Enhancing Thermal Stability of Lithium-Ion Battery Separators with Sub-Micron Boehmite Coating

Recently, lithium-ion batteries have been increasingly used as energy sources for electric vehicles, and research has highlighted the need to improve the stability of these batteries. In this study, we propose a novel inorganic coating method that utilizes sub-micron boehmite particles as coating agents to enhance the thermal and mechanical stability of the battery separator. Sub-micron-sized boehmite was synthesized via hydrothermal synthesis, with the addition of a specific amount of finely pulverized crystalline boehmite as an additive. And then, porous polyolefin separator was made of 14 um thick fabric using a pilot film forming process. The coating slurry was made using an aqueous binder and was coated to a thickness of 4 um on one side of the separator. The direct effect of the boehmite coating layer on the improvement of thermal stability was evaluated by comparing the shrinkage behavior before and after the thermal stability test. Electrochemical characteristic analysis was performed using a pouch-type cell, with graphite as an anode and NCM as a cathode. After 100 cycles of charging and discharging at 1C, the capacity maintenance was about 98%, and the rate capability was 76% compared to 0.1C and 2C capability. In particular, the 0.1C capacity measured after 2 weeks in a 60°C oven showed excellent thermal stability with a retention rate of about 100%.