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.     

Formation of Li2O in a chemically Li-intercalated V2O5 xerogel

We studied the electronic structure of a chemically Li-intercalated V₂O₅ xerogel. The technique used in the study was V 2p and O 1s X-ray absorption spectroscopy (XAS). The V ions in the as-prepared V₂O₅ xerogel are mostly in a pentavalent V⁵⁺ state. The spectra show that the V ions are partially reduced to V⁴⁺ and V³⁺ states upon Li intercalation. The results also show that low Li intercalation (x<1) affects mostly O 2p–V 3d mixed states, whereas for higher Li intercalation (x>1), this mechanism saturates and leads to Li₂O formation.     

Effect of Li2O doping on electrical properties of CoFe2O4

The solid–solid interactions between cobalt and ferric oxides to produce CoFe₂O₄ were followed up using XRD investigation. The effect of Li₂O-doping on the ferrite formation was also studied. The electrical and dielectric parameters of pure and doped mixed solids precalcined at 1273 K were measured using d.c and a.c instruments.The dopant concentration was varied between 0.5 and 6 mol% Li₂O. The results obtained revealed that Li₂O doping much enhanced the ferrite formation due to an increase in the mobility of the reacting species.

The addition of the smallest amount of Li₂O (0.5 mol%) resulted in measurable variations in the electrical constants (ρ, E_a, ′, ″ and tan δ). Resistivity increased upon increasing the dopant concentration up to 1.5 mol% exceeding the values measured for the undoped sample. Furthermore, the presence of 6 mol% Li₂O brought about a significant decrease of electrical resistivity. Also, the activation energy decreased with increasing the dopant concentration. The dielectric constant behaves according to ε=const. 1/ρ^1/2.

The Li₂O-doping modified the values of different dielectric constants, the change in these constants was found to be strongly dependent on the amount of Li₂O added.These results have been discussed in terms of the potentiality of Li₂O in increasing the mobility of the reacting species involved in the ferrite formation.     

Phase segregation of LixMn2O4 (0.6<x<1) in non-equilibrium reduction processes

Chemical synthesis routes to Li_xMn₂O₄ (0.15≤x≤1) in non-equilibrium reduction processes were developed to carry out detailed structural analysis. Non-equilibrium Li_xMn₂O₄ (0.15≤x≤1) samples were prepared by chemical lithiation of λ-MnO₂ with LiI for 24 h; longer than 1 week was needed to reach true equilibrium at room temperature. The samples were characterized by X-ray diffraction analysis. The phase diagram was different from that in the equilibrium state; three cubic phases (phases A, B and C) were observed for Li_xMn₂O₄ (0.15≤x≤1). There were two regions of two-phase coexistence: the region of 0.25<x<0.55 (phase B+phase C) and 0.6<x<1.0 (phase A+phase B). In the compositional range of 0.6<x<1.0, the lattice constants of phases A and B change with the lithium composition, this indicates that it is a structural anomaly with a metastable two-phase character in non-equilibrium reduction processes.     

Al,Fe, Mg掺杂Li2MnSiO4的电子结构和电化学性能的第一性原理研究

硅酸锰锂作为锂离子电池正极材料因具有高的理论电容量而一直备受关注, 但其较低的导电率和较差的循环性能阻碍了进一步的发展. 采用第一性原理广义梯度近似GGA+U的方法, 研究了Al, Fe, Mg掺杂Li₂MnSiO₄的电子结构、 脱嵌锂电压和导电性. 研究发现, Al 掺杂的Li₂Mn_0.5Al_0.5SiO₄结构中载流子的数目增加, 电子自旋向上和向下的态密度均穿过费米能级, 呈现金属特性, 提高了体系的导电率. 脱锂Li_xMnSiO₄ (x=1, 0)结构中, 通过计算一次脱锂相结构的形成能得到Al掺杂的一次脱锂结构最稳定, 并且Al掺杂的脱锂相结构体积变化小, 有利于材料循环性能的提高, 同时第一个锂离子脱嵌电压与未掺杂时(4.2 V)相比降低到2.7 V. Fe掺杂降低了Li₂MnSiO₄的带隙, 第一个锂离子脱嵌电压降低到3.7 V. 研究表明, Al的掺杂效果优于Fe和Mg, 更利于硅酸锰锂电化学性质的提高.     

Photoelectron spectroscopic study of Li oxides on Li over-deposited V2O5 thin film surfaces

The Li oxides species formed on Li over-deposited V₂O₅ thin film surfaces have been studied by using X-ray and UV induced photoelectron spectroscopy (XPS and UPS). The photoelectron spectroscopic data show that the Li over-deposited V₂O₅ system itself is not stable. Further chemical decomposition reactions are taken place even under UHV conditions and lead to form Li₂O and Li₂O₂ compounds on the surface. The formation of Li₂O₂ causes to arise an emission line at about 11.3 eV in the valence band spectra.     

Lithium insertion into V6O13 studied by deformation electron density refinement of single-crystal X-ray data

Deformation electron density refinement of single-crystal X-ray data has been performed for V₆O₁₃ and for one of its electrochemically lithiated phases Li₂V₆O₁₃. The electron rearrangement associated with lithium insertion is extracted by subtracting the two derived electron deformation models from one another. The reduction (from nominally V⁵⁺ to V⁴⁺) of one of the three independent vanadium atoms (V2) in the asymmetric unit can be identified, along with significant changes in the effective charges on certain of the oxygens.     

Structural and lithium intercalation studies of Mn(0.5−x)CaxTi2(PO4)3 phases (0≤x≤0.50)

Materials from the Mn_(0.5−x)Ca_xTi₂(PO₄)₃ (0≤x≤0.50) solid solution were obtained by solid-state reaction in air at 1000 °C. Selected compositions were investigated by powder X-ray diffraction analysis, ³¹P nuclear magnetic resonance (NMR) spectroscopy and electrochemical lithium intercalation. The structure of all samples determined by Rietveld analysis is of the Nasicon type with the R space group. Mn²⁺/Ca²⁺ ions occupy only the M1 sites in the Ti₂(PO₄)₃ framework. The divalent cations are ordered in one of two M1 sites, except for the Mn_0.50Ti₂(PO₄)₃ phase, where a small departure from the ideal order is observed by XRD and ³¹P MAS NMR. The electrochemical behaviour of Mn_0.50Ti₂(PO₄)₃ and Mn_(0.5−x)Ca_xTi₂(PO₄)₃ phases was characterised in Li cells. Two Li ions can be inserted without altering the Ti₂(PO₄)₃ framework. In the 0≤y≤2 range, the OCV curves of Li//Li_yMn_0.50Ti₂(PO₄)₃ cells show two main potential plateaus at 2.90 and 2.50–2.30 V. Comparison between the OCV curves of Li//Li_(1+y)Ti₂(PO₄)₃ and Li//Li_yMn_0.50Ti₂(PO₄)₃ shows that the intercalation occurs first in the unoccupied M1 site of Mn_0.50Ti₂(PO₄)₃ at 2.90 V and then, for compositions y>0.50, at the M2 site (2.50–2.30 V voltage range). The effect of calcium substitution in Mn_0.50Ti₂(PO₄)₃ on the lithium intercalation is also discussed from a structural and kinetic viewpoint. In all systems, the lithium intercalation is associated with a redistribution of the divalent cation over all M1 sites. In the case of Mn_0.50Ti₂(PO₄)₃, the stability of Mn²⁺ either in an octahedral or tetrahedral environment facilitates cationic migration.     

An electrochemical investigation of Li intercalation in the sol-gel LiMn2O4 spinel oxide

An alternative approach for obtaining the LiMn₂O₄ spinel phase is provided by the use of the sol-gel method in aqueous solution. The main electrochemical properties of the sol-gel LiMn₂O₄ phase are reported. In addition to chronopotentiometric and voltammetric experiments, the kinetics of the electrochemical insertion–extraction of lithium in Li_xMn₂O₄ (0.25<x<1) has been investigated using ac impedance spectroscopy. The strong variation of the chemical diffusion coefficient D_Li vs x, in the range 10⁻⁸–10⁻¹¹ cm² s⁻¹ (D_Li is found to be maximum for x=0.55) is critically discussed.     

Electrical properties of pure and Li2O-doped CuO/Fe2O3 system precalcined at different temperatures

The electrical properties of pure and Li₂O-doped CuO/Fe₂O₃ solids were investigated. Pure and variously doped solids were subjected to thermal treatment at 1073–1273 K and the amount of dopant was varied between 0.84 to 3.36 mol%. The effect of precalcination temperature and amount of Li₂O added on the electrical conductivity σ, activation energy E_a and dielectric constant * were studied. The variation of ′ and ″ as a function of frequency for pure and variously doped solids precalcined at different temperatures was also investigated. The results obtained were discussed.     

Lithium scandium phosphate-based electrolytes for solid state lithium rechargeable microbatteries

Li₃Sc₂(PO₄)₃ is a promising candidate for use as an electrolyte in solid state lithium rechargeable microbatteries due to its stability in air, ease of preparation, and resistance to dielectric breakdown. The room temperature ionic conductivity was optimized resulting in an increase of over two orders of magnitude to 3×10⁻⁶S/cm. The formation of Li₃(Sc_2−xM_x)(PO₄)₃, where M=Al³⁺ or Y³⁺, resulted in the decrease of porosity, greater sinterability, and considerable enhancement of the ionic conductivity. Yttrium substitutions enhanced the conductivity slightly while aluminum increased the room temperature ionic conductivity to 1.5×10⁻⁵S/cm for x=0.4. Preliminary electron beam evaporation of Li₃Sc₂(PO₄)₃ yielded amorphous thin films with ion ic conductivity as high as 5×10⁻⁵S/cm and a composition of Li_4.8Sc_1.4(PO₄)₃.     

BaO-Li2O-B2O3三元系中BaB2O4-Li2B2O4和BaB2O4-Li2O截面相平衡关系的研究

本文用X射线和差热分析方法对BaO-Li₂O-B₂O₃三元系中的两个截面:BaB₂O₄-Li₂B₂O₄和BaB₂O₄-Li₂O作了研究。在BaB₂O₄-Li₂B₂O₄赝二元系中发现了一个新的化合物4BaB₂O₄·Li₂B₂O₄。化合物在930±3℃由包晶反应形成,并与Li₂B₂O₄形成共晶反应。共晶温度为797±3℃,共晶点组分为79mol％Li₂B₂O₄。在BaB₂O₄-Li₂O截面中也存在化合物4BaB₂O₄·Li₂B₂O₄,其包晶反应温度从930±3℃随Li₂O含量增加下降到908±3℃。在组分60mol％Li₂O处形成另一个新的化合物2BaB₂O₄·3Li₂O。该化合物在630±3℃也是由包晶反应形成,并与Li₂O和Li₂CO₃分别形成共晶反应,共晶温度分别为400±3℃和612±3℃。在BaB₂O₄-Li₂B₂O₄和BaB₂O₄-Li₂O体系中都没有观察到固溶体。用计算机程序分别对化合物4BaB₂O₄·Li₂B₂O₄和2BaB₂O₄·3Li₂O的X射线粉末衍射图案进行了指标化,其结果:4BaB₂O₄·Li₂B₂O₄的空间群为Pmma,a=13.033?,b=14.630?,c=4.247?,每个单胞包含两个化合式单位;2BaB₂O₄·3Li₂O的空间群为Pmmm,a=4.814?,b=9.897?,c=11.523?,每个单胞也含有两个化合式单位。 关键词：     

冷冻干燥法制备Li2O氚增殖剂陶瓷小球

以Li₂CO₃粉末为原料,采用一种冷冻干燥湿法工艺,制备出综合性能较好的Li₂O陶瓷小球。通过研究冷冻成形、煅烧、分解和烧结等工艺过程,优化了Li₂O陶瓷小球的制备工艺,并对获得的Li₂O陶瓷小球进行了性能表征。结果表明:冷冻成形制备的凝胶小球在650 ℃煅烧后可得到纯净的Li₂CO₃小球,再于真空条件下多步程序升温至720 ℃可制得主要相为Li₂O的小球,小球尺寸分布均匀,直径约为0.8 mm,平均晶粒尺寸为9 μm,于900 ℃高温烧结后小球的密度可达理论密度的69.5%。     

二正丁基锡(IV)基羧酸酯的谱学表征

合成了10个二正丁基锡(IV)基羧酸酯化合物{[ⁿBu₂Sn (O₂CR)]₂O}₂(A1~A5)和ⁿBu₂Sn (O₂CR)₂(B1~B5)(R=1:CCl₃;2:CHCl₂;3:CH₂Cl;4:PhCH=CH;5:2,2,3,3-四甲基环丙基),其中A4、A5和B5为新化合物,对它们进行了元素分析和IR及、¹H、¹³C、¹¹⁹Sn NMR谱表征,重点讨论了¹³C和¹¹⁹Sn NMR谱的谱学特征及化学位移值与母体酸的PKa值大小的关系,并在此基础上推测了它们分子结构。     

硫化锂分子的分析势能函数和光谱

应用密度泛函理论的B3LYP方法和6-311++g（d,p）基组,研究Li₂、LiS和Li₂S分子的基态构型.结果表明它们的基电子态分别为X¹Σ_g⁺、X²Π和X¹Σ_g⁺.通过非线性曲线拟合,得到基态LiS和Li₂分子的4参数Murrell-Sorbie分析势能函数,计算它们的光谱参数和力常数.基于多体项展式理论得到了基态Li₂S分子的单重态势能面的分析函数.利用得到的分析势能函数重构基态单重Li₂S分子的旋转图、伸缩图和旋转伸缩图,准确地再现了Li₂S分子的静态特征,如平衡结构,最低能量,合理反应通道.从等值势能面图看出,反应Li+S+Li→Li₂S是一个无阈值反应.S原子攻击Li₂分子的反应通道上,有一个过渡态.Li原子攻击LiS分子通道上也有一个过渡态.     

Lithium insertion to ReO3-type metastable phase in the Nb2O5–WO3 system

Lithium insertion to distorted ReO₃-type metastable solid solution Nb_xW_1−xO_3−x/2 (0≤x<0.25) has been studied by chemical and electrochemical methods. In the course of lithium insertion into tetragonal compounds, transition to a cubic phase was found to occur in the region where values of y (in Li_yNb_xW_1−xO_3−x/2) fall between 0.2 and 0.3, and the phase transition was found to depend on the conditions of the reaction. Changes in OCV and lattice parameters in tetragonal region (y<0.2) were discussed from the viewpoint of the ordering of lithium ions. Also, the component diffusion coefficient of lithium in tetragonal compounds Li_0.1Nb_xW_1−xO_3−x/2 (0≤x≤0.23) was found to increase with niobium content when x≤0.10, and to saturate at 4×10⁻⁹ cm²/s.     

锂、硼、硅酸盐玻璃体系的11B核磁共振研究

利用¹¹B的核磁共振谱研究了锂、硼、硅酸盐(Li₂O·B₂O₃·SiO₂)三元玻璃体系,测量并分析了BO₄单元与对称和非对称的BO₃单元的比例。分析结果表明,三元体系的结构单元亦可适用于锂、硼玻璃的二元体系的FDB模型说明,其差异在于前者中的Li₂O由B₂O₃与SiO₂按比例分享。     

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.     

各Li吸附组分下硅烯氢存储性能的第一性原理研究

利用Li原子对硅烯进行表面修饰是提高硅烯氢存储能力的一种有效方法.为了充分挖掘Li修饰硅烯的氢存储性能,本文采用范德瓦耳斯作用修正的第一性原理计算方法,对不同Li吸附组分下硅烯的结构、稳定性和氢存储能力进行了研究.研究结果表明,硅烯体系能够在Li组分从0.11增加到0.50时保持稳定,其最大储氢量随Li组分的增加而增大,氢气平均吸附能则存在减小趋势;当Li组分达到0.50而饱和时,硅烯体系具有最大的储氢量,相应的质量储氢密度为11.46 wt%,平均吸附能为0.34 eV/H2,远高于美国能源部设定的储氢标准,表明提高Li组分甚至使其达到饱和在理论上能有效提高Li修饰硅烯的储氢性能.此外,通过对Mulliken电荷布居、差分电荷密度和态密度的分析,发现Li修饰硅烯的储氢机制与电荷转移诱导的静电相互作用和轨道杂化作用有关.研究结果可为Li修饰硅烯在未来氢存储领域的应用提供理论指导.     

Interaction of CO2 with Cs-promoted Fe(110) as compared to Fe(110)/K+CO2

The interaction of CO₂ with Cs-promoted Fe(110) at 85 K as well as temperature-dependent reactions between 100 and 700 K have been studied by means of ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). Several surface species could be detected at 85 K, i.e. carbon monoxide (CO), carbonate (COⁿ⁻₃), physisorbed linear carbon dioxide (CO^lin₂) and very small amounts of oxidic oxygen (O_ox). An oxalate species (C₂O^m−₄) could not be identified definitively, but from comparison with the literature there is evidence that C₂O^m−₄ is present. Increasing the temperature after saturation with CO₂ leads to a complicated reaction behaviour. CO₂ either desorbs or dissociates into CO and COⁿ⁻₃ or forms C₂O^m−₄ at temperatures between 85 and 160 K. Above 160 K C₂O^m−₄, decomposes in parallel reactions into CO₂, COⁿ⁻₃ and CO. Above 320 K, adsorbed CO either desorbs into the gas phase or dissociates into C and O. In the temperature region between 500 and 700 K a recombination of C and O to CO and the desorption of Cs take place. As in the case of Fe(110)/K+CO₂, at high alkali coverages two carbonate species could be detected which dissociate upon heating at different temperatures. The system Fe(110)/Cs+CO₂ is proved to be very similar to the system Fe(110)/K+CO₂.