Search NASA⌕ Search

Engineering topics

Wang, Fan

Publications and source records attributed to Wang, Fan.

Flux Synthesis of A-site Disordered Perovskite La 0.5 M 0.5 TiO 3 (M$=$Li, Na, K) Nanorods Tailored for Solid Composite Electrolytes

Inorganic fillers play an important role in improving the ionic conductivity of solid composite electrolytes (SCEs) for Li-ion batteries. Among inorganic fillers, perovskite-type lithium lanthanum titanate (LLTO) stands out for its high bulk Li + conductivity on the order of 10 -3 S cm -1 at room temperature. According to a literature survey, the optimal LLTO filler should possess the following characteristics: i) a single-crystal structure to minimize grain boundaries; ii) a small particle size to increase the filler/polymer interface area; iii) a 1D morphology for efficient interface channels; and iv) cubic symmetry to facilitate rapid bulk Li + diffusion within the filler. However, the synthesis of single crystal, 1D LLTO nanomaterials with cubic symmetry is challenging. Herein, a flux strategy is developed to synthesize La 0.5 M 0.5 TiO 3 (LMTO, M$=$Li, Na, and K) single-crystal nanorods with an A-site-disordered, cubic perovskite phase. The flux media promotes the oriented growth of nanorods, prevents nanorods from sintering, and provides multiple alkali metal ion doping at M sites to stabilize the cubic phase. SCEs compositing the Li + -conducting LMTO nanorods as fillers and poly[vinylene carbonate- co -lithium sulfonyl(trifluoromethane sulfonyl)imide methacrylate] matrix exhibit more than twice the conductivity of the neat polymer electrolyte (30.6 vs 14.0 µS cm -1 at 303 K).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Percolating Interfacial Layers Enhance Conductivity in Polymer–Composite Electrolytes

Here, this study investigates the impact of the ceramic particle size on the bulk and interfacial ion transport properties of composite polymer electrolytes. The ceramic particles used for this study are micrometer-sized commercial lithium lanthanum titanate (LLTO) powders and LLTO nanorods (NR) prepared in the laboratory. The polymer matrices are vinylene carbonate (VEC) based single-ion-conducting (SIC) and dual-ion-conducting (DIC) polymer electrolytes. Our results reveal that the addition of LLTO NR results in improved ion transport, while the addition of commercial LLTO is ineffective or even detrimental. We ascribe these results to the formation of an interfacial polymer layer around the LLTO particles with enhanced Li + mobility and estimate the thickness of the interfacial layer to be ∼5 nm. The high surface-to-volume ratio of the LLTO NR leads to the percolation of the interfacial region at a relatively low ceramic loading of 30 wt %. This study highlights the importance of achieving percolation of the interface region (as opposed to the particles themselves) within the composite electrolyte when the interfacial layer is the enhancement mechanism.

Ock, Ji-young↗

In Situ and Operando Observation of Zinc Moss Growth and Dissolution in Alkaline Electrolyte for Zinc–Air Batteries

As a promising battery technology, zinc–air batteries still face significant challenges, including the formation of a mossy structure on the zinc metal anode in alkaline electrolyte. Because a similar phenomenon also plagues lithium and sodium metal batteries, elucidating its mechanism has important implications for progress in energy storage. Herein, operando X-ray nanotomography was employed to visualize zinc moss growth and dissolution at the individual colony level. By tracking its microstructure evolution, zinc moss was found to display irreversible plating/stripping behavior. While zinc moss exhibits self-limiting growth and zinc deposition occurs mainly in its outer region, zinc dissolution is more uniformly distributed inside the moss colony upon stripping, leading to the formation of “dead” zinc and capacity loss. A direct correlation is established between the moss amount and zinc plating/stripping efficiency. Finally, results from this study offer new insights into mitigating the unstable zinc plating morphology and improving the cycle life of aqueous zinc–air batteries.

36 MATERIALS SCIENCE↗

Decadal Thermal Variability of the Upper Southern Ocean: Zonal Asymmetry

Abstract As the major sink of anthropogenic heat, the Southern Ocean has shown quasi-symmetric, deep-reaching warming since the mid-twentieth century. In comparison, the shorter-term heat storage pattern of the Southern Ocean is more complex and has notable impacts on regional climate and marine ecosystems. By analyzing observational datasets and climate model simulations, this study reveals that the Southern Ocean exhibits prominent decadal (>8 years) variability extending to ∼700-m depth and is characterized by out-of-phase changes in the Pacific and Atlantic–Indian Ocean sectors. Changes in the Pacific sector are larger in magnitude than those in the Atlantic–Indian Ocean sectors and dominate the total heat storage of the Southern Ocean on decadal time scales. Instead of heat uptake through surface heat fluxes, these asymmetric variations arise primarily from wind-driven heat redistribution. Pacemaker and preindustrial simulations of the Community Earth System Model version 1 (CESM1) suggest that these variations in Southern Ocean winds arise primarily from natural variability of the tropical Pacific, as represented by the interdecadal Pacific oscillation (IPO). Through atmospheric teleconnection, the positive phase of the IPO gives rise to higher-than-normal sea level pressure and anticyclonic wind anomalies in the 50°–70°S band of the Pacific sector. These winds lead to warming of 0–700 m by driving the convergence of warm water. The opposite processes, involving cyclonic winds and upper-layer divergence, occur in the Atlantic–Indian Ocean sector. These findings aid our understanding of the time-varying heat storage of the Southern Ocean and provide useful implications on initialized decadal climate prediction.

Meteorology & Atmospheric Sciences↗