In Situ TEM Observation of (Cr, Mn, Fe, Co, and Ni)3 O4 High-Entropy Spinel Oxide Formation During Calcination at Atomic Scale.

High-entropy oxides (HEOs) are promising anode materials for lithium-ion batteries (LIBs), owing to their stable crystal structure, superionic conductivity, and high capacity. In this study, the (Cr, Mn, Fe, Co, and Ni)3 O4 HEO via solid-state reaction is prepared. To improve the synthetic efficiency, it is necessary to understand the formation mechanism. Therefore, a high-resolution transmission electron microscopy (HRTEM) is used to record information during calcination at increasing temperature. The overall formation process included MnO2 and NiO aggregation at 500 °C, followed by (Mn, and Ni)3 O4 combined with Co3 O4 at 600 °C to form (Mn, Co, and Ni)3 O4 . At higher temperatures, Fe2 O3 and Cr2 O3 sequentially combined with (Mn, Co, and Ni)3 O4 and formed the (Cr, Mn, Fe, Co, Ni)3 O4 at 900 °C. In addition, the valence-state-changing mechanisms and ion arrangements of (Cr, Mn, Fe, Co, and Ni)3 O4 are determined using electron energy loss spectroscopy (EELS) and extended X-ray absorption fine structure (EXAFS). This study successfully revealed the formation of HEO at atomic scale. The results provide valuable insights for improving the manufacturing process of (Cr, Mn, Fe, Co, and Ni)3 O4 HEOs, which is expected to play a vital role in the development of anode materials for next-generation LIBs.

All-Solid-State Garnet-Based Lithium Batteries at Work-In Operando TEM Investigations of Delithiation/Lithiation Process and Capacity Degradation Mechanism.

Li7 La3 Zr2 O12 (LLZO)-based all-solid-state Li batteries (SSLBs) are very attractive next-generation energy storage devices owing to their potential for achieving enhanced safety and improved energy density. However, the rigid nature of the ceramics challenges the SSLB fabrication and the afterward interfacial stability during electrochemical cycling. Here, a promising LLZO-based SSLB with a high areal capacity and stable cycle performance over 100 cycles is demonstrated. In operando transmission electron microscopy (TEM) is used for successfully demonstrating and investigating the delithiation/lithiation process and understanding the capacity degradation mechanism of the SSLB on an atomic scale. Other than the interfacial delamination between LLZO and LiCoO2 (LCO) owing to the stress evolvement during electrochemical cycling, oxygen deficiency of LCO not only causes microcrack formation in LCO but also partially decomposes LCO into metallic Co and is suggested to contribute to the capacity degradation based on the atomic-scale insights. When discharging the SSLB to a voltage of ≈1.2 versus Li/Li+ , severe capacity fading from the irreversible decomposition of LCO into metallic Co and Li2 O is observed under in operando TEM. These observations reveal the capacity degradation mechanisms of the LLZO-based SSLB, which provides important information for future LLZO-based SSLB developments.

Atomic Imaging and Thermally Induced Dynamic Structural Evolution of Two-Dimensional Cr2S3.

In this study, facile salt-assisted chemical vapor deposition (CVD) was used to synthesize ultrathin non-van der Waals chromium sulfide (Cr2S3) with a thickness of ∼1.9 nm. The structural transformation of as-grown Cr2S3 was studied using advanced in situ heating techniques combined with transmission electron microscopy (TEM). Two-dimensional (2D) and quasi-one-dimensional (1D) samples were fabricated to investigate the connection between specific planes and the dynamic behavior of the structural variation. The rearrangement of atoms during the phase transition was driven by the loss of sulfur atoms at elevated temperatures, resulting in increased free energy. A decrease in the ratio of the (001) plane led to an overall increase in surface energy, thus lowering the critical phase transition temperature. Our study provides detailed insight into the mechanism of structural transformation and the critical factors governing transition temperature, thus paving the way for future studies on intriguing Cr-S compounds.