Dendrite formation, which could cause a battery short circuit, occurs in batteries that contain lithium metal anodes. In order to suppress dendrite growth, the use of electrolytes with a high shear modulus is suggested as an ionic conductive separator in batteries. One promising candidate for this application is Li7La3Zr2O12 (LLZO) because it has excellent mechanical properties and chemical stability. In this work, in situ scanning electron microscopy (SEM) technique was employed to monitor the interface behavior between lithium metal and LLZO electrolyte during cycling with pressure. Using the obtained SEM images, videos were created that show the inhomogeneous dissolution and deposition of lithium, which induce dendrite growth. The energy dispersive spectroscopy analyses of dendrites indicate the presence of Li, C, and O elements. Moreover, the cross-section mapping comparison of the LLZO shows the inhomogeneous distribution of La, Zr, and C after cycling that was caused by lithium loss near the Li electrode and possible side reactions. This work demonstrates the morphological and chemical evolution that occurs during cycling in a symmetrical Li–Li cell that contains LLZO. Although the superior mechanical properties of LLZO make it an excellent electrolyte candidate for batteries, the further improvement of the electrochemical stabilization of the garnet–lithium metal interface is suggested.

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Garnet-type lithium lanthanum zirconate (Li 7 La 3 Zr 2 O 12 , LLZO)based ceramic electrolyte has potential for further development of all-solid-state energy storage technologies including Li metal batteries as well as Li−S and Li−O 2 chemistries. The essential prerequisites such as LLZO's compactness, stability, and ionic conductivity for this development are nearly achievable via the solid-state reaction route (SSR) at high temperatures, but it involves a trade-off between LLZO's caveats because of Li loss via volatilization. For example, SSR between lithium carbonate, lanthanum oxide, and zirconium oxide is typically supplemented by dopants (e.g., gallium or aluminum) to yield the stabilized cubic phase (c-LLZO) that is characterized by ionic conductivity an order of magnitude higher than the other polymorphs of LLZO. While the addition of dopants as phase stabilizing agent and supplying extra Li precursor for compensating Li loss at high temperatures become common practice in the solid-state process of LLZO, the exact role of dopants and stabilization pathway is still poorly understood, which leads to several manufacturing issues. By following LLZO's chemical phase evolution in relation to Li loss at high temperatures, we here show that stabilized c-LLZO can directly be achieved by an in situ control of lithium loss during SSR and without needing dopants. In light of this, we demonstrate that dopants in the conventional SSR route also play a similar role, i.e., making more accessible Li to the formation and phase stabilization of c-LLZO, as revealed by our in situ X-ray diffraction analysis. Further microscopic (STEM, EDXS, and EELS) analysis of the samples obtained under various SSR conditions provides insights into LLZO phase behavior. Our study can contribute to the development of more reliable solid-state manufacturing routes to Garnet-type ceramic electrolytes in preferred polymorphs exhibiting high ionic conductivity and stability for all-solid-state energy storage.

Arrays of 12 flush-mounted Langmuir probes have been installed in both the upper and lower outboard divertor plates of TdeV (Tokamak de Varennes). Measurements of electron temperature and density are obtained using a novel method of analysis which assumes that charge collection is dominated by the finite size of the electrostatic sheath. The technique is validated by comparing measurements from a cylindrical and a flush probe which are operated simultaneously in the same plasma.