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Structural and Electrochemical Consequences of Al and Ga Cosubstitution in Li7La3Zr2O12 Solid Electrolytes.

Rettenwander D, Redhammer G, Preishuber-Pflügl F, Cheng L, Miara L, Wagner R, Welzl A, Suard E, Doeff MM, Wilkening M, Fleig J, Amthauer G - Chem Mater (2016)

Bottom Line: The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV.The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm(2), the lowest reported value for LLZO so far.These results illustrate that understanding the structure-properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Physics of Materials, University of Salzburg , 5020, Salzburg, Austria.

ABSTRACT

Several "Beyond Li-Ion Battery" concepts such as all solid-state batteries and hybrid liquid/solid systems envision the use of a solid electrolyte to protect Li-metal anodes. These configurations are very attractive due to the possibility of exceptionally high energy densities and high (dis)charge rates, but they are far from being realized practically due to a number of issues including high interfacial resistance and difficulties associated with fabrication. One of the most promising solid electrolyte systems for these applications is Al or Ga stabilized Li7La3Zr2O12 (LLZO) based on high ionic conductivities and apparent stability against reduction by Li metal. Nevertheless, the fabrication of dense LLZO membranes with high ionic conductivity and low interfacial resistances remains challenging; it definitely requires a better understanding of the structural and electrochemical properties. In this study, the phase transition from garnet (Ia3̅d, No. 230) to "non-garnet" (I4̅3d, No. 220) space group as a function of composition and the different sintering behavior of Ga and Al stabilized LLZO are identified as important factors in determining the electrochemical properties. The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV. The phase transition combined with microstructural changes concomitant with an increase of the Ga/Al ratio continuously improves the Li-ion conductivity from 2.6 × 10(-4) S cm(-1) to 1.2 × 10(-3) S cm(-1), which is close to the calculated maximum for garnet-type materials. The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm(2), the lowest reported value for LLZO so far. These results illustrate that understanding the structure-properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

No MeSH data available.


Related in: MedlinePlus

BSE-SEM image of polished embedded pellets of Li6.4Al0.2–xGaxLa3Zr2O12; from left to right, x = 0.00, 0.05, 0.10, 0.15, and 0.20.
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fig2: BSE-SEM image of polished embedded pellets of Li6.4Al0.2–xGaxLa3Zr2O12; from left to right, x = 0.00, 0.05, 0.10, 0.15, and 0.20.

Mentions: For the sake of simplicity, samples with formula Li6.4Al0.2–xGaxLa3Zr2O12 are denoted LLZO:Al0.20–xGax. First, the microstructure as a function of the Al:Ga ratio wasinvestigated. Back scattered electron (BSE)–SEM micrographsof the polished pellets are shown in Figure 2. Since BSE is sensitive to the atomic number,phases with different compositions can be easily distinguished. Nocomposition other than LLZO was observed, which is in agreement withPXRD and NPD data. The increase of Ga in LLZO:Al0.20–xGax is correlated witha denser studded microstructure with better connected grains and smallerpores. In contrast, the increase of Al leads simultaneously to morepronounced separation of grains and increased grain sizes (up to 200–300μm). The relative theoretical density for all samples is, however,almost the same and amounts to 85.0(3)%. The Al and Ga content (Al:Ga)of Li6.4Al0.2–xGaxLa3Zr2O12, with x = 0.00, 0.05, 0.10, 0.15, and 0.20, measuredby EDX is 0.19:0.00, 0.14:0.05, 0.12:0.08, 0.07:0.14, and 0.00:0.21,respectively (see also Table 1).


Structural and Electrochemical Consequences of Al and Ga Cosubstitution in Li7La3Zr2O12 Solid Electrolytes.

Rettenwander D, Redhammer G, Preishuber-Pflügl F, Cheng L, Miara L, Wagner R, Welzl A, Suard E, Doeff MM, Wilkening M, Fleig J, Amthauer G - Chem Mater (2016)

BSE-SEM image of polished embedded pellets of Li6.4Al0.2–xGaxLa3Zr2O12; from left to right, x = 0.00, 0.05, 0.10, 0.15, and 0.20.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4836877&req=5

fig2: BSE-SEM image of polished embedded pellets of Li6.4Al0.2–xGaxLa3Zr2O12; from left to right, x = 0.00, 0.05, 0.10, 0.15, and 0.20.
Mentions: For the sake of simplicity, samples with formula Li6.4Al0.2–xGaxLa3Zr2O12 are denoted LLZO:Al0.20–xGax. First, the microstructure as a function of the Al:Ga ratio wasinvestigated. Back scattered electron (BSE)–SEM micrographsof the polished pellets are shown in Figure 2. Since BSE is sensitive to the atomic number,phases with different compositions can be easily distinguished. Nocomposition other than LLZO was observed, which is in agreement withPXRD and NPD data. The increase of Ga in LLZO:Al0.20–xGax is correlated witha denser studded microstructure with better connected grains and smallerpores. In contrast, the increase of Al leads simultaneously to morepronounced separation of grains and increased grain sizes (up to 200–300μm). The relative theoretical density for all samples is, however,almost the same and amounts to 85.0(3)%. The Al and Ga content (Al:Ga)of Li6.4Al0.2–xGaxLa3Zr2O12, with x = 0.00, 0.05, 0.10, 0.15, and 0.20, measuredby EDX is 0.19:0.00, 0.14:0.05, 0.12:0.08, 0.07:0.14, and 0.00:0.21,respectively (see also Table 1).

Bottom Line: The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV.The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm(2), the lowest reported value for LLZO so far.These results illustrate that understanding the structure-properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Physics of Materials, University of Salzburg , 5020, Salzburg, Austria.

ABSTRACT

Several "Beyond Li-Ion Battery" concepts such as all solid-state batteries and hybrid liquid/solid systems envision the use of a solid electrolyte to protect Li-metal anodes. These configurations are very attractive due to the possibility of exceptionally high energy densities and high (dis)charge rates, but they are far from being realized practically due to a number of issues including high interfacial resistance and difficulties associated with fabrication. One of the most promising solid electrolyte systems for these applications is Al or Ga stabilized Li7La3Zr2O12 (LLZO) based on high ionic conductivities and apparent stability against reduction by Li metal. Nevertheless, the fabrication of dense LLZO membranes with high ionic conductivity and low interfacial resistances remains challenging; it definitely requires a better understanding of the structural and electrochemical properties. In this study, the phase transition from garnet (Ia3̅d, No. 230) to "non-garnet" (I4̅3d, No. 220) space group as a function of composition and the different sintering behavior of Ga and Al stabilized LLZO are identified as important factors in determining the electrochemical properties. The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV. The phase transition combined with microstructural changes concomitant with an increase of the Ga/Al ratio continuously improves the Li-ion conductivity from 2.6 × 10(-4) S cm(-1) to 1.2 × 10(-3) S cm(-1), which is close to the calculated maximum for garnet-type materials. The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm(2), the lowest reported value for LLZO so far. These results illustrate that understanding the structure-properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

No MeSH data available.


Related in: MedlinePlus