RESUMO
Thermal runaway is a major safety concern in the applications of Li-ion batteries, especially in the electric vehicle (EV) market. A key component to mitigate this risk is the separator membrane, a porous polymer film that prevents physical contact between the electrodes. Traditional polyolefin-based separators display significant thermal shrinkage (TS) above 100 °C, which increases the risk of battery failure; hence, suppressing the TS up to 180 °C is critical to enhancing the cell's safety. In this article, we deposited thin-film coatings (less than 10 nm) of aluminum oxide by atomic layer deposition (ALD) on three different types of separator membranes. The deposition conditions and the plasma pretreatment were optimized to decrease the number of ALD cycles necessary to suppress TS without hindering the battery performance for all of the studied separators. A dependency on the separator composition and porosity was found. After 100 ALD cycles, the thermal shrinkage of a 15 µm thick polyethylene membrane with 50% porosity was measured to be below 1% at 180 °C, with ionic conductivity >1 mS/cm. Full battery cycling with NMC532 cathodes demonstrates no hindrance to the battery's rate capability or the capacity retention rate compared to that of bare membranes during the first 100 cycles. These results display the potential of separators functionalized by ALD to enhance battery safety and improve battery performance without increasing the separator thickness and hence preserving excellent volumetric energy.
RESUMO
La comprensión de las relaciones de proporción se analiza de acuerdo con el rendimiento y las estrategias. La muestra se formó con 24 alumnos de quinto de primaria y 24 escolares de segundo de secundaria. La tarea consistió en resolver problemas numéricos e intuitivos de proporciones. Los resultados indican que los alumnos desarrollan más el razonamiento proporcional en los problemas intuitivos. Las estrategias lógicas se usan más en los problemas intuitivos por ambos grupos, mientras que las estrategias intuitivas se manifiestan más en los problemas numéricos en quinto grado y en los problemas intuitivos en segundo de secundaria. Existe una interacción entre el conocimiento formal e intuitivo respecto a las proporciones.
The purpose of this study was to examine understand of proportional relations according to improvement and strategies. Task problem-solving numerics and intuitive proportions were administered to 48 childrens in 5th grade and 8th grade. Results revealed that students developed more proportional reasoning in intuitive problems. Logic strategies were used more in intuitive problems by both groups. Intutive strategies were used more by 5th grade in numeric problems and by 8th in intuitive problems. There were interaction between intuitive and formal knowledge on proportions.
RESUMO
La comprensión de las relaciones de proporción se analiza de acuerdo con el rendimiento y las estrategias. La muestra se formó con 24 alumnos de quinto de primaria y 24 escolares de segundo de secundaria. La tarea consistió en resolver problemas numéricos e intuitivos de proporciones. Los resultados indican que los alumnos desarrollan más el razonamiento proporcional en los problemas intuitivos. Las estrategias lógicas se usan más en los problemas intuitivos por ambos grupos, mientras que las estrategias intuitivas se manifiestan más en los problemas numéricos en quinto grado y en los problemas intuitivos en segundo de secundaria. Existe una interacción entre el conocimiento formal e intuitivo respecto a las proporciones.(AU)
The purpose of this study was to examine understand of proportional relations according to improvement and strategies. Task problem-solving numerics and intuitive proportions were administered to 48 childrens in 5th grade and 8th grade. Results revealed that students developed more proportional reasoning in intuitive problems. Logic strategies were used more in intuitive problems by both groups. Intutive strategies were used more by 5th grade in numeric problems and by 8th in intuitive problems. There were interaction between intuitive and formal knowledge on proportions.(AU)