Formation of Diverse Supercrystals from Self-Assembly of a Variety of Polyhedral Gold Nanocrystals

Cubic, rhombic dodecahedral, octahedral, and corner-truncated octahedral gold nanocrystals with sizes of tens of nanometers have been used as building blocks to form micrometer-sized supercrystals by slowly evaporating a water droplet on a substrate placed in a moist environment. Drying the droplet at 90 °C was found to yield the best supercrystals. Supercrystals were evenly distributed throughout the entire substrate surface originally covered by the droplet. Diverse supercrystal morphologies have been observed. Nanocubes formed roughly cubic supercrystals. Rhombic dodecahedra were assembled into truncated triangular pyramidal supercrystals. Rhombic dodecahedral, octahedral, and hexapod-shaped supercrystals were generated through the assembly of octahedra. Corner-truncated octahedra formed tetrapod-shaped supercrystals at room temperature, but octahedral, truncated triangular pyramidal, and square pyramidal supercrystals at 90 °C. Nanocrystal assembly was found to be strongly shape-guided. Expulsion of excess surfactant to the surfaces of supercrystals suggests that responsive adjustment of surfactant concentration during particle assembly mediates supercrystal formation. Transmission X-ray microscopy and optical microscopy have been employed to follow the supercrystal formation process. Surprising rotational water current near the droplet perimeter carrying the initially formed supercrystals has been observed. Supercrystals appear to grow from the edge of the droplet toward the central region. Supercrystals assembled from octahedra inherently contain void spaces and possibly connected channels. The mesoporosity of these supercrystals was confirmed by infiltrating H₂PdCl₄ into the supercrystal interior and reducing the precursor to form Pd nanoparticles. The embedded Pd particles can still catalyze a Suzuki coupling reaction, demonstrating the application of these supercrystals for molecular transport, sensing, and catalysis

Exploring an Interesting Si Source from Photovoltaic Industry Waste and Engineering It as a Li-Ion Battery High-Capacity Anode

Low cost electrode materials are essential for the expansion of the applications of large-format Li-ion batteries (LIBs). Kerf-loss (KL) Si waste from the photovoltaic industry represents a low cost, high-purity Si source for the production of high capacity anodes of LIBs. Producing an energy storage device from solar-panel industry waste is a potential environment-friendly energy development. This study addressed the challenges of employing KL Si as high-capacity LIB anode. The abrasive SiC particle impurities in KL waste powder were used not only as a milling agent to reduce silicon particle size but also as mechanically and electrochemically robust pillars that resist microstructural degradation of the electrode caused by the expansion of Si during lithiation. High energy ball milling of Si with rigid SiC produced fused nanosilicon particles that were supported on micrometer-sized SiC; this resulted in substantially mitigated capacity fading. In addition, an effective conducting network was formed by incorporating Ni into the Si agglomerates, enabling high rate density and maintaining high powder tap density. The resulting Si–SiC–Ni composite powder exhibits high capacity and long-term stability

The Origin of Capacity Fade in the Li₂MnO₃·Li<i>M</i>O₂ (<i>M</i> = Li, Ni, Co, Mn) Microsphere Positive Electrode: An <i>Operando</i> Neutron Diffraction and Transmission X‑ray Microscopy Study

The mechanism of capacity fade of the Li₂MnO₃·Li<i>M</i>O₂ (<i>M</i> = Li, Ni, Co, Mn) composite positive electrode within a full cell was investigated using a combination of <i>operando</i> neutron powder diffraction and transmission X-ray microscopy methods, enabling the phase, crystallographic, and morphological evolution of the material during electrochemical cycling to be understood. The electrode was shown to initially consist of 73(1) wt % <i>R</i>3̅<i>m</i> Li<i>M</i>O₂ with the remaining 27(1) wt % <i>C</i>2/<i>m</i> Li₂MnO₃ likely existing as an intergrowth. Cracking in the Li₂MnO₃·Li<i>M</i>O₂ electrode particle under <i>operando</i> microscopy observation was revealed to be initiated by the solid-solution reaction of the Li<i>M</i>O₂ phase on charge to 4.55 V vs Li⁺/Li and intensified during further charge to 4.7 V vs Li⁺/Li during the concurrent two-phase reaction of the Li<i>M</i>O₂ phase, involving the largest lattice change of any phase, and oxygen evolution from the Li₂MnO₃ phase. Notably, significant healing of the generated cracks in the Li₂MnO₃·Li<i>M</i>O₂ electrode particle occurred during subsequent lithiation on discharge, with this rehealing being principally associated with the solid-solution reaction of the Li<i>M</i>O₂ phase. This work reveals that while it is the reduction of lattice size of electrode phases during charge that results in cracking of the Li₂MnO₃·Li<i>M</i>O₂ electrode particle, with the extent of cracking correlated to the magnitude of the size change, crack healing is possible in the reverse solid-solution reaction occurring during discharge. Importantly, it is the phase separation during the two-phase reaction of the Li<i>M</i>O₂ phase that prevents the complete healing of the electrode particle, leading to pulverization over extended cycling. This work points to the minimization of behavior leading to phase separation, such as two-phase and oxygen evolution, as a key strategy in preventing capacity fade of the electrode

Visualization of Lithium Plating and Stripping via <i>in Operando</i> Transmission X‑ray Microscopy

Lithium dendrite growth dynamics on Cu surface is first visualized through a versatile and facile experimental cell by <i>in operando</i> transmission X-ray microscopy (TXM). Galvanostatic plating and stripping cycle(s) are applied on each cell. Upon plating/stripping at ∼1 mA cm^–2, mossy lithium is clearly found growing and shrinking on the Cu surface as the application time increases. It is interesting to note that the aspect ratio (height/width) of deposited lithium has increased with charge passed during plating, indicating a faster growing from the base. In addition, the dendritic or mossy lithium has also been observed when various high current densities (25, 12.5, and 6.3 mA cm^–2) are applied in different cycles, showing a severe dendritic lithium formation that could be induced by inhomogeneous current distribution. The clear structure of dead lithium is found after the cycling, which also shows a lower efficiency and higher hazard when a higher current density is applied. This work explores TXM as a useful tool for <i>in operando</i> dynamic visualization and quantitative measurement of lithium dendrite, which is difficult to achieve with <i>ex situ</i> measurements and other microscopy techniques. The understanding of the growth mechanism from TXM can be beneficial for the development of safe lithium ion and lithium metal batteries