Highly improved thermal stability of the ceramic coating layer on the polyethylene separator via chemical crosslinking between ceramic particles and polymeric binders

The ceramic coating layer (CCL) on a polyolefin separator plays a pivotal role in securing the safety of lithium-ion batteries (LIBs) by suppressing the thermal shrinkage of the separator even under abnormal circumstances. However, an additional CCL inevitably leads to energy density loss and electrochemical performance degradation. To mitigate these weaknesses, we designed a new chemical crosslinking between ceramic particles and polymeric binders to minimize the thickness of the CCL while maintaining its thermal stability. For this purpose, a polydopamine (PD) nanolayer is preliminarily introduced on the surface of ceramic particles using a simple solution polymerization method. Then, a poly(acrylic acid) binder, which can react with the amine groups in the PD, is chosen for the aqueous ceramic coating slurry. Thus, this combination can create a number of crosslinking points within the CCL, which leads to higher adhesion within the CCL after electrolyte impregnation. As a result, the crosslinked PD ceramic-coated separator (xPD-CCS) can maintain its original dimension even at 160 °C for 1 h with a 9-μm polyethylene base film. In addition, a full cell (LiNi_0.8Co_0.1Mn_0.1O₂/graphite) with the xPD-CCS can show a comparable cycle performance (capacity retention of 89.2% after 400 cycles) to those of bare polyethylene and non-crosslinked PD-CCS cases.