Resolving the Grain Boundary and Lattice Impedance of Hot-Pressed Li7La3Zr2O12Garnet Electrolytes (original) (raw)
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Tantalum-doped garnet (Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 , LLZTO) is a promising candidate to act as a solid electrolyte in all-solid-state batteries owing to both its high Li + conductivity and its relatively high robustness against the Li metal. Synthesizing LLZTO using conventional solid-state reaction (SSR) requires, however, high calcination temperature (>1000°C) and long milling steps, thereby increasing the processing time. Here, we report on a facile synthesis route to prepare LLZTO using a molten salt method (MSS) at lower reaction temperatures and shorter durations (900°C, 5 h). Additionally, a thorough analysis on the properties, i.e., morphology, phase purity, and particle size distribution of the LLZTO powders, is presented. LLZTO pellets, either prepared by the MSS or the SSR method, that were sintered in a Pt crucible showed Li + ion conductivities of up to 0.6 and 0.5 mS cm −1 , respectively. The corresponding activation energy values are 0.37 and 0.38 eV, respectively. The relative densities of the samples reached values of approximately 96%. For comparison, LLZTO pellets sintered in alumina crucibles or with γ-Al 2 O 3 as sintering aid revealed lower ionic conductivities and relative densities with abnormal grain growth. We attribute these observations to the formation of Al-rich phases near the grain boundary regions and to a lower Li content in the final garnet phase. The MSS method seems to be a highly attractive and an alternative synthetic approach to SSR route for the preparation of highly conducting LLZTO-type ceramics.
2021
Solid state batteries, particularly for lithium ion based architecture have been the focus of development for over 20 years and are receiving even more attention today. Utilizing impedance spectroscopy (IS) measurements we investigate the response of conductivity versus incremental pressure increase by a piston-cylinder-type high pressure cell up to 1 GPa for some lithium conducting ceramics: LATP (Li1.3Al0.3Ti1.7(PO4)3), LLTO (Li5La3Ta2O12), LLT (Li0.33La0.55TiO3), LAGP (Li1.5Al0.5Ge1.5P3O12) and LLZO (Li7La3Zr2O12) for non-annealed and annealed samples.Isothermal, incremental pressure increase of powders allows for an in situ observation of the transition state conditions of poorly consolidated ceramic powders and the effects on grain boundary conditions prior to sintering. Specific conductance (σb) increased by several orders of magnitude in some samples, approaching 10-3 S∙cm-1, yet decreased in other samples. The affect of grain boundaries and affects of bulk capacitance as the...
Journal of Alloys and Compounds, 2019
The solid-state lithium batteries are more stable than the batteries with liquid electrolyte, however their performance are also worse especially due to the low ionic conduction of their electrolyte. Garnet-type Li 7 La 3 Zr 2 O 12 is a promising solid-state electrolyte candidate for lithium batteries. In this work the influence of gallium substitution on the electrical, crystal and electronic structure properties in the Li 7 La 3 Zr 2 O 12 material were studied. Li 7-3x Ga x La 3 Zr 2 O 12 solid electrolytes were synthesized by solid state reaction method and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), AC impedance spectroscopy and X-ray absorption spectroscopy (XAS) techniques. XRD and XAS analyses showed that the x=0.05 sample is formed in the tetragonal phase with a space group of I41/acd:2 and the rest are formed in the cubic phase with a space group of I-43d due to strong coupling between outer shell electrons of the oxygen (O) and gallium (Ga) atoms. Electrochemical impedance spectroscopy (EIS) studies indicated that the tetragonal phase has the highest ionic conductivity, 3.04x10-6 S cm-1 , among all other cubic phases.
2024
Solid-state batteries have garnered attention due to their potentiality for increasing energy density and enhanced safety. One of the most promising solid electrolytes is garnet-type Li7La3Zr2O12 (LLZO) ceramic electrolyte because of its high conductivity and ease of manufacture in ambient air. The complex gas-liquid-solid sintering mechanism makes it difficult to prepare LLZO with excellent performance and high consistency. In this study, an in-situ Li2O-atmosphere assisted solvent-free route is developed for producing the LLZO ceramics. First, the lithium-rich additive Li6Zr2O7 (LiZO) is applied to in-situ supply Li2O atmosphere at grain boundaries, where its decomposition products (Li2ZrO3) build the bridge between the grain boundaries. Second, comparisons were studied between the effects of dry and wet routes on the crystallinity, surface contamination, and particle size of calcined powders and sintered ceramics. Third, by analyzing the grain boundary composition and the evolution of ceramic microstructure, the impacts of dry and wet routes and lithium-rich additive LiZO on the ceramic sintering process were studied in detail to elucidate the sintering behavior and mechanism. Lastly, exemplary Nb-doped LLZO pellets with 2 wt% LiZO additives sintered at 1,300 °C × 1 min deliver Li+ conductivities of 8.39 × 10-4 S cm-1 at 25 °C, relative densities of 96.8%, and ultra-high consistency. It is believed that our route sheds light on preparing high-performance LLZO ceramics for solid-state batteries.
Fast Lithium Ion Conduction in Garnet-Type Li7La3Zr2O12
Angewandte Chemie International Edition, 2007
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
Nature Communications
Oxide solid electrolytes (OSEs) have the potential to achieve improved safety and energy density for lithium-ion batteries, but their high grain-boundary (GB) resistance generally is a bottleneck. In the well-studied perovskite oxide solid electrolyte, Li3xLa2/3-xTiO3 (LLTO), the ionic conductivity of grain boundaries is about three orders of magnitude lower than that of the bulk. In contrast, the related Li0.375Sr0.4375Ta0.75Zr0.25O3 (LSTZ0.75) perovskite exhibits low grain boundary resistance for reasons yet unknown. Here, we use aberration-corrected scanning transmission electron microscopy and spectroscopy, along with an active learning moment tensor potential, to reveal the atomic scale structure and composition of LSTZ0.75 grain boundaries. Vibrational electron energy loss spectroscopy is applied for the first time to reveal atomically resolved vibrations at grain boundaries of LSTZ0.75 and to characterize the otherwise unmeasurable Li distribution therein. We find that Li dep...
Journal of materials chemistry. A, Materials for energy and sustainability, 2015
Lithium aluminium titanium phosphate (LATP) belongs to one of the most promising solid electrolytes. Besides sufficiently high electrochemical stability, its use in lithium-based all-solid-state batteries crucially depends on the ionic transport properties. While many impedance studies can be found in literature that report on overall ion conductivities, a discrimination of bulk and grain boundary electrical responses via conductivity spectroscopy has rarely been reported so far. Here, we took advantage of impedance measurements that were carried out at low temperatures to separate bulk contributions from the grain boundary responses. It turned out that bulk ion conductivity is by at least three orders of magnitude higher than ion transport across the grain boundary regions. At temperatures well below ambient long-range Li ion dynamics is governed by activation energies ranging from 0.26 to 0.29 eV depending on the sintering conditions. As an example, at temperatures as low as 173 K, the bulk ion conductivity, measured in N 2 inert gas atmosphere, is in the order of 8.1 Â 10 À6 S cm À1. Extrapolating this value to room temperature yields ca. 3.4 Â 10 À3 S cm À1 at 293 K. Interestingly, exposing the dense pellets to air atmosphere over a long period of time causes a significant decrease of bulk ion transport. This process can be reversed if the phosphate is calcined at elevated temperatures again.
Reduction of Grain Boundary Resistance of La0.5Li0.5TiO3 by the Addition of Organic Polymers
Nanomaterials, 2020
The organic solvents that are widely used as electrolytes in lithium ion batteries present safety challenges due to their volatile and flammable nature. The replacement of liquid organic electrolytes by non-volatile and intrinsically safe ceramic solid electrolytes is an effective approach to address the safety issue. However, the high total resistance (bulk and grain boundary) of such compounds, especially at low temperatures, makes those solid electrolyte systems unpractical for many applications where high power and low temperature performance are required. The addition of small quantities of a polymer is an efficient and low cost approach to reduce the grain boundary resistance of inorganic solid electrolytes. Therefore, in this work, we study the ionic conductivity of different composites based on non-sintered lithium lanthanum titanium oxide (La0.5Li0.5TiO3) as inorganic ceramic material and organic polymers with different characteristics, added in low percentage (<15 wt.%)...
Structure and dynamics of the fast lithium ion conductor “Li7La3Zr2O12”
Physical Chemistry Chemical Physics, 2011
The solid lithium-ion electrolyte ''Li 7 La 3 Zr 2 O 12 '' (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, 6 Li and 7 Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24d Li site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy E a characterizing longrange ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 Â 10 À4 Scm À1 to 4 Â 10 À4 Scm À1 depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 Â 10 À6 Scm À1 , E a = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb-Wagner polarization technique. The electronic transference number t eÀ is of the order of 10 À7. Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.