscopic viscosity of electrolytes under study mainly governs their conductivity. Cyclic voltammetry, performed on negative (Li x C) and positive (Li x NiO 2) intercalation electrodes in the optimized electrolyte (LiClO 4 or LiPF 6 (1 M)-50:50 EC:DG), gives evidence for the formation of passive layers during the first cycle and reversible electrochemical intercalation during the following cycles. DSC results show that this electrolyte system is a potential candidate for Li secondary batteries or electrochromic devices working at ambient or higher temperatures as it is safe and stable at least to 200°C.

Factors Controlling the Stability of O3− and P2‐Type Layered MnO2 Structures and Spinel Transition Tendency in Li Secondary Batteries

Cathode properties of two layered manganese dioxides , where A is the pillaring alkali cations) having different crystal structures were compared in 3 V Li secondary batteries. The materials were prepared from the mixture of , LiOH, and MnO at 800 and 1050°C, respectively. The 800°C‐prepared has a trigonal space group with an O3‐type oxide‐packing pattern, whereas the 1050°C material has an orthorhombic Cmcm symmetry with a P2‐type oxide‐packing pattern. The gallery space where the pillaring cations and water molecules reside is wider in the case of the 800°C material. Due to the higher mobility of pillaring cations in the 800°C material and similarity in the oxide‐packing pattern (O3‐type) to the spinel phases, the pillaring cations are easily leached out during cell cycling, which ultimately leads to a lattice collapse and structural transition to the spinel‐related phases. By contrast, as the 1050°C material has rather immobile pillaring cations and its oxide‐packing pattern (P2‐type) is far different from that of the spinel phases, this cathode shows better cycling performance, with its structural integrity being well maintained. © 2000 The Electrochemical Society. All rights reserved.

Relationship between the charge capacity of a turbostratic carbon anode for a Li secondary battery and its structure

The relation between the charge capacity of a turbostratic carbon anode for a lithium secondary battery and carbon structure was investigated using mesocarbon microbeads, and a new theoretical equation for estimating the charge capacity was proposed. There was a linearity between the observed charge capacity and Warren's P value, which denotes the 1 probability for finding the AB-stacking area in a pair of adjacent carbon layer planes. Fourier analysis of X-ray diffraction patterns proposed by Houska and Warren revealed that an island structure composed of AA- and AB-stacking area by the rotational misorientation existed. Such an island structure reduced the formation area of in-plane ordering of stage I lithium-intercalated graphite LiC , because the intercalation reaction of Li into graphite requires the slipping of AB-stacking 6 )) ˛˛ to AA for the formation of the super lattice, p (3 3 3)R308. © 2000 Elsevier Science Ltd. All rights reserved.

Synthesis of LiCoO2 using acrylic acid and its electrochemical properties for Li secondary batteries

LiCoO2 powders were synthesized by the sol–gel process at various temperatures using acrylic acid as a chelating agent and their structural and electrochemical properties were systematically investigated by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), Electrochemical voltage spectroscopy (EVS), cyclic voltammetry (CV), and galvanostatic charge/discharge experiments. In this study, the gel-derived LiCoO2 samples calcined at 600°C or above were found to be a well-developed layered high temperature-LiCoO2 (HT-LiCoO2) . In the EVS of all the gel-derived HT-LiCoO2 samples, the peak potential separation of 10 mV was observed regardless of the calcination temperature, indicating that these samples have basically the same thermodynamic reversibility for intercalation/deintercalation of Li ions. The change of the main peak potentials and currents in cyclic voltammograms with increasing calcination temperature could be explained by the effect of particle size.

Synthesis and characterization of LiAlyCo1−yO2 and LiAlyNi1−yO2

Abstract Aluminum is of interest as a constituent in Li secondary battery cathodes due to its low cost and low mass. Increased intercalation potential for certain Al-doped intercalation oxides has also been predicted by ab initio calculations. We have synthesized single phase LiAl y Co 1− y O 2 and LiAl y Ni 1− y O 2 solid solutions from homogeneous hydroxide precursors. In LiAl y Ni 1− y O 2 , it was found that the addition of LiAlO 2 helps to stabilize LiNiO 2 in the α-NaFeO 2 structure during air firing, facilitating preparation of the ordered phase. A systematic increase in the open circuit voltage is observed with Al content in both LiAl y Co 1− y O 2 and LiAl y Ni 1− y O 2 solid solution, providing additional support for the ab initio calculations.

Synthesis, electrochemical, and microstructural study of precursor-derived LiMn2O4 powders

Stable and homogeneous alkoxide precursor solutions of lithium ethoxyethoxide and manganese ethoxyethoxide in 2-ethoxyethanol were synthesized by ligand exchange reaction of lithium isopropoxide and manganese 2-ethoxide, respectively, with 2-ethoxyethanol. [Li–Mn–O] precursor solution was prepared by mixing these modified alkoxide precursor solutions. LiMn2O4 powders were successfully synthesized by pyrolysis of the [Li–Mn–O] precursor powder in O2 temperature as low as 200 °C. The nanocrystalline LiMn2O4 powders 20–50 mm in diameter after heat treatment up to 700 °C consisted of the ordered (111) plane and performed with good cyclability as the cathode materials for Li secondary batteries.

A Mechanistic Study of the Influence of Proton Transfer Processes on the Behavior of Thiol/Disulfide Redox Couples

The mechanism of the oxidation of 2-mercapto-5-methyl-1,3,4-thiadiazole (McMT) to its disulfide dimer and its subsequent reduction has been examined with a combined approach employing experimental data and digital simulation. In order to elucidate the influence of proton transfers on these redox processes, special attention has been paid to the influence of various bases, including triethylamine, pyridine, 3-chloropyridine, lutidine and 2,6-di-tert-butylpyridine, and proton donors, including methanesulfonic acid and trifluoromethanesulfonic acid, on both the oxidation and reduction reactions. On the basis of detailed comparisons of the experimental data with simulations of several mechanistic models, it is found that proton transfer pathways have a pronounced influence on both the oxidative and reductive pathways. In particular, McMT oxidation is facilitated by a rapid bimolecular proton transfer from McMT to weak bases such as Py that produces McMT-, the thiolate form, which is then oxidized. There is no such facilitation in the presence of the sterically hindered base 2,6-di-tert-butylpyridine, suggesting that the facilitation occurs through the formation of a discrete hydrogen-bonded complex. The overall kinetic scheme by which these redox processes proceed both in the presence and absence of proton transfer agents is discussed, especially with regard to the potential use of a related dithiolate compound as a cathode material in Li secondary batteries.

Preparation of Layered MnO2 via Thermal Decomposition of KMnO4 and Its Electrochemical Characterizations

We report here the preparation of layered MnO2 and the preliminary results on its cathodic performance in Li secondary batteries. The thermal decomposition of KMnO4 powder at 250−1000 °C in air produces KxMnO2+δ·yH2O (x = 0.27−0.31, δ = 0.07−0.13, and y = 0.47−0.89) with a product yield of 67−79% based on the Mn molar quantity. It can be judged from the Rietveld refinement on the X-ray diffraction pattern that the 800 °C-prepared sample has a layered structure (hexagonal unit cell, space group = P63/mmc, a = 2.84 Å, and c = 14.16 Å), where the K+ ions and H2O molecules reside at the interlayer trigonal prismatic sites (P2-type structure). Contrary to the previous findings whereby the layered MnO2 transforms to α-/γ-MnO2 phases or manganese suboxides at >450 °C, such impurities are negligible in this synthesis even at higher temperatures. The success of synthesis is ascribed to the high population of K+ ions in the pyrolyzing media that act as pillaring cations to stabilize the layered framework. In addition, the absence of a suboxide transition is indebted to the highly oxidizing species such as O2, MnO42- and MnO43-, which are produced during the pyrolyzing process. The materials show a powder density as high as 1.36 g cm-3 and the Mn4+ fraction of >85%, which gives a theoretical capacity of 210−230 mA h g-1 based on a one-electron charge/discharge reaction. A higher product yield up to >98% is achieved by pyrolyzing KMnO4 with an addition of manganese suboxides (Mn2O3, Mn3O4, or MnO). Finally, the preliminary cell tests show that the materials give some promising features as the cathode materials for Li secondary batteries.

Anodic Properties of Needle Cokes-derived Graphitic Materials in Lithium Secondary Batteries

Two needle cokes (NC-A and NC-B) that differ in both the texture and impurity content to each other were graphitized at , and the average particle size, size distribution and surface area were compared after milling. Their anodic properties in Li secondary batteries were also analyzed. Two materials showed a higher degree of graphitization with an increase in the preparation temperature, however, the NC-B series was less graphitized than NC-A due to the presence of impurities and less ordered mosaic texture. The mein particle size of the milled powder was proportional to the degree of graphitization, but the surface area showed the opposite trend. The highly graphitized materials yielded powders of lower uniformity in the size distribution. The discharge capacity of the resulting carbons steadily decreased in the temperature range of 1000 to due to the depletion of carbonaceous interlayers that contain crystal defects. A later increase in the discharge capacity was observed at $>2000^{\circ}C$, which arises from the formation of graphitic interlayers. The milling process gave rise to a sloping discharge curve at >1.0 V, but this was converted to a plateau at . The discharge at >1.0V likely comes from the disordered surface structure formed during the milling process. The evolution of a plateau at

メカニカルアロイング（ＭＡ）によるリチウム二次電池用ＬｉＭｎ２Ｏ４スピネルの試作

Lithium manganese spinel (LiMn2O4) for Li-secondary battery was prepared by mechanical milling of raw materials in a argon atmosphere for 200 h. After milling and heating at 823 K for 3 h, the powder was observed X-ray diffraction pattern of lithium manganese spinel structure. The average milling powder diameter was approximately .0.1μm.The compounds of the MA-Li1.02Mn2O4 powder heated at 973 K for 3 h was evaluated as a 4 V cathode in a lithium non aqueous cell. The MA-Li1.02Mn2O4 have 136 Ah/kg of second discharge capacity.

The Hydrothermal Synthesis of KzMnO2 in the Presence of Citric Acid

ABSTRACTKxMnO2 exhibits a layered structure that provides attractive properties as a cathode material for secondary Li batteries. Therefore, in the present study, our attention was paid to the hydrothermal preparation of highly homogenous KxMnO2 in presence of citric acid. Out X-ray diffraction and SEM studies indicated that the final product markedly change the phase and morphology on vary the concentration of citric acid. The prepared products have also studied with the help of TGA and DTA. EDS and DCP made the chemical analysis of the compounds. The impedance data of the materials were explained in terms of the compounds formed.

First‐Principles Prediction of Insertion Potentials in Li‐Mn Oxides for Secondary Li Batteries

First‐principles methods have started to be widely used in materials science for the prediction of properties of metals, alloys, and compounds. In this study, we demonstrate how first‐principles methods can be used to predict the average open‐circuit voltage that can be obtained from a lithium battery with spinel or layered manganese oxides used as the cathode. For this purpose we combine a basic thermodynamical model with the ab initio pseudopotential method. The good agreement between the computed and experimental average output potentials suggests that first‐principles methods can be an important tool to design novel battery materials.