Solid-state batteries with desirable advantages, including high-energy density, wide temperature tolerance, and fewer safety-concerns, have been considered as a promising energy storage technology to replace organic liquid electrolyte-dominated Li-ion batteries. Solid-state electrolytes (SSEs) as the most critical component in solid-state batteries largely lead the future battery development. Among different types of solid-state electrolytes, garnet-type Li7La3Zr2O12 (LLZO) solid-state electrolytes have particularly high ionic conductivity (10–3 to 10–4 S/cm) and good chemical stability against Li metal, offering a great opportunity for solid-state Li-metal batteries. Since the discovery of garnet-type LLZO in 2007, there has been an increasing interest in the development of garnet-type solid-state electrolytes and all solid-state batteries. Garnet-type electrolyte has been considered one of the most promising and important solid-state electrolytes for batteries with potential benefits in energy density, electrochemical stability, high temperature stability, and safety. In this Review, we will survey recent development of garnet-type LLZO electrolytes with discussions of experimental studies and theoretical results in parallel, LLZO electrolyte synthesis strategies and modifications, stability of garnet solid electrolytes/electrodes, emerging nanostructure designs, degradation mechanisms and mitigations, and battery architectures and integrations. We will also provide a target-oriented research overview of garnet-type LLZO electrolyte and its application in various types of solid-state battery concepts (e.g., Li-ion, Li–S, and Li–air), and we will show opportunities and perspectives as guides for future development of solid electrolytes and solid-state batteries.

Analysed current trends in development of garnet-type structured Li7La3Zr2O12-based oxides as solid electrolytes for next-generation all-solid-state lithium batteries.

Cathodes prepared by infiltration of La 0.6 Sr 0.4 CoO 3Àd (LSC40) into a porous Ce 0.9 Gd 0.1 O 1.95 (CGO10) backbone have been developed for low temperature solid oxide fuel cells. The CGO10 backbone has been prepared by screen printing a CGO10 ink on both sides of a 180 m dense CGO10 electrolyte-tape followed by firing. LSC40 was introduced into the CGO10 porous backbone by multiple infiltrations of aqueous nitrate solutions followed by firing at 350 C. A systematic study of the performance of the cathodes was performed by varying the CGO10 backbone firing temperature, the LSC40 firing temperature and the number of infiltrations. The cathode polarization resistance was measured using electrochemical impedance spectroscopy on symmetrical cells in ambient air, while the resulting structures were characterized by scanning electron microscopy (SEM) and high temperature X-ray diffraction (HT-XRD). The firing temperature of 600 C for the LSC40 infiltrate was found to provide a balance between LSC40 material formation and high surface area micro=nanostructure. The lowest polarization resistances measured at 600 and 400 C were 0.044 and 2.3 X cm 2 in air, respectively. During degradation tests at 600 C, the cathode polarization resistance levels out after about 450 h of testing, giving a final polarization resistance of 0.07 X cm 2 .

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High temperature electrochemical devices, such as solid oxide fuel cells (SOFCs), will play a vital role in the future green and sustainable energy industries due to direct utilization of carbon-based fuels and their ability to couple with renewable energies to convert by-products into valuable fuels using solid oxide electrolysis cells (SOECs). All-solid-state design provides a great opportunity toward the optimization of durability, cost, efficiency and robustness. Electrodes, one of the most important components that facilitate the electrochemical redox reactions, have been actively investigated for several decades to optimize a matrix of chemical composition, microstructure, and performance. Although some mixed ionic electronic conductors (MIECs) can provide electrochemically active surface with excellent chemical tolerance comparing to the composite electrodes made of conventional ceramic electrolyte and metal (cermet), their electrochemical activities may not be high enough to obtain a desirable power, even at moderate temperature operation. This shortage could be improved by engineering the microstructure of the electrodes, which control electrochemically active sites in SOFCs and SOECs. In this article, the current trends in electrode-engineering techniques for advanced SOFCs are reviewed.