Phase evolution during reactive flash sintering of Li6.25Al0.25La3Zr2O12 starting from a chemically prepared powder

Recent advances in in situ and operando characterization techniques for Li7La3Zr2O12-based solid-state lithium batteries

Li₇La₃Zr₂O₁₂ (LLZO)-based solid-state Li batteries (SSLBs) have emerged as one of the most promising energy storage systems due to the potential advantages of solid-state electrolytes (SSEs), such as ionic conductivity, mechanical strength, chemical stability and electrochemical stability. However, there remain several scientific and technical obstacles that need to be tackled before they can be commercialised. The main issues include the degradation and deterioration of SSEs and electrode materials, ambiguity in the Li⁺ migration routes in SSEs, and interface compatibility between SSEs and electrodes during the charging and discharging processes. Using conventional ex situ characterization techniques to unravel the reasons that lead to these adverse results often requires disassembly of the battery after operation. The sample may be contaminated during the disassembly process, resulting in changes in the material properties within the battery. In contrast, in situ/operando characterization techniques can capture dynamic information during cycling, enabling real-time monitoring of batteries. Therefore, in this review, we briefly illustrate the key challenges currently faced by LLZO-based SSLBs, review recent efforts to study LLZO-based SSLBs using various in situ/operando microscopy and spectroscopy techniques, and elaborate on the capabilities and limitations of these in situ/operando techniques. This review paper not only presents the current challenges but also outlines future developmental prospects for the practical implementation of LLZO-based SSLBs. By identifying and addressing the remaining challenges, this review aims to enhance the comprehensive understanding of LLZO-based SSLBs. Additionally, in situ/operando characterization techniques are highlighted as a promising avenue for future research. The findings presented here can serve as a reference for battery research and provide valuable insights for the development of different types of solid-state batteries.

Processing and Properties of Garnet-Type Li7 La3 Zr2 O12 Ceramic Electrolytes

Garnet-type solid electrolyte Li₇ La₃ Zr₂ O₁₂ (LLZO) is widely considered as one of the most promising candidates for solid state batteries (SSBs) owing to its high ionic conductivity and good electrochemical stability. Since its discovery in 2007, great progress has been made in terms of crystal chemistry, chemical and electrochemical properties, and battery application. Nonetheless, reliable and controllable preparation of LLZO ceramics with desirable properties still remains as big challenges. Herein, this review summarizes various synthetic routes of LLZO ceramics and examines the influence of various key processing parameters on the chemical and electrochemical properties. Focusing on correlation of processing parameters and properties, this review aims to provide new insights on a reliable and controllable production of high-quality LLZO ceramic electrolytes for SSB application.

Structural, Vibrational, and Magnetic Characterization of Orthoferrite LaFeO3 Ceramic Prepared by Reaction Flash Sintering

LaFeO₃ perovskite ceramics have been prepared via reaction flash technique using Fe₂O₃ and La₂O₃ as precursors. The obtained pellets have been investigated using several techniques. The formation of LaFeO₃ has been clearly confirmed by X-ray diffraction. The scanning electron microscopy micrographs have shown the microporous character of the obtained pellets due to the low temperature and dwell time used in the synthesis process (10 min at 1173 K). The orthorhombic-rhombohedral phase transition has been observed at approximately 1273 K in differential thermal analysis measurements, which also allows us to determine the Néel temperature at 742 K. The fitted Mössbauer spectra exposed the presence of a single sextet ascribed to the Fe⁺³ ions in the tetrahedral site. Finally, magnetic measurements at room temperature indicate the antiferromagnetic character of the sample.

Developing Preparation Craft Platform for Solid Electrolytes Containing Volatile Components: Experimental Study of Competition between Lithium Loss and Densification in Li7La3Zr2O12

Li7La3Zr2O12 (LLZO) is one of the most promising candidate solid electrolytes for high-safety solid-state batteries. However, similar to other solid electrolytes containing volatile components during high-temperature sintering, the preparation of densified LLZO with high conductivity is challenging involving the complicated gas-liquid-solid sintering mechanism. Further attention on establishing low-cost laborastory-scale preparation craft platform of LLZO ceramic is also required. This work demonstrates a "pellet on gravel" sintering strategy, which is performed in a MgO crucible and box furnace under ambient air without any special equipment or expensive consumables. In addition, the competition between lithium loss from the sintering system and internal grain densification is critically studied, whereas the influences of particle surface energy, Li-loss amount, and initial excess Li2O amount are uncovered. Based on the sintering behavior and mechanism, optimized craft platform for preparing dense LLZO solid electrolytes including mixing, calcination, particle tailoring and sintering is provided. Finally, exemplary Ta-doped LLZO pellets with 2 wt % La2Zr2O7 additives sintered at 1260-1320 °C for 20 min deliver Li+ conductivities of ∼9 × 10-4 S cm-1 at 25 °C, relative densities of >96%, and a dense cross-sectional microstructure. As a practical demonstration, LLZO solid electrolyte with optimized performance is applied in both Li-Li symmetric cells and Li-S batteries. This work sheds light on the practical production of high-quality LLZO ceramics and provides inspiration for sintering ceramics containing volatile compounds.

Flash Sintering Research Perspective: A Bibliometric Analysis

Flash Sintering (FS), a relatively new Field-Assisted Sintering Technique (FAST) for ceramic processing, was proposed for the first time in 2010 by Prof. Rishi Raj’s group from the University of Colorado at Boulder. It quickly grabbed the attention of the scientific community and since then, the field has rapidly evolved, constituting a true milestone in materials processing with the number of publications growing year by year. Moreover, nowadays, there is already a scientific community devoted to FS. In this work, a general picture of the scientific landscape of FS is drawn by bibliometric analysis. The target sources, the most relevant documents, hot and trending topics as well as the social networking of FS are unveiled. A separate bibliometric analysis is also provided for Reaction or Reactive Flash Sintering (RFS), where not only the sintering, but also the synthesis is merged into a single step. To the best of our knowledge, this is the first study of this nature carried out in this field of research and it can constitute a useful tool for researchers to be quickly updated with FS as well as to strategize future research and publishing approaches.