Chemical Diffusion Coefficient Of Lithium Research Articles

Electrochemical characterization of a lithiated mixed nickel-cobalt oxide (LiNi0.5Co0.5O2) prepared by sol-gel process

Lithiated transition metal oxides having a layered structure and general formula LiMO2, have been extensively studied as positive electrode active materials for lithium or lithium-ion batteries. In particular, lithium nickel dioxide (LiNiO2) and lithium cobalt dioxide (LiCoO2) present a layered structure with high diffusion coefficients for the lithium ion. This latter property is very important in order to realize practical devices having high discharge rates. LiNiO2, compared with LiCoO2, has the advantage to be a cheaper material with a higher specific capacity for lithium cycling, but its stability upon cycling can be greatly influenced by the displacement of Ni ions from the Ni layers to the Li planes as the content in lithium is reduced over a certain value. Recently, solid solutions such as LiNixCo1−xO2 have been proposed to offer a compromise between stability, cost and capacity. In this work we have studied LiNi0.5Co0.5O2 prepared by the Complex Sol-Gel Process (CSGP). The advantage of this procedure toward the solid-state process is the high homogeneity in composition and in particle dimension of the synthesized compounds. The samples have been characterized electrochemically using chronopotentiometric, voltammetric and impedance measurements in liquid electrolyte. The results indicates that CSGP-synthesized LiNi0.5Co0.5O2 shows good cyclability (after 1000 cycles about 2/3 of the initial capacity can still be cycled) only if the anodic potential is limited to about 4.2 V. The quite low values of the specific capacity (∼70 mAh/g at C/1 charge-discharge rate) can be justified by the non-complete calcination reaction, as suggested by X-ray measurements. Kinetic properties have been evaluated by Electrochemical Impedance Spectroscopy measurements, which have shown quite high values for the lithium chemical diffusion coefficient (10−7÷10−8 cm2s−1) and its unexpected decrease as deintercalation proceeds from x=0.5 in LiNi0.5Co0.5O2.

Chemical Diffusion Coefficient of Lithium in Carbon Fiber

Electrochemical investigations on coal pitch‐based carbon fiber (heat‐treated at 2800°C) were carried out. The open‐circuit voltages of the cell were lower than 0.15 V vs. in the range of 0.15 < x < 0.65. The open‐circuit voltage profile vs. x showed no distinct two‐phase region in the present Li‐carbon system in 0 < x < 0.65. Almost constant capacity of 220 mAh/g was observed until the 140th cycle in the cycling tests of the Li|carbon fiber cell (current density 25 mA/g) The compositional variation of the chemical diffusion coefficient of lithium at ambient temperature was measured by two different methods, i.e., the current pulse relaxation method and the potential step chronoamperometric method. Excellent agreement within one order of magnitude was observed between the two sets of values obtained from these two methods. The values were around at x ≒ 0 and decreased with increasing x. The values lay between and in x > 0.2

Electrostatic spray deposition of thin layers of cathode materials for lithium battery

A novel fabrication technique, namely electrostatic spray deposition (ESD), has been developed in order to prepare thin layers of solid electrolytes and cathode materials for lithium batteries. In this study, the 4-volt cathode material LiCoO 2 was chosen, and prepared by spraying alcohol solutions of nitrates and acetates of cobalt. ESD set-ups, with either horizontal or vertical configurations, were used. Depending on the precursor and process deposition conditions, the morphology of the layers can be relatively dense, fractal-like porous, or unique 3-D cross-linked porous structures with a high porosity and a narrow pore size distribution. For low deposition temperatures, LiCoO 2 layers are XRD amorphous. Upon annealing, crystallized layers are obtained. The lithium chemical diffusion coefficient of the LiCoO 2 layers has been measured with Galvanostatic Intermittent Titration Technique (GITT), values range from 10 −14 to 10 −12 cm 2/s, depending on the lithium content and the annealing temperatures. Cyclic voltammograms of a test cell reveal that both lithium insertion and extraction are one-step processes.

Amorphous MoS 2 as the cathode of lithium secondary batteries

Amorphous MoS 2(a-MoS 2) was synthesized by the thermal decomposition of (NH 4) 2MoS 4 in a hydrogen gas flow at temperatures from 150 to 300 °C. The a-MoS 2 synthesized at 150 and 200 °C were almost amorphous. However, those prepared at 250 and 300 °C showed very small and broad peaks in powder X-ray diffraction patterns. Discharge/charge cycling measurements, revealed that the sample prepared at 150 °C showed the highest cycle capacity (100 Ah/kg) at the 100th cycle. The chemical diffusion coefficients of lithium were also highest for a-MoS 2 prepared at 150 °C, and the D ̃ values fell in the range of −10< log( D ̃ / cm 2 s −1 )<−9 .

In situ electrochemical characterization of lithium-alloying materials for rechargeable anodes in lithium batteries

In situ electrochemical techniques can be used to investigate the intercalation process of lithium into several inserting materials used in rechargeable lithium battery anodes. Alloying materials on the basis of aluminium, with the addition of small portions of a second metal such as nickel or manganese, are especially examined. The chemical diffusion coefficient of lithium was estimated using the potentiostatic transient technique. Chronoamperometry gives information on the diffusion process related to the chemical composition, grain structure and crystallinity of the alloying material. The measurements have been carried out in a 1 M LiClO 4/propylene carbonate solution at room temperature.

Diffusion enhancement in LixMn2O4

The electrochemical properties of Li x Mn 2 O 4 with 0.5≤ x≤2.5 as the lithium content in the starting materials, have been studied. A novel wet-chemical route has been developed. The lithium chemical diffusion coefficient in Li x Mn 2 O 4 as synthesized by this wet-chemical technique is at least 10 times higher than that of LiMn 2O 4 obtained by solid state reaction. In the observed two-phase regions near x = 0.75 and 1.75 diffusion enhancement ascribed to interfacial diffusion is observed. The results of cyclic voltammetry and impedance analysis provide additional evidence for this hypothesis.

A Basic Thin Film Study of Spinel Limn204As a Possible Cathode Material for Lithium Secondary Cells

ABSTRACTIn a series of fundamental studies on the cathode active materials for a lithium secondary cell using geometrically well-defined sample electrodes, thin films of spinel LiMn204on a platinum plate were investigated in this work in an LiCl04/propylene carbonate solution. These pyrolytically prepared films exihibit reversible extraction/insertion behavior for lithium under galvanostatic charge/discharge cycling between 4.3-3.5 V. The chemical diffusion coefficient of lithium in LixMn204determined by the galvanostatic intermittent titration technique (GITT) was in the order of 10−7-10−10cm2- s−1within a spinel single-phase region of 0.6&lt;x&lt;1.0 and increased with increasingx.

Reversible Electrochemical Insertion of Lithium in Fine Grained Polycrystalline Powders of SnO2

Fine grained SnO2powders have been obtained using an unconventional method. It deals with the well known polymerization method starting from the metallic halide SnCl4with polyethylene oxide (PEO). With this method, SnO2powders, which are free from water and hydroxyl group contaminations and possess small crystallite size (≈50 A∘), are obtained by appropriate pyrolysis of the polymer. Consequently, these powders show good ability to insert reversibly lithium ions in the Li/Li+/LixSnO2cell. Indeed, by minimizing the size of the crystallites, the formation of defect-bonds is favored, particularly at the crystallite surface, acting as reversible (de)grafting sites of Li+. Finally, an easy-to-carry out method to determine the chemical diffusion coefficient of lithium has been proposed.

Cycling performance of the Li xAl anode prepared by the compression method

A preparation method of LiAl anodes by compression of foils of the two metals at room and elevated temperatures is described. The chemical diffusion coefficient of lithium in the LiAl anodes is measured as a function of the lithium concentration of the β-phase range. The cycleability of the anodes prepared by this method with and without manganese is studied in laboratory coin cells, with L x MnO 2 cathodes, as a function of the depth-of-discharge (DOD). The cycling efficiency of the Mn-free anodes at DOD = 22% is very low, 88.9%, while that of the anodes with 1.0 and 2.6% Mn is considerably higher: 95.5% at DOD 17% and 94.4% at DOD 38%, respectively.

Coloration dynamics of tungsten oxide based all solid state electrochromic device

An electrochromic thin film of amorphous WO 3 nH 2O was fabricated by spin-coating a peroxo-polytungstate solution. Coloration and bleaching kinetics of the film in contact with a solid polymer electrolyte were investigated by a chrono-amperometric method using a cell, Li/Polymer/WO 3 nH 2O, ITO. The transition currents were analyzed on the basis of a newly proposed theory for the diffusion-controlled current generated by a voltage step in such a cell without a reference electrode. It was found that both kinetics were controlled by the diffusion process and the chemical diffusion coefficients of lithium were, in common, about 5 × 10 −12 cm 2 s −1.

Thermodynamic and kinetic properties of lithium insertion into titanium misfit layer sulfides

The thermodynamics and kinetics of the electrochemical intercalation of lithium into polycrystalline (PbS)1.18(TiS2)2, (BiS)1.14(TiS2)2, (PbS)1.18TiS2 and (SnS)1.20TiS2 have been studied by coulometric titration techniques. The highest values of the Gibbs energy of intercalation were obtained with (MS)1 +δ(TiS2)2 stoichiometries, particularly in (PbS)1.18(TiS2)2. The chemical diffusion coefficients of lithium for all compounds hardly varied with the amount of intercalated lithium and the maximum value, 6.5 × 10–10 cm2 s–1, was found in (PbS)1.18(TiS2)2. Micropolarization tests also showed that fast kinetics and better reversibility occurred in sulfides with (MS)1 +δ(TiS2)2 stoichiometry, probably due to the presence of true van der Waals gaps created at the TiS2/TiS2 interface.

Amorphous MnO 2 thin film cathode for rechargeable lithium batteries

MnO 2 thin films have been deposited electrochemically from a MnSO 4 solution. The deposition conditions have been optimized. The open circuit voltage versus lithium content of the Li x MnO 2 cathode shows a linear relation with a break in the slope at x=0.5. The specific energy density is 580 Wh/kg and the volume energy density 2916 Wh/ℓ. The chemical diffusion coefficient of lithium in the MnO 2 film is 4.27 to 4.85×10 −13 cm 2/s for 0≤ x≤0.2 and 1.1×10 −11 cm 2/s for x=0.9. The good reversibility of lithium insertion and extraction has been shown by voltammetry and shallow charge-discharge cycling.

Polycrystalline, glassy and thin films of LiMn 2O 4

The influence of sintering temperature on the formation, phase purity, and electrical conductivity of LiMn 2O 4 has been investigated by means of X-ray diffraction and ac impedance analysis. Higher sintering temperatures lead to increased unit cell constants more perfect lattices and a higher bulk electrical conductivity. Samples sintered at lower temperatures exhibit higher chemical diffusion coeficcients for lithium. Attempts to prepare glassy LiMn 2O 4B 2O 3 have been made. The conduction behaviour of the glass during the crystallization process has been studied. Polycrystalline thin films of LiMn 2O 4 have been prepared using electron beam evaporation. The temperature dependence of the electrical conductivity of the thin film did not differ substantially from that of bulk material, while the chemical diffusion coefficient for lithium is four orders of magnitude lower than that of samples sintered at 1100°C.

Thermodynamic and Kinetic Studies of Electrochemical Lithium Insertion into Quaternary Li‐Mn‐V‐O Spinel as Positive Materials for Rechargeable Lithium Batteries

The thermodynamics and kinetics of the lithium insertion process into the quaternary spinel have been studied. The partial molar quantities , , and of lithium in the quaternary spinels have been determined from electromotive force‐temperature measurements performed using 1M solution of propylene carbonate in the temperature range from 298 to 330 K. These thermodynamic functions varied with the lithium concentration in the oxide structure and a major variation was observed around in . The chemical diffusion coefficient for lithium in the spinel oxides has been measured as functions of the lithium composition and temperature by a current‐pulse relaxation technique. The values of , obtained in the value range from 0.5 to 1.0 at 298 K, were found to be several orders of magnitude higher than those in the value range from 1.3 to 2.5. The lithium self‐diffusion coefficient , partial lithium‐ion conductivity and activation energy for lithium diffusion have been calculated.

MnO thin film cathode for rechargeable microbatteries

Thin films of MnO were deposited by electron beam evaporation using a MnO or MnO 2 source. The thin films were charaterized by X-ray and electron diffraction. The Coulomb titration curve reveals a potential plateau of 2.9 V over the composition range 0.05< x<2.0. The chemical diffusion coefficient of lithium in thin films at 15°C is 2.7×10 −14 cm 2/ s for 0< x<0.01 and 2.2×10 −15 cm 2/s for 0.02< x<0.06. Good reversibility for lithium insertion and extraction is demonstrated by cyclic voltammetry.

Kinetic and Structural Studies of the Electrochemical Insertion of Lithium into Hexagonal‐type x ( A 2 O ) · WO 3 ( A = Na + , K + , NH 4 + )

The kinetic and thermodynamic studies of the insertion of lithium into hexagonal‐type (, ), obtained by heat‐treating the corresponding tungstic acid C phases, , at 350°C in air, were made. The variations of quasi‐open‐circuit potentials and x‐ray diffraction patterns of the tungsten oxides with lithium insertion revealed that a ternary phase, such as , is formed, while maintaining the original hexagonal‐type structure. The standard free energies for lithium insertion, , were −375, −389 and −400 kJ(mol)−1 at 298 K for , respectively. The chemical diffusion coefficients of lithium, , in the oxides were measured as functions of the lithium composition and temperature by an ac impedance method using carbonate as an electrolyte. The obtained values of , based on a geometrical surface area, were dependent on the lithium composition and temperature. The values of for were approximately 10−8 cm2 s−1 at and room temperature, decreasing to 10−10 cm2 s−1 with increasing . The self‐diffusion coefficient of lithium, , derived from the values, was of the order of 10−11 cm2s−1 at and room temperature, decreasing with increasing . Both the values of and for the hexagonal‐type oxides were by several orders of magnitude higher than those for the monoclinic . The activation energies for lithium diffusion in were , being typical of diffusion in layered insertion materials.

Electrochemical investigation of the diffusion of lithium in ?-LiAl alloy at room temperature

The chemical diffusion coefficients of lithium in β-LiAl alloy were measured by the use of transient techniques such as chronopotentiometry, chronoamperometry and a.c. impedance spectroscopy in 1 M LiClO4-propylene carbonate at 25° C. A β-LiAl layer, formed by electrodepositing lithium on a thin aluminium substrate having a microstructure of preferred (100) orientation, was mainly used. The values of the diffusion coefficients were found to be of the order of 10−10 cm2s−1, which are close to those reported in the literature. A scatter in the coefficient was discussed in terms of the formation and disruption of the passivating layer on the alloy.

Studies of the transport properties in lithium-intercalated NiPS 3

We have investigated the electrochemical and transport properties of lithium-intercalated NiPS 3. Thermodynamic and kinetic results have been obtained by the modified galvanostatic intermittent titration technique for the long-time regime in the compositional range 0 ⩽ x ⩽ 1.5. The chemical diffusion coefficient of lithium in Li x NiPS 3 is composition dependent and the average value is 10 −9 cm 2 s −1 at room temperature. The partial ionic conductivity is estimated from the experimental determination of D ∗ and W and a value of σ i t e ( Li) is 2 × 10 −3 ω −1 cm −1 at x = 1.0. These transport properties are compared with those obtained in a galvanic cell with a composite electrode, i.e. a mixture of active material, solid electrolyte, acetylene black and polytetrafluoroethylene. Electrochemical titration during the discharge under moderate current drain shows lower values for the transport properties in a medium which is out of equilibrium.

Preparation and electrochemical characteristics of new MnO 2V 2O 5 systems as positive materials for rechargeable lithium batteries

New binary oxides, MnO 2· xV 2O 5 ( x = 0–0.3), which were formed by heating mixtures of Mn(NO 3) 2·6H 2O and NH 4VO 3 at various V/Mn atomic ratios and at different temperatures in air, have been characterized by X-ray diffraction method, X-ray photoelectron spectroscopy and infrared spectroscopy. The amount of Li + ions inserted into the crystal lattice of the oxide increased with increasing x-value in MnO 2· xV 2O 5, and reached ca 1 Li/mole of the oxide with x = 0.6. Furthermore, the thermodynamic and kinetic studies showed that the standard free energy for the lithium insertion, Δ G 1, is −265 kJ mol −1 in the range of n = 0–1 in Li n MnO 2· xV 2O 5 at 25°C and that the chemical diffusion coefficients of lithium in the oxide matrices are in the range from 10 −9 to 10 −12cm 2s −1 at 25°C and increased with increasing V 2O 5 content in the mixed oxides.

Electrochemical insertion of lithium into YBa 2Cu 3O 7- y

Lithium insertion into the superconductor YBa 2Cu 3O 7- y has been studied with the cell Li| 1 M LiClO 4 in PC|Li x YBa 2 Cu 3O 7- y . The open circuit voltage of the cell decreases gradually from 3.4 V to 2.2 V as the lithium content x increases from 0 to 0.3. Then a voltage plateau is reached that continues up to x=1.0. The chemical diffusion coefficient of lithium has been determined by the galvanostatic intermittent titration technique. A value of 1.65 to 2.13 × 10 −7 cm 2/s for x<0.1 is obtained. The reversibility of the lithium insertion was shown by voltammetry and repeated cycling of YBa 2Cu 3O 7- y . A battery has been made with a capacity of 24.4 mAh, corresponding to a volume capacity of 256.7 Ah/1.