Optimization of the efficiency and cycling performance of Na0.1CrS2 electrodes in nonaqueous secondary lithium cells

The effect of the macrostructure (grain size) and the microstructure (crystal lattice parameters) factors on the coulombic efficiency of Na_0.1CrS₂ cathodes in secondary Li cells is studied. An attempt is made to employ Atlung's model in assessing the chemical diffusion coefficient of Li⁺ in the host structure leading to more realistic values with respect to effective interface area. The possibility of enhancing the mobility rate of Li⁺ by intercalation of water in the host structure is revealed. Using Atlung's model as a guideline it was possible to improve considerably the performance of the Na_0.1CrS₂ cathodes, while retaining their good cycling stability.     

Transport and equilibrium characteristics of γ-lithium vanadium bronze

The diffusion coefficient of Li⁺ in the γ-lithium vanadium bronze (Li_1+xV₃O₈) has been measured with the long-pulse galvanostatic technique. Values ranging from 1.7×10⁻⁷ cm²s⁻¹, at x=0.3, to 2.2×10⁻⁸ cm²s⁻¹, at x= 1.4, have been measured. The thermodynamic factors, d ln a/d ln c, determined from the OCV/x curve and from voltage relaxation after the current pulse, have a mean value of ∼15. The pseudo two-phase region observed in the OCV/x curve at high Li⁺ concentrations seems attributable to ordering of Li⁺ in specific sites and to alteration of the unit cell. This process is reversible as shown by X-ray diffractometry. Finally, from OCV/t plots at different x, the partial molar entropy of Li⁺ was determined. The values, on account of the large dE(x)/dt measured, are higher than those found for V₆O₁₃ or TiS₂.     

Jump diffusion coefficient of different cations intercalated into amorphous WO3

This work shows how the combination of quasi-equilibrium (chronopotentiometry) and kinetical measurements (electrochemical impedance) is able to extract ionic mobility values like the jump diffusion coefficient D_J. Results are presented on the jump diffusion coefficient variation with composition of several cations (Li⁺, Na⁺, and K⁺) intercalated into electron beam evaporation-prepared a-WO₃ thin films. D_J exhibits higher values for the smallest ion (Li⁺), and decreases as the ion size enlarges. In all cases D_J shows lower values for high intercalation levels. It is noted that the type of cation rather influences transport mechanisms than equilibrium properties (insertion thermodynamics). The energy barrier of ion hopping is analyzed in light of available microscopic diffusion models and theoretical simulations.     

Characteristics of molybdenum oxide and chromium oxide cathodes in primary and secondary organic electrolyte lithium batteries. Part II. Transport properties

Utilization and rate performance of metal chalcogenide host lattice cathodes depend on transport properties of phases Li_nMCh_x, i.e., on their electronic and Li⁺ conductivity. On the other hand, liquid phase Li⁺ diffusion in pores of the electrodes or rates of charge transfer and phase change reactions may also be limiting under certain conditions. For phases Li_nMO_x (M=Cr, Mo) and in particular for the model substance Li_nMoO₃ parameters controlling utilization and rate performance were followed during discharge and recharge, i,e., in dependence of composition and history. The main results can be summarized as below: Chemical diffusion coefficients D?_Li+in Li_nCrO_x and Li_nMoO₃ have their maxima close to n ca. 0.5 and drop sharply for n&>;1 - in the layered phase Li_nMoO₃, Li⁺ mobility is paralleled by the interplanar distance; D?_Li+ in discharged Li_nCrO_x and Li_nMoO₃ partly recovers during recharge, but never reaches the top values of the 1st discharge - this is related with irreversible structural disintegration of the host matrix; At the end of discharge (n ca. 1.5) a porous layer of a final discharge product is formed on Li_nCrO_x and Li_nMoO₃ particles. This layer is electronically insulating and Li⁺ transport through this layer is predominantly by liquid phase diffusion in the pores; The electrochemical intercalation of Li⁺ into Li_nCrO_x or Li_nMoO₃ is a 1st order reaction with respect to Li⁺ concentration in the electrolyte.     

Transport and dielectric properties of lisicon

The ionic and electronic conductivities of Lisicon with compositions Li₁₄Zn(GeO₄)₄-(A) and Li₁₂Zn₂(GeO₄)₄-(B) have been determined in the temperature range 306–578 K. It has thus been shown that the ionic transport number is nearly unity throughout the temperature range. The activation energies for lithium motion were found to be 0.6 eV and 0.47 eV for compounds A and B. These values are very close to the values of the heat of transport q¹_Li⁺ 0.59 eV and 0.50 eV respectively, obtained from thermoelectric power (θ_t) measurements. The total ionic conductivity of the pellets of Lisicon was found to decrease with increasing average grain size in the range 20–78 μ. Electrode effects on the ionic conductivity are also reported for silver and TiS₂ electrodes. The electron/hole conductivity was studied using the Wagner cell technique. The activation energies for electron and hole transport for A were estimated as 1.02 eV and 1.39 eV and for B as 0.89 eV and 1.49 eV, respectively. The variation of the dielectric parameters ?', ?” and tan δ have been studied for sample A between 10 Hz-100 kHz. The high frequency dielectric constant (at 100 kHz) was 21.4. The ?' versus ?” (Cole-Cole plot) is also presented.     

Evidence for ammonia oxidation and the ionic nature of ammoniated titanium disulfide

In order to elucidate the nature of Lewis bases in layered transition metal dichalcogenides (TX₂), ammoniated titanium disulfide, (NH₃)_yTiS₂ with 0.4 ? y ? 0.6, has been synthesized using stoichiometric TiS₂ and investigated by X-ray diffraction, vapor pressure measurements, thermogravimetric analysis, differential scanning calorimetry, and SQUID magnetrometry. These intercalation compounds lose ammonia rapidly at ambient temperature to form primarily a stage II structure. Upon heating, about half of the ammonia is weakly bound (deintercalation enthalpy ?2.6 kcal/mol) and leaves the TiS₂ host at low temperatures (?75°C), whereas the other half is bound more strongly (deintercalation enthalpy ?6.3 kcal/mol) and deintercalates only at higher temperatures (?150°C). The more strongly bound ammonia is identified as NH₄⁺, and an electron is donated to the TiS₂ conduction band for each NH₄⁺-ion present. Hence, the ionic formulation (NH₄⁺)_y' (NH₃)_y'TiS₂^{y' -} best describes these materials, where the NH₄⁺ ions are analogous to alkali-metal cations M⁺ in metal-ammonia intercalation complexes. The presence of a substantial concentration of NH₄⁺ provides a simple explanation of the unusual observation that the C₃ axis of NH₃ is parallel to the TiS₂ layers. The results of this study show that redox reactions do indeed play an important role in ammonia intercalation into TiS₂ and probably also into other TX₂ hosts.     

插层化合物LixTiS2中Li离子-空位二维有序结构稳定性的第一性原理研究

根据局域密度近似下的密度泛函理论，用第一性原理方法对TiS₂，LiTiS₂和Li_xTiS₂(x=1/4, 1/3, 1/2, 2/3, 3/4)有序系统进行了几何优化和总能量计算.将计算结果与已有的实验和理论结果进行了对比，得到的归一化结构参量增量Δa₀和Δc₀随离子浓度单调地增加，与实验结果符合较好.Li_{关键词： x}TiS₂')" href="#">Li_xTiS₂ 有序结构 第一性原理计算 密度泛函理论     

快离子导体AgxTiS2中Ag+离子－空位的二维基态结构与能量性质研究

根据Ag⁺离子-空位的二维有序结构建立了三维晶胞模型.采用局域密度近似下的平面波赝势方法,对有序Ag_xTiS₂(x=0,1/4,1/3,1/2,2/3,3/4,1)系列进行了几何结构优化和总能量计算,并与Li_xTiS₂系列进行了对比研究.有序Ag_xTiS₂系统的晶格参量增量Δa_{关键词： x}TiS₂')" href="#">Ag_xTiS₂ 有序—无序相变 离子扩散 第一性原理计算     

Lithium mobility in the layered oxide Li1−xCoO2

The Li⁺-ion chemical diffusion coefficient in the layered oxide Li_0.65CoO₂ has been measured to be $\text{D}\text{?}\text{= 5 × 10}{}^{\mathrm{?12}}$ m² s^?1 by three independent techniques: (1) from the Warburg prefactor, (2) from the transition frequency for semi-infinite to finite diffusion lengths in steady-state ac-impedence measurements and (3) from a modified Tubandt method that uses ac-impedance data to distinguish interfacial and surface-layer resistances from the bulk resistance of the sample. This value and a small increase in D? with (1 ? x) in Li_1?xCoO₂, 0.45 < (1 ? x) < 0.80, compare favorably with the $\text{D}\text{?}\text{= 5}\text{to}\text{7 × 10}{}^{-12}\text{m}{}^2\text{s}{}^{-1}$ obtained by Honders for this system with pulse techniques. A qualitative discussion is presented as to why this composition dependence and why D? for this system is a factor of five larger than that for Li⁺-ion diffusion in Li_xTiS₂.     

Size effect on electrochemical property of nanocrystalline LiCoO2 synthesized from rapid thermal annealing method

Nano-sizing of cathode materials for higher power Li-ion rechargeable batteries is an effective method to shorten a Li-ion diffusion path and achieve fast charge transfer. Nanocrystalline LiCoO₂ was synthesized through a combination of rapid thermal annealing method and a sol–gel method assisted with a triblock copolymer surfactant, and the electrochemical properties including the Li-ion chemical diffusion coefficient was investigated. Li-ion deintercalation/intercalation experiments suggested an extreme small amount of cation mixing between Li⁺ and Co³⁺ within a layered structure of LiCoO₂, which was not observable in the Raman spectroscopy. The analysis based on the solution for the diffusion equation of the cylinder model revealed that the cation mixing strongly decelerates the Li-ion diffusion in LiCoO₂.     

Lithium intercalation into TiS<Subscript>2</Subscript> cathode material: phase equilibria in a Li–TiS<Subscript>2</Subscript> system

Lithium-intercalated titanium disulfide Li _x TiS₂ had been extensively studied as prototypical cathode material for high-energy-density reversible lithium batteries with moderate voltage. Today, this phase is one of the leading candidates for all-solid-state lithium batteries with durable high energy and high rate performance. However, fundamental knowledge of Li⁺ insertion into TiS₂ is still incomplete; available information on the phase diagram of the Li–TiS₂ system is limited by x?=?1 due to difficulties in preparing lithium-rich equilibrated samples. The goals of this work were to re-examine Li _x TiS₂ single phase boundaries and to clarify the existence of lithium-rich intercalates with x?>?1. А new preparation technique was developed to obtain 1T-Li _x TiS₂ samples as good-quality equilibrated products with desirable lithium content. Phase equilibria in a quasibinary Li–TiS₂ system were studied by X-ray diffraction, emf measurements (25 °C) and thermal analysis (25–350 °C) over a wide range of Li:Ti ratios (0 to 4).     

Intercalation of lithium ions into bulk and powder highly oriented pyrolytic graphite

The electrochemical reactions of highly oriented pyrolytic graphite (HOPG) bulk and powder electrodes in 1 M LiPF₆ 1:1 EC/DMC solution were investigated and the results show that the intercalation reaction of lithium ion into HOPG electrode occurs only at the edge plane and SEI formation reaction on the basal plane is negligible in comparison with that on the edge plane. The active surface area of HOPG powder electrode could be deduced by comparing the peak area (consumed charge for SEI formation) at potential of 0.5 V on voltammograms with that of bulk HOPG edge electrode. The diffusion coefficients of lithium ion in HOPG bulk layers and in HOPG powder was for the first time measured by use of electrochemical impedance spectra and potential step chronamperameter methods. It was found that the diffusion coefficients of lithium in HOPG were in the range of 10⁻¹¹-10⁻¹² cm² s⁻¹ for the lithium-HOPG intercalation compounds at potentials from 0.2 (vs. Li/Li⁺) to 0.02 V, decreasing with the increase of lithium intercalation degree. A good agreement was obtained between the results from bulk and powder HOPG electrodes by electrochemical impedance spectra method.     

BF+2注入多晶硅栅F迁移特性的分析与模拟

在深入分析BF⁺₂注入多晶硅栅F在多晶硅栅中迁移特性的基础上，建立了F在多晶硅栅中的迁移方程.采用有限差分法，模拟了BF⁺₂注入多晶硅栅F在多晶硅栅中的分布.模拟结果与二次离子质谱(SIMS)分析结果相符.给出了80keV，2×10¹⁵cm^-2 BF⁺₂注入多晶硅栅900℃，30min退火条件下F在多晶硅中的发射系数e=6×10关键词：     

PAN为基凝胶聚合物电解质自扩散系数的NMR研究

利用脉冲梯度场NMR方法直接测量了不同温度下的不同组分的PAN为基凝胶聚合物电解抽PAN-EC/PL-LiClO₄中锂离子的自扩散系数D.结果表明,锂离子的自扩散系数D依赖于锂盐质量分数x％,关且在x从5到20范围内,x=10时D有最大值.这与锂离子跳跃的传输机制及同时受到增塑剂EC与聚合物PAN网络的相互作用有关. 关键词：     

Anomalous bragg peak widths in LixTiS2

We have performed X ray diffraction experiments on Li_xTiS₂ and have found an experimental correlation between features observed in the (00?) peak width and -δx/δV data. (00?) peak broadening is indicative of imperfect order in the c direction of the lattice. This suggests that three dimensional models for lithium intercalation in TiS₂ should be investigated.     

Physical and electrochemical properties of Li-intercalated Sn oxide films made by sputtering

Sn oxide films were made by reactive rf magnetron sputtering under conditions that led to both electronic and ionic conductivity. The film structure was studied by X-ray diffraction and Atomic Force Microscopy (AFM). Li⁺ intercalation produced electrochromism with coloration efficiency peaked in the infrared. Cyclic voltammograms taken at different sweep rates were interpreted in terms of a unique structural parameter related to the fractal dimension of a self-affine surface relief and in excellent agreement with the fractal dimension as obtained with AFM. Mössbauer spectroscopy was used to determine the valence state of the Sn-atoms; a change from Sn⁴⁺ to Sn²⁺ was detected after electrochemical intercalation of Li⁺.     

Diffusion of 55Fe in Fe2O3 single crystals

The diffusion of ⁵⁵Fe has been measured parallel to the c axis of Fe₂O₃ single crystals at temperatures in the range 708–1303°C and at an oxygen activity of unity. The tracer penetration profiles were determined using sectioning techniques. For temperatures above 900°C the tracer diffusion coefficient is given byD¹(Fe) = 1.6 × 10⁹ exp[?6.0 (eV)/kT] cm² s^?1 and below 900°C by 2.8 × 10^?9 exp[?1.8 (eV)kT]. The high-temperature behaviour is probably characteristic of pure Fe₂O₃, whereas diffusion at lower temperatures may be influenced by impurities. The most likely defects responsible for diffusion of Fe are iron interstitials and, for oxygen, oxygen vacancies, and the observed activation energies are discussed in terms of the properties of these defects. The diffusion data and defect models have been used to predict the rate of growth of Fe₂O₃ and indicate that outward Fe diffusion is the dominant transport process. Previously published data for Fe₂O₃ growth in a variety of experimental situations have been corrected to a single rate constant using a model for multilayer growth. The corrected data are all in good agreement but are approximately two orders of magnitude greater than predicted from diffusion data, which suggests that grain boundary diffusion controls the growth of Fe₂O₃ in practice.     

Lithium ordering and NMR linewidth in Li0.33TiS2

The low temperature ⁷Li linewidths and second moments have been analyzed for Li_0.33 TiS₂ and Li_0.97 TiS₂. Moment calculations demonstrate that the linewidth is a sensitive indicator of order on a two dimensional lattice of dipoles. The calculated dipolar second moment is not consistent with a simple √3 a_o superlattice in Li_0.33 TiS₂, but is consistent with a random arrangement of lithium ions and several more complex superlattices recently proposed by Kanamori and Kaburagi.     

Determination of proton diffusion in solid electrolytes

Two electrochemical methods have been used to determine the proton diffusion in solid electrolytes. One is based on transient ionic current measurements and a reasonable physical model; the other one is a quick determination using steady-state transport. The results of proton diffusion coefficients of 10⁻⁶ and 10⁻⁵ cm²/s obtained for the α- and β-phases of Li₂SO₄, respectively, using these two methods are in a good agreement with published results. The methods turned out to be very useful for determining proton diffusion in solid electrolytes, especially when the electrolytes contain more than one type of the mobile ionic species and a low concentration of the protons. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

New prospects in studying Li diffusion—two-time stimulated echo NMR of spin-3/2 nuclei

The measurement of diffusion parameters like activation energies and translational jump rates of small cations plays a key role in materials science. Especially the in-depth investigation of Li diffusion in ionic conductors is of great interest, because suitable ionic conductors are needed for, e.g., the development of new secondary ion battery systems. As the standard tracer method is not applicable to study Li diffusion due to the lack of a suitable radioactive isotope, Li diffusion is alternatively probed by solid state NMR techniques. With the different NMR methods being available, diffusion processes can be studied on different length- and timescales. In the present paper we use two-time spin-alignment echo (SAE) NMR for the direct, i.e., model independent, measurement of extremely small translational Li jump rates. To this end, different crystalline and glassy ion conductors like Li_xTiS₂, Li₄SiO₄ as well as LiNbO₃ served as model substances to reveal the special features of this technique. SAE-NMR, which was originally developed for deuterons, has also been applied in a few cases to spin-3/2 nuclei, like ⁷Li, before. The corresponding correlation functions yield not only information about diffusion parameters but also about geometric properties of the diffusion pathways, making SAE-NMR a powerful method which complements well-established NMR techniques.