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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

Activationenergy (Ea) as a functionof the Al:Ga portion in Li6.4Al0.2–xGaxLa3Zr2O12 (x = 0.00, 0.05, 0.10, 0.15,and 0.20). A significant decrease in Ea for x = 0.05 and 0.15 can be observed. Dashed linesare included to guide the eye. The gray areas at x = 0.00 and 0.20 indicate values obtained from experiment (exp.)and calculations (calc.) from literature.
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fig7: Activationenergy (Ea) as a functionof the Al:Ga portion in Li6.4Al0.2–xGaxLa3Zr2O12 (x = 0.00, 0.05, 0.10, 0.15,and 0.20). A significant decrease in Ea for x = 0.05 and 0.15 can be observed. Dashed linesare included to guide the eye. The gray areas at x = 0.00 and 0.20 indicate values obtained from experiment (exp.)and calculations (calc.) from literature.

Mentions: As shown in Figure 7a, the σtotal values (= σbulk above−20 °C) obtained by using blocking (blue circle) and ohmic(red squares) electrodes are in very good agreement and increase almostlinearly as a function of the Ga content (slope 4.4 × 10–4 S cm–1/0.1 Ga pfu). The σtotal values of LLZO:Al0.20Ga0.00 arevery similar to values reported previously.3,11−16 Significantly, the σtotal value of LLZO:Al0.00Ga0.20 is one of the highest values found forLi-oxide garnets.17,33 Comparably high values were onlyreported by Bernuy-Lopez et al. as well as Li et al. for Li6.4Ga0.2La3Zr2O12 (σtotal = 1.0 × 10–3 S cm–1 at 25 °C) and Li6.4La3Zr1.4Ta0.6O12, (σtotal = 1.3 ×10–3 S cm–1 at 25 °C), respectively(although the σtotal values of samples studied hereinare measured at 20 °C).17,34 The values are veryclose to the Li-ion conduction limit suggested by Jalem et al. onthe basis of force field based simulations (σbulk = 1.7 × 10–3 S cm–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)

Activationenergy (Ea) as a functionof the Al:Ga portion in Li6.4Al0.2–xGaxLa3Zr2O12 (x = 0.00, 0.05, 0.10, 0.15,and 0.20). A significant decrease in Ea for x = 0.05 and 0.15 can be observed. Dashed linesare included to guide the eye. The gray areas at x = 0.00 and 0.20 indicate values obtained from experiment (exp.)and calculations (calc.) from literature.
© Copyright Policy
Related In: Results  -  Collection

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

fig7: Activationenergy (Ea) as a functionof the Al:Ga portion in Li6.4Al0.2–xGaxLa3Zr2O12 (x = 0.00, 0.05, 0.10, 0.15,and 0.20). A significant decrease in Ea for x = 0.05 and 0.15 can be observed. Dashed linesare included to guide the eye. The gray areas at x = 0.00 and 0.20 indicate values obtained from experiment (exp.)and calculations (calc.) from literature.
Mentions: As shown in Figure 7a, the σtotal values (= σbulk above−20 °C) obtained by using blocking (blue circle) and ohmic(red squares) electrodes are in very good agreement and increase almostlinearly as a function of the Ga content (slope 4.4 × 10–4 S cm–1/0.1 Ga pfu). The σtotal values of LLZO:Al0.20Ga0.00 arevery similar to values reported previously.3,11−16 Significantly, the σtotal value of LLZO:Al0.00Ga0.20 is one of the highest values found forLi-oxide garnets.17,33 Comparably high values were onlyreported by Bernuy-Lopez et al. as well as Li et al. for Li6.4Ga0.2La3Zr2O12 (σtotal = 1.0 × 10–3 S cm–1 at 25 °C) and Li6.4La3Zr1.4Ta0.6O12, (σtotal = 1.3 ×10–3 S cm–1 at 25 °C), respectively(although the σtotal values of samples studied hereinare measured at 20 °C).17,34 The values are veryclose to the Li-ion conduction limit suggested by Jalem et al. onthe basis of force field based simulations (σbulk = 1.7 × 10–3 S cm–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