Molten salt synthesis and characterization of fast ion conductor Li<Subscript>6.75</Subscript>La<Subscript>3</Subscript>Zr<Subscript>1.75</Subscript>Ta<Subscript>0.25</Subscript>O<Subscript>12</Subscript>

The limited electrochemical stability and the flammability of the liquid electrolytes presently used in Li-ion batteries stimulates the search for alternatives including ceramic solid electrolytes. Moreover, solid electrolytes also fulfil crucial functions in various large-scale energy storage systems, e.g. as anode-protecting membranes in aqueous Li-air batteries. Here, the processing of the solid electrolytes Li₇La₃Zr₂O₁₂ is studied for applications in Li-air batteries. Molten salt method (MSM) was adopted previously on synthesis of simple oxides; to the best of our knowledge, we report for the first time the adaptation of the MSM to prepare this class of solid electrolytes. As a model compound, we prepared the garnet-related Li_6.75La₃Zr_1.75Ta_0.25O₁₂. It has been prepared by using stoichiometric amounts of La₂O₃, ZrCl₄, and Ta₂O₅ in excess 0.88 M LiNO₃:0.12 M LiCl molten salt. Subsequently, samples were heated to various temperatures in the range 600–900 °C for 6 h in air in a recrystallized alumina crucible and finally washed with distilled water to remove excess salts. The obtained Li_6.75La₃Zr_1.75Ta_0.25O₁₂ electrolyte powder was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman, and impedance spectroscopy as well as surface area measurements. The cubic single phase was obtained for samples prepared at temperatures ≥700 °C. The effects of washing with water or aqueous LiOH solution on the structure and conductivity of the phases will be discussed.     

Cathode half-cell of all-solid-state battery,modified with LiPO<Subscript>3</Subscript> glass

Electrochemical Methods were used to study the Pt|Li_0.9CoO₂|(Li₇La₃Zr₂O₁₂ + LiPO₃ glass)|Li_0.9CoO₂|Pt symmetric cell simulating the operation of the cathode of a solid-state power cell. It was shown that the glassy electrolyte serves in the system for organizing an ionic contact between the solid electrolyte and the cathode material. The current-breaking method and impedance spectroscopy demonstrated that the resistance of the cell is about 600 Ω at a temperature of 325°C. The overvoltage is 88 mV at a current density of 13 µA cm^–2. The plot describing the dependence of the current density on voltage is of the activation type, i.e., the main contribution to the polarization comes from the activation component.     

Study of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> interaction with solid lithium-containing electrolytes

Compatibility of the lithium-titanium spinel Li₄Ti₅O₁₂ in contact with precursors of lithium-conducting solid electrolytes of composition Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP), Li_0.5La_0.5TiO₃ (LLT) was studied. It was found that, in sintering of Li₄Ti₅O₁₂ brought in contact with LATP and LAGP, a solid-phase reaction occurs to give nonconducting phases (TiO₂ and Li₃PO₄). The conductivity of the stable composite Li₄Ti₅O₁₂/LLT (10%) is higher than that of the starting Li₄Ti₅O₁₂, which makes it possible to regard the composite as a promising anode material for lithium-ion batteries.     

Quantum-Chemical Modeling of the Surface Contact of Superionic Conductor Li<Subscript>10</Subscript>GeP<Subscript>2</Subscript>S<Subscript>12</Subscript> with Different Materials

The bulk and surface of crystalline lithium-ion conductor Li₁₀GeP₂S₁₂ have been modeled by the density functional theory method in the generalized gradient approximation (GGA). It has been found that barriers to the migration of cations are small both along and across the unit cell, and that in this compound, ionic conductivity is possible in three dimensions. Modeling of the crystal surface has shown that it has a “bumpy” structure and poorly contacts with “hard” crystalline surfaces. With liquid electrolytes (for example, DMSO), such problems do not arise, and lithium cations can pass from one electrolyte to another without overcoming significant potential barriers. Upon contact with metallic lithium, Li₁₀GeP₂S₁₂ decomposes.     

Electrochemical behavior of composite cathodes in contact with solid electrolyte La<Subscript>10</Subscript>Ge<Subscript>6</Subscript>O<Subscript>27</Subscript>

The cathodic overvoltage of composite cathodes 50 wt % La_0.8Sr_0.2MnO₃ (LSM) + 50 wt % La₁₀Ge₆O₂₇ (LGO) (further on, LSM-LGO), LSM-SSZ (Zr_0.835Sc_0.165O_2?δ), Ag-Pd-LGO, and Ag-Pd-SSZ in contact with the LGO electrolyte is measured. The temperature dependences of the polarization conductivity and the working-current densities of the same composite cathodes are investigated. The study is performed at 700–900°C. A comparison with the SSZ electrolyte is conducted. The chemical interaction in the LSM-LGO composition is studied. It is demonstrated that the interaction of lanthanum-strontium manganite with lanthanum germanate occurs with the dissolution of the initial phases in one another and with the formation of fresh phases at elevated temperatures. Coefficients of linear thermal expansion of the LGO and SSZ electrolytes and the LSM, LSM-LGO, and LSM-SSZ electrode materials are compared at 40–900°C. Most of the studied electrodes in contact with the LGO electrolyte demonstrate thermomechanical stability and high electrochemical activity.     

Excellent Stability of a Lithium‐Ion‐Conducting Solid Electrolyte upon Reversible Li+/H+ Exchange in Aqueous Solutions

Batteries with an aqueous catholyte and a Li metal anode have attracted interest owing to their exceptional energy density and high charge/discharge rate. The long‐term operation of such batteries requires that the solid electrolyte separator between the anode and aqueous solutions must be compatible with Li and stable over a wide pH range. Unfortunately, no such compound has yet been reported. In this study, an excellent stability in neutral and strongly basic solutions was observed when using the cubic Li₇La₃Zr₂O₁₂ garnet as a Li‐stable solid electrolyte. The material underwent a Li⁺/H⁺ exchange in aqueous solutions. Nevertheless, its structure remained unchanged even under a high exchange rate of 63.6 %. When treated with a 2 M LiOH solution, the Li⁺/H⁺ exchange was reversed without any structural change. These observations suggest that cubic Li₇La₃Zr₂O₁₂ is a promising candidate for the separator in aqueous lithium batteries.     

Lithium-conducting solid electrolytes of Li<Subscript>4</Subscript>GeO<Subscript>4</Subscript>-Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> system with additions of zirconium ions

The effect of partial substitution of Zr⁴⁺ ions for Ge4+ ions in highly conducting lithium-cationic solid electrolyte Li_3.75Ge_0.75P_0.25O₄ is studied. It is found that the introduction of zirconium ions considerably raises the conductivity of basic electrolyte in the high-temperature range. For the optimal composition, the conductivity is 2.82 × 10⁻¹ S cm⁻¹ at 400°C and 1.55 S cm⁻¹ at 700°C. Possible reasons for the effects are discussed.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

A Perovskite Electrolyte That Is Stable in Moist Air for Lithium‐Ion Batteries

Solid‐oxide Li⁺ electrolytes of a rechargeable cell are generally sensitive to moisture in the air as H⁺ exchanges for the mobile Li⁺ of the electrolyte and forms insulating surface phases at the electrolyte interfaces and in the grain boundaries of a polycrystalline membrane. These surface phases dominate the total interfacial resistance of a conventional rechargeable cell with a solid–electrolyte separator. We report a new perovskite Li⁺ solid electrolyte, Li_0.38Sr_0.44Ta_0.7Hf_0.3O_2.95F_0.05, with a lithium‐ion conductivity of σ_Li=4.8×10^?4 S cm^?1 at 25 °C that does not react with water having 3≤pH≤14. The solid electrolyte with a thin Li⁺‐conducting polymer on its surface to prevent reduction of Ta⁵⁺ is wet by metallic lithium and provides low‐impedance dendrite‐free plating/stripping of a lithium anode. It is also stable upon contact with a composite polymer cathode. With this solid electrolyte, we demonstrate excellent cycling performance of an all‐solid‐state Li/LiFePO₄ cell, a Li‐S cell with a polymer‐gel cathode, and a supercapacitor.     

Synthesis of La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> by thermal treatment of mechanically activated salt mixture

A lanthanum zirconate La₂Zr₂O₇ was synthesized by soft mechanochemical method using zirconium oxynitrate ZrO(NO₃)₂·6H₂O and lanthanum carbonate La₂(CO₃)₃·8H₂O as reagents. Mechanical activation of the reagents was carried out in a centrifugal planetary ball mill. The processes occurring during calcination of the jointly and the separately mechanically activated salt mixture were studied using DSC, TG coupled with mass spectrometry, XRD analysis, and FTIR spectroscopy. It was shown that in the course of joint mechanical activation in the mill alongside with intimate mixing of the reagents and their amorphization exchange reaction occurred, producing lanthanum nitrate, basic lanthanum nitrate, basic zirconium carbonate, and hydrated zirconium oxide. The DSC curve of the jointly mechanically activated salt mixture showed a strong exothermic peak at 878 °C which was not associated with mass loss. This peak was attributed to La₂Zr₂O₇ crystallization in agreement with XRD data. Nanocrystalline lanthanum zirconate synthesized by annealing of the jointly mechanically activated salt mixture was characterized using XRD analysis, scanning, and transmission electron microscopy.     

Improvement of the cycle life of composite xerogel V<Subscript>2</Subscript>O<Subscript>5</Subscript>/C in aqueous LiNO<Subscript>3</Subscript> solution by addition of vinylene carbonate

The xerogel V₂O₅/C composite was synthesized by a sol-gel method, using the suspension of carbon black in the solution of crystalline V₂O₅ in hydrogen peroxide as the precursor solution. The Li⁺ intercalation/deintercalation reactions of the xerogel V₂O₅/C composite, used as an anode material of a two-electrode cell with an aqueous LiNO₃ solution as the electrolyte, was studied before and after the addition of vinylene carbonate (VC). Upon addition of vinylene carbonate in an amount of only l wt %, the coulombic capacity during galvanostatic cycling, instead of commonly observed permanent fade, displayed an initial increase and then a stable plateau.     

Electrochemical performance of novel Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites as electrodes for energy storage devices

The novel Li₃V₂(PO₄)₃ glass-ceramic nanocomposites were synthesized and investigated as electrodes for energy storage devices. They were fabricated by heat treatment (HT) of 37.5Li₂O–25V₂O₅–37.5P₂O₅?mol% glass at 450 °C for different times in the air. XRD, SEM, and electrochemical methods were used to study the effect of HT time on the nanostructure and electrochemical performance for Li₃V₂(PO₄)₃ glass-ceramic nanocomposites electrodes. XRD patterns showed forming Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The crystalline sizes were found to be in the range of 32–56 nm. SEM morphologies exhibited non-uniform grains and changed with variation of HT time. The electrochemical performance of Li₃V₂(PO₄)₃ glass-ceramic nanocomposites was investigated by using galvanostatic charge/discharge methods, cyclic voltammetry, and electrochemical impedance spectroscopy in 1 M H₂SO₄ aqueous electrolyte. The glass-ceramic nanocomposites annealed for 4 h, which had a lower crystalline size, exhibited the best electrochemical performance with a specific capacity of 116.4 F g^?1 at 0.5 A g^?1. Small crystalline size supported the lithium ion mobility in the electrode by decreasing the ion diffusion pathway. Therefore, the Li₃V₂(PO₄)₃ glass-ceramic nanocomposites can be promising candidates for large-scale industrial applications in high-performance energy storage devices.     

Temperature dependence of the polarization resistance of the O<Subscript>2</Subscript>,Au/La<Subscript>0.88</Subscript>Sr<Subscript>0.12</Subscript>Ga<Subscript>0.82</Subscript>Mg<Subscript>0.18</Subscript>O<Subscript>2.85</Subscript> electrode system

The impedance of a porous gold electrode in contact with solid electrolyte La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 and the effect of the manufacture conditions on its polarization resistance are studied at 600–800°C in air. The overall oxygen reaction rate on a gold electrode is described as the sum of two partial constituents, namely, the oxygen exchange at the gas/electrolyte interface at the gold/gas/electrolyte triple-phased boundary.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 190–197.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Khlupin, Beresnev.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Synthesis and charge-discharge performance of Li<Subscript>5</Subscript>SiN<Subscript>3</Subscript> as a cathode material of lithium secondary batteries

Li₅SiN₃ crystals are synthesized by direct reaction between Li₃N and Si₃N₄ with the molar ratio Li₃N/Si₃N₄ of 10:1. Reaction is performed at 1073 K for 1 h under a nitrogen atmosphere of 700 Torr. The lattice constant determined by the X-ray powder diffraction method is 4.718 Å. Four broad Raman peaks are observed at 196, 286, 580, and 750 cm^?1. By analogy with LiMgN, the broad peak at 580 cm^?1 with a half width of 140 cm^?1 is attributed to homogenously random distribution of Li and Si atoms. The band gap of Li₅SiN₃ is found to be a direct gap of about 2.5 eV by optical absorption and photoacoustic spectroscopy methods. Comparison with the conventional cathode materials for lithium ion batteries, this gap value is close to d-d transition energy of Mn in LiMn₂O₄ (1.63 eV or 2.00 eV) and that of Co in LiCoO₂ (2.1 eV), suggesting that Li₅SiN₃ is a possible cathode material. The 5 × 5 mm²-sized lithium secondary battery of Li₅SiN₃ cathode/propylene carbonate + LiClO₄ electrolyte/Li anode structure shows a discharge capacity of 2.4 μAh cm^?2 for a discharge current of 1.0 μA.     

Ion mobility and conductivity in the Li(NH<Subscript>3</Subscript>CH<Subscript>2</Subscript>COO)(NO<Subscript>3</Subscript>) compound

(⁷Li, ¹H) NMR and impedance spectroscopy methods are used to study the ion mobility and conductivity in a complex of the composition Li(NH₃CH₂COO)(NO₃) (I), which has a layered crystal structure. The character of ion motions in lithium and proton sublattices with temperature variation is considered; the types of motions and temperature ranges in which they occur are determined. It is found that above 350 K the dominant process in the lithium sublattice of the compound is Li⁺ ion diffusion. Possible migration paths of lithium ions in the lattice of the compound are analyzed. The specific conductivity of the compound is found to be 2.4×10^–6 S/cm at 393 K.     

Influence of manganese ions dissolved from LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode on the degradation of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>-based lithium-ion batteries

A systematic investigation is conducted to evaluate the influence of dissolved manganese ions from LiMn₂O₄ cathode on the degradation of Li₄Ti₅O₁₂-based lithium-ion batteries. Worse capacity fading is found in Li₄Ti₅O₁₂-based full cells with increasing manganese ion addition. The interfacial film covered on Li₄Ti₅O₁₂ anode is affected by the manganese ion contamination during cycling, which becomes thicker but more non-uniform, and is composed by less ratio of compact components and more ratio of loose components compared with that free of contamination. Such flawed passivation film cannot restrain the further penetration of electrolyte and inhibit the contact between electrolyte and Li₄Ti₅O₁₂ anodes efficiently, thus triggering more interfacial reactions and that should be the reason for the more severe capacity degradation. Accordingly, we suggest that in addition to optimizing the chemistry and microstructure of Li₄Ti₅O₁₂ electrode, more attention should also be paid to minimizing the destructive effect imposed on the passivation film of Li₄Ti₅O₁₂ electrode by the transition metal ion contaminations.     

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication     

X-ray diffraction and thermodynamic characteristics for tellurite of the composition Li<Subscript>2</Subscript>CeTeO<Subscript>5</Subscript>

Tellurite of the composition Li₂CeTeO₅ is synthesized by solid-phase method from cerium(IV) and tellurium(IV) oxides and lithium carbonate. The type of syngony, the unit cell parameters, and the compound’s X-ray and pycnometry densities are determined via X-ray diffraction analysis. The isobaric heat capacity of lithium–cerium tellurite is studied by means of dynamic calorimetry in the temperature range of 298.15–673 K; the results serve as the basis for deriving C _p ^° ~ f(T) dependency equations and determining the compound’s thermodynamic functions. λ-shaped anomalous effects, due probably to Type II phase transitions, are found on the C _p ^° ~ f(T) dependence.     

Impurity and radiation defects in LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> crystals. The nature of centers in LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> crystals,which are responsible for coloration during the long-term operation of optical elements

An attempt is made to explain the causes of coloration of LiB₃O₅ crystals after their long-term operation as laser elements. By EPR and optical spectroscopy the impurity and radiation centers are studied in as-grown LiB₃O₅ crystals and in the crystals whose color appeared after the long-term operation as laser elements. In a number of as-grown crystals a copper impurity is detected. EPR spectral parameters and the structural positions of Cu²⁺ ions are found. Defect formation features in electron irradiated as-grown LiB₃O₅ crystals and in the most colored regions of crystals of spent laser elements are analyzed. It is shown that in both growth crystals and crystals after long-term operation as laser elements the same set of radiation defects is observed: oxygen O^– in the interstitial position, an O^– hole center in the crystal structure, and the B²⁺ electron center due to the removal of an oxygen atom near the lithium vacancy. The only distinction is that the concentration of these radiation defects in crystals long used as laser elements is higher than that in growth ones by an order of magnitude. The results obtained enable the conclusion that the cause of coloration of LiB₃O₅ crystals is photo-induced diffusion of lithium atoms and their capture by cation vacancies in the dark part of the crystal, which provides the formation and accumulation of lithium vacancies in the region where the laser beam passes.     

Hydride lithiation of spinels LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

Undoped lithiation of stoichiometric spinel using lithium hydride LiH up to the composition Li_2.25Mn₂O₄ was performed. A homogeneous material with a given Li: Mn ratio was obtained by mechanochemical activation with sequential annealing of a LiMn₂O₄–LiH mixture in a high-purity argon atmosphere and then in air or oxygen at 373–553 K.