Grain
boundary (GB) structure is a critical parameter that significantly
affects the macroscopic properties of materials; however, the evaluation
of GB characteristics by modern analytical methods remains an extremely
challenging task. In this work, Li+ conductivity degradation
at the GBs of cubic Li7La3Zr2O12 (LLZO) with a garnet framework (which represents the most
promising candidate material for solid electrolytes utilized in all-solid-state
batteries) has been investigated by various molecular dynamics approaches
combined with newly developed analytical techniques. It was found
that the transboundary diffusion of Li ions was generally slower than
their diffusion in the bulk regardless of the GB symmetry; however,
this effect strongly depended on the concentration of Li-deficient
sites (trapping Li vacancies) in the GB layer. Furthermore, the compactness
and density of the combined GB regions represent the key parameters
affecting the overall Li+ conductivity of polycrystalline
LLZO films.
High-quality, idiomorphic, single-phase Li5La3Nb2O12 crystals were successfully
grown using
a LiOH flux cooling method at the relatively low temperature of 500
°C at a solute concentration of 5 mol %. The grown Li5La3Nb2O12 crystals had polyhedral
shapes with well-developed, flat {211} and {110} faces. Their shapes
were relatively uniform, and the average crystal size was approximately
59.2 μm. No aggregation was observed in scanning electron microscopy
images. The high crystallinity of the Li5La3Nb2O12 crystals was confirmed by transmission
electron microscopy images. Their lattice parameter was determined
from the X-ray diffraction pattern to be a = 1.281
nm, which is consistent with the literature value (a = 1.282 nm). Furthermore, the crystal phase, form, size, and crystallinity
of the flux-grown Li5La3Nb2O12 crystals were obviously dependent on the growth conditions
including the solute concentration and holding temperature.
Hollow-structured LiMn 2 O 4 crystals are grown in molten KCl (flux) for the first time via an oxidation reaction of metallic Mn followed by a lithiation reaction. Characterization of the formation process, which is achieved using thermogravimetric differential thermal analysis, X-ray diffraction, and scanning electron microscopy observation, reveals that the hollow structures are formed via a mechanism analogous to the microscale Kirkendall effect, which results from the difference between the solid-state diffusion rates of the core materials and the rate of O 2 diffusion through the shell at elevated temperatures occurring during oxidation. Interestingly, the development of well-defined crystal facets is observed on the surfaces of the LiMn 2 O 4 crystals, implying that the crystal growth is driven by supersaturation in the same manner as the flux growth. We also examine two possible approaches to reduce the volume of the inner space in the crystal: crystal growth under O 2 flow for enhancement of the O 2 diffusion and insertion of a Co and Ni layer between Mn and the substrate to induce the formation of the LiNi 1/3 Co 1/3 Mn 1/3 O 2 phase.
We demonstrate a new way to prepare hollow-structured LiCoO2 crystals directly on a Pt substrate for the first time through a combination of semi-additive electrodeposition of a Co core and subsequent flux growth in molten LiNO3.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.