Electrodes For Rechargeable Lithium Batteries Research Articles

TEM Study of Electrochemical Cycling‐Induced Damage and Disorder in LiCoO2 Cathodes for Rechargeable Lithium Batteries

Among lithium transition metal oxides used as intercalation electrodes for rechargeable lithium batteries, is considered to be the most stable in the structure type. It has previously been believed that cation ordering is unaffected by repeated electrochemical removal and insertion. We have conducted direct observations, at the particle scale, of damage and cation disorder induced in cathodes by electrochemical cycling. Using transmission electron microscopy imaging and electron diffraction, it was found that (i) individual particles in a cathode cycled from 2.5 to 4.35 V against a Li anode are subject to widely varying degrees of damage; (ii) cycling induces severe strain, high defect densities, and occasional fracture of particles; and (iii) severely strained particles exhibit two types of cation disorder, defects on octahedral site layers (including cation substitutions and vacancies) as well as a partial transformation to spinel tetrahedral site ordering. The damage and cation disorder are localized and have not been detected by conventional bulk characterization techniques such as X‐ray or neutron diffraction. Cumulative damage of this nature may be responsible for property degradation during overcharging or in long‐term cycling of rechargeable lithium batteries. © 1999 The Electrochemical Society. All rights reserved.

Electrophoretic Fabrication of Positive Electrodes for Rechargeable Lithium Batteries

Electrophoretic Fabrication of Positive Electrodes for Rechargeable Lithium Batteries

Electrochemical Properties of Li-Zn Alloy Electrodes Prepared by Kinetically Controlled Vapor Deposition for Lithium Batteries

A Li-Zn alloy electrode prepared by a kinetically controlled vapor deposition (KCVD) is examined for use as the negative electrode for rechargeable lithium batteries. Results indicate that filamentary or dendritic growth of lithium on a Li-Zn alloy electrode prepared by the KCVD technique are dramatically suppressed due to fast diffusion of lithium in the alloy electrode, suggesting that the Li-Zn prepared by the KCVD method may be used effectively to improve the rechargeability of negative electrodes. © 2000 The Electrochemical Society. S1099-0062(00)02-103-9. All rights reserved.

ChemInform Abstract: The Intercalation Compound Li(Mn0.9Co0.1)O2 as a Positive Electrode for Rechargeable Lithium Batteries.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Improving the performance of graphite anodes in rechargeable lithium batteries

A low cost graphite was examined as a negative electrode for rechargeable lithium batteries. The use of an electrolyte solution consisting of LiPF6 (1 mol dm−3) in ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 2:1 resulted in a capacity loss of 35% on the first cycle. When small quantities of dimethyl pyrocarbonate (DMPC) were added to the binary electrolyte system, the capacity loss on the first cycle was only 18% and thereafter a practical capacity value of 357 mA h g−1 was sustained for more than 50 cycles, representing more than 2000 h of cycling.

Fabrication of LiV2O5 thin-film electrodes for rechargeable lithium batteries

LiV2O5 thin-film electrodes have been prepared for the first time by using the plasma enhanced chemical vapor deposition (PECVD) technique. A novel lithium precursor, lithium hexafluoroisopropoxide ((CF3)2CHOLi), has been synthesized to take advantage of its low sublimation temperature (∼50°C). Vanadium oxytrichloride (VOCl3) is used as the vanadium precursor. These two precursors are introduced into the plasma chamber by using argon as the carrier gas. Hydrogen and oxygen gases are also introduced into the chamber to facilitate the reactions. The gas compositions in the chamber and other deposition conditions have been optimized to obtain LiV2O5 films. The structure and electrochemical properties of the films depend strongly on the substrate temperature and deposition power. The optimized substrate temperature and radiofrequency (RF) power are 250°C and 50 W, respectively. The charge capacity of the film is approximately 300 mA/h/cm3, with two plateaus at 3.5–3.6 V on the discharge profile. The films can be cycled reversibly in the range of 0<x<1 (in LixV2O5) for 2000 cycles with a capacity loss of 0.0076% per cycle and are good candidates for use as the cathode in thin-film lithium ion batteries.

Thermodynamics of Oxides with Substitutional Disorder: A Microscopic Model and Evaluation of Important Energy Contributions

The first‐principles calculation of finite‐temperature phase stability and thermodynamic properties of multicomponent oxides presents a significant challenge. The time scale on which substitutional disorder occurs prevents the use of standard simulation methods, and a correct description of entropic effects requires that excitation energies can be calculated accurately on the scale of kBT. A model is presented in which substitutional disorder is parameterized with a cluster expansion. The thermodynamics of this model can be easily obtained with lattice model statistical mechanics. The only input required to the procedure is a description of bonding in the system, which is used to calculate the energy of ordered ionic configurations. This method is applied to the CaO‐MgO, Gd2O3‐ZrO2, CaO‐ZrO2 systems, and to LixCoO2 (x between 0 and 1) electrodes for rechargeable lithium batteries. In almost all cases, a correct description of the charge state of the ions is essential to obtain the proper mixing behavior. Only for a highly ionic material such as CaO‐MgO does the charge state of the ions remain unvaried upon mixing. We find that approximate energy models that employ fixed charges will tend to overestimate the energy required for mixing, hence the order‐disorder transition temperature.

Electron Microscopy Investigation of the Cycling-Induced Phase Transformation in LiMnO2 Compounds

ABSTRACTLithium transition metal oxides used as intercalation electrodes for rechargeable lithium batteries are widely studied in search of structural stability and improved electrochemical performance. Recent studies showed that the orthorhombic and monoclinic LiMnO2 compounds, unlike LiMn204 spinels, could be cycled on both the 4 V and 2.9 V plateaus with high and stable discharge capacity. In this study, we have performed direct high resolution observations of electrochemically cycled LiMnO2 particles in the fully discharged state. Extensive damage including local strain variation, nanodomain formation, and changes in cation ordering, has been observed. Individual particles retain overall single crystallinity despite having differing structures at the nanodomain level. While cycling causes a macroscopic transformation to spinel cation ordering, the formation of nanodomains differing in cation ordering and/or composition appears to accommodate or prevent the destructive Jahn-Teller distortion that normally occurs at high lithium concentration, thereby resulting in cycling stability.

The intercalation compound Li(Mn0.9Co0.1)O2 as a positive electrode for rechargeable lithium batteries

By replacing only 10% of the Mn by Co in the layered lithium intercalation compound LiMnO2 the amount of lithium that can be removed and reinserted is increased by 50% corresponding to an increase in the ability to store charge from 130 to 200 mA h g–1 at 100 µ A cm–2 and rendering this low cost/toxicity material of potential interest as a positive electrode in rechargeable lithium batteries; furthermore the cooperative Jahn–Teller distortion due to localised high spin Mn3+(3d4) in LiMnO2 appears to be suppressed for Lix(Mn0.9Co0.1)O2; x<0.9 (80% Mn3+ assuming Co3+).

Electrochemical characterization of various metal foils as a current collector of positive electrode for rechargeable lithium batteries

Electrochemical characterization of various metal foils as a current collector of the positive electrode for rechargeable lithium batteries was carried out by cyclic voltammetry, potentiostatic electrolysis and a.c. impedance measurement. Products of the potentiostatic electrolysis were determined by atomic absorption spectroscopy and gas chromatography/mass spectrometry. As a result, it was found that an aluminum foil seems to be the most suitable material as a current collector of the positive electrode, whose electrochemical stability in 1 M LiClO 4/ethylene carbonate—diethyl carbonate and 1 M LiPF 6/ethylene carbonate—diethyl carbonate solutions increases with increasing aluminum purity.

Recent trends in carbon negative electrode materials

The use of graphite-type materials as the negative electrodes for rechargeable lithium batteries is increasing. For graphite-type materials, we proposed the intercalation mechanism taking into account the influence of crystallite size and stacking of the graphitic layers. We found graphite-type materials with a reversible capacity of 430 mAh g −1 over a theoretical limit capacity of 372 mAh g −1. This higher capacity is due to cavities existing in carbon that are capable of storing lithium ions.

Structural stability of LiMn 2O 4 electrodes for lithium batteries

The structural stability of LiMn 2O 4, which is of interest as an insertion electrode for rechargeable lithium batteries, is discussed with respect to processing techniques, composition, Li-Mn-O phase diagram, and electrochemical behavior. Particular attention is paid to processing conditions that result in the formation of lithium-manganese-oxide spinel products in which Mn 2+ ions partially occupy the tetrahedral sites of the spinel structure. The electrochemical behavior of electron-beam and r.f. magnetron sputtered thin-film electrodes suggests the existence of partially inverse Li 1 − x Mn 2O 4 spinel structures during an initial charge to 5.3 V.

Electrochemical properties of a new non-stoichiometric spinel oxide (Mn 2.5O 4) as Li insertion compound

Preliminary results on electrochemical and structural properties of the cation deficient oxide Mn 2.5O 4 system are discussed in terms of its viability as an electrode for rechargeable lithium batteries. Chronopotentiometric measurements show two well-defined steps in the potential range of 3.5 V-2.0 V and 2.0 V-1.5 V, involving faradaic yields of ≈ 0.6 and ≈ 1.0 F mol −1 respectively. A loss of structural integrity was observed for Li ion contents higher than 0.65 per mol. Galvanostatic cycling experiments were performed in the voltage range 4.0-2.0 V and a specific capacity of 43 mAh g −1 was obtained after the twentieth cycle.

Amorphous and Nanocrystalline Oxide Electrodes for Rechargeable Lithium Batteries

ABSTRACTOxo ions (MO4)n- (M = V, Cr, Mn and Mo) have been reduced in aqueous solutions with potassium borohydride to obtain the binary oxides MO2+δ. While the vanadium and manganese oxides are nanocrystalline, the chromium and molybdenum oxides are amorphous. The nanocrystalline VO2 having a metastable structure and the amorphous CrO2 and MoO2.3 transform to the thermodynamically more stable phases upon heating above 300–400 °C. These metastable oxides after heating in vacuum at 200–300 °C to remove water show good electrode performance in lithium cells. VO2, CrO2 and MoO2.3 show a reversible capacity of, respectively, 290 mAh/g in the range 4–1.5 V, 180 mAh/g in the range 3.3–2.3 V, and 220 mAh/g in the range 3–1 V. MnO2 obtained by this process does not show good electrode properties.

Solid-state chemistry of lithium power sources†

This article describes the solid-state chemistry of intercalation compounds that underpins a revolutionary new rechargeable lithium battery which has recently achieved phenomenal commercial success. The battery can store more than twice the energy compared with conventional alternatives of the same size and mass and holds the key to the future improvement of consumer electronic products (e.g. mobile telephones), electric vehicles and implantable medical devices (e.g. the artificial heart). Attention is focused on those lithium intercalation compounds that are useful as positive electrodes in rechargeable lithium batteries. The basic operation of the cell is summarised briefly and the structure/property relationships are developed that are important for the solid-state chemist when attempting to design and synthesise new lithium intercalation compounds capable of operating as positive electrodes. Finally, the structure, electronic structure and intercalation chemistry of several important positive intercalation electrodes are discussed including some which show considerable promise for applications in future generations of rechargeable lithium batteries.

ChemInform Abstract: Synthesis of Layered LiMnO2 as an Electrode for Rechargeable Lithium Batteries.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of layered LiMnO2 as an electrode for rechargeable lithium batteries

RECHARGEABLE lithium batteries can store more than twice as much energy per unit weight and volume as other rechargeable batteries1,2. They contain lithium ions in an electrolyte, which shuttle back and forth between, and are intercalated by, the electrode materials. The first commercially successful rechargeable lithium battery3, introduced by the Sony Corporation in 1990, consists of a carbon-based negative electrode, layered LiCoO2 as the positive electrode, and a non-aqueous liquid electrolyte. The high cost and toxicity of cobalt compounds, however, has prompted a search for alternative materials that intercalate lithium ions. One such is LiMn2O4, which has been much studied as a positive electrode material4–7; the cost of manganese is less than 1% of that of cobalt, and it is less toxic. Here we report the synthesis and electrochemical performance of a new material, layered LiMnO2, which is structurally analogous to LiCoO2. The charge capacity of LiMnO2 (∼270mAhg–1) compares well with that of both LiCoO2 and LiMn2O4, and preliminary results indicate good stability over repeated charge–discharge cycles.

Lithium intercalation in MoO3-nH2O

Oxide-hydrates of molybdenum (OHM) are of interest as lithium insertion electrodes for rechargeable lithium batteries because they offer wide operating temperature, long shelf life and low cost. We have studied the electrochemical characteristics of Li/OHM batteries using two types of commercial materials. Results are as follows. (a) The discharge potential (Φ) ranges between 3.0 and 1.5 V and it is a function of the water content into the cathode. (b) The electro-insertion of Li occurs mainly in two steps in the compositional range 0<x(Li)<1.5. (c) The discharge/charge (Φ-x) curves are very well fitted using a theoretical relationship based on the mean field approximation of a lattice-gas model including an ion-ion interaction term. (d) Kinetics show that Li-ions are highly mobile in the OHM framework. Long-term cycling has been investigated and a detailed analysis of the residual fading capacity during cycling is given.

Non-cooperative Jahn-Teller effect in LiNiO 2: An EXAFS study

Lithium nickel oxide, used as positive electrode in rechargeable lithium batteries, exhibits a layered structure made of NiO 2 slabs between which Li + ions are inserted in an octahedral environment. In fact, stoichiometric LiNiO 2 has never been reported, the true formula is Li 1−zNi 1+zO 2 (0.0<z≤0.20). z depending on the experimental conditions. Special attention devoted to the synthesis conditions, has allowed us to obtain quasi-2D LiNiO 2. EXAFS spectroscopy shows clearly the existence of two different NiO bond lengths: at 1.91 Å (for four of them) and 2.09 Å for the two last ones. This local distortion of the NiO 6 octahedra results from the Jahn-Teller effect of the trivalent nickel ion in the low spin state t 2 6e 1.

Charge/discharge characteristics of polyaniline-based polymer composite positives for rechargeable lithium batteries

The structure of a polyaniline-poly(styrene-4-sulfonate) (PAn-PSS) composite film was optimized as the positive electrode for rechargeable lithium batteries to improve the charge/discharge characteristics in organic electrolyte solutions. The composite films prepared in aqueous poly(styrene-4-sulfonic acid) (PSSH) solutions containing small amounts of HClO 4 showed higher charge/discharge capacities than those prepared in PSSH without HClO 4. However, the utilization of Li +-ion transport in the redox process decreased with an increase in the HClO 4 concentration. A stacked PAn-ClO 4/PAn-PSS film, which consists of an inner PAn layer doped with smaller size anion (ClO 4 −) and an outer PAn-PSS composite layer, was prepared by the electrolysis of aniline in aqueous HClO 4 followed by the polymerization in a PSSH solution. The resulting films gave improved charge/discharge characteristics in organic electrolyte solutions and lead to higher energy density of the full cell with lithium negative electrode.