Optimization polypropylene separator by ultrathin Ti0.6Fe0.4O2 nanosheet coating for Li-metal battery

Abstract

Separator play a crucial role in the performance of lithium metal batteries (LMBs). However, the commonly utilized polyolefin separators exhibit significant drawbacks, including poor thermal stability, low electrolyte affinity, and limited effectiveness in suppressing lithium dendrite growth, which restricts their practical application in LMBs. In this study, we developed an ultra-thin (∼700 nm) Ti_0.6Fe_0.4O₂ nanosheet coating on the surface of polypropylene (PP) separators using a spray coating process. The resulting Ti_0.6Fe_0.4O₂ nanosheet-modified composite separator demonstrates superior electrolyte affinity, thermal stability, and mechanical properties compared to the unmodified PP separator. Furthermore, the Ti_0.6Fe_0.4O₂ nanosheet coating facilitates the regulation of homogeneous electrolyte distribution, thereby promoting uniform and rapid ionic transport. Li//Li symmetric cells employing the modified composite separators exhibit lower polarization values and more stable voltage fluctuations over extended cycling periods, specifically after 500, 200, and 100 cycles at current densities of 1.0, 2.0, and 5.0 mA cm⁻², respectively, when compared to those utilizing pristine PP separators. Additionally, full cells incorporating the modified composite separator exhibit enhanced cycling stability and rate capability at 1C, 2C, and 5C rates. The straightforward and efficient method presented in this study offers promising potential for the mass production of metal oxide-modified composite separators.