Search for: All records

Rechargeable batteries are crucial for energy storage across consumer electronics and automobile propulsion applications, facilitating the transition towards carbon neutrality and advancing clean energy technologies. Despite great success of Li-ion batteries (LIBs) in the commercial market, alternative technologies based on beyond-Li chemistry are highly demanded for large-scale and power-intensive applications necessitating enhanced energy density, lifetime, and safety, where fundamental understanding of the structure-property relationship of novel battery materials is critically needed. Transmission electron microscopy (TEM) is an indispensable method to characterize materials structures and compositions at the atomic scale, which is of particular importance for battery research to investigate crystal lattices, defects, as well as microstructural and chemical heterogeneities within materials used in electrodes, electrolytes, and their interfaces. Further, with rapid technical development, in-situ TEM has enabled real-time observations of various dynamical phenomena and chemical processes during battery cycling and phase transformations. Leveraging advanced in-situ TEM techniques, our collaborative endeavors with Dr. Marca Doeff have enabled us to conduct comparative analyses of Li and Na reactions within battery electrodes, offering unique insights into in early-stage beyond-Li chemistry. Herein, we present a systematic exploration of in-situ TEM studies for LIBs and beyond, focusing on electrode materials through intercalation, alloying, and conversion reaction mechanisms. By direct comparison between electrochemical reactions with Li and Na, we found substantial differences in reaction mechanisms, pathways, and kinetics between lithiation and sodiation processes, which are fundamentally related to various factors, such as ionic diffusion barrier, electrochemically induced stress, and geometric constraints. This concept has been demonstrated in multiple case studies that allows us to enhance the sodiation kinetics by tuning the overall reaction energetics through nanostructure optimization and interfacial engineering. We envision that the knowledge learned from in-situ TEM will provide valuable insights into understanding the alkali-ion electrochemistry and kinetics, thereby serving as foundational principles guiding the advancement of beyond Li-ion battery technologies. 

Abstract The creation of metal‐metal oxide interfaces is an important approach to fine‐tuning catalyst properties through strong interfacial interactions. This article presents the work on developing interfaces between Pt and CeO_xthat improve Pt surface energetics for the hydrogen evolution reaction (HER) within an alkaline electrolyte. The Pt‐CeO_xinterfaces are formed by depositing size‐controlled Pt nanoparticles onto a carbon support already coated with ultrathin CeO_xnanosheets. This interface structure facilitates substantial electron transfer from Pt to CeO_x, resulting in decreased hydrogen binding energies on Pt surfaces, and water dissociation for the HER, as predicted by the density functional theory (DFT) calculations. Electrochemical testing indicates that both Pt specific activity and mass activity are improved by a factor of 2 to 3 following the formation of Pt‐CeO_xinterfaces. This study underscores the significance and potential of harnessing robust interfacial effects to enhance electrocatalytic reactions. 

Surface-assisted, tile-based DNA self-assembly is a powerful method to construct large, two-dimensional (2D) nanoarrays. To further increase the structural complexity, one idea is to incorporate different types of tiles into one assembly system. However, different tiles have different adsorption strengths to the solid surface. The differential adsorptions make it difficult to control the effective molar ratio between different DNA tile concentrations on the solid surface, leading to assembly failure. Herein, we propose a solution to this problem by engineering the tiles with comparable molecular weights while maintaining their architectures. As a demonstration, we have applied this strategy to successfully assemble binary DNA 2D arrays out of very different tiles. We expect that this strategy would facilitate assembly of other complicated nanostructures as well. 

Abstract Garnet‐type Li₇La₃Zr₂O₁₂(LLZO) solid‐state electrolytes hold great promise for the next‐generation all‐solid‐state batteries. An in‐depth understanding of the phase transformation during synthetic processes is required for better control of the crystallinity and improvement of the ionic conductivity of LLZO. Herein, the phase transformation pathways and the associated surface amorphization are comparatively investigated during the sol–gel and solid‐state syntheses of LLZO using in situ heating transmission electron microscopy (TEM). The combined ex situ X‐ray diffraction and in situ TEM techniques are used to reveal two distinct phase transformation pathways (precursors → La₂Zr₂O₇ → LLZO and precursors → LLZO) and the subsequent layer‐by‐layer crystal growth of LLZO on the atomic scale. It is also demonstrated that the surface amorphization surrounding the LLZO crystals is sensitive to the postsynthesis cooling rate and significantly affects the ionic conductivity of pelletized LLZO. This work brings up a critical but often overlooked issue that may greatly exacerbate the Li‐ion conductivity by undesired synthetic conditions, which can be leveraged to ameliorate the overall crystallinity to improve the electrochemical performance of LLZO. These findings also shed light on the significance of optimizing surface structure to ensure superior performance of Li‐ion conductors.