Polymer-in-ceramic flexible separators for Li-ion batteries

A separator between a battery’s anode and cathode is crucial to isolate the electrodes and prevent an electrical short circuit. Separators in Li-ion batteries are generally made of polyolefins, such as polyethylene (PE) and polypropylene (PP). However, the relatively low thermal stability and mechanical strength of polyolefin-based separators have raised safety concerns, especially when overheating occurs. Ceramic coatings, for instance, Al2O3 and ZrO2, have been applied to improve the thermal and mechanical properties of polyolefin separators. Here, we developed Al2O3 and Li7La3Zr2O12 (LLZO)-based polymer-in-ceramic membranes and studied their porosity, thermal stability, electrolyte wettability, and ionic conductivity as Li-ion battery separators. In particular, the polymer-in-LLZO separator showed higher thermal stability, higher ionic conductivity, and better wettability with the 1 M LiPF6/EC: DEC (1:1) electrolyte than the commercial PP separator Celgard 2400. The performance of the polymer-in-LLZO separator was also evaluated in a Li|NCM811 cell with the 1 M LiPF6/EC: DEC (1:1) electrolyte.