电池正极材料中Li+运动特性的7Li NMR研究

利用变温⁷LiNMR实验对Li-电池正极材料LiMn₂O₄和LiCoO₂中Li⁺的运动特性进行了研究,结果表明,随实验温度的提高,LiMn₂O₄的⁷LiNMR谱线窄化,表明其中Li⁺迁移能力增加,而LiCoO₂的谱线无变化.此外随温度提高,LiMn₂O₄的⁷Li的T₁变短,而LiCoO₂的T₁变长,产生这种不同变化趋势的原因在于LiMn₂O₄和LiCoO₂晶相结构的差异造成其中Li⁺迁移能力的差别,它们各自的相关时间τ_c使⁷Li核的T₁分别位于T₁-τ_c曲线极小点两侧.     

Lithium ion transport in germanophosphate glasses

Glasses in the system Li₂O–GeO₂–P₂O₅ have been prepared using melt quenching route. Li⁺ ion transport has been investigated in these glasses using both d.c. and a.c. conductivity measurements. Arrhenius plots of d.c. conductivity exhibits two different slopes, which has been discussed in the light of cluster-tissue model. A.c. conductivity data has been fitted to single power law. Dielectric relaxation has been analyzed based on the behaviour of moduli. Good collapse on to master plots is observed for both a.c. conductivity and moduli. The behaviour of E_dc, s and β are found to be consistent when conductivity mechanism is considered as involving NBO–BO switching as the first step, which is followed by Li⁺ ion migration.     

Studies of lithium intercalation in 3R-WS2

The lithium intercalation into the layered dichalcogenide 3R-WS₂ has been investigated by electrochemical reduction and by chemical reaction in n-butyl lithium solution. Essential results are (a) a charge transfer of nearly 0.6e⁻/W in Li_xWS₂, (b) a small increase of the c-axis parameter of about 0.6%, and (c) a high mobility of the Li⁺-ions. The chemical diffusion coefficient of Li⁺-ions is estimated to be 8 × 10⁻⁹ cm² s⁻¹ in the composition range 0 ≤ x ≤ 0.25. The appearance of a structural transformation from 3R-WS₂ to 2H-Li_xWS₂ is interpreted on grounds of instabilities in the interlayer structure.     

Preparation, characterization and oxide ion conductivity in U-substituted Bi4V2O11

A Bi₂V_{1 − x − y}U_xBi_yO_{5.5 + 0.5x − y} solid solution derived from Bi₄V₂O₁₁ has been prepared and characterized with x up to 0.125 for y = 0. Partial substitution of U⁶⁺ for V⁵⁺ in Bi₄V₂O₁₁ leads to the stabilization at room temperature of the high-oxide ion conducting γ-phase, in contrast with other M⁶⁺ dopants which stabilize the β-phase. The lower conductivity in U substituted system compared with BICUVOX.10 is attributed to its higher activation energy. Conductivity values and activation energies of the U substituted phases compare well with Bi₂UO₆.     

Features of the electrochemical lithium insertion into monophosphate tungsten bronzes (PO2)4(WO3)2m (m=9 and 10)

Electrochemical lithium insertion into (PO₂)₄(WO₃)_2m, where m=9 and 10, has allowed the determination of several phases Li_x(PO₂)₄(WO₃)_2m between 3.4 and 0.01 V vs Li⁺/Li⁰. After the first cycle the electrochemical system was unable to maintain the high specific capacity of the cells (540 Ah/kg) due to irreversible processes. Nevertheless at high voltage values, above 1.4 V vs Li⁺/Li⁰, the lithium insertion proceeded through a reversible mechanism. By means of X-ray diffraction experiments we have detected the nature of different phases Li_x(PO₂)₄(WO₃)_2m formed and we have established a correlation with the reversible/irreversible processes detected during the electrochemical insertion.     

Na+替位掺杂对Li2MnSiO4的电子结构以及Li+迁移过程的影响

在锂二次电池中, 硅酸锰锂作为正极材料得到广泛研究, 但其固有的电子和离子电导率较低, 直接影响着电池的功率密度和充放电速率. 本文建立了不同浓度的Na⁺离子替位掺杂Li⁺离子形成的Li_1-xNa_xMnSiO₄(x=0, 0.125, 0.25, 0.5)结构, 采用第一性原理的方法, 研究了掺杂前后硅酸锰锂的电子结构以及Li⁺离子的跃迁势垒. 发现在Li⁺位替代掺杂Na⁺, 导带底的能级向低能方向发生移动, 降低了Li₂MnSiO₄ 材料的禁带宽度, 有利于提升材料的电子导电性能. 随着掺杂浓度的升高, 禁带宽度逐渐变窄. CI-NEB结果表明, 在Li₂MnSiO₄体系中具有两条有效的Li⁺离子迁移通道, 掺杂Na⁺以后扩大了Li⁺ 离子在[100]晶向上的迁移通道, Li⁺离子的跃迁势垒由0.64 eV降低为0.48, 0.52和0.55 eV. 掺杂浓度为 x=0.125时, 离子迁移效果最佳. 研究表明Na⁺掺杂有利于提高Li₂MnSiO₄材料的离子和电子电导率.     

Electric conductivity and relaxation in ZnF2–AlF3–PbF2–LiF glasses

The electric conductivity of ZnF₂–AlF₃–PbF₂–LiF glasses has been studied in the frequency range 10 Hz–2 MHz and in the temperature range from 300 K to just below the glass transition temperature. The conductivity decreases with the increase in the LiF content in the composition, which results from the trapping of F⁻ ions by Li⁺ ions. Small values of the stretching exponent β are observed for the present glasses. The value of the decoupling index decreases with an increase in LiF content, consistent with the composition dependence of the conductivity.     

Ionic conduction properties of layer-type oxides NaxMx/2Ti1−x/2O2 (M=Ni, Co; 0.60≤x≤1.0)

Layer-type oxide Na_xM_x/2^IITi_1−x/2^IVO₂ (M=Co, Ni; 0.60≤x≤1.0) has been prepared by solid state reactions. In both series, two structural variants of type -NaFeO₂ (O3) and β-RbScO₂ (P2) have been obtained consecutively as x decreases with a borderline composition around x_c0.7. With the decrease of x, the ionic conductivity has been found to increase up to 8.4×10⁻² S cm⁻¹ at 770 K (Na_0.67Co_0.33Ti_0.67O₂). Compositions of P2 have been found to exhibit the conductivity values two to five times greater than those of O3, primarily due to the larger rectangular threshold available for the diffusion of Na⁺ ions. Such a structural effect has also been considered to depend on the polarizability of alkali ion. HT-XRD and ²³Na-NMR data of Na_0.67Co_0.33Ti_0.67O₂ strongly suggest that the diffusion of Na⁺ ion is deeply related with the local distortion of trigonal prismatic sites, leading to the change of activation energy around 430 K.     

The role of Bi2O3 as a network modifier and a network former in xBi2O3 · (1 − x)LiBO2 glass system

The effect of Bi₂O₃ on the glass transition temperature, electrical conductivity and structure of LiBO₂ glass has been investigated. T_g vs. composition curve shows three different linear regions, while there is an overall decrease in T_g with the increase in Bi₂O₃ content. The slope of these three straight lines is in a decreasing order. These results are interpreted in terms of the increase in the number of non-bridging oxygen atoms, substitution of Bi-O bond in place of B-O bond and change in Li⁺ ion concentration. The conductivity vs. composition curve exhibits two maxima which are interpreted in terms of the structural modification effect of Bi₂O₃ on LiBO₂ network and mixed-former effect, respectively. Results obtained from the XPS studies of the samples of composition x 0.005, have shown that the number of non-bridging oxygen atoms from B-O bond increases with the increase in Bi₂O₃ content. It has a maximum value at x = 0.003 where the conductivity has also exhibited a maximum value. Further increase of Bi₂O₃ content causes decrease in it. For higher Bi₂O₃ content (x * > 0.005), O 1s spectra of Bi₂O₃ has been separated out from that of Bi₂O₃. Bismuth ions have been substituted for boron ions as network former ions.     

Two separate Li ionic motions observed by Li and B NMR in xLi2S + (1 − x)B2S3 glassy fast ionic conductors

Studies of ion dynamics in the highly conductive glassy fast ionic conductor (FIC) xLi₂S + (1 − x)B₂S₃ (x = 0.65 and 0.70) were made with NMR nuclear spin lattice relaxation (NSLR) R₁(ω, T) of both mobile ⁷Li and immobile ¹¹B ions, and ⁷Li NMR line narrowing δν(T). The possible dependence of ion dynamics on the short range order structures (SRO) and the distribution of activation energies (DAE) in this highly conductive FIC was investigated. Two Gaussian DAE were employed to fit ⁷Li NSLR data, where each Gaussian DAE was correlated to a separate ¹¹B NSLR in a BS₃ and in a BS₄ group. The long range diffusion of Li ions among BS₃ groups and a seemingly localized ionic hopping motion around BS₄ group is suggested as a microscopic model for the ion dynamics in thioborate glasses, namely a ‘two channel relaxation’.     

Characterization of Ce1−xZrxO2 thin films prepared by pyrolytic spray technique

It was demonstrated that spray pyrolysis can be used to prepare Ce_1−xZr_xO₂ thin films with x between 0 and 1. The composition of these films was determined by electron probe microanalysis (EPMA), and the crystalline structure by X-ray diffraction (XRD) and Raman spectroscopy (RS). Cyclic voltammetry (CV) was performed in an electrolyte of propylene carbonate with 1 M LiClO₄. Films with high Zr content were incapable of charge exchange of Li⁺ ions. In the contrast, films with high Ce content were found to be able to insert/extract large charge densities of Li⁺ ions. They also remained transparent during Li⁺ intercalation.     

Material design of new lithium ionic conductor, thio-LISICON, in the Li2S–P2S5 system

A new lithium ionic conductor of the thio-LISICON (LIthium SuperIonic CONductor) family was found in the binary Li₂S–P₂S₅ system; the new solid solution with the composition range 0.0≤x≤0.27 in Li_3+5xP_1−xS₄ was synthesized at 700 °C and characterized by X-ray diffraction measurements. Its electrical and electrochemical properties were studied by ac impedance and cyclic voltammetry measurements, respectively. The solid solution member at x=0.065 in Li_3+5xP_1−xS₄ showed the highest conductivity value of 1.5×10⁻⁴ S cm⁻¹ at 27 °C with negligible electronic conductivity and the activation energy of 22 kJ mol⁻¹ which is characteristic of high ionic conduction state. The extra lithium ions in Li₃PS₄ created by partial substitution of P⁵⁺ for Li⁺ led to the large increase in ionic conductivity. In the solid solution range examined, the minimum conductivity was obtained for the compositions, Li₃PS₄ (x=0.0 in Li_3+5xP_1−xS₄) and Li₄P_0.8S₄ (x=0.2 in Li_3+5xP_1−xS₄); this conductivity behavior is similar to other thio-LISICON family with the general formula, Li_xM_1−yM_y′S₄ (M=Si, Ge, and M′=P, Al, Zn, Ga, Sb). Conduction mechanism and the material design concepts are discussed based on the conduction behavior and the structure considerations.     

(e,2e)反应三重微分截面的计算

给出了利用BBK模型计算电子碰撞电离H,He⁺,He和Li⁺三重微分截面的通用方法,适用于中、高入射能量下的各种几何条件。计算结果与其它理论结果和实验数据进行了比较,符合得很好。     

Li~+,Zn~(2+),Mg~(2+)掺杂Lu_2O_3∶Er~(3+)荧光粉的制备及发光特性

用微波高温固相法合成了Er~(3+)单掺Lu_2O_3,Li~+与Er~(3+)共掺Lu_2O_3及Li~+,Zn~(2+),Mg~(2+)掺杂Lu_2O_3∶Er~(3+)的荧光粉。实验表明金属离子Li~+、Zn~(2+)、Mg~(2+)、Er~(3+)掺杂Lu_2O_3,不影响Lu_2O_3的立方晶相。扫描电子显微镜测量表明,Li~+掺杂可以有效改善粉体的分散性和形貌,Li~+,Zn~(2+),Mg~(2+)共掺杂获得的粉体颗粒分布更加均匀,粒径范围为80～100 nm。379 nm激发下,Li~+与Er~(3+)共掺样品发光较单掺Er~(3+)样品在565 nm处的发光增强了4.5倍,而Li~+、Zn~(2+)、Mg~(2+)与Er~(3+)共掺样品较其发光增强5.3倍。980 nm激发下,Li~+与Er~(3+)共掺样品,Li~+、Zn~(2+)、Mg~(2+)与Er~(3+)共掺样品的发光分别比单掺Er~(3+)样品在565 nm处发光增强23倍与39倍,在662 nm处发光强度分别增强20倍与43倍。379 nm激发下,较单掺Er~(3+)的样品,掺杂Li~+的样品和Li~+,Zn~(2+),Mg~(2+)和Er~(3+)共掺的样品荧光寿命均有所增加,而Zn~(2+)、Er~(3+)共掺及Mg~(2+)、Er~(3+)共掺样品的荧光寿命则有所缩短。     

Mixed conductivity in SrCe0.95Yb0.05O3 protonic conductors

The results of electrical conductivity measurements on SrCe_0.95Yb_0.05O₃ under controlled oxygen partial pressure and temperature are presented. A defect model consistent with experimental results is proposed which provides for P_O2^−1/4 dependent n-type, P_o2-independent oxygen ion and P_O2^+1/4 dependent p-type conductivity components. The band gap, reduction, oxidation and ion-migration energies are determined from an analysis of the data in terms of the proposed defect model. These results suggest that some earlier data interpreted in terms of protonic conduction may require re-evaluation.     

Carrier and mobility profile measurements in n-type ion-implanted GaAs by the differential sheet resistivity and Hall effect technique

Multiple energy ion implantation facilities have been used to prepare essentially box-shaped dopant profiles in GaAs with plateau concentrations between 2 x 10¹⁶ and 8 x 10¹⁷ cm^-3. The implanted species was ²⁸Si⁺. The ion energies ranged between 40 and 400 keV. The depletion depth correction applied to the carrier and mobility profiles in the plateaux did not affect the data values but only their depth scale. Thus, in these regions the measured data (without any feed-back correction) were used to study the electrical properties of the implanted layers. Doping efficiencies between 65% and 81% and carrier mobilities in the range 3000 to 6000 cm² V^-1s^-1 were measured. Activation thresholds in the range 10¹⁵ to 10¹⁶ cm^-3 were estimated.     

Ionic conductivity and phase stabilization in Cu- and Tl-substituted CsAg2I3

Samples of general formula CsAg_2−xM_xI₃, x=0–0.4 and M=Cu and Tl, have been prepared and studied by powder X-ray diffraction, DSC and electrical conductivity measurements. X-ray diffractograms and DSC curves showed the possibility of stabilizing the high-temperature -phase at lower temperatures in Tl-substituted samples, while such results were not obtained in Cu-substituted samples. Ionic conductivity measurements showed two regions corresponding to the low- and high-temperature phases. The transition temperature between the two phases was found to remain unchanged with the addition of Cu⁺ and decreased gradually with increasing Tl⁺. The ionic conductivity decreased in Cu-substituted samples and enhanced with the incorporation of Tl⁺ ion in the lattice of CsAg₂I₃. Dielectric constant was found to show behaviour similar to that of the ionic conductivity, and this is an evidence of the predominant effect of ion hopping on this property.     

Ba5SiO4Cl6: Yb3+, Er3+, Li+荧光粉的制备及上转换发光性质研究

本文采用高温固相反应法制备了Ba₅SiO₄Cl₆: Yb³⁺, Er³⁺, Li⁺ 荧光粉, 并对其上转换发光性质及其发光机理进行了研究. 在980 nm 激光的激发下, Ba₅SiO₄Cl₆: Yb³⁺, Er³⁺ 荧光粉呈现较强的红色(662 nm) 和较弱的绿色(550 nm) 的上转换发光, 红色和绿色的上转换发光分别对应于Er³⁺ 离子的⁴S_3/2/²H_11/2→⁴I_15/2 和⁴F_9/2→⁴I_15/2 跃迁, 且随着掺杂的Er³⁺ 和Yb³⁺ 离子浓度增加, 样品的上转换发光强度增加, 这是因为Yb³⁺ 离子和Er³⁺ 离子之间的能量传递效率增加引起的. 在0.5—0.8 W 功率激发下,样品属于双光子发射, 而在0.9—1.2 W 功率激发下样品具有新的上转换发光机理——光子雪崩效应. 探讨了Li⁺ 掺杂对Ba₅SiO₄Cl₆: Yb³⁺, Er³⁺ 样品的上转换发光性质的影响, Li⁺ 离子的掺杂引起Ba₅SiO₄Cl₆:Yb³⁺, Er³⁺ 上转换发光强度增加, 这是由于Li⁺ 离子的掺入降低了晶体场的对称性引起的.     

The microscopic features of (Li0.5La0.5)TiO3

In ionic conducting materials, the crystal structure is closely related to the ionic conductivity. In this research we studied the microscopic features of Li_0.5La_0.5TiO₃ which exhibited a lithium ionic conductivity as high as 1×10⁻³ Scm⁻¹ at room temperature by XRD, TEM and SIMS. It was found that the superstructure was caused by the ordering of La⁺³ and vacancy, producing the 2a_p×2a_p×2a_p unit cell. This ordering was found to be regular in microscopic region, but became irregular in macroscopic region. Li⁺ showed a random distribution which meet the needs for the fast ionic conduction. The second phase was found to be Li₂TiO₃ which existed in the grain boundary junctions.     

Conductivity relaxation parameters of some H and K conducting in the polycrystalline compound KDyHP3O10

Polycrystalline samples of KDyHP₃O₁₀ was obtained by heating for 12 hour at 553 K a mixture containing K₂CO₃, Dy₂O₃ and H₃PO₄. Samples were characterized through X-ray diffraction, examined by IR vibrational spectroscopy and impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of some H⁺ and K⁺ conducting in this compound have been determined from an analysis of ac conductivity data measured in a wide temperature range. Transport properties in this material appears as due to H⁺ and K⁺ ions hopping mechanism. The stretched exponential function exp[−(t/τ_σ)^β] has been used to describe the conductivity relaxation. The relaxation parameters have been investigated as a function of the nature of mobile ions. The results obtained are shown to be in good agreement with the predictions of the Ngai coupling model.