Positive Electrode For Lithium-ion Batteries Research Articles

Surface Reactivity of a Positive Electrode for Lithium-Ion Batteries: LiCoO2

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Surface Analysis of Positive Electrode for Lithium-Ion Batteries by FT-IR

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Особенности процессов, протекающих на LiFePO4 электроде в литий-ионных аккумуляторах

Features of lithiated iron phosphate behavior (PH/P1, Phostech Lithium Inc, Canada) used as positive electrode of lithium-ion battery with LiPF6-based electrolyte were investigated. It was shown that lihiated iron phosphate potential does not depend of lithium contents in active material. It was shown that cycle life of the positive electrode strongly depends on charge/discharge current. Fast degradation of the positive electrode takes place at low current rates (0.25 and 0.5C). At the same time degradation is considerably lower at 1 and 2.5C rates.

A 3.6 V lithium-based fluorosulphate insertion positive electrode for lithium-ion batteries

Li-ion batteries have contributed to the commercial success of portable electronics, and are now in a position to influence higher-volume applications such as plug-in hybrid electric vehicles. Most commercial Li-ion batteries use positive electrodes based on lithium cobalt oxides. Despite showing a lower voltage than cobalt-based systems (3.45 V versus 4 V) and a lower energy density, LiFePO(4) has emerged as a promising contender owing to the cost sensitivity of higher-volume markets. LiFePO(4) also shows intrinsically low ionic and electronic transport, necessitating nanosizing and/or carbon coating. Clearly, there is a need for inexpensive materials with higher energy densities. Although this could in principle be achieved by introducing fluorine and by replacing phosphate groups with more electron-withdrawing sulphate groups, this avenue has remained unexplored. Herein, we synthesize and show promising electrode performance for LiFeSO(4)F. This material shows a slightly higher voltage (3.6 V versus Li) than LiFePO(4) and suppresses the need for nanosizing or carbon coating while sharing the same cost advantage. This work not only provides a positive-electrode contender to rival LiFePO(4), but also suggests that broad classes of fluoro-oxyanion materials could be discovered.

Thermal Analysis of Positive Electrodes of Lithium-ion Batteries

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Thermal Stability of Metal Fluorides as Positive Electrodes for Lithium-ion Batteries

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Optimization of Li1+x(Ni1/2-yMn1/2-yCo2y)1-xO2 - Type Materials as Positive Electrodes for Lithium-ion Batteries

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The influence of electrolyte and graphite type on the [formula omitted] intercalation behaviour at high potentials

Several graphite types were investigated in respect to their PF 6 - intercalation ability in various electrolytes during electrochemical cycling at positive potentials up to 5.5 V vs. Li/Li +. It revealed that the electrochemical behaviour is related to the structural changes of the graphite particles, especially in terms of exfoliation and surface film formation, as deduced from post-mortem scanning electron microscopy (SEM). Small particle size SFG6 graphite in ethylene carbonate/dimethyl carbonate electrolyte showed reversible cycling and retention of the structure. With other tested electrolytes, the graphite could not be cycled reversibly under the given conditions. High crystalline, heat-treated SFG44 graphite exfoliated even at less positive potentials (4.8 V vs. Li/Li +) whatever electrolyte was used. These results provide guidance about the applicability of different graphites as a conductive additive for positive electrodes of lithium-ion batteries, in order to maintain the structural integrity of the electrode during cycling.

Alkylphosphate-based nonflammable gel electrolyte for LiMn 2O 4 positive electrode in lithium-ion battery

Polymeric gel containing alkylphosphate has been examined as nonflammable gel electrolyte for LiMn 2O 4 positive electrode of lithium-ion battery (LIB). The gel was composed of a polymer matrix of poly(vinylidenefluoride- co-hexafluoropropylene) (PVdF-HFP) and a liquid component consisting of ternary solvent of trimethyl phosphate (TMP) mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) that dissolves lithium salt (LiPF 6 or LiBF 4). The gel composition of 0.8 M (mol dm −3) LiX (X = PF 6 and BF 4) dissolved in EC + DEC + TMP (55:25:20) with PVdF-HFP showed excellent nonflammable characteristics and high ionic conductivity of ca. 3.1 mS cm −1 at room temperature (20 °C). The charge–discharge cycling test of LiMn 2O 4 positive electrode gave good reversibility with high capacitance in the gel electrolyte. With respect to the electrolyte salt, LiBF 4 was better than LiPF 6 due to its thermal stability during the gel preparation.

XAFS Study on Thermal Decomposition Behavior of Positive Electrode of Lithium-ion Batteries

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Electrochemical AFM study of LiMn 2O 4 thin film electrodes exposed to elevated temperatures

Surface morphology changes of LiMn 2O 4 thin film positive electrodes in lithium-ion batteries after repeated potential cycling or storage at elevated temperatures were observed by in situ atomic force microscopy (AFM) to elucidate the origin of capacity fading of LiMn 2O 4. After repeated potential cycling in the overall potential range from 3.50 to 4.30 V at elevated temperatures, the entire thin film surface was covered with small round-shaped particles accompanied by capacity fading of the electrode, while no significant changes were observed at 25 °C. The discharge capacity decreased more significantly when cycled in the lower potential range (3.81–4.07 V) than when cycled in the higher potential range (4.04–4.30 V). After storage at elevated temperatures at a depth of discharge (DOD) of 75%, which is located in the lower potential range, similar surface morphology changes were observed. In addition, discharge capacity markedly decreased, and the crystallinity of the LiMn 2O 4 thin film was lowered after storage. Hence, the observed changes in morphology at elevated temperatures are closely related to capacity fading of the LiMn 2O 4 thin film. The loss of crystallinity was caused by the formation of small particles on the LiMn 2O 4 surface, which would be accelerated on the LiMn 2O 4 surface in contact with an electrolyte solution through some kind of dissolution/precipitation reaction.

Investigation of positive electrodes after cycle testing of high-power Li-ion battery cells: III: An approach to the power fade mechanism using FT-IR-ATR

Surface materials on positive electrodes of lithium-ion batteries which have been degraded are characterized by ATR technique of FT-IR. Lithium carbonate, P O bond based material, lithium alkyl carbonate (ROCO 2Li), and polycarbonate-type compound are detected which have been formed by decomposition reactions of electrolyte solvent and LiPF 6 as lithium salt. Stability of lithium carbonate for charging to SOC = 100% is depended on the condition during degradation. Especially, it changes to unstable by long time cycling at low temperatures. Formation of polycarbonate-type compound during cycling is remarkable at elevated temperatures. Degradation of batteries is larger in higher temperatures, and it is suggested that the variation of surface structure has relation to degradation of batteries.

Investigation of positive electrodes after cycle testing of high-power Li-ion battery cells IV: An approach to the power fading mechanism by depth profile analysis of electrodes using glow discharge optical emission spectroscopy

Depth profile of constituent elements of positive electrodes in lithium-ion batteries was analyzed by using glow discharge optical emission spectroscopy (GD-OES) from the surface to the interface with the current collector. Not only in pristine electrode but also in degraded electrode after 50,000 cycles of high rate charge and discharge, almost homogeneous concentration profile of lithium was observed, suggesting that particles of active electrode material in the deep region inside the electrode layer also concerned in the electrochemical reaction as well as the particles in the surface area. From observation of particles shape by scanning electron microscope (SEM), remarkable cracks were not observed in particles inside the electrode even in the degraded electrodes.

Synthesis of Poly(4-methacryloyloxy-TEMPO) via Group-Transfer Polymerization and Its Evaluation in Organic Radical Battery

Novel group-transfer polymerization (GTP) of 4-methacryloyloxy-TEMPO for the preparation of poly(4-methacryloyloxy-TEMPO) (PTMA) has been developed. The new PTMA has been tested as an active electrode material in rechargeable organic radical battery (ORB). The advantage of the GTP method is that it affords PTMA containing the theoretical amount of nitroxide groups. Furthermore, cross-linked PTMA was prepared in the presence of small amounts of ethylene glycol dimethacrylate. Cyclic voltammetry of this PTMA showed a single, highly reversible redox couple at a potential of ca. 3.6 V (vs Li/Li+). This potential is similar to the potential of materials (e.g., LiCoO2) used for the positive electrode in lithium-ion batteries. In galvanostatic cycling experiments between 3.0 and 4.0 V in a half-cell setup vs metallic Li as counter and reference electrode a reversible specific charge of ca. 103 Ah kg-1 at current rates up to 1 C was obtained with the cross-linked PTMA. The useable charge capacity is very stable w...

A computational investigation on the electrochemical properties of spinel-like LiCoAsO 4 as positive electrode for lithium-ion batteries

The electrochemical properties of spinel-LiCoAsO 4, recently reported, as potential electrode materials for rechargeable lithium batteries has been investigated from first principles calculations and compared to those of the ambient pressure polymorph olivine-LiCoAsO 4. The predicted lithium deinsertion voltage of this material, 4.75 V towards lithium metal, is promising. From the optimized crystalline structures of lithiated (As[LiCo]O 4) and delithiated (As[Co]O 4) materials it is inferred that major structural rearrangements would occur upon lithium deinsertion. The calculated electronic structure indicates that spinel-like LiCoAsO 4 is an insulating compound, suggesting that efficient lithium removal would be hindered by a very poor intrinsic electronic conductivity. The ionic mobility of lithium ions in the octahedral sites of the spinel structure is also expected to be low. Therefore, in spite of the promising insertion voltage, structural and electrical considerations rule out the effective utilization of the spinel-like As[LiCo]O 4 as positive electrode for lithium cells. While predicting lithium insertion voltages by first principles methods is a powerful screening tool in the search for novel electrode materials, the electronic and crystalline information obtained from the calculation should not be overlooked to evaluate the potential interest of an electrode material.

Oxide Materials as Positive Electrodes of Lithium‐Ion Batteries

AbstractFor Abstract see ChemInform Abstract in Full Text.

Film Formation at Positive Electrodes in Lithium-Ion Batteries

Post mortem scanning electron microscopy was used to study the surface film formation on different cathode materials for lithium-ion batteries. The effect of the kind of oxide, the type of solvent and conducting salt, as well as the influence of additives on this process was investigated. In the case of an electrolyte containing ethylene carbonate (EC) and propylene carbonate (PC) (1:1, w/w) with 1 M LiPF 6 , film formation was observed on LiCoO 2 , LiMn 2 O 4 , and especially pronounced on LiNiO 2 oxide materials. In contrast, with EC, dimethyl carbonate (1:1, w/w) 1 M LiPF 6 containing electrolyte, no solid electrolyte interface formation was detected. The substitution of LiClO 4 for LiPF 6 with PC-based electrolytes leads to a less prominent layer. If 2% vinylene carbonate was added to the PC-based electrolyte a pronounced film, presumably consisting of polymerization products of this additive, was created.

Effect of Carbon Source as Additives in LiFePO[sub 4] as Positive Electrode for Lithium-Ion Batteries

The electrochemical properties of LiFePO4 cathodes with different carbon contents were studied to determine the role of carbon as conductive additive. LiFePO4 cathodes containing from 0 to 12% of conductive additive ~carbon black or mixture of carbon black and graphite! were cycled at different C rates. The capacity of the LiFePO4 cathode increased as conductive additive content increased. Carbon increased the utilization of active material and the electrical conductivity of electrode, but decreased volumetric capacity of electrode. This composition ~LiFePO4 with 3 wt % of carbon and 3 wt % of Graphite! is suitable for HEV application.

Sup 7]Li and [sup 1]H MAS NMR Observation of Interphase Layers on Lithium Nickel Oxide Based Positive Electrodes of Lithium-Ion Batteries

7Li and 1 H magic-angle spinning (MAS) NMR spectra were recorded for Li(Ni.Co,Al)O 2 samples. The 7 Li MAS NMR signal of the layer on the pristine material is close to that of Li 2 CO 3 in close contact with it. Its lineshape, due to dipolar interaction with electron spins of the material, is drastically different from that of pure Li 2 CO 3 . Upon hydration, this layer grows, while 1 H NMR suggests that some lithium in the material is replaced by protons. Upon electrochemical cycling, the original layer is replaced by a different one, the solid electrolyte interphase, with distinct 7 Li and 1 H NMR signatures, showing its largely organic nature.

Characterization and electrochemical performance of Li-rich manganese oxide spinel/poly(3,4-ethylenedioxythiophene) as the positive electrode for lithium-ion batteries

The characterization of commercial and home-made non-stoichiometric Li-rich manganese oxide spinels covered by poly(3,4-ethylenedioxythiophene) (pEDOT) chemically grown on the oxide particle surface is reported. The results of the characterization of these materials by IR spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and laser particle size analysis are reported and compared to those of spinels without polymer covering. The results of the electrochemical tests on composite electrodes based on the pEDOT-covered spinels are compared to those of electrodes based on spinels without polymer covering, and demonstrate the reliability of this new composite polymer material as a positive electrode for lithium-ion batteries, also confirmed by preliminary tests in battery configuration.