Mechanism of Li-insertion into spinel-structured Li0.5TiO2

First-principles calculations of Li-insertion into spinel-structured titanate Li(0.5)TiO2 reveal a mechanism underlying the intercalation behaviour of this material. A key factor is the accommodation of charge density transferred to the host lattice upon lithium insertion. The strong coupling between the electronic degrees of freedom and structural deformations is responsible for the observed two-phase intercalation behaviour in spinel-structured titanate.     

Study of lithium ion intercalation/de-intercalation into LiNi1/3Mn1/3Co1/3O2 in aqueous solution using electrochemical impedance spectroscopy

The mechanism of lithium ion intercalation/de-intercalation into LiNi_1/3Mn_1/3Co_1/3O₂ cathode material prepared by reactions under autogenic pressure at elevated temperatures method is investigated both in aqueous and non-aqueous electrolytes using electrochemical impedance spectroscopy (EIS) technique. In accordance with the results obtained an equivalent circuit is used to fit the impedance spectra. The kinetic parameters of intercalation/de-intercalation processes are evaluated with the help of the same equivalent circuit. The dependence of charge transfer resistance (R _ct), exchange current (I ₀), double layer capacitance (C _dl), Warburg resistance (Z _w), and chemical diffusion coefficient (D _Li+) on potential during intercalation/de-intercalation is studied. The behavior of EIS spectra and its potential dependence is studied to get the kinetics of the mechanism of intercalation/de-intercalation processes, which cannot be obtained from the usual electrochemical studies like cyclic voltammetry. The results indicate that intercalation and de-intercalation of lithium ions in aqueous solution follows almost similar mechanism in non-aqueous system. D _Li+ values are in the range of 10^?8 to 10^?14?cm²?s^?1 in aqueous 5?M LiNO₃ and that in non-aqueous 1?M LiAsF₆/EC+DMC electrolyte is in the order of 10^?12?cm²?s^?1 during the intercalation/de-intercalation processes. A typical cell LiTi₂ (PO4)₃/5?M LiNO₃/LiNi_1/3Mn_1/3Co_1/3O₂ is constructed and the cycling stability is compared to that with an organic electrolyte.     

Carbon Nanofibers Decorated with Molybdenum Disulfide Nanosheets: Synergistic Lithium Storage and Enhanced Electrochemical Performance

Traditional lithium‐ion batteries that are based on layered Li intercalation electrode materials are limited by the intrinsically low theoretical capacities of both electrodes and cannot meet the increasing demand for energy. A facile route for the synthesis of a new type of composite nanofibers, namely carbon nanofibers decorated with molybdenum disulfide sheets (CNFs@MoS₂), is now reported. A synergistic effect was observed for the two‐component anode, triggering new electrochemical processes for lithium storage, with a persistent oxidation from Mo (or MoS₂) to MoS₃ in the repeated charge processes, leading to an ascending capacity upon cycling. The composite exhibits unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior high‐rate capability, suggesting its potential application in high‐energy lithium‐ion batteries.     

Li intercalation and anion/cation substitution of transition metal chalcogenides: Effects on crystal structure,microstructure, magnetic properties and Li+ ion mobility

We investigated experimentally the effect of Li intercalation on the structural, microstructural and magnetic properties as well as on the Li ion diffusivity of the complex chalcogenides Cr_5?yTi_ySe₈. In addition, the effect of anion substitution in TiS_2?zSe_z on the Li diffusion parameters was studied by ⁷Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements.For Cr_5?yTi_ySe₈ the Li⁺ insertion is accompanied by an irreversible phase transition from monoclinic to trigonal symmetry which is electronically driven. The maximal Li content in the host material depends on the Ti content and decreases with increasing y in Cr_5?yTi_ySe₈. The intercalated materials can be deintercalated and the minimal Li content in the residual compound increases with Ti abundance. The intercalation process is accompanied by drastic changes of the microstructure. Electrochemical discharge curves depend significantly on the Ti. According to the results of XANES investigations performed on Cr₄TiSe₈, Ti is first reduced during Li uptake and Cr atoms accept electrons at later stages of the intercalation reaction. In-situ energy dispersive X-ray diffraction experiments show that the Li intercalation at room temperature proceeds via two different mechanisms while intercalation at 60 °C is faster and is dominated by one mechanism. ⁷Li MAS NMR measurements revealed a variety of transition metal environments around the Li sites corresponding to the Cr/Ti disorder. The NMR studies also indicate fast Li dynamics. The magnetism of the educts is dominated by strong antiferromagnetic exchange interactions in the high temperature region and by spin-glass behavior in the low temperature range. Intercalation of Li weakens the antiferromagnetic exchange and for fully intercalated materials ferromagnetic exchange is observed. The interpretation of the experimental results is supported by accompanying band structure calculations.In layer-structured Li_xTiS_2?zSe_z (x ≈ 0.7) the Li diffusivity was investigated by various NMR techniques and compared with results obtained for the pure end members Li_xTiS₂ and Li_xTiSe₂. In particular, anion substitution clearly influences the slopes of the low-T flanks of the diffusion induced NMR relaxation-rate peaks. The corresponding activation barriers characterizing local hopping processes are reduced in the mixed samples with 0 < z < 2 and can be explained by a domain model. DFT calculations yield very small hopping barriers along S-rich and Se-rich domain boundaries while the barriers for Li migration inside the domains are rather high. It is therefore assumed that Li migrates along the domain boundaries.     

Atomistic insights into the conversion reaction in iron fluoride: a dynamically adaptive force field approach

Nanoscale metal fluorides are promising candidates for high capacity lithium ion batteries, in which a conversion reaction upon exposure to Li ions enables access to the multiple valence states of the metal cation. However, little is known about the molecular mechanisms and the reaction pathways in conversion that relate to the need for nanoscale starting materials. To address this reaction and the controversial role of intercalation in a promising conversion material, FeF(2), a dynamically adaptive force field that allows for a change in ion charge during reactions is applied in molecular dynamics simulations. Results provide the atomistic view of this conversion reaction that forms nanocrystals of LiF and Fe(0) and addresses the important controversy regarding intercalation. Simulations of Li(+) exposure on the low energy FeF(2) (001) and (110) surfaces show that the reaction initiates at the surface and iron clusters as well as crystalline LiF are formed, sometimes via an amorphous Li-F. Li intercalation is also observed as a function of surface orientation and rate of exposure to the Li, with different behavior on (001) and (110) surfaces. Intercalation along [001] rapid transport channels is accompanied by a slight reduction of charge density on multiple nearby Fe ions per Li ion until enough Li saturates a region and causes the nearby Fe to lose sufficient charge to become destabilized and form the nanocluster Fe(0). The resultant nanostructures are fully consistent with postconversion TEM observations, and the simulations provide the solution to the controversy regarding intercalation versus conversion and the atomistic rationale for the need for nanoscale metal fluoride starting particles in conversion cathodes.     

锂在共轭双键高分子中的电化学嵌入反应I.锂在聚吡咯中嵌入过程的电子能谱研究

通过电子能谱(AES 和ESCA)研究了锂-聚吡咯电池的放电反应,认为该电池的放电是锂在聚吡咯的嵌入过程,嵌入的锂主要是以Li[+]存在,其1s电子的结合能为56.0eV.Li[+]在嵌合物中的扩散系数D为10[-12]一10[-13]cm[2].s[-1]数量级。     

Atomistic Conversion Reaction Mechanism of WO3 in Secondary Ion Batteries of Li,Na, and Ca

Intercalation and conversion are two fundamental chemical processes for battery materials in response to ion insertion. The interplay between these two chemical processes has never been directly seen and understood at atomic scale. Here, using in situ HRTEM, we captured the atomistic conversion reaction processes during Li, Na, Ca insertion into a WO₃ single crystal model electrode. An intercalation step prior to conversion is explicitly revealed at atomic scale for the first time for Li, Na, Ca. Nanoscale diffraction and ab initio molecular dynamic simulations revealed that after intercalation, the inserted ion–oxygen bond formation destabilizes the transition‐metal framework which gradually shrinks, distorts and finally collapses to an amorphous W and M_xO (M=Li, Na, Ca) composite structure. This study provides a full atomistic picture of the transition from intercalation to conversion, which is of essential importance for both secondary ion batteries and electrochromic devices.     

Atomistic Conversion Reaction Mechanism of WO3 in Secondary Ion Batteries of Li,Na, and Ca

Intercalation and conversion are two fundamental chemical processes for battery materials in response to ion insertion. The interplay between these two chemical processes has never been directly seen and understood at atomic scale. Here, using in situ HRTEM, we captured the atomistic conversion reaction processes during Li, Na, Ca insertion into a WO₃ single crystal model electrode. An intercalation step prior to conversion is explicitly revealed at atomic scale for the first time for Li, Na, Ca. Nanoscale diffraction and ab initio molecular dynamic simulations revealed that after intercalation, the inserted ion–oxygen bond formation destabilizes the transition‐metal framework which gradually shrinks, distorts and finally collapses to an amorphous W and M_xO (M=Li, Na, Ca) composite structure. This study provides a full atomistic picture of the transition from intercalation to conversion, which is of essential importance for both secondary ion batteries and electrochromic devices.     

Electrochemical Behavior of Partially-Discharged Li x V2O5 Electrodes upon Interruption of Current

A mathematical diffusion model, which takes into account the electrochemical behavior of partially-discharged thin-layer electrodes made of intercalation materials upon interruption of circuit, is put forward. The applicability of the model is tested by the example of Li _x V₂O₅ films. According to theoretical calculations and experimental data, the equilibrium potential of the films studied depends practically linearly on the degree of intercalation with a slope of –0.8 V for intercalation degrees of 0.3–0.7. The chemical diffusion coefficient of lithium in the films is equal to 1.5 × 10^–11 cm²/s and changes insignificantly at these intercalation degrees.     

Electrochemical behavior of Li[Li0.2Co0.3Mn0.5]O2 as cathode material in Li2SO4 aqueous electrolyte

Layered, lithium-rich Li[Li_0.2Co_0.3Mn_0.5]O₂ cathode material is synthesized by reactions under autogenic pressure at elevated temperature (RAPET) method, and its electrochemical behavior is studied in 2?M Li₂SO₄ aqueous solution and compared with that in a non-aqueous electrolyte. In cyclic voltammetry (CV), Li[Li_0.2Co_0.3Mn_0.5]O₂ electrode exhibits a pair of reversible redox peaks corresponding to lithium ion intercalation and deintercalation at the safe potential window without causing the electrolysis of water. CV experiments at various scan rates revealed a linear relationship between the peak current and the square root of scan rate for all peak pairs, indicating that the lithium ion intercalation–deintercalation processes are diffusion controlled. The corresponding diffusion coefficients are found to be in the order of 10^?8?cm²?s^?1. A typical cell employing Li[Li_0.2Co_0.3Mn_0.5]O₂ as cathode and LiTi₂(PO₄)₃ as anode in 2?M Li₂SO₄ solution delivers a discharge capacity of 90?mA?h g^?1. Electrochemical impedance spectral data measured at various discharge potentials are analyzed to determine the kinetic parameters which characterize intercalation–deintercalation of lithium ions in Li[Li_0.2Co_0.3Mn_0.5]O₂ from 2?M Li₂SO₄ aqueous electrolyte.     

Synchrotron light scattering on nanostructured V/Ce oxide films intercalated with Li+ ions

Vanadium oxide and new V/Ce oxide films on a glass substrate were obtained by the sol-gel process. The morphology of these nanostructured and porous films was studied by grazing-incidence small-angle X-ray scattering (GISAXS) at the ELETTRA synchrotron (Italy, Trieste). The aim of performing GISAXS was to study changes, which might occur in the grain sizes and the porosity of vanadium oxide and V/Ce oxide at 38 and 55 atom % of V, upon the intercalation of Li+ ions. The average grain radius obtained by GISAXS varied with the layer thickness and upon the intercalation of Li+ ions. The layer structure in V/Ce oxides was revealed by the grazing-incidence X-ray reflectivity (GIXR) method. The average grain radius , obtained by GISAXS, was correlated with the intercalation of Li+ ions. The specific surface area of these films was also determined and generally varied from 0.5 nm(-1) to 0.03 nm(-1).     

Phase Formation and Kinetics of Electrochemical Intercalation of Lithium into Intermetallic Compounds MgCd and MgCd3

Electrochemical intercalation of lithium into intermetallic compounds (IMC) MgCd and MgCd₃ out of propylene carbonate solutions of LiBF₄ is studied. According to chronopotentiometry data, during the intercalation, lithium forms compounds with cadmium: Li₃Cd on MgCd or LiCd and Li₃Cd on MgCd₃. Reactions of solid-phase substitution, which occur on the electrodes, are accompanied by the destruction of initial IMC and generation of magnesium atoms. Chronoamperometry of MgCd–(Li) and MgCd₃–(Li) shows the lithium intercalation to be limited by nonstationary diffusion of lithium in the solid phase. The lithium diffusion in MgCd is slower and that in MgCd₃is faster than in Cd. The calculated potential dependences of the diffusion coefficient for lithium in MgCd and MgCd₃ are linear in semilogarithmic coordinates.     

SnO2 negative electrode for lithium ion cell: in situ Mössbauer investigation of chemical changes upon discharge

In situ ¹¹⁹Sn Mössbauer study of an SnO₂ electrode was performed during discharge of a lithium ion cell. The first step is lithium intercalation into the SnO₂ host structure. This lithium intercalation results in reinforcement of the SnO₂ lattice instead of direct decomposition of the oxide upon reduction. This first step is followed by the reduction of tin dioxide into unusual tin species (possibly “exotic” forms of Sn(II) or Sn(0)). The last step of the discharge consists in Li-Sn alloy formation. However, non-reduced SnO₂ is present nearly up to the end of the discharge despite a very low discharge regime. It seems highly probable that this fact is related both to slow Li diffusion and disconnection of SnO₂ particles due to Li₂O formation. The working electrode appears to be rather far from equilibrium during continuous discharge, which means that ideal succession of well-defined stages cannot describe the real phenomena involved in the operating battery.     

Electrochemical intercalation reaction of lithium into sulfides of nonlayer structure: I. Lithium intercalation in lead sulfide

The reaction mechanism of cell Li/PbS has been studied with coulombic titration, cyclic voltammetry and X-ray diffraction methods. It was found that in the first stage of discharge (0< y ≤1.5), the intercalation of lithium into lead sulfide took place. The X-ray diffraction patterns showed that the main crystalline structure of PbS remained unchanged after lithiation, and the lithium intercalated probably locates in the center of the cubic-interspace of the crystal. The intercalation free energy of Li into PbS forming LiPbS was found to be ?300.48 KJ·mol^?1 (at 25°C). The chemical diffusion coefficient of lithium in Li_yPbS (0<y≤1) was determined by electrochemical method to be about 10^?11 cm²S-1.     

The crystal structure of the inorganic surface films formed on Mg and Li intercalation compounds and the electrode performance

A crystallographic approach was applied to elucidate the influence of the nature of the surface films on the electrochemical behavior of Li and Mg intercalation compounds. This paper presents two examples: (1) protection of graphite electrodes by Li₂CO₃ surface films, and (2) the unique electrochemical behavior of Mg-containing Chevrel phases (MgCP) obtained by different synthetic routes. In the former case, the elucidation of the protection mechanism and the explanation of the high performance of such protected electrodes are based on the analysis of possible Li-ion motion in the carbonate crystal structure. In the latter case, a combination of synthesis, electrochemistry and XRD analysis was used to explain an unusual phenomenon: the difference between the excellent electrochemical behavior of the Chevrel phase (CP) based on Cu-leached Cu₂Mo₆S₈ (CuCP), and the poor electrochemical activity of the high-temperature synthesized MgCP, with the same phase composition. It is shown that this phenomenon is caused by MgO formation on the surface of the latter material. The different surface chemistry of the MgCPs obtained by the two different synthetic routes was substantiated by revealing the correlation between the electrochemical activity and the chemical stability of these materials under ambient atmosphere conditions. Dedicated to Prof. Mikhail A. Vorotyntsev on the occasion of his 60th birthday.     

Organic Dicarboxylate Negative Electrode Materials with Remarkably Small Strain for High‐Voltage Bipolar Batteries

As advanced negative electrodes for powerful and useful high‐voltage bipolar batteries, an intercalated metal–organic framework (iMOF), 2,6‐naphthalene dicarboxylate dilithium, is described which has an organic‐inorganic layered structure of π‐stacked naphthalene and tetrahedral LiO₄ units. The material shows a reversible two‐electron‐transfer Li intercalation at a flat potential of 0.8 V with a small polarization. Detailed crystal structure analysis during Li intercalation shows the layered framework to be maintained and its volume change is only 0.33 %. The material possesses two‐dimensional pathways for efficient electron and Li⁺ transport formed by Li‐doped naphthalene packing and tetrahedral LiO₃C network. A cell with a high potential operating LiNi_0.5Mn_1.5O₄ spinel positive and the proposed negative electrodes exhibited favorable cycle performance (96 % capacity retention after 100 cycles), high specific energy (300 Wh kg^?1), and high specific power (5 kW kg^?1). An 8 V bipolar cell was also constructed by connecting only two cells in series.     

The utility of photoemission spectroscopy in the study of intercalation reactions

In this brief review, the general effects of the intercalation of alkali metals (Na, Li) into V₂O₅ thin films, observed by photoemission spectroscopy (XPS and UPS), are summarized and discussed in order to better understand the involved intercalation mechanisms and surface reactions in the view points of crystal structure and electronic structure. The correlation of the change in work function and the shift in Fermi level of the host due to the intercalation of alkali metals is outlined. Finally, the contribution of different mechanisms to the batteries' voltages, as deduced from photoemission spectroscopic data, is given. Copyright © 2006 John Wiley & Sons, Ltd.     

Electrochemical and structural evolution of structured V_2O_5 microspheres during Li-ion intercalation

With the development of stable alkali metal anodes,V₂O₅ is gaining traction as a cathode material due to its high theoretical capacity and the ability to intercalate Li,Na and K ions.Herein,we report a method for synthesizing structured orthorhombic V₂O₅ microspheres and investigate Li intercalation/deintercalation into this material.For industry adoption,the electrochemical behavior of V₂O₅ as well as structural and phase transformation attributing to Li intercalation reaction must be further investigated.Our synthesized V₂O₅ microspheres consisted of small primary particles that were strongly joined together and exhibited good cycle stability and rate capability,triggered by reversible volume change and rapid Li ion diffusion.In addition,the reversibility of phase transformation(a,e,d,c and xLixV₂O₅)and valence state evolution(5+,4+,and 3.5+)during intercalation/de-intercalation were studied via in-situ X-ray powder diffraction and X-ray absorption near edge structure analyses.     

<Emphasis Type="Italic">In-situ</Emphasis> TEM investigation of MoS<Subscript>2</Subscript> upon alkali metal intercalation

Phase transition in two dimensional molybdenum disulfide (MoS₂) can be induced by several methods and has been investigated for decades. Alkali metal insertion of MoS₂ had been proved an effective method to cause phase transition early in 1970s, and has been gaining renewed interest recently, due to the possible application of MoS₂ in energy storage. The alkali metal intercalation of MoS₂ has been studied by various techniques, among which in-situ transmission electron microscopy (TEM) provides unique capability of real time resolving the structural evolution of the materials at high spatial resolutions. Here by in-situ TEM technique we investigated the structural evolution of MoS₂ upon lithium and sodium intercalation, along with transformation of the nanosheet and variation of the electron diffraction patterns. The intercalation process is accompanied by emergence of superstructures, which exist in several forms. The ion intercalation results in phase transition of MoS₂ from 2H to 1T, and the driving mechanism of the phase transition are discussed. The work provides a more comprehensive understanding of ion intercalation induced phase transition of MoS₂.     

Intermediate phases during alkali metal intercalation in HfNCl

The mechanism of the chemical and electrochemical alkali metal intercalation reactions in β-HfNCl has been investigated through electrochemical potential spectroscopy (EPS), in-situ powder X-ray diffraction during electrochemical intercalation and room temperature chemical intercalation experiments. EPS experiments in lithium cells reveal the presence of a plateau, at 1.8 V vs. Li⁺/Li⁰ accounting for ca. 0.14 mol Li, that indicates the formation of a new intermediate phase, and then a gradual decrease of potential with composition that extends up to very high lithium contents (ca. 1.1 per formula), consistent with the formation of a solid solution. Sodium electrochemical intercalation experiments showed a relatively similar behaviour with a plateau at 1.4 V vs. Na⁺/Na⁰, corresponding to ca. 1.7 V vs. Li⁺/Li⁰. In-situ monitored powder X-ray diffraction electrochemical intercalation experiments showed that the electrolyte solvent (ethylene carbonate/dimethyl carbonate, EC/DMC or propylene carbonate, PC) co-intercalated with the alkaline atom. This leads to a large expansion of the interlayer spacing that reaches a value of 21.06 Å in the lithium co-intercalated phase with EC/DMC, Li_x(EC/DMC)_yHfNCl, and 22.01 Å in the sodium co-intercalated phase with PC, Na_x(PC)_yHfNCl. Chemical intercalation using naphthyl-sodium solutions in tetrahydrofuran (THF) leads to solvent-free, multiple-phase samples showing in different proportions the pristine and the superconducting stage 2 and stage 1 phases. The composition of the intercalated samples depends on the pristine sample, the concentration of the naphthyl-sodium solution, the ratio Na:HfNCl and the reaction time. Pristine samples exhibiting low lithium intercalation degree upon electrochemical reduction gave the second stage as the major phase when treated with short reaction times or using low Na:HfNCl ratios, coexisting either with the host or with the first stage phase, whereas stage 1 is obtained as the major phase from pristine samples showing high electrochemical capacities. The staging behaviour and the multiphase nature of these samples account for the wide superconducting transitions and the different critical temperatures observed in these superconductors.