Study of Improving the Thermal Stability of Ceramic Coated Separator Via Chemical Crosslinking between Ceramic Particles and Polymeric Binders

Lithium-ion batteries (LIBs) are used in everyday applications such as portable electronics and electric vehicles (EVs) in our daily life. In large-scale batteries such as EVs, high energy density has been developed to secure longer mileage with one charge. Securing battery safety becomes extremely challenging as densifying the cell energy and increasing the battery. The safety of batteries must be guaranteed from the cell to the module, the pack, and the system, and it must not be ignored at every step. The separator is highlighted at the cell level as it plays an essential part in safety. To guarantee the safety of large-scale LIBs, it is essential to employ a ceramic-coated separator (CCS). To secure thermal stability using CCSs, the certain thickness of ceramic coating layer (CCL) is required. In contrast, the thicker CCL can act as a resistive layer in the cell, and in the worst case, the ceramic that has fallen off the CCS surface can act as a side reactant in the cell. However, if the CCL is thin, the desired thermal stability may not be obtained. The key technology is to improve adhesion while reducing the thickness of the CCL. For this purpose, polydopamine nano layer is preliminary introduced on the surface of ceramic particles via simple solution polymerization. Then, poly(acrylic acid) binder, which can react with amine groups in polydopamine, is chosen for aqueous ceramic coating slurry. Thus, this combination can make several crosslinking points within CCL, which lead to higher adhesion within the CCL after electrolyte impregnation. As a result, the adhesion within the CCL of cross-linked CCS is increased by 70% compared to the non-crosslinked CCS. Furthermore, the adhesion does not decrease when impregnated with the electrolyte. Also, cross-linked CCS showed better shrinkage property than commercialized CCS with the same composition because the cross-linked CCS did not shrink even when exposed for 1 hour at a high temperature of 160 °C. From this study, with crosslinking reaction within coating layer, it is possible to improving heat resistance and physical properties of separator without increasing thickness of CCL.