Zeolite coated polypropylene separators with tunable surface properties for lithium-ion batteries

The separator is a critical component in liquid electrolyte batteries, and closely related to the battery performance such as cycle number and safety. In this work, thin (∼2 μm) films of MFI zeolite with different Si/Al ratios are coated on both sides of the commercial polypropylene separator for lithium ion batteries. The electrolyte solvent wettability of the MFI zeolite coated separators decreases with increasing Si/Al ratio of the zeolite films. Polypropylene separator coated with MFI zeolite (Si/Al = 25) film (ZCPP25) shows very high wettability for electrolyte. The Li4Ti5O12/Li cell with ZCPP25 separator exhibits best charge and discharge performance among the cells with pure or coated polypropylene separators. Under relatively high current rate, the cell with MFI zeolite coated separator shows better charge and discharge capacities and cycling stability than that of uncoated polypropylene separator. The cell with MFI zeolite coated separator also performs better than the cell with uncoated polypropylene separator in a wider temperature range. The enhanced performance for cells with MFI zeolite coated separator is caused by the better filling of the electrolyte at the separator/electrode interface due to the improved electrolyte solvent wettability.