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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

(a) Ia3̅d structures usedfor site energy difference calculations. The nearest and the farthesttetrahedral Ga–Li configuration is indicated. (b) Subtractingthe difference of the total energy calculations for the nearest lessthe farthest configurations. It is evident that Al3+ isless repulsive than Ga3+, and thus the Ga3+ actsto smooth the energy landscape more than Al3+.
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fig8: (a) Ia3̅d structures usedfor site energy difference calculations. The nearest and the farthesttetrahedral Ga–Li configuration is indicated. (b) Subtractingthe difference of the total energy calculations for the nearest lessthe farthest configurations. It is evident that Al3+ isless repulsive than Ga3+, and thus the Ga3+ actsto smooth the energy landscape more than Al3+.

Mentions: To understand the first dropin activation energy we calculatedsite energy differences using DFT. The migration pathway for Li-ionmotion involves a series of transitions between tetrahedral and neighboringoctahedral sites. The low energy sites are tetrahedral, but as theLi-ion concentration increases, the Li ions occupy the higher energyoctahedral sites.27 In order for the Liion to migrate throughout the crystal structure, they must pass throughthe tetrahedral site located close to the supervalent cation.37 We performed DFT calculations on structureswith a single Al3+ or Ga3+ cation and a singleLi+ with a compensating background charge and then computedthe total energy difference in structures with the Li ion close to,or far from, the cation as shown in Figure 8a.


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)

(a) Ia3̅d structures usedfor site energy difference calculations. The nearest and the farthesttetrahedral Ga–Li configuration is indicated. (b) Subtractingthe difference of the total energy calculations for the nearest lessthe farthest configurations. It is evident that Al3+ isless repulsive than Ga3+, and thus the Ga3+ actsto smooth the energy landscape more than Al3+.
© Copyright Policy
Related In: Results  -  Collection

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

fig8: (a) Ia3̅d structures usedfor site energy difference calculations. The nearest and the farthesttetrahedral Ga–Li configuration is indicated. (b) Subtractingthe difference of the total energy calculations for the nearest lessthe farthest configurations. It is evident that Al3+ isless repulsive than Ga3+, and thus the Ga3+ actsto smooth the energy landscape more than Al3+.
Mentions: To understand the first dropin activation energy we calculatedsite energy differences using DFT. The migration pathway for Li-ionmotion involves a series of transitions between tetrahedral and neighboringoctahedral sites. The low energy sites are tetrahedral, but as theLi-ion concentration increases, the Li ions occupy the higher energyoctahedral sites.27 In order for the Liion to migrate throughout the crystal structure, they must pass throughthe tetrahedral site located close to the supervalent cation.37 We performed DFT calculations on structureswith a single Al3+ or Ga3+ cation and a singleLi+ with a compensating background charge and then computedthe total energy difference in structures with the Li ion close to,or far from, the cation as shown in Figure 8a.

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