Development of Moisture Absorbent Ceramic-Coated Separators for Advanced Lithium-Ion Batteries

Abstract

In the present human life, various electric devices and machines are worked by lithium-ion batteries (LIBs). The batteries have still remained challenges such as, the low cycling stability due to side reactions during charge-discharge cycling and the weak thermal stability at high temperatures. Accordingly, research on improving resistance to high temperatures and impregnability by coating ceramic particles and polymer binders on the surface of the separator is being conducted. The ceramic coating separator is manufactured by connecting small-sized inorganic particles to each other using a small amount of binder. The inorganic particles have high hydrophilicity and high specific surface area, so the ceramic separator has excellent wettability to the electrolyte. As a ceramic coating, alumina is currently commercialized, and a slurry is prepared by mixing a binder, etc., and then coated on a separator and then dried. LG Energy Solutions has commercialized a ceramic composite separator called SRS (Safety-reinforcing separator) and is applying it to batteries. By introducing a ceramic layer on the surface of a polyolefin-based separator, the heat resistance and mechanical strength of the separator have been greatly improved, and it has been widely used in high-capacity and large-sized batteries. when the temperature of the LIBs rises and the separator shrinks or ruptures, a large amount of lithium ions may move, making control difficult and creating a risk of explosion. Therefore, shutdown occurs, but a separator with good shape retention at high temperature is required. Accordingly, research on improving resistance to high temperatures by coating ceramic particles and a polymer binder on the surface of the separator is being conducted. In this work, Ceramic-coated separator membrane film was fabricated using aluminum fluoride (AlF3) materials for a powerful moisture (H2O) scavenger. Accordingly, research on improving high temperature resistance and impregnation property by coating ceramic particles and a polymer binder on the surface of the separator is in progress. First of all, a-AlF₃ nanorods with an average length of 1.882 μm and a diameter of 320 nm were synthesized under low supersaturation conditions. Then, PVdF-HFP [Poly(vinylidene fluoride-co-hexafluoropropylene)]-acetone solution was mixed and coated on a polypropylene membrane. The AlF₃-coated separator exhibited thermal shrinkage of 4%, 8%, and 18% at 130, 140, and 150°C, respectively, confirming that thermal stability was improved. In addition, as a result of the impregnation test, it was confirmed that the impregnation property of the coated separator was improved compared to the existing polypropylene separator. In addition, it was confirmed that the full cell manufactured using the a-AlF₃-coated membrane film has improved cycle stability and high-speed, high-capacity compared to the full cell manufactured using the existing non-coated separator.