Lithium Ion Deintercalation Research Articles

Soft X-Ray Absorption Spectroscopic Study of a LiNi0.5Mn0.5 O 2 Cathode during Charge

Soft X-ray (200 to 1000 eV) absorption spectroscopy at the O K-edge and the metal -edges, in both the fluorescence yield (FY) and the partial electron yield (PEY) mode, has been used to probe the electronic structure of electrochemically deintercalated FY and PEY spectra of the transition metal -edges, indicated that Mn ions remain mostly unchanged in the state at all levels of charge. However, the Ni FY L-edge spectra show a continuous shift to higher energy during charge, but remain mostly unchanged in the PEY data. The results of the FY data show that the Ni ions in the bulk are oxidized form to during charge. The difference between the surface-sensitive PEY data and the bulk-sensitive FY data indicates that the surface of has a different electronic structure than the bulk. The shift in the O K-edge to lower energies and the development of a shoulder on the low energy side of the first pre-edge peak indicates that the holes compensating the lithium ion deintercalation are located in O 2p states as well as Ni 3d states. These results show that soft X-ray absorption is a powerful technique for studying the electronic structure of new battery materials and it provides unique complementary information to that obtained from hard X-ray (above 1000 eV) absorption studies at the transition metal K-edges. © 2004 The Electrochemical Society. All rights reserved.

Mixed-valence induced during the intercalation of lithium ions into uranium fluorides

The mixed-valence in uranium fluorides LiU 4F 16 and UF 4 can be induced (or eliminated) by the intercalation (deintercalation) of lithium ions into these compounds. These processes can be electrochemically performed both with LiU 4F 16 (or LiTh 4F 16) and with monoclinic UF 4 as starting materials using a liquid electrolyte composed of propylene carbonate as solvent and LiClO 4 as salt. In the cases of UF 4 and LiU 4F 16, the electrochemical intercalation of Li + into the host matrix is reversible and a maximum of three Li + ions per U 4F 16 unit can be reversibly intercalated. Additional experimental evidences of the mixed-valence in these fluorides are presented such as the Electron Paramagnetic Resonance characterization of the starting materials and of those electrochemically modified.

Thin film of CeO2-SiO2: a new ion storage layer for smart windows

Abstract Thin solid films of CeO 2 -SiO 2 , used as a counter-electrode layer in electrochromic devices, were prepared by the sol–gel dip coating, using an aqueous-based process. The influence of the SiO 2 addition on electrochemistry of the CeO 2 oxide coatings was determined by chronoamperometric measurements. The films exhibit a larger charge storage capacity, which was determined as a function of the coatings thickness. The peak occurrence in the chronoamperometric curve during the deintercalation of lithium ions in the cerium/silicon films is analyzed in terms of trapping energy levels for Li + ions into the film. In situ UV–Vis spectroelectrochemical measurements of the CeO 2 -SiO 2 coatings indicated that the films remained transparent in the visible spectral range during the intercalation process. Powders were characterized by X-ray diffraction after the same thermal treatment of the films, indicating a decrease of crystallinity with the doping. The feasibility for use of these electrodes as ion storage for electrochromic devices was investigated.

Kinetics of lithium transport through a hard carbon electrode studied by analysis of current transients

The kinetics of lithium transport through a Carbotron-P hard carbon composite electrode was investigated by analysis of the current transients based upon the modified McNabb-Foster equation. The electrode potential curve ran continuously throughout the whole deintercalation of lithium ions, without the appearance of any potential plateau. However, the anodic current transients showed inflexion points, indicating that several kinds of lithium deintercalation sites present within the electrode are kinetically distinguishable among themselves. Moreover, the anodic current transients did not follow Cottrell behaviour but Ohmic behaviour. The anodic current transients experimentally measured coincided well with those transients numerically simulated based upon the modified McNabb-Foster equation as a governing equation and the "cell-impedance-controlled" constraint as a boundary condition. This strongly indicates that lithium transport is governed by "cell impedance" and at the same time the difference in activation energies for lithium deintercalation between the four different lithium deintercalation sites existing within the electrode accounts for the different kinetics of lithium transport between these sites.

Sulphide based anode material for lithium rechargeable battery

In this study, lead sulphide (PbS) was prepared by the chemical bath deposition technique. The sample was characterized by X-ray diffraction (XRD), Energy Dispersive Analysis of X-rays (EDAX) and cyclic voltammetry. EDAX spectrum shows peaks attributable to lead and sulphur. The EDAX analysis also shows that the prepared sample is stoichiometric. Cyclic voltammetry experiments were recorded at 100 mV·s−1 and 400 mV·s−1 scan rates. Results show that the rate controlling electrochemical reaction is electron transfer. The presence of redox waves shows that the lithium intercalation and deintercalation can occur as a result of lattice expansion in PbS. There were no differences in the PbS XRD data before and after the cyclic voltammetry experiments indicating that the PbS structure is not modified upon lithium ion intercalation and deintercalation in PbS. The discharge characteristics for 35 cycles of the cell using the LiCoO2/PbS couple is presented indicating the possible development of such materials as anode in lithium ion cells.

Cycling Behavior of Binder-Free Graphite-Lithium Intercalation Anode In AICI3-EMIC-LiCI-SOCI2Room-Temperature Molten Salt

The electrochemical behavior of binder-free carbon anode, comprising of only artificial and natural graphite (AG and NG) particles, for intercalation and deintercalation of lithium ion <TEX>$(Li^+)$</TEX> in aluminum chloride (AICI_3)-I-ethyl­3-methylimidazolium chloride (EMIC)-lithium chloride (LiCl)-thionyl chloride <TEX>$(SOCI_2)$</TEX> room-temperature molten salt (RTMS) was studied. Binder-free carbon electrodes were fabricated using electrophoretic deposition (EPD) method. The binder-free carbon anodes provided a relatively flat charge and discharge potentials <TEX>$(0\;to\;0.2V\;vs.\;Li/Li^+)$</TEX> and current capabilities <TEX>$(250-340mAh{\cdot}g^{-1})$</TEX> for the intercalation and deintercalation of <TEX>$Li^+$</TEX>. Stability of the binder-free carbon anodes for intercalation and deintercalation of 50 cycles was confirmed.

Synthesis of electrochromic praseodymium-doped vanadium oxide films by molten salt electrolysis

The praseodymium oxide (PrxOy) and praseodymium-doped vanadium oxide films were synthesized onto the ITO electrode by electrolysis in molten dimethylsulphone (DMSO 2)–PrCl 3, DMSO 2–PrCl 3–LiNO 3 and DMSO 2–PrCl 3–V 2O 5 system at the temperature about 150 °C. The obtained films were characterized by X-ray diffraction (XRD) and spectroscopic measurements. Moreover, the electrochromic (EC) reactions of the oxide films in solution of propylene carbonate (PC) were investigated. The absorption spectrum of praseodymium oxide films obtained by electrodeposition in DMSO 2–PrCl 3 systems had 560- and 390-nm peaks due to mixed valence of Pr 3+ and Pr 2+. And the effect of lithium ion intercalation or deintercalation was shown in color change of oxide films. The cyclic voltammograms (CV) of praseodymium-doped vanadium oxide films obtained by electrodeposition in DMSO 2–PrCl 3–V 2O 5 systems showed the good reversibility of EC reactions.

Microstructural development and electrochemical characteristics of lithium cobalt oxide powders prepared by the water-in-oil emulsion process

Abstract Lithium cobalt oxide (LiCoO 2 ) powders, utilized as cathode materials in lithium–ion secondary batteries, have been synthesized through the emulsion process. When the emulsion-derived precursors are calcined at elevated temperatures, the amounts of residual Co 3 O 4 and organic species decrease and the crystallinity of LiCoO 2 gradually improves with a rise in the calcination temperature. After calcination at 800 °C for 1 h, monophasic LiCoO 2 powders with a R 3 m structure are successfully obtained. Compared to the traditional solid-state reaction, the emulsion process not only significantly curtails the reaction time to prepare LiCoO 2 , but also reduces the particle size. In the electrochemical test, both the specific discharge/charge capacity and the coulomb efficiency of LiCoO 2 increase with a rise in the calcination temperature. Increasing the calcination temperature results in the formation of pure LiCoO 2 without residual reactants, and also enhances the crystallinity of LiCoO 2 as well as the ordering arrangement of lithium and cobalt cations in the layered structure, thereby facilitating the intercalation and deintercalation of lithium ions. As a result, the combination of the emulsion method with proper calcination processes is highly successful in producing LiCoO 2 powders having large specific capacity and good cyclic stability along with high coulomb efficiency.

Structural, electrical and electrochemical properties of LiNiO 2

This paper presents structural and electrical properties of LiNiO 2 cathode material. The influence of cation mixing on the structural and electrical properties were determined. It has been found that deintercalation of lithium ions from the LiNiO 2 lattice influences the properties of the compound towards metallic ones. A model of electronic structure of LiNiO 2 has been proposed.

Changes in electronic structure by Li ion deintercalation in LiNiO 2 from nickel L-edge and O K-edge XANES

Change in electronic structure by lithium ion deintercalation in LiNiO 2 was investigated by Ni L-edge and O K-edge X-ray absorption near edge structure (XANES). The Ni L-edge XANES for LiNiO 2 indicated the Ni occurs in LiNiO 2 as Ni 2+ ions. The Ni L-edge XANES for Li x NiO 2 showed no chemical shift to indicate that the Ni ion in Li x NiO 2 is still Ni 2+, even at low x value. The O K-edge XANES for Li x NiO 2 also indicated that the holes compensating the lithium ion deintercalation are located primarily in oxygen 2p states rather than in Ni 3d states.

Changes in electronic structure by Li ion deintercalation in LiCoO2 from cobalt L-edge and oxygen K-edge XANES.

Cobalt L-edge and oxygen K-edge X-ray Absorption Near Edge Structure (XANES) investigated change in electronic structure by electrochemical lithium ion de-intercalation in LiCoO2. The Co L-edge XANES of Li(1-x)CoO2 did not show any chemical shift even at high x value. The oxygen K-edge XANES of Li(1-x)CoO2 indicated that the holes compensating the lithium ion deintercalation are located primarily in the oxygen 2p states rather than in the Co 3d states.

Synthesis of Nanosized Lithium Manganate For Lithium-ion Secondary Batteries

ABSTRACTNanosized lithium manganate powders are successfully synthesized via a newly developed reverse-microemulsion (RμE) process. Monophasic LiMn2O4 powders are obtained after calcining the precursor powders at 700°C. The particle size of the spinel compound significantly depends on the concentration of the aqueous phase. Increasing the water-to-oil volume ratio results in an increase in the particle size. While the aqueous phase is equal to 0.5 M, the size of the obtained LiMn2O4 powder is around 60-70 nm. It is found that the specific capacity of nanosized LiMn2O4 particles is greater than that of submicron particles. The large surface area of ultrafine particles is considered to facilitate the intercalation and deintercalation of lithium ions during the cycling test.

Structure, chemical bonding and electrochemical behavior of heteroatom-substituted carbons prepared by arc discharge and chemical vapor deposition

Abstract The structural characteristics, chemical bonding and electrochemical properties of the heteroatom-substituted carbons synthesized by arc discharge and chemical vapor deposition have been investigated. C x N was prepared only as a soot by arc discharge in nitrogen atmosphere; BC x and B x C y N z were obtained both as soot and cathode deposits by arc discharge of graphite rods having B 4 C and boron nitride (BN) in argon and nitrogen atmospheres, respectively. Transmission electron microscopic study showed that C x N, BC x and B x C y N z soots were composed of nanoparticles with diameters of 20–100 nm, while cathode deposits contained nanotubes with diameters of ca. 20 nm or less and nanoparticles with diameters less than 100 nm. It was found from XPS study that C x N contained a large amount of pyridine type nitrogen atoms at the edge of graphene layer; the BBC 2 structure was dominant in BC x ; and B 3 N, B 2 NC and BNC 2 structures might exist in B x C y N z . Carbon- and C x N-coated graphite were prepared by deposition of carbon and C x N onto natural graphite powder, respectively. The concentrations of coated C x N layers were between C 21 N and C 62 N. Charge–discharge profiles of C x N, BC x and B x C y N z soots prepared by arc discharge were similar to each other, giving linearly increasing potential with lithium ion deintercalation. C x N soot heat-treated at 3000°C showed a similar profile for charge–discharge curves to that of graphite with a charge capacity of 334 mAh g −1 . On the other hand, C x N-coated graphite exhibited as high as 397 mAh g −1 larger than ∼365 mAh g −1 for carbon-coated graphite and that of heat-treated C x N soot.

Precursor derived LiMn2O4 thin films as ionic conductor

Thin films of spinel LiMn2O4 have been fabricated using a metallorganic precursor. Crystalline films have been deposited on Au substrates to exhibit as the cathode in rechargeable thin film lithium batteries. The nucleation and growth of spinel LiMn2O4 crystallites were investigated with heat treatment of the deposited thin films. Film capacity density as high as 22 µAh/cm2 was measured for LiMn2O4. The film heat treated at 700 °C were cycled electrochemically up to 30 cycles against Li metal without any degradation of the capacity. There were neither open area nor amorphous layers which prevent the Li+ions transfer at the boundaries in the LiMn2O4 thin film. The microscopic study revealed that (111) planes in the two grains directly bonded at the grain boundary which could proceed the lithium ion intercalation or deintercalation smoothly.

Electrochemical behavior of surface-fluorinated graphite

Electrochemical intercalation and deintercalation of lithium ions have been investigated using surface-fluorinated graphite electrodes in 1 M LiCl0 4-EC/DEC (1:1) at 25°C. The 2 and 10 min-fluorinated graphite samples contained small amounts of fluorine, 0.5–2.2 at% and 0.6–3.7 at%, while their surface fluorine concentrations were 6.0–14.6 at% and 7.1–18.1 at%, respectively. Raman spectra indicated that the surface fluorination caused the surface disordering of graphite. The 2 min-fluorinated graphite samples showed the higher charge capacities than original graphite by about 5–10%, that is, 380–400 mA h g −1 and the half of 10 min-fluorinated graphite samples also gave the high charge capacities of about 380 mA h g −1. XPS and Raman spectroscopy revealed that the most of fluorine atoms were removed from graphite surface and the surface disordering of graphite was increased by charge–discharge cycling. Based on these results, the mechanism on the capacity increase by the surface fluorination of graphite was discussed.

Electrochemical behaviors of carbon alloy BCx and of BCx-coated graphite prepared by chemical vapor deposition

Boron-substituted carbons (C/B=3.8–18.8) have been synthesized by chemical vapor deposition (CVD) using benzene, boron trichloride and hydrogen at 800–1000°C in the presence of a nickel catalyst under atmospheric pressure. BCx prepared with the nickel catalyst had a higher crystallinity than that prepared in the absence of nickel. BCx samples prepared by short duration deposition showed relatively higher charge capacities and better cycleability due to a smaller amount of the less organized region. A longer duration of the reaction, however, yielded a larger amount of less crystallized regions within BCx. BCx compounds have also been coated by CVD using cyclohexane as a carbon source on two kinds of graphite: natural graphite powder and graphite treated with 94% HNO3. XPS and Raman spectroscopy indicated that these materials were not mixtures of BCx and graphite, but BCx-coated graphites. The BCx-coating modified the charge–discharge profiles of natural graphite. The potential of the electrode was low and flat and gradually increased during the last stage of lithium ion deintercalation reaction.

Tensile Fracturing of Stiff Rock Layers under Triaxial Compressive Stress States

In an attempt to reduce the Li+ concentration polarization and electrolyte depletion from the electrode porous space, sulfonated polyether ether ketone with pendant lithiated fluorinated sulfonic groups (SPEEK-FSA-Li) is prepared and attempted as ionic conductivity binder. Sulfonated aromatic poly(ether ether ketone) exhibits strong adhesion and chemical stability, and lithiated fluorinated sulfonic side chains help to enhance the ionic conductivity and Li+ ion diffusion due to the charge delocalization over the sulfonic chain. The performances are evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, charge–discharge cycle testing, 180° peel testing, and compared with the cathode prepared with polyvinylidene fluoride binder. The electrode prepared with SPEEK-FSA-Li binder forms the relatively smaller resistances of both the SEI and the charge transfer of lithium ion transport. This is beneficial to lithium ion intercalation and de-intercalation of the cathode during discharging–charging, therefore the cell prepared with SPEEK-FSA-Li shows lower charge plateau potential and higher discharge plateau potential. Compared with PVDF, the electrode with ionic binder shows smaller decrease in capacity with the increasing of cycle rate. Meanwhile, adhesion strength of electrode prepared with SPEEK-FSA-Li is more than five times greater than that with PVDF.

Effect of fluoroesters on the low temperature electrochemical characteristics of graphite electrode

The electrochemical behavior of graphite electrode has been investigated in 1 M LiClO 4-ethylene carbonate (EC)/diethyl carbonate (DEC) and fluoroester-mixed (4.8 vol %) EC/DEC solutions at low temperatures to evaluate the effect of addition of fluoroesters on the electrochemical characteristics. The cyclic voltammetry study revealed that the fluoroesters used were electrochemically reduced at more positive potentials between 0.87 V and 1.41 V vs. Li/Li +, mainly at 0.99–1.10 V, than EC reduced at 0.60 V, and with decreasing reduction potentials of the fluoroesters, the larger reduction and oxidation currents reversibly flowed in the fluoroester-mixed solvents than in EC/DEC at 0 °C. The charge-discharge cycling accompanying the lithium ion deintercalation and intercalation reactions has been also studied by a constant current method at 25 °C, 0 °C and −4 °C. A low molecular weight ftuoroester, CHF 2COOCH 3-mixed EC/DEC demonstrated the much larger charge capacities than EC/DEC itself and other fluoroester-mixed solvents at 0 °C and −4 °C, though its capacity was comparable to that in EC/DEC at 25 °C. The charge capacities obtained in the solvents mixed with other fluoroesters having larger molecular weights were not largely different from that in EC/DEC at 0 °C.

Electrochemical behavior of carbon alloy C N prepared by CVD using a nickel catalyst

Carbon–nitrogen layered compounds, C14N to C62N have been synthesized by thermal decomposition of acetonitrile at 800–1100°C in the presence of nickel catalyst. The CxN samples prepared with nickel had higher crystallinity and less pyridine-type nitrogens existing at the edge of graphene layers than CxN prepared in the absence of nickel. With an increase in the deposition temperature of CxN , the cycleability for electrochemical intercalation–deintercalation of lithium ions was improved and the profile of the charge–discharge curve approached that of natural graphite powder due to an increase in the crystallinity and a decrease in the incorporated nitrogens. Surface oxidation of the CxN by nitric acid solutions gave rise to an increase in the surface oxygens and a slight decrease in nitrogens without any change of crystallinity. The surface modification improved the cycleability for lithium ion intercalation–deintercalation reaction.

Electrochemical Properties of Nitrogen-Substituted Carbon and Organofluorine Compounds

ABSTRACTThe CxN samples(C14N-C62N) prepared with a nickel catalyst had the higher crystallinity and less pyridine-type nitrogens existing at the edge of graphene layers than CxN prepared in the absence of a catalyst. With increase in the deposition temperature of CxN, the cy-cleability for electrochemical intercalation-deintercalation of lithium ions was improved and the profile of the charge-discharge curve approached that of graphite due to increase in the crystallinity and decrease in the incorporated nitrogens. CxN-coated graphites demonstrated gradual increase in the potential at the last stage of lithium ion deintercalation process.The effect of fluoroester-mixing in 1 M LiClO4-EC/DEC was also investigated at a low temperature. It was found that CHF2COOCH3 with a low molecular weight and a small number of fluorine atoms was effective as a mixing agent.