RESUMO
Herein, we report the effect of using nanoparticles of LiFePO4 on the electrochemical properties of all-solid-state batteries (ASSBs) with a solid electrolyte. LiFePO4 (LFP) cathode materials are promising cathode materials in polymer-based composite solid electrolytes because of their limited electrochemical window range. However, LFP cathodes exhibit poor electric conductivity and sluggish lithium ion diffusion. In addition, there is a disadvantage in that the interfacial resistance increases due to poor contact between the LFP cathode material and the solid electrolyte when composing the composite cathode. The nano-sized LFP cathode material increases the contact area between solid electrolyte in the positive electrode and enhances lithium ion diffusion. Therefore, the structural differences and electrochemical performance of these nanoscale LFP cathode materials in the ASSB were studied by X-ray diffraction, scanning electron microscopy, and electrochemical analysis.
RESUMO
Using two complementary approaches, this study examines the deterioration of the Korean labor market during the first 10 months of the global COVID-19 pandemic. Applying the synthetic control method, we first find that the COVID-19 outbreak has eliminated 1.1 million jobs (4.2% of nonfarm employment) nationwide in April 2020. However, a difference-in-differences approach shows that local variation in COVID-19 intensity, which captures the "regional" effect of the pandemic, explains only 9% of the national shock. The portion of the regional effect remains low until December. This is mainly because the nationwide fear and policies such as social distancing measures also have a "common" effect on local economies. Our findings suggest that the COVID-19 shock may last long in the labor market due to this common effect unless the risk of infection is completely eliminated.
RESUMO
In this study, we evaluated the properties exhibited by a composite solid electrolyte (CSE) prepared via tailoring the particle size of an active filler, Li6.4La3Zr1.4Ta0.6O12 (LLZTO). The average particle size was reduced to 2.53 µm via ball milling and exhibited a specific surface area of 3.013 m2 g-1. Various CSEs were prepared by combining PEO and LLZTO/BM-LLZTO. The calculated lithium ionic conductivity of the BM-LLZTO CSE was 6.0 × 10-5 S cm-1, which was higher than that exhibited by the LLZTO CSE (4.6 × 10-5 S cm-1). This result was confirmed via 7Li nuclear magnetic resonance (NMR) analysis, during which lithium-ion transport pathways varied as a function of the particle size. NMR analysis showed that when BM-LLZTO was used, the migration of Li ions through the interface occurred at a fast rate owing to the small size of the constituent particles. During the Li/CSEs/Li symmetric cell experiment, the BM-LLZTO CSE exhibited lower overvoltage characteristics than the LLZTO CSE. A comparison of the characteristics exhibited by the LFP/CSEs/Li cells confirmed that the cells using BM-LLZTO exhibited high discharge capacity, rate performance, and cycling stability irrespective of the CSE thickness.