Transport processes in heavy metal fluoride glasses

Na self-diffusion, Li self-diffusion, Na⁺–Li⁺ ion exchange, electrical conductivity, and mechanical relaxation have been studied below T_g on glasses of the system ZrF₄–BaF₂–LaF₃–AF (A=Na, Li), with A=10, 20, 30 mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of Li increases with increasing LiF content. Both the electrical conductivity and the Na⁺–Li⁺ ion exchange reach a minimum at ≈ 20 mol% LiF, and the mechanical relaxation shows one peak for the 20 and 30 mol% LiF-glasses and two peaks for the glass with 10 mol% LiF, evidencing both a contribution of F⁻ and Li⁺ ions to the transport. Moreover, the presence of the three partially interacting mobile species F⁻, Na⁺, Li⁺ obviously leads to an anionic–cationic mixed ion effect. Applying the Nernst–Einstein equation to the Li⁺ transport in LiF-containing glasses shows that its mechanism is dissimilar to that in oxide glasses. Calculated short jump distances possibly can be interpreted as an Li⁺ movement via energetically suitable sites near F⁻ ions. Likewise the Nernst–Planck model, successfully applied to the ionic transport in mixed alkali silicate glasses, obviously does also not hold for the present heavy metal fluoride glasses.     

Hybrid solid electrolytes with excellent electrochemical properties and their applications in all-solid-state cells

Three types of inorganic electrolytes [Li₁₀GeP₂S₁₂ (LGPS), 75Li₂S·24P₂S₅·1P₂O₅ (LPOS), Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP)] with different particle sizes and electrochemical properties are selected as active fillers incorporated into poly(ethylene oxide) (PEO) matrix to fabricate hybrid solid electrolytes. The optimum composition of each filler is found in consideration of ionic conductivity. Their electrochemical characteristics are investigated. The optimal conductivities are 1.60 × 10^?5, 1.18 × 10^?5, and 2.12 × 10^?5 S cm^?1 at room temperature for PEO-1%LGPS, PEO-1%LPOS, and PEO-20%LAGP, respectively. The electrochemical stability windows of these hybrid solid electrolytes are all above 5 V (vs. Li⁺/Li). The results show that these fillers have positive effects on the ionic conductivity, lithium ion transference number, and electrochemical stability. The relationship between the type of filler and electrochemical properties has been investigated. All-solid-state cells LiFePO₄/Li are fabricated and present fascinating electrochemical performance with high capacity retention and good cycling stability. This work provides promising electrolytes prepared by a simple method.     

Correlations entre la conductivite ionique et la concentration en ions alcalins dans les borates de lithium vitreux

The electrical transport properties of the B₂O₃ - xLi₂O glasses have been investigated. An electrochemical approach allows to give an interpretation of the conductivity based on the carrier concentration in relation with Li₂O content. The mobility of the Li⁺ ions does not seem to depend on the composition.     

High lithium ion conducting glass-ceramics in the system Li2S–P2S5

Highly ion-conductive Li₂S–P₂S₅ glass-ceramic electrolytes were prepared by controlling the compositions and heat treatment temperatures of the glasses. The 70Li₂S·30P₂S₅ (mol%) glass-ceramic heated at 360 °C showed the highest conductivity of 3.2 × 10^− 3 S cm^− 1 at room temperature and the lowest activation energy of 12 kJ mol^− 1 for conduction in the binary system Li₂S–P₂S₅. The outstanding property was attributed to both the precipitation of the new crystal as a metastable phase and the increase in crystallinity of the phase. With increasing heat treatment temperatures, the metastable phase changed into thermodynamically stable phases such as the Li₄P₂S₆ crystal by heat treatment up to 550 °C, resulting in low conductivities of the glass-ceramics. It was, thus, found that the formation of superionic metastable phases by heating the Li₂S–P₂S₅ glasses is responsible for the marked enhancement on the conducting properties of the glass-ceramics.     

Investigation of ion transport in Li<Subscript>8</Subscript>ZrO<Subscript>6</Subscript> and Li<Subscript>6</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> solid electrolytes

Lithium ionic conductivity and spin-lattice relaxation rates were measured in Li₈ZrO₆ and Li₆Zr₂O₇ solid electrolytes. It was found that the Li₈ZrO₆ solid electrolyte undergoes a transition to the superionic state in the temperature range 673–703 K. It was shown that Li⁺ ions are mobile in particular lattice positions of the Li₆Zr₂O₇ phase, and that ionic conductivity is monotonic at an activation energy of 79.4 kJ/mol.     

Effect of rapid quenching on electrical properties of lithium conductive glasses

A twin roller apparatus has been designed to be used in a controlled environment, so that even hydroscopic and oxidizable glasses may be prepared by rapid quenching. xLi₂O(1?x)P₂O₅ and xLi₂S(1?x)GeS₂ glasses have been prepared and their electrical conductivity measured as a function of temperature. The electrical characteristics of rapidly quenched and conventional glasses are compared in order to study the influence of the cooling rate. The results are quite different for oxide and sulfide glasses. Rapid quenching does not much affect oxide glasses whereas for sulfide glasses important decreases in activation energies and pre-exponential factors are observed.     

LiF-LiCl-B2O3系统非晶态快离子导体结构的研究

本文通过对¹¹B核磁共振(¹¹B-NMR)、红外光谱等实验方法,研究了LiF-LiCl-B₂O₃三元系统玻璃的结构和离子导电性,着重于F^-离子在玻璃网络中所起的作用,以及F^-,Cl^-和Li⁺离子对导电率的影响。LiF-LiCl-B₂O₃三元系统玻璃,随LiF含量的增加,B由三角体向四面体变化,从而F^-离子进入网络,使玻璃结构由[B₂O₃]三角体层状结构向三维空间延展,形成了含有[BO₃F]基团的三维空间网络,Cl^-离子以游离的离子存在于网络中,起着松散网络的作用,对提高电导率有利,而Li⁺离子作为传导离子,对电导率的贡献是主要的。本系统玻璃的电导率是随LiF,LiCl含量的增加而增大,在300℃时测得电导率σ=6.12×10^-4Ω^-1·cm^-1。 关键词：     

Electronic to ionic conductivity of glasses in the Li2S–Sb2S3–P2S5 system

There is great interest in sulfide glasses because of their high lithium ion conductivity. New sulfide glasses in the Li₂S–Sb₂S₃–P₂S₅ system have been synthesized by classical quenching technique. The glass domain relays on the medium-lithium content (up to 50% molar).Electrical conductivities of the samples have been determined by Impedance Spectroscopy. The isothermal conductivity curves exhibit two regions on dependence of lithium content implying that the conductivity mechanisms in these two regions are different. The compositions of low lithium content (below 20% mol.) have presented low electronic conductivities close to 10^− 8 S/cm at room temperature. The compositions of medium lithium content (30–50% mol.) could be mixed ionic–electronic conductors with predominant ionic conductivities with a maximum close to 10^− 6 S/cm for sample with 50% Li₂S at room temperature. Arrhenius exponential behavior is verified between 25 °C and T_g for all glasses. The activation energies, determined from temperature dependence, are 0.55–0.64 eV. A comparative study with glasses belonging to the other chalcogenide systems has been undertaken on base of the weak electrolyte model and the values of decoupling index, R_τ, are reported. The impedance of the 0.5Li₂S–0.3Sb₂S₃–0.2P₂S₅ ionic conductor can be described by an equivalent circuit R(RQ)(RQ).     

A novel PEO-based blends solid polymer electrolytes doping liquid crystalline ionomers

A novel PEO-based blends solid polymer electrolytes doping liquid crystalline ionomers (LCI), PEO/PMMA/LiClO₄/LCI, and PEO/LiClO₄/LCI were prepared by solution casting technology. Scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) analysis proved that LCI uniformly dispersed into the solid electrolytes and restrained phase separation of PEO and PMMA. Differential scanning calorimetry (DSC) results showed that LCI decreases the crystallinity of blends solid polymer electrolytes. Thermogravimetric analysis (TGA) proved LCI not only improved thermal stability of PEO/PMMA/LiClO₄ blends but also prevent PEO/PMMA from phase separation. Infrared spectra results illustrated that there exists interaction among Li⁺ and O, and LCI that promotes the synergistic effects between PEO and PMMA. The EIS result revealed that the conductivity of the electrolytes increases with LiClO₄ concentration in PEO/PMMA blends, but it increases at first and reaches maximum value of 2.53?×?10^?4 S/cm at 1.0 % of LCI. The addition of 1.0 % LCI increases the conductivity of the electrolytes due to that LCl promoting compatibility and interaction of PEO and PMMA. Under the combined action of rigidity induced crystal unit, soft segment and the terminal ionic groups in LCI, PEO/PMMA interfacial interaction are improved, the reduction of crystallinity degree of PEO leads Li⁺ migration more freely.     

Vibrational,electrical, and structural properties of PVDF–LiBOB solid polymer electrolyte with high electrochemical potential window

Polyvinylidene difluoride (PVDF)–lithium bis(oxalato)borate (LiBOB) solid polymer electrolytes (SPEs) have been prepared by solution casting. The highest ionic conductivity achieved is 3.4610^?3 S cm^?1. Electrochemical potential window of the SPEs is found around 4.7 V. Interaction between PVDF and LiBOB is studied systematically. The changes of C–C, CF₂, and CH₂ vibration modes with an emerging shoulder are analyzed. At higher salt content, this shoulder becomes more prominent peak at the expense of CF₂ vibration mode. This suggests the possible Li⁺?F coordination. Deconvolution of IR spectra region from 1750 to 1850 cm^?1 has been carried out to estimate the relative percentage of free ions and contact ions. The finding is in good agreement with conductivity and XRD results. When more salt is present, the number of free ions percentage increases and the Full width at half-maximum (FWHM) of (110) plane is broadening. The Li⁺?F interaction breaks the folding patterns of polymer chain and enhances amorphousness domain.     

Characterization and electrical behavior of new lithium chalcoborate thin films

Thin films obtained with glasses of the B₂S₃Li₂S and B₂S₃Li₂SLiI systems, using a vacuum evaporation technique have been investigated. In each system, amorphous thin films and starting glasses have the same composition and similar conductivities, about 10^?4 and 10^?3Ω^?1cm^?1 respectively at 25°C. The deposition rate was in both cases 140 Å s^?1. However, a thermal treatment at 90°C of the thin films containing lithium iodide enhances the conductivity by a factor of 10 and leads to lower activation energy (0.18 eV). This behavior has been identified as a Phipps effect and can be attributed to a quick ion diffusion along thin film - substrate interface. This interfacial region was found to show unique conduction properties including a very low Li⁺ migration enthalpy.     

Characterization of solid electrolytes prepared from ionic glass and ionic liquid for all-solid-state lithium batteries

Glassy solid electrolytes were prepared by combining the 50Li₂SO₄·50Li₃BO₃ (mol%) ionic glass and the 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMI]BF₄) ionic liquid. High-energy ball milling was carried out for the mixture of the inorganic ionic glass and the organic ionic liquid. The ambient temperature conductivity of the glass electrolyte with 10 mol% [EMI]BF₄ was 10⁻⁴ S cm⁻¹, which was three orders of magnitude higher than that of the 50Li₂SO₄·50Li₃BO₃ glass. The addition of [EMI]BF₄ to the ionic glass decreased glass transition temperature (T_g) of the glass and the decrease of T_g is closely related to the enhancement of conductivity of the glass. Morphology and local structure of the glass electrolyte was characterized. The dissolution of an ionic liquid in an ionic glass with Li⁺ ion conductivity is a novel way to developing glass electrolytes for all-solid-state lithium secondary batteries.     

Conductivity studies on LiX–Li2S–Sb2S3–P2S5 (X = LiI or Li3PO4) glassy system

New sulfide glasses in the Li₂S–Sb₂S₃–P₂S₅ system have been prepared by classical quenching technique where glassy domain remains up to 50% molar addition of Li₂S and electrical conductivities have been determined by impedance spectroscopy. Room temperature DC conductivity vs Li₂S content exhibits two regions implying different conductivity mechanisms. The compositions of low lithium content presented low electronic conductivities close to 0.01 μS/cm at room temperature (due to Sb₂S₃ semiconducting properties). The compositions of medium lithium content could result to mixed ionic–electronic conductors with predominant ionic conductivity with a maximum close to 1 μS/cm; Arrhenius behavior is found between 25 °C and T _g for all glasses, but activation energy is found to be somehow above most similar systems. A comparative study with glasses belonging to the other chalcogenide systems has been undertaken and values of the decoupling index are reported, and in order to validate conductivity data, a circuit equivalent circuit was proposed and fitted parameters were calculated with good agreement.     

Characterization of hybrid electrolytes prepared from the Li2S-P2S5 glasses and alkanediols

Inorganic-organic hybrid electrolytes were prepared by the mechanochemical method using the Li⁺ ion conductive 70Li₂S·30P₂S₅ glass and various alkanediols. Local structure of the prepared electrolytes was analyzed by FT-IR and Raman spectroscopy. The effects of the proportion and chain length of alkanediols on conductivity of the hybrid electrolytes were investigated. The hybrid electrolyte with 2 mol.% of 1,4-butanediol exhibited the conductivity of 9.7 × 10^− 5 S cm^− 1 at room temperature and the unity of lithium ion transference number. The use of alkanediols with shorter chain length was effective in increasing conductivity of hybrid electrolytes. The electrolyte using ethyleneglycol showed the highest conductivity of 1.1 × 10^− 4 S cm^− 1 at room temperature. Lowering glass transition temperature by incorporation of alkanediols is responsible for the enhancement of conductivity of hybrid electrolytes.     

New Li+ ion conductors in the system Li4SiO4−Li3AsO4

In the system Li₄SiO₄-Li₃AsO₄, Li₄SiO₄ forms a short range of solid solutions containing up to 14 to 20% Li₃AsO ₄, depending on temperature, and γ-Li₃AsO₄ forms a more extensive range of solid solutions containing up to ≈55% Li₄SiO₄. The Li₄SiO₄-Li₃AsO₄ phase diagram has been determined and is of binary eutectic character. The ac conductivity of polycrystalline samples was measured over the range 0 to at least 300°C for nine different compositions. The two solid solution series have much higher conductivity than the pure end-members; maximum conductivity was observed in the γ-Li₃AsO₄ solid solutions containing ≈40 to 55% Li₄SiO₄, with values of $\text{≈2×10}{}^{\mathrm{?6}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 20°C rising to ≈0.02 Ω^?1 cm^?1 at 300°C. These values are comparable to those found in the system Li₄SiO₄-Li₃PO₄. The variation with composition of the Arrhenius prefactor and activation energy has been interpreted in terms of the mechanisms of conduction. Li₃AsO₄ is a poor conductor essentially because the number of mobile Li⁺ ions is very small. This number, and hence the conductivity, increases dramatically on forming solid solutions with Li₄SiO₄, by the creation of interstitial Li⁺ ions. At ≈40 to 55% Li₄SiO₄, the number of mobile Li⁺ ions appears to be optimised. An explanation for the change in activation energy of conduction at ≈290°C in Li₄SiO₄ and at higher temperatures in Li₄SiO₄ solid solutions is given in terms of order-disorder of the Li⁺ ions.     

MO2,M2O5和MO3氧化物对锂硼酸盐玻璃离子导电性的影响

本工作测量了45Li₂O·50B₂O₃·5M_mO_n(M=Al,Ti,Zr,P,V,Nb,Ta,Cr,Mo,W)玻璃的总电导率和电子电导率,以Raman光谱研究了玻璃结构,依据作为锂离子定域体的阴离子团的性质讨论了MO₂,M₂O₃和MO₃氧化物对玻璃离子导电性的影响。 关键词：     

Synthesis and electrochemical properties of Li2S–B2S3–Li4SiO4

New Li⁺ ion-conductive glasses Li₂S–B₂S₃–Li₄SiO₄ were synthesized by rapid quenching, and they were transformed into glass ceramics by heat treatment. The heat treatment increased the ionic conductivities of the Li₄SiO₄-doped glasses, and the highest ionic conductivity observed in the system was 1.0 × 10^− 3 S cm^− 1 at room temperature. The glass ceramics were highly stable against electrochemical oxidation with a wide electrochemical window of 10 V.     

Reference electrode formation in potentiometric CO2 sensors with alkali ion conducting alumosilicate glasses as solid electrolytes

Potentiometric CO₂ gas sensors with Li conducting glasses/glass ceramics of the system Li₂O-Al₂O₃-SiO₂ (different nominal composition) as solid electrolytes have been investigated. Li₂CO₃ was used as CO₂ and O₂ sensitive auxiliary electrode. During the sensor test measurements, the CO₂ partial pressure was varied between 1×10⁻³ and 1×10⁻¹ bar at a constant O₂ partial pressure of 2.1×10⁻¹ bar whereas N₂ was used as carrier gas. Comparative measurements were accomplished with sensors comprising Na and K ion conducting glasses. A metastable reference electrode was formed at the contact zone between the Au metal electrode and the former Li glasses of definite nominal composition by crystallization processes taking place, which lead to stable, reproducible CO₂ dependent EMF signals for more than 90d. The thermodynamically expected EMF difference and the observed EMF difference agree quite well between 500 and 600 °C. At 600 °C, the drift of sensors with glasses as solid electrolytes and direct Au glass/glass ceramics contact as reference electrode amounts typically 0.32 mV/d (p(CO₂)=1×10⁻³ bar, p(O₂)=2.1×10⁻¹ bar at the measuring electrode), if a metastable multiphase equilibrium is formed. At identical partial pressures of CO₂ and O₂, the signal reproducibility of these sensors with different solid electrolyte glasses of the same nominal composition lies within 30 mV at 600 °C. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Lithium-ion conductivity in the novel La1/3−xLi3xNbO3 solid solution with perovskite-related structure

The stoichiometric range, crystal chemistry, ionic conductivity and electrochemical window of the La_1/3−xLi_3xNbO₃ solid solution with a perovskite-related structure have been studied. The range of existence of the solid solution appears to be 0≤x≤0.06. These niobates have a basic diagonal unit cell a≈√2a_p b√2a_p c≈2a_p. Ionic conductivity of the materials and its dependence with the composition and temperature have been examined. We have found that the highest conductivity value is 4.3×1O⁻⁵ S cm⁻¹ at 300 K for x=0.04. The electrochemical window of the compounds has been investigated by potentiostatic discharge and charge. Electrochemical experiments show that the use of the materials as solid electrolytes in secondary batteries is limited down to 1.75 V using Li metal as anode.     

Factors affecting ionic conductivity in the lithium conducting glassy solid electrolytes

The electrical conductivity results of lithium borosilicate glasses with addition of Li₂SO₄ and LiCl have been critically analyzed. In general, it is observed that the factors viz. lithium fraction, f_Li and the number of non-bridging oxygens (NBOs) govern the ionic conductivity in the lithium conducting glasses. For the same f_Li, the presence of mixed formers in the glass gives higher conductivity compared to that of the glass with only one former. Thus the competitive network of glass in mixed former systems provides higher mobilities for lithium ions and hence high ionic conductivity. The addition of Li₂SO₄ and LiCl in the lithium borosilicate glasses gave enhancement in the conductivity. However, the mechanism of enhancement in conductivity is different in the two glass systems. The comparison of the result of binary, ternary and quaternary glass systems suggests that in general, the decrease in activation energy, increase in f_Li and increase in NBOs gives rise to enhancement in conductivity. For the same value of f_Li the higher conductivity is exhibited by glasses with lower value of K (K=SiO₂/B₂O₃). Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.