Li15Al3Si6 (Li14.6Al3.4Si6), a compound displaying a heterographite‐like anionic framework

The title compound, lithium aluminium silicide (15/3/6), crystallizes in the hexagonal centrosymmetric space group P6₃/m. The three‐dimensional structure of this ternary compound may be depicted as two interpenetrating lattices, namely a graphite‐like Li₃Al₃Si₆ layer and a distorted diamond‐like lithium lattice. As is commonly found for LiAl alloys, the Li and Al atoms are found to share some crystallographic sites. The diamond‐like lattice is built up of Li cations, and the graphite‐like anionic layer is composed of Si, Al and Li atoms in which Si and Al are covalently bonded [Si—Al = 2.4672 (4) Å].     

Lithium Ion Mobility in Lithium Phosphidosilicates: Crystal Structure, 7Li, 29Si,and 31P MAS NMR Spectroscopy,and Impedance Spectroscopy of Li8SiP4 and Li2SiP2

The need to improve electrodes and Li‐ion conducting materials for rechargeable all‐solid‐state batteries has drawn enhanced attention to the investigation of lithium‐rich compounds. The study of the ternary system Li‐Si‐P revealed a series of new compounds, two of which, Li₈SiP₄ and Li₂SiP₂, are presented. Both phases represent members of a new family of Li ion conductors that display Li ion conductivity in the range from 1.15(7)×10^?6 Scm^?1 at 0 °C to 1.2(2)×10^?4 Scm^?1 at 75 °C (Li₈SiP₄) and from 6.1(7)×10^?8 Scm^?1 at 0 °C to 6(1)×10^?6 Scm^?1 at 75 °C (Li₂SiP₂), as determined by impedance measurements. Temperature‐dependent solid‐state ⁷Li NMR spectroscopy revealed low activation energies of about 36 kJ mol^?1 for Li₈SiP₄ and about 47 kJ mol^?1 for Li₂SiP₂. Both compounds were structurally characterized by X‐ray diffraction analysis (single crystal and powder methods) and by ⁷Li, ²⁹Si, and ³¹P MAS NMR spectroscopy. Both phases consist of tetrahedral SiP₄ anions and Li counterions. Li₈SiP₄ contains isolated SiP₄ units surrounded by Li atoms, while Li₂SiP₂ comprises a three‐dimensional network based on corner‐sharing SiP₄ tetrahedra, with the Li ions located in cavities and channels.     

Fast Li Ion Dynamics in the Solid Electrolyte Li7P3S11 as Probed by 6,7Li NMR Spin‐Lattice Relaxation

The development of safe and long‐lasting all‐solid‐state batteries with high energy density requires a thorough characterization of ion dynamics in solid electrolytes. Commonly, conductivity spectroscopy is used to study ion transport; much less frequently, however, atomic‐scale methods such as nuclear magnetic resonance (NMR) are employed. Here, we studied long‐range as well as short‐range Li ion dynamics in the glass‐ceramic Li₇P₃S₁₁. Li⁺ diffusivity was probed by using a combination of different NMR techniques; the results are compared with those obtained from electrical conductivity measurements. Our NMR relaxometry data clearly reveal a very high Li⁺ diffusivity, which is reflected in a so‐called diffusion‐induced ⁶Li NMR spin‐lattice relaxation peak showing up at temperatures as low as 313 K. At this temperature, the mean residence time between two successful Li jumps is in the order of 3×10⁸ s^?1, which corresponds to a Li⁺ ion conductivity in the order of 10^?4 to 10^?3 S cm^?1. Such a value is in perfect agreement with expectations for the crystalline but metastable glass ceramic Li₇P₃S₁₁. In contrast to conductivity measurements, NMR analysis reveals a range of activation energies with values ranging from 0.17 to 0.26 eV, characterizing Li diffusivity in the bulk. In our case, through‐going Li ion transport, when probed by using macroscopic conductivity spectroscopy, however, seems to be influenced by blocking grain boundaries including, for example, amorphous regions surrounding the Li₇P₃S₁₁ crystallites. As a result of this, long‐range ion transport as seen by impedance spectroscopy is governed by an activation energy of approximately 0.38 eV. The findings emphasize how surface and grain boundary effects can drastically affect long‐range ionic conduction. If we are to succeed in solid‐state battery technology, such effects have to be brought under control by, for example, sophisticated densification or through the preparation of samples that are free of any amorphous regions that block fast ion transport.     

Preparation of the Solid Electrolytes Li4+xAlxSi1‐xO4‐yLi3PO4 and Their Ionic Conductivity

The ion conductors Li_4+xAl_xSi_1‐xO₄‐yLi₃PO₄ (x = 0 to 0.5, y = 0 to 0.6) were prepared by the Sol‐Gel method. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The conductivity and sinterability increased when y increased from 0 to 0.4 in the Li_4+xAl_xSi_1‐xO₄‐yLi₃PO₄. The particle size of the powder samples is about 0.13 μm. The maximum conductivity at 20 °C is 3.128 × 10^?5s cm^?1 for Li_4.4Al_0.4Si_0.6O₄‐0.4 Li₃PO₄.     

Synthesis,Crystal Structure and Lithium Motion of Li8SeN2 and Li8TeN2

The compounds Li₈EN₂ with E = Se, Te were obtained in form of orange microcrystalline powders from reactions of Li₂E with Li₃N. Single crystal growth of Li₈SeN₂ additionally succeeded from excess lithium. The crystal structures were refined using single‐crystal X‐ray diffraction as well as X‐ray and neutron powder diffraction data (I4₁md, No. 109, Z = 4, Se: a = 7.048(1) Å, c = 9.995(1) Å, Te: a = 7.217(1) Å, c = 10.284(1) Å). Both compounds crystallize as isotypes with an anionic substructure motif known from cubic Laves phases and lithium distributed over four crystallographic sites in the void space of the anionic framework. Neutron powder diffraction pattern recorded in the temperature range from 3 K to 300 K and X‐ray diffraction patterns using synchrotron radiation taken from 300 K to 1000 K reveal the structural stability of both compounds in the studied temperature range until decomposition. Motional processes of lithium atoms in the title compounds were revealed by temperature dependent NMR spectroscopic investigations. Those are indicated by significant changes of the ⁷Li NMR signals. Lithium motion starts for Li₈SeN₂ above 150 K whereas it is already present in Li₈TeN₂ at this temperature. Quantum mechanical calculations of NMR spectroscopic parameters reveal clearly different environments of the lithium atoms determined by the electric field gradient, which are sensitive to the anisotropy of charge distribution at the nuclear sites. With respect to an increasing coordination number according to 2 + 1, 3, 3 + 1, and 4 for Li(3), Li(4), Li(2), and Li(1), respectively, the values of the electric field gradients decrease. Different environments of lithium predicted by quantum mechanical calculations are confirmed by ⁷Li NMR frequency sweep experiments at low temperatures.     

Synthesis,crystal structures and chemical bonding of RE5−xLixGe4 (RE = Nd,Sm and Gd; x≃ 1) with the orthorhombic Gd5Si4 type

The syntheses and single‐crystal and electronic structures of three new ternary lithium rare earth germanides, RE_5−xLi_xGe₄ (RE = Nd, Sm and Gd; x≃ 1), namely tetrasamarium lithium tetragermanide (Sm_3.97Li_1.03Ge₄), tetraneodymium lithium tetragermanide (Nd_3.97Li_1.03Ge₄) and tetragadolinium lithium tetragermanide (Gd_3.96Li_1.03Ge₄), are reported. All three compounds crystallize in the orthorhombic space group Pnma and adopt the Gd₅Si₄ structure type (Pearson code oP36). There are six atoms in the asymmetric unit: Li1 in Wyckoff site 4c, RE1 in 8d, RE2 in 8d, Ge1 in 8d, Ge2 in 4c and Ge3 in 4c. One of the RE sites, i.e. RE2, is statistically occupied by RE and Li atoms, accounting for the small deviation from ideal RE₄LiGe₄ stoichiometry.     

The Ionic Conductivity of Solid Electrolytes for Li4+xMxSi1–xO4‐yLi2O (M=Al,B) Systems

The Li_4+xM_xSi_4+xO₄‐yLi₂O (M=Al, B; x = 0 to 0.6, y = 0 to 0.5) ion conductors were prepared by the Sol‐Gel method and examined in detail. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The experimental results show that the conductivity and sinterability in creased with the amount of excess lithium oxide in the silicate. The Li₂O phase acts as a flux to accelerate the sintering process and to obtain high conductivity of grain boundaries. The particle size of the sintered pellets is about 0.25 μm. The maximum conductivity at 200 °C is 5.40 × 10^?3s cm^?1 for Li_4.4Al_0.4 Si_0.6O₄‐0.3Li₂O.     

Li9Al4Sn5 as a new ordered superstructure of the Li13Sn5 type

Alloys from the ternary Li–Al–Sn system have been investigated with respect to possible applications as negative electrode materials in Li‐ion batteries. This led to the discovery of a new ternary compound, a superstructure of the Li₁₃Sn₅ binary compound. The ternary stannide, Li₉Al₄Sn₅ (nonalithium tetraaluminium pentastannide; trigonal, P m 1, hP18 ), crystallizes as a new structure type, which is an ordered variant of the binary Li₁₃Sn₅ structure type. One Li and one Sn site have m . symmetry, and all other atoms occupy sites of 3m . symmetry. The polyhedra around all types of atoms are rhombic dodecahedra. The electronic structure was calculated by the tight‐binding linear muffin‐tin orbital atomic spheres approximation method. The electron concentration is higher around the Sn and Al atoms, which form an [Al₄Sn₅]^m− polyanion.     

Structure and lithium dynamics of Li2AuSn2--a ternary stannide with condensed AuSn4/2 tetrahedra

The new stannide Li₂AuSn₂ was prepared by reaction of the elements in a sealed tantalum tube in a resistance furnace at 970 K followed by annealing at 720 K for five days. Li₂AuSn₂ was investigated by X‐ray diffraction on powders and single crystals and the structure was refined from single‐crystal data: Z=4, I4₁/amd, a=455.60(7), c=1957.4(4) pm, wR2=0.0681, 278 F² values, 10 parameters. The gold atoms display a slightly distorted tetrahedral tin coordination with Au? Sn distances of 273 pm. These tetrahedra are condensed through common corners leading to the formation of two‐dimensional AuSn_4/2 layers. The latter are connected in the third dimension through Sn? Sn bonds (296 pm). The lithium atoms fill distorted hexagonal channels formed by the three‐dimensional [AuSn₂] network. Modestly small ⁷Li Knight shifts are measured by solid‐state NMR spectroscopy that are consistent with a nearly complete state of lithium ionization. The noncubic local symmetry at the tin site is reflected by a nuclear electric quadrupolar splitting in the ¹¹⁹Sn Mössbauer spectra and a small chemical shift anisotropy evident from ¹¹⁹Sn solid‐state NMR spectroscopy. Variable‐temperature static ⁷Li solid‐state NMR spectra reveal motional narrowing effects at temperatures above 200 K, revealing lithium atomic mobility on the kHz time scale. Detailed lineshape as well as temperature‐dependent spin lattice relaxation time measurements indicate an activation energy of lithium motion of 27 kJ mol^?1.     

Boosting Solid‐State Diffusivity and Conductivity in Lithium Superionic Argyrodites by Halide Substitution

Developing high‐performance all‐solid‐state batteries is contingent on finding solid electrolyte materials with high ionic conductivity and ductility. Here we report new halide‐rich solid solution phases in the argyrodite Li₆PS₅Cl family, Li_6?xPS_5?xCl_1+x, and combine electrochemical impedance spectroscopy, neutron diffraction, and ⁷Li NMR MAS and PFG spectroscopy to show that increasing the Cl^?/S^2? ratio has a systematic, and remarkable impact on Li‐ion diffusivity in the lattice. The phase at the limit of the solid solution regime, Li_5.5PS_4.5Cl_1.5, exhibits a cold‐pressed conductivity of 9.4±0.1 mS cm^?1 at 298 K (and 12.0±0.2 mS cm^?1 on sintering)—almost four‐fold greater than Li₆PS₅Cl under identical processing conditions and comparable to metastable superionic Li₇P₃S₁₁. Weakened interactions between the mobile Li‐ions and surrounding framework anions incurred by substitution of divalent S^2? for monovalent Cl^? play a major role in enhancing Li⁺‐ion diffusivity, along with increased site disorder and a higher lithium vacancy population.     

7Li and 29Si solid state NMR and chemical bonding of La2Li2Si3

The ternary silicide La₂Li₂Si₃ was synthesized from the elements in a sealed niobium tube. La₂Li₂Si₃ was characterized by powder and single crystal X-ray diffraction: Ce₂Li₂Ge₃ type, Cmcm, a = 450.03(8), b = 1880.3(4), c = 689.6(1) pm, wR2 = 0.0178, 597 F² values, and 26 parameters. The La₂Li₂Si₃ structure contains two crystallographically independent silicon sites, both in slightly distorted trigonal prismatic coordination. The Si1 atoms are located in condensed La₆ prisms and form cis–trans chains (two-bonded silicon) with Si1–Si1 distances at 238 and 239 pm, indicating single bond character. The Si2 atoms are isolated within La₂Li₄ prisms. La₂Li₂Si₃ might be formally considered as an electron precise Zintl phase with an electron partition (2La³⁺)(2Li⁺)(2Si1^2–)(Si2^4–). Electronic structure calculations show a trend in this direction based on a charge density analysis with large electron localization around the Si1–Si1 chains. The compound is found weakly metallic with chemical bonding reminiscent of LaSi and additional features brought in by Li and Si2. High resolution solid state ⁷Li and ²⁹Si MAS-NMR spectra are in agreement with the crystal structural information, however, the ²⁹Si resonance shifts observed suggest strong Knight shift contributions, at variance with the Zintl concept. Variable temperature solid state ⁷Li spectra indicate the absence of motional narrowing on the kHz timescale within the temperature range 300K < T < 400 K.     

The Ionic Conductivity of Ultrafine Solid Electrolytes for Li4.4Al0.4Si0.6O4‐xY2O3 Systems

The Li_4.4Al_0.4Si_0.6O₄‐xY₂O₃ (x = 0 to 0.5) ion conductors were prepared by the Sol‐Gel method and examined in detail. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The experimental results show that the conductivity and sinterability increased with the amount of excess Y₂O₃ in the silicate. The particle size of the powder samples is about 0.12 μm. The maximum conductivity at 16 °C is 2.925 × 10^?5s·cm^?1 for Li_4.4Al_0.4Si_0.6O₄‐0.3 Y₂O₃.     

LiLa5Si4N10O and LiPr5Si4N10O – Chain‐Type Oxonitridosilicates

The isotypic lithium rare‐earth oxonitridosilicates LiLn₅Si₄N₁₀O (Ln = La, Pr) were synthesized at temperatures of 1200 °C in weld shut tantalum ampoules employing liquid lithium as flux. Thereby, a silicate substructure with a low degree of condensation was obtained. LiLa₅Si₄N₁₀O crystallizes in space group P$\bar{1}$ [Z = 1, LiLa₅Si₄N₁₀O: a = 5.7462(11), b = 6.5620(13), c = 8.3732(17) Å, α = 103.54(3), β = 107.77(3), γ = 94.30(3), wR₂ = 0.0405, 1315 data, 96 parameters]. The nitridosilicate substructure consists of loop branched dreier single‐chains of vertex sharing SiN₄ tetrahedra. Lattice energy calculations (MAPLE) and EDX measurements confirmed the electrostatic bonding interactions and the chemical compositions. The ⁷Li solid‐state MAS NMR investigation is reported.     

Li47B3P14N42—A Lithium Nitridoborophosphate with [P3N9]12−, [P4N10]10−, and the Unprecedented [B3P3N13]15− Ion

Li₄₇B₃P₁₄N₄₂, the first lithium nitridoborophosphate, is synthesized by two different routes using a Li₃N flux enabling a complete structure determination by single‐crystal X‐ray diffraction data. Li₄₇B₃P₁₄N₄₂ comprises three different complex anions: a cyclic [P₃N₉]¹²⁻, an adamantane‐like [P₄N₁₀]¹⁰⁻, and the novel anion [P₃B₃N₁₃]¹⁵⁻. [P₃B₃N₁₃]¹⁵⁻ is the first species with condensed B/N and P/N substructures. Rietveld refinement, ⁶Li, ⁷Li, ¹¹B, and ³¹P solid‐state NMR spectroscopy, FTIR spectroscopy, EDX measurements, and elemental analyses correspond well with the structure model from single‐crystal XRD. To confirm the mobility of Li⁺ ions, their possible migration pathways were evaluated and the temperature‐dependent conductivity was determined by impedance spectroscopy. With the Li₃N flux route we gained access to a new class of lithium nitridoborophosphates, which could have a great potential for unprecedented anion topologies with interesting properties.     

Site‐Specific Substitution Preferences in the Solid Solutions Li12Si7–xGex,Li12–yNaySi7, Na7LiSi8–zGez,and Li3NaSi6–vGev

The mixed silicide‐germanides Li₁₂Si_7–xGe_x, Na₇LiSi_8–zGe_z, and Li₃NaSi_6–vGe_v which could serve as potential precursors for Si_1–xGe_x materials were synthesized and characterized by X‐ray diffraction methods. The full solid solution series Li₁₂Si_7–xGe_x (0 ≤ x ≤ 7) is easily accessible from the elements and features preferential occupation of the more negatively charged crystallographic tetrel positions by Ge, which is the more electronegative element. In case of Na₇LiSi_8–zGe_z a broad solid solution range of 1.3 ≤ x ≤ 8 is available but the ternary silicide Na₇LiSi₈ could not be obtained by the tested methods of synthesis. The solubility of Ge in Li₃NaSi_6–vGe_v is highly limited to a maximum of v ≈ 0.5, and again the formally more negatively charged tetrel positions are preferred by Ge. Additionally, the two crystallographic Li positions in Li₁₂Si₇ with unusually large displacement parameters can be partially substituted by Na in Li_12–yNa_ySi₇ with 0 ≤ y ≤ 0.6. The statistical mixing of Li and Na in this solid solution contrasts the typical ordering of Li and Na in most ternary tetrelides.     

Li4Ca3Si2N6 and Li4Sr3Si2N6 – Quaternary Lithium Nitridosilicates with Isolated [Si2N6]10– Ions

The isotypic nitridosilicates Li₄Ca₃Si₂N₆ and Li₄Sr₃Si₂N₆ were synthesized by reaction of strontium or calcium with Si(NH)₂ and additional excess of Li₃N in weld shut tantalum ampoules. The crystal structure, which has been solved by single‐crystal X‐ray diffraction (Li₄Sr₃Si₂N₆: C2/m, Z = 2, a = 6.1268(12), b = 9.6866(19), c = 6.2200(12) Å, β = 90.24(3)°, wR₂ = 0.0903) is made up from isolated [Si₂N₆]^10– ions and is isotypic to Li₄Sr₃Ge₂N₆. The bonding angels and distances within the edge‐sharing [Si₂N₆]^10– double‐tetrahedra are strongly dependent on the lewis acidity of the counterions. This finding is discussed in relation to the compounds Ca₅Si₂N₆ and Ba₅Si₂N₆, which also exhibit isolated [Si₂N₆]^10– ions.     

NMR investigations on the lithiation and delithiation of nanosilicon-based anodes for Li-ion batteries

Lithiation and delithiation of nanosilicon anodes of 100–200 nm diameter have been probed by ex situ solid-state high-resolution ⁷Li nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) methods. Samples were charged within pouch cells up to capacities of 1,500 mAh/g at 0.1 C, and subsequently discharged at the same rate. The NMR spectra reveal important quantitative information on the local lithium environments during the various stages of the charging/discharging process. The TEM experiments show that the electrochemical lithiation of nanosilicon particles results in core-shell materials, consisting of Li_xSi shells surrounding a core of residual silicon. The NMR spectra yield approximate Li/Si ratios of the lithium silicides present in the shells, based on the distinct local environments of the various types of ⁷Li nuclei present. The combination of NMR with TEM gives important quantitative conclusions about the nature of the electrochemical lithiation process: Following the initial formation of the solid electrolyte interphase layer, which accounts for an irreversible capacity of 240 mAh/g, lithium silicide environments with intermediate Li concentrations (Li₁₂Si₇, Li₇Si₃, and Li₁₃Si₄) are formed at the 500 to 1,000 mAh/g range during the charging process. At a certain penetration depth, further lithiation does not progress any further toward the interior of the silicon particles but rather leads to the formation of increasing amounts of the lithium-richest silicide, Li₁₅Si₄-type environments. Delithiation does not result in the reappearance of the intermediate-stage phases but rather only changes the amount of Li₁₅Si₄ present, indicating no microscopic reversibility. Based on these results, a detailed quantitative model of nanophase composition versus penetration depth has been developed. The results indicate the power and potential of solid-state NMR spectroscopy for elucidating the charging/discharging mechanism of nano-Si anodes.     

Structural Characterisation of the Li Argyrodites Li7PS6 and Li7PSe6 and their Solid Solutions: Quantification of Site Preferences by MAS‐NMR Spectroscopy

Li₇PS₆ and Li₇PSe₆ belong to a class of new solids that exhibit high Li⁺ mobility. A series of quaternary solid solutions Li₇PS_6?xSe_x (0≤x≤6) were characterised by X‐ray crystallography and magic‐angle spinning nuclear magnetic resonance (MAS‐NMR) spectroscopy. The high‐temperature (HT) modifications were studied by single‐crystal investigations (both F$\bar 4$ 3m, Z=4, Li₇PS₆: a=9.993(1) Å, Li₇PSe₆: a=10.475(1) Å) and show the typical argyrodite structures with strongly disordered Li atoms. HT‐Li₇PS₆ and HT‐Li₇PSe₆ transform reversibly into low‐temperature (LT) modifications with ordered Li atoms. X‐ray powder diagrams show the structures of LT‐Li₇PS₆ and LT‐Li₇PSe₆ to be closely related to orthorhombic LT‐α‐Cu₇PSe₆. Single crystals of the LT modifications are not available due to multiple twinning and formation of antiphase domains. The gradual substitution of S by Se shows characteristic site preferences closely connected to the functionalities of the different types of chalcogen atoms (S, Se). High‐resolution solid‐state ³¹P NMR is a powerful method to differentiate quantitatively between the distinct (PS_4?nSe_n)^3? local environments. Their population distribution differs significantly from a statistical scenario, revealing a pronounced preference for P? S over P? Se bonding. This preference, shown for the series of LT samples, can be quantified in terms of an equilibrium constant specifying the melt reaction Se_P+S^2??S_P+Se^2?, prior to crystallisation. The ⁷⁷Se MAS‐NMR spectra reveal that the chalcogen distributions in the second and third coordination sphere of the P atoms are essentially statistical. The number of crystallographically independent Li atoms in both LT modifications was analysed by means of ⁶Li{⁷Li} cross polarisation magic angle spinning (CPMAS).     

Superstructure in the Metastable Intermediate‐Phase Li2/3FePO4 Accelerating the Lithium Battery Cathode Reaction

LiFePO₄ is an important cathode material for lithium‐ion batteries. Regardless of the biphasic reaction between the insulating end members, Li_xFePO₄, x≈0 and x≈1, optimization of the nanostructured architecture has substantially improved the power density of positive LiFePO₄ electrode. The charge transport that occurs in the interphase region across the biphasic boundary is the primary stage of solid‐state electrochemical reactions in which the Li concentrations and the valence state of Fe deviate significantly from the equilibrium end members. Complex interactions among Li ions and charges at the Fe sites have made understanding stability and transport properties of the intermediate domains difficult. Long‐range ordering at metastable intermediate eutectic composition of Li_2/3FePO₄ has now been discovered and its superstructure determined, which reflected predominant polaron crystallization at the Fe sites followed by Li⁺ redistribution to optimize the Li? Fe interactions.     

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 Li₂S-SiS₂-Al₂S₃ and Li₂S-SiS₂-P₂S₅ systems. Their structures of new materials, Li_4+xSi_1−xAl_xS₄ and Li_4−xSi_1−xP_xS₄ 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, Li₄SiS₄ is related to the γ-Li₃PO₄-type structure, and when the Li⁺ interstitials or Li⁺ vacancies were created by the partial substitutions of Al³⁺ or P⁵⁺ for Si⁴⁺, large increases in conductivity occur. The solid solution member x=0.6 in Li_4−xSi_1−xP_xS₄ showed high conductivity of 6.4×10^-4 S cm⁻¹ at 27°C with negligible electronic conductivity. The new solid solution, Li_4−xSi_1−xP_xS₄, 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_0.6S₄ electrolyte, LiCoO₂ cathode and In anode.