Li 2s Research Articles

Silicone as a binder in composite electrolytes

A liquid silicone was used as a binder to make composite solid electrolytes from lithium-ion conductive inorganic solid electrolytes (ISEs): an oxysulfide glass, 0.01Li 3PO 4–0.63Li 2S–0.36SiS 2 and/or a lithium germanium thio-phosphate, Li 3.25Ge 0.25P 0.75S 4. Ionic conductivities of the composites were of the order of 10 −4 Scm −1, even when the silicone was enriched to 10% (v/v). On the other hand, the composite with styrene–butadiene block co-polymer (SBR) or polypropylene oxide–polyethylene oxide (PO–EO) co-polymer as binder showed much lower conductivity. In the composite electrolyte, the silicone rubber must partly cover the surface of the ISE particles because the composite electrolyte is molded before the vulcanization of the fluid liquid silicone; and thus, it must rarely interfere with the conduction between the ISE particles. Hydrocarbons were found to be suitable in the preparation process of the composite solid electrolyte (CSE).

Solid-state lithium battery with graphite anode

Solid-state lithium batteries with a unique construction are reported in this paper. These batteries contain two kinds of lithium ion-conductive solid electrolytes, LiI–Li 2S–P 2S 5 glass contacted with the anode material and Li 3PO 4–Li 2S–SiS 2 glass or Li 2S–GeS 2–P 2S 5 crystalline material contacted with the cathode. The former electrolyte was selected as that stable to electrochemical reduction, and the latter two to oxidation. This construction made it possible to use graphite as the anode and LiCoO 2 as the cathode in the solid-state lithium battery. The energy density of the battery is 390 W h·l −1 and 160 W h·kg −1 per total volume and weight of the cathode and anode layers, respectively, which are comparable to those of commercialized Li-ion batteries.

Formation and ionic conductivity of Li 2S–GeS 2–Ga 2S 3 glasses and thin films

Li 2S–GeS 2–Ga 2S 3 glasses and thin films were prepared and their conductivities were compared. Bulk glasses were melted in Si-coated silica tubes. The glass-forming region was observed at cation ratios of 0 or 40–70% Li and less than 50% Ga. Thin films with a wider composition range were formed by RF sputtering. Conductivities were almost identical in bulk glasses and films of similar composition and increased along with increasing Li 2S content. Conductivity and glass transition temperature ( T g) increased slightly with addition of a moderate amount of Ga 2S 3. These results are due to the mixed-former effect.

Formation of superionic crystals from mechanically milled Li 2S–P 2S 5 glasses

A superionic crystal analogous to highly conductive thio-LISICON, which is a series of sulfide crystalline solid electrolytes such as Li 4GeS 4–Li 3PS 4, was successfully formed by the crystallization of mechanically milled Li 2S–P 2S 5 glasses. The thio-LISICON phases have not been obtained by solid-phase reaction in the Li 2S–P 2S 5 binary system so far, and this report is the first case of obtaining the thio-LISICON analogue in the binary system. The formation of this superionic crystal enhanced the conductivities of the glass, and the high ambient temperature conductivity of 7.2×10 −4 S cm −1 was achieved in the glass–ceramics derived from the Li-rich 80Li 2S·20P 2S 5 (mol%) glass.

Atomic scattering in the diffraction limit: electron transfer in keV Li+–Na(3s, 3p)collisions

We measure angle differential cross sections (DCS) in Li+ + Na → Li + Na+electron transfer collisions in the 2.7–24 keV energy range. We do thiswith a newly constructed apparatus which combines the experimentaltechnique of cold target recoil ion momentum spectroscopy with a laser-cooledtarget. This setup yields a momentum resolution of 0.12 au, an order ofmagnitude better angular resolution than previous measurements on thissystem. This enables us to clearly resolve Fraunhofer-type diffractionpatterns in the angle DCS. In particular, the angular width of the ringstructure is given by the ratio of the de Broglie wavelength λdB = 150 fm at avelocity v = 0.20au and the effective atomic diameter for electron capture 2R = 20 au.Parallel AO and MO semiclassical coupled-channel calculations of the Na(3s, 3p)→Li(2s, 2p) state-to-state collision amplitudes have been performed, and quantumscattering amplitudes are derived by the eikonal method. The resultingangle-differential electron transfer cross sections and their diffraction patternsagree with the experimental level-to-level results over most scattering angles inthe energy range.

New lithium ion conducting glass-ceramics prepared from mechanochemical Li 2S–P 2S 5 glasses

Amorphous solid electrolytes in the system Li 2S–P 2S 5 were prepared from a mixture of crystalline Li 2S and P 2S 5 using a mechanical milling technique at room temperature. In the composition range x≤87.5 of xLi 2S·(100− x)P 2S 5, conductivities of the glassy powders mechanically milled for 20 h were as high as 10 −4 S cm −1 at room temperature. The heat treatment of the 80Li 2S·20P 2S 5 glassy powders at around 220 °C produced dense glass-ceramics with high conductivity around 10 −3 S cm −1 at room temperature. The crystallization of conductive phases of Li 7PS 6, Li 3PS 4 and unknown crystals from the glass matrix and the decrease of grain boundaries by the softening of the glassy powders are simultaneously achieved at relatively low temperatures, around 220 °C.

Synthesis of New Lithium Ionic Conductor Thio-LISICON—Lithium Silicon Sulfides System

The new lithium ionic conductors, thio-LISICON (LIthium SuperIonic CONductor), were found in the ternary Li 2S–SiS 2–Al 2S 3 and Li 2S–SiS 2–P 2S 5 systems. Their structures of new materials, Li 4+ x Si 1− x Al x S 4 and Li 4− x Si 1− x P x S 4 were determined by X-ray Rietveld analysis, and the electric and electrochemical properties were studied by electronic conductivity, ac conductivity and cyclic voltammogram measurements. The structure of the host material, Li 4SiS 4 is related to the γ-Li 3PO 4-type structure, and when the Li + interstitials or Li + vacancies were created by the partial substitutions of Al 3+ or P 5+ for Si 4+, large increases in conductivity occur. The solid solution member x=0.6 in Li 4− x Si 1− x P x S 4 showed high conductivity of 6.4×10 –4 S cm −1 at 27°C with negligible electronic conductivity. The new solid solution, Li 4− x Si 1− x P x S 4, also has high electrochemical stability up to ∼5 V vs Li at room temperature. All-solid-state lithium cells were investigated using the Li 3.4Si 0.4P 0.6S 4 electrolyte, LiCoO 2 cathode and In anode.

Solid electrolyte composed of 95(0.6Li 2S·0.4SiS 2)·5Li 4SiO 4 glass and high molecular weight branched poly(oxyethylene)

Novel single ion-conductive inorganic/organic composites were prepared from 95(0.6Li 2S·0.4SiS 2)·5Li 4SiO 4 oxysulfide glass and a high molecular weight branched poly(oxyethylene) (POE). The ionic conductivity of the composites increased with an increase of the glass. The ionic conductivity of the composite with 1 wt.% branched poly(oxyethylene) was in the orders of 10 −5 S/cm at 30 °C and 10 −4 S/cm at 80 °C. The composite exhibited an electrochemical stability window up to ca. 4.5 V versus Li +/Li and thermal stability against lithium metal up to 200 °C. Addition of LiClO 4 to the polymer matrix of the composite improved the ionic conductivity. In this case, the composite was a dual-ion conductor, i.e., both Li + and ClO 4 − contributed to the conductivity.

Antifluorite to Ni 2In-type phase transition in K 2S at high pressures

The high-pressure behaviour of dipotassium sulfide K 2S with the antifluorite structure (Fm 3 ̄ m, Z=4) has been studied up to 23.0 GPa by in situ synchrotron angle-dispersive X-ray powder diffraction in a diamond anvil cell at room temperature. There occurs a transformation into a distorted Ni 2In-type structure (Pmma, Z=4) at about 6 GPa upon compression. A mixture of several phases is observed at lower pressures. Unlike in the case of pressure-induced modifications of Li 2S and Na 2S, none of them is of the anticotunnite-type (Pnma, Z=4). The Ni 2In-related structure of K 2S is compared with the cationic arrays found in different polymorphs of K 2SO 3 and K 2SO 4.

Characterization of Li 2S–SiS 2–Li 3MO 3 (M=B, Al, Ga and In) oxysulfide glasses and their application to solid state lithium secondary batteries

The electrical, thermal and electrochemical properties of the Li 2S–SiS 2–Li 3MO 3 (M=B, Al, Ga and In) oxysulfide glasses were investigated. The addition of small amounts of Li 3BO 3 or Li 3AlO 3 to the Li 2S–SiS 2 sulfide system kept high conductivity over 10 −3 S cm −1 at room temperature and improved thermal stability against crystallization. In the case of the addition of Li 3GaO 3 or Li 3InO 3, the conductivity monotonically decreased with an increase in Li 3MO 3 content in the glasses. 29Si MAS-NMR spectra of these glasses revealed that the amounts of SiO 2S 2 and SiO 3S tetrahedral units, which lowered the conductivity of the glasses, were larger in the glasses added with Li 3GaO 3 and Li 3InO 3 than in those with Li 3BO 3 and Li 3AlO 3. Cyclic voltammetry suggested that the oxysulfide glasses with small amounts of Li 3MO 3 exhibited wide potential window of 10 V. The glasses with Li 3BO 3 were the most electrochemically stable. The solid-state cells with Li 3BO 3 glasses as solid electrolytes were fabricated and their charge–discharge performance was investigated. These cells worked as lithium secondary batteries under various current densities from 64 to 2038 μA/cm 2 and exhibited excellent cycling performance over 100 times.

Li insertion in thin film anatase TiO 2: identification of a two-phase regime with photoelectron spectroscopy

Li insertion into a thin anatase TiO 2 film is studied for the first time in an ultra-high vacuum (UHV) environment. Using synchrotron radiation photoelectron spectroscopy, we demonstrate that the evaporated Li is inserted into the anatase and that the maximum amount that can be dissolved is 0.41 Li/Ti. Two most important properties are found in the UHV insertion process that can be directly related to electrochemical insertion: first, the Li 1s spectra suggest a two-phase regime and second, the insertion process is curtailed at the threshold for a phase transition that is not possible without the electrochemical driving force.

Preparation and thermal properties of novel Li 2S–Sb 2S 3 glassy system

There is great interest in sulfide glasses because of their high lithium ion conductivity. A new Li 2S–Sb 2S 3 glassy system has been prepared by a classical quenching technique. Thermal characterization has been carried out and it has been observed that the T g decreases with an increase in the concentration of Li 2S. However, this tendency stops around 17% Li 2S content. Results have been discussed on the basis of the modification that would occur in the base Sb 2S 3 glass network by the addition of Li 2S.

Preparation and electrochemical properties of lithium–sulfur polymer batteries

The lithium/sulfur (Li–S) batteries consist of a composite cathode, a polymer electrolyte, and a lithium anode. The composite cathode is made from elemental sulfur (or lithium sulfide), carbon black, PEO, LiClO 4, and acetonitrile. The polymer electrolyte is made of gel-type linear poly(ethylene oxide) (PEO) with tetra ethylene glycol dimethyl ether. Cells based on Li 2S or sulfur have open-circuit voltages of about 2.2 and 2.5 V, respectively. The former cell shows two reduction peaks and one oxidation peak. It is suggested that the first reduction peak is caused by the change from polysulfide to short lithium polysulfide, and the second reduction peak by the change from short lithium polysulfide to lithium sulfide (Li 2S, Li 2S 2). The cell based on sulfur has the same reduction mechanism as that of Li 2S, which is caused by the multi process (first and second reduction) of lithium polysulfide. On charge–discharge cycling, the first discharge has a higher capacity than subsequent discharges and the flat discharge voltage is about 2.0 V. As the current load is increased, the discharge capacity decreases. One reason for this fading capacity and low sulfur utilization is the aggregation of sulfur (or polysulfide) with cycling.

In situ sulfur K-edge X-ray absorption near edge structure of an embedded pyrite particle electrode in a non-aqueous Li +-based electrolyte solution

Changes in the composition of embedded pyrite (FeS 2) particle electrodes in 1 M LiClO 4 propylene carbonate solutions as a function of the applied potential have been examined in situ by S K-edge fluorescence X-ray absorption near edge structure (XANES), using a specially designed cell that minimizes attenuation of low energy X-rays. Pyrite electrodes that had been scanned from 3.0 V versus Li/Li +, i.e. close to the open circuit voltage, down to 1.0 V (fully discharged state, i.e. 4e −-reduction) and then half recharged (2e −-reoxidation) by scanning the potential in the positive direction up to 2.2 V versus Li/Li +, revealed features consistent with the presence of Li 2FeS 2, in agreement with in situ Fe K-edge results reported earlier by this research group. Moreover, only subtle changes were discerned between the in situ S K-edge XANES of the half-, and fully-recharged electrodes. This close resemblance may reflect similarities between the spectral signatures of Li 2FeS 2 and Fe 1− x S (pyrrhotite), which is the main product of the discharge reaction. Evidence for the formation of elemental sulfur and Li 2S, which are believed to be minor products of the reaction, was obtained from analysis of the first differential S XANES and selected difference spectra. The compositional variations of the embedded pyrite particles throughout the course of the electrochemical processes occur in the presence of a persistent sulfate coating.

Sulfur–carbon nano-composite as cathode for rechargeable lithium battery based on gel electrolyte

Sulfur–carbon nano-composite with elemental sulfur incorporated in porous carbon was prepared by thermal treatment of a mixture of sulfur and active carbon. The new material was characterized by X-ray diffraction, BET and scanning electron microscopy. The nano-composite, tested at room temperature as cathode in a nonaqueous lithium cell based on PVDF gel electrolyte, exhibited a reversible capacity of 440 mAh g −1 at a current density of 0.3 mA cm −2. The utilization of electrochemically active sulfur was about 90% assuming a complete reaction to the product of Li 2S during cycling.

Studies on plasticized PEO–lithium triflate–ceramic filler composite electrolyte system

Composite polymer electrolytes (CPEs), polyethylene oxide (PEO)+Li triflate with Li Nasicompound [Li 1.4(Al 0.4Ge 1.6)(PO 4) 3] as the ceramic filler and EC+PC as the plasticizer, have been studied as thin films. Their crystallinity, thermal behaviour, mechanical strength, ionic conductivity, interfacial stability and Li(1s) XPS binding energies (BEs) have been examined. Changes in T g, melting temperatures ( T m1 and T m2), tensile strength (TS) and maximum elongation at break of the CPE films have been studied as a function of different wt.% plasticizer. With the addition of plasticizer, an order of magnitude increase in the ionic conductivity was obtained for temperature T<60 °C. The σ− T data of the CPEs have been fitted to either Arrhenius-type or Vogel–Tamman–Fulcher (VTF)-type behaviour depending on the T range and plasticizer content. Interfacial stability was found to be enhanced with the addition of plasticizer. The variation in the Li(1s) binding energies correlates well with that of σ values. Present study shows that CPEs with 5–10 wt.% plasticizer exhibit the optimum performance.

The electronic band structure of Li2O:testing theoretical predictions using electron momentumspectroscopy

Using the technique of electron momentum spectroscopy (EMS) wehave measured the oxygen 2p- and 2s-derived valence bands and lithium 1s-derived core level in lithium oxide. All three setsof bands have been measured in a single experiment allowing theenergy gap between the bands to be determined. At theΓ point the O(2p)-O(2s) band gap is measured to be16.1±0.2 eV, and the O(2s)-Li(1s) band gap is34.3±0.2 eV. We can also determine bandwidths since EMS measures the fullband structure directly, resolved both in energy and momentum.As expected, the O(2s) and Li(1s) bands are essentiallynon-dispersing, while the O(2p) has an observed width of 1.6±0.2 eV. The experiment is compared with calculationsusing the linear combination of atomic orbitals approach. At the Hartree-Fock (HF)level these calculationsoverestimate the gap between the valence bands and the width of theO(2p) band. The three density functional methods usedgive a reduced intervalence band gap and bandwidth. The hybridgradient corrected method, PBE0 (where PBE standsfor `Perdew-Burke-Ernzerhof'), gives the closest agreement forthe band gap at 16.7 eV, while the gradient corrected method, PBE, gives the best value for the bandwidth at 2.0 eV. At alllevels the O(2s)-Li(1s) gap is underestimated; HF gives theclosest agreement at 31.8 eV.

Characterization of Li 2S–SiS 2–Li xMO y (M=Si, P, Ge) amorphous solid electrolytes prepared by melt-quenching and mechanical milling

The oxysulfide amorphous materials in the systems 95(0.6Li 2S·0.4SiS 2)·5Li x MO y (M=Si, P, and Ge) were prepared by melt-quenching and mechanical milling techniques. These amorphous materials exhibited high conductivity over 10 −4 S cm −1 at room temperature, a lithium transport number of unity, and a wide potential window of 10 V. The solid-state cells with the oxysulfide amorphous materials as solid electrolytes worked as lithium secondary batteries and exhibited excellent cycling performance over 100 times. The local structure of the mechanically milled amorphous materials containing Li 4SiO 4 was similar to that of the corresponding melt-quenched glasses, in which the SiS 4 and SiOS 3 tetrahedral units were mainly present. The SiO n S 4− n ( n=1, 2, 3) tetrahedral units were formed in the case of the addition of Li 4SiO 4 and Li 4GeO 4 to the base sulfide system, while these units were not present in the addition of Li 3PO 4. We have concluded that the reactivity of Li x MO y derived from its basicity affected the structure and formation process of the oxysulfide materials prepared by mechanical milling.

Syntheses, oxidations, and palladium complexes of fluorous dialkyl sulfides: new precursors to highly active catalysts for the Suzuki coupling

Reactions of R f8(CH 2) n I (R f8=CF 3(CF 2) 7) with Li 2S give the fluorous dialkyl sulfides (R f8(CH 2) n ) 2S ( n=2, 1 , 71%; 3, 2 , 67%) as low melting white solids that are soluble in most fluorous and organic solvents. Reactions of 1 and 2 with CH 3CO 3H yield the corresponding sulfoxides (R f8(CH 2) n ) 2SO (85; 80%), which are soluble in CF 3C 6F 5 at room temperature, but insoluble in most other solvents. At higher temperatures, solubilities can become appreciable. Reactions of 1 and 2 with Na 2PdCl 4 (ca. 0.5 equiv.) give palladium complexes [(R f8(CH 2) n ) 2S] 2PdCl 2 ( 5 , 94%; 6 , 95%), which are soluble in only a limited range of fluorinated solvents at room temperature. The CF 3C 6F 11/toluene partition coefficients of 1 and 2 are 98.7:1.3 and 96.6:3.4 (24°C). The Suzuki coupling of aryl bromides and PhB(OH) 2 to biaryls is catalyzed by 5 and 6 (0.02 mol%) in CF 3C 6F 11/DMF/H 2O in the presence of K 3PO 4, generally at room temperature. Turnover numbers of 4500–5000 are easily achieved. However, activities decrease under fluorous biphase recycling conditions, and implications for the nature of the catalytically active species are discussed.

One-electron pseudopotential calculations of excited states of LiAr, NaAr, and KAr

The potential curves and spectroscopic constants of the excited states of alkali–argon diatomics MRg (M=Li, Na and K, Rg=Ar) are calculated using usual semilocal single valence electron pseudopotentials on alkali atoms [M+]-core pseudopotentials), semilocal pseudopotentials replac(ing all the electrons of argon ([Ar]-core pseudopotentials), and core polarization pseudopotentials on both centers. All states dissociating into Li(2s, 2p, 3s, 3p, 3d, 4s, and 4p), Na(3s, 3p, 3d, 4s, 4p, 4d, 5p) and K(4s, 4p, 5s, 3d, 5p, 4d, 6s, 4f, 6p, 5d, 7s, 5f) are considered. The core–core interactions for Li+Ar and Na+Ar are included using the accurate ab initio potentials of Ahmadi et al. [G. R. Ahmadi, J. Almlöf, and I. Roeggen, Chem. Phys. 199, 33 (1995); G. R. Ahmadi and I. Roeggen, J. Phys. B 27, 5603 (1994)] while the K+Ar ion data are determined by MP2 all-electron calculations.