Rechargeable (secondary) all-solid-state lithium batteries are considered to be the next-generation high-performance power sources and are believed to have remarkable advantages over already commercialized lithium ion batteries utilizing aprotic-solution, gel, or polymeric electrolytes with regard to battery miniaturization, high-temperature stability, energy density, and battery safety. Solid electrolytes with high Li ion conductivity but negligible electronic conductivity, with stability against chemical reactions with elemental Li (or Limetal alloys) as the negative electrode (anode) and Co-, Ni-, or Mn-containing oxides as the positive electrode (cathode), and with decomposition voltages higher than 5.5 V against elemental Li are especially useful to achieve high energy and power densities as well as long-term stability.Lithium ion conduction has been reported for a wide range of crystalline metal oxides and halides with different types of structures. [1,2] In general, oxide materials are believed to be superior to non-oxide materials for reasons of handling and mechanical, chemical, and electrochemical stability.[1] So far, most of the discovered inorganic lithium ion conductors have had either high ionic conductivity or high electrochemical stability, but not both. Some oxides are excellent lithium ion conductors; for example, Li 3x La (2/3)Àx & (1/3)À2x TiO 3 (0 < x < 0.16; "LLT"; & represents a vacancy) exhibits a bulk conductivity of 10 À3 S cm À1 and a total (bulk + grain-boundary) conductivity of 7 10 À5 S cm À1 at 27 8C and x % 0.1. However, this compound becomes predominantly electronically conducting within the lithium activity range given by the two electrodes.[3] It has been attempted to replace the transition metal Ti in LLT with Zr, which is fixed-valent and more stable (against chemical reaction with elemental lithium); however, this attempt was unsuccessful owing to the ready formation of the pyrochlore phase La 2 Zr 2 O 7 . [4] Although a large number of possible lithium electrolytes have been reported for the Li 2 O-ZrO 2 system, none of them is suitable for battery applications because of their low conductivity and sensitivity to air. [5] A novel class of fast lithium ion conducting metal oxides with the nominal chemical composition Li 5 La 3 M 2 O 12 (M = Nb, Ta), possessing a garnet-related structure, has been reported from our laboratory.[6] The bond-valence analysis of Li + ion distribution confirms transport pathways which relate to the experimentally observed high Li + ion conductivity, and the Li + ions are predicted to move in a 3D network of energetically equivalent, partially occupied sites. [7] Li 5 La 3 M 2 O 12 (M = Nb, Ta) were the first examples of fast lithium ion conductors possessing garnet-like structures and gave rise to further investigations of conductivity optimization by chemical substitutions and structural modifications. [8, 9] Among the investigated compounds with garnet-related structures, Li 6 BaLa 2 Ta 2 O 12 exhibited the highest Li + ion conductivity of 4 ...

An electrochemical galvanostatic intermittent titration technique (GITT) is described which combines both transient and steady‐state measurements to obtain kinetic properties of solid mixed‐conducting electrodes, as well as thermodynamic data. The derivation of quantities such as the chemical and component diffusion coefficients, the partial conductivity, the mobility, the thermodynamic enhancement factor, and the parabolic rate constant as a function of stoichiometry is presented. A description of the factors governing the equilibration of composition gradients in such phases is included. The technique is applied to the determination of the kinetic parameters of the compound “Li3normalSb,” which has a narrow composition range. For Li2.9994normalSb the chemical diffusion coefficient is 2×10−5 cm2 sec−1 at 360°C. This value is quite high, due to a large thermodynamic enhancement factor of 1.3×104 . The lithium component diffusion coefficient is comparatively small at this composition, 1.5×10−9 cm2 sec−1 . The partial conductivity and electrical mobility of lithium are 1.5×10−4 Ω−1 cm−1 and 3×10−8 cm2 V−1 sec−1 , respectively, at the same stoichiometry and temperature. Because of the very large values of the chemical diffusion coefficient and the fact that 3 moles of lithium can react per mole of antimony, this system may be of interest for use in new types of secondary batteries.

To date, the highest bulk lithium ion-conducting solid electrolyte is the perovskite (ABO3)-type lithium lanthanum titanate (LLT) Li3 x La(2/3)-x □(1/3) - 2 x TiO3 (0 < x < 0.16) and its related structure materials. The x ≈ 0.1 member exhibits conductivity of 1 × 10-3 S/cm at room temperature with an activation energy of 0.40 eV. The conductivity is comparable to that of commonly used polymer/liquid electrolytes. The ionic conductivity of LLT mainly depends on the size of the A-site ion cation (e.g., La or rare earth, alkali or alkaline earth), lithium and vacancy concentration, and the nature of the B−O bond. For example, replacement of La by other rare earth elements with smaller ionic radii than that of La decreases the lithium ion conductivity, while partial substitution of La by Sr (larger ionic radii than that of La) slightly increases the lithium ion conductivity. The high lithium ion conductivity of LLT is considered to be due to the large concentration of A-site vacancies, and the motion of lithium by a vacancy mechanism through the wide square planar bottleneck between the A sites. It is considered that BO6/TiO6 octahedra tilting facilitate the lithium ion mobility in the perovskite structure. The actual mechanism of lithium ion conduction is not yet clearly understood. In this paper, we review the structural properties, electrical conductivity, and electrochemical characterization of LLT and its related materials.

The compositional variations of the thermodynamic and mass transport properties of the ~ phase "LiAr' in the lithium-aluminum system have been investigated over the temperature range from 415 ~ to 600~ At 415~ the emf of the single phase "LiAI" lies between 300 and 70 mV relative to pure Li and this corresponds to a 'Li activity increasing from 0.0063 to 0.31 over the phase stability range from 46.8 to 55.0 atomic percent Li. At the ideal stoichiometry, the standard Gibbs free energy of formation of "LiAI" is --29.2 kJ/mole at 415~ and the corresponding enthalpy and entropy are --43.3 kJ/mole and --20.6 J/mole ~ respectively. Two different electrochemical transient techniques have been used to measure the chemical diffusion coefficient in "LiAI" as a function of the stoichiometry; the experimental results obtained are in good agreement. On the lithium deficit side of the ideal stoichiometry, the chemical diffusion coefficient increases with decreasing Li concentration, becoming about 10 -4 cm2/sec near the phase boundary. On the other hand, it is composition independent on the Li excess side of "LiAI," varying with temperature from 2.4 • 10 -6 cm2/sec at 415~ to 1.8 • 10-~ * Electrochemical Society Active Member.

Tetraalkoxy(hydroxy)phosphoranes were postulated as intermediates in the hydrolysis of alkyl(ary1)phosphates some time ago ['], but until now could only be synthesized in a few cases by oxidation of the corresponding hydrogen phosphoraned*]. Hydrolysis of the halospirophosphoranes 2a and 2b, obtainable by treating the trihalophosphor a n e~[~" ' l a and l b with dilithium perfluoropinacolate in neutral or alkaline aqueous ether solution, led to the hydroxyphosphorane 3 (m. p. = 72 "C, 78% yield) and potassium phosphorane oxide 5 (m. p. = 118 "C, 100% yield), respectively, without cleavage of the P-0 ring bonds to form a P=O bond. A tautomeric monocyclic form[21 of 3 is not observed. The methoxy derivative 4 (m. p. = 68 "C, 92% yield) is obtained in the same way using methanol. X 3 R = H 1, R = M e 2 5 Scheme I. @ I : I ; -196 to + 160°C (10 h) and + 2 0 " C (24 h), respectively, petroleum ether extraction, Et:O, sublimation: 2a (62%, m. p.=62"C) and 2b(43%, m.p.= 82"C), respectively. @ I mL of water or methanol is added to a stirred solution of 0.003 mol 2a or 2b in 20 mL of EbO; after 30 min the organic phase is separated off and the aqueous phase extracted three times with ether. The mixture was then dried over Na2S04, concentrated and the product recrystallized from Et,O. 0 1.0 g of KOH in 5 mL of water is added to a stirred solution of 0.01 mol 2a or 2b in 30 mL of EtrO; after 1 h the mixture is extracted three times with 20 mL of ether, dried over NarS04 and the solvent removed; yield 7.5 g 5.

Recent research has shown that certain Li-oxide garnets with high mechanical, thermal, chemical, and electrochemical stability are excellent fast Li-ion conductors. However, the detailed crystal chemistry of Li-oxide garnets is not well understood, nor is the relationship between crystal chemistry and conduction behavior. An investigation was undertaken to understand the crystal chemical and structural properties, as well as the stability relations, of Li(7)La(3)Zr(2)O(12) garnet, which is the best conducting Li-oxide garnet discovered to date. Two different sintering methods produced Li-oxide garnet but with slightly different compositions and different grain sizes. The first sintering method, involving ceramic crucibles in initial synthesis steps and later sealed Pt capsules, produced single crystals up to roughly 100 μm in size. Electron microprobe and laser ablation inductively coupled plasma mass spectrometry (ICP-MS) measurements show small amounts of Al in the garnet, probably originating from the crucibles. The crystal structure of this phase was determined using X-ray single-crystal diffraction every 100 K from 100 K up to 500 K. The crystals are cubic with space group Ia3̅d at all temperatures. The atomic displacement parameters and Li-site occupancies were measured. Li atoms could be located on at least two structural sites that are partially occupied, while other Li atoms in the structure appear to be delocalized. (27)Al NMR spectra show two main resonances that are interpreted as indicating that minor Al occurs on the two different Li sites. Li NMR spectra show a single narrow resonance at 1.2-1.3 ppm indicating fast Li-ion diffusion at room temperature. The chemical shift value indicates that the Li atoms spend most of their time at the tetrahedrally coordinated C (24d) site. The second synthesis method, using solely Pt crucibles during sintering, produced fine-grained Li(7)La(3)Zr(2)O(12) crystals. This material was studied by X-ray powder diffraction at different temperatures between 25 and 200 °C. This phase is tetragonal at room temperature and undergoes a phase transition to a cubic phase between 100 and 150 °C. Cubic "Li(7)La(3)Zr(2)O(12)" may be stabilized at ambient conditions relative to its slightly less conducting tetragonal modification via small amounts of Al(3+). Several crystal chemical properties appear to promote the high Li-ion conductivity in cubic Al-containing Li(7)La(3)Zr(2)O(12). They are (i) isotropic three-dimensional Li-diffusion pathways, (ii) closely spaced Li sites and Li delocalization that allow for easy and fast Li diffusion, and (iii) low occupancies at the Li sites, which may also be enhanced by the heterovalent substitution Al(3+) ⇔ 3Li.

Oxides with the nominal chemical formula Li6ALa2Ta2O12 (A = Sr, Ba) have been prepared via a solid‐state reaction in air using high purity La2O3, LiOH·H2O, Sr(NO3)2, Ba(NO3)2, and Ta2O5 and are characterized by powder X‐ray diffraction (XRD) in order to identify the phase formation and AC impedance to determine the lithium ion conductivity. The powder XRD data of Li6ALa2Ta2O12 show that they are isostructural with the parent garnet‐like compound Li5La3Ta2O12. The cubic lattice parameter was found to increase with increasing ionic size of the alkaline earth ions (Li6SrLa2Ta2O12: 12.808(2) Å; Li6BaLa2Ta2O12: 12.946(3) Å). AC impedance results show that both the strontium and barium members exhibit mainly a bulk contribution with a rather small grain‐boundary contribution. The ionic conductivity increases with increasing ionic radius of the alkaline earth elements. The barium compound, Li6BaLa2Ta2O12, shows the highest ionic conductivity, 4.0×10–5 S cm–1 at 22 °C with an activation energy of 0.40 eV, which is comparable to other lithium ion conductors, especially with the presently employed solid electrolyte lithium phosphorus oxynitride (Lipon) for all‐solid‐state lithium ion batteries. DC electrical measurements using lithium‐ion‐blocking and reversible electrodes revealed that the electronic conductivity is very small, and a high electrochemical stability (&#62; 6 V/Li) was exhibited at room temperature. Interestingly, Li6ALa2Ta2O12 was found to be chemically stable with molten metallic lithium.

Li1.33Ti1.67O4 synthesized from Li2CO3 and TiO2 was electrochemically inserted with lithium at room temperature. The defect spinel Li1.33Ti1.67O4 and the fully lithiated Li2.33Ti1.67O4 with ordered rock‐salt‐type structure show nearly identical X‐ray diffractions. Due to similar lattice constants of both phases and the low scattering factor of the lithium ions, the identification of the insertion mechanism using X‐ray powder diffraction is possible only by using high angle X‐ray scans of several samples inserted with different amounts of lithium. Precise analysis of the obtained data supplies the evidence for the presence of two distinct phases which are mutually interconvertible upon lithium exchange. This result is in good agreement with electrochemical data postulating a two‐phase mechanism from the constant electrical potential found during cycling. © 1999 The Electrochemical Society. All rights reserved.