Electrochemical lithium insertion in two polymorphs of a reduced molybdenum oxide (γ and γ′- Mo4O11)

A study of the electrochemical lithium insertion in two polymorphs of a reduced molybdenum oxide, Mo₄O₁₁, is presented in this work. When used as active materials in cells discharged down to 1 V vs. Li⁺/Li, both forms, the orthorhombic γ-Mo₄O₁₁ and the monoclinic γ′-Mo₄O₁₁, incorporated a similar number of lithium atoms per metal atom (Li/Mo=2.12 and 2.25, respectively). Step potential electrochemical spectroscopy experiments proved that the insertion reaction proceeds in both cases through different mechanisms. In situ X-ray diffraction studies showed an almost complete loss of crystallinity of both compounds after the first discharge, leading to amorphous materials with different electrochemical behaviour on cycling. When discharged to low potentials (0.5 V vs. Li⁺/Li), the γ′-Mo₄O₁₁ polymorph showed very good cycling behaviour for at least five lithium atoms per formula unit, corresponding to a specific capacity of 230 Ah/kg after seven complete charge-discharge cycles. Received: 20 April 1999 / Accepted: 20 June 1999     

An aqueous rechargeable lithium-ion battery based on LiCoO2 nanoparticles cathode and LiV3O8 nanosheets anode

Nanoparticles of lithium cobalt oxide (LiCoO₂) and nanosheets of lithium vanadium oxide (LiV₃O₈) were synthesized by a citrate sol–gel combustion route. The physical characterizations of the electrodic materials were carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and also X-ray diffraction (XRD) measurements. Near spherical nanoparticles of ≈100 nm and compact nanosheets with a few nanometers thick were observed by SEM and TEM for LiCoO₂ and LiV₃O₈, respectively. XRD data indicated that the as-prepared active materials presented pure phase of rhombohedral LiCoO₂ with R-3m symmetry and monoclinic LiV₃O₈ with p2₁/m symmetry. The kinetics of electrochemical intercalation of lithium ion into the nanoparticles of LiCoO₂ and nanosheets of LiV₃O₈ from 1.0 mol l⁻¹ LiNO₃ aqueous solution were investigated by cyclic voltammetry and chronoamperometry. An aqueous rechargeable lithium-ion battery consisting of LiCoO₂ nanoparticles as positive and LiV₃O₈ nanosheets as negative electrode was assembled. This battery represented a discharge voltage of about 1 V with good cycling performance.     

Electrochemical lithium intercalation into WO3 and lithium tungstates Li x WO3+ x /2 of various structures

Hexagonal and monoclinic tungsten trioxides WO₃ and hexagonal lithium tungstates Li _x WO_{3+ x /2} (x = 0.10–0.42) from a soft chemistry route were used as the active cathode material in secondary lithium batteries. The hexagonal structures, regardless of their being an oxide or a tungstate, showed higher specific capacities and better cycling behavior in Li⁺ intercalation reactions than the monoclinic form. The presence of pre-allocated lithium (as Li₂O) in hexagonal tungstates decreased the capacity for lithium intercalation. Additionally, the plot of open-circuit voltage (OCV) against the depth of intercalation (n) for anhydrous tungstates showed two straight lines with different slopes that can be related to the structural changes in lithium intercalation. The effective diffusion coefficients of lithium insertion into the host structure, D˜, were also found to be dependent on the structure and the composition of these compounds. Received: 28 November 1997 / Accepted: 6 March 1998     

High-temperature combustion synthesis and electrochemical characterization of LiNiO2, LiCoO2 and LiMn2O4 for lithium-ion secondary batteries

Lithium nickelate (Li_0.88Ni_1.12O₂), lithium cobaltate (LiCoO₂) and lithium manganate (LiMn₂O₄) were synthesized by fast self-propagating high-temperature combustion and their phase purity and composition were characterized by X-ray diffraction and inductively coupled plasma spectroscopy. The electrochemical behaviour of these oxides was investigated with regard to potential use as cathode materials in lithium-ion secondary batteries. The cyclic voltammograms of these cathode materials recorded in 1 M LiClO₄ in propylene carbonate at scan rates of 0.1 and 0.01 mV s^–1 showed a single set of redox peaks. Charge-discharge capacities of these materials were calculated from the cyclic voltammograms at different scan rates. The highest discharge capacity was observed in the case of Li_0.88Ni_1.12O₂. In all the cases, at a very slow scan rate (0.01 mV s^–1) the capacity of the charging (oxidation) process was higher than the discharging (reduction) process. A strong influence of current density on the charge-discharge capacity was observed during galvanostatic cycling of Li_0.88Ni_1.12O₂ and LiMn₂O₄ cathode materials. LiMn₂O₄ can be used as cathode material even at higher current densities (1.0 mA cm^–2), whereas in the case of Li_0.88Ni_1.12O₂ a useful capacity was found only at lower current density (0.2 mA cm^–2). For the fast estimation of the cycling behaviour of LiMn₂O₄, a screening method was used employing a simple technique for immobilizing microparticles on an electrode surface. Electronic Publication     

Synthesis and electrochemical properties of yttrium-doped LiMn<Subscript>0.98</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>2</Subscript> for lithium secondary batteries

Yttrium-doped lithium manganese oxide (LiMn_0.98Y_0.02O₂) was prepared by ion exchange of lithium for sodium in NaMn_0.98Y_0.02O₂ precursors obtained by using rheological phase reaction method. This material had small particle size, which was composed of grain size of about 100 nm. Especially, LiMn_0.98Y_0.02O₂ delivered the initial discharge capacity of about 191 mA h g⁻¹ at room temperature when cycled between 2.0 and 4.4 V vs Li/Li⁺. Moreover, it showed an excellent cycling behavior, its specific capacity remained above 173 mA h g⁻¹ after 20 cycles, and the material did not transform into spinel structure during the electrochemical cycling according to the cyclic voltammograms and X-ray powder diffraction. The electrochemical results revealed that the doping of Y³⁺ improved the performance of LiMnO₂ considerably.     

Intercalation processes influence the structure and electrophysical properties of lithium-conducting compounds having defect perovskite structure

The structural features and electrophysical properties of lithium-conducting compounds having defect perovskite structure based on Li_0.5La_0.5Nb₂O₆ and Li_0.5La_0.5TiO₃ were studied using X-ray diffraction and synchrotron analyses, potentiometry, and complex impedance spectroscopy. Intercalated lithium was found to differently influence ion conductance in titanium- and niobium-containing materials. This difference was found to arise from the structural features of the materials. The systems studied have high chemical diffusion coefficients of lithium (D _Li⁺ = 1 × 10⁻⁶ cm²/s for Li_0.5La_0.5Nb₂O₆ and D _Li⁺ = 3.3 × 10⁻⁷ cm²/s for Li_0.5La_0.5TiO₃).     

Structural and conductivity studies in LiFeP2O7, LiScP2O7, and NaScP2O7

Structural studies of LiScP₂O₇ by Rietveld refinement confirm that this material is isostructural with LiFeP₂O₇ studied previously. However, NaScP₂O₇ shows a structure different from the structural types of the basic group of Na^IM^IIIP₂O₇ known thus far. Systematic ranges for the six structural types of A^IM^IIIP₂O₇ are presented in terms of ion radii sums and ratios. The framework of LiMP₂O₇ (M=Sc, Fe) has rather wide tunnels running along the crystallographic c-axis. This feature has determined our interest to check the ion conductivity in A^IM^IIIP₂O₇ (A=Li, Na; M=Sc, Fe). The bulk conductivity, however, is low in these compounds, 10⁻⁶–10⁻⁷ S/cm at 300 °C, as determined by impedance spectroscopy. In order to facilitate the conductivity via normal lithium sites, heterovalent substitution is used. Received: 30 April 1999 / Accepted: 15 June 1999     

Synthesis and electrochemical properties of nanostructured LiAl x Mn2 − x O4 − y Br y particles

Nanostructured LiAl _x Mn_2 − x O_4 − y Br _y particles were synthesized successfully by annealing the mixed precursors, which were prepared by room-temperature solid-state coordination method using lithium acetate, manganese acetate, lithium bromide, aluminum nitrate, citric acid, and polyethylene glycol 400 as starting materials. X-ray diffractometer patterns indicated that the particles of the as-synthesized samples are well-crystallized pure spinel phase. Transmission electron microscopy images showed that the LiAl _x Mn_2 − x O_4 − y Br _y samples consist of small-sized nanoparticles. The results of galvanostatic cycling tests revealed that the initial discharge capacity of LiAl_0.05Mn_1.95O_3.95Br_0.05 is 119 mAh g⁻¹; after the 100th cycle, its discharge capacity still remains at 92 mAh g⁻¹. The introduction of Al and Br in LiMn₂O₄ bring a synergetic effect and is quite effective in increasing the capacity and elevating cycling performance.     

Influence of Li source on tap density and high rate cycling performance of spherical Li[Ni<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>]O<Subscript>2</Subscript> for advanced lithium-ion batteries

Spherical Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode materials with different microstructure have been prepared by a continuous carbonate co-precipitation method using LiOH⋅H₂O, Li₂CO₃, CH₃COOLi⋅2H₂O and LiNO₃ as lithium source. The effects of Li source on the physical and electrochemical properties of Li[Ni_1/3Co_1/3Mn_1/3]O₂ are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The results show that the morphology, tap density and high rate cycling performance of Li[Ni_1/3Co_1/3Mn_1/3]O₂ spherical particles are strongly affected by Li source. Among the four Li sources used in this study, LiOH⋅H₂O is beneficial to enhance the tap density of Li[Ni_1/3Co_1/3Mn_1/3]O₂, and the tap density of as-prepared sample reaches 2.32 g cm⁻³. Meanwhile, Li₂CO₃ is preferable when preparing the Li[Ni_1/3Co_1/3Mn_1/3]O₂ with high rate cycling performance, upon extended cycling at 1 and 5C rates, 97.5% and 92% of the initial discharge capacity can be maintained after 100 cycles.     

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.     

Synthesis of nanosized materials for lithium-ion batteries by mechanical activation. Studies of their structure and properties

This short review reports on the synthesis of nanosized electrode materials for lithium-ion batteries by mechanical activation (MA) and studies of their properties. Different structural types of compounds were considered, namely, compounds with a layered (LiNi_{1 − x − y} Co _x Mn _y O₂), spinel (LiMn₂O₄, Li₄Ti₅O₁₂), and framework (LiFePO₄, LiTi₂(PO₄)₃) structures. The compounds also differed in electronegativity, which varied from 10⁻⁴ S cm⁻¹ for LiCoO₂ to 10⁻⁹ S cm⁻¹ for LiFePO₄. The preliminary MA of mixtures of reagents in energy intensive mechanoactivators led to the formation of highly reactive precursors, and annealing of the latter formed nanosized products (the mean particle size is 50–200 nm). The local structure of the synthesized compounds and the composition of their surface were studied by spectral methods. An increase in the dispersity and defect concentration, especially in the region of the surface, improved some electrochemical characteristics. It increased the stability during cycling (LiMn₂O₄, at 3 V) and the regions of the formation of solid solutions during cycling (Li₄Ti₅O₁₂, LiFePO₄), led to growth of surface Li-ion conductivity (LiTi₂(PO₄)₃), etc. The mechanochemical approach was also used for the synthesis of core-shell type composite materials (LiFePO₄/C, LiCoO₂/MeO _x ) and materials based on two active electrode components (LiCoO₂/LiMn₂O₄).     

Controllable solvo-hydrothermal electrodeposition of lithium vanadate uniform carnation-like nanostructure and their electrochemical performance

In this paper, we successfully developed a novel method to synthesize uniform carnation-like lithium vanadate nanostructures by combining electrochemical deposition and solvo-hydrothermal method. The samples were characterized by field emission scanning electron microscopy, power X-ray diffraction, and thermogravimetric analysis. The results show that the LiV₃O₈·H₂O carnation-like nanostructure is 2–3 μm in diameter and assembled from nanosheets with thickness of 10–20 nm. Based on a series of experiments, we proposed a possible growth mechanism, in which the supersaturation derived from electric field and high conductivity under solvo-hydrothermal conditions due to the successive growth of lithium vanadate. In our work, we have discussed three different solvo-hydrothermal systems. It is proved that the morphology of coating materials could be conveniently controlled by selecting alcohols with different chain of alkyl. Compared with short-chain alcohol, CH₃–(CH₂)₆–CH₂–OH was beneficial to promote the oriented growth of nanosheets. Electrochemical performances of lithium vanadate cathode materials were characterized by galvanostatic charge–discharge, and LiV₃O₈ synthesized in n-octanol aqueous solution exhibits the highest capacity of 357 mAh g⁻¹ and best cycle stability. Furthermore, the influence of solvo-hydrothermal conditions on the morphology and electrochemical performance of products has also been studied.     

Synthesis and characterization of LiCo<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4</Subscript> powder by a novel CAM microwave-assisted sol–gel method for Li ion battery

LiMn₂O₄-based spinels are of great interest as positive electrode materials for lithium ion batteries. LiCo _x Mn_2−x O₄ (x = 0.0, 0.1, 0.2, 0.3, and 0.4) spinel phases have been synthesized by novel citric acid-modified microwave-assisted sol–gel method. The structural properties of the synthesized products have been investigated by X-ray powder diffraction and scanning electron microscopy. To improve the recharge capacity of Li/LiCo _x Mn_2−x O₄ cells, the electrochemical features of LiCo _x Mn_2−x O₄ compounds have been evaluated as positive electrode materials. The structural properties of Co-doped oxides are very similar to LiMn₂O₄ electrode. Techniques like cyclic voltammetry, charge–discharge and cycle life are also used to characterize the LiCo _x Mn_2−x O₄ (x = 0.0, 0.1, 0.2, 0.3, and 0.4) electrodes.     

Preparation and characterisation of monomeric molybdate(VI) anion-doped polypyrrole electrodes

Stable monomeric molybdate(VI) anion-doped polypyrrole composites [P_py(Mo)] have been prepared from sulfuric acid solution containing Mo(VI) by an electrochemical potential cycling method. P_py(Mo) films exhibit redox waves inherent to the polypyrrole moiety only, and the built-in Mo(OH)₅O⁻ is found to be electroinactive. X-ray photoelectron spectroscopic examination of oxidised and reduced P_py(Mo) films confirms this phenomenon. Received: 5 January 1998 / Accepted: 10 January 1999     

Effect of electrochemical processing of a γ-butyrolactone-based electrolyte on the cyclability of lithium electrodes

Effect of a preliminary electrolysis of electrolyte on the lithium electrode cyclability in a 1 M LiC1O₄ solution in γ-butyrolactone is studied. On its repeated cycling in the same electrolyte, the lithium electrode’s efficiency decreases and the overvoltage of cathodic and anodic processes considerably increases. Soluble products of electrochemical destruction of the electrolytic system accumulate in solution during the lithium electrode cycling, the products being prone to polymerization. In the presence of these products, the lithium passivation rate increases and the cycling efficiency decreases significantly. It is concluded that the soluble products of the destruction are oligomers formed during electrochemical polymerization of γ-butyrolactone     

Effects of complexants on [Ni1/3Co1/3Mn1/3]CO3 morphology and electrochemical performance of LiNi1/3Co1/3Mn1/3O2

LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials for the application of lithium ion batteries were synthesized by carbonate co-precipitation routine using different ammonium salt as a complexant. The structures and morphologies of the precursor [Ni_1/3Co_1/3Mn_1/3]CO₃ and LiNi_1/3Co_1/3Mn_1/3O₂ were investigated through X-ray diffraction, scanning electron microscope, and transmission electron microscopy. The electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ were examined using charge/discharge cycling and cyclic voltammogram tests. The results revealed that the microscopic structures, particle size distribution, and the morphology properties of the precursor and electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ were primarily dependent on the complexant. Among all as-prepared LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials, the sample prepared from Na₂CO₃–NH₄HCO₃ routine using NH₄HCO₃ as the complexant showed the smallest irreversible capacity of 19.5 mAh g⁻¹ and highest discharge capacity of 178.4 mAh g⁻¹ at the first cycle as well as stable cycling performance (98.7% of the initial capacity was retained after 50 cycles) at 0.1 C (20 mA g⁻¹) in the voltage range of 2.5–4.4 V vs. Li⁺/Li. Moreover, it delivered high discharge capacity of over 135 mAh g⁻¹ at 5 C (1,000 mA g⁻¹).     

Effect of synthesis temperature and molar ratio of organic lithium salts on the properties and electrochemical performance of LiFePO4/C composites

LiFePO₄/C cathode materials were synthesized through in situ solid-state reaction route using Fe₂O₃, NH₄H₂PO₄, Li₂C₂O₄, and lithium polyacrylate as raw materials. The precursor of LiFePO₄/C was investigated by thermogravimetric/differential thermal analysis. The effects of synthesis temperature and molar ratio of organic lithium salts on the performance of samples were characterized by X-ray diffraction, scanning electron microscopy, electrochemical impedance spectra, cyclic voltammogram, and constant current charge/discharge test. The sample prepared at optimized conditions of synthesis temperature at 700 °C and molar ratio with 1.17:1 exhibits excellent rate performance and cycling stability at room temperature.     

Synthesis of Single‐Crystalline Spinel LiMn2O4 Nanorods for Lithium‐Ion Batteries with High Rate Capability and Long Cycle Life

The long‐standing challenge associated with capacity fading of spinel LiMn₂O₄ cathode material for lithium‐ion batteries is investigated. Single‐crystalline spinel LiMn₂O₄ nanorods were successfully synthesized by a template‐engaged method. Porous Mn₃O₄ nanorods were used as self‐sacrificial templates, into which LiOH was infiltrated by a vacuum‐assisted impregnation route. When used as cathode materials for lithium‐ion batteries, the spinel LiMn₂O₄ nanorods exhibited superior long cycle life owing to the one‐dimensional nanorod structure, single‐crystallinity, and Li‐rich effect. LiMn₂O₄ nanorods retained 95.6 % of the initial capacity after 1000 cycles at 3C rate. In particular, the nanorod morphology of the spinel LiMn₂O₄ was well‐preserved after a long‐term cycling, suggesting the ultrahigh structural stability of the single crystalline spinel LiMn₂O₄ nanorods. This result shows the promising applications of single‐crystalline spinel LiMn₂O₄ nanorods as cathode materials for lithium‐ion batteries with high rate capability and long cycle life.     

Electrospun V2O5 Nanostructures with Controllable Morphology as High‐Performance Cathode Materials for Lithium‐Ion Batteries

Porous V₂O₅ nanotubes, hierarchical V₂O₅ nanofibers, and single‐crystalline V₂O₅ nanobelts were controllably synthesized by using a simple electrospinning technique and subsequent annealing. The mechanism for the formation of these controllable structures was investigated. When tested as the cathode materials in lithium‐ion batteries (LIBs), the as‐formed V₂O₅ nanostructures exhibited a highly reversible capacity, excellent cycling performance, and good rate capacity. In particular, the porous V₂O₅ nanotubes provided short distances for Li⁺‐ion diffusion and large electrode–electrolyte contact areas for high Li⁺‐ion flux across the interface; Moreover, these nanotubes delivered a high power density of 40.2 kW kg^?1 whilst the energy density remained as high as 201 W h kg^?1, which, as one of the highest values measured on V₂O₅‐based cathode materials, could bridge the performance gap between batteries and supercapacitors. Moreover, to the best of our knowledge, this is the first preparation of single‐crystalline V₂O₅ nanobelts by using electrospinning techniques. Interestingly, the beneficial crystal orientation provided improved cycling stability for lithium intercalation. These results demonstrate that further improvement or optimization of electrochemical performance in transition‐metal‐oxide‐based electrode materials could be realized by the design of 1D nanostructures with unique morphologies.     

The influence of Li sources on physical and electrochemical properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials for lithium-ion batteries

LiNi_0.5Mn_1.5O₄ cathode materials were successfully prepared by sol–gel method with two different Li sources. The effect of both lithium acetate and lithium hydroxide on physical and electrochemical performances of LiNi_0.5Mn_1.5O₄ was investigated by scanning electron microscopy, Fourier transform infrared, X-ray diffraction, and electrochemical method. The structure of both samples is confirmed as typical cubic spinel with Fd3m space group, whichever lithium salt is adopted. The grain size of LiNi_0.5Mn_1.5O₄ powder and its electrochemical behaviors are strongly affected by Li sources. For the samples prepared with lithium acetate, more spinel nucleation should form during the precalcination process, which was stimulated by the heat released from the combustion of extra organic acetate group. Therefore, the particle size of the obtained powder presents smaller average and wider distribution, which facilitates the initial discharge capacity and deteriorates the cycling performance. More seriously, there exists cation replacement of Li sites by transition metal elements, which causes channel block for Li ion transference and deteriorates the rate capability. The compound obtained with lithium hydroxide exhibits better electrochemical responses in terms of both cycling and rate properties due to higher crystallinity, moderate particle size, narrow size distribution and lower transition cation substitute content.