Reduction Processes in the Course of Mechanochemical Synthesis of Li1+xV3O8

Mechanical activation (MA) of the LiOH+V₂O₅ and Li₂CO₃+V₂O₅ mixtures followed by brief heating at 673 K was used to prepare dispersed Li_1+xV₃O₈. It was shown that structural transformations during MA are accompanied by reduction processes. EPR spectra of Li_1+xV₃O₈ are attributed to vanadyl VO²⁺ ions with weak exchange interaction. The interaction of localized electrons (V⁴⁺ ions) with electron gas (delocalized electrons), which is exhibited through the dependence of EPR line width of vanadium ions versus measurement temperature (C–S–C relaxation), is revealed. It is shown that C–S–C relaxation is different for intermediate and final products. The properties of mechanochemically prepared Li_1+xV₃O₈ are compared with those of HT-Li_1+xV₃O₈, obtained by conventional solid state reaction. Mechanochemically prepared Li_1+xV₃O₈ is characterized by a similar amount of vanadium ions, producing electron gas, but a higher specific surface area.     

Ab initio Studies on Li4+xTi5O12 Compounds as Anode Materials for Lithium‐Ion Batteries

The structural and electronic properties of Li_4+xTi₅O₁₂ compounds (with 0≤x≤6)—to be used as anode materials for lithium‐ion batteries—are studied by means of first principles calculations. The results suggest that Li₄Ti₅O₁₂ can be lithiated to the state Li_8.5Ti₅O₁₂, which provides a theoretical capacity that is about 1.5 times higher than that of the compound lithiated to Li₇Ti₅O₁₂. Further insertion of lithium species into the Li_8.5Ti₅O₁₂ lattice results in a clear structural distortion. The small lattice expansion observed upon lithium insertion (about 0.4 % for the lithiated material Li_8.5Ti₅O₁₂) and the retained [Li₁Ti₅]^16dO₁₂ framework indicate that the insertion/extraction process is reversible. Furthermore, the predicted intercalation potentials are 1.48 and 0.05 V (vs Li/Li⁺) for the Li₄Ti₅O₁₂/Li₇Ti₅O₁₂ and Li₇Ti₅O₁₂/Li_8.5Ti₅O₁₂ composition ranges, respectively. Electronic‐structure analysis shows that the lithiated states Li_4+xTi₅O₁₂ are metallic, which is indicative of good electronic‐conduction properties.     

Structural and Electrochemical Study of Vanadium‐Doped TiO2 Ramsdellite with Superior Lithium Storage Properties for Lithium‐Ion Batteries

Titanium‐oxide‐based materials are considered attractive and safe alternatives to carbonaceous anodes in Li‐ion batteries. In particular, the ramsdellite form TiO₂(R) is known for its superior lithium‐storage ability as the bulk material when compared with other titanates. In this work, we prepared V‐doped lithium titanate ramsdellites with the formula Li_0.5Ti_1?xV_xO₂ (0≤x≤0.5) by a conventional solid‐state reaction. The lithium‐free Ti_1?xV_xO₂ compounds, in which the ramsdellite framework remains virtually unaltered, are easily obtained by a simple aqueous oxidation/ion‐extraction process. Neutron powder diffraction is used to locate the Li channel site in Li_0.5Ti_1?xV_xO₂ compounds and to follow the lithium extraction by difference‐Fourier maps. Previously delithiated Ti_1?xV_xO₂ ramsdellites are able to insert up to 0.8 Li⁺ per transition‐metal atom. The initial gravimetric capacities of 270 mAh g^?1 with good cycle stability under constant current discharge conditions are among the highest reported for bulk TiO₂‐related intercalation compounds for the threshold of one e^? per formula unit.     

Electrochemically Generated γ‐LixV2O5 as Insertion Host for High‐Energy Li‐Ion Capacitors

In this study, we explored the feasibility of using electrochemically generated γ‐Li_xV₂O₅ as an insertion‐type anode in the lithium‐ion capacitor (LIC) with activated carbon (AC) as a cathode. Along with the native form of V₂O₅, their carbon composites are also used as the electrode material which is prepared by high‐energy ball milling. The electrochemical pre‐lithiation strategy is used to generate the desired γ‐phase of V₂O₅ (γ‐Li_xV₂O₅). Under the optimized mass loading conditions, the LICs are assembled with γ‐Li_xV₂O₅ as anode and AC as a cathode in the organic medium. Among the different LICs fabricated, AC/γ‐Li_xV₂O₅‐BM50 configuration delivered an energy density of 33.91 Wh kg^?1 @ 0.22 kW kg^?1 with excellent capacity retention characteristics. However, a dramatic increase in energy density (43.98 Wh kg^?1@0.28 kW kg^?1) is noted after the electrolyte modification with fluoroethylene carbonate. The high temperature performance of the assembled LIC is also studied and found that γ‐Li_xV₂O₅ phase can be used as a potential battery‐type component to construct high‐performance hybrid charge storage devices.     

In-situ imaging of Li-ion migration at interfaces in an all solid Li-ion battery

We investigated the migration of Li ions at an interface between a Li_xTi₅O₁₂ (LTO) and a solid electrolyte in an all-solid Li-ion battery. The optical reflection of LTO changes with variations in the Li content because the band structures of LTO vary with the changes in the Li content. This enables us to observe Li-ion migration in the interface between the LTO and the solid electrolyte using an optical microscope. To observe the LTO particles optically, they were coated on an indium tin oxide on a glass substrate. Variations in Li migration caused by charging/discharging were clearly observed through the changes in the reflection of the LTO. LTO changed between an insulator Li₄Ti₅O₁₂ of the spinel structure and a conductor Li₇Ti₅O₁₂ of the rock-salt structure according to the changes in the Li content. The spinel LTO has a bandgap energy of approximately 2 eV. When electron–hole pairs were generated, electric strains were produced. Surface force microscopy detected the strains and imaged the distribution of lithiation/delithiation of LTO. Interfacial conduction between a sputtered LTO and Li₃PO₄ particles was imaged with high spatial resolution.     

The electronic structure and properties of Ni1−xLixO1−y (0⩽x⩽1/4, 0⩽y⩽1/8)

The electronic structures of NiO, Ni_0.875O, NiO_0.875, Ni_0.875Li_0.125O, Ni_0.875Li_0.125O_0.875 and Ni_0.75Li_0.25O_0.875 with a NaCl-type crystal structure have been calculated using the ab initio linear muffin-tin orbitals method in the LSDA+U approximation. The effect of vacancies in the metal and metalloid sublattices and lithium ions on parameters of the NiO electronic spectrum (the energy gap and the valence band widths, etc.) has been analyzed. It is shown that the defects like the dipole LiV_O and the tripole LiV_OLi impaired stability and could reduce electrical conductivity of the nickel–oxide-based phases.     

Effect of intercalation of metal ions on the colloidal and solid properties of vanadium pentaoxide hydrate,V2O5 nH2O

The colloidal stability of V₂O₅ nH₂O was studied on the basis of the measurements of critical flocculation concentration (CFC) by metal ions, amount of ions exchanged (or intercalated), and -potential. In total, the CFC values obeyed the Schulze Hardy law and strong Hofmeister's series was found in the systems including alkaline ions. The sequence of colloidal stability of V₂O₅ nH₂O in the electrolyte solutions was related to the intercalation of metal ions in the interlayer spaces of the solid. The largest CFC value for Li⁺ (87 mmol dm^–3) was explained by smaller affinity of Li⁺ to be intercalated in V₂O₅ nH₂O as well as smaller Hamaker constant of the intercalated solid compared to the other systems.Effect of intercalation of metal ions on the crystalline properties of the materials was measured by use of XRD and electron microscope. Under highly dehydrated condition the ions whose radii are smaller than 0.1 nm are captured in the structure of V₂O₅ nH₂O without changing interlayer distances, while those larger than 0.1 nm increase the interlayer distance. In a saturated H₂O vapor interlayer distances increased with increasing charge of intercalated ions. However, when intercalated with ions carrying the same valency the interlayer distances of the sample decreased with decrease in the hydration property of ions. Hydrolyzable Cr³⁺ gave exceptionally larger interlayer distances, both in a vacuum and in H₂O vapor.     

XPS study of the Li intercalation process in sol–gel‐produced V2O5 thin film: influence of substrate and film synthesis modification

We report on the process of lithium intercalation in V₂O₅ thin films deposited onto standard ITO‐coated glass substrates. The films were deposited via a well‐established sol–gel route, and the samples were examined as working electrodes in a range of potentials versus lithium reference electrode. This paper follows up issues arising from parallel spectroscopic characterizations of the films by X‐ray photoelectron spectroscopy (XPS). Specifically, the XPS examination showed that not all of the Li‐ion charge inserted was accounted for by the V(5) to V(4) reduction, but the stoichiometric balance could be maintained only by considering additional oxygens arising from the intercalation procedure, leading to Li₂O formation. In this work, we have examined the possibility that the source of oxygen is the ITO substrate. To this purpose, films of V₂O₅ deposited on silicon substrates have been prepared using the sol–gel process and examined by XPS after electrochemical intercalation/de‐intercalation cycles. We show that in this case a perfect balance between electrochemical charge, inserted Li and reduced vanadium is obtained. A further indication of ITO‐substrate effects was obtained from examination, by the same methods, of some unconventional V₂O₅ films that had been co‐precipitated with a siloxane, designed to provide a template structure. The results obtained from this material imply that a barrier layer is formed at the ITO interface and, therefore, the formation of Li₂O is avoided. The results are discussed in terms of the possible degradation of conventional V₂O₅ on ITO as a result of electrochemically induced interface reactions. Copyright © 2005 John Wiley & Sons, Ltd.     

Emptying and filling a tunnel bronze

The classical orthorhombic layered phase of V₂O₅ has long been regarded as the thermodynamic sink for binary vanadium oxides and has found great practical utility as a result of its open framework and easily accessible redox states. Herein, we exploit a cation-exchange mechanism to synthesize a new stable tunnel-structured polymorph of V₂O₅ (ζ-V₂O₅) and demonstrate the subsequent ability of this framework to accommodate Li and Mg ions. The facile extraction and insertion of cations and stabilization of the novel tunnel framework is facilitated by the nanometer-sized dimensions of the materials, which leads to accommodation of strain without amorphization. The topotactic approach demonstrated here indicates not just novel intercalation chemistry accessible at nanoscale dimensions but also suggests a facile synthetic route to ternary vanadium oxide bronzes (M_xV₂O₅) exhibiting intriguing physical properties that range from electronic phase transitions to charge ordering and superconductivity.     

Lithium vanadate Li3+xV6O13 at low temperature

The structure of Li_3+xV₆O₁₃ [x = 0.24 (3)] at 95 K has been solved and refined using single‐crystal X‐ray diffraction. The refined lithium content corresponds to two fully occupied Li sites and one partially occupied Li site. A doubling of the c axis is observed upon cooling from room temperature, and this change is associated with shifts of the V atoms. The resulting space group is C2/c. The Li disorder present in the Li₃V₆O₁₃ phase at room temperature is also observed in the low‐temperature phase reported here.     

LixNi0.5Co0.5O2的态密度计算及电化学性能研究

>为获得综合性能更好的锂离子二次电池正极材料, 分析了Co掺杂对Li_xNiO₂电化学性能的影响. 采用密度泛函DFT理论对Li_xNiO₂和Li_xNi_0.5Co_0.5O₂的平均放电电压和态密度进行了计算. 同时, 用共沉淀法制备了Li_xNiO₂和Li_xNi_0.5Co_0.5O₂锂离子二次电池正极材料, 并对其进行了XRD结构分析和恒流充放电测试. 实验和计算结果表明: 随锂离子嵌入正极(电池放电), 电池的电压逐渐降低, 材料的态密度峰向低能量方向移动; 与Li_xNiO₂相比, Li_xNi_0.5Co_0.5O₂的电压平台相对较高(当0.25≤x≤0.5), 而且在Li^＋嵌/脱时, Li_xNi_0.5Co_0.5O₂的结构变化相对较小; Co离子的掺入, 减小了NiO₆八面体的畸变度, 使材料的电化学稳定性得以提高. 在钴掺杂镍酸锂体系中, NiO₆和CoO₆具有相互的稳定作用.     

Ba3Li2V2O7Cl4, a new vanadate with a channel structure

The tribarium dilithium divanadate tetrachloride Ba₃Li₂V₂O₇Cl₄ is a new vanadate with a channel structure and the first known vanadate containing both Ba and Li atoms. The structure contains four non‐equivalent Ba²⁺ sites (two with m and two with 2/m site symmetry), two Li⁺ sites, two nonmagnetic V⁵⁺ sites, five O²⁻ sites (three with m site symmetry) and four Cl⁻ sites (m site symmetry). One type of Li atom lies in LiO₄ tetrahedra (m site symmetry) and shares corners with VO₄ tetrahedra to form eight‐tetrahedron Li₃V₅O₂₄ rings and six‐tetrahedron Li₂V₄O₁₈ rings; these rings are linked within porous layers parallel to the ab plane and contain Ba²⁺ and Cl⁻ ions. The other Li atoms are located on inversion centres and form isolated chains of face‐sharing LiCl₆ octahedra.     

Simultaneous Carbon Coating and Lithiation of Oxides by Contact Reaction

Chemical lithiation and carbon coating of cathode materials can lead to strongly improved electrochemical properties, especially if the active materials have low electronic conductivity. This behavior is quite often the case for new high‐capacity materials. A novel synthesis method is presented in which the two processes are performed simultaneously by employing Li₂C₂ as both the carbon and the lithium source. In this contact reaction, the acetylide anion C₂^2? is oxidized to carbon and deposited directly on the surface of the active material, while lithium is reductively inserted into the oxidant. Two different synthesis routes are demonstrated: a tribochemical approach at room temperature and heat treatments between 150 and 600 °C. The applicability of these new carbon‐coating methods are demonstrated on various crystalline and amorphous Li_xV₂O₅ phases. The composites obtained were characterized by powder X‐ray diffraction, transmission electron microscopy, and Raman spectroscopy. In addition, electrochemical data confirm the chemical lithiation and show that lithiated Li_xV₂O₅ with specific phases can be prepared selectively.     

Effect of the high pressure on the structure and intercalation properties of lithium-nickel-manganese oxides

Lithium-nickel-manganese oxides (Li_1+x(Ni_1/2Mn_1/2)_1−xO₂, x=0 and 0.2), having different cationic distributions and an oxidation state of Ni varying from 2+ to 3+, were formed under a high-pressure (3 GPa). The structure and cationic distribution in these oxides were examined by powder X-ray diffraction, infrared (IR) and electron paramagnetic resonance (EPR) in X-band (9.23 GHz) and at higher frequencies (95 and 285 GHz). Under a high pressure, a solid-state reaction between NiMnO₃ and Li₂O yields LiNi_0.5Mn_0.5O₂ with a disordered rock-salt type structure. The paramagnetic ions stabilized in this oxide are mainly Ni²⁺ and Mn⁴⁺ together with Mn³⁺ (about 10%). The replacement of Li₂O by Li₂O₂ permits increasing the oxidation state of Ni ions in lithium-nickel-manganese oxides. The higher oxidation state of Ni ions favours the stabilization of the layered modification, where the Ni-to-Mn ratio is preserved: Li(Li_0.2Ni_0.4Mn_0.4)O₂. The paramagnetic ions stabilized in the layered oxide are mainly Ni³⁺ and Mn⁴⁺ ions. The disordered and ordered phases display different intercalation properties in respect of lithium. The changes in local Ni,Mn-environment during the electrochemical reaction are discussed on the basis of EPR and IR spectroscopy.     

Molybdenum Substitution for Improving the Charge Compensation and Activity of Li2MnO3

Lithium‐rich layer‐structured oxides xLi₂MnO₃? (1?x)LiMO₂ (0<x<1, M=Mn, Ni, Co, etc.) are interesting and potential cathode materials for high energy‐density lithium ion batteries. However, the characteristic charge compensation contributed by O^2? in Li₂MnO₃ leads to the evolution of oxygen during the initial Li⁺ ion extraction at high voltage and voltage fading in subsequent cycling, resulting in a safety hazard and poor cycling performance of the battery. Molybdenum substitution was performed in this work to provide another electron donor and to enhance the electrochemical activity of Li₂MnO₃‐based cathode materials. X‐ray diffraction and adsorption studies indicated that Mo⁵⁺ substitution expands the unit cell in the crystal lattice and weakens the Li?O and Mn?O bonds, as well as enhancing the activity of Li₂MnO₃ by lowering its delithiation potential and suppressing the release of oxygen. In addition, the chemical environment of O^2? ions in molybdenum‐substituted Li₂MnO₃ is more reversible than in the unsubstituted sample during cycling. Therefore molybdenum substitution is expected to improve the performances of the Li₂MnO₃‐based lithium‐rich cathode materials.     

Electronic State of Vanadium Ions in Li1+xV3O8 According to EPR Spectroscopy

EPR spectroscopy is used to study the electronic state of vanadium ions in HT- and LT-Li_1+xV₃O₈. It is shown that in both cases the EPR spectra observed are attributed to vanadyl VO²⁺ ions (localized electron centers) with weak exchange interaction. The other type of registered electrons is characterized by larger mobility through a few V⁵⁺ ions, i.e., by a higher degree of delocalization (electron gas). Based on the analysis of the temperature dependence of the EPR line width, it is stated that the exchange interaction between localized electron centers proceeds through electron gas (C-S-C relaxation). It is found that HT-Li_1+xV₃O₈ differs from LT-Li_1+xV₃O₈ by the sloping form of its spectrum at g_∥ range connected with two types of VO²⁺ ions different in the direction of the crystal field axis corresponding to a short V=O²⁺ bond.     

锂离子电池镍掺杂尖晶石LiMn2O4正极材料的电子结构

采用密度泛甬平面波赝势方法对LiMn2O4和LiNi0.5Mn1.5O4的几何结构进行了优化,并计算了相应的电子结构.计算的结果表明:在Li 脱嵌前后,LiMn2O4和LiNi0.5Mn1.5O4均为导体,且锂元素主要以离子形式存在于两种材料中,O2p轨道与Mn(Ni)的3d轨道形成了较强的共价键.Li 嵌入导致Mn(Ni)3d轨道的态密度峰发生移动.Ni的掺杂导致Mn(Ni)和O2p轨道的成键作用得以加强,电子在Mn(Ni)3d轨道的填充发生变化,从而提高了电池的充放电电压.     

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.     

Mechanism of electrochemical reduction of vanadium oxides

We specify the different electrochemical processes occurring when V₂O₅ is electrochemically reduced, yielding insertion products with lithium. Under low current density, V₂O₅ is of a ternary phase of approximate stoichiometry, V₂O₅Li_0.5. During the second step a further reversible insertion of Li⁺ occurs, yielding V₂O₅Li without any important modification of the crystalline structure, thus making the reduction reversible. During the two last steps, Li⁺ incorporation is much more difficult and rapidly causes an important and irreversible modification of the crystalline structure, thus making the reduction irreversible.V₂O₃, has nearly the same faradaic capacity as V₂O₅ but, unlike V₂O₅, it can be hardly be used in batteries since its discharge occurs in a wide potential range.     

Porous nanostructured V2O5 film electrode with excellent Li-ion intercalation properties

Porous nanostructured V₂O₅ films were prepared by electrodeposition from V₂O₅ sol with the addition of block copolymer Pluoronic P123, and they can be readily applied as Li-ion battery cathode without adding any polymer binder or conductive additives. SEM images showed an ideal morphology for Li⁺ intercalation favored charge transfer kinetics, which is a combination of homogeneously distributed nano-pores and V₂O₅ nanoparticles. Electrochemical measurements revealed that, the porous nanostructured V₂O₅ films have a high discharge capacity of 160 mAh/g at 9 A/g, and maintain 240 mAh/g after 40 cycles at 300 mA/g. The excellent Li⁺ intercalation property could be ascribed to the high surface area, sufficient contact between electrode materials and electrolyte, short Li⁺ diffusion path, as well as the good accommodation for volume change which are benefited from homogeneously distributed nano-pores and V₂O₅ nanoparticles.