Syntheses and Characterization of Novel Perovskite-Type LaScO3-Based Lithium Ionic Conductors

Perovskite-type lithium ionic conductors were explored in the (Li_xLa_1−x/3)ScO₃ system following their syntheses via a high-pressure solid-state reaction. Phase identification indicated that a solid solution with a perovskite-type structure was formed in the range 0 ≤ x < 0.6. When x = 0.45, (Li_0.45La_0.85)ScO₃ exhibited the highest ionic conductivity and a low activation energy. Increasing the loading of lithium as an ionic diffusion carrier expanded the unit cell volume and contributed to the higher ionic conductivity and lower activation energy. Cations with higher oxidation numbers were introduced into the A/B sites to improve the ionic conductivity. Ce⁴⁺ and Zr⁴⁺ or Nb⁵⁺ dopants partially substituted the A-site (La/Li) and B-site Sc, respectively. Although B-site doping produced a lower ionic conductivity, A-site Ce⁴⁺ doping improved the conductive properties. A perovskite-type single phase was obtained for (Li_0.45La_0.78Ce_0.05)ScO₃ upon Ce⁴⁺ doping, providing a higher ionic conductivity than (Li_0.45La_0.85)ScO₃. Compositional analysis and crystal-structure refinement of (Li_0.45La_0.85)ScO₃ and (Li_0.45La_0.78Ce_0.05)ScO₃ revealed increased lithium contents and expansion of the unit cell upon Ce⁴⁺ co-doping. The highest ionic conductivity of 1.1 × 10⁻³ S cm⁻¹ at 623 K was confirmed for (Li_0.4Ce_0.15La_0.67)ScO₃, which is more than one order of magnitude higher than that of the (Li_xLa_1−x/3)ScO₃ system.     

Li7P3S11电解质的合成、传导及应用

固态电解质是固态电池中的关键材料,开发具有高离子电导率、高化学/电化学稳定性、电极兼容性良好的固态电解质正成为研究热点。硫化物固态电解质相较其它固态电解质具有更高的离子电导率和良好的机械加工性能等优势,是最有前景实现实用化的固态电解质之一。在众多硫化物固态电解质中,Li₇P₃S₁₁因其高的离子电导率和较低的原料成本而极具研究意义。本文首先介绍了Li₇P₃S₁₁电解质的结构、Li⁺传导机理及合成路径;其次,针对该电解质的电导率提高、空气/水稳定性提升、固固界面稳定性及电解质自身稳定性改善等问题,综述了目前常用的改性策略研究;再次,总结了基于Li₇P₃S₁₁电解质的全固态锂离子电池和全固态锂硫电池的构筑;最后,本文分析了Li₇P₃S₁₁电解质的研究和应用面临的挑战,并指出该电解质未来发展的趋势。     

Ionic conduction of lithium for Perovskite-type compounds, Li x La(1− x )/3NbO3 and (Li0.25La0.25)1− x Sr0.5 x NbO3

Perovskite-type compounds, Li _x La_{(1− x )/3}NbO₃ and (Li_0.25La_0.25)_{1− x} Sr_{0.5 x} NbO₃ as lithium ionic conductors, were synthesized by a solid-state reaction. From powder X-ray diffraction, the solid solution ranges of the two compounds were determined to be 0≤x≤0.25 and 0≤x≤0.125, respectively. In the Li _x La_{(1− x )/3}NbO₃ system, the ionic conductivity of lithium at room temperature, σ₂₅, exhibited a maximum value of 4.7 × 10⁻⁵ S · cm⁻¹ at x = 0.10. However, because of the decrease in the lattice parameters with increasing Li concentration x˙, σ₂₅ of the samples decreased with increasing x from 0.10 to 0.25. Also, in the (Li_0.25La_0.25)_{1− x} Sr_{0.5 x} NbO₃ system, the lattice parameter increased with the increase of Sr concentration and the σ₂₅ achieved a maximum (7.3 × 10⁻⁵ S · cm⁻¹ at 25 °C) at x = 0.125. Received: 12 September 1997 / Accepted: 15 November 1997     

Fast Li-Ion Conduction in Spinel-Structured Solids

Spinel-structured solids were studied to understand if fast Li⁺ ion conduction can be achieved with Li occupying multiple crystallographic sites of the structure to form a “Li-stuffed” spinel, and if the concept is applicable to prepare a high mixed electronic-ionic conductive, electrochemically active solid solution of the Li⁺ stuffed spinel with spinel-structured Li-ion battery electrodes. This could enable a single-phase fully solid electrode eliminating multi-phase interface incompatibility and impedance commonly observed in multi-phase solid electrolyte–cathode composites. Materials of composition Li_1.25M(III)_0.25TiO₄, M(III) = Cr or Al were prepared through solid-state methods. The room-temperature bulk Li⁺-ion conductivity is 1.63 × 10⁻⁴ S cm⁻¹ for the composition Li_1.25Cr_0.25Ti_1.5O₄. Addition of Li₃BO₃ (LBO) increases ionic and electronic conductivity reaching a bulk Li⁺ ion conductivity averaging 6.8 × 10⁻⁴ S cm⁻¹, a total Li-ion conductivity averaging 4.2 × 10⁻⁴ S cm⁻¹, and electronic conductivity averaging 3.8 × 10⁻⁴ S cm⁻¹ for the composition Li_1.25Cr_0.25Ti_1.5O₄ with 1 wt. % LBO. An electrochemically active solid solution of Li_1.25Cr_0.25Mn_1.5O₄ and LiNi_0.5Mn_1.5O₄ was prepared. This work proves that Li-stuffed spinels can achieve fast Li-ion conduction and that the concept is potentially useful to enable a single-phase fully solid electrode without interphase impedance.     

Lithium Ion Pathway within Li7La3Zr2O12‐Polyethylene Oxide Composite Electrolytes

Polymer–ceramic composite electrolytes are emerging as a promising solution to deliver high ionic conductivity, optimal mechanical properties, and good safety for developing high‐performance all‐solid‐state rechargeable batteries. Composite electrolytes have been prepared with cubic‐phase Li₇La₃Zr₂O₁₂ (LLZO) garnet and polyethylene oxide (PEO) and employed in symmetric lithium battery cells. By combining selective isotope labeling and high‐resolution solid‐state Li NMR, we are able to track Li ion pathways within LLZO‐PEO composite electrolytes by monitoring the replacement of ⁷Li in the composite electrolyte by ⁶Li from the ⁶Li metal electrodes during battery cycling. We have provided the first experimental evidence to show that Li ions favor the pathway through the LLZO ceramic phase instead of the PEO‐LLZO interface or PEO. This approach can be widely applied to study ion pathways in ionic conductors and to provide useful insights for developing composite materials for energy storage and harvesting.     

Water‐Mediated Synthesis of a Superionic Halide Solid Electrolyte

To promote the development of solid‐state batteries, polymer‐, oxide‐, and sulfide‐based solid‐state electrolytes (SSEs) have been extensively investigated. However, the disadvantages of these SSEs, such as high‐temperature sintering of oxides, air instability of sulfides, and narrow electrochemical windows of polymers electrolytes, significantly hinder their practical application. Therefore, developing SSEs that have a high ionic conductivity (>10^?3 S cm^?1), good air stability, wide electrochemical window, excellent electrode interface stability, low‐cost mass production is required. Herein we report a halide Li⁺ superionic conductor, Li₃InCl₆, that can be synthesized in water. Most importantly, the as‐synthesized Li₃InCl₆ shows a high ionic conductivity of 2.04×10^?3 S cm^?1 at 25 °C. Furthermore, the ionic conductivity can be recovered after dissolution in water. Combined with a LiNi_0.8Co_0.1Mn_0.1O₂ cathode, the solid‐state Li battery shows good cycling stability.     

Chemistry Design Towards a Stable Sulfide‐Based Superionic Conductor Li4Cu8Ge3S12

Sulfide‐based superionic conductors with high ionic conductivity have been explored as candidates for solid‐state Li batteries. However, moisture hypersensitivity has made their manufacture complicated and costly and also impeded applications in batteries. Now, a sulfide‐based superionic conductor Li₄Cu₈Ge₃S₁₂ with superior stability was developed based on the hard/soft acid–base theory. The compound is stable in both moist air and aqueous LiOH aqueous solution. The electrochemical stability window was up to 1.5 V. An ionic conductivity of 0.9×10^?4 S cm with low activation energy of 0.33 eV was achieved without any optimization. The material features a rigid Cu‐Ge‐S open framework that increases its stability. Meanwhile, the weak bonding between Li⁺ and the framework promotes ionic conductivity. This work provides a structural configuration in which weak Li bonding in the rigid framework promotes an environment for highly conductive and stable solid‐state electrolytes.     

Structure,Microstructure, Composition and Properties of Lanthanum Lithium Titanates and some Substituted Analogues

The very high value of ionic conductivity at room temperature reported for La_0.51Li_0.34TiO_2.94 some years ago did originate a great deal of interest in the study of materials of general formula La_2/3–xLi_3xTiO₃ (LaLiTiO) and related systems. These oxides have shown to be potential solid electrolytes for lithium secondary batteries, but other aspects, apart from the conducting properties, such as their dielectric behaviour and crystal structure, have been the main focus of important studies in the area of inorganic solid‐state chemistry. LaLiTiO‐related compounds have the perovskite‐type structure (ABO₃) with A‐cation ordering. However, essential details of their crystal structure, as for instance the location of the lithium atoms, are still under discussion and are the subject of current work. We show in this short review of mainly our own work that the complex microstructure of these materials, which has been studied in detail by transmission electron microscopy, is the cause of the difficulties on the precise determination of their crystal structure. We have developed a new approach for crystal structure refinement, which takes into account the microstructural effects, obtaining significantly better results than conventional methods of refinement. The microstructure of these oxides also affects their conducting and dielectric properties. Therefore, different parameters such as composition and microstructure must be considered to understand and, eventually, optimise, as we have done, the conducting properties of LaLiTiO‐related systems.     

Li2S-P2S5体系电解质及其在全固态锂离子电池中的应用研究进展

全固态锂离子电池具有安全性能好、能量密度高、工作温区广等优点,被广泛应用于便携式电子设备。固态电解质是全固态锂离子电池的关键材料之一,其中的硫化物电解质具有离子电导率高、电化学窗口宽、晶界电阻低和易成膜等特点,被认为最有希望应用于全固态锂离子电池。本文综述了Li_2S-P_2S_5体系电解质的发展状况,包括固态电解质的制备、改性、表征以及电极/固态电解质之间的固-固界面的稳定兼容问题。本文还涉及了以Li_2S-P_2S_5为电解质的全固态锂离子电池性能的研究进展。     

Enabling ultrafast lithium-ion conductivity of Li2ZrCl6 by indium doping

Solid-state batteries with high energy density and safety are promising next-generation battery systems. However, lithium oxide and lithium sulfide electrolytes suffer low ionic conductivity and poor electrochemical stability, respectively. Lithium halide solid electrolyte shows high conductivity and good compatibility with the pristine high-voltage cathode but limited applications due to the high price of rare metal. Zr-based lithium halides with low cost and high stability possess great potential. Herein, a small amount of In³⁺ is introduced in Li₂ZrCl₆ to synthesize Li_2.25Zr_0.75In_0.25Cl₆ electrolytes with a high room temperature Li-ion conductivity of 1.08 mS/cm. Solid-state batteries using Li_2.25Zr_0.75In_0.25Cl₆/Li_5.5PS_4.5Cl_1.5 bilayer solid electrolytes combined with Li-In anode and pristine LiNi_0.7Mn_0.2Co_0.1O₂ cathode deliver high initial discharge capacities under different cut-off voltages. This work provides an effective strategy for enhancing the conductivity of Li₂ZrCl₆ electrolytes, promoting their applications in solid-state batteries.     

Lithium-cationic conductivity in the Li4 − 2x Cd x GeO4 system

The lithium-conducting solid electrolytes in the Li_{4 ? 2x} Cd _x GeO₄ (0 ≤ x ≤ 0.6) system are synthesized. Their crystal structure and temperature and concentration dependences of conductivity are studied. The specimens with the highest conductivity have a γ-Li₃PO₄-derivative structure. The solid solutions with x = 0.15–0.25 are stable at the room temperature, whereas the specimens with x ≥ 0.3 decompose yielding Li₂CdGeO₄ below 310 ± 10°C. Li_3.6Cd_0.2GeO₄ solid solution exhibits the highest conductivity (5.25 × 10^?2 S cm^?1 at 300°C). The factors, which affect the conductivity of synthesized solid electrolytes, are considered.     

Effect of selected dopants on conductivity and moisture stability of Li3PS4 sulfide solid electrolyte: a first-principles study

The first principle computational screening was performed to investigate the effect of selected dopants for Li₃PS₄ sulfide solid electrolyte on its ionic conductivity and stability toward moisture. The results suggest that substitution P⁵⁺ using isovalent cations whose electronegativity (EN) value is closer to the value of S has more significant effects on the ionic conductivity, whereby W⁵⁺ and Sb⁵⁺ can improve most. Similarly, aliovalent cation substitutions with compensating changes in the lithium-ion concentration, particularly those with a lower oxidation state and higher EN, such as Cu²⁺, effectively enhance the lithium-ion conductivity in this structure. For cation dopants, it is found that ionic conductivity improvement of Li₃PS₄ is the synergetic effect of EN and oxidation number of the dopant as well as the material's lattice parameter change. Oxides of the considered cation dopants can also improve the ionic conductivity of the material but have much lower lithium-ion conductivity than the cases of cation dopants. However, the metal oxide dopants, particularly those derived from soft Lewis' acid cations, show a marginal improvement in moisture stability of the Li₃PS₄ electrolyte. The effect of halides and metal halide dopants on the lithium-ion conductivity and moisture stability of Li₃PS₄ electrolyte are also studied. It is found that metal halides are more effective than any other dopants in improving the ionic conductivity of Li₃PS₄.     

Synthesis of the perovskite ceramic Li3xLa2/3–xTiO3 by a chemical solution route using a triblock copolymer surfactant

The synthesis of the perovskite Li_3xLa_2/3–x□_1/3–2xTiO₃ by a chemical solution route, using a triblock copolymer surfactant, PEO_n–PPO_m–PEO_n, is described. This titanate is a non-hygroscopic fast lithium conductor and therefore is a good candidate for electrochemical applications. It is generally prepared by a conventional solid-state reaction (SSR) method. However this synthesis method does not allow the preparation of nanopowders or the formation of thin films. For these special purposes, synthesis by a chemical solution route, with the formation of a polymeric precursor during synthesis, has been investigated. By using the above-mentioned non-ionic surfactant, the preparation of nanopowders of complex oxides can be done. Furthermore, this way of synthesis leads to the formation of an intermediate polymeric precursor which can be easily spread on substrates to obtain films. We show that the formation of a pure phase of the perovskite Li_3xLa_2/3–x□_1/3–2xTiO₃ is highly dependent on the synthesis conditions, namely the presence of water in the solvent, the EO/metal ratio, the Li⁺ content in the precursor and the calcination temperature. The influence of these parameters on the microstructure of the oxide is studied by X-ray diffraction, scanning electron microscopy and granulometry. A powder of Li_3xLa_2/3–x□_1/3–2xTiO₃ (x = 0.10), with an average particles size of 200 nm, has been obtained. The ionic conductivity of this oxide is the same as the one obtained with oxide prepared by SSR (a bulk conductivity of 1.4 × 10⁻³ S/cm at 37 °C). The ceramic obtained from this powder after sintering at 1,150 °C shows a good pH response. This material can then be used as a sensitive membrane in a potentiometric pH sensor. The presence of hydrophobic PPO groups in the polymer precursor allowed preparing films of Li_3xLa_2/3–x□_1/3–2xTiO₃ with a good adherence on Pt substrate. This kind of synthesis is then very promising to prepare micro pH sensors.     

Ionic conductivity and interfacial stability of Li6PS5Cl–Li6.5La3Zr1.5Ta0.5O12 composite electrolyte

Solid electrolytes which possess excellent lithium-ion conductivity and chemical compatibility with electrode materials are necessary for the commercialization of all-solid-state lithium batteries. However, a single solid electrolyte meeting above requirements is difficult. Consequently, the composite electrolytes have attracted more attention. In this paper, Li₆PS₅Cl–xLi_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) (x = 0, 2.5 wt%, 5 wt%, 10 wt%) composite electrolytes are prepared by a simple planetary grinding process. It has been found that adding an appropriate amount of LLZTO can increase the lithium-ion conductivity. At 30 °C, the lithium-ion conductivity increases from 2.6 × 10⁻⁴ S/cm (Li₆PS₅Cl) to 5.4 × 10⁻⁴ S/cm (Li₆PS₅Cl-5 wt% LLZTO). Besides, the addition of LLZTO to the Li₆PS₅Cl can influence the growth rate of the SEI. It has been shown that the SEI growth rate obeys a parabolic rate law, and the growth rates of Li₆PS₅Cl, Li₆PS₅Cl-2.5 wt% LLZTO, Li₆PS₅Cl-5 wt% LLZTO, and Li₆PS₅Cl-10 wt% LLZTO are 8.62, 3.53, 3.33, and 3.38 Ω/h^1/2 at 60 °C, respectively. In lithium plating and stripping experiment, the voltage of symmetrical Li/Li₆PS₅Cl/Li cell suddenly drops to 0 V after cycling 39 h at 0.103 mA/cm² (0.097 mAh/cm²). On the contrary, the Li/Li₆PS₅Cl–xLLZTO (x = 2.5 wt%, 5 wt%, 10 wt%)/Li symmetrical cell exhibits a stable voltage profile over 100 h at the same test conditions. The corresponding interfacial impedance of Li/Li₆PS₅Cl–xLLZTO (x = 2.5 wt%, 5 wt%, 10 wt%) remains stable after 10, 30, and 50 charge/discharge cycles.

     

Etude par RMN de la mobilité du lithium dans trois oxydes à structure pseudo-bidimensionnelle: Li8SnO6, Li7NbO6 et Li6In2O6

The lithium ion mobility in three solid electrolytes (Li₈SnO₆, Li₇NbO₆, and Li₆In₂O₆) has been studied by NMR at several resonance frequencies from 170 to 500°K. The ⁷Li quadrupolar lineshape evolution shows the predominant influence on the conductivity mechanism of the vacancies in the octahedral sites of the oxygen close packing. In Li₈SnO₆, which has no vacancies, the lithium ions situated in the tetrahedral sites have the highest mobility. Spin-lattice relaxation times are in good agreement with the hypothesis of a Li₇NbO₆ 2D conductivity. The values of the activation energy, increasing from Li₇NbO₆ to Li₆In₂O₆ and to Li₈SnO₆, are found to be three times lower than those obtained from conductivity measurements.     

Synthesis, Phase Diagram, and Conductivity Study in a La0.5+x+yLi0.5−3xTi1−3yMn3yO3System

The stoichiometry, polymorphysm, and electrical behaviour of solid solutions of La_0.5+y+xLi_0.5−3xTi_1−3yMn_3yO₃with perovskite-type structure have been studied. Data are given in the form of a solid solution triangle, phase diagrams, XRD patterns for the three polymorphs, A,β, and C, composition-dependence of their lattice parameters, and ionic and electronic conductivity plots. Microstruture and composition were studied by SEM/EDS and electron probe microanalysis. These compounds are mixed conductors. Ionic conductivity decreases when the amount of lithium diminishes and electronic conductivity increases with manganese content.     

固体电解质Li9-nxMn+xN2Cl3(M=Na、Mg、Al)的合成及表征

高温固相反应合成了固体电解质Ｌｉ９－ｎｘＭ＾ｎ＋ｘＮ２Ｃｌ３（Ｍ＝Ｎａ、Ｍｇ、Ａｌ）。利用粉末Ｘ射线衍射测定样品结构,测定了离子电导率,分解电压和电子电导。得出掺杂可以提高快离子快离子导体材料Ｌｉ９Ｎ２Ｃｌ３中的Ｌｉ＾＋离子可以很大程度的提高其电导率。     

Synthesis of garnet structured Li7+x La3Y x Zr2-x O12 (x = 0–0.4) by modified sol–gel method

Preparation of lithium garnet Li₇La₃Zr₂O₁₂ (LLZ) in cubic phase by solid state method requires high temperature sintering around 1,200 °C for 36 h in Al₂O₃ crucible with intermittent grinding. Synthesis of LLZ in cubic phase at lower temperatures by wet chemical methods was reported earlier, however that decompose at high temperature around 850 °C. In this work we report the systematic studies on synthesis of garnet structured electrolytes by modified sol–gel method by the simultaneous substitution of Li⁺ and Y³⁺ for Zr⁴⁺ according to the formulae Li_7+x La₃Y _x Zr_2-x O₁₂ (x = 0, 0.1, 0.2, 0.3 and 0.4). The present investigation revealed that the cubic garnet phase is obtained at much lower temperature for Li₇La₃Zr₂O₁₂ and the simultaneous increase of both Li⁺ and Y³⁺ in Li_7+x La₃Y _x Zr_2-x O₁₂ requires slightly higher sintering temperatures for the formation of cubic garnet phase. SEM micrographs of the Li_7+x La₃Y _x Zr_2-x O₁₂ (x = 0, 0.1, 0.2, 0.3 and 0.4) annealed at minimum sintering temperature required for the formation of cubic garnet phase revealed the increase in grain size and relatively dense structure with increase of x in Li_7+x La₃Y _x Zr_2-x O₁₂.     

Variation in structure and Li<Superscript>+</Superscript>-ion migration in argyrodite-type Li<Subscript>6</Subscript>PS<Subscript>5</Subscript>X (X = Cl,Br, I) solid electrolytes

All-solid-state rechargeable lithium-ion batteries (AS-LIBs) are attractive power sources for electrochemical applications due to their potentiality in improving safety and stability over conventional batteries with liquid electrolytes. Finding a solid electrolyte with high ionic conductivity and compatibility with other battery components is a key factor in raising the performance of AS-LIBs. In this work, we prepare argyrodite-type Li₆PS₅X (X = Cl, Br, I) using mechanical milling followed by annealing. X-ray diffraction characterization reveals the formation and growth of crystalline Li₆PS₅X in all cases. Ionic conductivity of the order of 7?×?10^?4 S cm^?1 in Li₆PS₅Cl and Li₆PS₅Br renders these phases suitable for AS-LIBs. Joint structure refinements using high-resolution neutron and laboratory X-ray diffraction provide insight into the influence of disorder on the fast ionic conductivity. Besides the disorder in the lithium distribution, it is the disorder in the S^2?/Cl^? or S^2?/Br^? distribution that we find to promote ion mobility, whereas the large I^? cannot be exchanged for S^2? and the resulting more ordered Li₆PS₅I exhibits only a moderate conductivity. Li⁺ ion migration pathways in the crystalline compounds are modelled using the bond valence approach to interpret the differences between argyrodites containing different halide ions.     

Integrated lithium metal anode protected by composite solid electrolyte film enables stable quasi-solid-state lithium metal batteries

Lithium (Li) metal, possessing an extremely high theoretical specific capacity (3860 mAh/g) and the most negative electrode potential (−3.040 V vs. standard hydrogen electrode), is one the most favorable anode materials for future high-energy-density batteries. However, the poor cyclability and safety issues induced by extremely unstable interfaces of traditional liquid Li metal batteries have limited their practical applications. Herein, a quasi-solid battery is constructed to offer superior interfacial stability as well as excellent interfacial contact by the incorporation of Li@composite solid electrolyte integrated electrode and a limited amount of liquid electrolyte (7.5 μL/cm²). By combining the inorganic garnet Al-doped Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZO) with high mechanical strength and ionic conductivity and the organic ethylene-vinyl acetate copolymer (EVA) with good flexibility, the composite solid electrolyte film could provide sufficient ion channels, sustained interfacial contact and good mechanical stability at the anode side, which significantly alleviates the thermodynamic corrosion and safety problems induced by liquid electrolytes. This innovative and facile quasi-solid strategy is aimed to promote the intrinsic safety and stability of working Li metal anode, shedding light on the development of next-generation high-performance Li metal batteries.