We introduce a new type of liquid cell for in-situ electron microscopy based upon entrapment of a liquid film between layers of graphene. We employ this cell to achieve high-resolution imaging of colloidal platinum nanocrystal growth. The ability to directly image and resolve critical steps at atomic resolution provides new insights into nanocrystal coalescence and reshaping during growth.

The precipitation and dissolution of water-soluble minerals in aqueous systems is a familiar process occurring commonly in nature. Understanding mineral nucleation and growth during its precipitation is highly desirable, but past in situ techniques have suffered from limited spatial and temporal resolution. Here, by using in situ graphene liquid cell electron microscopy, mineral nucleation and growth processes are demonstrated in high spatial and temporal resolution. We precipitate the mineral thenardite (Na2SO4) from aqueous solution with electron-beam-induced radiolysis of water. We demonstrate that minerals nucleate with a two-dimensional island structure on the graphene surfaces. We further reveal that mineral grains grow by grain boundary migration and grain rotation. Our findings provide a direct observation of the dynamics of crystal growth from ionic solutions.

The ambient-temperature rechargeable lithium/sulfur (Li/S) cell is a strong candidate for the beyond lithium ion cell since significant progress on developing advanced sulfur electrodes with high sulfur loading has been made. Here we report on a new sulfur electrode active material consisting of a cetyltrimethylammonium bromide-modified sulfur-graphene oxide-carbon nanotube (S-GO-CTA-CNT) nanocomposite prepared by freeze-drying. We show the real-time formation of nanocrystalline lithium sulfide (Li2S) at the interface between the S-GO-CTA-CNT nanocomposite and the liquid electrolyte by in situ TEM observation of the reaction. The combination of GO and CNT helps to maintain the structural integrity of the S-GO-CTA-CNT nanocomposite during lithiation/delithiation. A high S loading (11.1 mgS/cm2, 75% S) S-GO-CTA-CNT electrode was successfully prepared using a three-dimensional structured Al foam as a substrate and showed good S utilization (1128 mAh/g S corresponding to 12.5 mAh/cm2), even with a very low electrolyte to sulfur weight ratio of 4. Moreover, it was demonstrated that the ionic liquid in the electrolyte improves the Coulombic efficiency and stabilizes the morphology of the Li metal anode.

This article reviews the advancements and prospects of liquid cell transmission electron microscopy (TEM) imaging and analysis methods in understanding the nucleation, growth, etching, and assembly dynamics of nanocrystals. The bonding of atoms into nanoscale crystallites produces materials with nonadditive properties unique to their size and geometry. The recent application of in situ liquid cell TEM to nanocrystal development has initiated a paradigm shift, (1) from trial-And-error synthesis to a mechanistic understanding of the synthetic reactions responsible for the emergence of crystallites from a disordered soup of reactive species (e.g., ions, atoms, molecules) and shape-defined growth or etching; and (2)A from post-processing characterization of the nanocrystals' superlattice assemblies to inA situ imaging and mapping of the fundamental interactions and energy landscape governing their collective phase behaviors. Imaging nanocrystal formation and assembly processes on the single-particle level in solution immediately impacts many existing fields, including materials science, nanochemistry, colloidal science, biology, environmental science, electrochemistry, mineralization, soft condensed-matter physics, and device fabrication.