ChemInform Abstract: Synthesis and Structure Analysis of Tetragonal Li7La3Zr2O12 with the Garnet‐Related Type Structure.

Awaka, Junji; Kijima, Norihito; Hayakawa, Hiroshi; Akimoto, Junji

doi:10.1002/chin.200945013

Cited by 31 publications

(59 citation statements)

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“…This is in line with previous observations, where the cubic phase is observed in undoped LLZO nanowires, but extended calcination causes particle growth and concomitant appearance of t-LLZO. 24 Reducing the size of LLZO to nanometric dimensions has been demonstrated 24 to produce undoped cubic LLZO (c-LLZO, space group Ia3̅ d), 3 whereas the thermodynamically favorable but poorly conducting tetragonal phase (t-LLZO, space group I4 1 /acd) 32 is formed in bulk LLZO in the absence of aliovalent dopants. This effect was also observed incidentally in several reports, 6,7,25,33 though not discussed in detail, and is hypothesized to originate from a sizestabilization effect of c-LLZO in undoped nanostructures.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Nonaqueous Polymer Combustion Synthesis of Cubic Li₇La₃Zr₂O₁₂ Nanopowders

Weller

Whetten

Chan

2019

ACS Appl. Mater. Interfaces

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Garnet-type lithium lanthanum zirconate (Li 7 La 3 Zr 2 O 12 , LLZO) shows great promise as a solid electrolyte for future solid-state lithium batteries as it possesses a uniquely beneficial combination of high ionic conductivity, electrochemical stability against metallic lithium, and generally low reactivity in ambient conditions. Conventionally synthesized by using solid-state reactions, LLZO powders have also been prepared by using variations of sol− gel or combustion synthesis with sacrificial organic templates or polymers containing metal nitrate precursors. Herein, a novel nonaqueous polymer (NAP) method using metalorganic precursors and poly(vinylpyrrolidone) is demonstrated to easily form LLZO nanopowders. Compared to similar techniques using aqueous solutions with metal nitrates, the NAP method confers greater control over synthesis conditions. Undoped cubic phase LLZO is obtained after calcination at 700−800 °C between 0 and 4 h, and the NAP process is easily extended to Ta-doped LLZO. To elucidate the general formation mechanism of nanosized LLZO in the NAP combustion synthesis, scanning transmission electron microscopy is used to perform energy dispersive X-ray and electron energy loss spectral imaging. The results show that in situ formation of a carbonaceous foam during combustion physically segregates pockets of reagents and is responsible for maintaining the small particle size of the as-synthesized material during combustion and crystallization. The room temperature ionic conductivity of nanosized Ta-doped LLZO synthesized by using the NAP method was studied under various sintering conditions, with ionic conductivities between 0.24 and 0.67 mS cm −1 , activation energies between 0.34 and 0.42 eV, and relative densities in excess of 90% obtained by sintering at 1100 °C for between 6 and 15 h.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Nonaqueous Polymer Combustion Synthesis of Cubic Li₇La₃Zr₂O₁₂ Nanopowders

Weller

Whetten

Chan

2019

ACS Appl. Mater. Interfaces

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“…This value is considerably lower than in other experiments where lower density materials were studied. 14,15,49 In the case of films with lower density, the contribution of the surface diffusion to the total conductivity will be more relevant. Assuming that the transport on the surface requires a higher activation energy, the effective activation energy of the films with a larger proportion of grain boundaries therefore will be higher.…”

Section: Li-ion Conductivitymentioning

confidence: 99%

Aluminum-Assisted Densification of Cosputtered Lithium Garnet Electrolyte Films for Solid-State Batteries

Sastre

Lin

Filippin

et al. 2019

ACS Appl. Energy Mater.

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Garnet Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte due to its wide electrochemical stability window and high Li-ion conductivity. This electrolyte has potential to be employed in the form of thin films for solid-state batteries, a promising approach in the quest for safer batteries with higher energy densities at lower fabrication costs. In this study, we use a scalable cosputtering process to fabricate LLZO thin films with subsequent postannealing at a temperature of 700 °C, significantly below the sintering temperatures employed in ceramic pellet processing. We investigate the roles that Li excess and incorporation of Al play in the film’s crystalline phase, microstructure, phase stability, and, ultimately, ionic conductivity. Our results reveal that improving the conductivity of LLZO thin films requires not only the stabilization of the cubic phase but especially the densification of the film and the minimization of the proton exchange degradation mechanism in the presence of moisture and CO2. These issues can be mitigated by effectively controlling the amount of Li and incorporating Al as sintering agent. An ionic conductivity at room temperature of 1.9 × 10–5 S cm–1 was achieved with a 400 nm Al-substituted LLZO thin film. Finally, we prove that these LLZO thin films can be successfully deposited and crystallized on a LiCoO2 cathode.

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“…2 Later, it was revealed that the garnet type structure of LLZO exists in two polymorphs: tetragonal structure (I4 1 /acd) stable at low temperature and cubic structure (Ia3̅ d) stable at high temperature; and the conductivity of the former is two order of magnitude lower than that of the latter. 3 Therefore, how to obtain garnet with the nominal composition of "Li 7 La 3 Zr 2 O 12 " and cubic structure has been attracting much attention. It has been suggested that supervalent cations can stabilize the cubic structure at room temperature by introducing Li vacancies and/ or decreasing the Li content.…”

Section: Introductionmentioning

confidence: 99%

Ionic Conductivity and Air Stability of Al-Doped Li₇La₃Zr₂O₁₂ Sintered in Alumina and Pt Crucibles

Xia

Duan

et al. 2016

ACS Appl. Mater. Interfaces

248

190

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Li7La3Zr2O12 (LLZO) is a promising electrolyte material for all-solid-state battery due to its high ionic conductivity and good stability with metallic lithium. In this article, we studied the effect of crucibles on the ionic conductivity and air stability by synthesizing 0.25Al doped LLZO pellets in Pt crucibles and alumina crucibles, respectively. The results show that the composition and microstructure of the pellets play important roles influencing the ionic conductivity, relative density, and air stability. Specifically, the 0.25Al-LLZO pellets sintered in Pt crucibles exhibit a high relative density (∼96%) and high ionic conductivity (4.48 × 10(-4) S cm(-1)). The ionic conductivity maintains 3.6 × 10(-4) S cm(-1) after 3-month air exposure. In contrast, the ionic conductivity of the pellets from alumina crucibles is about 1.81 × 10(-4) S cm(-1) and drops to 2.39 × 10(-5) S cm(-1) 3 months later. The large grains and the reduced grain boundaries in the pellets sintered in Pt crucibles are favorable to obtain high ionic conductivity and good air stability. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy results suggest that the formation of Li2CO3 on the pellet surface is probably another main reason, which is also closely related to the relative density and the amount of grain boundary within the pellets. This work stresses the importance of synthesis parameters, crucibles included, to obtain the LLZO electrolyte with high ionic conductivity and good air stability.

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ChemInform Abstract: Synthesis and Structure Analysis of Tetragonal Li₇La₃Zr₂O₁₂ with the Garnet‐Related Type Structure.

Cited by 31 publications

References 1 publication

Nonaqueous Polymer Combustion Synthesis of Cubic Li₇La₃Zr₂O₁₂ Nanopowders

Nonaqueous Polymer Combustion Synthesis of Cubic Li₇La₃Zr₂O₁₂ Nanopowders

Aluminum-Assisted Densification of Cosputtered Lithium Garnet Electrolyte Films for Solid-State Batteries

Ionic Conductivity and Air Stability of Al-Doped Li₇La₃Zr₂O₁₂ Sintered in Alumina and Pt Crucibles

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ChemInform Abstract: Synthesis and Structure Analysis of Tetragonal Li7La3Zr2O12 with the Garnet‐Related Type Structure.

Cited by 31 publications

References 1 publication

Nonaqueous Polymer Combustion Synthesis of Cubic Li7La3Zr2O12 Nanopowders

Nonaqueous Polymer Combustion Synthesis of Cubic Li7La3Zr2O12 Nanopowders

Aluminum-Assisted Densification of Cosputtered Lithium Garnet Electrolyte Films for Solid-State Batteries

Ionic Conductivity and Air Stability of Al-Doped Li7La3Zr2O12 Sintered in Alumina and Pt Crucibles

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ChemInform Abstract: Synthesis and Structure Analysis of Tetragonal Li₇La₃Zr₂O₁₂ with the Garnet‐Related Type Structure.

Nonaqueous Polymer Combustion Synthesis of Cubic Li₇La₃Zr₂O₁₂ Nanopowders

Nonaqueous Polymer Combustion Synthesis of Cubic Li₇La₃Zr₂O₁₂ Nanopowders

Ionic Conductivity and Air Stability of Al-Doped Li₇La₃Zr₂O₁₂ Sintered in Alumina and Pt Crucibles