Lithium intercalation mechanism for β-SnSb in Sn-Sb thin films

Based on the first-principles plane wave pseudo-potential method, the electronic structure and electrochemical performance of Li_xSn₄Sb₄ (x=2, 4, 6, and 8) and Li_xSn_1-xSb₄ (x=9, 10, 11, and 12) phases were calculated. A Sn-Sb thin film on a Cu foil was also prepared by radio frequency magnetron sputtering. The surface morphology, composition, and lithium intercalation/extraction behavior of the fabricated film were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV). Lithium atoms can easily insert into and extract out of the β-SnSb cell due to the low lithium intercalation formation energy. It is found that lithium atoms first occupy the interstitial sites, and then Sn atoms at the lattice positions are replaced by excessive lithium. The dissociative Sn atoms continue to produce different Li-Sn phases, which will affect the electrode stability and lead to the undesirable effect due to their large volume expansion ratio. The calculated lithium intercalation potential is stable at about 0.7 V, which is consistent with the experimental result.     

First-principles calculations of the β′-Mg<Subscript>7</Subscript>Gd precipitate in Mg-Gd binary alloys

The metastable β’ phase is often the most effective hardening precipitate in Mg-Gd based alloys.In this paper,the structural,elastic and electronic properties of the recently identified β’-Mg7Gd precipitate in Mg-Gd binary alloys were investigated using first-principles calculations based on density functional theory.The lattice mismatches between the coherent β’-Mg7Gd precipitate and α-Mg matrix are discussed and used to rationalize the experimentally observed morphology of the precipitate.The mechanical properties were investigated through analysis of the single-crystal elastic constants and the polycrystalline elastic moduli.It is found that β’-Mg7Gd is brittle in nature.Strong covalent bonding in β’-Mg7Gd,as inferred from its electronic structure,further explains its mechanical properties.Our theoretical results show good agreement with experimental measurements.     

The roles of π electrons in the electronic structures and optical properties of graphyne

The electronic structures and optical properties of graphyne consisting of sp-and sp 2-hybridized carbon atoms are studied using first-principles calculations.A tight-binding model of the 2p z orbitals are proposed to describe the electronic bands near the Fermi level.The results show that the natural band gap of graphyne originates from the inhomogeneous bindings between differently-hybridized carbon atoms.The interlayer interactions of bulk graphyne narrow the band gap to 0.16 eV and result in redshift of the optical spectral peaks as compared to single-layered graphyne.     

Peculiarity of magnetoresistance of discontinuous ferromagnetic thin films

The magnetoresistive properties of discontinuous ferromagnetic Fe and Co thin films deposited by electron-beam sputtering onto glass substrates at room temperature were investigated. Tunnel magnetoresistance (MR) was observed for all of the as-deposited samples. The maximum MR was observed for Fe thin films with an effective thickness of 17 nm. In the case of the Co thin films, the annealing process led to a change of the type of MR to anisotropic at Co film thicknesses (d_Co) of 15 ≤ d_Co ≤ 25 nm and to positive isotropic at thicknesses of d_Co < 15 nm. By contrast, the MR type of Fe thin films did not change.     

Preparation and performance of novel LLTO thin film electrolytes for thin film lithium batteries

We prepared a series of lithium lanthanum titanate(LLTO) thin film electrolytes by radio frequency(RF) magnetron sputtering using LLTO targets in a N2 atmosphere.We also deposited the LLTO thin films in an Ar atmosphere under a same condition as references for comparison.The microstructure morphology and the composition of the thin films were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS),respectively.Results show that the thin film has an amorphous structure with a uniform surface and it is free of pinholes and cracks.Impedance measurements reveal that the ionic conductivity of the electrolytes is beneficial for all solid lithium batteries dependent on the lithium content at room temperature.We found that the amorphous LLTO thin film performs well and it has potential application in microbatteries for use in microelectronic devices.     

Structural predictions based on the compositions of cathodic materials by first-principles calculations

A first-principles method is applied to comparatively study the stability of lithium metal oxides with layered or spinel structures to predict the most energetically favorable structure for different compositions. The binding and reaction energies of the real or virtual layered LiMO₂ and spinel LiM₂O₄ (M=Sc-Cu, Y-Ag, Mg-Sr, and Al-In) are calculated. The effect of element M on the structural stability, especially in the case of multiple-cation compounds, is discussed herein. The calculation results indicate that the phase stability depends on both the binding and reaction energies. The oxidation state of element M also plays a role in determining the dominant structure, i.e., layered or spinel phase. Moreover, calculation-based theoretical predictions of the phase stability of the doped materials agree with the previously reported experimental data.     

Progress on Sn-based thin-film anode materials for lithium-ion batteries

Thin-film lithium-ion batteries are the most competitive power sources for various kinds of micro-electro-mechanical systems and have been extensively researched.The present paper reviews the recent progress on Sn-based thin-film anode materials,with particular emphasis on the preparation and performances of pure Sn,Sn-based alloy,and Sn-based oxide thin films.From this survey,several conclusions can be drawn concerning the properties of Sn-based thin-film anodes.Pure Sn thin films deliver high reversible capacity but very poor cyclability due to the huge volume changes that accompany lithium insertion/extraction.The cycle performance of Sn-based intermetallic thin films can be enhanced at the expense of their capacities by alloying with inactive transition metals.In contrast to anodes in which Sn is alloyed with inactive transition metals,Sn-based nanocomposite films deliver high capacity with enhanced cycle performance through the incorporation of active elements.In comparison with pure Sn anodes,Sn-based oxide thin films show greatly enhanced cyclability due to the in situ formation of Sn nanodispersoids in an Li2O matrix,although there is quite a large initial irreversible capacity loss.For all of these anodes,substantial improvements have been achieved by micro-nanostructure tuning of the active materials.Based on the progress that has already been made on the relationship between the properties and microstructures of Sn-based thin-film anodes,it is believed that manipulating the multi-phase and multi-scale structures offers an important means of further improving the capacity and cyclability of Sn-based alloy thin-film anodes.     

Influence of microstructure on the corrosion resistance of Fe–44Ni thin films

An Fe–44Ni nanocrystalline (NC) alloy thin film was prepared through electrodeposition. The relation between the microstructure and corrosion behavior of the NC film was investigated using electrochemical methods and chemical analysis approaches. The results show that the NC film is composed of a face-centered cubic phase (γ-(Fe,Ni)) and a body-centered cubic phase (α-(Fe,Ni)) when it is annealed at temperatures less than 400℃. The corrosion resistance increases with the increase in grain size, and the corresponding corrosion process is controlled by oxygen reduction. The NC films annealed at 500℃ and 600℃ do not exhibit the same pattern, although their grain sizes are considerably large. This result is attributed to the existence of an anodic phase, Fe_0.947Ni_0.054, in these films. Under this condition, the related corrosion process is synthetically controlled by anodic dissolution and depolarization.     

Evolution of insoluble eutectic Si particles in anodic oxidation films during adipic-sulfuric acid anodizing processes of ZL114A aluminum alloys

The effects of insoluble eutectic Si particles on the growth of anodic oxide films on ZL114A aluminum alloy substrates were investigated by optical microscopy (OM) and scanning electron microscopy (SEM). The anodic oxidation was performed at 25℃ and a constant voltage of 15 V in a solution containing 50 g/L sulfuric acid and 10 g/L adipic acid. The thickness of the formed anodic oxidation film was approximately 7.13 μm. The interpore distance and the diameters of the major pores in the porous layer of the film were within the approximate ranges of 10-20 nm and 5-10 nm, respectively. Insoluble eutectic Si particles strongly influenced the morphology of the anodic oxidation films. The anodic oxidation films exhibited minimal defects and a uniform thickness on the ZL114A substrates; in contrast, when the front of the oxide oxidation films encountered eutectic Si particles, defects such as pits and non-uniform thickness were observed, and pits were observed in the films.     

Facile synthesis of nanostructured LiFePO4/C cathode material for lithium-ion batteries

Nanostructured LiFePO4/C cathode material was prepared by FePO4·2H2O/C precursor by in situ restriction reaction.The synthesized LiFePO4/C cathode material presents a narrow distribution of nano-sized particles and exhibits an excellent electrochemical property with various rates.The facile synthesis route for the preparation of nano-sized LiFePO4 material has the particular advantage of simple synthesis process and low synthesis cost.     

Effect of modified elastomeric binders on the electrochemical properties of silicon anodes for lithium-ion batteries

Silicon has been investigated intensively as a promising anode material for rechargeable lithium-ion batteries. The choice of a binder is very important to solve the problem of the large capacity fade observed along cycling. The effect of modified elastomeric binders on the electrochemical performance of crystalline nano-silicon powders was studied. Compared with the conventional binder (polyvinylidene fluoride (PVDF)), Si electrodes using the elastomeric styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (SCMC) combined binder show an improved cycling performance. The reversible capacity of the Si electrode with the SCMC/SBR binder is as high as 2221 mA·h/g for 30 cycles in a voltage window between 0.005 and 2 V. The structure changes from SEM images of the silicon electrodes with different binders were used to explore the property improvement.     

Comparative study of LiNiO2, LiNi0.8Co0.2O2 and LiNi0.75Al0.25O2 for lithium-ion batteries

The comparative study of LiNi0.8Co0.2O2 and LiNi0.75Al0.25O2 was carried out by X-ray diffraction (XRD) and electrochemical methods. The results show that Co and Al doping suppress the phase transition during charge-discharge. The experiments indicate that LiNi0.75Al0.25O2 has the better cycle-ability and over-charge resistance comparing with LiNi0.8Co0.2O2. The interfacial behavior was studied by use of electrochemical impedance spectroscopy (EIS). The results show that LiNi0.75Al0.25O2 has a slightly larger polarization character than LiNi0.8Co0.2O2.     

Wire-like nano-polyaniline deposited electrochemically in a reverse micelle electrolyte as a pH sensor

Wire-like polyaniline (PANI) films were successfully electrodeposited onto an indium tin oxide (ITO) substrate using a pulse galvanostatic method (PGM) in a reverse micelle electrolyte. The as-prepared PANI films were electrochemically analyzed by cyclic voltammetry and electrochemical impedance spectroscopy in 1 mol·L-1 HClO₄ solution. It is found that the as-prepared PANI films are highly porous, exhibit the diameters of approximately 100 nm and the lengths exceeding 3 μm, and have favorable electrochemical activities. Furthermore, the as-prepared wire-like PANI films show a good linear relationship of the potentiometric response curve over the pH value range of 3–10 with a slope of 74.13 mV·pH-1 in 0.5 mol·L-1 K₂HPO₄ basal solutions. The results demonstrate that the prepared wire-like PANI films are promising pH sensors.     

Eutectic reaction and cored dendritic morphology in yttrium doped Zr-based amorphous alloys

The microalloying effect of yttrium on the crystallization behaviors of (Zr_0.525Al_0.10Ti_0.05Cu_0.179Ni_0.146)_100-x Y_x, and (Zr_0.55Al_0.15-Ni_0.10Cu_0.20)_100-x Y_x (x=0, 0.4, and 1, thus the two alloy systems were denoted as Zr52.5, Zr52.5Y0.4, Zr52.5Y1, and Zr55, Zr55Y0.4, Zr55Y1, respectively) was studied. Transmission electron microscopy (TEM) results suggested that the crystalline phases were different in the two Zr-based alloys and with different yttrium contents. ZrNi-phase and Al₃Zr₅ phase precipitations can be well explained by the mechanisms of nucleation and growth. Al₃Zr₅ phase is mainly formed by a peritectic-like reaction, while ZrNi-phase by a eutectic reaction. The contents of elements Y, Al, and Ti may dominate the reaction types. The orientation relationship between Y₂O₃ particles and Al₃Zr₅ phase is also discussed.     

Effect of rare earth elements on the structures and mechanical properties of magnesium alloys

By means of first-principles calculations,we have investigated the effects of rare earth elements (REEs) on the structures and mechanical properties of magnesium.The lattice parameters,elastic constants,bulk moduli,shear moduli,Young’s moduli and anisotropic parameter of these solid solutions have been calculated and analyzed.The nearest-neighbor distance between Mg and the REEs is also analyzed to explore the correlation with the bulk moduli.The results show that the 4f-electrons and atomic radii play an important role in the strengthening process.The anomalies of the lattice parameters and mechanical properties at Eu and Yb are due to the half-filled and full-filled 4f-electron orbital states.Finally,the increase of directional bonding character near the alloying elements may account for the anisotropy and brittleness of these magnesium alloys.     

Preparation of CoP films by ultrasonic electroless deposition at low initial temperature

Electroless deposition technology has been considered as a kind of common ways to obtain cobalt alloy films. However, in order to get cobalt alloy films, high temperature(353 K) is necessary during the electroless deposition process which will increase costs and energy consumption. Ultrasonic was introduced during electroless plating process to obtain cobalt alloy films at lower initial temperature. It was found that the cobalt thin films could be prepared at lower initial temperature(323 K) with the introduction of ultrasonic. Therefore, different powers of ultrasonic were applied during the electroless deposition process to prepare CoP thin films on copper substrates from an alkaline bath in this investigation. The effects of different powers of ultrasonic on deposition rate, surface morphology, anticorrosion performance and magnetic property of films were studied. It was found that the deposition rate increased gradually with the rise in ultrasonic powers due to cavitation phenomenon. All the CoP films presented the typical spherical nodular structures with the impact of ultrasonic. Smaller and regular shaped structures could be observed when the films were deposited with higher power of ultrasonic which contributed directly to enhancement of anticorrosion performance. Saturation magnetization and coercivity of thin films increased gradually with the rise in ultrasonic powers during the electroless deposition process due to the higher amounts of cobalt.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Effect of the synthesis method of SnSb anode materials on their electrochemical properties

SnSb alloy powders for the anode of Li-ion batteries were synthesized by two kinds of reduction precipitation methods: solution titration and rapid mixing. Two kinds of SnSb alloy powders showed different phase compositions and particle morphologies although the same starting materials were used. The SnSb alloy electrode synthesized by titration exhibits high reversible specific capacity and good cycling stability, whereas the rapid-mixing sample shows high irreversible capacity and fast capacity fade. The broad particle size distribution of SnSb powders synthesized by titration is considered to be responsible for the improvement of cycling stability. The initial charge-discharge efficiency exceeding 80% has been obtained for the titration sample. The electrochemical reaction process of two kinds of synthesized SnSb composite electrodes was characterized by cyclic voltammetry and AC impedance techniques.     

Preparation and electrochemical properties of re-synthesized LiCoO2 from spent lithium-ion batteries

A new idea for reuse of the cathode materials of lithium-ion batteries(LIBs) is investigated to develop an environmentally friend-ly process for recycling spent batteries.LiCoO2 is re-synthesized from spent LIBs by leaching and a sol-gel method calcined at high temperature.Thermogravimetric analysis(TGA) and differential scanning calorimetry(DSC) are employed to study the re-actions occurring calcination that are responsible for the weight losses.X-ray diffraction(XRD) and scanning electron microscopy(SEM) are used to determine the structures of the LiCoO2 powders.It was found that a pure phase of LiCoO2 can be obtained by the re-synthesis process.Cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS) are used to evaluate the electrochemical properties of the LiCoO2 powders.The discharge capacity of re-synthesized LiCoO2 is 137 mAh g-1 at the 0.1 C rate,and the capacity retention of the re-synthesized LiCoO2 is 97.98% after 20 cycles at the 0.1 C rate,and 88.14% after 40 cy-cles.The results indicate that the re-synthesized LiCoO2 displays good charge/discharge performance and cycling behavior.     

Electronic origin of the anomalous solid solution hardening of Y and Gd in Mg: A first-principles study

Y and Gd demonstrate anomalous solid solution hardening efficiency,which cannot be understood using the elastic impuritydislocation interaction theory.We performed first-principles calculations to investigate the effect of different alloying elements such as Al,Zn,Y,and Gd on the chemical bonding of Mg solid solutions.The present calculations clearly show that the anomalous solid solution hardening of Y and Gd in Mg may be understood based on the increased bonding strength of both Mg-Y (Gd) and Mg-Mg.     

Inorganic-Organic Composite Materials for Lithium Batteries

1 Results In order to develop high capacity anode materials for enhancing the performance of lithium-ion batteries,silicon (Si) and a variety of metals that alloy with lithium,such as Sn,Sb,and Al,were studied and found to be promising candidates as anode materials[1-4].Among them,Si appears to be the most attractive candidate due to its large theoretical lithium insertion capacity of 4 200 mAh g-1[1].Unfortunately,there is one severe problem with the application of Si anode,i.e., the large volume chang...