Highlights: Further performance improvements of sodium-ion batteries require better-performing electrode materials, particularly anodes. The layered lepidocrocite-type sodium titanate (Na0.74Ti1.815□0.185O4·1.27H2O), showing a high Na+ storage capacity of 229 mAh g−1 at relatively low average voltage of ca. 0.6 V vs. Na+/Na, is a promising candidate anode material. Abstract: A lepidocrocite-structured sodium titanate prepared by ion-exchange of a Cs-containing precursor shows promise as an anode material for sodium ion batteries, with a discharge capacity of up to 229 mAh g−1 at an average potential of about 0.6 V vs. Na+/Na. Titanium vacancies in the metal oxide layers provide additional sites for sodium intercalation in addition to interlayer sites, which accounts for the higher capacity compared to other previously reported lepidocrocite-structured titanates. By screening a series of electrolyte formulations and binders, we were able to improve the first-cycle coulombic efficiency to 81.8% and 94.7% respectively using CMC/SBR-based and binder-free electrodes in ether electrolytes. The electrochemical consequences of short-term air-exposure on the electrodes are also discussed. Graphic abstract: [Figure not available: see fulltext.]

Unveiling materials corrosion pathways is significant for understanding the corrosion mechanisms and designing corrosion-resistant materials. Here, we investigate the corrosion behavior of Sn@Ni3Sn4 and Sn nanocrystals in an aqueous solution in real time by using high-resolution liquid cell transmission electron microscopy. Our direct observation reveals an unprecedented level of detail on the corrosion of Sn metal with/without a coating of Ni3Sn4 at the nanometric and atomic levels. The Sn@Ni3Sn4 nanocrystals exhibit pitting corrosion, which is initiated at the defect sites in the Ni3Sn4 protective layer. The early stage isotropic etching transforms into facet-dependent etching, resulting in a cavity terminated with low-index facets. The Sn nanocrystals under fast etching kinetics show uniform corrosion, and smooth surfaces are obtained. Sn nanocrystals show creeping-like etching behavior and rough surfaces. This study provides critical insights into the impacts of coating, defects, and ion diffusion on corrosion kinetics and the resulting morphologies.

We have developed a facile procedure that can create asymmetrical building blocks by uniformly deforming nanospheres into C(∞v) symmetry at low cost and high quality. Concave polystyrene@carbon (PS@C) core-shell nanospheres were produced by a very simple microwave-assisted alcohol thermal treatment of spherical PS@C nanoparticles. The dimensions and ratio of the concave part can be precisely controlled by temperature and solvents. The concavity is created by varying the alcohol-thermal treatment to tune the swelling properties that lead to the mechanical deformation of the PS@C core-shell structure. The driving force is attributed to the significant volume increase that occurs upon polystyrene core swelling with the incorporation of solvent. We propose a mechanism adapted from published models for the depression of soft capsules. An extrapolation from this model predicts that the rigid shell is used to generate a cavity in the unbuckled shell, which is experimentally confirmed. This swelling and deformation route is flexible and should be applicable to other polymeric nanoparticles to produce asymmetrical nanoparticles.

Sodium titanate anodes synthesized via “chimie-douce” methods generally require a post-synthesis dehydration step. Their crystal structures are sensitive to the heating conditions such as temperature, resulting in distinct sodium storage performance. Herein, using in situ and ex situ high-temperature X-ray diffraction, we studied in detail the structural changes of Na0.74Ti1.815□0.185O4·1.27H2O (NTO) under various heating conditions. Electrochemical characterization revealed that NTOs heated at lower temperatures with layered structures deliver larger capacities than those heated at high temperatures with tunnel structures. Heat treatment at moderate temperatures greatly improves the capacity retention of NTO, especially stabilizing the high voltage processes that are major contributors to the capacity fading, because of the modified crystal structure and surface chemistry. Our findings suggest that post-synthesis heating is a simple and effective strategy to tailor the crystal structure, surface chemistry, and electrochemical properties of sodium titanate anodes.

Oriented attachment of nanocrystals is an important route to constructing epitaxially-connected nanocrystal superlattices for various applications. During oriented attachment of semiconductor nanocrystals, neck can be formed between nanocrystals and it strongly influences the properties of the resulting superlattice. However, the neck formation mechanism is poorly understood. Here, we use in situ liquid cell transmission electron microscopy to directly observe the initiation and growth of homoepitaxial necks between PbSe nanocrystals with atomic details. We find that neck initiation occurs slowly (~ 10 s) when two nanocrystals approach to each other within an edge-to-edge distance of 0.6 nm. During neck initiation, Pb and Se atoms defuse from other facets into the gap, forming “dynamic reversible” filaments. Once the filament (neck) width is larger than a critical size of 0.9 nm, it gradually (15 s) widens into a 3-nm-wide neck. The atomic structure of the neck is further obtained using ex situ aberration-corrected scanning TEM imaging. Neck initiation and growth mechanisms are elucidated with density functional theory calculations. Our direct unveiling of the atomic pathways of neck formation during oriented attachment shed light into the fabrication of nanocrystal superlattices with improved structural order and electronic properties. [Figure not available: see fulltext.].

The behavior of individual nanocrystals during superlattice phase transitions can profoundly affect the structural perfection and electronic properties of the resulting superlattices. However, details of nanocrystal morphological changes during superlattice phase transitions are largely unknown due to the lack of direct observation. Here, we report the dynamic deformability of PbSe semiconductor nanocrystals during superlattice phase transitions that are driven by ligand displacement. Real-time high-resolution imaging with liquid-phase transmission electron microscopy reveals that following ligand removal, the individual PbSe nanocrystals experience drastic directional shape deformation when the spacing between nanocrystals reaches 2 to 4 nm. The deformation can be completely recovered when two nanocrystals move apart or it can be retained when they attach. The large deformation, which is responsible for the structural defects in the epitaxially fused nanocrystal superlattice, may arise from internanocrystal dipole-dipole interactions.

Prediction from the dual-phase nature of superionic conductors-both solid and liquid-like-is that mobile ions in the material may experience reversible extraction-reinsertion by an external electric field. However, this type of pseudoelectroelasticity has not been confirmed in situ, and no details on the microscopic mechanism are known. Here, we in situ monitor the pseudoelectroelasticity of monocrystalline Cu₂S nanowires (NWs) using transmission electron microscopy (TEM). Specifically, we reveal the atomic scale details including phase transformation, migration and redox reactions of Cu⁺ ions, nucleation, growth, as well as spontaneous shrinking of Cu protrusion. Caterpillar-diffusion-dominated deformation is confirmed by the high-resolution transmission electron microscopy (HRTEM) observation and  ab initio calculation, which can be driven by either an external electric field or chemical potential difference. The observed spring-like behavior was creatively adopted for electric nanoactuators. Our findings are crucial to elucidate the mechanism of pseudoelectroelasticity and could potentially stimulate in-depth research into electrochemical and nanoelectromechanical systems.

Metal-organic layers (MOLs) are highly attractive for application in catalysis, separation, sensing and biomedicine, owing to their tunable framework structure. However, it is challenging to obtain comprehensive information about the formation and local structures of MOLs using standard electron microscopy methods due to serious damage under electron beam irradiation. Here, we investigate the growth processes and local structures of MOLs utilizing a combination of liquid-phase transmission electron microscopy, cryogenic electron microscopy and electron ptychography. Our results show a multistep formation process, where precursor clusters first form in solution, then they are complexed with ligands to form non-crystalline solids, followed by the arrangement of the cluster-ligand complex into crystalline sheets, with additional possible growth by the addition of clusters to surface edges. Moreover, high-resolution imaging allows us to identify missing clusters, dislocations, loop and flat surface terminations and ligand connectors in the MOLs. Our observations provide insights into controllable MOL crystal morphology, defect engineering, and surface modification, thus assisting novel MOL design and synthesis.

We report an investigation of the pseudo-photocatalytic behavior of rutile TiO2 nanorods for water splitting observed with liquid cell transmission electron microscopy (TEM). The electron beam serves as a “light” source to initiate the catalytic reaction and a “water-in-salt” aqueous solution is employed as the electrolyte. The observation reveals that bubbles are generated preferentially residing near the {110} facet of a rutile TiO2 nanorod under a low electron dose rate (9.3–18.6 e-/Å2·s). These bubbles are ascribed to hydrogen gas generated from the pseudo-photocatalytic water splitting. As the electron beam current density increases to 93 e-/Å2 ·s, bubbles are also found at the {001} and {111} facets as well as in the bulk liquid solution, demonstrating the dominant effects of water electrolysis by electron beam under higher dose rates. The facet-dependent pseudo-photocatalytic behavior of rutile TiO2 nanorods is further validated using density functional theory (DFT)calculation. Our work establishes a facile liquid cell TEM setup for the study of pseudo-photocatalytic water splitting and it may also be applied to investigation of other photo-activated phenomena occurring at the solid-liquid interfaces.