LIGA Research Articles

Microstructural Engineering of Li7La3Zr2O12 Solid Electrolytes for Enhanced Stability in H2O/CO2

Solid-state batteries with nonflammable inorganic solid electrolytes provide a fundamental solution for resolving safety concerns. Moreover, mechanically robust solid electrolytes can physically block the penetration of Li dendrites, and thus, Li metal can be applied as an anode (negative electrode), boosting the energy density of the batteries. Garnet-type cubic Li7La3Zr2O12 (LLZO) has been considered as a promising candidate for solid electrolytes, due to its high Li+ conductivity and chemical/electrochemical compatibility with Li metal. When exposed to the ambient air, however, LLZO electrolytes are known to react with H2O and CO2 to form Li2CO3. Li2CO3 also grows along the grain boundaries, resulting in the significant degradation in Li+-conducting properties.In an effort to develop LLZO electrolytes with enhanced interfacial stability, here, we investigate the composition–microstructure–stability relationship of LLZO modified with aliovalent elements (Ta and Ga) under controlled H2O and CO2 atmospheres. Dense LLZO electrolytes doped with Ta (LLZTO) and Ta/Ga (Ga-LLZTO) are synthesized via a sol-gel process, followed by high-temperature sintering (1100 °C). Microstructural analyses show that the elemental doping has a crucial role in the grain growth behavior during the sintering process, thereby modifying the density, morphology, and atomic structure of grain boundaries. The interfacial stability of doped LLZO electrolytes is examined under accelerated durability test (ADT) conditions, where the concentration of O2/H2O/CO2 is precisely controlled to promote the interfacial reaction. During the ADTs, the degradation kinetics of Li+-conducting properties is quantitatively determined using in situ AC-impedance measurements combined with ex situ surface characterizations. The Li+ conductivity of Ga-LLZTO is almost retained during the ADT, while LLZTO shows only 27% of its initial conductivity value after 24 h of ADT. The significant degradation of LLZTO is caused by the formation of Li2CO3, which is further verified by Raman mapping and X-ray photoelectron spectroscopy analysis. On the other hand, the compositional and structural characterizations suggest that the enhanced interfacial stability of Ga-LLZTO is attributed to the reduced grain boundary density with enlarged grains and the segregation of H2O/CO2-tolerant Li–Ga–O species in the grain boundaries. The findings of this study would be essential in understanding the degradation of Li+-conducting properties and in developing highly conductive and stable LLZO solid electrolytes.

Ab initio molecular dynamics study on the disordered Li-Ga-Sn system.

The eutectic Ga91.6Sn8.4 liquid metal could serve as the anode in Li-ion batteries to avoid dendrite growth issue and volume expansion, and maintain a good cycle life. However, the microstructure and the basic physical properties of the lithiated Ga91.6Sn8.4 are ignored in experiments and still unclear. In this work, we assume that a disordered structure is formed in the initial stage of lithiation of Ga91.6Sn8.4, and the structure, equilibrium density, thermal expansion coefficient, mixing enthalpy, self-diffusion coefficient and viscosity of the disordered Li-Ga-Sn system are investigated systematically by ab initio molecular dynamics. The radial distribution function, structure factor and bond angle distribution function are calculated to obtain local structure information. Our calculations show that the lithiation of Ga91.6Sn8.4 is exothermic, and for most cases, the diffusion coefficients for Li, Ga and Sn decrease with increasing Li content. Based on structural information and diffusion coefficients, we reveal that the lithiation of Ga91.6Sn8.4 will make the liquid Ga91.6Sn8.4 alloy form a solid-like structure. With the increase of Li content, it is more likely to form a solid-like structure. Furthermore, our simulations reveal that the chemical interaction of Li-Sn and Li-Ga is stronger than that of Ga-Sn, and Li is prone to combine with Sn firstly in the lithiation process of Ga91.6Sn8.4.

Instability of Ga-substituted Li7La3Zr2O12 toward metallic Li

Li6.4Ga0.2La3Zr2O12 can be reduced by Li, which results in Ga leaching out of the garnet structure to form the Li–Ga alloy. The penetrated alloy can short-circuit the battery when Ga-substituted LLZO is used as a solid electrolyte.

Structural and Electrochemical Properties of Type VIII Ba8Ga16-δSn30+δ Clathrate (δ ≈ 1) during Lithiation.

Clathrates of the tetrel (Tt = Si, Ge, Sn) elements are host–guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba8Ga16−δSn30+δ (δ ≈ 1) during lithiation are investigated and compared to those in β-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis. The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (LixBa0.17Ga0.33Sn0.67, x = 2–3) with local structures similar to those in the crystalline binary Li–Sn phases that form during the lithiation of β-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs Li/Li+) compared to β-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than in β-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The local structure in the clathrate featuring Ba atoms surrounded by a cage of Ga and Sn atoms is hypothesized to kinetically circumvent the formation of Li–Sn or Li–Ga crystalline phases, which results in better cycling and a lower reaction voltage. Based on the improved electrochemical performance, clathrates could act as tunable precursors to form amorphous Li alloying phases with novel electrochemical properties.

Enrichment of Li–Ga–Zr–Hf and Se–Mo–Cr–V–As–Pb Assemblages in the No. 11 Superhigh Organic Sulfur Coal from the Sangshuping Coal Mine, Weibei Coalfield, Shaanxi, North China

Superhigh organic sulfur(SHOS) coals have currently attracted great attention due to their typical depositional environments and formation history as well as their great negative impact on the ecosystem. This study investigated the geochemistry of the No. 11coalof the Late Carboniferous Taiyuan Formation from the Sangshuping coalmine, Hancheng miningarea, Weibei coalfield, Shaanxi, North China. The No. 11 coal is a high-sulfur coal with a large proportion of organic sulfur content (3.7 to 5.5%, avg. 4.4%) and belongs to typical SHOS coal. The high sulfur content in the Sangshuping coal mine has been mainly caused by the combined influences of seawater and hydrothermal fluids. The SHOS in No. 11 coal was formed in the Fe-poor and S-rich high-marine influenced occlusive environment. During the late coalification stage, a high proportion of pyritic sulfur was formed due to sufficient Fe supply from the Fe–S-rich epigenetic hydrothermal fluids. The No. 11 SHOS coal is enriched in Li–Ga–Zr–Hf and Se–Mo–Cr–V–As–Pb element assemblages. The sediment provenance of the Sangshuping coal mine is predominantly felsic–intermediate rocks from both the Yinshan and Qinling Oldland. However, the elevated concentrations of critical elements (Li, Ga, Zr, and Hf) in the No. 11 coal are primarily inherited from the Yinshan Oldland. The enrichment of the Se–Mo–Cr–V–As–Pb assemblage in No. 11 coal can be ascribed to the influence of both seawater and epigenetic hydrothermal activity.

Candidates for p-type doping of ZnGeN2

Various candidates for p-type doping in ZnGeN2 are considered and computationally studied using first-principles calculations. First, a brief update is made on our previous work about self-doping by deviations from stoichiometry, in the form of ZnGe, and Ga doping, GaGe. Both of these are hindered by competing donors in the form of GeZn and GaZn. We also consider Al instead of Ga doping. Cu would form an acceptor on both Zn and Ge sites. We determine the site-preference and consider also interstitial Cui. We find that CuZn, which is the preferred site, has a too deep level in the gap above the valence band maximum to be a useful p-type dopant. For C, we consider the CN acceptor as well as competing sites, inert CGe, and the Ci donor. We find that Ci forms a split-interstitial configuration and CGe is energetically close to CN, but the main conclusion is that the latter has a deep acceptor level unsuitable for p-type doping. Finally, we consider alkali metal doping. The LiGa defect is found to have the most favorable acceptor level position among the defects studied here, but it will suffer from possible compensation by Lii. Na and K are found to give deeper levels.

Self-trapped hole and impurity-related broad luminescence in β-Ga2O3

This work explores the luminescence properties of self-trapped holes and impurity-related acceptors using one-dimensional configuration coordinate diagrams derived from hybrid functional calculations. The photoluminescence spectrum of as-grown β-Ga2O3 typically consists of a broad band in the wavelength region from ultraviolet to green and is often dominated by an impurity independent ultraviolet band that is commonly attributed to self-trapped holes. Here, we use the self-trapped hole as a benchmark to evaluate the accuracy of the theoretical defect luminescence spectra and estimate the optical properties of MgGa, BeGa, CaGa, CdGa, ZnGa, LiGa, and NO acceptor impurities, as well as their complexes with hydrogen donors. We also explore VGa acceptors complexed with hydrogen and SiGa donor impurities. The results show that these defects can give rise to broad luminescence bands peaking in the infrared to visible part of the spectrum, making them potential candidates for the defect origin of broad luminescence bands in β-Ga2O3.

Host minerals of Li–Ga–V–rare earth elements in Carboniferous karstic bauxites in southwest China

The Carboniferous karstic bauxite-bearing rock series in central Guizhou Province in southwest (SW) China is rich in trace elements, particularly Li, Ga, V, and rare earth elements (REEs), which have potential for comprehensive utilization as independent deposits or associated resources. However, the host minerals of Li, Ga, V, and REEs are not well-constrained because the sedimentary rocks are characteristics by complex mineral composition and fine mineral particles. This situation considerably hinders the compressive utilization of these trace elements in bauxite. Herein, laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) was successfully applied to element geochemistry analysis of hydrous minerals (diaspore/boehmite, kaolinite, and illite) in karstic bauxite samples, based on the principle that laser ablation data of all oxides were normalized to the sum of 100% minus the total volatile components of the mineral chemical formula. The analysis showed signal stabilization. Results indicated that the bivariate plots of selected elements had characteristics similar to statistical results of whole-rock samples from global bauxites, thereby indicating that the LA–ICP–MS analysis data were reliably but artificially herein. Combined with whole-rock geochemistry studies, the analysis results revealed that smectite may be the main host minerals of Li. Furthermore, Ga was enriched in diaspore/boehmite; V was mainly enriched in iron-bearing minerals, particularly chlorite; and REE-independent minerals, such as monazite, were the main host minerals of REEs in the Carboniferous karstic bauxite in SW China. This study contributed to the knowledge on the use of in-situ method for the element geochemistry investigation of hydrous minerals and sedimentary rocks.

All-solid-state battery Li–Ga–Ag | Li7La3Zr2O12 + Li2O–Y2O3–SiO2 | Li2O–V2O5–B2O3

Electrochemical cell Li–Ga–Ag | Li7La3Zr2O12 + 5 wt % 40.2Li2O·5.7Y2O3·54.1SiO2 glass | 25Li2O·30B2O3·45V2O5 glass ceramic was studied. The glassy materials 40.2Li2O·5.7Y2O3·54.1SiO2 and 25Li2O·30B2O3·45V2O5 were produced by melt quenching. The use of a glassy cathode based on vanadium oxide enabled a close contact between the cathode and the solid electrolyte. At a temperature of 280°C, the electrochemical cell under study can be charged to 3.33 V. It was found that the deintercalation of lithium is hindered in the course of charging and discharge.

IR Li2Ga2GeS6 nanocrystallized GeS2-Ga2S3-Li2S electroconductive chalcogenide glass with good nonlinearity.

GeS2-Ga2S3-Li2S electroconductive glasses were prepared by the conventional melt-quenching method through carefully controlling the heating rate. Comparing with the reference of glass-forming region, our investigated GeS2-Ga2S3-Li2S system was extended to the cation ratio of 0–20% Li with around 40% Ga. GeS2-Ga2S3-Li2S glass-ceramics containing IR Li2Ga2GeS6 nonlinear nanocrystals were obtained by the more carefully controlled heating rate. Its optical nonlinearity was investigated by the Maker fringe measurements, the maximum second harmonic intensity was observed to be 0.35 of the reference Z-cut quartz. IR Li2Ga2GeS6 nonlinear crystals were directly obtained at the composition of 40GeS2-30GaS1.5-30LiS0.5.

Fabrication of high hardness Ni mold with electroless nickel–boron thin layer

The nickel electroforming method using a high-concentration nickel sulfamate bath is commonly used to fabricate micro metal molds in the LIGA process; however, this method does not produce micro me...

Nano-glass–ceramics containing chromium-doped LiGaSiO4 crystalline phases

Abstract Chromium-doped nano-glass–ceramic samples containing crystallites of α- and γ-polymorphous modifications of eucryptite-like LiGaSiO 4 were fabricated by devitrification of Cr–Li–Ga–Si–O glass of various compositions. Evaluated sizes of the crystallites in synthesized samples are from tens of nanometers (in the case of ceramming at 570–650 °C during 2 h) up to tens of microns (additional heat treatment at 900 °C during 5 min). Spectroscopic investigations (absorption and fluorescence spectra, fluorescence decay kinetics) of the prepared vitreous precursors and of the nano-glass–ceramic samples were performed. The absorption bands of Cr 3+ and Cr 6+ ions were observed in the vitreous precursors, whereas the absorption of Cr 4+ ions prevails in the samples after ceramming. The measured fluorescent properties of the glass–ceramics containing only α-LiGaSiO 4 :Cr 4+ crystallites are as follows: the fluorescence peak position is 1280 nm, the FWHM of the fluorescence band is 270 nm, the lifetime of the excited 3 T 2 (Cr 4+ ) state is ∼12 μs at 300 K and 65–70 μs at 77 K. These properties are similar to those of the earlier investigated Cr:LiGaSiO 4 single crystals. One more Cr 4+ fluorescent center with a shorter decay time (1–1.5 μs at room temperature and 7–9 μs at 77 K) was observed in the samples in which γ-LiGaSiO 4 :Cr 4+ crystallites were present. The origin of this fluorescence is so far unclear.

Second-order optical nonlinearity and ionic conductivity of nanocrystalline GeS2–Ga2S3–LiI glass-ceramics with improved thermo-mechanical properties

IR-transparent chalcogenide glass-ceramics were fabricated through a careful ceramization process of the as-prepared 65 GeS(2) x 25 Ga(2)S(3) x 10 LiI glasses at a temperature of 403 degrees C for various durations. Owing to the precipitation of Li(x)Ga(y)S(z) crystals with a Ga(2)S(3)-like structure, clear second-harmonic generation was observed in the sample crystallized at 403 degrees C for 60 h, which has a greatly improved resistance to environmental impairment. Additionally, it is found that the shorter crystallization process (< or = 60 h) contributed to the enhancement of Li(+) ionic conductivity, whereas a longer heat-treatment (80 h) would impair that of the glass-ceramics. The micro-structural origin of these varied properties was elucidated in detail. The corresponding results will be of benefit for the optimization of designed transparent chalcogenide glass-ceramics with improved thermo-mechanical properties, a permanent second-order optical nonlinearity, or a well-enhanced ionic conductivity for application in amorphous solid electrolytes.

Reducing GaH and GaC Bonds in Close Proximity to Oxidizing Peroxo Groups: Conflicting Properties in Single Molecules

Treatment of [Li(H(2)Ga{CH(SiMe(3))(2)}(2))]2 OEt(2) (12 OEt(2)) with two equivalents of tert-butyl hydrogen peroxide, H-O-O-CMe(3), afforded the organogallium peroxide [({(Me(3)Si)(2)HC}(2)Ga(OH)(OOCMe(3))Li)(2)] (3), which possesses oxidizing peroxo groups in close proximity to reducing Ga-C bonds. The lithium atoms of the dimeric formula units are coordinated by both oxygen atoms of the peroxides and by two hydroxo groups. The cleavage of the Ga--C bond was not observed, even when an excess of H-O-O-CMe(3) was applied. Instead, the adduct [{(Me(3)Si)(2)HC}(2)Ga(OH)(OOCMe(3))(2)Li(2)(HOOCMe(3))] (4) was isolated, which has an intact H-O-O-CMe(3) molecule terminally attached to lithium. A similar structural motif was found for the compound [(LiOOCMe(3))(2)(HOOCMe(3))(2)] (5). The trihydrido gallanate [Li(H(3)Ga-{CH(SiMe(3))(2)})]OEt(2) (2) yielded the unique peroxide [({(Me(3)Si)(2)HC}--Ga(H)(OOCMe(3))(2)Li)(2)] (6) under similar conditions that possesses Ga-C and even more reactive Ga-H bonds beside peroxo groups. It decomposed at room temperature by the insertion of oxygen atoms into the Ga-H bonds and the formation of [({(Me(3)Si)(2)HC}-Ga(OH)(OCMe(3))(OOCMe(3))Li)(2)] (7), which was isolated in a low yield. Further decomposition gave the complete degradation of all peroxo groups with the formation of a relatively complicated Li(4)Ga(4)O(8) cage (8).

Some magnetic properties of Li–Ga ferrite in low magnetic field

Li–gallium ferrites with the chemical formula Li 0.5Ga x Fe 2.5− x O 4 ( x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) have been prepared by the ceramic method technique. The spinel structure in homogenous state was realized by X-ray diffraction analysis. The lattice parameter was determined for each composition and it was found approximately constant value (0.832 nm). Some magnetic properties such as magnetization M, and ( B- H) loop were measured at room temperature. The magnetization M was measured in the range of magnetizing field up to 800 A m −1. The B- H loops were measured at elevated temperature and magnetizing current ( I = 1 A which is equivalent to 200 A m −1). At room temperature the relative permeability ( μ r) was calculated from M– H relation. Also, remanence magnetization ( M r), saturation magnetization ( M s) and apparent loss energy ( P s) were estimated from B- H loops. It was found that μ r, M r, M s and P s are composition dependent. The initial permeability ( μ i) was measured as a function of temperature from room temperature up to 893 K. The Curie temperature T C and paramagnetic temperatures ( T p and T s) were determined. These values of temperature have been found to decrease with increasing Ga 3+ content.

ChemInform Abstract: Ternary Nitrides for Hydrogen Storage: Li—B—N, Li—Al—N and Li—Ga—N Systems.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The conduction mechanism of Li–Ga ferrite

Gallium substituted lithium–ferrite having the general formula Li 0.5Fe 2.5 − x Ga x O 4 with 0.0 ≤ x ≤ 0.5 in steps of 0.1 were synthesized by the standard ceramic technique. The variation of DC and AC conductivities with temperature have been reported in a wide range of temperature from room temperature 293 K up to 1023 K in static air. AC measurements were carried out in a wide range of frequencies from 100 Hz up to 1 MHz. The values of activation energies for the compositions containing gallium approximately is twice the activation energy of x = 0. The electron mobility in Li 0.5Fe 2.5O 4 shows an activation energy of 0.36 eV, while the activation energy of Li–Ga ferrites are ranging from 0.64 to 0.77 eV. These values are due to a narrow-band conduction mechanism and a formation of small polaron.

The infrared absorption and dielectric properties of Li–Ga ferrite

The investigated compositions of the Li–Ga ferrite system Li0.5Fe2.5−xGaxO4 (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) were studied by means of infrared (IR) spectroscopy. The analysis of IR spectra indicates the presence of splitting in the absorption band due to the presence of Fe2+ ions in ferrite. The dielectric constant ɛ′, the dielectric loss ɛ″ and the loss tangent tan δ were measured at elevated temperatures ranging from room temperature up to 850 K as a function of frequency (f = 102–106 Hz) for the investigated compositions. Maximum peak in tan δ and inverse peaks in ɛ′ appeared for some samples due to the resonance phenomenon. The obtained data were discussed based on the valence exchange between (Fe3+ and Fe2+) and (Ga3+ and Ga2+), i.e. hopping mechanism.

NMR Study on Defect Structure in β-LiGa

The mechanism of superionic conductivity in β-LiGa has been investigated by 7 Li and 71 Ga NMR spin–lattice relaxation rates 1/ T 1 in Li excess 50.0 at. %, Li deficient 44.0 and 47.0 at. % samples. The activation energies of Li + ionic diffusions through free Li vacancy V Li and through bound Li vacancy trapped by antisite Li Ga have been estimated to be 0.13 and 0.064 eV by applying Bloembergen–Purcell–Pound (BPP) type equation to 1/ T 1 in 50.0 at. % Li sample. In Li deficient samples, the same activation energy, 0.11–0.13 eV, for Li + ionic diffusion through free V Li has been obtained at high temperatures, and evidence for the ordering of V Li has been also detected by anomalies at 200–240 K in the temperature dependence of 1/ T 1 for 7 Li. However, the motional narrowing observed in 7 Li NMR line width above 110–130 K indicates that disorder in V Li can still remain even below its ordering temperature in 44.0 and 47.0 at. % Li samples.

Lithium isotope effect accompanying electrochemical insertion of lithium into gallium

Lithium has been electrochemically inserted from a 1:2 (v/v) mixed solution of ethylene carbonate (EC) and methylethyl carbonate (MEC) containing 1 M LiClO 4 or from dimethyl sulfoxide (DMSO) containing 1 M LiCl into gallium, and the lithium isotope fractionation accompanying the insertion has been observed. The lighter isotope was preferentially fractionated into gallium, which was in accordance with the theory of the equilibrium isotope fractionation arising from molecular vibrational quantum effects. The single-stage lithium isotope separation factor ranged from 1.015 to 1.025 at 25 °C. It was independent both of the kind of electrolyte solution and of the chemical composition of the Li–Ga alloys formed within the experimental range studied and within experimental uncertainty.