Ge adsorption on Ag(111): A density-functional theory investigation

First-principles density-functional theory has been used to investigate the adsorptions of Ge on Ag(111) surfaces for a wide range of coverage. Preferred adsorption sites, adsorption energies, surface structures, and the electronic properties are studied. Our results show that adsorption on the surface in fcc- sites is energetically favorable. The adsorption energies decrease as increasing Ge atoms, while the work functions of Ag surface decrease. The contour maps of the difference charge show that there exists covalent bonding in lower coverage systems to some extent for Ge on Ag(111) surface, and the interaction of Ge and Ag atoms becomes weaker with the increase of adsorption degree. The calculated density of states indicates that the adsorption structures have metallic character, while the number of electron transition is small and the interaction is not strong between Ge and Ag atoms.     

The formal combination of three singlet biradicaloid entities to a singlet hexaradicaloid metalloid Ge14[Si(SiMe3)3]5[Li(THF)2]3 cluster

The reaction of GeBr with LiSi(SiMe(3))(3) leads to the metalloid cluster compound [(THF)(2)Li](3)Ge(14)[Si(SiMe(3))(3)](5) (1). After the introduction of a first cluster of this type, in which 14 germanium atoms form an empty polyhedron, [(THF)(2)Li](3)Ge(14)[Ge(SiMe(3))(3)](5) (2), we present here further investigations on 1 to obtain preliminary insight into its chemical and bonding properties. The molecular structure of 1 is determined via X-ray crystal structure solution using synchrotron radiation. The electronic structure of the Ge(14) polyhedron is further examined by quantum chemical calculations, which indicate that three singlet biradicaloid entities formally combine to yield the singlet hexaradicaloid character of 1. Moreover, the initial reactions of 1 after elimination of the [Li(THF)(2)](+) groups by chelating ligands (e.g., TMEDA or 12-crown-4) are presented. Collision induced dissociation experiments in the gas phase, employing FT-ICR mass spectrometry, lead to the elimination of the singlet biradicaloid Ge(5)H(2)[Si(SiMe(3))(3)](2) cluster. The unique multiradicaloid bonding character of the metalloid cluster 1 might be used as a model for reactions and properties in the field of surface science and nanotechnology.     

Li4Ge2B as a new derivative of the Mo2B5 and Li5Sn2 structure types

Binary and multicomponent intermetallic compounds based on lithium and p‐elements of Groups III–V of the Periodic Table are useful as modern electrode materials in lithium‐ion batteries. However, the interactions between the components in the Li–Ge–B ternary system have not been reported. The structure of tetralithium digermanium boride, Li₄Ge₂B, exhibits a new structure type, in the noncentrosymmetric space group R3m, in which all the Li, Ge and B atoms occupy sites with 3m symmetry. The title structure is closely related to the Mo₂B₅ and Li₅Sn₂ structure types, which crystallize in the centrosymmetric space group Rm. All the atoms in the title structure are coordinated by rhombic dodecahedra (coordination number = 14), similar to the atoms in related structures. According to electronic structure calculations using the tight‐binding–linear muffin‐tin orbital–atomic spheres approximation (TB–LMTO–ASA) method, strong covalent Ge—Ge and Ge—B interactions were established.     

In-Situ Synthesis of N,O, P-Doped Hierarchical Porous Carbon from Poly-bis(phenoxy)phosphazene for Polysulfide-Trapping Interlayer in Lithium-Sulfur Batteries

The shuttling of polysulfides is the most detrimental contribution to degrading the capacity and cycle stability of lithium-sulfur (Li−S) batteries. Adding a carbon interlayer to prevent the polysulfides from migrating is feasible, and a rational design of the structures and surface properties of the carbon layer is essential to increasing its effectiveness. Herein, we report a hierarchical porous carbon (HPC) created by carbonization of bis(phenoxy)phosphazene and in-situ doping of triple heteroatoms into the carbon lattice to fabricate an effective polysulfide-trapping interlayer. The generated carbon integrates the advantages of a hierarchical porous structure, a high specific area and rich dopants (N, O and P), to yield chemisorption and physical confinement for polysulfides and fast ion-transport synergistically. The HPC interlayer significantly improves the electrochemical performance of Li−S batteries, including an exceptional discharge capacity of 1509 mA h/g at 0.06 C and a high capacity retention of 83.7 % after 250 cycles at 0.3 C. This work thus proposes a facile in-situ synthesis of heteroatom-doped carbon with rational porous structures for suppressing the shuttle effect.     

Interaction of triatomic germanium with lithium atoms: electronic structure and stability of Ge3Lin clusters

Quantum chemical calculations were applied to investigate the electronic structure of mono-, di-, and tri- lithiated triatomic germanium (Ge3Lin) and their cations (n = 0-3). Computations using a multiconfigurational quasi-degenerate perturbation approach (MCQDPT2) based on complete active space CASSCF wavefunctions, MRMP2 and density functional theory reveal that Ge3Li has a 2A' ground state with a doublet-quartet gap of 24 kcal/mol. Ge3Li2 has a singlet ground state with a singlet-triplet (3A' '-1A1) gap of 30 kcal/mol, and Ge3Li3 a doublet ground state with a doublet-quartet (4A' '-2A') separation of 16 kcal/mol. The cation Ge3Li+ has a 1A' ground state, being 18 kcal/mol below the 3A' state. The computed electron affinities for triatomic germanium are EA(1) = 2.2 eV (experimental value is 2.23 eV), EA(2) = -2.5 eV, and EA(3) = -5.9 eV, for Ge3-, Ge32-, and Ge33-, respectively, indicating that only the monoanion is stable with respect to electron detachment, in such a way that Ge3Li is composed of Ge3-Li+ ions. An atoms in molecules (AIM) analysis shows the absence of a Ge-Ge-Li ring critical point in Ge3Li. An electron localization function (ELF) map of Ge3Li supports the view that the Ge-Li bond is predominantly ionic; however, a small covalent character could be anticipated from the Laplacian at the Ge-Li bond critical point. The ionic picture of the Ge-Li bond is further supported by the natural bond orbital (NBO) results. The calculated Li affinity value for Ge3 is 2.17 eV, and the Li+ cation affinity value for Ge3- amounts to 5.43 eV. The larger Li+ cation affinity of Ge3- favors an electron transfer, resulting in a Ge3-Li+ interaction.     

功率型锂/氟化碳一次电池的优化设计研究进展

锂/氟化碳电池作为固态正极中理论比能量较高（2203 Wh/kg）的一种一次电池体系,受到极大的关注,在诸多领域已有应用。本文对高功率锂/氟化碳电池的优化设计的最新研究进展进行了综述,详细讨论了氟化碳材料的前驱体、氟化方法、氟化碳材料表面改性、电极结构设计等因素对电池倍率性能的影响,并对今后功率型锂/氟化碳一次电池的发展方向进行了展望。     

Interaction of diatomic germanium with lithium atoms: electronic structure and stability

Quantum chemical calculations were applied to investigate the electronic structure of mono-, di-, and trilithiated digermanium (Ge2Lin) and their cations (n=0-3). Computations using a multiconfigurational quasidegenerate perturbation approach based on complete active space self-consistent-field wave functions, and density functional theory reveal that Ge2Li has a 2B1 ground state with a doublet-quartet energy gap of 33 kcal/mol. Ge2Li2 has a singlet ground state with a 3Au-1A1 gap of 29 kcal/mol, and Ge2Li3 a doublet ground state with a 4B2-2A2 separation of 22 kcal/mol. The cation Ge2Li+ has a 3B1 ground state, being 13 kcal/mol below the open-shell 1B1 state. The computed electron affinities for diatomic germanium are EA(1)=1.9 eV, EA(2)=-2.5 eV, and EA(3)=-6.0 eV, for Ge2-, Ge2 (2-), and Ge2 (3-), respectively, indicating that only the monoanion is stable with respect to electron detachment, in such a way that Ge2Li is composed by Ge2-Li+ ions. An "atoms-in-molecules" analysis shows the absence of a ring critical point in Ge(2)Li. An electron localization function analysis on Ge2Li supports the view that the Ge-Li bond is predominantly ionic; however, a small covalent character could be anticipated from the analysis of the Laplacian at the Ge-Li bond critical point. The ionic picture of the Ge-Li bond is further supported by a natural-bond-order analysis and the Laplacian of the electron density. The calculated Li affinity value for Ge2 is 2.08 eV, while the Li+ cation affinity value for Ge2- is 5.7 eV. The larger Li+ cation affinity value of Ge2- suggests a Ge2-Li+ interaction and thus supports the ionic nature of Ge-Li bond. In GeLi4 and Ge2Li, the presence of trisynaptic basins indicates a three-center bond connecting the germanium and lithium atoms.     

多孔泡沫铜和硫脲协同作用构筑无枝晶锂负极

锂金属作为下一代储能电池的理想负极材料一直受到极大的关注,然而锂枝晶的不可控生长和负极副反应带来的低库伦效率问题严重限制了锂金属电池的发展。这里,我们提出了一种多孔泡沫铜和硫脲协同作用的策略,利用硫脲分子的超填充作用实现锂金属在多孔泡沫铜表面的均匀沉积。在电解液中添加0.02 mol·L^-1硫脲作为电解质添加剂,采用多孔泡沫铜的Li||Cu半电池在循环300圈以后,库伦效率仍保持在98%以上。此外,在5C的高倍率条件下,Li||Li FePO4全电池循环300圈以后仍有94%的容量保持率。本工作为锂金属负极保护提供了一种新的策略并且该策略也可以扩展到其他金属负极保护中,非常有利于下一代高能量密度储能电池的开发。     

Recent Development of Polyolefin‐Based Microporous Separators for Li−Ion Batteries: A Review

Secondary Li?ion batteries have been paid attention to wide‐range applications of power source for the portable electronics, electric vehicle, and electric storage reservoir. Generally, lithium‐ion batteries are comprised of four components including anode, cathode, electrolyte and separator. Although separators do not take part in the electrochemical reactions in a lithium‐ion (Li?ion) battery, they conduct the critical functions of physically separating the positive and negative electrodes to prevent electrical short circuit while permitting the free flow of lithium ions through the liquid electrolyte that fill in their open porous structure. Hence, the separator is directly related to the safety and the power performance of the battery. Among a number of separators developed thus far, polyethylene (PE) and polypropylene (PP) porous membrane separators have been the most dominant ones for commercial Li?ion batteries over the decades because of their superior properties such as cost‐efficiency, good mechanical strength and pore structure, electrochemical stability, and thermal shutdown properties. However, there are main issues for vehicular storage, such as nonpolarity, low surface energy and poor thermal stability, although the polyolefin separators have proven dependable in portable applications. Hence, in this review, we decide to provide an overview of the types of polyolefin microporous separators utilized in Li?ion batteries and the methods employed to modify their surface in detail. The remarkable results demonstrate that extraordinary properties can be exhibited by mono‐ and multilayer polyolefin separators if they are modified using suitable methods and materials.     

Structure and Thermodynamic Characteristics of Impurity Centers in Lithium-Doped Cadmium Oxide: an <Emphasis Type="Italic">Ab Initio</Emphasis> Paw-Study

The ab initio projector augmented wave (PAW) method is used to calculate the electronic structure of Li-doped cadmium oxide with NaCl structure. The preference energy for Li atoms in interstitial sites and the energy of impurity oxidation are calculated. Interstitial positions for Li atoms are shown to be stable under thermodynamic equilibrium, but Li atoms can substitute Cd atoms in presence of vacancies in the oxygen sublattice. We consider the following complexes: one Li atom in the interstitial site and the other Li atom in Cd position; one Li atom in Cd position and one oxygen vacancy; a pair of oxygen vacancies; and show that these complexes are formed to have the shortest possible distance between their components. The band gap substantially decreases when Li atoms occupy interstitial sites to explain considerable increase of experimental conductivity.     

二次离子电池高比容量负极碳载体的研究进展

二次离子电池商业化负极石墨的比容量已接近理论比容量. 合金型负极和金属负极因具有高比容量而受到广泛关注, 但其循环性能差和安全性问题限制了实际应用, 据此提出载体设计策略. 碳材料具有来源广泛、 易于调控等特性, 常用作二次离子电池高比容量负极的载体. 本文从碳载体的孔结构、 比表面积、 电子导电率、 离子导电率、 杂原子掺杂和界面修饰的角度出发, 综述了其在硅基、 磷基、 锗基、 锡基负极以及金属锂、 钠等负极中的研究进展, 展望了碳载体的发展前景和方向.     

LiBH4-X（X=O,F和Cl）体系解氢性能的第一原理计算

采用基于密度泛函理论的第一原理方法,计算了LiBH4-X(X=O,F和Cl)体系的晶体与电子结构及解氢性能.生成热和H原子解离能的计算结果表明:O原子掺杂优先占据LiBH4间隙位,F置换氢原子位,而Cl则取代BH4单元;O,F和Cl掺杂的LiBH4体系结构稳定性发生变化,其中O提高体系解氢效果明显,而F和Cl掺杂受H原子区域环境的影响.态密度、Mulliken电子占据数和电子密度的分析结果表明:B—H之间较强的共价键是LiBH4结构稳定、解氢困难的电子结构根源,O,F和Cl对LiBH4解氢能力影响主要是掺杂改变了H的s态与B的sp态的杂化特性、以及BH4单元与Li的成键作用.     

Thermodynamic properties and electrochemical behavior of lithium–germanium alloys

Published data on the phase diagram of the lithium–germanium system, on the thermodynamic properties of Li–Ge alloys, on their electrochemical behavior in various media, and on prospects for using them in lithium–ion batteries and in other chemical current sources are analyzed.     

Stable structure and effects of sulfur in CdTe/CdS heterojunctions

Structural and electronic properties of S in the CdTe/CdS(0001) interface are studied using the density functional theory. The interstitial S atom may induce the inversion of the surface Cd atoms and sublayer Te atoms of the Cd‐terminated surface, while S atoms may adsorb at the top sites, substitute Te atoms or accumulate at the voids inside the Te‐terminated (111) CdTe surface. Isovalent substituting S for Te in the CdTe(111)/CdS(0001) heterojunctions can reduce the strain arising from lattice mismatch and cause a reduction of interface states, so it may be better for solar cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Amorphous hierarchical porous GeO(x) as high-capacity anodes for Li ion batteries with very long cycling life

Many researchers have focused in recent years on resolving the crucial problem of capacity fading in Li ion batteries when carbon anodes are replaced by other group-IV elements (Si, Ge, Sn) with much higher capacities. Some progress was achieved by using different nanostructures (mainly carbon coatings), with which the cycle numbers reached 100-200. However, obtaining longer stability via a simple process remains challenging. Here we demonstrate that a nanostructure of amorphous hierarchical porous GeO(x) whose primary particles are ~3.7 nm diameter has a very stable capacity of ~1250 mA h g(-1) for 600 cycles. Furthermore, we show that a full cell coupled with a Li(NiCoMn)(1/3)O(2) cathode exhibits high performance.     

Electronic stress tensor analysis of molecules in gas phase of CVD process for gesbte alloy

We analyze the electronic structure of molecules which may exist in gas phase of chemical vapor deposition process for GeSbTe alloy using the electronic stress tensor, with special focus on the chemical bonds between Ge, Sb, and Te atoms. We find that, from the viewpoint of the electronic stress tensor, they have intermediate properties between alkali metals and hydrocarbon molecules. We also study the correlation between the bond order which is defined based on the electronic stress tensor, and energy‐related quantities. We find that the correlation with the bond dissociation energy is not so strong while one with the force constant is very strong. We interpret these results in terms of the energy density on the “Lagrange surface,” which is considered to define the boundary surface of atoms in a molecule in the framework of the electronic stress tensor analysis. © 2015 Wiley Periodicals, Inc.     

Model Ge microstructures as anodes for Li-ion batteries

We examine the properties of microstructured Ge electrodes for Li-ion battery applications. Model-microfabricated single-crystalline Ge electrode structures are used to investigate the effects of Cu coating and partial discharging on cycle life. Results show that the Ge microstructures insert Li more isotropically than do comparable ones comprised of Si. A model Ge microbar electrode with a Cu coating is capable of 95 % coulombic efficiency after 40 cycles when the amount of charge is limited. The microstructured Ge electrode is found to exhibit poor performance at higher delithiation rates (above C/5) relative to microstructured Si electrodes. These results provide an understanding of the effects of electrochemical processes on model-microstructured Ge electrodes which may ultimately aid in the development of advanced anodes for Li-ion batteries.     

锂金属负极亲锂骨架的研究进展

随着电动汽车和便携式电子产品的快速发展, 人们对于高比能二次电池的需求越来越迫切. 锂金属以其极高的理论比容量和极低的电极电势被视为下一代高比能电池理想负极材料之一. 但是, 锂枝晶的生长及体积膨胀等问题限制了金属锂负极的实际应用. 在金属锂负极中引入三维骨架可以有效抑制锂枝晶生长, 缓解体积膨胀. 其中亲锂骨架可以降低锂的形核能垒, 诱导锂的均匀成核, 更加有效地调控锂沉积行为. 本文结合国内外的研究进展总结了锂金属负极中亲锂骨架的研究成果. 根据亲锂材料的不同对亲锂骨架进行了分类, 总结了各类亲锂骨架在调控锂沉积行为和提高电池性能方面取得的成果, 并对其今后的研究和发展进行了展望.     

石墨烯负载的氧配位钴单原子稳定金属锂负极

Lithium (Li)-based batteries are the dominant energy source for consumer electronics, grid storage, and electrified transportation. However, the development of batteries based on graphite anodes is hindered by their limited energy density. With its ultrahigh theoretical capacity (3860 mAh∙g⁻¹), low redox potential (−3.04 V), and satisfactorily low density (0.54 g∙cm⁻³), Li metal is the most promising anode for next-generation high-energy-density batteries. Unfortunately, the limited cycling life and safety issues raised by dendrite growth, unstable solid electrolyte interphase, and "dead Li" have inhibited their practical use. An effective strategy is to develop a suitable lithiophilic matrix for regulating initial Li nucleation behavior and controlling subsequent Li growth. Herein, single-atom cobalt coordinated to oxygen sites on graphene (Co-O-G SA) is demonstrated as a Li plating substrate to efficiently regulate Li metal nucleation and growth. Owing to its dense and more uniform lithiophilic sites than single-atom cobalt coordinated to nitrogen sites on graphene (Co-N-G SA), high electronic conductivity, and high specific surface area (519 m²∙g⁻¹), Co-O-G SA could significantly reduce the local current density and promote the reversibility of Li plating and stripping. As a result, the Co-O-G SA based Li anodes exhibited a high Coulombic efficiency of 99.9% at a current density of 1 mA∙cm⁻² with a capacity of 1 mAh∙cm⁻², and excellent rate capability (high current density of 8 mA∙cm⁻²). Even at a high plating capacity of 6 mAh∙cm⁻², the Co-O-G SA electrode could stably cycle for an ultralong lifespan of 1300 h. In the symmetric battery, the Co-O-G SA based Li anode (Co-O-G SA/Li) possessed a stable voltage profile of 18 mV for 780 h at 1 mA∙cm⁻², and even at a high current density of 3 mA∙cm⁻², its overpotential maintained a small hysteresis of approximately 24 mV for > 550 h. Density functional theory calculations showed that the surface of Co-O-G SA had a stronger interaction with Li atoms with a larger binding energy, −3.1 eV, than that of Co-N-G SA (−2.5 eV), leading to a uniform distribution of metallic Li on the Co-O-G SA surface. More importantly, when matched with a sulfur cathode, the resulting Co-O-G SA/lithium sulfur full batteries exhibited a high capacity of 1002 mAh∙g⁻¹, improved kinetics with a small polarization of 191 mV, and an ultralow capacity decay rate of 0.036% per cycle for 1000 cycles at 0.5C (1C = 1675 mA∙g⁻¹) with a steady Coulombic efficiency of nearly 100%. Therefore, this work provides novel insights into the coordination environment of single atoms for the chemistry of Li metal anodes for high-energy-density batteries.     

三维大孔/介孔碳-碳化钛复合材料用于无枝晶锂金属负极

金属锂具有超高的理论容量(3860 mAh·g^-1)和低氧化还原电位(-3.04 V vs.标准氢电极),是极具吸引力的下一代高能量密度电池的负极材料。然而,循环过程中的体积膨胀、锂枝晶生长和“死锂”等问题严重的限制了其实际应用。合理设计三维骨架调控金属锂的成核行为是抑制锂枝晶生长的有效策略。本文中,我们发展了一种“软硬双模板”的方法合成了兼具大孔和介孔的三维碳-碳化钛(Three-dimensional macro-/mesoporous C-TiC,表示为3DMM-C-TiC)复合材料。多级孔道为金属锂的沉积提供了足够的空间,缓冲充放电中巨大的体积变化。此外,TiC的引入显著增强多孔骨架的导电性,改善锂金属的成核行为,促进金属锂的均匀成核和沉积,抑制锂枝晶生长。3DMM-C-TiC||Li电池测试表明,在循环300圈以后,库伦效率仍保持在98%以上。此外,所得材料与LiFePO₄ (LFP)组成的全电池也表现出优异的倍率和循环性能。本工作为无枝晶锂金属负极的设计提供了新的思路。