Structural and Electrochemical Consequences of Al and Ga Cosubstitution in Li7La3Zr2O12Solid Electrolytes.
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 × 10-4S cm-1to 1.2 × 10-3S 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 cm2, 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.
Department of Chemistry and Physics of Materials, University of Salzburg , 5020, Salzburg, Austria.
Daniel
D
Rettenwander
Department of Chemistry and Physics of Materials, University of Salzburg , 5020, Salzburg, Austria.
Günther
G
Redhammer
Christian Doppler Laboratory for Lithium Batteries, Institute for Chemistry and Technology of Materials, DFG Research Unit 1277 molife, Graz University of Technology (NAWI Graz) , 8010, Graz, Austria.
Florian
F
Preishuber-Pflügl
Lawrence Berkeley National Laboratory, Energy Storage and Distributed Resources Division, University of California, Berkeley, California 94720, United States; Department of Materials Science and Engineering, University of California, Berkeley, 94720, United States.
Lei
L
Cheng
Samsung Advanced Institute of Technology , 255 Main Street, Cambridge, Massachusetts 02140, United States.
Lincoln
L
Miara
Department of Chemistry and Physics of Materials, University of Salzburg , 5020, Salzburg, Austria.
Reinhard
R
Wagner
Institute for Chemical Technologies and Analytics, Vienna University of Technology , 1060 Vienna, Austria.
Andreas
A
Welzl
Diffraction group, Institute Laue-Langevin (ILL) , 71 avenue des Martyrs, 38000 Grenoble, France.
Emmanuelle
E
Suard
Lawrence Berkeley National Laboratory, Energy Storage and Distributed Resources Division, University of California , Berkeley, California 94720, United States.
Marca M
MM
Doeff
Christian Doppler Laboratory for Lithium Batteries, Institute for Chemistry and Technology of Materials, DFG Research Unit 1277 molife, Graz University of Technology (NAWI Graz) , 8010, Graz, Austria.
Martin
M
Wilkening
Institute for Chemical Technologies and Analytics, Vienna University of Technology , 1060 Vienna, Austria.
Jürgen
J
Fleig
Department of Chemistry and Physics of Materials, University of Salzburg , 5020, Salzburg, Austria.
Georg
G
Amthauer