Finding Stable Solid Electrolyte-Cathode Interfaces for Li7La3Zr2O12 Garnet - a DFT Study

Lithium garnets with the general formula Li₇La₃Zr₂O₁₂ (LLZO) have many properties of an ideal electrolyte in all-solid state lithium batteries. However, internal resistance in batteries utilizing these electrolytes remains high. For widespread adoption, performance must be improved by improving bulk conductivity, reducing grain boundary resistance, and/or pairing LLZO with an appropriate cathode to minimize interfacial resistance. 

Despite high bulk conductivity, any electrolyte is impractical if a large interfacial resistance is present, arising either from decomposition products formed between cathode and electrolyte at high sintering temperatures or from electrochemical decomposition at the interface during cycling. The origin of the observed interfacial resistance in all solid state batteries is currently a matter of some debate. There are usually two explanations given in the literatures: the buildup of a space-charge layer at the interface, and interfacial phase-decomposition^1–5

In this work we use first principles calculations to identify the thermodynamic driving forces for reactions between the electrolyte and electrode across the lithium chemical potential range experienced during operation. We examine LLZO and the similar material Li₅La₃Ta₂O₁₂(LLTO) against common cathodes.  We perform a careful thermodynamic assessment of the interface equilibrium using a grand canonical ensemble. We also provide valuable information when choosing a system for all-solid-state battery construction using LLZO or LLTO as an electrolyte.

References

(1)       Takada, K.; Ohta, N.; Zhang, L.; Xu, X.; Hang, B. T.; Ohnishi, T.; Osada, M.; Sasaki, T. Solid State Ionics 2012, 225, 594–597.

(2)       Maier, J. Nat. Mater. 2005, 4, 805–815.

(3)       Takada, K.; Ohta, N.; Zhang, L.; Fukuda, K.; Sakaguchi, I.; Ma, R.; Osada, M.; Sasaki, T. Solid State Ionics 2008, 179, 1333–1337.

(4)       Takada, K. Langmuir 2013, 29, 7538–7541.

(5)       Haruyama, J.; Sodeyama, K.; Han, L.; Takada, K.; Tateyama, Y. Chem. Mater. 2014, 26, 4248–4255.